2012/03/15 by Vishnu Namboodiri, Namboodiri, Vishnu, B. Sundar Rajan +1
Computer Science · Engineering · Mathematics · #Advanced MIMO Systems Optimization #Advanced Wireless Communication Technologies #Cooperative Communication and Network Coding #FOS: Computer and information sciences #Information Theory (cs.IT) #cs.IT #math.IT
paper · pdf · doi:10.48550/arxiv.1203.3269
12 Figures and 3 Tables
arxiv created 2012/03/15 · openalex publication_date 2012/03/15 · arxiv updated 2012/03/16 · openalex created_date 2022/10/01 · openalex updated_date 2026/07/28
The design of modulation schemes for the physical layer network-coded two way relaying scenario has been extensively studied recently with the protocol which employs two phases: Multiple access (MA) Phase and Broadcast (BC) Phase. It was observed by Koike-Akino et al. that adaptively changing the network coding map used at the relay according to the channel conditions greatly reduces the impact of multiple access interference which occurs at the relay during the MA Phase and all these network coding maps should satisfy a requirement called the exclusive law. Only the scenario in which the end nodes use M-PSK signal sets is extensively studied in \citeNVR using Latin Sqaures. In this paper, we address the case in which the end nodes use M-QAM signal sets (where M is of the form 22λ, λ being any positive integer). In a fading scenario, for certain channel conditions γej θ, termed singular fade states, the MA phase performance is greatly reduced. We show that the square QAM signal sets give lesser number of singular fade states compared to PSK signal sets. Because of this, the complexity at the relay is enormously reduced. Moreover, lesser number of overhead bits are required in the BC phase. The fade state γej θ=1 is singular for all constellations of arbitrary size including PSK and QAM. For arbitrary PSK constellation it is well known that the Latin Square obtained by bit-wise XOR mapping removes this singularity. We show that XOR mapping fails to remove this singularity for QAM of size more greater than 4 and show that a doubly block circulant Latin Square removes this singularity. Simulation results are presented to show the superiority of QAM over PSK.