Title of Invention	APPARATUS FOR CONTROLLING CELL SELECTION IN A CELLULAR COMMUNICATION SYSTEM
Abstract	A base station (101) may transmit using different modulation schemes. The transmit power of a pilot signal used for cell selection varies depending on the modulation schemes currently used, for example due to varying power amplifier back-up requirements. The base station (101) comprises a modulation scheme processor (113) determining a modulation scheme distribution for a plurality of communication channels of the cell. The modulation scheme distribution reflects the current modulation scheme utilisation for the pilot signal and is indicative of the power variation of the pilot signal. A cell selection processor (115) modifies a cell selection criterion in response to the modulation scheme distribution. In particular, the cell selection processor (115) determines a cell selection power offset to be applied to measurements of the signal levels of the pilot signal. The cell selection power offset preferably corresponds to the average power variation resulting from the current modulation scheme utilisation thereby allowing this to be compensated.

Title of Invention

APPARATUS FOR CONTROLLING CELL SELECTION IN A CELLULAR COMMUNICATION SYSTEM

Abstract

A base station (101) may transmit using different modulation schemes. The transmit power of a pilot signal used for cell selection varies depending on the modulation schemes currently used, for example due to varying power amplifier back-up requirements. The base station (101) comprises a modulation scheme processor (113) determining a modulation scheme distribution for a plurality of communication channels of the cell. The modulation scheme distribution reflects the current modulation scheme utilisation for the pilot signal and is indicative of the power variation of the pilot signal. A cell selection processor (115) modifies a cell selection criterion in response to the modulation scheme distribution. In particular, the cell selection processor (115) determines a cell selection power offset to be applied to measurements of the signal levels of the pilot signal. The cell selection power offset preferably corresponds to the average power variation resulting from the current modulation scheme utilisation thereby allowing this to be compensated.

