Abstract
In this paper, a comprehensive design and analysis of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment is investigated, where a multi-antenna amplify-and-forward FD relay station serves multiple half-duplex (HD) multi-antenna users. The pivotal obstacles of loopback self-interference (LI) and multiple co-channel interferers (CCI) at the relay and destination when employing FD relaying in cellular networks are addressed. In contrast to the HD relaying mode, the CCI in the FD relaying mode is predicted to double since the uplink and downlink communications are simultaneously scheduled via the same channel. In this paper, the optimal layout of transmit (receive) precoding (decoding) weight vectors which maximizes the overall signal-to-interference-plus-noise ratio is constructed by a suitable optimization problem, and then a closed-form sub-optimal formula based on null space projection is presented. The proposed hop-by-hop rank-1 zero-forcing (ZF) beamforming vectors are based on added ZF constraints used to suppress the LI and CCI channels at the relay and destination, i.e., the source and relay perform transmit ZF beamforming, while the relay and destination employ receive ZF combining. To this end, unified accurate expressions for the outage probability and ergodic capacity are derived in closed form. In addition, simpler tight lower bound formulas for the outage probability and ergodic capacity are presented. Moreover, the asymptotic approximations for outage probability are considered to gain insights into system behavior in terms of the diversity order and array gain. Numerical and simulation results show the accuracy of the presented exact analytical expressions and the tightness of the lower bound expressions. The case of hop-by-hop maximum-ratio transmission/maximal-ratio combining beamforming is included for comparison purposes. Furthermore, our results show that while multi-antenna terminals improve the system performance, the detrimental effect of CCI on FD relaying is clearly seen. Therefore, our findings unveil that MIMO FD relaying could significantly improve the system performance compared to its conventional MIMO HD relaying counterpart.
Highlights
T RADITIONAL dual-hop relaying networks and base stations operate in the half-duplex (HD) mode, thereby two orthogonal channels are essential to initiate communications
Inspired by the above stated limitations, this paper provides a thorough investigation for the impact of loopback self-interference (LI) and co-channel interferers (CCI) at the relay and destination on the performance of amplifyand-forward FD relaying networks with multi-antenna nodes by employing hop-by-hop ZF beamforming
Note that in the proposed ZF beamforming scheme, the optimal source and relay transmit powers are given by their maximum values, i.e., ES and ER, respectively, as they result in the maximum overall signal-to-interefernce-plus-noise ratio (SINR)
Summary
T RADITIONAL dual-hop relaying networks and base stations operate in the half-duplex (HD) mode, thereby two orthogonal channels (i.e., in a time division duplex or frequency division duplex manner) are essential to initiate communications. To our best knowledge, the effect of co-channel interference (CCI) on the overall performance of FD relaying with multiple-antenna terminals has not been investigated yet, i.e., the general case of multiple antenna terminals with CCI at the relay and destination, utilizing transmit (receive) ZF beamforming (combining) has not been analyzed in the literature for both HD and FD relaying modes.. In [23], the average spectral efficiency of a stochastic geometry small cell networks, when both the base stations and user equipments operate in FD mode (i.e., terminals have dedicated antennas for transmission and reception) is presented Note that all these previous works are restricted to single antenna terminals. Inspired by the above stated limitations, this paper provides a thorough investigation for the impact of LI and CCI at the relay and destination on the performance of amplifyand-forward FD relaying networks with multi-antenna nodes by employing hop-by-hop ZF beamforming.
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