Title of Invention

A METHOD FOR PAGING USER EQUIPMENTS

Abstract

The invention relates to a paging procedure and mapping of the paging information for the 3GPP L TE E-UTRA. The invention dfscloses an algorithm to group UEs together based on their IMSI and DRX cycle length and to associate these groups to specific riCH information bits. The invention proposes two methods of multi-level grouping of UEs based on whether the IMSI allocation is completely random or not. First, a lower band or a higher band for a UE is decided based on the least significant bit representation of the BCD representation of the 7th digit of the IMSI and consequently two groups are formed. Next, the paging location for the UE is calculated based on the equation: Paging location = {(IMSI mod (DRX cycle length)) + n * DRX cycle length + Sub-Frame-offset, Where n = 0,1,2... as long as SFN (System frame Number) is below its maximum value. In this way, UEs are further grouped based on the pagin' location that they have to monitor. Next, UEs which satisfy the criteria (IM~ div (DRX Cycle length)) mod Np are grouped together,Where Np = number paging indicators.

Full Text

FIELD OF INVENTION The present invention in general relates to the field of Mobile communication. The concept of paging is evident in mobile communication technologies like GSM, UMTS. This invention proposes a paging procedure and mapping of the paging information for the 3GPP LTE E-UTRA. More particularly, this invention proposes system and method for mapping mobile equipments into paging groups for a power-efficient paging procedure applied in 3GPP LTE. DESCRIPTION OF RELATED ART The concept of paging as applied in UMTS (3GPP) is illustrated in the 3GPP specification number 25.211 and 25.304 (References 7, 8). Paging is the term used to address the mechanism by which the cellular network (BS) contacts the mobile station (UE) when an incoming call for that UE needs to be serviced. As a brief background, paging procedure as in GSM (References 10, 11) is accomplished by assignment of a paging channel (time/frequency resource) in the downlink which UE monitors. Each group of UEs is allocated a particular paging channel which it is required to monitor periodically (technically every DRX cycle). In order to conserve UE battery power, UE is allowed to enter into 'sleep mode' (consuming very less power) in between two paging occasions. When the network is required to page a particular UE (eg. due to an incoming call request for that 4 UE) it sends the UE ID for that particular UE and the cause of paging etc, in the paging channel that is assigned to the group of UEs containing that UE. UE decodes the paging message which the network has send in the assigned paging channel and extracts the UE ID and validates it to confirm if the paging message is actually meant for itself. Similar concept of paging exists for UMTS technology. A subtle difference from the GSM technology is that a new paging indicator channel (PICH) is defined which is synonymous to paging channel in GSM except for that fact that it doesn't carries UE ID instead it carries an indication if a paging message will come for the associated group of UEs in the forthcoming (pre configured) paging channel (PCH) whereby the UEs in that group need to read the associated PCH and extract the UE ID and then validate to confirm if the paging message is actually meant for itself. In the upcoming 3GPP LTE forum (WG1) various companies have proposed paging procedure on similar lines as in UMTS but none of the contributions (References 1-5, 9) actually detail the mapping of the paging information. The prior contributions present the way the paging procedure has to take place in 3GPP LTE E-UTRA illustrating the usage of the Paging Indicator channel (PICH) and the actual Paging channel (PCH) thereby gaining on the battery power of the UE. The prior contributions also deal with the placement of the PICH and PCH in the Downlink channel structure (time/frequency assignment) of the 3GPP LTE E- UTRA. The prior contributions do not talk about the way to group UEs to form paging groups based on IMSI and DRX cycle. It is to be noted that even though the concept of grouping the UEs exists in UMTS but the numbers that form the parameters for grouping the UEs are different in 3GPP LTE E-UTRA as compared to UMTS which lead to changes in the equations which govern the grouping of UEs. The references for the prior contributions in 3GPP LTE E-UTRA are 1-5, 9. The