Abstract
Relays are being deployed in both fourth generation cellular systems and wide metropolitan area networks in order to increase coverage and spectral efficiency. In this article, we consider a network with three half-duplex relays assisting the transmission from a source towards a destination. By assuming that transmission time consists of a sequence of phases, we develop a transmission scheme in which spatial multiplexing is achieved by alternating the transmission of a single relay in odd phases and a couple of relays employing Slepian-Wolf encoding in even phases. Moreover, to simplify Slepian-Wolf decoding (consisting of a scheme with successive interference cancelation), we propose a suboptimal scheme in which cooperative relays employ quantized QAM constellations to yield at the destination the desired QAM constellation with no interference. We formalize the problem of maximizing network spectral efficiency optimizing (a) QAM size, (b) power allocation, (c) time allocation, and (d) relays transmitting and receiving at each phase. The performance of the proposed scheme is compared against existing techniques in typical wireless scenarios showing the merits of the proposed approach.
Highlights
Relays or cooperative networks where the transmission between a source and a destination is assisted by other nodes have shown to be an interesting solution to implement distributed multiple input multiple output (MIMO) systems
We indicate with R(A) the spectral efficiency related to the couple of cooperative relays and with R(B) the spectral efficiency related to the remaining relay
Note that the symbol transmitted by relay rmax and the quantized QAM symbol transmitted by relay rmin combine at the destination into a QAM symbol that can be detected using conventional methods; node D is unaware of the private transmission from relay rmax, it obtains the benefit of an higher signal to noise ratio (SNR)
Summary
Relays or cooperative networks where the transmission between a source and a destination is assisted by other nodes have shown to be an interesting solution to implement distributed multiple input multiple output (MIMO) systems. The achievable rates for various techniques have been derived in [8] for the case of half duplex relays in the absence of interference for a network with two relays. We consider a network with three relays operating in half duplex mode.
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