Channel Allocation for GPRS From: IEEE Tran. Veh. Technol., Vol. 50, no. 2, Author: P. Lin and Y.-B. Lin CSIE, NTU & CSIE, NCTU

Outline Introduction GPRS architecture Packet data logical channel Channel allocation schemes System model Analysis results Simulation method Performance Conclusion

Introduction GPRS shares GSM frequency bands with telephone and circuit-switched data traffic GPRS uses the same TDMA/ FDMA structure as that of GSM to form physical channels Allocation of channel for GPRS is flexible where one to eight channels can be allocated to a user or one channel can be shared by several users

GPRS architecture

Packet data logical channel  Packet data traffic channel (PDTCH) Employed for transferring of user data  Packet broadcast control channel (PBCCH) Broadcast control  Packet common control channel (PCCCH) The packet random access channel (PRACH) The packet paging channel (PPCH) The packet access grant channel (PAGCH) The packet notification channel (PNCH)  Packet dedicated control channels The packet associated control channel (PACCH) The packet timing advance control channel (PTCCH)

Packet data logical channel (cont ’ d) GroupNameDirectionFunction PTCPDTCHDownlink and uplinkData PBCCH DownlinkBroadcast PCCCHPRACHUplinkRandom access PPCHDownlinkPaging PAGCHDownlinkAccess grant PNCHDownlinkMulticast PDCHPTCCHDownlink and uplinkTiming advance PACCHDownlink and uplinkAssociated control

Dynamic allocation: uplink data transfer

Dynamic allocation: downlink data transfer

Channel allocation schemes: Fixed Resource Allocation (FRA): For a data request of K channels, the BS assigns exact K channels to GPRS packet request Dynamic Resource Allocation (DRA): For a data request of K channels, DRA allocates at most K channels to the request Fixed Resource Allocation with Queue Capability (FRAQ) FRAQ_N: a queue for the new calls only FRAQ_H: a queue for the handoff calls only FRAQ_NH: a queue for both new and handoff calls Dynamic Resource Allocation with Queue Capability (DRAQ ) DRAQ_N: similar to FRAQ_N DRAQ_H: similar to FRAQ_H DRAQ_NH: similar to FRAQ_NH

A GPRS data request specifies K channels for transmission The GSM voice call arrival and GPRS packet requests to a cell form Poisson streams with rates and, respectively The voice call holding time and packet transmission time are exponentially distributed with mean times and, respectively System model

: the residence time of voice user at a cell j, which are independent and identically distributed random variables with a general function with mean : the voice call holding time, which is assumed to be exponentially distributed with the density function The timimg diagram

: the new call blocking probability for the GSM : dropping/ blocking probability for the GPRS : voice handoff call arrival rate to a cell : GSM voice user mobility rate : probability that a GSM voice call is not completed (either blocked or forced to terminate) : the GSM voice call traffic load : the GPRS packet call traffic load

Analytic model for FRA where (1) (2)

Analytic model for FRA (cont ’ d) (3) (4) state space : stationary probability:

Analytic model for FRA (cont ’ d) where (5) (7) (6)

The iterative algorithm for FRA Step 1: Select an initial value for Step 2: Step 3: Compute and using (2) and (4)-(7) Step 4: Compute using (1) Step 5: If then go to step 2. Otherwise,go to step 6. Note that is a predefined threshold say Step 6: The values for, and converge. Compute from (3)

Analytic model for DRA where The state transition for DRA Let’s consider the case when K=3

Analytic model for DRA (cont ’ d) The balance equations for the Markov process are expressed:

Analytic model for DRA (cont ’ d) : the set of the states where no free channel is available

Analytic model for FRAQ

Analytic model for FRAQ (cont ’ d)

: a packet request is dropped if the number of free channels is smaller than K

Simulation method We consider a 6x6 wrapped mesh cell structure The model follows the discrete event simulation approach 6X6 wrapped mesh cell structure

Performance of FRA ( ) Performance of GPRS data rate: increase as K increase Effects of packet size :in Fig. 6(b) Effect of voice call arrival: in Fig. 6(c) Effect of voice user mobility: in Fig. 6(d) voice user mobility has no apparent effect on

Performance of FRA ( ) Effect of packet size: in Fig. 7(b) Effect of voice call arrival: in Fig. 7(c) packet request have less chance to served as K increases, and decreases as K increases Effect of voice user mobility: in Fig. 7(d) high mobility, handoffs are more likely to occur in a voice call,thus for high mobility is larger

Comparison for the FRA and DRA algorithms Performance of DRA algorithms (with or without queueing) always outperform FRA (with or without queueing) Performance of the DRAQ_NH outperforms other algorithms

Effect of the variations of the distribution for input parameters

The average number of channels assigned to packet transmission

The average waiting time for the accepted voice call request

Conclusion The dynamic allocation effectively increases the GPRS packet acceptance rate and queueing mechanisms significantly reduce the voice call incompletion probability