references for the prior contributions in UMTS are 7, 8. LIMITATIONS None of the prior contributions (References 1-5, 9) in 3GPP LTE forum (WG1) dealt with the mapping of the paging information on the PICH and grouping of the UEs to form paging groups based on IMSI and DRX cycle. The present invention proposes a way to group UEs into various paging groups (based on IMSI and DRX cycle length) and the PICH time frequency arrangement. It is again emphasized that even though the concept of grouping the UEs exists in UMTS (References 7, 8) the numbers that form the parameters for grouping the UEs are different in 3GPP LTE E-UTRA as compared to UMTS which lead to changes in the equations which govern the grouping of UEs. 'S— SUMMARY OF THE INVENTION The present invention proposes to devise an algorithm to formulate groups of UEs based on their IMSI and DRX cycle length and associate these groups to specific PICH information bits. The present invention proposes to spread the load evenly over the entire system (in time). The present invention proposes a system and method of grouping mobile equipments in 3GPP LTE (OFDM based) system into two groups based on the least significant bit of the BCD representation of the 7th digit of the IMSI for evenly segregating the mobile equipments in LTEJDLE state in the Lower frequency Band or the Upper frequency Band of the E-UTRA, typically employed with 10 MHz capable mobile equipments in a 20 MHz Cellular spectrum, as in Figure 4. The present invention further proposes a system and method of grouping mobile equipments in 3GPP LTE (OFDM based) system based on the Paging location they have to monitor; group mobile equipments which satisfy the criteria (IMSI mod (DRX cycle length)) together, thus creating 'DRX cycle length' number of groups. The present invention proposes a method of grouping mobile equipments in 3GPP LTE (OFDM based) system based on the number of sub-frames per frame in the system (Ns), thus mobile equipments which satisfy the criteria 'IMSI mod (total number of sub-frames per frame) or IMSI mod Ns (or in the case we have 20 sub-frames per frames as agreed in the 3GPP RAN1 discussion, the formulae reduces to IMSI mod 20), are put in the same group. The present invention further proposes a method of grouping mobile equipments, in 3GPP LTE (OFDM based) system based on the information carried in the PICH, where there is Np groups, (2,4,8); At one time network can page Np group of mobile equipments together, where out of the 8 available bits in PICH, UE checks a group of bits which correspond to its paging group as given in Tablel. There are Np possible groups where mobile equipments which satisfy the criteria IMSI mod (Ns * Max (DRX Cycle length)) (or in the case we have 29 as the maximum DRX cycle length, and 20 sub-frames per frame the formulae reduces to (IMSI div (10240)) mod Np) are grouped together. The prior contributions (References 1-5, 9) in 3GPP LTE forum (WG1) till date do not deal with grouping of UEs and their association with PICH information bits. Accordingly the invention explains a method for mapping mobile equipments into paging groups for a power-efficient paging procedure applied in 3GPP LTE wherein the said method groups UEs together based on their IMSI and DRX cycle length and associate these groups to specific PICH information bits. Accordingly the invention also explains a system for mapping mobile equipments into paging groups for a power-efficient paging procedure applied in 3GPP LTE wherein the said system comprising UEs grouped together based on their IMSI and DRX cycle length and associate these groups to specific PICH information bits. These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS Figure 1 gives a description of the general downlink channel structure (time/frequency assignment) as in the proposals referenced herein - and the placement of PICH and PCH channels Figure 2 illustrates the mapping of the groups to PICH information bits. Figure 3 illustrates the structure of PICH channel in UMTS Figure 4 illustrates Load Sharing by IMSI (divided into GRP_1 and GRP_2) * DETAILED DESCRIPTION OF INVENTION The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. In the first place a description of the grouping of UEs as is done in UMTS will be presented and then the invention that is the system and method for grouping of UEs in 3GPP LTE E-UTRA will be detailed. Paging procedure and grouping of UEs in UMTS (References 7, 8) A UE is required to monitor