A Delay-aware Auto Sleep Mode Operation for Power Saving WiMAX 1 Shengqing Zhu, 1 Xiaoyu Ma, and 2 Lujian Wang ( 南京大學. 計算機科學 ) ( 浙江大學城市學院. 信息工程 ) 1 Department of Electronic and Information, Nanjing University, China 2 Department of Communication Engineering, Zhejiang University City College

Outline Introduction Motivation Proposed algorithm –Dynamic Tuning of Initial Sleep Window (DTISW) –Delay-aware Sleep Mechanism (DSM) Simulation Conclusion

Introduction Mobile stations are usually powered by battery, and therefore power saving is a critical concern in designing the medium access control. One of core techniques of WiMAX is a sleep mode operation, which is employed to save power in IEEE e. –type I : for BE and NRT-VR traffic. –type II : for UGS and RT-VR traffic. –type III : for multicast connections and management operations. This paper addresses only power saving class of type I. –only downlink (from BS to MS) is considered.

Introduction new sleep window = min {2 × (previous sleep window), initial sleep window × 2 (final sleep window exponent) } normal operation sleep windows listening windows … MOB_SLP-REQ MOB_SLP-RSP BS MS MOB_TRF-IND (-) MOB_TRF-IND (+)DATA t t initial sleep window DATA

Introduction To bound the delay in the required range, a heuristic algorithm is proposed to adapt the parameters of sleep mechanism to the traffic load and the delay requirement. –This paper describes the performance of WiMAX sleep mode operation by means of a simple Markov chain model.

Motivation When the MS enters into sleep mode, the BS buffers all packets addressed to the MS until it wakes up. –Power consumption –Delay normal operation sleep windows listening windows MOB_SLP-REQ MOB_SLP-RSP BS MS MOB_TRF-IND (-)MOB_TRF-IND (+)DATA t t MOB_SLP-REQ MOB_SLP-RSP MOB_TRF-IND (-)MOB_TRF-IND (+)DATA MOB_SLP-REQ MOB_SLP-RSP …

Motivation When the MS enters into sleep mode, the BS buffers all packets addressed to the MS until it wakes up. –Power consumption –Delay normal operation sleep windows listening windows t t … MOB_SLP-REQ MOB_SLP-RSP BS MS MOB_TRF-IND (-) MOB_TRF-IND (+)DATA delay

Motivation The size of initial sleep window and the traffic load influence the following sleep operation and efficiency.

Motivation The queuing length in the buffer increases with the sleep interval, and so that packets’ end-to-end delay increases with the sleep interval.

Motivation Initial sleep window is the key of tradeoff between power consumption and delay.

Dynamic Tuning of Initial Sleep Window (DTISW) Markov Chain Model The ith sleep interval T i = 2 i Tb, (Tb = initial sleep window), 0 ≤ i ≤ M The behaviors of an MS working in power saving mode can be described with a bi-dimensional random process {s(t), b(t)} s(t), b(t) The MS stays in the ith sleep interval The status of the MS 0 ： MS is sleeping s ： MS is receiving packets from BS normal operation sleep windows listening windows MS t T0T0 T1T1 T2T2 T3T3 sleep modenormal mode

Dynamic Tuning of Initial Sleep Window (DTISW) Markov Chain Model normal operation sleep windows listening windows MS t T0T0 T1T1 T2T2 T3T3 sleep modenormal mode 0, si, sM, s 0, 0 i, 0M, 0 1, s 1, 0 MOB_TRF-IND(-) (-) (+) 1111 …… … (-) Tb

Dynamic Tuning of Initial Sleep Window (DTISW) β i : the transition probability from state (i,0) to state (i+l,0) (or from (M,0) to (M,0) when i=M), where equal to the probability that no packets arrive in the ith sleep state 1- β i : the transition probability from (i,0) to related serving state (i,s) MS t T0T0 T1T1 T2T2 T3T3 0, 01, 02, 03, 04, s 0, s1, si, sM, s 0, 0 1, 0i, 0M, 0 β0β0 β1β1 β i-1 βiβi β M-1 1-β 0 1-β 1 1-β i 1-β M 1111 …… βMβM Tb T4T4

Dynamic Tuning of Initial Sleep Window (DTISW) The initial sleep window should depend on the number of packets j served in the ith serving state 0, s1, si, sM, s 0, 0 1, 0i, 0M, 0 β0β0 β1β1 β i-1 βiβi β M-1 1-β 0 1-β 1 1-β i 1-β M 1111 …… βMβM Tb MS t T0T0 T1T1 T2T2 TiTi 2i2i …

Dynamic Tuning of Initial Sleep Window (DTISW) Ex ：有 5 個 packets 於 T 3 到達，則下次的 initial sleep window T b * = 24 / (INT) (log 2 5) = 24 / 2 = 12 (T 2 ) MS t T0T0 T1T1 T2T2 TiTi 2i2i … t T 0 (3) T 1 (6) T 2 (12) T 3 (24) 5

Dynamic Tuning of Initial Sleep Window (DTISW) Ex ：有 5 個 packets 於 T 3 到達，則下次的 initial sleep window T b * = 24 / (INT) (log 2 5) = 24 / 2 = 12 (T 2 ) MS t T 0 (3) T 1 (6) T 2 (12) T 3 (24) 5 3, s 0, 0 1, 02, 03, 0 β0β0 β1β1 β2β2 1-β 3 1 Tb 3, s 0, 0 1, 02, 03, 0 β0β0 β1β1 β2β2 1-β 3 1 Tb

Delay-aware Sleep Mechanism (DSM) A high initial sleep window results in high delay, and thus the selection of the initial sleep window should take the effect of delay into account. θ is the initial sleep window corresponding to the delay requirement D 0. –with the delay requirement D 0 given, θ can be computed with formula T * b. 0, s1, si, sM, s 0, 0 1, 0i, 0M, 0 β0β0 β1β1 β i-1 βiβi β M-1 1-β 0 1-β 1 1-β i 1-β M 1111 …… βMβM Tb

Delay-aware Sleep Mechanism (DSM) 在 T i 中累積 j 個封包的機率 在 T i 中， j 個封包的平均 delay T i (MS 收資料 ) 的機率 封包在 T i (MS Sleep) 時 到達的 delay 總和 0, s1, si, sM, s 0, 0 1, 0i, 0M, 0 β0β0 β1β1 β i-1 βiβi β M-1 1-β 0 1-β 1 1-β i 1-β M 1111 …… βMβM Tb Poisson 機率公式 Serving time per packet Packet arrival rate 封包到達總數

Simulation Standard DTISW DSM

Simulation Standard DTISW DSM

Conclusion The DSM adapts the initial sleep window to the traffic load and the delay requirement. A marked gain in the power consumption compared to the traditional sleep mechanism can be found.

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