|Title of Invention
A METHOD FOR TRANSMITTING A PIECE OF CONTROL INFORMATION FROM A BASE STATION TO A MOBILE STATION
|The transmission of control infonnation from a base station to at least one mobile station in the cell of a cellular radio system takes place using a first channel and a second channel. At a first moment of time, there is an indication on the first channel about the location of the piece of control infonnation on the second channel. At a second moment of time, later than said first moment, the piece of control infonnation is transmitted on the second channel.
Method for using effectively the broadeast capacity in a cell
1 he invention concerns the technology of broadcasting an amount of general information to a multitude of radio receivers in a way that uses effectively the radio resources that arc available. Especially the invention concerns the application of such technology in a cellular radio network.
In cellular networks there is commonly known the concept of cell broadcasting. It means that the base station of a cell transmits some information that is meant to be received by all mobile stations within the reach of the base station, or at least by a significant number of them. In a cell of a typical prior art cellular radio network there is determined a so-called common control channel or a BCCH (Broadcast Control CHannel) that is receivable by all mobile stations in the cell. Although BCCH is a reserved name of a channel in a particular second generation cellular radio network (the GSM; Global System for Mobile telecommunications) it is used here as the general denomination of a common control channel without limiting the scope of the discussion to any particular system. The BCCH is used to convey information about e.g. the identity of the neighboring cells and their BCCH frequencies so that a mobile station may monitor the level of power it receives on those frequencies, A significant rise in the BCCH power level of a neighboring cell indicates that the mobile station is moving towards a position where a handover or cell reselection to the neighboring base station will be performed.
At the time of filing this patent application the third generation of cellular radio networks is under specification. Already it is seen that the amount of information that should be transmitted on a BCCH or the like will eventually be larger in the third generation systems than in the present second generation systems. For example, at a certain location there may be an overlap of cells from a macrocell RAN (Radio Access Network) and a nanocell RAN, whereby the mobile station should he informed not only about the identities of the neighboring cells but also about their characteristics (highest possible rate of transmitted user data, available modulation methods etc.) so that the mobile station could determine, which one of the neighboring and/or overlapping cells would be the best possible candidate for a handovei or cell reselection.
transmission power whereby in the latter case the applied channel coding could be reduced. However, radio resources (time, frequency, power) are scarce in a cell, so giving more capacity to a common channel reduces the capacity available for dedicated channels. Additionally the amount of information to be broadcast may vary from one cell to another, because not everywhere ia the network are there numerous neighboring or overlapping cells, the characteristics of which should be transmitted. If a very large portion of the available capacity is given to the BCCH, it may happen that in many cells a significant portion of this papacity is underutilized while simultaneously some connection setup requests must be turned down because all capacity available for dedicated channels is occupied. Eyen in areas where there actually is a lot of BCCH information to be transmitted, some BCCH capacity should be reserved for future additions and this capacity would be underutilized
everywhere at least during the initial service life of the system.
From the patent US 4 850 033 there is known a method in which a transmission channel of each base station is assigned as a simplex message transmission channel in which a given base station transmits to the mobile stations information describing the structure of the control channels. Such information includes references to message transmission channels of adjoining base stations, and references to one or more control channels assigned to the given base station. The message transmission channels are thus at a higher level in the hierarchy of references than the control channels. Access by several different kinds of subscriber sets and different services can be provided by transmitting a relatively small number of references.
From the Finnish patent application number FI980014 there is known a method in which the otherwise unused capacity of a paging channel is used to transmit information logically belonging to other channels. Since the mobile stations must listen to the paging channel regardless of whether there are paging messages or not, the periods during which their receivers are switched on can this way be utilized better than just for listening to an empty paging channel.
It is an object of this invention to present a method and a system for enabling the transmission of a variable amount of common control data in a cell. It is a further object of this invention that in a method and a system according to the invention, future additions to the common control arrangement would be possible without initially reserving significant capacity for them.
different parts can he found in the time and frequency co-ordinate system of the cell.
The method according to the invention is characterised in that it comprises the slops of
- at a first moment of time, indicating on the first channel the location of the piece
of control information on the second channel and
- at a second moment of time, later than said first moment; transmitting the piece of
control information on the second channel.