Full Text	Field of the invention The invention relates to an apparatus and method for controlling cell selection in a cellular communication system and in particular a cellular communication system supporting a plurality of modulation schemes. Background of the Invention In a cellular communication system a geographical region is divided into a number of cells each of which is served by base station. The base stations are interconnected by a fixed network which can communicate data between the base stations. A mobile station is served via a radio communication link by the base station of the cell within which the mobile station is situated. As a mobile station moves, it may move from the coverage of one base station to the coverage of another, i.e. from one cell to another. As the mobile station moves towards base station, it enters a region of overlapping coverage of two base stations and within this overlap region it changes to be supported by the new base station. As the mobile station moves further into the new cell, it continues to be supported by the new base station. This is known as a handover or handoff of a mobile station between cells. A cellular communication system extends coverage over typically an entire country and comprises hundreds or even thousands of cells supporting thousands or even millions of mobile stations. Communication from a mobile station to a base station is known as uplink, and communication from a base station to a mobile station is known as downlink. The fixed network interconnecting the base stations is operable to route data between any two base stations, thereby enabling a mobile station in a cell to communicate with a mobile station in any other cell. In addition, the fixed network comprises gateway functions for interconnecting to external networks such as the Public Switched Telephone Network (PSTN), thereby allowing mobile stations to communicate with landline telephones and other communication terminals connected by a landline. Furthermore, the fixed network comprises much of the functionality requited for managing a conventional cellular communication network including functionality for routing data, admission control, resource allocation, subscriber billing, mobile station authentication etc. Currently, the most ubiquitous cellular communication system is the 2nd generation communication system known as the Global System for Mobile communication (GSM). GSM uses a technology known as Time Division Multiple Access (TDMA) wherein user separation is achieved by dividing frequency carriers into 8 discrete time slots, which individually can be allocated to a user. A base station may be allocated a single carrier or a multiple of carriers. One carrier is used for a pilot signal which further contains broadcast information. This carrier is used by mobile stations for measuring of the signal level of transmissions from different base stations, and the obtained information is used for determining a suitable serving cell during initial access or handovers. GSM uses a constant amplitude phase modulation scheme known as Gaussian Minimum Shift Keying (GMSK). Further description of the GSM TDMA communication system can be found in 'The GSM System for Mobile Communications' by Michel Mouly and Marie Bernadette Pautet, Bay Foreign Language Books, 1992, ISBN 2950719007. To further enhance the services and performance of the GSM communication system, a number of enhancements and additions have been introduced to the GSM communication system over the years. One such enhancement is the General Packet Radio System (GPRS), which is a system developed for enabling packet data based communication in a GSM communication system. Thus, the GPRS system is compatible with the GSM (voice) system and provides a number of additional services including provision of packet data communication, which augments and complements the circuit switched communication of a traditional communication system. Furthermore, the packet based data communication may also support packet based speech services. The GPRS system has been standardised as an add-on to an existing GSM communication system, and can be introduced to an existing GSM communication system by introducing new network elements. Specifically, a number of Serving GPRS Support Nodes (SGSN) and Gateway GPRS Support Nodes (GGSN) may be introduced to provide a packet based fixed network communication. Another enhancement is the Enhanced Data rate for GSM Evolution (EDGE) system, which comprises an air interface transmission protocol using a number of techniques to provide higher throughput over the air interface. Specifically, EDGE utilises higher order modulation schemes (8-PSK modulation), channel adaptation, Automatic Repeat Request (ARQ) schemes and incremental redundancy to provide a high data throughput. Furthermore, EDGE is particularly suited for packet based communication over the air interface. In particular, a radio access network known as a GERAN (GSM/EDGE Radio Access Network) has been standardised. The GERAN allows for traditional GSM services to be provided as well as the enhanced services and performance provided by EDGE and GPRS. Currently, 3rd generation systems are being rolled out to further enhance the communication services provided to mobile users. The most widely adopted 3rd generation communication systems are based on Code Division Multiple Access (CDMA) wherein user separation is obtained by allocating different spreading and scrambling codes to different users on the same carrier frequency, The transmissions are spread by multiplication with the allocated codes thereby causing the signal to be spread over a wide bandwidth. At the receiver, the codes are used to de-spread the received signal thereby regenerating the original signal. Each base station has a code dedicated for a pilot and broadcast signal, and as for GSM this is used for measurements of multiple cells in order to determine a serving cell. An example of a communication system using this principle is the Universal Mobile Telecommunication System (UMTS), which is currently being deployed. Further description of CDMA and specifically of the Wideband CDMA (WCDMA) mode of UMTS can be found in 'WCDMA for UMTS', Harri Holma (editor), Antti Toskala (Editor), Wiley & Sons, 1091, ISBN 0471486876; In a UMTS CDMA communication system, the communication network comprises a core network and a UMTS Radio Access Network (UTRAN). The core network is operable to route data from one part of the RAN to another, as well as interfacing with other communication systems. In addition, it performs many of the operation and management functions of a cellular communication system, such as billing. The RAN is operable to support wireless user equipment over a radio link being part of the air interface. The RAN comprises the base stations, which in UMTS are known as Node Bs, as well as Radio Network Controllers (RNC) which control the Node Bs and the communication over the air interface. In order to increase the spectral efficiency, increase data rates, provide a variety of services and support a variety of equipment and standards, cellular communication systems increasingly support a number of different modulation schemes. Thus, in current and future wireless packet/circuit switched data and voice systems, one of the techniques used to offer variable rates is through varying the modulation scheme of the transmitted signal. In particular, an EDGE GSM communication system supports both GMSK modulation and 8- PSK modulation. Among other things, this allows EDGE capable mobile stations to utilise the additional features of EDGE while ensuring the legacy mobile stations may still be supported. One issue that is generally encountered when adopting such a technique is that the hardware capability of the transmitters of base stations and handsets, hi connection with the characteristics and requirements of the individual modulation schemes, results in the maximum transmit power of a base station being dependent on the selected modulation scheme. For example, GMSK is a constant amplitude modulation scheme and is accordingly not sensitive to non-linearities of the transmit path, such as non- linearities occurring in the power amplifier. Accordingly, the power amplifier may be operated in a non-linear region and without backing off. This allows for the power amplifier to be used at a maximum output power level. In contrast, 8-PSK is a non-constant amplitude linear modulation scheme which requires a substantially linear processing. Therefore, the power amplifier must be operated in a substantially linear region requiring a back off of typically around 4-5 dB. In order to reduce cost, the same power amplifier is used for both GMSK and 8-PSK and the maximum power transmitted for 8- PSK is consequently typically around 4-5 dB less than for GMSK. This may cause a significant variation in the transmitted power levels depending on the modulation schemes used. In cellular communication systems, power level measurements of uplink or downlink signals are frequently used for cell selection procedures. However, as the transmitted power levels may depend on the modulation schemes used, the cell selection procedures are not optimal. The transmit power variations caused by the variations in modulation scheme may degrade the performance of the cell selection procedures and accordingly the load control and resource management may be less effective resulting in a reduced capacity of the communication system as a whole. In particular, in an EDGE GSM communication system, cell selection is based on power level measurements of the BCCH carrier. The BCCH carrier is divided into eight time slots with one time slot reserved for broadcast of control information. The remaining seven time slots may be used for user traffic and may use GMSK or 8'PSK modulation schemes. The BCCH carrier is always transmitted at a maximum power level to provide large cell coverage and a suitable power reference for signal level measurements. However, as the maximum power level differs for different modulation schemes, the cell selection may be affected by the choice of modulation schemes in each time slot. This may complicate and degrade resource and cell load management. For example, a BCCH of one cell supporting GMSK in seven time slots will have an average transmit power almost 4-5 dB higher than a BCCH of another cell supported by a base station having the same power amplifier characteristics but using 8-PSK in seven time slots. Thus, due to the difference in modulation schemes the mobile stations will be biased from the cell supporting EDGE towards the cell supporting GMSK. This may for example cause the EDGE cell to be underloaded while the GMSK cell is overloaded thereby reducing the capacity of the cellular"communication system. Hence, an improved system of cell selection would.be advantageous and in particular a system allowing increased flexibility, improved cell selection control, improved insensitivity to dynamic variations, improved cell selection performance and/or increased capacity of a cellular communication system would be advantageous. Summary of the Invention Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination. According to a first aspect of the invention there is provided an apparatus for controlling cell selection in a cellular communication system supporting a plurality of modulation schemes, the apparatus comprising: means for determining a modulation scheme distribution for a plurality of communication channels of at least one cell; and means for modifying a cell selection criterion in response to the modulation scheme distribution. The invention may allow cell selection to take the modulation scheme distribution in the cellular communication system into account. The modulation scheme distribution is an indication of the modulation scheme utilisation in the cellular communication and may in particular reflect the modulation schemes used in the at least one cell. The cell selection criterion may be optimised or improved for the modulation scheme utilisation. This may result in improved cell selection performance and/or may allow more reliable and/ or accurate control of the cell selection procedures. The resource management may be improved and in particular the management and control of the loading of cells may be improved. This may reduce the probability of overloaded cells and may increase the capacity of the cellular communication system and improve the user service. For example, the number of dropped calls or access denials in the communication system may be reduced. In particular, the invention may compensate or offset a bias in the cell selection performance due to the used modulation schemes. According to a preferred feature of the invention, the plurality of communication channels are communication channels of a single carrier. This may provide a flexible and targeted modification of a cell selection criterion in response to the characteristics of a specific carrier. In particular, the carrier may be a carrier which is monitored by a cell selection procedure. The carrier may for example be a frequency carrier of a TDMA system such as GSM. According to a preferred feature of the invention, the plurality of communication channels are communication channels of a pilot carrier. Cell selection is in many cellular communication systems based on signal level measurements of a pilot carrier and modifying the cell selection criterion in response to a modulation scheme distribution associated with the pilot carrier may provide improved cell selection performance and may in particular compensate or offset undesired biasing of cells due to the specific modulation schemes used. For an EDGE GSM cellular communication system, the pilot carrier may in particular be the BCCH carrier. According to a preferred feature of the invention, the plurality of communication channels are communication channels supporting an active communication. An active communication may in particular be a communication which has been ongoing during a time interval for which the modulation scheme distribution has been determined. The modulation scheme distribution may specifically reflect a current modulation scheme distribution for a given time interval. The invention may thus provide for a dynamic modification of the cell selection criterion in response to the current modulation scheme utilisation. This may provide for an improved cell selection performance. It may alternatively or additionally facilitate network resource management as short term variations may automatically be compensated by the modification of the cell selection criterion. According to a preferred feature of the invention, the means for modifying is further operable to modify the cell selection criterion in response to a power characteristic associated with each modulation scheme. The power characteristic may be a parameter or a requirement associated with the modulation scheme, such as for example a peak to average power level measure. This may provide improved accuracy and improved cell selection performance. According to a preferred feature of the invention, the power characteristic is a linearity requirement. In particular, the power characteristic is preferably a power back-off requirement of a power amplifier. Typically, the power amplifier back-off required for different modulation schemes will result in transmit power variations between these, and modifying the cell selection criterion in response to these parameters may improve cell selection and in particular compensate or offset the bias introduced by the modulation schemes. According to a preferred feature of the invention, the means for modifying a cell selection criterion is operable to determine a cell selection power offset for a signal level measurement. This provides a particularly advantageous means of modifying the cell selection criterion. In particular, it allows easy implementation, provides high cell selection performance and/or is suitable for cellular systems wherein cell selection is in response to signal level measurements in the remote units. In EDGE GSM, the signal level measurements may particularly be mobile measurements of the received BCCH signal level. According to a preferred feature of the invention, the apparatus further comprises means for transmitting cell selection criterion modification information to remote units. This is particularly advantageous where cell selection is performed by the remote unit. The cell selection criterion modification information may specifically be cell selection power offsets to be applied to signal level measurements made by the remote unit and used for selecting a cell. According to a preferred feature of the invention, the apparatus further comprises^ means for determining a long term modulation scheme distribution for the plurality of communication channels, the long term modulation scheme distribution reflecting a distribution of modulation scheme usage determined over a longer time interval than for the modulation scheme distribution; means for determining a default cell selection criterion; and the means for modifying the cell selection criterion is operable to temporarily modify a parameter of the default cell selection criterion. This may allow a high performance cell selection algorithm and/or facilitate implementation. For example, a default cell selection criterion may be determined to suit the average conditions in the cellular communication system and this may be dynamically varied to suit the dynamic variations in modulation scheme utilisation. According to a preferred feature of the invention, the means for modifying is further operable to modify the cell selection criterion in response to a loading of the cell. This may improve cell selection and provide additional control of the resource distribution between cells. According to a preferred feature of the invention, the means for modifying is further operable to modify the cell selection criterion in response to a loading of a different cell of the cellular communication system. This may improve cell selection and provide additional control of the resource distribution between cells. According to a preferred feature of the invention, the modulation scheme distribution is determined for a plurality of cells. This may improve cell selection and provide additional control of the resource distribution between cells. According to a preferred feature of the invention, the means for determining the modulation scheme distribution is operable to determine the modulation scheme distribution in response to a number of active communications employing each supported modulation scheme. This may allow a simple and easy to implement way of determining a modulation scheme distribution suitable for modifying the cell selection criterion thereby improving the cell selection performance. According to a preferred feature of the invention, the modulation scheme distribution comprises a plurality of modulation scheme categories and an indication of a current usage level of the modulation schemes of each category. This may provide a simple modulation scheme distribution representing the current modulation scheme utilisation and is suitable for modifying the cell selection criterion thereby improving the cell selection performance. According to a preferred feature of the invention, the cell selection criterion is an idle mode cell selection criterion. The invention may provide improved idle mode cell selection performance thereby improving the performance of the cellular communication system as a whole. According to a preferred feature of the invention, the cell selection criterion is a handover criterion. The invention may provide improved handover cell selection performance thereby improving the performance of the cellular communication system as a whole. Preferably, the cellular communication system comprises EDGE communication means. The cellular communication system preferably comprises a GERAN (GSM EDGE Radio Access Network). In particular the cellular communication system may be an EDGE GSM cellular communication system. Preferably the cellular communication system comprises a first and second apparatus as described above and further comprising means for exchanging modulation scheme distribution information. This may provide a suitable way of communicating information allowing a modification of the cell selection criterion in response to the modulation scheme distribution of a plurality of cells. According to a second aspect of the invention, there is provided a method of controlling cell selection in a cellular communication system supporting a plurality of modulation schemes, the method comprising the steps of determining a modulation scheme distribution for a plurality of communication channels of at least one cell; and modifying a cell selection criterion in response to the modulation scheme distribution. These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. An embodiment of the invention will be described, by way of example only, with reference to the drawings, in which FIG. 1 is an illustration of part of a cellular communication system in accordance with an embodiment of the invention; and FIG. 2 illustrates a method of controlling cell selection in accordance with an embodiment of the invention. Detailed Description of a Preferred Embodiment of the Invention The following description focuses on an embodiment of the invention i applicable to an EDGE GSM cellular communication system. However, it will be appreciated that the invention is not limited to this application but may be applied to many other cellular communication systems supporting a plurality of modulation schemes such as a combined 2nd and 3rd Generation cellular communication system. FIG. 1 is an illustration of part of a cellular communication system 100 in accordance with an embodiment of the invention. FIG. 1 illustrates a first base station 101 comprising an apparatus for controlling cell selection in accordance with an embodiment of the invention. Only the parts of the base station 101 associated with the cell selection apparatus have been illustrated, and it will be apparent to the person skilled in the art that the base station 101 additionally comprises the required functionality for operating in accordance with the specifications of the cellular communication system. The base station 101 is connected to a fixed network 103 which is further connected to other base stations of which one neighbour base station 105 is shown. FIG. 1 further illustrates a remote unit 107 which is in idle mode and situated in a location where it is able to receive signals from both the first base station 101 and the neighbour base station 105. The first base station 101 comprises a base station controller 109 which is operable to control the operation of the base station. In particular, the base station controller 109 interfaces with the fixed network 103 and controls the base station 101 to transmit user data and control messages in accordance with the requirements of the EDGE GSM cellular communication system. The base station controller 109 is coupled to a transmitter 111 which transmits signals to the remote units 107 over the EDGE GSM air interface in accordance with the EDGE GSM technical specifications. In particular the transmitter 111 is under the control of the base station controller 109 operable to transmit data using different modulation schemes. The modulation scheme used in each time slot depends on the service supported by that time slot and may also depend on the current propagation conditions. If a time slot is used to support a GSM communication, the transmitter uses GMSK modulation whereas a time slot supporting an EDGE communication may use an 8-PSK modulation scheme. The transmitter 111 comprises a power amplifier which amplifies the modulated signal to a suitable power level for transmission. For the constant amplitude modulation of GMSK, the power amplifier may be used up to the maximum output power that can be provided by the power transmitter. However, for the linear non-constant amplitude modulation of 8-PSK, it is important that the power amplifier is used in a substantially linear region. This requires that the power amplifier is backed off and typically a back off of around 4 to 5 dBs are required. Accordingly, the