Channel Allocation for the GPRS Design and Performance Study Huei-Wen Ferng, Ph.D. Assistant Professor Department of Computer Science and Information Engineering (CSIE) Nation Taiwan University of Science and Technology (NTUST) Wireless Communications and Networking Engineering (WCANE) Lab URL: mail.ntust.edu.tw/~hwferng

NTUST WCANE Lab CSIE 2 Outline Introduction Channel allocation schemes System model and assumptions Performance study and numerical examples Conclusions

NTUST WCANE Lab CSIE 3 GPRS Architecture

NTUST WCANE Lab CSIE 4 Service Requirements Blocking vs. forced termination From the viewpoint of users, one may feel more uncomfortable when an on-going call is abruptly terminated than directly getting blocked before his service. Generally speaking, less forced termination than blocking. Delay-sensitive vs. non-delay-sensitive Voice is more sensitive than data.

NTUST WCANE Lab CSIE 5 Design Principles Channel reservation It privileges handoff calls. Priority Priority among buffers Differentiation between voice and data requests Service priority between new voice calls and handoff voice calls Differentiation between new calls and handoff calls Buffering strategy Allows more net input rates Threshold control Throttles different rates of new calls and handoff calls

NTUST WCANE Lab CSIE 6 Channel Allocation Schemes An example of dynamic allocation of the uplink data transfer

NTUST WCANE Lab CSIE 7  Basic Dynamic Channel Allocation (DCA):  For a data request, DCA allocates at most n channels to the request.  For a voice call, only one channel is allocated.  Five DCAs are proposed based on service priority, threshold control, channel reservation, and buffering strategies. Channel Allocation Schemes :no priority for voice and data buffers,no threshold control. :higher priority for voice buffer,no threshold control. :higher priority for voice buffer with threshold control. :similar to the 2nd scheme with handoff the highest pri. :similar to the 2nd scheme with channel reservation. :no priority for voice and data buffers,no threshold control. :higher priority for voice buffer,no threshold control. :higher priority for voice buffer with threshold control. :similar to the 2nd scheme with handoff the highest pri. :similar to the 2nd scheme with channel reservation.

NTUST WCANE Lab CSIE 8 CAS 1 Scheme Voice buffer Data buffer New voice (handoff) calls New data packets FIFO This scheme is proposed for reference.

NTUST WCANE Lab CSIE 9 Voice buffer Data buffer New voice (handoff) calls New data packets High priority Low priority When buffer is empty. CAS 2 Scheme

NTUST WCANE Lab CSIE 10 New voice (handoff) calls New data packets CAS 3 Scheme When buffer is empty Handoff call first. Then, new voice call. Voice buffer Data buffer High priority Low priority

NTUST WCANE Lab CSIE 11 Voice buffer Data buffer High priority Low priority New data packets New voice (handoff) calls CAS 4 Scheme When buffer is empty Handoff voice calls Blocked when exceeding the threshold New voice calls

NTUST WCANE Lab CSIE 12 New voice (handoff) calls New data packets New call and handoff call Handoff call When buffer is empty. CAS 5 Scheme Voice buffer Data buffer High priority Low priority

NTUST WCANE Lab CSIE 13  GSM (new) voice call and GPRS (new) data packet arrive according to Poisson processes with ratesλ v and λ d, respectively.  GSM (new and handoff) voice call holding time, GPRS packet transmission time, and GSM user dwelling time follow exponential distributions with mean 1/μ v, 1/μ d and 1/η, respectively..  Static data users are assumed for simplicity.  Each GSM user moves to any adjacent cell in a uniform manner; same traffic load as well as same number of channels are assumed to any cell. (resulting in homogenous cells). System Model and Assumptions

NTUST WCANE Lab CSIE 14 Simulation Environment Square cell structure 6x6 wrapped mesh cells Homogeneous cells

NTUST WCANE Lab CSIE 15  Define state space  Write balance equations based on the state transition diagram  Use the recursive approach to obtain results Analysis of Channel Allocation Scheme

NTUST WCANE Lab CSIE 16 Define state space

NTUST WCANE Lab CSIE 17 State transition diagram For convenience, let us define two sets of indicator functions

NTUST WCANE Lab CSIE 18 State transition diagram

NTUST WCANE Lab CSIE 19 State transition diagram

NTUST WCANE Lab CSIE 20 Blocking probabilities

NTUST WCANE Lab CSIE 21 Delay times Using Little’s formula:

NTUST WCANE Lab CSIE 22 Number of channels (C ) 7 Voice buffer size 7 Maximum available number of channels for data packets (n) 3 Voice holding time Data transmission time Data arrival rate Parameters Setting

NTUST WCANE Lab CSIE 23 Performance Measures Blocking probability for a new voice call Forced termination probability for a handoff voice call Data packet dropping probability Delays Cost comparisons among different schemes

NTUST WCANE Lab CSIE 24 The Effect of Data Buffering (on new voice blocking probability)

NTUST WCANE Lab CSIE 25 The Effect of Data Buffering (on forced termination probability)

NTUST WCANE Lab CSIE 26 The Effect of Data Buffering (on data dropping probability)

NTUST WCANE Lab CSIE 27 The Effect of Data Buffering (on delays of data packet) Delays of new voice calls and handoff voice calls are similar to probabilities.

NTUST WCANE Lab CSIE 28 The Effect of Data Buffering  Data buffer size affects little to new call blocking probability and handoff call forced termination probability, except CAS 1.  Increasing data buffer size greatly improves data dropping probability.  The effects on delays of new voice calls and handoff calls are similar to blocking probability and forced termination probability, respectively.  Increasing data buffer size raises data packet delay time.

NTUST WCANE Lab CSIE 29 The Effect of Threshold Control ( on blocking/termination probability ) Decreasing T v makes new voice call blocking increase and improves forced termination probability.

NTUST WCANE Lab CSIE 30 The Effect of Threshold Control ( on data dropping probability ) Because lower value of T v permits fewer queued new voice calls in the system; therefore, data packets have a better chance to be served, thus data dropping probability decreases.

NTUST WCANE Lab CSIE 31 The Effect of Threshold Control ( on delays of new voice calls and handoff voice calls )

NTUST WCANE Lab CSIE 32 The Effect of Threshold Control ( on delays of data packets )

NTUST WCANE Lab CSIE 33 Schemes Comparison ( new voice blocking probability for various traffic load ) The best to worst schemes are CAS 2, CAS 3, CAS 4, and CAS 5.

NTUST WCANE Lab CSIE 34 Schemes Comparison ( forced termination probability for various traffic load ) The best to worst schemes are CAS 5, CAS 4, CAS 3 and, CAS 2.

NTUST WCANE Lab CSIE 35 Schemes Comparison ( data dropping probability for various traffic load ) CAS 4 performs best in terms of data dropping probability.

NTUST WCANE Lab CSIE 36 Schemes Comparison ( delays of new voice calls for various traffic load )

NTUST WCANE Lab CSIE 37 Schemes Comparison ( delays of handoff voice calls for various traffic load )

NTUST WCANE Lab CSIE 38 Schemes Comparison ( delays of data packets for various traffic load )

NTUST WCANE Lab CSIE 39 Effect of data user mobility and computation illustration on channel reservation The performance of voice calls is not sensitive to variation of η d because voice calls have higher precedence over data packets. When C G increases, performance of new voice calls and data packets becomes poor.

NTUST WCANE Lab CSIE 40 Effect of different data traffic models  The exponential distribution may not be appropriate in modeling data traffic.  Instead, the Pareto distribution can be used to capture the nature of data traffic.

NTUST WCANE Lab CSIE 41 Cost comparisons (fixedτ 3 ) Cost function:

NTUST WCANE Lab CSIE 42 Cost comparisons ( fixedτ 2 )

NTUST WCANE Lab CSIE 43 Cost comparisons ( fixedτ 1 )

NTUST WCANE Lab CSIE 44 Conclusions We conclude:  Buffering for both voice calls and data packets reduces blocking probability, forced termination probability, and data dropping probability but it increases delay times.  The threshold control is an effective approach to reduce forced termination and data dropping probabilities. But it enlarges new voice call blocking probability. We have examined and compared the improvement of channel allocation schemes using four techniques.

NTUST WCANE Lab CSIE 45 Conclusions  Finally, we suggest scheme CAS 3 and CAS 4 to be used in the GPRS system.  Although reservation greatly improves forced termination probability and delay time for handoff voice call, it causes the performance of new voice call and data service poor.

NTUST WCANE Lab CSIE 46 The End Thank You!