Two-hop Full-duplex Relay Research Articles

On Blind Channel Estimation in Full-Duplex Wireless Relay Systems

We investigate the feasibility of second-order statistics-based blind channel estimation in the context of two-hop full-duplex relay systems. To that end, the performance of blind and traditional pilot-based (training sequence based) channel estimation approaches are compared. This is accomplished by deriving the Cramer-Rao Lower Bound (CRLB) expressions for both blind and pilot-based schemes, and comparing them to each other and to the mean-squared error (MSE) values measured via simulation. Post-equalization SINR expressions are also derived for both blind and pilot-based methods. Furthermore, a modified post-equalization SINR expression, where the channel estimation error is replaced by the inverse of the Fisher information matrix (FIM) is proposed, providing an upper bound for the post-equalization SINR. These analytically-predicted SINR values for the blind approach are compared to the SINR measured via link simulation. The performance of the two channel estimation methods is analyzed by comparing the CRLB, post-equalization SINR, and BER performance for two significantly different transmission packet sizes. All of the above metrics indicate that blind estimation provides clear performance advantages relative to the pilot-based counterpart. Additionally, the blind approach eliminates the overhead associated with the pilot-based method, where a portion of the system resources is allocated to the pilot sequence. To quantify this, the spectral efficiency of the FD relay system employing blind and pilot-based channel estimation methods are compared, indicating that at high SNR, the blind approach provides around 2-bps/Hz spectral efficiency gain relative to a typical pilot-based method. Finally, the computational complexity of the two channel estimation techniques are evaluated and compared. The blind approach has a clear computational advantage for larger packet sizes.

Buffer-aided relaying for the two-hop full-duplex relay channel with self-interference

In this paper, we investigate the two-hop full-duplex (FD) relay channel with self-interference and fading, which is comprised of a source, an FD relay, and a destination, where a direct source-destination link does not exist and the FD relay is impaired by self-interference. For this channel, we propose three buffer-aided relaying schemes with adaptive reception-transmission at the FD relay for the cases when the source and the relay both perform adaptive-power allocation, fixed-power allocation, and fixed-rate transmission, respectively. The proposed buffer-aided relaying schemes significantly improve the achievable rate and the throughput of the considered relay channel by enabling the FD relay to adaptively select to either receive, transmit, or simultaneously receive and transmit in a given time slot based on the qualities of the receiving, transmitting, and self-interference channels. Our numerical results show that significant performance gains are achieved using the proposed buffer-aided relaying schemes compared to conventional FD relaying, where the FD relay is forced to always simultaneously receive and transmit, and to buffer-aided half-duplex relaying, where the half-duplex relay cannot simultaneously receive and transmit.

Capacity of the Gaussian Two-Hop Full-Duplex Relay Channel With Residual Self-Interference

In this paper, we investigate the capacity of the Gaussian two-hop full-duplex (FD) relay channel with residual self-interference. This channel is comprised of a source, an FD relay, and a destination, where a direct source-destination link does not exist and the FD relay is impaired by residual self-interference. We adopt the worst case linear self-interference model with respect to the channel capacity, and model the residual self-interference as a Gaussian random variable whose variance depends on the amplitude of the transmit symbol of the relay. For this channel, we derive the capacity and propose an explicit capacity-achieving coding scheme. Thereby, we show that the optimal input distribution at the source is Gaussian and its variance depends on the amplitude of the transmit symbol of the relay. On the other hand, the optimal input distribution at the relay is discrete or Gaussian, where the latter case occurs only when the relay-destination link is the bottleneck link. The derived capacity converges to the capacity of the two-hop ideal FD relay channel without self-interference and to the capacity of the two-hop half-duplex (HD) relay channel in the limiting cases when the residual self-interference is zero and infinite, respectively. Our numerical results show that significant performance gains are achieved with the proposed capacity-achieving coding scheme compared with the achievable rates of conventional HD relaying and/or conventional FD relaying.

Improving efficiency of resource usage in two-hop full duplex relay systems based on resource sharing and interference cancellation

This letter presents a new full duplex relay (FDR) system that features more efficient use of time resource and antennas. The proposed FDR system is constructed based on time and antenna-sharing and elimination of underlying interference. The underlying interference caused by time- and antenna-sharing is eliminated using precoding. We propose a design for the precoder and decoder, and investigate the achievable rate of the proposed FDR system when the precoder and decoder are applied. Simulation results show improved achievable rate and BER performances with the proposed FDR system compared to half duplex and conventional full duplex relay systems.