maximum power output of the power amplifier is around 4-5 dB lower for 8-PSK than for GMSK. In an EDGE GSM cellular communication system, the BCCH carrier is used as a pilot signal. The received signal level of the BCCH carrier is measured by the remote units and is used to determine a serving cell. In particular, idle mode mobiles measure the received BCCH signal levels of a number of base stations and select the cell being received with the highest signal level as the serving cell. Active remote units measure signal levels of a number of neighbouring cells and report these back to the base station and the fixed network for determining if a handover to another cell should be carried out. Hence, the remote unit 107 measures the BCCH signal from base station 101 and base station 103 and cell selection is performed in response to these measurements in accordance with a suitable cell selection criterion. In the idle mode case, the remote unit 107 may simply select the base station having the highest received signal level. In order to provide a suitable reference signal, power control is not performed on the BCCH carrier which instead is transmitted at the maximum power • level available from the base station. However, when different modulation schemes are used by the base station 201, the differences in the required back- off between constant amplitude and non-constant amplitude modulation schemes result in the average transmit power being dependent on the modulation schemes used. As a specific example, the base station controller 109 may control the transmitter 111 to transmit a GMSK modulated signal in all time slots of the BCCH carrier in which case the average transmit power within the measurement time interval of the remote unit (typically around five seconds) is the maximum power level of the power amplifier. However, at another time, seven out of eight time slots of the BCCH carrier which are available for user traffic may support EDGE communications using 8-PSK. Accordingly, the power amplifier will be backed off by 4-5 dBs for seven out of the eight time slots, resulting in the received signal level at the remote unit 107 being reduced by around 4 dB. Thus, the transmit power level of the BCCH carrier may fluctuate in response to the applied modulation schemes resulting in a reduced performance of the cell selection process. The variation in transmit power of the BCCH can furthermore complicate resource management and reduce the capacity of the cellular communication system. For example, cells having a high number of EDGE communications supported by the BCCH will be measured with a lower signal level than if the cell supported fewer EDGE communications. This will tend to shift remote units away from EDGE supporting cells which may result in the cell being under loaded while neighbour cells are overloaded. The base station 101 of FIG. 2 further comprises a modulation scheme processor 113 which is operable to determine a modulation scheme distribution for a plurality of communication channels of the cell of the base station. The modulation scheme processor 113 is coupled to a cell selection processor 115 which is operable to modify a cell selection criterion in response to the modulation scheme distribution. In the described embodiment, the cell selection processor 115 is coupled to the transmitter 111 in order to transmit information of the modifications to the cell selection criterion to the remote units of the cell. The information of the modifications of the cell selection criterion may be communicated on the BCCH broadcast channel thereby being broadcast to all remote units capable of receiving the BCCH signal. The modulation scheme processor'113 may determine the modulation scheme distribution in accordance with any suitable method or algorithm. The modulation scheme distribution is an indication of the modulation scheme utilisation. In particular, the modulation scheme distribution may reflect which modulation schemes may currently active or which modulation schemes are allocated to different time slots, channels and/or carriers. Specifically, the modulation scheme distribution may be an indication of the modulation scheme utilisation which allows for the impact on the transmit power of a base station to be determined. The cell selection processor 115 may determine a modification to a cell selection criterion which takes into account the modulation scheme utilisation, and in particular the cell selection criterion may be modified to compensate for a change in the transmit power of a base station caused by the modulation schemes used. It will be appreciated that any suitable cell selection criterion or modification thereof may be used without detracting from the invention. For example, a cell selection algorithm may comprise a number of alternative conditions for selecting a cell and the modification of the cell selection criterion may be achieved by selecting a specific condition to apply for cell selection. In other embodiments, a parameter or relationship used by the cell selection algorithm may be modified in response to the modulation scheme distribution. Hence, the embodiment may allow a cell selection criterion to be modified to compensate for variations in the modulation schemes used. This may improve cell selection performance, enhance and facilitate the control of the cell selection and increase the capacity of the communication system as a whole. A specific example of the operation of the EDGE GSM communication system, wherein power variations of the BCCH carrier are compensated, will be described in the following. FIG. 2 illustrates a method of controlling cell selection in accordance with an embodiment of the invention. The method is in the following example performed by the base station 101 of FIG. 1 and will be described with reference to this. The example is suitable for a cell selection algorithm for idle mode remote units where the cell selection criterion is applied by the remote unit and is based on BCCH signal level measurements made by the remote unit. Specifically, the remote unit may select the cell having the highest received signal level after compensation. In the example, the modulation scheme processor 113 determines a modulation scheme distribution in step 201. The modulation scheme distribution is determined in response to the communication channels of a single carrier and specifically the modulation scheme distribution is determined for the pilot carrier in the form of the BCCH carrier. In addition, the modulation scheme distribution is determined to reflect the current dynamic conditions and is thus determined for the communication channels supporting an active communication. Thus, the modulation scheme distribution is determined by evaluating which modulation schemes are used in the time slots of the BCCH carrier. Furthermore, the modulation scheme distribution is determined in response to a number of active communications employing each supported modulation scheme. The modulation scheme distribution of the described embodiment comprises a plurality of modulation scheme categories. As a simple example, the modulation scheme of each time slot is either a GMSK modulation scheme or an 8-PSK modulation scheme and the modulation scheme distribution therefore simply comprises a first category corresponding to GMSK modulation and a second category corresponding to 8-PSK modulation. In the example, the modulation scheme distribution comprises an indication of a current usage level of the modulation schemes of each category and in particular the modulation scheme distribution comprises an indication of the number of time slots currently using GMSK and the number of time slots currently using 8-PSK. As a specific example, the BCCH carrier may use GMSK for the control time slot 0, 8-PSK in time slots 1 to 4 and GMSK in time slot 5 to 7. The modulation scheme processor 113 will be provided with this information from the base station controller 209 and will accordingly generate a modulation scheme distribution indicating that 4 time slots fall in the GMSK category and 4 time slots fall in the 8-PSK category. Step 201 is followed by step 203 wherein the cell selection processor 115 determines a modification to the cell selection criterion. In the example, the modification is effected by setting a cell selection power offset. The cell selection power offset corresponds to an offset which is to be applied to the signal level measurements of the BCCH carrier performed by the remote unit 107. In the example, the cell selection processor 115 determines the cell selection power offset in response to the modulation scheme distribution and a power characteristic associated with each modulation scheme. The power characteristic is in this example a characteristic which is indicative of the transmit power that is used for the specific modulation scheme. In the specific embodiment, the power reduction of the transmit power depends on the linearity required by the power amplifier. Typically, the higher the linearity requirement for a modulation scheme the higher the required back off of the transmit power amplifier and thus the lower the maximum transmit power. As a specific example, the cell selection processor 115 may have information that for a GMSK signal no back-off is required whereas for an 8-PSK signal a back off of 6 dB is required in order to meet the linearity requirement for the non-constant amplitude modulation scheme. Hence, when receiving a modulation scheme distribution from the modulation scheme processor 113 indicating that the BCCH carrier uses GMSK in four time slots and QPSK in four time slots, the cell selection processor 115 determines that the power amplifier is backed off by 6 dB, and thus that the output power is reduced by 6 dB for half the duration. Thus, the average transmit power is 3 dB lower than the transmit power if all time slots use GMSK modulation. Hence, the cell selection processor 115 determines a cell selection power offset of 3 dB which is to be applied to measurements of the BCCH carrier of base station 101 made by the remote unit 107. Step 203 is followed by step 205 wherein the cell selection power offset is fed from the cell selection processor 115 to the transmitter 111 for transmission to the remote units. Thus, the base station 201 transmits cell selection criterion modification information in the form of the cell selection power offset to remote units. In particular, the base station may broadcast the cell selection power offset by including it in a system information message of the BCCH carrier. In the example, the remote unit 107 is in idle mode and performs a cell selection in response the received signal level measurements of the BCCH carriers of the surrounding base stations. In particular, the remote unit receives the BCCH carrier of the first and second base station 101, 103 and measures the signal level averaged over a time interval (e.g. 5 seconds). In addition, the remote unit demodulates time slot 0 of the BCCH carriers and decodes the transmitted system information messages. The system information messages from the first base station comprises the cell selection power offset and the remote unit adds the cell selection power offset to the measured signal level of the first base station 101. Thus, 3 dB is in the specific example added to the signal level measurement of the first base station 101 thereby, compensating for the reduction of transmit power caused by the use of 8-PSK modulation in four time slots. In the embodiment, the signal level measurements are compensated for transmit power variations caused by the use of different modulation schemes and cell selection may be performed on the basis of the compensated signal levels. In particular, the remote unit may select the base station resulting in the highest compensated signal level corresponding to the lowest propagation loss. Thus, improved cell selection may be achieved. In the described embodiment, a default cell selection criterion consisting in selecting the cell having the highest received signal level is modified by dynamically compensating the measured signal levels in response to the current modulation scheme distribution. Thus, a default cell selection criterion based on an assumption of a maximum transmit power is temporarily modified by introducing a cell selection power offset representing transmit power variations due to the actual modulation schemes used. In some embodiments, the default cell selection criterion is not simply based on a static assumption but is based on a long term evaluation of the modulation scheme distribution. Thus, the base station 201 may in such an embodiment comprise means for determining a long term modulation scheme distribution. The long term modulation scheme distribution is determined over a longer time interval than for the modulation scheme distribution determined by the modulation scheme processor 113. In particular, the long term modulation scheme distribution may be determined, by averaging the modulation scheme distribution over a suitable time interval. For example, a new modulation scheme distribution may be determined at ten minute intervals whereas the long term modulation scheme distribution may be determined on a daily or weekly basis. In the embodiment, the long term modulation scheme distribution thus reflects the long term average modulation scheme utilisation whereas the modulation scheme distribution reflects the short term variations. The base station may in response to the long term modulation scheme distribution determine a default cell selection criterion suitable for the average conditions. For example, the default cell selection criterion may be a comparison between measured signal levels assuming a transmit power equal to the average transmit power for the long term modulation scheme distribution. The base station may further vary this temporarily in response to the modulation scheme distribution, for example by applying temporary cell selection power offsets. It will be appreciated that the cell selection processor 115 may consider other parameters or characteristics when modifying the cell selection criterion than the modulation scheme distribution. For example, in some embodiments, the cell selection processor 115 may further modify the cell selection criterion in response to a loading of the cell and/or of other cells. In a specific such embodiment, the cell selection criterion is only modified if the cell or one of the surrounding cells is loaded above a given level. Thus, in situations where no cell is in danger of being overloaded, no modification is made to the cell selection criterion as this is unlikely to be critical or result in reduced performance. However, in situations where the cell selection is critical because one or more of the involved cells may be approaching congestion, a more accurate cell selection criterion may be used which more closely reflects the actual conditions and therefore provides an improved cell selection. In the described embodiment, the modulation scheme distribution was determined only for one cell. However, it will be appreciated that in other embodiments, the modulation scheme distribution may reflect the modulation scheme utilisation of a plurality of cells. For example, the modulation scheme processor 113 may receive information from other base stations indicating which modulation schemes are used in the time slots of the BCCH carriers of those cells. The modulation scheme distribution may for example comprise information that in base station 101 four time slots use GMSK and four time slots use 8-PSK and that in the ' second base station 103 six time slots use GMSK and two time slots use 8" PSK. In response, the cell selection processor 115 may for example determine a cell selection power offset reflecting' the average transmit power difference between the first base station 101 and the second base station 105 rather than a relative offset to the maximum transmit power of the base station itself. Hence, in the example, a cell selection power offset of 1.8 dB may be transmitted to the remote unit 107 to be applied when comparing the signal level measurements of the first and second base station. Furthermore, in some embodiments different cells may autonomously determine suitable cell selection power offsets and transmit these. For example, in an EDGE GMSK systems the remote units decode the BCCH of not only the serving cell but also of the neighbour cells being monitored. In this case, each base station may determine a suitable cell selection power offsets for the cell supported by the base station and may transmit this information on the BCCH. The remote unit will thus receive suitable cell selection power offsets from the neighbour cells and may apply these to the appropriate BCCH signal level measurements. In some embodiments, only the pilot signal of the currently selected cell is decoded. For example, for packet communication using a PBCCH (Packet BCCH), the remote unit decodes only that of the serving cell and the neighbour cell data is broadcast on the PBCCH of the serving cell. In this embodiment, neighbouring cells may exchange information related e.g. to the cell selection power offsets of the cells and the cell selection power offsets for both the serving cell and neighbouring cells may be broadcast on the PBCCH of the serving cell. The above description has focussed on an embodiment wherein an idle mode remote unit performs cell selection in response to measurements and information transmitted from a base station. However, it will be appreciated that the cell selection may be performed at other locations and in particular may be performed in the network. Thus, not only the cell selection processor modifying the cell selection criterion but also the cell selection algorithm itself may be performed in the network. The cell selection may thus be performed in the base station, in the fixed network or may be distributed between these. For example, the cell selection may be a handover cell selection performed in a BSC based on measurements of BCCHs made by the remote unit 107 and transmitted to the base station 101. In such an example, each base station may comprise a modulation scheme processor 113 determining a current modulation scheme distribution and reporting this to the BSC. The BSC may then proceed to offset all neighbour measurements from the remote unit 107 by a value indicative of the transmit power reduction due to the modulation schemes used of the individual base station. Hence, an improved handover performance may be achieved. The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. However, preferably, the invention is implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors. Although the present invention has been described in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the term comprising does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor, Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality. We Claim : 1. An apparatus for controlling cell selection in a cellular communication system supporting a plurality of modulation schemes, the apparatus comprising: means for determining a distribution of active modulations for a plurality of communication channels of at least one cell; and means for modifying a cell selection criterion in response to the distribution of active modulations. 2. An apparatus as claimed in claim 1, wherein the plurality of communication channels are communication channels of a single carrier. 3. An apparatus as claimed in claim 1 or 2, wherein the plurality of communication channels are communication channels of a pilot carrier. 4. An apparatus as claimed in any one of the preceding claims, wherein the plurality of communication channels are communication channels supporting an active communication. 5. An apparatus as claimed in any one of the preceding claims, wherein the means for modifying is operable to modify the cell selection criterion in response to a power characteristic associated with each modulation scheme. 6. An apparatus as claimed in claim 5, wherein the power characteristic is a linearity requirement. 7. An apparatus as claimed in claim 6, wherein the power characteristic is a power back-off requirement of a power amplifier. 8. An apparatus as claimed in any one of the preceding claims, wherein the means for modifying a cell selection criterion is operable to determine a cell selection power offset for a signal level measurement. 9. An apparatus as claimed in any one of the preceding claims, having means for transmitting cell selection criterion modification information to remote units. 10. An apparatus as claimed in any one of the preceding claims, having means for determining a long term distribution of active modulations for the plurality of communication channels, the long term distribution of active modulations reflecting a distribution of modulation scheme usage determined over a longer time interval than for the distribution of active modulations; means for determining a default cell selection criterion; and wherein the means for modifying the cell selection criterion is operable to temporarily modify a parameter of the default cell selection criterion. 11. An apparatus as claimed in any one of the preceding claims, wherein the means for modifying is operable to modify the cell selection criterion in response to a loading of the cell. 12. An apparatus as claimed in any one of the preceding claims, wherein the means for modifying is operable to modify the cell selection criterion in response to a loading of a different cell than the at least one cell of the cellular communication system. 13. An apparatus as claimed in any one of the preceding claims, wherein the distribution of active modulations is determined for a plurality of cells. 14. An apparatus as claimed in any one of the preceding claims, wherein the means for determining the distribution of active modulations is operable to determine the distribution of active modulations in response to a number of active communications employing each supported modulation scheme. 15. An apparatus as claimed in any one of the preceding claims, wherein the distribution of active modulations comprises a plurality of modulation scheme categories and an indication of a current usage level of the modulation schemes of each category. 16. An apparatus as claimed in any one of the preceding claims, wherein the cell selection criterion is an idle mode cell selection criterion. 17. An apparatus as claimed in any one of the preceding claims, wherein the cell selection criterion is a handover criterion. 18. An apparatus as claimed in any one of the preceding claims, wherein the cellular communication system comprises EDGE communication means. 19. A base station for a cellular communication system comprising an apparatus as claimed in any one of the preceding claims 1 to 18. 20. A cellular communication system comprising a first apparatus as claimed in any of the preceding claims 1 to 18. 21. A cellular communication systern as claimed in claim 20, wherein the cellular communication system comprises a second apparatus as claimed in any one of the preceding claims 1 to 18 and wherein the first and second apparatus comprise means for exchanging distribution of active modulations information. A base station (101) may transmit using different modulation schemes. The transmit power of a pilot signal used for cell selection varies depending on the modulation schemes currently used, for example due to varying power amplifier back-up requirements. The base station (101) comprises a modulation scheme processor (113) determining a modulation scheme distribution for a plurality of communication channels of the cell. The modulation scheme distribution reflects the current modulation scheme utilisation for the pilot signal and is indicative of the power variation of the pilot signal. A cell selection processor (115) modifies a cell selection criterion in response to the modulation scheme distribution. In particular, the cell selection processor (115) determines a cell selection power offset to be applied to measurements of the signal levels of the pilot signal. The cell selection power offset preferably corresponds to the average power variation resulting from the current modulation scheme utilisation thereby allowing this to be compensated.

