Two-way relaying in wireless systems has initiated a large research effortduring the past few years. While one-way relay with a single data flowintroduces loss in spectral efficiency due to its half-duplex operation,two-way relaying based on wireless network coding regains part of this loss bysimultaneously processing the two data flows. In a broader perspective, thetwo-way traffic pattern is rather limited and it is of interest to investigateother traffic patterns where such a simultaneous processing of informationflows can bring performance advantage. In this paper we consider a scenariobeyond the usual two-way relaying: a four-way relaying, where each of the twoMobile Stations (MSs) has a two-way connection to the same Base Station (BS),while each connection is through a dedicated Relay Station (RS). While both RSsare in the range of the same BS, they are assumed to have antipodal positionswithin the cell, such that they do not interfere with each other. We introduceand analyze a two-phase transmission scheme to serve the four-way trafficpattern defined in this scenario. Each phase consists of combined broadcast andmultiple access. We analyze the achievable rate region of the new schemes fortwo different operational models for the RS, Decode-and-Forward (DF) andAmplify-and-Forward (AF), respectively. We compare the performance with astate-of-the-art reference scheme, time sharing is used between the two MSs,while each MS is served through a two-way relaying scheme. The results indicatethat, when the RS operates in a DF mode, the achievable rate regions aresignificantly enlarged. On the other hand, for AF relaying, the gains arerather modest. The practical implication of the presented work is a novelinsight on how to improve the spatial reuse in wireless cellular networks bycoordinating the transmissions of the antipodal relays.
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