The general inventive idea of dividing the control channel information into parts that are separately available may be realised using two alternative approaches or a hybrid approach containing features from both of the two alternatives. The first alternative approach is to define a group of different information unit types, designated as Protocol Data Units or PDUs in an exemplary manner, and to set up a transmission schedule which relates the PDU types to certain frames of the control channel information. The most important PDU type will appear most often,
preferably in each frame containing control channel information, and the other PDU
types will appear in every second frame, every third frame or generally in every Nth
frame according to PDU type, where N is an integer. The schedule of appearance of
different PDU types and the type of information contained within each PDU type
will be communicated to the mobile stations, so they may decide, which PDU types
they need to receive. i
The second alternative is to send a part of the common control information on some other channel and indicating in a common control channel frame where among the other channels the additional common control information can be found. The information units contained within a common control channel frame and indicating the location of some other common control information are called pointers. The location indicated by a pointer may be for example in some traffic channel configured to be a point-to-multipoint channel. In an advantageous embodiment of the invention the pointer indicates not only the location but also the type of information contained within some other channel so that the mobile stations may decide, whether they need to receive the additional information or not.
every Mth common control channel frame, where M is an integer defined statically in the system specifications or dynamically, either by the base station transmitting the control channel information or by the radio network controller controlling the
operation of the base station.
The novel features which are considered as characteristic of the invention are set
forth in particular in the appended Claims. The invention itself, however, both as to
its construction and its method of operation, together with additional objects and
advantages thereof, will be best understood from the following description of
specific embodiments when read in connection with the accompanying drawings.
Fig. 1 illustrates a system according to the first alternative approach of the
invention, Fig. 2 illustrates an exemplary schedule of PDU types in the system of Fig. 1,
Fig. 3 illustrates a system according to the second alternative approach of the
I Fig. 4 illustrates the contents of an exemplary pointer used in the system of Fig.
Fig. 5 illustrates a system according to the hybrid approach of the invention,
i Fig. 6a illustrates a first embodiment of the method according to the invention and
Fig. 6b illustrates a second embodiment of the method according to the invention.
For conveying IK CM data Horn the base station to the mobile stations a control information channel 103 has been specified as occupying certain predetermined parts of the time and frequency co-ordinate system of the cell. If CDMA ((Ode Division Multiple Access) or other spread spectrum technology is used in the cellular radio system, also the spreading code used to spread the control information must be used as a co-ordinate that defines the radio resources reserved for the control information channel. The control information channel is called the IK Til for short, although it should be understood that denominations like BCCII used in this patent application do not limit the applicability of the invention to any specific cellular radio systems.
BCCII data is arranged into mutually independent units called Protocol Data Units or PDUs 104. On the other hand, transmission in general is arranged to take place in transmission frames, the temporal duration of which is constant. According to the first alternative approach of the invention there are several PDU types, known as PDU type 1, PDU type 2 and so on, and the appearance of PDUs representing a certain PDU type follows a certain schedule with regard to the transmission frames. Fig. 2 is an exemplary schedule for PDU types 1, 2, 3 and 4. The frame numbers at the top of Fig. 2 are proportional so that in a certain predetermined overall frame structure like a superframe or hyperframe there can be defined a certain frame 1, frame 2 and so on until after frame 9 the numbering cycle is restarted from frame 1 until all the frames in the frame structure have been numbered. It can be seen from Fig. 2 that PDUs of type 1 appear in each frame, PDUs of type 2 appear in every third frame starting from frame 1, PDUs of type 3 appear only in odd-numbered
frames and PDUs of type 4 appear only in frames 2 and 6.
For the method to be flexibly adaptable to different amounts of BCCH data, the schedule of appearance of different PDU types is not fixedly specified but it can vary from one cell to another. The information about which types of PDUs are transmitted and in which frames is communicated from the base station to the mobile stations by using a certain PDU known as the channel configuration PDU. Alternatively each PDU may contain an information element indicating the period of appearance of this PDU type in frames (when the PDU type appears periodically) or the proportional frame numbers in which this PDU type appears.
mobile stations the possibility of deciding beforehand, which PDUs they want to receive. Having the receiver switched on in a mobile station consumes energy depleting the battery of the mobile station, so it is advantageous to have the receiver of a mobile station switched off always when there is nothing important to be
i The capacity reserved for the BCCH limits the number of; PDUs that can be transmitted' within each transmission frame. It is on the responsibility of the base station or the radio network controller controlling its operation to arrange the PDUs into the available capacity so that all BCCH data will eventually be transmitted. Typically in an area where there is a large amount of BCCH data to be transmitted the base
station or radio network controller will increase the number of frames between
successive transmissions of PDUs of certain type so that effective bit rate available for the transmission of the information conveyed in PDUs of that type will be lower than in areas where the amount of BCCH data to be transmitted is small.
Fig. 3 illustrates a system according to the second alternative approach of the invention. Base station 301 again transmits control information to a multitude of mobile stations 302, for which a control information channel 303 has been specified, but there are also specified other channels called point-to-multipoint (PTM) traffic channels 304 between the base station and the mobile stations. A base station or a radio network controller may specify a certain channel or a number of channels as point-to-multipoint traffic channels when needed by transmitting a respective channel configuration message to the mobile stations. If no such specification is made, the respective capacity is available for dedicated (point-to-point) traffic channels.