Full Text

Field of the invention
The invention relates to an apparatus and method for controlling cell selection
in a cellular communication system and in particular a cellular communication
system supporting a plurality of modulation schemes.
Background of the Invention
In a cellular communication system a geographical region is divided into a
number of cells each of which is served by base station. The base stations are
interconnected by a fixed network which can communicate data between the
base stations. A mobile station is served via a radio communication link by the
base station of the cell within which the mobile station is situated.
As a mobile station moves, it may move from the coverage of one base station
to the coverage of another, i.e. from one cell to another. As the mobile station
moves towards base station, it enters a region of overlapping coverage of two
base stations and within this overlap region it changes to be supported by the
new base station. As the mobile station moves further into the new cell, it
continues to be supported by the new base station. This is known as a
handover or handoff of a mobile station between cells.
A cellular communication system extends coverage over typically an entire
country and comprises hundreds or even thousands of cells supporting
thousands or even millions of mobile stations. Communication from a mobile

station to a base station is known as uplink, and communication from a base
station to a mobile station is known as downlink.
The fixed network interconnecting the base stations is operable to route data
between any two base stations, thereby enabling a mobile station in a cell to
communicate with a mobile station in any other cell. In addition, the fixed
network comprises gateway functions for interconnecting to external networks
such as the Public Switched Telephone Network (PSTN), thereby allowing
mobile stations to communicate with landline telephones and other
communication terminals connected by a landline. Furthermore, the fixed
network comprises much of the functionality requited for managing a
conventional cellular communication network including functionality for
routing data, admission control, resource allocation, subscriber billing, mobile
station authentication etc.
Currently, the most ubiquitous cellular communication system is the 2nd
generation communication system known as the Global System for Mobile
communication (GSM). GSM uses a technology known as Time Division
Multiple Access (TDMA) wherein user separation is achieved by dividing
frequency carriers into 8 discrete time slots, which individually can be
allocated to a user. A base station may be allocated a single carrier or a
multiple of carriers. One carrier is used for a pilot signal which further
contains broadcast information. This carrier is used by mobile stations for
measuring of the signal level of transmissions from different base stations, and
the obtained information is used for determining a suitable serving cell during
initial access or handovers. GSM uses a constant amplitude phase modulation
scheme known as Gaussian Minimum Shift Keying (GMSK). Further
description of the GSM TDMA communication system can be found in 'The
GSM System for Mobile Communications' by Michel Mouly and Marie
Bernadette Pautet, Bay Foreign Language Books, 1992, ISBN 2950719007.

