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Channel Allocation for GPRS

Channel Allocation for GPRS. From: IEEE Tran. Veh. Technol., Vol. 50, no. 2, 2001. 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

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Channel Allocation for GPRS

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  1. Channel Allocation for GPRS From: IEEE Tran. Veh. Technol., Vol. 50, no. 2, 2001. Author: P. Lin and Y.-B. Lin CSIE, NTU & CSIE, NCTU

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

  3. 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

  4. GPRS architecture

  5. 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)

  6. Packet data logical channel (cont’d)

  7. Dynamic allocation: uplink data transfer

  8. Dynamic allocation: downlink data transfer

  9. 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

  10. System model • 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

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

  12. : voice handoff call arrival rate to a cell : the new call blocking probability for the GSM : dropping/ blocking probability for the GPRS : 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

  13. Analytic model for FRA (1) where (2)

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

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

  16. The iterative algorithm for FRA • Step 1: Select an initial value for • Step 2: • Step 3: Compute and using (2) and (4)-(7) • Step4: 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)

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

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

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

  20. Analytic model for FRAQ

  21. Analytic model for FRAQ (cont’d)

  22. : a packet request is dropped if the number of free channels is smaller than K Analytic model for FRAQ (cont’d)

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

  24. 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

  25. 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

  26. 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

  27. Effect of the variations of the distribution for input parameters

  28. The average number of channels assigned to packet transmission

  29. The average waiting time for the accepted voice call request

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

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