Relaying to Enhance the Coverage Range of a Voice over WLAN System


Azadeh Ettefagh, Marc Kuhn, and Armin Wittneben


International ITG Workshop on Smart Antennas, WSA 2006, Ulm, Germany, Mar. 2006.

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We consider a high-quality voice over Wireless Local Area Network (WLAN) system and we are interested in enhancing the coverage range of such a system by relaying while complying with Quality of Service (QoS) requirements. We show that in contrast to data networks we cannot gain from multi-hop communications with large number of hops so we consider the network under a two-hop traffic pattern. We distinguish two scenarios: single-antenna and multiple-antenna case. In the first scenario all nodes, i.e. Access Point (AP), Station (STA) and relay are equipped with a single antenna and Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying schemes are applied. In the second case we consider a two-hop Multiple Input Multiple Output (MIMO) system and diversity techniques are applied to enhance the range of the AP. In both scenarios only one relay assists the communication between the AP and the STA. Since WLANs are optimised for data we need to consider different aspects of QoS restrictions for a Voice over WLAN (VoWLAN) system. We point out such differences and provide appropriate solutions wherever applicable. The coverage range of the two-hop link for such a system is investigated and compared with that of cordless digital phones as well as single-hop link. We show the feasibility of relaying in a WLAN system by introducing three simple Medium Access Control (MAC) protocols for it. We focus on one of these schemes which is appropriate for VoWLAN. This new scheme is based on IEEE 802.11e standard and easy to implement while QoS features are guaranteed.


Relaying, Voice over WLAN, MAC scheme

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Copyright Notice: © 2006 A. Ettefagh, M. Kuhn, and A. Wittneben.

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