A Cognitive Approach to Achieve Fair Uplink and Downlink Utilities in Wireless Networks

[[abstract]]The paper investigates on fairness of utilities between uplink and downlink traffic flows in IEEE 802.11 Wireless Local Area Networks (WLAN) with an infrastructure mode. We propose a cognitive resource allocation scheme to tackle the fairness problem. The proposed scheme is cognitive by using neural networks to on-line learn the nonlinear function between the adopted Medium Access Control (MAC) parameters and the corresponding throughput. Thus, the learned knowledge can be exploited to adjust MAC parameters dynamically toward the utility fairness between uplink and downlink flows. Simulations results demonstrate that our adaptive scheme can effectively provide fair uplink and downlink utilities in a varying heterogeneous WLAN environment.

On Fairness in Heterogeneous WLAN Environments

[[abstract]]We analyze the fairness of IEEE 802.11 DCF in heterogeneous wireless LAN environments where users experience unequal channel conditions due to the mobility and fading effects. Previous works [3] [4] show that the 802.11 CSMA/CA can present fairness characteristics in both long- term and short-term. However, the conclusion is only valid under the condition of homogeneous link qualities, which may be impractical. In this paper, we consider heterogeneous channel conditions based on an analytical approach of extending a verified two dimensional Markov chain model of DCF proposed by Bianchi [10]. From our analytical results, it is shown that 802.11 CSMA/CA can present fairness among hosts with identical link qualities regardless of equal or different data rates applied, which is consistent with the observations of previous works. Our analytical results also demonstrate that the presence of heterogeneous channel conditions can pose significant unfairness of channel sharing even with a link adaptation mechanism since the MCSs (modulation and coding schemes) available are limited.

A Cross-Layer Link Adaptation Algorithm for IEEE 802.11 WLAN with Multiple Nodes

[[abstract]]IEEE 802.11 wireless local area network (WLAN) physical layer (PHY) offers multiple data rates. In multi-rate WLANs, 802.11 distributed coordination function (DCF) presents the phenomenon so called ldquoperformance anomalyrdquo: when some hosts transmit at lower data rates, throughput of others at high rates will be restricted within the lowest rate, leading to the degradation of overall performance. Therefore, the link adaptation scheme for 802.11 WLAN should consider not only throughput of the observed host but also system throughput in order to optimize the overall performance. In this paper we propose a cross-layer link adaptation algorithm which improves system throughput by regarding the situation of PHY rate degradation more thoughtfully and critically, and meanwhile compensates the throughput of hosts with bad link qualities by applying differentiated channel access parameters. Simulation results demonstrate the effectiveness of the propose algorithm.

Achieving time-based fairness for VoIP applications in IEEE 802.11 WLAN using a cross-layer approach

[[abstract]]IEEE 802.11 Wireless Local Area Network (WLAN) Physical Layer (PHY) offers multiple data rates. In multi-rate WLANs, 802.11 Medium Access Control (MAC) protocol, Distributed Coordination Function (DCF), essentially provides equal transmission opportunities to each sender host, causing the degradation of system throughput due to some hosts using low rates. In this paper we propose a cross-layer link adaptation scheme which improves throughput by adjusting MAC parameters according to PHY data rates to achieve time-based fairness instead of throughput-based fairness. Most importantly, in comparison with other approaches using a deterministic manner for temporal fairness (e.g. OAR), our random-access-based approach in statistic can be more effective to restrict the maximum packet delay within a bound when the number of stations grows. We conduct the transmission scenario of VoIP applications to evaluate the performance of our proposed scheme and the results demonstrate its effectiveness.

Adaptive Admission Control Algorithm in IEEE 802.16e Broadband Wireless Access Networks

[[abstract]]The emerging IEEE 802.16e Broadband Wireless Access (BWA) network is one of the most promising solutions to provide ubiquitous wireless access with high data rates, high mobility, and wide coverage. In the paper we develop a novel Connection Admission Control (CAC) algorithm for IEEE 802.16e mobile BWA networks to simultaneously improve the utilization efficiency of network resources and guarantee Quality of Services (QoS) for handoff connections. The proposed CAC scheme dynamically adjusts the amount of reserved bandwidth for handoff users according to the arrival distributions of handoff and new coming connections. Simulation results demonstrate that the proposed CAC algorithm can increase the number of admitted connections and also provide handoff QoS.