Beamforming techniques for enabling spatial-reuse in MCCA 802.11s networks
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Beamforming techniques for enabling spatialreuse in MCCA 802.11s networks Y Lebrun1,2*, K Zhao4, S Pollin1, A Bourdoux1, F Horlin3, S Du4 and R Lauwereins1,2
Abstract We address the problem of co-channel interference (CCI) in wireless mesh networks based on the IEEE802.11s extension. The carrier sensing mechanism deployed in those networks insufficiently addresses the CCI problem, causing the hidden and exposed node problems; consequently degrading the throughput and latency. In this paper, we show how beamforming techniques can be implemented on top of the IEEE802.11s medium access control protocol and, using the information readily available, cancel the interference to mitigate this inefficiency of carrier sense and improve the spatial-reuse gain. In addition, we propose the signal-to-jamming-noise ratio (SJNR) beamformer and show that it significantly improves the spatial-reuse gain compared to the simple zero-forcing (ZF) beamformer and the basic IEEE802.11s access scheme. We derive the ergodic capacity of the ZF beamformer and the basic IEEE802.11s access scheme and simulate the performance of the various schemes. We show that improvements of up to 85% are achieved as function of the scenario simulated and the beamforming technique used and that the SJNR scheme outperforms the standard ZF beamformer. Keywords: wireless mesh network (WMN), IEEE802.11s, beamforming, zero-forcing (ZF), signal-to-jamming-noise ratio (SJNR), spatial-reuse
1. Introduction A wireless mesh network (WMN) based on the IEEE802.11s extension [1], as shown in Figure 1, can exploit neighbor nodes to relay the information through multiple hops in the network and increase the spectral and power efficiency. WMNs have recently been considered in wireless standards, e.g., the 802.15.5 [2] and the 802.16e [3], and are still seen as a promising research area in wireless communications. In such networks, an efficient spatial-reuse is imperative to maximize the use of the available spectrum and provide the required quality of service (QoS) in terms of throughput and latency [4]. Spatial-reuse means that multiple nodes communicate concurrently, using the same time/frequency resources. However, the medium access control (MAC) protocol of IEEE802.11s networks relies on carrier sensing for granting access to the medium. This carrier sense mechanism causes the hidden node problem, i.e., when a node that is able to interfere with an ongoing * Correspondence: [email protected] 1 Interuniversity Micro-Electronics Center (IMEC), Kapeldreef 75, 3001 Leuven, Belgium Full list of author information is available at the end of the article
transmission is not silenced, and the exposed node problem, i.e., when a node is silenced even when a transmission from this node does not cause a collision at the receiver. These problems are known to limit the spatial reuse, consequently degrading the performance of the network [5]. When sensing the medium as busy, nodes part of an IEEE802.11s network refrain from transmitting to prevent collisions at t
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