In Fig. 3 there is a certain minimum amount of BCCH data that is transmitted in respective PDUs 305 on the BCCH. The amount and content of this minimum amount of BCCII data depends on the cellular radio system to which the invention is applied, but it is expected that at least information giving identification of the
The third and fourth fields 403 and 404 identify the location where the pointer PDU points to. Field 403 is a one-octet long Carrier Number and field 404 is a one-octet long Channel Identifier. They identify the carrier (in a multifrequency system) or the spreading code (in a single-frequency spread spectrum system) and the channel in which the actual BCCH data is located. Field 405! contains the Timing
Information which is used to indicate, when the BCCH data concerned will be available at the specified location. The proposed length of this field is 2 octets and several alternative time coding schemes are possible. For example the Timing Information may be a frame number in a superfirame or a hyperframe, indicating the first frame in that larger aggregate of frames where the BCCH data will be available, together with a period code indicating the number of frames between successive appearances of the data within the superframe of hyperframe. The period code is naturally applicable only if the BCCH data concerned will appear
periodically. Another possibility for indicating a certain! frame in the Timing
Information is to indicate the number of frames between the current frame and the first following frame containing the BCCH data concerned, again possibly combined with a period code. Other alternatives for using the Timing Information field arc easily presented by a person skilled in the art.
The composition of a pointer PDU illustrated in Fig. 4 is naturally only exemplary.
Other fields that it might include are for example a length indicator indicating the
overall length of the pointer PDU (in case it is not constant) and other fields typical
to Layer 3 messages. The lengths of the fields proposed above are probably some-
what too pessimistic; several effective coding schemes are known from the
technology of Layer 3 messaging for reducing the length of separate fields. For
example, a single bit could suffice for the Updated field, whereby its value would
indicate whether the information has been updated during a certain passed time
period or not. j
After having received the pointer PDUs a mobile station analyses, which BCCH
data it needs to receive, and tunes its receiver to the correct channel at the correct
time for receiving the BCCH data. Alternatively the mobile station may inform its
user about the need for downloading certain information conveyed as BCCH data,
and ask for a permission to receive the BCCH data. This alternative is especially
useful when the amount of data to be downloaded is large and its downloading
would incur significant costs.
The flexibility of the second alternative approach to the invention, discussed above with reference to Figs. 3 and 4, is readily seen. The base station or radio network controller may allocate capacity from a point-to-multipoint channel for the purposes of conveying BCCH data as needed, and cancel the allocations whenever the amount of BCCH data falls below a certain predetermined threshold. Although a point-to-multipoint-type traffic channel has been described above as the favourable medium for transmitting the actual BCCH data, a pointer PDU may basically point to any location in the channel allocation scheme of a cell or even to some location in some different set of communication resources available to the mobile stations. For example in the above-mentioned case where the mobile stations asks the user for a permission before downloading certain information conveyed as BCCH data, even a dedicated traffic channel could be used. After having received the permission from the user, the mobile station will then transmit a channel request to the base station and indicate in some specific message that it would like to receive certain information conveyed as BCCII data. A connection using a dedicated traffic channel will be established and the requested information will be transmitted to (ho mobile station that requested it
data transmission network the pointer PDU may point lo a certain network address. like an Internet address A mobile station that receives the pointer PDU and wants lo receive the information identified in the pointer PDU will then send a packet to (he indicated address, containing a request for downloading the information. The network server responsible for the resources behind said address will then send the requested data in packetized form to the mobile station. Here again the mobile station may ask its user for a permission before sending the packet containing the request.
Another important application of the pointer PDU approach is the scheduling of transmissions in order to balance the loading of the control information channels between rush hours and more quiet times. It is commonly known that during the very early hours in the morning the momentary need for both transmitted control information and reserved dedicated channels in the cells of a cellular radio system is very small, because a majority of the users are asleep and their mobile stations are stationary and idle if not totally switched off. During these times there is plenty of free capacity in the network so the transmission of even large amounts of information conveyed as BCCH data is possible. During active daytime a system according to this particular embodiment of the invention can transmit pointer PDUs indicating that large blocks of information are available for downloading next night or some other time in the future. If the nature of the information is such that the mobile stations do not need it right away, they can just memorize the announced future transmission time of the information and wait until something like 03.00 AM before downloading the information from a location somewhere within a point-to multipoint channel, pointed to by the pointer PDUs. On the other hand, during daytime the same information could be offered to users that need it immediately, whereby those users will have to request for an immediate transmission on a dedicated traffic channel - and probably pay more because their request and its fulfilment consume the radio resources of that cell.
