We consider a single station (STA) in the Power Save Mode (PSM) of an IEEE 802.11 infrastructure WLAN. This STA is assumed to be carrying uplink and downlink traffic via the access point (AP). We assume that the transmission queues of the AP and the STA are saturated, i.e., the AP and the STA always have at least one packet to send. For this scenario, it is observed that uplink and downlink throughputs achieved are different. The reason behind the difference is the long term attempt rates of the STA and the AP due to the PSM protocol. In this paper we first obtain the the long term attempt rates of the STA and the AP and using these, we obtain the saturation throughputs of the AP and the STA. We provide a validation of analytical results using the NS-2 simulator.
Krashinsky and Balakrishnan @cite_10 and Quiao and Shin @cite_4 focus on the interaction of the TCP slow start, RTT and PSM. @cite_0 propose a way to minimize energy and delay by scheduling and informing the schedule to STAs through beacon frames. @cite_3 propose to take advantage of throttling done by the TCP server in media streaming applications. In all of these papers, the authors focus on the energy saving either by modifying the PSM protocol @cite_0 , or by modifying the sleep wake schedule of the radio depending upon the characteristics of the application level traffic @cite_10 , @cite_4 and @cite_3 .
@cite_0 @cite_3 @cite_10 @cite_4
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Power conservation is a general concern for mobile computing and communication. In this paper, we investigate the performance of the current 802.11 power saving mechanism (unscheduled PSM) and demonstrate that background network traffic can have a significant impact on the power consumption of mobile stations. To improve power efficiency, a scheduled PSM protocol based on time slicing is proposed in this paper. The protocol adopts the mechanism of time division, schedules the access point to deliver pending data at designated time slices, and adaptively adjusts the power state of the mobile stations. The proposed scheme is near theoretical optimal for power saving in the sense that it greatly reduces the effect of background traffic, minimizes the station idle time, and maximizes its energy utilization. Comprehensive analysis and simulations are conducted to evaluate the new protocol. Our results show that it provides significant energy saving over the unscheduled PSM, particularly in circumstances where multiple traffic streams coexist in a network. Moreover, it achieves the saving at the cost of only a slight degradation of the one-way delay performance. While the 802.11 power saving mode (PSM) and its enhancements can reduce power consumption by putting the wireless network interface (WNI) into sleep as much as possible, they either require additional infrastructure support, or may degrade the transmission throughput and cause additional transmission delay. These schemes are not suitable for long and bulk data transmissions with strict QoS requirements on wireless devices. With increasingly abundant bandwidth available on the Internet, we have observed that TCP congestion control is often not a constraint of bulk data transmissions as bandwidth throttling is widely used in practice. In this paper, instead of further manipulating the trade-off between the power saving and the incurred delay, we effectively explore the power saving potential by considering the bandwidth throttling on streaming downloading servers. We propose an application-independent protocol, called PSM-throttling. With a quick detection on the TCP flow throughput, a client can identify bandwidth throttling connections with a low cost Since the throttling enables us to reshape the TCP traffic into periodic bursts with the same average throughput as the server transmission rate, the client can accurately predict the arriving time of packets and turn on off the WNI accordingly. PSM-throttling can minimize power consumption on TCP-based bulk traffic by effectively utilizing available Internet bandwidth without degrading the application's performance perceived by the user. Furthermore, PSM-throttling is client-centric, and does not need any additional infrastructure support. Our lab-environment and Internet-based evaluation results show that PSM-throttling can effectively improve energy savings (by up to 75 ) and or the QoS for a broad types of TCP-based applications, including streaming, pseudo streaming, and large file downloading, over existing PSM-like methods. On many battery-powered mobile computing devices, the wireless network is a significant contributor to the total energy consumption. In this paper, we investigate the interaction between energy-saving protocols and TCP performance for Web-like transfers. We show that the popular IEEE 802.11 power-saving mode (PSM), a "static" protocol, can harm performance by increasing fast round trip times (RTTs) to 100 ms; and that under typical Web browsing workloads, current implementations will unnecessarily spend energy waking up during long idle periods.To overcome these problems, we present the Bounded-Slowdown (BSD) protocol, a PSM that dynamically adapts to network activity. BSD is an optimal solution to the problem of minimizing energy consumption while guaranteeing that a connection's RTT does not increase by more than a factor p over its base RTT, where p is a protocol parameter that exposes the trade-off between minimizing energy and reducing latency. We present several trace-driven simulation results that show that, compared to a static PSM, the Bounded-Slowdown protocol reduces average Web page retrieval times by 5-64 , while simultaneously reducing energy consumption by 1-14 (and by 13× compared to no power management). Static PSM (power-saving mode) schemes employed in the current IEEE 802.11 implementations could not provide any delay-performance guarantee because of their fixed wakeup intervals. In this paper, we propose a smart PSM (SPSM) scheme, which directs a wireless station to sleep wake up according to an "optimal" sequence, such that the desired delay performance is guaranteed with minimum energy consumption. Instead of constructing the sequence directly, SPSM takes a unique two-step approach. First, it translates an arbitrary user-desired delay performance into a generic penalty function. Second, it provides a generic algorithm that takes the penalty function as the input and produces the optimal station action sequence automatically. This way, the potentially-complicated energy-consumption-minimization problem subject to delay-performance constraints is simplified and solved systematically. Our simulation results show that, with a two-stair penalty function, SPSM achieves delay performance similar to the BSD (bounded slowdown) protocol under various scenarios, but always with less energy consumption, thanks to its capability to adapt to changes in the response-time distribution. Moreover, because of SPSM's two-step design feature, it is more flexible than BSD in the sense of being able to meet arbitrary user-desired delay requirement, e.g., providing soft delay-bound guarantees with power penalty functions.