Performance Evaluation
4.2 Simulation Results
(a) Delay bound 64ms
ON IN
ip p
- =0.1
- The delay bound δ = 64, 128, 256ms - T =2ms, T =10ms
- Initial T 1024 - λ =1 arrivals/ms, μ =6
- Number of bursts in simulation = 10000
d
LC
p
ms
30
(b) Delay bound 128ms
(c) Delay bound 256ms
Figure 4.1: The packet delay CDF of proposed scheme
31
The packet delay CDF of proposed scheme is shown in Figure 4.4. In our scheme, we prove that the delay requirement (90% packet delay under the delay bound δ) in different inter-burst arrival time is obeyed. From the figure, we can see the packet delay CDF has linear-like relationship with delay. And the turning points of these lines occur in the delay valueTSC-T . ON
In the following figures, we show that the active ratio and delay probabilities respectively compare with fixed cycle scheme in different delay requirement as well as burst arrival rateib.Fixed cycle does not use Short Cycle in DRX operation, and use smaller fixed Long Cycle than delay bound instead.
(a) Active ratio (Delay bound 64ms) (b) Packet delay at 90% (Delay bound 64ms)
Figure 4.2: Performance comparison among proposed scheme and fixed cycle in delay bound 64ms
32
Table 4.2 Parameters of Delay bound 64ms (TSC 64ms)
(a) Active ratio (Delay bound 128ms) (b) Packet delay at 90% (Delay bound 128ms)
Figure 4.3: Performance comparison among proposed scheme and fixed cycle in delay bound 128ms
Table 4.3 Parameters of Delay bound 128ms (TSC 128ms)
λib 0.0005 0.001 0.002 0.005 0.01 0.02
TLC 160 320 1024 1024 1024 1024
NSC 11 14 11 5 3 2
λib 0.0005 0.001 0.002 0.005 0.01 0.02
TLC 64 80 160 1024 1024 1024
NSC 0 11 14 11 7 4
33
(a) Active ratio (Delay bound 256ms) (b) Packet delay at 90% (Delay bound 256ms)
Figure 4.4: Performance comparison among proposed scheme and fixed cycle in delay bound 256ms
Table 4.4 Parameters of Delay bound 256ms (TSC 256ms)
λib 0.0005 0.001 0.002 0.005 0.01 0.02
TLC 640 1024 1024 1024 1024 1024
NSC 14 9 5 3 2 1
34
(a) Active ratio (b) Packet delay at 90%
Figure 4.5: Performance comparison among proposed scheme and fixed cycle in different delay bound
From Figure 4.5, it can be observed that the active ratio of proposed scheme is lower than the compared fixed cycle scheme but the packet delay is higher than the compared fixed cycle scheme. In other words, we sacrifice some packet delay to reduce the active ratio. From Table 4.2, Table 4.3, and Table 4.4, it is clear that instead of decreasing the Long DRX Cycle, enabling Short DRX Cycle with appropriate Short Cycle Timer can effectively decrease packet delay.
Then, we should note that as the value of ib increases, active ratio will increase because the Inactivity Timer extends UE’s on-duration. When the value of delay bound is small, meeting the delay requirement will lead to increase in active ratio.
Note that the proposed scheme has similar performance as the compared fixed
35
cycle scheme. That is because as the value of p increases, the time UE operates in d short cycles also increases. When UE almost operates in short cycles, the performance will approach the fixed cycle scheme (the Short Cycle value used by our scheme is equal to the cycle value of fixed cycle scheme). The worst situation of our algorithm to select the DRX parameters with satisfying delay requirement is selecting the same as fixed cycle scheme. As seen in Table 4.2, in λib =0.0005 case we choose Long DRX Cycle = 64ms and disable Short DRX Cycle to meet our delay requirement.
36
Chapter 5.
Conclusion
In this thesis, we take an overview of LTE DRX mechanism with adjustable DRX cycles and derive a mathematical model based on bursty packet traffic model. The analytical results match the simulation results. Through this model, we propose an algorithm for choosing DRX parameters. This algorithm tends to choose bigger long DRX cycle with smaller short cycle timer to satisfy the quality of service. Despite it may not have the guarantee to minimize the power consumption, it provides a simple way to choose DRX parameter with satisfying the delay requirement.
