15th International Conference on Electronics Computer and Computation (ICECCO 2019) AN EFFICIENT SLEEP-WINDOW-BASED POWER SAVING SCHEME (ESPSS) IN IEEE 802.16e NETWORKS Daniel Dauda Wisdom Department of Mathematics Usmanu Danfodiyo University Sokoto, Nigeria danieldaudawisdom1@gmail.com Ibrahim Saidu Department of ICT Usmanu Danfodiyo University Sokoto, Nigeria ibrrasaidu@gmail.com Ahmed Yusuf Tambuwal Department of ICT Usmanu Danfodiyo University Sokoto, Nigeria ahmed_tambuwal@yahoo.com Samson Isaac Department of Computer Science Kaduna State University Kaduna, Nigeria samson.isaac@kasu.edu.ng Muhammad Aminu Ahmad Department of Computer Science Kaduna State University Kaduna, Nigeria muhdaminu@kasu.edu.ng Nasir Faruk Department of Telecommunication Science University of Ilorin Kwara, Nigeria Faruk.n@unilorin.edu.ng ABSTRACT IEEE known as WiMAX supports wider coverage, higher bandwidth, and quality of service (QoS). 802.16e was introduced which made battery-life of Mobile Station (MS) a critical challenge Since MS are battery powered with an impose rechargeable life. An Efficient Battery Lifetime Aware Power Saving Scheme was proposed to minimize frequent transition of MS to listening-wake mode in order-to reduce power consumption. However, it increases average response delay due to a longer sleep interval used. Thus, an efficient sleep window based power saving scheme (ESPSS) is proposed to reduce the response delay. The ESPSS introduces an average based sleep window to minimize the longer sleep interval. The scheme also proposed a modified minimum and maximum sleep interval to reduce the response delay. The ESPSS was evaluated using a discrete event simulator. The results showed that ESPSS achieves a superior performance compared to the existing Scheme in terms of response delay while improving QoS. KEYWORDS: Battery Life, Longer-Sleep-Intervals, Power Consumption, Response Delay and QoS. I. INTRODUCTION Formally, the IEEE 802.16 is designed for a fixed MS [1] while subsequent version of the IEEE 802.16e is an extension of the former standard with mobility features so that MS could move freely whenever it is in an active state [2]. Due to this features added to the legacy standard. The 802.16e Standard use three power saving classes (PSC) to extend the battery life of a MS. The PSC includes PSC I, PSC II and PSC III. PSC I is designed for Best effort (BE) and non-real-time variable rate (NRT-VR) traffics. PSC II for unsolicited grant service (UGS) and real time variable rate (RT-VR) traffics and PSC of PSC III is used for managing operations and multicast connections respectively. Hence, Several Power Saving Schemes have been proposed in order to improve on power efficiency of MS in [3][4][5]. However, the schemes in [4][6] wastes power due to their excessive listening operations and or frequent switching frequency from sleep/wake mode while [7][8] Use half of it last sleep interval, to adjust the Tmin when it exits from the previous sleep-mode operation as the initiate sleep interval in the next sleep-mode operation to reduce 1 |978-1-7281-5160-1/19/$31.00 ©2019 IEEE the excessive listening operations of MS. However, the scheme has excessive response delay due to its longer sleep interval, which also results to congestion, buffer overflow as well as overall performance degradation of a MS. In this Paper an Efficient Sleep Window Based Power Saving Scheme (ESPSS) is proposed. The scheme introduces an average based sleep window to minimize the longer sleep intervals of the existing scheme. The proposed scheme also proposes a modified minimum and maximum sleep interval in order to reduce the response delay while retaining power savings. 1. PSC I, II and III Power Saving Class of Type I is designed for Best effort (BE) and non-real-time variable rate (NRT-VR) traffics, it consists of listening window and sleep window. The length of the listening window in this power saving class is fixed and a MS with PSC I subsequently checks if there are some buffered packets for it in the listening window [8][9]. If there were buffered packets, the MS will revert to normal operation mode to receive the packet s Figure 1 and 2. Otherwise, the sleep window is activated in order to save power. Then this procedure repeats and the length of the sleep window is doubled until it reaches the maximum length of the sleep window [10] which may be activated only by a Positive MOBTRF-IND-Message from the Base State (BS) to MS. Type