Yayu Gao

Throughput Optimization of Heterogeneous IEEE 802.11 DCF Networks

This paper presents the throughput analysis of an M-group heterogeneous IEEE 802.11 DCF network where nodes in different groups have distinct input rates and initial backoff window sizes. An explicit expression of the network steady-state operating point is obtained based on the fixed-point equation of the limiting probability of successful transmission of Head-of-Line (HOL) packets given that the channel is idle, which is shown to be closely dependent on the backoff parameters of saturated groups and the input rates of unsaturated groups. Both the network throughput and the group throughput performance are further characterized, and the maximum network throughput is derived as an explicit function of the holding times of HOL packets in successful transmission and collision states. The analysis reveals that to achieve the maximum network throughput, the optimal set of input rates of unsaturated groups and initial backoff window sizes of saturated groups should satisfy a constraint that is determined by the group sizes of saturated groups. Given the input rates of unsaturated groups, for instance, the initial backoff window sizes of saturated groups should linearly increase with their group sizes, and those with higher increasing rates achieve lower group throughput.

IEEE 802.11e EDCA Networks: Modeling, Differentiation and Optimization

Enhanced distributed channel access (EDCA) is an extension of the distributed coordination function to support quality-of-service for IEEE 802.11 wireless local area networks. By assigning distinct backoff parameters to each access category (AC), differentiated throughput performance can be achieved when the network is saturated. Although it has been long observed that the network throughput with the current EDCA standard setting may significantly degrade as the network size grows, how to properly tune the backoff parameters to optimize the network throughput under a certain differentiation requirement remains largely unknown. In this paper, a new analytical model is proposed to address this open issue. Specifically, we focus on an M-AC IEEE 802.11e EDCA network where nodes in the same AC have identical backoff parameters, including the initial backoff window sizeW(g), the cutoff phaseK(g), and the arbitration interframe spaces (AIFS) numberA(g), g = 1, . . . , M. The network steady-state operating point in saturated conditions, i.e., pA, is characterized by using the steady-state probability of successful transmission of head-of-line (HOL) packets given that the channel is idle, based on which explicit expressions of node throughput and network throughput are further obtained. For given target ratios of node throughput of ACs, the optimal initial backoff window sizes and AIFS numbers to maximize the network throughput are derived and verified by simulation results. The analysis reveals that the maximum network throughput is solely determined by the holding time of HOL packets in successful transmission and collision states. To achieve the maximum network throughput, the initial backoff window size of each AC should be linearly increased with the network size. In the meantime, the increasing rate of the initial backoff window size, or the AIFS number, of each AC should be also carefully set according to the target ratios of node throughput. Although the maximum network throughput with pre-specified target ratios of node throughput of ACs can be achieved in both ways, the backoff window size differentiation could be a more preferable option as it requires fewer tuning parameters and provides better precision than the AIFS differentiation.

Optimal Downlink/Uplink Throughput Allocation for IEEE 802.11 DCF Networks

In this letter, we study how to adaptively tune system parameters to optimize the downlink and uplink throughput performance of IEEE 802.11 networks. In contrast to previous studies which only focus on achieving a target downlink/uplink throughput ratio, we show that by properly choosing the initial backoff window sizes of the access point and mobile stations, the total network throughput (i.e., the sum of downlink throughput and uplink throughput) can be maximized while maintaining the downlink/uplink throughput ratio at the target level simultaneously. Explicit expressions of the optimal initial backoff window sizes are obtained, and verified by simulation results.

Throughput Optimization of Multi-BSS IEEE 802.11 Networks With Universal Frequency Reuse

For IEEE 802.11 networks with multiple basic service sets (BSSs), most studies have focused on how to allocate different frequency sub-channels to BSSs for minimizing the co-channel interference. With the significant increase of the sub-channel bandwidth, however, it becomes increasingly important to study the network performance with universal frequency reuse. In this paper, we focus on an uplink

Throughput Optimization of non-real-time flows with delay guarantee of real-time flows in WLANs

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On the throughput of CSMA

-BSS IEEE 802.11 network, where all the BSSs share the frequency band rather than operate at different sub-channels. By dividing the nodes in each BSS into multiple groups according to the set of access points (APs) they can be heard by, the steady-state points of

Throughput optimization of heterogeneous IEEE 802.11 DCF networks

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Achieving optimum network throughput and service differentiation for IEEE 802.11e EDCA networks

BSSs in saturated conditions are obtained as the functions of the number of nodes in each group and the initial backoff window size of nodes of each BSS. The maximum network throughput is further characterized by optimally choosing the initial backoff window sizes of all the nodes and shown to be closely dependent on the percentage of nodes that can be heard by multiple APs. The comparison with orthogonal frequency division reveals that although the maximum network throughput is degraded due to interference among BSSs, a higher network data rate can still be achieved by universal frequency reuse, which makes it a preferable option for multi-BSS IEEE 802.11 networks.

Achieving Load Balancing in High-Density Software Defined WiFi Networks

Due to the rapid growth of real-time applications in wireless local area networks (WLANs), quality-of-service (QoS) guarantee becomes one of the key issues for IEEE 802.11e enhanced distributed channel access (EDCA) networks. In contrast to most existing studies which only focus on providing delay guarantee to real-time flows, in this paper we study the open question of how to adaptively tune system parameters to maximize the aggregate throughput of non-real-time flows with a certain mean access delay constraint on real-time flows for saturated IEEE 802.11e EDCA networks. Explicit expressions of the maximum aggregate throughput of non-real-time flows and the optimal initial backoff window sizes are obtained, and verified by simulation results. The analysis shows that for a given mean access delay constraint, the maximum aggregate throughput of non-real-time flows declines as the number of real-time nodes grows. It drops to zero when the number of realtime nodes exceeds a critical threshold, indicating that the delay requirement cannot be satisfied. An admission control scheme is further proposed, where the maximum number of real-time nodes that can be enrolled is derived as a linearly increasing function of the mean access delay constraint.

Performance Evaluation for WiFi DCF Networks from Theory to Testbed

In this paper, a semi-Markov model is established to characterize the throughput performance of CSMA networks. Based on the assumption of Poisson distributed aggregate traffic, the throughput expression of p-persistent CSMA is derived, which includes the results of 1-persistent CSMA and non-persistent CSMA presented in Kleinrock and Tobagis landmark paper [2] as two special cases. The analysis further reveals that the Poisson assumption requires that the transmission probability of packets is small enough, in which case the throughput performance becomes insensitive to the rescheduling policy of packets, i.e., p-persistent or non-persistent, and is solely determined by the normalized propagation delay.