37
Bibliography
[1] 3GPP Technical Specification Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA) - Medium Access Control (MAC) protocol specification (Release 10), 3GPP TS 36.321 V10.5.0, Mar. 2012.
[2] CATT, “Signaling Overhead for IM traffic and Background traffic,” 3GPP TSG-RAN WG2 Meeting #77 R2-120258
[3] 3GPP Technical Specification Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2(Release 11), 3GPP TS 36.300 V11.1.0, Mar. 2012.
[4] ETSI, “Universal Mobile Telecommunications System (UMTS); Selection Procedures for the Choice of Radio Transmission Technologies of the UMTS,”
Technical Report UMTS 30.03, version 3.2.0, Apr. 1998.
[5] S. Yang, S. Yan, and H. Hung, “Modeling UMTS Power Saving with Bursty Packet Data Traffic,” IEEE Trans. Mobile Computing, vol. 6, no. 12, pp. 1398–1409, Dec.
2007.
[6] L. Zhou, H. Xu, H. Tian, Y. Gao, L. Du, and L. Chen, “Performance Analysis of Power Saving Mechanism with Adjustable DRX Cycles in 3GPP LTE,” Proc. IEEE VTC-fall, pp. 1–5, Sep. 2008.
[7] S. Jin, and D. Qiao, “Numerical Analysis of the Power Saving in 3GPP LTE Advanced Wireless Networks,” IEEE Trans. Vehicular Technology, vol. 61, no. 4, MAY. 2012.
38
[8] K. Aho, T. Henttonen, J. Puttonen and T. Ristaniemi, “Trade-off Between Increased Talk-time and LTE Performance,” International Conference on Networks (ICN) 2010.
[9] M. Polignano, D. Vinella, D. Laselva, J. Wigard, and T. B. Sorensens, “Power Savings and QoS Impact for VoIP Application with DRX/DTX Feature in LTE,”
Proc. IEEE VTC-spring, pp. 1–5, May. 2011.
[10] J. Wigard, T. Kolding, L. Dalsgaard, C. Coletti, “On the User Performance of LTE UE Power Savings Schemes with Discontinuous Reception in LTE,” IEEE International Conference on Communications Workshops 2009.
[11] Research In Motion UK Limited, “DRX and Relationship to QoS,” 3GPP TSG-RAN WG2 Meeting #75bis R2-115246
[12] 3GPP Technical Specification Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA) - Radio Resource Control (RRC) protocol specification (Release 10), 3GPP TS 36.331 V10.5.0, Mar. 2012.
39
Appendix
Based on Section 3.1, we set the On Duration Timer and the Inactivity Timer minimum enough value to operate DRX mechanism. So we ignore the influence of On Duration Timer and Inactivity Timer in Section 3.2. In this chapter, we try to consider the influence of Inactivity Timer. When a burst arrives in the period of Inactivity Timer, it will restart another Inactivity Timer. If the longer T we use, the bigger impact of in Inactivity Timer it will be. Therefore, we must consider the impact of Inactivity Timer within big T . in
Now, we define R as the total time of T extended until in T expires. By using in the same method in Equation (3.6) we have
1
where q is the probability of bursts arrive in one subframe. Then, we want to calculate a new [E Nk']to replace [E Nk], where E N[ k'] is the average number of total short DRX cycle length in one generating cycle with considering the Inactivity Timer. We define W as the extended short DRX cycle after initial Inactivity Timer expired. As seen in
Table A.1, if a burst arrives in the interval A, B, or C, it will start the Inactivity Timer and reset the Short Cycle Timer.
40 Burst arrives in interval C 2
(1 )
Now, we can represent the general form
It can be applied to modify our Equation 3.21 with longer Inactivity Timer.
41
Figure A.1: Performance comparison among analytical results and simulation results for different TIN.
Figure A.1 shows the Performance comparison among analytical results and simulation results for different Tin where NSC=6, TSC=64ms, δ=75ms, λ=0.005 TLC=256ms. As we can see, the simulation results are similar to the analytical results.
Furthermore, the probability of bursts fail to meet the delay requirement will decrease with TIN increase.
Note that when Tin is small, they have similar probability of bursts fail to meet delay requirement. Thus, while using a small Tin, we can neglect the influence of Tin in analytical model.