PICH channel every DRX cycle length (in frames, where one frame in UMTS occupies a length of 10 ms). In order to distribute the UEs evenly in time the UEs are distributed among the various PICH channels available as per the available (and PCH carrying) S- CCPCH's Then the group of UEs which corresponds to one PICH is further evenly spread out over the entire DRX cycle length. This results in associating a group of UEs (which is a subset of the group of UEs which correspond to one PICH) with a paging occasion. Finally the UEs which correspond to a particular PICH and a particular paging occasion on the associated PICH are further grouped to correspond to an information bit carried in PICH. In case of UMTS PICH carries 288 bits which can be grouped to form 144 or 72 or 36 or 18 information bits. The process of multi-level grouping is detailed in steps below:- STEPS 1 - In UMTS PICH channel is tied up with the associated S-CCPCH channel which carries the PCH. Up to 150 SCCPCH channels are possible in the system out of which only a maximum of 16 are allowed to carry PCH. A particular UE is associated to a SCCPCH via its IMSI by the following equation:- "Index of selected SCCPCH" = IMSI mod K, where K is equal to the number of listed S-CCPCH's which carry a PCH. This enables a UE to know when to read PICH in time with respect to the chip offset from the PCCPCH. STEP 2 - Since a UE is required to listen to PICH only once in DRX cycle length, it needs to be associated to a paging occasion as illustrated in the figure. This step corresponds to further evenly spreading out the group of UEs formed in STEP1 over the entire DRX cycle length. Paging Occasion = {(IMSI div K) mod (DRX cycle length div PBP)} * PBP + n * DRX cycle length + Frame Offset Where n = 0, 1,2... as long as SFN is below its maximum value. STEP 3 - Next a UE needs to be associated with a particular information bit 'Pq' in the PICH channel where it will be signaled for paging. See the figure for PICH channel structure. The Page Indicator to use is calculated by using the following formula: PI = DRX Index mod Np, where DRX Index = IMSI div 8192 The corresponding bit to read in the PICH channel will be based on the table below Number of paging indicators per frame (Np) Pq = 1 Pq = 0 Np=18 {b16q, ..., b16q+15} = {1,1 1} {b16q b16q+15} = {0, 0.....0} Np=36 {b8q, ..., b8q+7} = {1, 1.....1} {b8q, b8q+7} = {0, 0 0} Np=72 {b4q b4q+3} = {1, 1 1} {b4q, ..., b4q+3} = {0, 0 0} Np=144 {b2q, b2q+1} = {1, 1} {b2q, b2q+1} = {0, 0} Invention for paging procedure and grouping of UEs as proposed for 3GPP LTE E-UTRA:- (References 1-5, 9) PICH will be multiplexed with L1/L2 Control signaling (which is scheduled once in every sub-frame at the first OFDM symbol location), which will be transmitted on at-least a 5MHz spectrum with 8/9 bits PICH [9]. (As in [6], number of available sub-carriers for 5MHz is 300, with an R=1/3 coding (with CRC and Tail-biting), and QPSK Modulation). An IMSI is usually fifteen digits long. Example IMSI: 310150123456789, MCC 310 USA MNC 150 Cingular Wireless MSIN 123456789; DRX Cycle length is defined as in case of UTRA as 2Ak where k = (3....9) frames, and is negotiated between the UE and the eNodeB, using a NAS signaling procedure; default value of k = 8. A UE is required to monitor PICH channel every DRX cycle length (in frames, where one frame in 3GPP LTE E-UTRA occupies a length of 10 ms). In case of 3GPP LTE E-UTRA only one PICH exists. It comes multiplexed in the L1/L2 control signaling which is assigned first symbol in all the sub-frames. See figure. (There are 20 sub-frames in one frame; in general there can be Ns number of sub-frames per frame) , UEs need to be evenly spread out over the entire DRX cycle length. This results in associating a group of UEs with a paging location. Then the UEs need to be evenly spread over all the 20 (or Ns) sub-frames within a frame. Finally the group of UEs which are associated with a particular sub-frame, in a particular frame which repeats every DRX cycle length, is further grouped down to V correspond to a information bit carried in PICH. In case of 3GPP LTE E-UTRA PICH can carry 8 bits which can be mapped to represent 8 or 4 or 2, groups of UEs. This process of multi-level grouping is detailed in steps below:- STEP 1 - The frequency layer of the UE in LTEJDLE state will be controlled by the aGW, where in the UE frequency layer, Lower Band or Upper Band, can be decided by the least significant bit of the BCD representation