Downloading the scheduled information from a previously announced point ■■to-multipoint channel at a previously announced time naturally requires that, the mobile station will be switched on at the previously announced time. It could be useful to arrange for the User Interface (III) of the mobile station to warn the user about the scheduled downloading if an attempt is made to power down the mobile station before the announced lime.
stations about the location of some actual block of BCCH! data like in the second approach discussed above. However, the pointer PDUs only appear as
representatives of one PDU type, which has its own transmission schedule as in the
first approach discussed above. BCCH data can be classified into a relatively large number of groups according to some indication of its importance and urgency. The most urgent and most important BCCH data will then be transmitted in each transmission frame, some less urgent data will be transmitted perhaps not more often tnan in every third transmission frame, and the least urgent BCCH data
somewhere else in the channel structure, as indicated by pointer PDUs on the actual
Figs. 6a and 6b illustrate the operation of a Base Station (BS) and a Mobile Station (MS) according to the invention. The straight arrows indicate the propagation from one functional step to another in each device and the curved arrows indicate the mutual relations between transmit and receive functions. In Fig. 6a the base station goes through the functional steps 601, 602 and 603 regularly or according to the need of transmitting BCCH data on the second channel. After having received, at step 604, an indication about an incoming BCCH data transmission on the second channel the mobile station will prepare itself for reception and consecutively receive the BCCH data at step 605. In Fig, 6b there is the difference that the mobile station has to ask for the BCCH data transmission at step 606 (request received at step 607) before the base station will transmit.
If the mobile station is equipped to warn the user against powering down the mobile station before an already indicated BCCH data transmission will take place, the warning step will be found in Figs. 6a and 6b somewhere after step 604 and before step 605.
The invention does not restrict the nature of the information sent directly on the BCCH or in some location pointed to by a pointer PDU on the BCCH. Typical examples of such information that has a volume large enough to justify the "enlarged BCCH" concept of the invention are software updates to the mobile stations and service provider information. The latter can include both information about the service providers whose services are available and description of the services themselves.
used on the BCCII and the instructions for decoding a pointer PDU to he able to utilize those services and functions that had been specified at the moment when the mobile station left the facilities of its manufacturer and/or programmer. All information meant only for more advanced or more recently released mobile stations will appear as unidentified PPUs or unidentified information elements to the basic mode mobile station, whereby it ignores them and utilizes only those services and functions which it identifies and understands.
1. A method for transmitting a piece of control information from a base station
(BS) to at least one mobile station (MS) in the cell of a cellular radio system using a
first channel and a second channel, characterised in that it comprises the steps of
- at a first moment of time, indicating (602) on the first channel the location of the
piece of control information on the second channel and
- at a second moment of time, later than said first moment, transmitting (603) the
piece of control information on the second channel,
2. A method according to claim 1, characterised in that the first channel is a broadcast control channel and the second channel is a traffic channel of point-to-multipoint type.
3. A method according to claim 2, characterised in that it comprises the steps of
- before said first moment of time, determining (601) the time for transmitting the
piece of information on the second channel,
- at said first moment of time, indicating (602) on the first channel the determined time for transmitting the piece of information on the second channel, and
- transmitting (603) the piece of control information on the second channel at the
determined and indicated time, which is said second moment of time.
4. A method according to claim 1, characterised in that the first channel is a
broadcast control channel and the second channel is a traffic channel of point-to-point type.
5. A method according to claim 4, characterised in that it comprises the step of
- between said first moment of time and said second moment of time, transmitting
(606) from a mobile station to the base station a request for transmitting the piece of
the second moment of time is during a period of low traffic and signalling load in ihr eellulnr radio system.
S A method for receiving a piece of control information from a base station (MS)
at a mobile station (MS) in the cell of a cellular radio system using a first channel
and a second channel, characterised in that it comprises the steps of
-at a t first moment of time, receiving an indication (604) on the first channel the
location of the piece of control information on the second channel and
- at a second moment of time, later than said first moment, receiving (605) the piece
of control information on the second channel.
9. A method according to claim 8, characterised in that it comprises, between
said first moment of time and said second moment of time, a step of informing the
user of the mobile station about the intended receptidn of a piece of control
information at said second moment of time. I
10. A method according to claim 9, characterised in that said step of informing
the user of the mobile station takes place as a response to an attempt to power down
the mobile station.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|NOKIA MOBILE PHONES LTD
|KEILALAHDENT 4, FIN-02150 ESPOO,
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date