Azadeh Ettefagh

Performance analysis of distributed cluster-based MAC protocol for multiuser MIMO wireless networks

It is known that multiuser multiple-input multiple-output (MIMO) communication can enhance the performance of wireless networks. It can substantially increase the spectral efficiency of wireless networks by utilising multiuser interference rather than avoiding it. This paradigm shift has most impact on the medium access control (MAC) protocol because most existing MAC protocols are designed to reduce the interference. In this article, we propose a novel cluster-based carrier sense multiple access with collision avoidance (CB-CSMA/CA) scheme. The proposed scheme enables multiuser MIMO transmissions in wireless local area networks (WLANs) by utilising the multiuser interference cancellation capability of the physical layer. In this article we focus on the performance analysis of CB-CSMA/CA. We investigate saturation throughput applying optimum backoff parameters and in the presence of synchronisation errors. Furthermore, we study the impact of different clustering methods on non-saturation throughput. We show that CB-CSMA/CA improves throughput significantly compared to the CSMA/CA scheme used in the IEEE 802.11 system. It is a promising approach for a variety of network configurations including typical infrastructure WLANs as well as many other wireless cooperative networks.

Performance of a cluster-based MAC protocol in multiuser MIMO wireless LANs

The IEEE 802.11n specifies MIMO techniques to enhance data rate in WLANs. However, using carrier sense multiple access with collision avoidance (CSMA/CA), it can support only point-to-point links. On the other hand, it is known that multiuser MIMO techniques significantly increase the spectral efficiency of a network. There are already some enhanced MIMO signal processing techniques available which enable concurrent multiuser transmissions by utilising multiuser interference cancellation techniques. Multiuser interference can also be cancelled in a distributed manner. To enhance IEEE 802.11n systems such that multiple users can transmit simultaneously, we propose a novel cluster-based CSMA/CA (CB-CSMA/CA) protocol. According to this protocol, nodes in a network are grouped in clusters such that the nodes which belong to the same cluster can transmit or receive simultaneously. In this paper, we explain the basics of the protocol and investigate throughput performance of the CB-CSMA/CA. We apply the CB-CSMA/CA to a multiuser zero-forcing relaying network, where several amplify-and-forward relays assist the communication between multiple source and destination pairs and perform distributed channel orthogonalisation. This cooperative network can be considered as a future application for next generation WLANs. As it is shown, the CB-CSMA/CA provides a significant throughput gain over point-to-point systems.

On the Range Performance of Decode-And-Forward Relays in IEEE 802.11 WLANs

We consider a wireless local area network (WLAN) in the 5 GHz band. The coverage is one of the main challenges in high-frequency wireless systems and we focus on enhancing the coverage range of such a system by relaying. So far no relaying functions are defined in IEEE 802.11 medium access control (MAC). We introduce three simple MAC schemes for multihop communications and classify them based on delay, simplicity, capacity and application. We also point out the deficiency of the actual standard regarding multihop connections. We study the outage behaviour of a single input single output (SISO) two-hop link and improve it by developing a multiple input multiple output (MIMO) system. We investigate the tradeoff between coverage range and number of relays in a two-dimensional scenario. We also discuss the tradeoffs between having relays instead of adding more access points (APs) to the system and give an estimation of the number of required APs/relays to fully cover an area. In other words we show how much range one can gain from decode-and-forward (DF) relaying in a WLAN scenario

Throughput Performance of Two-way Relaying in IEEE 802.11 Networks

Conventional half-duplex relaying suffers from a pre- log factor of frac12 in the capacity equation which reduces the spectral efficiency significantly. On the other hand half-duplex two-way relaying, which can compensate this spectrum efficiency loss and could be a suitable substitute for conventional relaying, requires two nodes to transmit at the same time and frequency. Therefore to realise two-way relaying a modification of the current IEEE 802.11/e Medium Access Control (MAC) is necessary. In this paper we propose an appropriate MAC scheme for two-way relaying. The main objective is to investigate for realistic network configurations how much the throughput is improved by two-way and semi-two-way relaying under the proposed MAC compared to conventional relaying.

Comparison of Distributed and Co-located Antenna Diversity Schemes for the Coverage Improvement of VoWLAN Systems

This paper concerns the coverage range of a high quality voice over wireless local area network (VoWLAN) system based on the IEEE 802.11a standard. Techniques for enhancing the coverage range of each access point (AP) using co-located and distributed antenna diversity schemes are proposed and it is shown that the number of required APs and therefore the infrastructure cost may thus be reduced. Comparisons are made between the coverage range of the 802.11a and that of DECT (digital enhanced cordless telecommunication), and simulations and channel measurements devised for predicting the effect of diversity techniques on the range of APs are described. The results of two different measurement campaigns are presented, one with co-located antennas and the other with locally distributed antennas. The coverage enhancement gained within these scenarios by employing diversity techniques is thus deduced