II for unsolicited grant service (UGS) and real time variable rate (RT-VR) traffics, similarly PSC of type II consisted of listening window and sleep window that is the sleep window is interleaved with a listening window. However, unlike type I, the length of listening and sleep windows are both fixed for PSC of type II and the sum of them is called, sleep cycle. Unlike type I, PSC II is also capable of transmitting data packets without returning to normal operation. Thus, the length of listening window is long enough to receive all packets arriving during a single sleep cycle in PSC II [11][12] Figure 1. PSC of type III is use for managing operations and multicast connections. These three PSC differ from each other by their parameter sets, methods of activation/deactivation, as well as the policies of MS availability for data transmission [13]. 15th International Conference on Electronics Computer and Computation (ICECCO 2019) Unlike PSC I and II, PSC III comprises of a single sleep window and is mainly used for multicast services (Figure 1). By activating this PSC, a single sleep window with defined length in WiMAX standard starts and subsequently the MS returns to normal mode operation [7]. Figure1: Types of Power Saving Classes These PSCs use three parameters to improve on power savings, namely, idle threshold, initial sleep window and final sleep window [13][14]. The idle threshold is the time interval in which the MS is in a waiting state, it has no messages to send or receive before moving to inactive state. The MS before moving to inactive state negotiates with it BS for approval in order to switch to a period of inactivity. The BS allocates the sleep parameters namely: initial sleep window (Tmin), final sleep window (Tmax) and listening window (L) to the MS, the MS transmits to it period of inactivity after it receives these parameters [13][14]. The Tsmin is the range of the first-sleep session (T) that an MS will go to sleep. After which it wakes up for the first T to listen to the traffic indication messages from the BS within the duration of the L. When the traffic indication messages indicate negative, the MS continues to sleep mode after the L duration. Else, the traffic indication message is positive, and the MS return to an active session. The T together with it L is the sleep cycle [15][16]. Whenever MS remain in a period of inactivity, then the next sleep cycle start as well as the T is doubled. These process is repeated until the Tsmax is achieved which is the maximum length of the sleep interval. When the Tsmax is achieved the MS remains in sleep mode until a Positive MOB-TRF-IND Message is sent from BS to MS (Figure 2) where the MS then wakes up to transmit/receive intending Packets Figure2: IEEE 802.16e Sleep Mode Parameters The rest of this Paper is organized as follows: Section II present Related Works, Section III Presents Proposed Algorithm, Section IV Presents Performance Evaluation and Section V Concludes this research study. II. Related Works This section presents related work on existing schemes. These schemes are review by highlighting their Operational, Strength and Weaknesses of each scheme as follows: 2 |978-1-7281-5160-1/19/$31.00 ©2019 IEEE Power Saving Mechanism with periodic traffic indications was proposed in [3] to minimize delay of MS. The mechanism uses traffic indication (TRFID) messages to initiate transmission at every constant time. The TRF-IND messages consist of a listening interval, wake interval and a sleep interval. During the listening interval a MS synchronizes with the current base station (BS) and decides whether to switch to awake-mode or remain in a sleep-mode. If there are data traffics in the buffer for the tagged MS, the BS sends a positive TRFIND message and the MS switch to awake-mode. The BS sends data during the wake-mode and the wake-mode terminates if no traffic arrives during a time-out/fixed time of a constant length T. If any data traffic arrives during inactive time T, the MS switches to wake mode and transmits the data. Otherwise, goes to a sleep-mode from the wake-mode without exchanging MOB-SLPREQ/RSP messages. The mechanism reduced the average response delay because of its frequent switching from sleep/wake mode, at the expense of an increase in energy-consumption. A Battery Lifetime-Aware Power Saving Scheme (BLAPS) was proposed in [17] to extend the battery life of mobile station (MS). The scheme dynamically adjusts three operating