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.
In a seminal paper, Bianchi @cite_1 proposed an approximate model for the throughput performance of a single-cell IEEE 802.11 network that uses DCF as the medium access mechanism and in which all the nodes are saturated. @cite_2 extended the model and provided some new insights. In both of these papers, the authors evaluated the attempt probability @math (also, the long term attempt rate) in a system slot as a function of the number of contending nodes. While in this paper, we obtain the attempt probability and saturation throughput for a scenario, which requires different analysis than presented in @cite_1 and @cite_2 , due to the different behavior of the PSM. In our earlier submission @cite_9 , we focussed on the performance of PSM under application level downlink traffic over TCP. While in this paper, we consider both uplink and downlink traffic, which is different from TCP. We analyze attempt probability of the AP and the STA and saturation throughputs, which makes this paper more basic than our earlier submission @cite_9 .
@cite_9 @cite_1 @cite_2
2162598825 2166657206
The IEEE has standardized the 802.11 protocol for wireless local area networks. The primary medium access control (MAC) technique of 802.11 is called the distributed coordination function (DCF). The DCF is a carrier sense multiple access with collision avoidance (CSMA CA) scheme with binary slotted exponential backoff. This paper provides a simple, but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions. The proposed analysis applies to both the packet transmission schemes employed by DCF, namely, the basic access and the RTS CTS access mechanisms. In addition, it also applies to a combination of the two schemes, in which packets longer than a given threshold are transmitted according to the RTS CTS mechanism. By means of the proposed model, we provide an extensive throughput performance evaluation of both access mechanisms of the 802.11 protocol. We study a fixed-point formalization of the well-known analysis of Bianchi. We provide a significant simplification and generalization of the analysis. In this more general framework, the fixed-point solution and performance measures resulting from it are studied. Uniqueness of the fixed point is established. Simple and general throughput formulas are provided. It is shown that the throughput of any flow will be bounded by the one with the smallest transmission rate. The aggregate throughput is bounded by the reciprocal of the harmonic mean of the transmission rates. In an asymptotic regime with a large number of nodes, explicit formulas for the collision probability, the aggregate attempt rate, and the aggregate throughput are provided. The results from the analysis are compared with ns2 simulations and also with an exact Markov model of the backoff process. It is shown how the saturated network analysis can be used to obtain TCP transfer throughputs in some cases.