To further enhance the services and performance of the GSM communication
system, a number of enhancements and additions have been introduced to the
GSM communication system over the years.
One such enhancement is the General Packet Radio System (GPRS), which is
a system developed for enabling packet data based communication in a GSM
communication system. Thus, the GPRS system is compatible with the GSM
(voice) system and provides a number of additional services including
provision of packet data communication, which augments and complements
the circuit switched communication of a traditional communication system.
Furthermore, the packet based data communication may also support packet
based speech services. The GPRS system has been standardised as an add-on
to an existing GSM communication system, and can be introduced to an
existing GSM communication system by introducing new network elements.
Specifically, a number of Serving GPRS Support Nodes (SGSN) and Gateway
GPRS Support Nodes (GGSN) may be introduced to provide a packet based
fixed network communication.
Another enhancement is the Enhanced Data rate for GSM Evolution (EDGE)
system, which comprises an air interface transmission protocol using a
number of techniques to provide higher throughput over the air interface.
Specifically, EDGE utilises higher order modulation schemes (8-PSK
modulation), channel adaptation, Automatic Repeat Request (ARQ) schemes
and incremental redundancy to provide a high data throughput. Furthermore,
EDGE is particularly suited for packet based communication over the air
interface.
In particular, a radio access network known as a GERAN (GSM/EDGE Radio
Access Network) has been standardised. The GERAN allows for traditional
GSM services to be provided as well as the enhanced services and performance
provided by EDGE and GPRS.

Currently, 3rd generation systems are being rolled out to further enhance the
communication services provided to mobile users. The most widely adopted 3rd
generation communication systems are based on Code Division Multiple
Access (CDMA) wherein user separation is obtained by allocating different
spreading and scrambling codes to different users on the same carrier
frequency, The transmissions are spread by multiplication with the allocated
codes thereby causing the signal to be spread over a wide bandwidth. At the
receiver, the codes are used to de-spread the received signal thereby
regenerating the original signal. Each base station has a code dedicated for a
pilot and broadcast signal, and as for GSM this is used for measurements of
multiple cells in order to determine a serving cell. An example of a
communication system using this principle is the Universal Mobile
Telecommunication System (UMTS), which is currently being deployed.
Further description of CDMA and specifically of the Wideband CDMA
(WCDMA) mode of UMTS can be found in 'WCDMA for UMTS', Harri Holma
(editor), Antti Toskala (Editor), Wiley & Sons, 1091, ISBN 0471486876;
In a UMTS CDMA communication system, the communication network
comprises a core network and a UMTS Radio Access Network (UTRAN). The
core network is operable to route data from one part of the RAN to another, as
well as interfacing with other communication systems. In addition, it performs
many of the operation and management functions of a cellular communication
system, such as billing. The RAN is operable to support wireless user
equipment over a radio link being part of the air interface. The RAN comprises
the base stations, which in UMTS are known as Node Bs, as well as Radio
Network Controllers (RNC) which control the Node Bs and the communication
over the air interface.
In order to increase the spectral efficiency, increase data rates, provide a
variety of services and support a variety of equipment and standards, cellular

communication systems increasingly support a number of different modulation
schemes. Thus, in current and future wireless packet/circuit switched data and
voice systems, one of the techniques used to offer variable rates is through
varying the modulation scheme of the transmitted signal. In particular, an
EDGE GSM communication system supports both GMSK modulation and 8-
PSK modulation. Among other things, this allows EDGE capable mobile
stations to utilise the additional features of EDGE while ensuring the legacy
mobile stations may still be supported.
One issue that is generally encountered when adopting such a technique is
that the hardware capability of the transmitters of base stations and handsets,
hi connection with the characteristics and requirements of the individual
modulation schemes, results in the maximum transmit power of a base station
being dependent on the selected modulation scheme.
For example, GMSK is a constant amplitude modulation scheme and is
accordingly not sensitive to non-linearities of the transmit path, such as non-
linearities occurring in the power amplifier. Accordingly, the power amplifier
may be operated in a non-linear region and without backing off. This allows for
the power amplifier to be used at a maximum output power level.
In contrast, 8-PSK is a non-constant amplitude linear modulation scheme
which requires a substantially linear processing. Therefore, the power
amplifier must be operated in a substantially linear region requiring a back off
of typically around 4-5 dB. In order to reduce cost, the same power amplifier is
used for both GMSK and 8-PSK and the maximum power transmitted for 8-
PSK is consequently typically around 4-5 dB less than for GMSK. This may
cause a significant variation in the transmitted power levels depending on the
modulation schemes used.

In cellular communication systems, power level measurements of uplink or
downlink signals are frequently used for cell selection procedures. However, as
the transmitted power levels may depend on the modulation schemes used, the
cell selection procedures are not optimal. The transmit power variations
caused by the variations in modulation scheme may degrade the performance
of the cell selection procedures and accordingly the load control and resource
management may be less effective resulting in a reduced capacity of the
communication system as a whole.
In particular, in an EDGE GSM communication system, cell selection is based
on power level measurements of the BCCH carrier. The BCCH carrier is
divided into eight time slots with one time slot reserved for broadcast of
control information. The remaining seven time slots may be used for user
traffic and may use GMSK or 8'PSK modulation schemes. The BCCH carrier
is always transmitted at a maximum power level to provide large cell coverage
and a suitable power reference for signal level measurements. However, as the
maximum power level differs for different modulation schemes, the cell
selection may be affected by the choice of modulation schemes in each time
slot. This may complicate and degrade resource and cell load management.

For example, a BCCH of one cell supporting GMSK in seven time slots will
have an average transmit power almost 4-5 dB higher than a BCCH of another
cell supported by a base station having the same power amplifier
characteristics but using 8-PSK in seven time slots. Thus, due to the difference
in modulation schemes the mobile stations will be biased from the cell
supporting EDGE towards the cell supporting GMSK. This may for example
cause the EDGE cell to be underloaded while the GMSK cell is overloaded
thereby reducing the capacity of the cellular"communication system.
Hence, an improved system of cell selection would.be advantageous and in
particular a system allowing increased flexibility, improved cell selection

control, improved insensitivity to dynamic variations, improved cell selection
performance and/or increased capacity of a cellular communication system
would be advantageous.
Summary of the Invention
Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate
one or more of the above mentioned disadvantages singly or in any
combination.
According to a first aspect of the invention there is provided an apparatus for
controlling cell selection in a cellular communication system supporting a
plurality of modulation schemes, the apparatus comprising: means for
determining a modulation scheme distribution for a plurality of
communication channels of at least one cell; and means for modifying a cell
selection criterion in response to the modulation scheme distribution.
The invention may allow cell selection to take the modulation scheme
distribution in the cellular communication system into account. The
modulation scheme distribution is an indication of the modulation scheme
utilisation in the cellular communication and may in particular reflect the
modulation schemes used in the at least one cell.
The cell selection criterion may be optimised or improved for the modulation
scheme utilisation. This may result in improved cell selection performance
and/or may allow more reliable and/ or accurate control of the cell selection
procedures. The resource management may be improved and in particular the
management and control of the loading of cells may be improved. This may
reduce the probability of overloaded cells and may increase the capacity of the
cellular communication system and improve the user service. For example, the

number of dropped calls or access denials in the communication system may be
reduced.
In particular, the invention may compensate or offset a bias in the cell
selection performance due to the used modulation schemes.
According to a preferred feature of the invention, the plurality of
communication channels are communication channels of a single carrier.
This may provide a flexible and targeted modification of a cell selection
criterion in response to the characteristics of a specific carrier. In particular,
the carrier may be a carrier which is monitored by a cell selection procedure.
The carrier may for example be a frequency carrier of a TDMA system such as
GSM.
According to a preferred feature of the invention, the plurality of
communication channels are communication channels of a pilot carrier. Cell
selection is in many cellular communication systems based on signal level
measurements of a pilot carrier and modifying the cell selection criterion in
response to a modulation scheme distribution associated with the pilot carrier
may provide improved cell selection performance and may in particular
compensate or offset undesired biasing of cells due to the specific modulation
schemes used. For an EDGE GSM cellular communication system, the pilot
carrier may in particular be the BCCH carrier.
According to a preferred feature of the invention, the plurality of
communication channels are communication channels supporting an active
communication. An active communication may in particular be a
communication which has been ongoing during a time interval for which the
modulation scheme distribution has been determined. The modulation scheme
distribution may specifically reflect a current modulation scheme distribution

for a given time interval. The invention may thus provide for a dynamic
modification of the cell selection criterion in response to the current
modulation scheme utilisation. This may provide for an improved cell selection
performance. It may alternatively or additionally facilitate network resource
management as short term variations may automatically be compensated by
the modification of the cell selection criterion.
According to a preferred feature of the invention, the means for modifying is
further operable to modify the cell selection criterion in response to a power
characteristic associated with each modulation scheme. The power
characteristic may be a parameter or a requirement associated with the
modulation scheme, such as for example a peak to average power level
measure. This may provide improved accuracy and improved cell selection
performance.
According to a preferred feature of the invention, the power characteristic is a
linearity requirement. In particular, the power characteristic is preferably a
power back-off requirement of a power amplifier. Typically, the power
amplifier back-off required for different modulation schemes will result in
transmit power variations between these, and modifying the cell selection
criterion in response to these parameters may improve cell selection and in
particular compensate or offset the bias introduced by the modulation
schemes.
According to a preferred feature of the invention, the means for modifying a
cell selection criterion is operable to determine a cell selection power offset for
a signal level measurement. This provides a particularly advantageous means
of modifying the cell selection criterion. In particular, it allows easy
implementation, provides high cell selection performance and/or is suitable for
cellular systems wherein cell selection is in response to signal level
measurements in the remote units. In EDGE GSM, the signal level

measurements may particularly be mobile measurements of the received
BCCH signal level.
According to a preferred feature of the invention, the apparatus further
comprises means for transmitting cell selection criterion modification
information to remote units. This is particularly advantageous where cell
selection is performed by the remote unit. The cell selection criterion
modification information may specifically be cell selection power offsets to be
applied to signal level measurements made by the remote unit and used for
selecting a cell.
According to a preferred feature of the invention, the apparatus further
comprises^ means for determining a long term modulation scheme distribution
for the plurality of communication channels, the long term modulation scheme
distribution reflecting a distribution of modulation scheme usage determined
over a longer time interval than for the modulation scheme distribution;
means for determining a default cell selection criterion; and the means for
modifying the cell selection criterion is operable to temporarily modify a
parameter of the default cell selection criterion.
This may allow a high performance cell selection algorithm and/or facilitate
implementation. For example, a default cell selection criterion may be
determined to suit the average conditions in the cellular communication
system and this may be dynamically varied to suit the dynamic variations in
modulation scheme utilisation.
According to a preferred feature of the invention, the means for modifying is
further operable to modify the cell selection criterion in response to a loading
of the cell. This may improve cell selection and provide additional control of
the resource distribution between cells.

