The role of SNR in achieving MIMO rates in cooperative systems

Chris T.K. Ng, J. Nicholas Laneman, Andrea J. Goldsmith

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Scopus citations


We compare the rate of a multiple-antenna relay channel to the capacity of multiple-antenna systems to characterize the cooperative capacity in different SNR regions. While it is known that in the asymptotic regime, at a high SNR or with a large number of cooperating nodes, cooperative systems lack full multiplexing gain, in this paper we consider cooperative capacity gain at moderate SNR with a fixed number of cooperating antennas. We show that up to a lower bound to an SNR threshold, a cooperative system performs at least as well as a MIMO system with isotropic inputs; whereas beyond an upper bound to the SNR threshold, the cooperative system is limited by its coordination costs, and the capacity is strictly less than that of a MIMO orthogonal channel. The SNR threshold depends on the network geometry (the power gain g between the source and relay) and the number of cooperating antennas M; when the relay is close to the source (g ≫ 1), the SNR threshold lower and upper bounds are approximately equal. As the cooperating nodes are closer, i.e., as g increases, the MIMO-gain region extends to a higher SNR. Whereas for a populous cluster, i.e., when M is large, the coordination-limited region sets in at a lower SNR.

Original languageEnglish (US)
Title of host publication2006 IEEE Information Theory Workshop, ITW 2006
Number of pages5
StatePublished - 2006
Externally publishedYes
Event2006 IEEE Information Theory Workshop, ITW 2006 - Punta del Este, Uruguay
Duration: Mar 13 2006Mar 17 2006

Publication series

Name2006 IEEE Information Theory Workshop, ITW 2006


Other2006 IEEE Information Theory Workshop, ITW 2006
CityPunta del Este

All Science Journal Classification (ASJC) codes

  • General Engineering


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