of the 7th digit of the IMSI. Example IMSI: 310150123456789, MCC 310 USA MNC 150 Cingular Wireless MSIN 123456789; Check on the least significant bit of BCD representation of Digit 1. Thus, there are two groups as follows GRP_1 = Least significant bit of the BCD representation of the 7th digit of the IMSI = 0, and GRP_2 = Least significant bit of the BCD representation of the 7th digit of the IMSI = 1 STEP 2 - The UE needs to start decoding a PICH at the right paging location (at the correct sub-frame), which will be calculated as follows. Paging location = {(IMSI mod (DRX cycle length)) + n * DRX cycle length + Sub-Frame-offset. Where n = 0, 1,2... as long as SFN (System frame Number) is below its maximum value. Sub-Frame-offset is the sub-frame number in the 10 ms frame, and is calculated as, (IMSI div DRX cycle length) mod (total number of sub-frames per frame), Or (IMSI div DRX cycle length) mod Ns Or (IMSI div DRX cycle length) mod 20 Thus, within the individual groups (GRP_1 and GRP_2), the UEs are further grouped based on the Paging location they have to monitor, thus UEs which satisfy the criteria (IMSI mod (DRX cycle length)), are grouped together, there are 'DRX cycle length' number of Groups in this case, thus GRP_1_0 = Group of UEs in GRP_1, with (IMSI mod (DRX cycle length) = 0) GRP_1_1 = Group of UEs in GRP_1, with (IMSI mod (DRX cycle length) = 1) GRP_1_ (DRX_Cycle_length-1) = Group of UEs in GRP_1, with (IMSI mod (DRX cycle length) = DRX_Cycle_length-1) And, GRP_2_0 = Group of UEs in GRP_2, with (IMSI mod (DRX cycle length) = 0) GRP_2_1 = Group of UEs in GRP_2, with (IMSI mod (DRX cycle length) = 1) GRP_2_ (DRX_Cycle_length-1) = Group of UEs in GRP_2, with (IMSI mod (DRX cycle length) = DRX_Cycle Jength-1) These groups (GRP_1_0 .... GRP_2_ (DRX_CycleJength-1)) are further divided into number of sub-frames in the system, thus UEs which satisfy the criteria 'IMSI mod (total number of sub-frames per frame) or IMSI mod Ns or IMSI mod 20', are put in the same group thus GRP_1_0_0 = Group of UEs in GRP_1_0, with (IMSI mod 20 = 0) GRP_1_0_1 = Group of UEs in GRP_1_0 with (IMSI mod 20 = 1) GRP_1_0_19 = Group of UEs in GRP_1_0, with (IMSI mod 20 = 19) And, GRP_1_1_0 = Group of UEs in GRP_1_1, with (IMSI mod 20 = 0) GRP_1_1_1 = Group of UEs in GRP_1_1, with (IMSI mod 20 = 1) GRP_1_1_19 = Group of UEs in GRP_1_1, with (IMSI mod 20 = 19) And, GRP_2_0_0 = Group of UEs in GRP_2_0, with (IMSI mod 20 = 0) GRP_2_0_1 = Group of UEs in GRP_2_0 with (IMSI mod 20 = 1) GRP_2_0_19 = Group of UEs in GRP_2_0, with (IMSI mod 20 = 19) And, GRP_2_1_0 = Group of UEs in GRP_2_1, with (IMSI mod 20 = 0) GRP_2_1_1 = Group of UEs in GRP_2_1, with (IMSI mod 20 = 1) GRP_2_1_19 = Group of UEs in GRP_2_1, with (IMSI mod 20 = 19) And, so on STEP 3 - In our scheme we have assumed 8 bits information for PICH. In each PICH frame, Np paging indicators {Po, ..., Pnm) are transmitted, where Np=2, 4, or 8. If the paging indicator 'Pq' in the PICH is set to "1" it is an indication that UEs associated with this paging group should read the corresponding PCH. Where, q = (IMSI div (Max DRX Cycle length * total number of sub-frames per frame))) mod Np, which reduces to: (IMSI div 512* Ns) mod Np or, (IMSI div 10240) mod Np We can have a table as follows. Number of paging indicators per frame (Np) Pq = 1 Pq = 0 Np=2 {b4q b4q+3} = {1, 1, 1,1} {b4q, ..., b4q+3} = {0, 0, 0, 0} Np=4 {b2q,b2q+1} = {1,1} {b2q,b2q+1} = {0, 0} Np=8 bq = {1} bq = {0} Table 1 Mapping of paging indicators Pq to PICH bits Thus, the last level of grouping is based on the information carried in the PICH, where we have Np groups possible, (2,4,8); At one time network can page Np group of UEs together, where out of the 8 available bits in PICH, UE checks a group of bits which are given in Tablel. There are Np possible groups where UEs which satisfy the criteria (IMSI div (DRX Cycle length)) mod Np are grouped together, thus 0_0, with ((IMSI div 10240) mod Np 0_0, with ((IMSI div 10240) mod Np GRP_1_0_0_ (Np-1) = Group of UEs in GRP_1_0_0, with ((IMSI div 10240) mod Np = Np-1), And, GRP_1_0_1_0 = Group of UEs in GRP_1_0_1, with ((IMSI div 10240) mod Np = 0) GRP_1_0_1_1 = Group of UEs in GRP_1_0_1, with ((IMSI div 10240) mod Np = 1) GRP_1_0_1_ (Np-1) = Group of UEs in GRP_1_0_1, with ((IMSI div 10240) mod Np = Np-1), GRP_1_0_0_0 = Group of UEs in GRP_1 = 0) GRP_1_0_0_1 = Group of UEs in GRP_1 = 1) And, GRP_2_1_19_0 = Group of UEs in GRP_2_1_19, with ((IMSI div 10240) mod Np = 0) GRP_2_1_19_1 = Group of UEs in GRP_2_1_19, with ((IMSI div 10240) mod Np = 1) GRP_2_1_19_ (Np-1) = Group of UEs in GRP_2_1_19, with ((IMSI div 10240) mod Np = Np-1), And so on. ADVANTAGES In a case when there are about 100,000 users (hypothetical), under one aGW with a DRX Length of 64 (k=6), and Np = 8, approximately 10 UEs are grouped together which read one bit of PICH for reading their paging indicator, and approximately 80 UEs wake up together to read the PICH in one sub- frame duration (0.5 ms). This is a fair distribution of the load. It will also be obvious to those skilled in the art that other control methods and apparatuses can be derived from the combinations of the various methods and apparatuses of the present invention as taught by the description and the accompanying drawings and these shall also be considered within the scope of the present invention. Further, description of such combinations and variations is therefore omitted above. It should also be noted that the host for storing the applications include but not limited to a microchip, microprocessor, handheld communication device, computer, rendering device or a multi function device. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart there from. REFERENCES [1] R1-061662 SCH Structure and Cell Search Method for E-UTRA Downlink (NTT DoCoMo, Fujitsu, NEC, Toshiba Corporation) [2] R1-061683 Physical Allocation of PCH for 20MHz Operating Bandwidth (Sharp) [3] R1-061688 Performance Comparison between 1.25 MHz and 5 MHz BCH Transmission Bandwidths (Samsung) [4] R1-061905 PCH and paging indicator presence on LTE Layer 1 (Nokia) [5] R1-061237 LTE Cell search (Nokia) [6] 3GPP TR 25.814 V7.0.0 (2006-06) [7] 3GPP TS 25.211 V7.0.0 (2006-03) [8] 3GPP TS 25.304 V7.0.0 (2006-03) [9] R1-061912 TR25814CR0001 (Rel7, F) "Paging indicators on LTE Layer 1 (Nokia) [10] 3GPP TS 05.02 [11] 3GPPTS 04.08 [12] 3GPP TS 36.211 [13] 3GPP TS 36.213 GLOSSARY OF TERMS AND DEFINITIONS THEREOF aGW - Access Gateway 3GPP - Third Generation Partnership Project LTE - Long Term Evaluation E-UTRA - Evolved Universal Terrestrial Radio Access PICH - Paging Indicator Channel PCH - Paging Channel SCCPCH - Secondary Common Control Physical Channel PCCPCH - Primary Common Control Physical Channel UMTS - Universal Mobile Telecommunications System DRX - Discontinuous Reception IMSI - International Mobile Subscriber Identity UE - User Equipment BS - Base Station ME - Mobile Equipment WG - Working Group RAN - Radio Access Network We Claim, 1. A method for mapping mobile equipments into paging groups for a power- efficient paging procedure applied in 3GPP LTE wherein the said method groups UEs together based on their IMSI and DRX cycle length and associate these groups to specific PICH information bits. 2. A method as claimed in claim 1 wherein grouping of UEs are based on whether the IMSI allocation is completely random or not. 3. A method as claimed in claim 1 wherein , a lower band or a higher band for a UE is decided based on the least significant bit representation of the BCD representation of the 7th digit of the IMSI and consequently forming two groups. 4. A method as claimed in claim 1 wherein , the paging location for the UE is calculated based on the equation: Paging location = {(IMSI mod (DRX cycle length)) + n * DRX cycle length + Sub-Frame-offset, Where n = 0, 1, 2... as long as SFN (System frame Number) is below its maximum value. 5. A method as claimed in claim 1 wherein , UEs are further grouped based on the paging location that they have to monitor. 6. A method as claimed in claim 1 wherein the, UEs which satisfy the criteria (IMSI div (DRX Cycle length)) mod Np are grouped together,Where Np = number of paging indicators. 7. A system for mapping mobile equipments into paging groups for a power- efficient paging procedure applied in 3GPP LTE wherein the said system comprising UEs grouped together based on their IMSI and DRX cycle length and associate these groups to specific PICH information bits. 8. A method for mapping mobile equipments into paging groups for a power- efficient paging procedure applied in 3GPP LTE illustrated and explained with respect to the accompanied drawings. 9. A system for mapping mobile equipments into paging groups for a power- efficient paging procedure applied in 3GPP LTE illustrated and explained with respect to the accompanied drawings.

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1519-CHE-2006 ABSTRACT.pdf

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