Energy-aware architecture for multi-rate ad hoc networks

AbstractThe backbone of ad hoc network design is energy performance and bandwidth resources limitations. Multi-rate adaptation architectures have been proposed to reduce the control overhead and to increase bandwidth utilization efficiency. In this paper, we propose a multi-rate protocol to provide the highest network performance under very low control overhead. The efficiency of the proposed auto multi-rate protocol is validated extensive simulations using QualNet network simulator. The simulation results demonstrate that our solution significantly improves the overall network performance

A Dynamic and Adaptive Transmission Scheme for Both Solving Uplink/Downlink Unfairness and Performance Anomaly Problems in a Multi-Rate WLAN

Abstract: Uplink/downlink fairness and performance efficiency are both considerable issues in an IEEE 802.11 multi-rate Wireless Local Area Network (WLAN). The IEEE 802.11 Distributed Coordination Function (DCF) provides equal medium access probability to all transmitters that cause the access point (AP) to obtain less bandwidth than that of the wireless mobile stations to download traffic when the number of mobile stations is larger than one. Furthermore, the WLAN with infrastructure mode also has the performance anomaly problem that the system throughput was seriously degraded by the transmissions of lower date rate transmitters in a multi-rate environment. In the past studies, many mechanisms have been proposed to solve the uplink/downlink unfairness problem, such as the transmission opportunity mechanism (TXOP), the multiple backoff timer mechanism (MBT) and the asymmetric access point mechanism (AAP). In order to improve the performance efficiency, contention window differentiation mechanism (CWD), packet size differentiation mechanism (PSD) and interframe gap differentiation mechanism (IFG) have been proposed recently. The proposed mechanisms, however, did not take both uplink/downlink unfairness and performance anomaly problems into consideration at the same time. In fact, the two problems occur simultaneously in practical WLAN environments. In this paper, we propose a dynamic and adaptive transmission scheme (DAT) to deal with the both problems. Each wireless mobile station will consider its data rate to decide the number of packets to transmit when it gets the privilege to access medium. Moreover, the AP has more right to download more packets for the purpose of balancing total uplink traffic. The system throughput of the proposed DAT is discussed and validated by the simulations and analytical results. The simulations also show that the proposed DAT outperforms the previous mechanisms

Exploiting multi-user diversity in wireless LANs with channel-aware CSMA/CA

© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents a channel-aware access scheme for Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) aiming to take advantage of multi-user diversity and improve throughput, while supporting distributed and asynchronous operation. By dynamically adjusting the contention window of each station (STA) according to its channel state, this method prioritizes STAs that gain most from using a channel, and hence, enhances channel utilization in comparison with a simple random access scheme. To model the proposed Adaptive CSMA/CA (A-CSMA/CA) protocol, a three-dimensional Markov chain is developed. With the aid of such model, performance of the proposed A-CSMA/CA is analytically studied in terms of saturation throughput. Furthermore, illustrative results confirm that A-CSMA/CA significantly improves the throughput, specifically in a large network

Distributed MAC Strategy for Exploiting Multi-user Diversity in Multi-rate IEEE 802.11 Wireless LANs

Fast rate adaptation has been established as an effective way to improve the PHY-layer raw date rate of wireless networks. However, within the current IEEE 802.11 legacy, MAC-layer throughput is dominated by users with the lowest data rates, resulting in underutilization of spectrum bandwidth. In this paper, we propose a novel distributed MAC strategy, referred to as Rate-aware DCF (R-DCF), to leverage the potential of rate adaptation in IEEE 802.11 WLANs. The key feature of R-DCF is that by introducing different mini slots according to the instantaneous channel conditions, only contending stations with the highest data rate can actually access the channel. In this way, the R-DCF protocol not only effectively exploits multi-user diversity in a fully distributed manner but also drastically reduces the loss of throughput due to collisions. Through analysis, we derive a closed-form network throughput expression for R-DCF. Based on the analysis, we further derive the maximal throughput that can be achieved by R-DCF. For practical implementation, an offline adaptive backoff method is developed for R-DCF to achieve a close-to-optimal performance at low runtime complexity. The superiority of R-DCF is proven by extensive analyses and simulations. 1