Multipair Twoway HalfDuplex Relaying with Massive Arrays and Imperfect CSI
Abstract
We consider a twoway halfduplex relaying system where multiple pairs of single antenna users exchange information assisted by a multiantenna relay. Taking into account the practical constraint of imperfect channel estimation, we study the achievable sum spectral efficiency of the amplifyandforward (AF) and decodeandforward (DF) protocols, assuming that the relay employs simple maximum ratio processing. We derive an exact closedform expression for the sum spectral efficiency of the AF protocol and a largescale approximation for the sum spectral efficiency of the DF protocol when the number of relay antennas, $M$, becomes sufficiently large. In addition, we study how the transmit power scales with $M$ to maintain a desired qualityofservice. In particular, our results show that by using a large number of relay antennas, the transmit powers of the user, relay, and pilot symbol can be scaled down proportionally to $1/M^\alpha$, $1/M^\beta$, and $1/M^\gamma$ for certain $\alpha$, $\beta$, and $\gamma$, respectively. This elegant power scaling law reveals a fundamental tradeoff between the transmit powers of the user/relay and pilot symbol. Finally, capitalizing on the new expressions for the sum spectral efficiency, novel power allocation schemes are designed to further improve the sum spectral efficiency.
 Publication:

arXiv eprints
 Pub Date:
 July 2016
 arXiv:
 arXiv:1607.01598
 Bibcode:
 2016arXiv160701598K
 Keywords:

 Computer Science  Information Theory
 EPrint:
 64 pages, 19 figures, Submitted to IEEE Transactions on Information Theory, July 2016