According to a preferred feature of the invention, the means for modifying is
further operable to modify the cell selection criterion in response to a loading
of a different cell of the cellular communication system. This may improve cell
selection and provide additional control of the resource distribution between
cells.
According to a preferred feature of the invention, the modulation scheme
distribution is determined for a plurality of cells. This may improve cell
selection and provide additional control of the resource distribution between
cells.
According to a preferred feature of the invention, the means for determining
the modulation scheme distribution is operable to determine the modulation
scheme distribution in response to a number of active communications
employing each supported modulation scheme. This may allow a simple and
easy to implement way of determining a modulation scheme distribution
suitable for modifying the cell selection criterion thereby improving the cell
selection performance.
According to a preferred feature of the invention, the modulation scheme
distribution comprises a plurality of modulation scheme categories and an
indication of a current usage level of the modulation schemes of each category.
This may provide a simple modulation scheme distribution representing the
current modulation scheme utilisation and is suitable for modifying the cell
selection criterion thereby improving the cell selection performance.
According to a preferred feature of the invention, the cell selection criterion is
an idle mode cell selection criterion. The invention may provide improved idle
mode cell selection performance thereby improving the performance of the
cellular communication system as a whole.

According to a preferred feature of the invention, the cell selection criterion is
a handover criterion. The invention may provide improved handover cell
selection performance thereby improving the performance of the cellular
communication system as a whole.
Preferably, the cellular communication system comprises EDGE
communication means. The cellular communication system preferably
comprises a GERAN (GSM EDGE Radio Access Network). In particular the
cellular communication system may be an EDGE GSM cellular communication
system.
Preferably the cellular communication system comprises a first and second
apparatus as described above and further comprising means for exchanging
modulation scheme distribution information. This may provide a suitable way
of communicating information allowing a modification of the cell selection
criterion in response to the modulation scheme distribution of a plurality of
cells.
According to a second aspect of the invention, there is provided a method of
controlling cell selection in a cellular communication system supporting a
plurality of modulation schemes, the method comprising the steps of
determining a modulation scheme distribution for a plurality of
communication channels of at least one cell; and modifying a cell selection
criterion in response to the modulation scheme distribution.
These and other aspects, features and advantages of the invention will be
apparent from and elucidated with reference to the embodiment(s) described
hereinafter.

An embodiment of the invention will be described, by way of example only,
with reference to the drawings, in which
FIG. 1 is an illustration of part of a cellular communication system in
accordance with an embodiment of the invention; and
FIG. 2 illustrates a method of controlling cell selection in accordance with an
embodiment of the invention.
Detailed Description of a Preferred Embodiment of the Invention
The following description focuses on an embodiment of the invention
i applicable to an EDGE GSM cellular communication system. However, it will
be appreciated that the invention is not limited to this application but may be
applied to many other cellular communication systems supporting a plurality
of modulation schemes such as a combined 2nd and 3rd Generation cellular
communication system.

FIG. 1 is an illustration of part of a cellular communication system 100 in
accordance with an embodiment of the invention.
FIG. 1 illustrates a first base station 101 comprising an apparatus for
controlling cell selection in accordance with an embodiment of the invention.
Only the parts of the base station 101 associated with the cell selection
apparatus have been illustrated, and it will be apparent to the person skilled
in the art that the base station 101 additionally comprises the required
functionality for operating in accordance with the specifications of the cellular
communication system. The base station 101 is connected to a fixed network
103 which is further connected to other base stations of which one neighbour

base station 105 is shown. FIG. 1 further illustrates a remote unit 107 which
is in idle mode and situated in a location where it is able to receive signals
from both the first base station 101 and the neighbour base station 105.
The first base station 101 comprises a base station controller 109 which is
operable to control the operation of the base station. In particular, the base
station controller 109 interfaces with the fixed network 103 and controls the
base station 101 to transmit user data and control messages in accordance
with the requirements of the EDGE GSM cellular communication system.
The base station controller 109 is coupled to a transmitter 111 which
transmits signals to the remote units 107 over the EDGE GSM air interface in
accordance with the EDGE GSM technical specifications. In particular the
transmitter 111 is under the control of the base station controller 109 operable
to transmit data using different modulation schemes. The modulation scheme
used in each time slot depends on the service supported by that time slot and
may also depend on the current propagation conditions. If a time slot is used to
support a GSM communication, the transmitter uses GMSK modulation
whereas a time slot supporting an EDGE communication may use an 8-PSK
modulation scheme.
The transmitter 111 comprises a power amplifier which amplifies the
modulated signal to a suitable power level for transmission. For the constant
amplitude modulation of GMSK, the power amplifier may be used up to the
maximum output power that can be provided by the power transmitter.
However, for the linear non-constant amplitude modulation of 8-PSK, it is
important that the power amplifier is used in a substantially linear region.
This requires that the power amplifier is backed off and typically a back off of
around 4 to 5 dBs are required. Accordingly, the maximum power output of the
power amplifier is around 4-5 dB lower for 8-PSK than for GMSK.

In an EDGE GSM cellular communication system, the BCCH carrier is used
as a pilot signal. The received signal level of the BCCH carrier is measured by
the remote units and is used to determine a serving cell. In particular, idle
mode mobiles measure the received BCCH signal levels of a number of base
stations and select the cell being received with the highest signal level as the
serving cell. Active remote units measure signal levels of a number of
neighbouring cells and report these back to the base station and the fixed
network for determining if a handover to another cell should be carried out.
Hence, the remote unit 107 measures the BCCH signal from base station 101
and base station 103 and cell selection is performed in response to these
measurements in accordance with a suitable cell selection criterion. In the idle
mode case, the remote unit 107 may simply select the base station having the
highest received signal level.
In order to provide a suitable reference signal, power control is not performed
on the BCCH carrier which instead is transmitted at the maximum power •
level available from the base station. However, when different modulation
schemes are used by the base station 201, the differences in the required back-
off between constant amplitude and non-constant amplitude modulation
schemes result in the average transmit power being dependent on the
modulation schemes used.
As a specific example, the base station controller 109 may control the
transmitter 111 to transmit a GMSK modulated signal in all time slots of the
BCCH carrier in which case the average transmit power within the
measurement time interval of the remote unit (typically around five seconds)
is the maximum power level of the power amplifier. However, at another time,
seven out of eight time slots of the BCCH carrier which are available for user
traffic may support EDGE communications using 8-PSK. Accordingly, the
power amplifier will be backed off by 4-5 dBs for seven out of the eight time
slots, resulting in the received signal level at the remote unit 107 being

reduced by around 4 dB. Thus, the transmit power level of the BCCH carrier
may fluctuate in response to the applied modulation schemes resulting in a
reduced performance of the cell selection process.
The variation in transmit power of the BCCH can furthermore complicate
resource management and reduce the capacity of the cellular communication
system. For example, cells having a high number of EDGE communications
supported by the BCCH will be measured with a lower signal level than if the
cell supported fewer EDGE communications. This will tend to shift remote
units away from EDGE supporting cells which may result in the cell being
under loaded while neighbour cells are overloaded.
The base station 101 of FIG. 2 further comprises a modulation scheme
processor 113 which is operable to determine a modulation scheme
distribution for a plurality of communication channels of the cell of the base
station. The modulation scheme processor 113 is coupled to a cell selection
processor 115 which is operable to modify a cell selection criterion in response
to the modulation scheme distribution. In the described embodiment, the cell
selection processor 115 is coupled to the transmitter 111 in order to transmit
information of the modifications to the cell selection criterion to the remote
units of the cell. The information of the modifications of the cell selection
criterion may be communicated on the BCCH broadcast channel thereby being
broadcast to all remote units capable of receiving the BCCH signal.
The modulation scheme processor'113 may determine the modulation scheme
distribution in accordance with any suitable method or algorithm. The
modulation scheme distribution is an indication of the modulation scheme
utilisation. In particular, the modulation scheme distribution may reflect
which modulation schemes may currently active or which modulation schemes
are allocated to different time slots, channels and/or carriers. Specifically, the
modulation scheme distribution may be an indication of the modulation

scheme utilisation which allows for the impact on the transmit power of a base
station to be determined.
The cell selection processor 115 may determine a modification to a cell
selection criterion which takes into account the modulation scheme utilisation,
and in particular the cell selection criterion may be modified to compensate for
a change in the transmit power of a base station caused by the modulation
schemes used. It will be appreciated that any suitable cell selection criterion or
modification thereof may be used without detracting from the invention. For
example, a cell selection algorithm may comprise a number of alternative
conditions for selecting a cell and the modification of the cell selection criterion
may be achieved by selecting a specific condition to apply for cell selection. In
other embodiments, a parameter or relationship used by the cell selection
algorithm may be modified in response to the modulation scheme distribution.
Hence, the embodiment may allow a cell selection criterion to be modified to
compensate for variations in the modulation schemes used. This may improve
cell selection performance, enhance and facilitate the control of the cell
selection and increase the capacity of the communication system as a whole.
A specific example of the operation of the EDGE GSM communication system,
wherein power variations of the BCCH carrier are compensated, will be
described in the following. FIG. 2 illustrates a method of controlling cell
selection in accordance with an embodiment of the invention. The method is in
the following example performed by the base station 101 of FIG. 1 and will be
described with reference to this. The example is suitable for a cell selection
algorithm for idle mode remote units where the cell selection criterion is
applied by the remote unit and is based on BCCH signal level measurements
made by the remote unit. Specifically, the remote unit may select the cell
having the highest received signal level after compensation.