parameters, idle threshold, Tmin and Tmax base on the residual power and the traffic loads. It extended the battery life at the cost of an increase in energy consumption, more so the scheme frequently goes to listening mode if the traffic arrival is low thereby causing an average increase in the power consumption. Hence, an Efficient Battery Lifetime-Aware Power Saving Scheme (EBLAPS) was proposed in [18] to minimize the energy consumption of the existing BLAPS in [17]. The EBLAPS adaptively adjust the three parameters namely: idle threshold, initial sleep window, and final sleep window based on traffic arrival pattern. It employs an improved sleep mode control algorithm in the downlink Operation of the 802.16e in order to reduce the frequent transition to listening mode under low traffic arrival rate. And the scheme successfully minimized the average energy consumption but increases the response delay of MS which subsequently results in a longer sleep interval due to the larger sleep interval used in the scheme which led to congestion, packet loss/buffer overrun which is a motivation for this research study. More so, the scheme has a high consumption rate Hence, In [19] a Hyper-Erlang Battery-Life Energy Scheme (HBLES) was proposed to analytically adjust the sleep parameters based on the remaining battery power and the traffic pattern to simultaneously reduce the energy consumption and the average delay. It uses a HyperErlang distribution to determine the behaviour of the traffic. The scheme improves the energy efficiency. However, it ignores uplink traffics. A Delay Aware Power Saving Scheme (DAPSS) was introduce in [20] to minimize the longer sleep intervals of the existing Scheme. The proposed scheme successfully minimized the longer sleep intervals of MS; thereby, minimizing the average response delay of the scheme while maintaining power savings respectively. However, the scheme ignores in-cooperating real time services, which may further improve on the overall performance of the MS. Thus, an Enhanced Battery Life power saving scheme was proposed in [21] to in-cooperate real time services, which is an improvement of the existing DAPSS. The Scheme in-cooperates real time services and successfully extend the battery life performance at the expense of an average increase in energy consumption. 15th International Conference on Electronics Computer and Computation (ICECCO 2019) III. Proposed ESPSS T av erag e = In this section, an Efficient Sleep-Window-Based Power Saving Scheme (ESPSS) in IEEE 802.16e Networks for mobile broadband network services (MBNS) is propose, which is a modification of the existing Scheme described in [22] However, the shortcoming of the existing EBLAPS is first discussed. The scheme dynamically adjusts three sleep parameters namely: Iddle threshold (Tt), Minimum sleep intervals (Tmin) and Maximum Sleep intervals to reduce the energy consumption of a MS. It successfully minimized the frequent transition of MS to sleep mode, at the expense of an increase longer sleep interval (session). The increase longer sleep intervals resulted to an increase in both delay and slight power consumption due to the switching (cost) time taken for a mobile device to revert (return) from sleep to active mode respectively. To address the problems highlighted above; an ESPSS Scheme is proposed. Firstly, the scheme introduces an average based sleep window (Tj) given in Equation (1) to reduce the longer sleep intervals   1 + λk  2 j −1 T m in,   T j =  .T j −1 + Tm ax ,  2  if k  j −1  T m in < T m ax , λ ≠ 0  1+  2  λ  (1) O therw ise Where Tj is the jth sleep window, sleep intervals, Tm a x T m in is the minimum is the maximum sleep intervals, j is a positive integer. T m i n is determined by examining the inter arrival time of a downlink frame(s) in order to reduce the average response delay the downlink frames may had incurred in waiting for the MS to wake up. Then, the idle threshold is adopted from [24] computed as follows: The idle threshold (Tt) is adaptively updated based on the downlink traffic arrival pattern in order to predict the best duration for the next idle threshold. This best duration provides better idle time that considerably minimize response delay of MS which is obtained as follows:   σ    Tt = min(max(λ.dft  ,Tt _ min),max   n  dft) Tt _min )  (2)     Taverage       Where Tt is the idle threshold, Tt-dft is the default idle threshold. Next, the modified minimum sleep intervals (Tmin) is obtained as follows: First, the weighted average inter arrival time (Taverage) in between the downlink frame from BS to the MS is obtained as follows: 3 |978-1-7281-5160-1/19/$31.00 ©2019 IEEE (1 − β )T m in + β Td (3) Td is the time taken after which the DL frames arrive at the BS for MS since it went into sleep mode last, β is a positive integer. Second, the weighted average variance ( σ n ) of the inter arrival time of the downlink frame, is also obtained as follows: σ n = (1− β ) σ n−1 + β T average − Td (4) Finally, the modified minimum sleep intervals (Tmin) is obtained as follows: T m in = m ax (  T a v e ra g e − kσ n  , 1 ) (5 ) β and k are positive integers given as 0<β<1 and 0<k<0.5 The modified Tmin is dynamically adjusted base on the DL traffic load arrival in order to transmit/process packets appropriately or just in time. The appropriate adjustment of the Tmin predict the next actual arrival of the downlink frames which significantly minimize the average number of listening intervals in the sleep window. Thus, the possible duration (Pr) of a sequence of sleep cycles is dynamically calculated as follows: ∞ P r [ j ] =  k =1 P r ( j = k ) Finally, the modified maximum sleep intervals (Tmax) is obtained as follows: In this paper, we have introduced a Modified Tmax that takes the average of the sleep window based on the traffic load in order to minimize the longer sleep intervals which subsequently results in response delay. The reduction of the longer sleep intervals has minimized the longer response delay of the MS as well. The (Tmix) is computed when initial sleep window and frame response delay are known. Unlike the existing scheme which has a Tmin value that is fixed and the sleep window is also made to be constant to Tmax. In the existing scheme the Tmax sleep interval is maintained, hence, when the sleep interval approaches Tmax in Equation (2) of the existing Scheme, the sleep time becomes larger resulting to a longer sleep interval subsequently, which is a challenge. Since, traffics arrives with an increase sleep (intervals) time, and is observed in Figure 1, that until at the listening intervals the MS remains in Sleep Mode. In this paper, frame arrival has been assumed to follow a Poisson distribution with arrival rate λ. Tj is the length of the jth sleep interval and L is the length of the sleep interval, to obtain the final Tmax sleep window; First, we assumed an incoming frame arrival at the MS during its idle state, and the probability (Pr) of frame arrival is given as follows: 15th International Conference on Electronics Computer and Computation (ICECCO 2019) Pr ( n = Tt ) = Pr ( e1 = true ) = 1 − e =  ∞ P r (n = k k =1 ) −λ ( Tj + L ) (6) M −1 (T j + L ) j =1 k (7 ) Second, we assumed that there is at least one frame arrival at the MS in the jth sleep window. Its implies that no packets in the 1st, 2nd, 3rd, 4th up to (j−1)th sleep interval but there is at least one arriving frame in the jth sleep interval. The (Pr) probability of frame arrival in the jth sleep interval is obtained as follows: j-1 Pr (n = j) = ∏i=1 Pr ( ei = false) Pr ( ej = true) = e j-1 -λ (Tj +L) -λ (Tj +L) i=1 1- e (8) Let M satisfy the following:  k  j-1 1+  2 Tmin,  λ  k  j-1 if 1+  2 Tmin< Tmax ;  λ M is an integer. Third, the jth sleep window is obtained as follows: k  j −1  (1 + λ ) 2 T m i n If j< M Tj =  (9 )  T j −1 + T m a x O th e r w is e  2 Assuming the packets resulting to the outflow/overrun from the sequence of sleep cycles will arrive at any moment during the last cycle with uniform probability. The length of jth cycle is ( T + L ) and the possible response delay of j packets is obtained in Equation (11). From Equation  k  1+  2 λ   (1) above, M −1 k  Q =  1 +  and λ  we let M satisfy − λ  Q 2 j−1 Tmin + jL .  e  if 4 j =M e − λ Q.2 j −1Tmin + jL    .Z (13) − λ ( Q .2 j −1 −1Tmin − L + LM +Tt )   (14) Unlike the existing scheme that makes use of larger sleep windows and the full length of the Tmax sleep intervals Figure 1, which subsequently results in a longer sleep period (time). The proposed ESPSS has introduced an average based sleep window that takes the average Tmax values in order to significantly minimize the longer response delay of the variant EBLAPS scheme. More so, when the sleep intervals subsequently approaches Tmax, the sleep intervals is increased incrementally as an average of the jth sleep window (Equation 1 and 9) in order to minimize the longer sleep intervals/response