In the example, the modulation scheme processor 113 determines a
modulation scheme distribution in step 201. The modulation scheme
distribution is determined in response to the communication channels of a
single carrier and specifically the modulation scheme distribution is
determined for the pilot carrier in the form of the BCCH carrier.
In addition, the modulation scheme distribution is determined to reflect the
current dynamic conditions and is thus determined for the communication
channels supporting an active communication. Thus, the modulation scheme
distribution is determined by evaluating which modulation schemes are used
in the time slots of the BCCH carrier.
Furthermore, the modulation scheme distribution is determined in response to
a number of active communications employing each supported modulation
scheme. The modulation scheme distribution of the described embodiment
comprises a plurality of modulation scheme categories. As a simple example,
the modulation scheme of each time slot is either a GMSK modulation scheme
or an 8-PSK modulation scheme and the modulation scheme distribution
therefore simply comprises a first category corresponding to GMSK
modulation and a second category corresponding to 8-PSK modulation.
In the example, the modulation scheme distribution comprises an indication of
a current usage level of the modulation schemes of each category and in
particular the modulation scheme distribution comprises an indication of the
number of time slots currently using GMSK and the number of time slots
currently using 8-PSK.
As a specific example, the BCCH carrier may use GMSK for the control time
slot 0, 8-PSK in time slots 1 to 4 and GMSK in time slot 5 to 7. The modulation
scheme processor 113 will be provided with this information from the base
station controller 209 and will accordingly generate a modulation scheme

distribution indicating that 4 time slots fall in the GMSK category and 4 time
slots fall in the 8-PSK category.
Step 201 is followed by step 203 wherein the cell selection processor 115
determines a modification to the cell selection criterion. In the example, the
modification is effected by setting a cell selection power offset. The cell
selection power offset corresponds to an offset which is to be applied to the
signal level measurements of the BCCH carrier performed by the remote unit
107.

In the example, the cell selection processor 115 determines the cell selection
power offset in response to the modulation scheme distribution and a power
characteristic associated with each modulation scheme. The power
characteristic is in this example a characteristic which is indicative of the
transmit power that is used for the specific modulation scheme. In the specific
embodiment, the power reduction of the transmit power depends on the
linearity required by the power amplifier. Typically, the higher the linearity
requirement for a modulation scheme the higher the required back off of the
transmit power amplifier and thus the lower the maximum transmit power.

As a specific example, the cell selection processor 115 may have information
that for a GMSK signal no back-off is required whereas for an 8-PSK signal a
back off of 6 dB is required in order to meet the linearity requirement for the
non-constant amplitude modulation scheme. Hence, when receiving a
modulation scheme distribution from the modulation scheme processor 113
indicating that the BCCH carrier uses GMSK in four time slots and QPSK in
four time slots, the cell selection processor 115 determines that the power
amplifier is backed off by 6 dB, and thus that the output power is reduced by 6
dB for half the duration. Thus, the average transmit power is 3 dB lower than
the transmit power if all time slots use GMSK modulation. Hence, the cell
selection processor 115 determines a cell selection power offset of 3 dB which is

to be applied to measurements of the BCCH carrier of base station 101 made
by the remote unit 107.
Step 203 is followed by step 205 wherein the cell selection power offset is fed
from the cell selection processor 115 to the transmitter 111 for transmission to
the remote units. Thus, the base station 201 transmits cell selection criterion
modification information in the form of the cell selection power offset to remote
units. In particular, the base station may broadcast the cell selection power
offset by including it in a system information message of the BCCH carrier.
In the example, the remote unit 107 is in idle mode and performs a cell
selection in response the received signal level measurements of the BCCH
carriers of the surrounding base stations. In particular, the remote unit
receives the BCCH carrier of the first and second base station 101, 103 and
measures the signal level averaged over a time interval (e.g. 5 seconds). In
addition, the remote unit demodulates time slot 0 of the BCCH carriers and
decodes the transmitted system information messages. The system
information messages from the first base station comprises the cell selection
power offset and the remote unit adds the cell selection power offset to the
measured signal level of the first base station 101. Thus, 3 dB is in the specific
example added to the signal level measurement of the first base station 101
thereby, compensating for the reduction of transmit power caused by the use of
8-PSK modulation in four time slots.
In the embodiment, the signal level measurements are compensated for
transmit power variations caused by the use of different modulation schemes
and cell selection may be performed on the basis of the compensated signal
levels. In particular, the remote unit may select the base station resulting in
the highest compensated signal level corresponding to the lowest propagation
loss. Thus, improved cell selection may be achieved.

In the described embodiment, a default cell selection criterion consisting in
selecting the cell having the highest received signal level is modified by
dynamically compensating the measured signal levels in response to the
current modulation scheme distribution. Thus, a default cell selection criterion
based on an assumption of a maximum transmit power is temporarily modified
by introducing a cell selection power offset representing transmit power
variations due to the actual modulation schemes used.
In some embodiments, the default cell selection criterion is not simply based
on a static assumption but is based on a long term evaluation of the
modulation scheme distribution. Thus, the base station 201 may in such an
embodiment comprise means for determining a long term modulation scheme
distribution. The long term modulation scheme distribution is determined over
a longer time interval than for the modulation scheme distribution determined
by the modulation scheme processor 113. In particular, the long term
modulation scheme distribution may be determined, by averaging the
modulation scheme distribution over a suitable time interval. For example, a
new modulation scheme distribution may be determined at ten minute
intervals whereas the long term modulation scheme distribution may be
determined on a daily or weekly basis.
In the embodiment, the long term modulation scheme distribution thus
reflects the long term average modulation scheme utilisation whereas the
modulation scheme distribution reflects the short term variations. The base
station may in response to the long term modulation scheme distribution
determine a default cell selection criterion suitable for the average conditions.
For example, the default cell selection criterion may be a comparison between
measured signal levels assuming a transmit power equal to the average
transmit power for the long term modulation scheme distribution. The base
station may further vary this temporarily in response to the modulation

scheme distribution, for example by applying temporary cell selection power
offsets.
It will be appreciated that the cell selection processor 115 may consider other
parameters or characteristics when modifying the cell selection criterion than
the modulation scheme distribution.
For example, in some embodiments, the cell selection processor 115 may
further modify the cell selection criterion in response to a loading of the cell
and/or of other cells.
In a specific such embodiment, the cell selection criterion is only modified if
the cell or one of the surrounding cells is loaded above a given level. Thus, in
situations where no cell is in danger of being overloaded, no modification is
made to the cell selection criterion as this is unlikely to be critical or result in
reduced performance. However, in situations where the cell selection is critical
because one or more of the involved cells may be approaching congestion, a
more accurate cell selection criterion may be used which more closely reflects
the actual conditions and therefore provides an improved cell selection.
In the described embodiment, the modulation scheme distribution was
determined only for one cell. However, it will be appreciated that in other
embodiments, the modulation scheme distribution may reflect the modulation
scheme utilisation of a plurality of cells.
For example, the modulation scheme processor 113 may receive information
from other base stations indicating which modulation schemes are used in the
time slots of the BCCH carriers of those cells. The modulation scheme
distribution may for example comprise information that in base station 101
four time slots use GMSK and four time slots use 8-PSK and that in the
' second base station 103 six time slots use GMSK and two time slots use 8"

PSK. In response, the cell selection processor 115 may for example determine
a cell selection power offset reflecting' the average transmit power difference
between the first base station 101 and the second base station 105 rather than
a relative offset to the maximum transmit power of the base station itself.
Hence, in the example, a cell selection power offset of 1.8 dB may be
transmitted to the remote unit 107 to be applied when comparing the signal
level measurements of the first and second base station.
Furthermore, in some embodiments different cells may autonomously
determine suitable cell selection power offsets and transmit these. For
example, in an EDGE GMSK systems the remote units decode the BCCH of
not only the serving cell but also of the neighbour cells being monitored. In
this case, each base station may determine a suitable cell selection power
offsets for the cell supported by the base station and may transmit this
information on the BCCH. The remote unit will thus receive suitable cell
selection power offsets from the neighbour cells and may apply these to the
appropriate BCCH signal level measurements.
In some embodiments, only the pilot signal of the currently selected cell is
decoded. For example, for packet communication using a PBCCH (Packet
BCCH), the remote unit decodes only that of the serving cell and the
neighbour cell data is broadcast on the PBCCH of the serving cell. In this
embodiment, neighbouring cells may exchange information related e.g. to the
cell selection power offsets of the cells and the cell selection power offsets for
both the serving cell and neighbouring cells may be broadcast on the PBCCH
of the serving cell.
The above description has focussed on an embodiment wherein an idle mode
remote unit performs cell selection in response to measurements and
information transmitted from a base station. However, it will be appreciated
that the cell selection may be performed at other locations and in particular

may be performed in the network. Thus, not only the cell selection processor
modifying the cell selection criterion but also the cell selection algorithm itself
may be performed in the network. The cell selection may thus be performed in
the base station, in the fixed network or may be distributed between these.
For example, the cell selection may be a handover cell selection performed in a
BSC based on measurements of BCCHs made by the remote unit 107 and
transmitted to the base station 101. In such an example, each base station
may comprise a modulation scheme processor 113 determining a current
modulation scheme distribution and reporting this to the BSC. The BSC may
then proceed to offset all neighbour measurements from the remote unit 107
by a value indicative of the transmit power reduction due to the modulation
schemes used of the individual base station. Hence, an improved handover
performance may be achieved.
The invention can be implemented in any suitable form including hardware,
software, firmware or any combination of these. However, preferably, the
invention is implemented at least partly as computer software running on one
or more data processors and/or digital signal processors. The elements and
components of an embodiment of the invention may be physically, functionally
and logically implemented in any suitable way. Indeed the functionality may
be implemented in a single unit, in a plurality of units or as part of other
functional units. As such, the invention may be implemented in a single unit
or may be physically and functionally distributed between different units and
processors.
Although the present invention has been described in connection with the
preferred embodiment, it is not intended to be limited to the specific form set
forth herein. Rather, the scope of the present invention is limited only by the
accompanying claims. In the claims, the term comprising does not exclude the
presence of other elements or steps. Furthermore, although individually listed,

a plurality of means, elements or method steps may be implemented by e.g. a
single unit or processor, Additionally, although individual features may be
included in different claims, these may possibly be advantageously combined,
and the inclusion in different claims does not imply that a combination of
features is not feasible and/or advantageous. In addition, singular references
do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do
not preclude a plurality.

We Claim :
1. An apparatus for controlling cell selection in a cellular communication system
supporting a plurality of modulation schemes, the apparatus comprising:
means for determining a distribution of active modulations for a plurality of
communication channels of at least one cell; and
means for modifying a cell selection criterion in response to the distribution of
active modulations.
2. An apparatus as claimed in claim 1, wherein the plurality of communication
channels are communication channels of a single carrier.
3. An apparatus as claimed in claim 1 or 2, wherein the plurality of communication
channels are communication channels of a pilot carrier.
4. An apparatus as claimed in any one of the preceding claims, wherein the plurality
of communication channels are communication channels supporting an active
communication.
5. An apparatus as claimed in any one of the preceding claims, wherein the means for
modifying is operable to modify the cell selection criterion in response to a power
characteristic associated with each modulation scheme.
6. An apparatus as claimed in claim 5, wherein the power characteristic is a linearity
requirement.
7. An apparatus as claimed in claim 6, wherein the power characteristic is a power
back-off requirement of a power amplifier.

8. An apparatus as claimed in any one of the preceding claims, wherein the means for
modifying a cell selection criterion is operable to determine a cell selection power offset
for a signal level measurement.
9. An apparatus as claimed in any one of the preceding claims, having means for
transmitting cell selection criterion modification information to remote units.
10. An apparatus as claimed in any one of the preceding claims, having
means for determining a long term distribution of active modulations for the
plurality of communication channels, the long term distribution of active modulations
reflecting a distribution of modulation scheme usage determined over a longer time
interval than for the distribution of active modulations;
means for determining a default cell selection criterion; and
wherein the means for modifying the cell selection criterion is operable to
temporarily modify a parameter of the default cell selection criterion.
11. An apparatus as claimed in any one of the preceding claims, wherein the means for
modifying is operable to modify the cell selection criterion in response to a loading of the
cell.
12. An apparatus as claimed in any one of the preceding claims, wherein the means for
modifying is operable to modify the cell selection criterion in response to a loading of a
different cell than the at least one cell of the cellular communication system.
13. An apparatus as claimed in any one of the preceding claims, wherein the
distribution of active modulations is determined for a plurality of cells.
14. An apparatus as claimed in any one of the preceding claims, wherein the means for
determining the distribution of active modulations is operable to determine the distribution
of active modulations in response to a number of active communications employing each
supported modulation scheme.

15. An apparatus as claimed in any one of the preceding claims, wherein the
distribution of active modulations comprises a plurality of modulation scheme categories
and an indication of a current usage level of the modulation schemes of each category.
16. An apparatus as claimed in any one of the preceding claims, wherein the cell
selection criterion is an idle mode cell selection criterion.
17. An apparatus as claimed in any one of the preceding claims, wherein the cell
selection criterion is a handover criterion.
18. An apparatus as claimed in any one of the preceding claims, wherein the cellular
communication system comprises EDGE communication means.
19. A base station for a cellular communication system comprising an apparatus as
claimed in any one of the preceding claims 1 to 18.
20. A cellular communication system comprising a first apparatus as claimed in any of
the preceding claims 1 to 18.
21. A cellular communication systern as claimed in claim 20, wherein the cellular
communication system comprises a second apparatus as claimed in any one of the
preceding claims 1 to 18 and wherein the first and second apparatus comprise means for
exchanging distribution of active modulations information.
A base station (101) may transmit using different modulation schemes. The transmit power of a pilot
signal used for cell selection varies depending on the modulation schemes currently used, for example
due to varying power amplifier back-up requirements. The base station (101) comprises a modulation
scheme processor (113) determining a modulation scheme distribution for a plurality of communication
channels of the cell. The modulation scheme distribution reflects the current modulation scheme
utilisation for the pilot signal and is indicative of the power variation of the pilot signal. A cell selection
processor (115) modifies a cell selection criterion in response to the modulation scheme distribution. In
particular, the cell selection processor (115) determines a cell selection power offset to be applied to
measurements of the signal levels of the pilot signal. The cell selection power offset preferably
corresponds to the average power variation resulting from the current modulation scheme utilisation
thereby allowing this to be compensated.

Documents:

02347-kolnp-2006-abstract.pdf

02347-kolnp-2006-assignment.pdf

02347-kolnp-2006-claims.pdf

02347-kolnp-2006-correspondence others-1.1.pdf

02347-kolnp-2006-correspondence others.pdf

02347-kolnp-2006-correspondence-1.2.pdf

02347-kolnp-2006-description(complete).pdf

02347-kolnp-2006-drawings.pdf

02347-kolnp-2006-form-1.pdf

02347-kolnp-2006-form-18.pdf

02347-kolnp-2006-form-3.pdf

02347-kolnp-2006-form-5.pdf

02347-kolnp-2006-gpa.pdf

02347-kolnp-2006-international publication.pdf

02347-kolnp-2006-international search authority report.pdf

02347-kolnp-2006-pct others.pdf

02347-kolnp-2006-priority document.pdf

2347-KOLNP-2006-(23-03-2012)-CORRESPONDENCE.pdf

2347-KOLNP-2006-ABSTRACT 1.1.pdf

2347-KOLNP-2006-AMANDED CLAIMS.pdf

2347-KOLNP-2006-CORRESPONDENCE 1.1.pdf

2347-KOLNP-2006-CORRESPONDENCE-1.2.pdf

2347-KOLNP-2006-CORRESPONDENCE.pdf

2347-KOLNP-2006-DESCRIPTION (COMPLETE) 1.1.pdf

2347-KOLNP-2006-DRAWINGS 1.1.pdf

2347-KOLNP-2006-EXAMINATION REPORT.pdf

2347-KOLNP-2006-FORM 1-1.1.pdf

2347-KOLNP-2006-FORM 18.pdf

2347-KOLNP-2006-FORM 2.pdf

2347-KOLNP-2006-FORM 3-1.1.pdf

2347-KOLNP-2006-FORM 3.pdf

2347-KOLNP-2006-FORM 5-1.1.pdf

2347-KOLNP-2006-FORM 5.pdf

2347-KOLNP-2006-GPA.pdf

2347-KOLNP-2006-GRANTED-ABSTRACT.pdf

2347-KOLNP-2006-GRANTED-CLAIMS.pdf

2347-KOLNP-2006-GRANTED-DESCRIPTION (COMPLETE).pdf

2347-KOLNP-2006-GRANTED-DRAWINGS.pdf

2347-KOLNP-2006-GRANTED-FORM 1.pdf

2347-KOLNP-2006-GRANTED-FORM 2.pdf

2347-KOLNP-2006-GRANTED-SPECIFICATION.pdf

2347-KOLNP-2006-OTHERS.pdf

2347-KOLNP-2006-OTHERS1.1.pdf

2347-KOLNP-2006-PETITION UNDER RULE 137.pdf

2347-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

253561

Indian Patent Application Number

2347/KOLNP/2006

PG Journal Number

31/2012

Publication Date

03-Aug-2012

Grant Date

31-Jul-2012

Date of Filing

18-Aug-2006

Name of Patentee

MOTOROLA,INC.

Applicant Address

1303 EAST ALGONQUIN ROAD SCHAUMBURG, ILLINOIS 60196 U.S.A.

Inventors:

#	Inventor's Name	Inventor's Address
1	MOLKDAR DAVOOD	THAMESDOWN DRIVE SWINDON WILTSHIRE SN254XY GREAT BRITAIN
2	THOMAS HOWARD	THAMESDOWN DRIVE SWINDON WILTSHIRE SN254XY GREAT BRITAIN

PCT International Classification Number

G06F 3/00

PCT International Application Number

PCT/US2005/015140

PCT International Filing date

2005-04-29

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	0410007.9	2004-05-05	U.K.