delay respectively. Thus, minimizing the response delay the downlink frame may had incurred subsequently while appropriately or just in time processing/transmitting packets within their life time Figure 2. T j −1 + Tmax T j −1 + Tmax ∞ P j 4 = 4 j=M e − λ  Q .2 j −1 −1 Tmin − L + LM +Tt    ( ) (15) The sum of the average response delay of the ESPSS scheme is also expressed as follows: [D ] 2 E ∞ =   ∞ P j = 1 2 P j (T [D E T j + L ) ( 1 6 ) j + ] ( 1 L 7 ) Tmin − L+ LM + T  t Z = j<M  T P r   ∞ [D ] =  j=1 j (10) if j≥M T j −1 + Tmax 2 + L    (1 1 ) 2 From Equation (11) and Equation (10) the expected response delay is expressed as follows: M −1 P r j j =1 Tj 2 + T j −1 + T m ax 2 (2 ) ∞  Pr j Substituting 14 and 15 into 13, we have T m a x 2E = e Finally, Let D represents frame response delay and the traffic arrival follow a Poisson distribution. The expected (E) response delay is obtained as follows: L + 2 T j −1 + Tmax = rj e Tm in = Tm a x  − λTt Pr ( n = j ) =  Ze−λ  Q2J−1 −1 , ( )  Ze  E [D ] = P 4  2 j −2 j =1 e ∞ T j −1+Tmax j = λ Q Tmin +L  e  E R = Qe λ Q .Tmin + L  − λTt j = 1 and M is an integer. The jth sleep interval is given in Equation (9) above. And then we substitute Equation (9) into Equation (8) and we have: Where From Equation (12) we have (12) j=M 4 |978-1-7281-5160-1/19/$31.00 ©2019 IEEE [D] - L - 2R - λ  Q . 2 j -1 -1 Tmin - L + LM + Tt   - T j -1 4 (18) A. Procedure of Parameters Adjustment The procedures of parameters adjustment of ESPSS are: The MS begins in a normal mode operation. And subsequently request for sleep if the mobile sleep request (MOB-SLP-REQ) is granted, the MS transits to sleep mode else a positive (+) mobile traffic indication message (MOB-TRF-IND) is sent to the MS from the BS and the MS wakes up and process data packets on the queue. This process is repeated until a Negative (-) Mobile Sleep Response (MOB-SLP-RSP)) is granted by the BS (Figure 6). Otherwise the MS reverts to normal mode operation and continue the process else end the process. 15th International Conference on Electronics Computer and Computation (ICECCO 2019) (Figure Figure 3: Procedure of Adjustment of the ESPSS 3.2 Algorithm 1: The proposed ESPSS VI. Performance Evaluation This section presents the performance evaluation of the propose ESPSS against that of the Existing Scheme using a DES. The evaluation is based on the average power savings and response delay respectively. The simulation topology consists of a base station (BS) with MS connected around it 5 |978-1-7281-5160-1/19/$31.00 ©2019 IEEE 6 Figure 4: Illustrates average power consumption VS Mean arrival rates. From the beginning the Proposed ESPSS has a slightly lower Consumption rate as compared to the existing schemes, due to the introduction of the average based sleep window. However, at a higher traffic arrival both schemes have similar performance. Figure 5: Illustrates average Response Delay VS Mean arrival rates. From the beginning the propose ESPSS Scheme have significantly minimized the longer sleep interval. Hence, minimizing the response delay due to the Modified Tmin and Tmax as well as the introduction of an average based sleep window. However, when there are higher traffic arrival both schemes have similar performance. Thus, the proposed ESPSS and the existing scheme converge towards same point respectively. V. Conclusion In this paper, a new Scheme called an Efficient SleepWindow-Based Power Saving Scheme (ESPSS) in IEEE 802.16e Networks is proposed. The scheme introduces an average based sleep window to minimize the longer sleep intervals of the existing scheme. The proposed scheme also 15th International Conference on Electronics Computer and Computation (ICECCO 2019) proposed a modified minimum and maximum sleep interval in order to reduce the response delay while retaining power savings. The proposed ESPSS was evaluated using a discrete event simulator. The simulation results show that the proposed ESPSS achieves superior performance as compared to the existing Scheme in terms of response delay while maintaining the average power consumption. In addition, the result also indicates that the proposed Scheme extend the battery life of MS by 19.88% and reduces the average delay by 47% while improving the QoS. References [1] IEEE 802.16 WG, “Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems” [IEEE 802.16 working Group and others, IEEE Std, 802.16, 2004]. 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