Wenfeng Ma

Hardware Impairments Aware Transceiver for Full-Duplex Massive MIMO Relaying

This paper studies the massive MIMO full-duplex relaying (MM-FDR), where multiple source-destination pairs communicate simultaneously with the help of a common full-duplex relay equipped with very large antenna arrays. Different from the traditional MM-FDR protocol, a general model where sources/destinations are allowed to equip with multiple antennas is considered. In contrast to the conventional MIMO system, massive MIMO must be built with low-cost components which are prone to hardware impairments. In this paper, the effect of hardware impairments is taken into consideration, and is modeled using transmit-receive distortion noises. We propose a low complexity hardware impairments aware transceiver scheme (named as HIA scheme) to mitigate the distortion noises by exploiting the statistical knowledge of channels and antenna arrays at sources and destinations. A joint degree of freedom and power optimization algorithm is presented to further optimize the spectral efficiency of HIA based MM-FDR. The results show that the HIA scheme can mitigate the “ceiling effect” appears in traditional MM-FDR protocol, if the numbers of antennas at sources and destinations can scale with that at the relay.

On the design of relay selection strategy for two-way amplify-and-forward mobile relaying

Opportunistic relay selection (RS) is an efficient method to obtain diversity gain in analogue network coding (ANC) protocol with multiple relays. However, in networks with mobile relays, the channel state information (CSI) used in the RS procedure becomes outdated because of the time-varying nature of fading channels, which severely deteriorates the system performance. In this study, the authors study the RS strategy which aims to optimise the outage performance of the ANC protocol with multiple mobile relays. RS schemes for two different cases are designed, that is, (i) the scheme with only the outdated CSI during the RS procedure, and (ii) the scheme with both the outdated CSI and the statistical knowledge of channels during the RS procedure. The closed-form expressions of the outage probabilities as well as the asymptotic expressions are analytically derived for the proposed schemes, and moreover, the achievable diversities are analysed based on the asymptotic expressions. Simulation results are presented to evaluate the performances while validate the theoretical analyses for the proposed schemes.

On the Equivalence of Two Optimal Power-Allocation Schemes for A-TWRC

Power allocation (PA) is an efficient approach to enhance the system performance of an analog network coding (ANC)-based two-way relay channel (A-TWRC). In previous works, optimal PAs, in the sense of minimizing the outage probability and maximizing the achievable sum rate for A-TWRCs, were studied, respectively. In this paper, by virtue of the Lagrange method, we theoretically prove that optimal PA problems in the sense of minimizing the outage probability and maximizing the achievable sum rate are equivalent to each other. Meanwhile, a unified optimal PA scheme for A-TWRCs is proposed. We show that some previous optimal PA schemes are special cases of the proposed unified scheme under certain conditions. Simulation results show that the proposed unified PA scheme obtains the optimal outage probability and achievable sum-rate performance, whereas previous works approach the proposed unified PA scheme on either outage or achievable sum-rate performance.

Full-Duplex Massive MIMO AF Relaying With Semiblind Gain Control

This paper proposes an amplify-and-forward-based massive multiple-input-multiple-output full-duplex relaying (AF-MM-FDR) protocol, where multiple source-destination pairs communicate simultaneously with a common full-duplex relay. A zero-forcing (ZF)-based relay transceiver design with semiblind gain control is presented, considering the problem of relay oscillation. The asymptotic expression of end-to-end signal-to-interference-plus-noise power (SINR) is derived under the general power scaling scheme. The scaling behaviors of echo interference (EI) and effective channel estimation error are determined. Scaling results show that the deployment of very large antenna arrays at the relay has the potential to eliminate the effect of EI due to the full-duplex operation, if the power scaling scheme is selected properly. Moreover, based on the asymptotic analysis, a low-complexity power control scheme is proposed to optimize the spectral efficiency of AF-MM-FDR. Simulation results show that the proposed power control scheme improves the spectral-energy efficiency tradeoff of AF-MM-FDR significantly.

NTC-HARQ: Network–Turbo-Coding Based HARQ Protocol for Wireless Broadcasting System

Wireless broadcasting systems employ multiple retransmissions to guarantee the correct reception of each packet. The traditional hybrid automatic retransmission request (HARQ) protocol retransmits one packet per slot. Hence, a large amount of retransmissions is required to correctly receive all the packets, which leads to low spectrum efficiency. In this paper, we propose a Network-coding-and-distributed-Turbo-Coding-based type-III HARQ (NTC-HARQ) protocol, including an xoring Network Coding Combined (XNCC) retransmission strategy at the access node (AN) and a joint network-turbo decoding (JNTD) strategy at the user equipment (UE). Specifically, to reduce the overall number of retransmissions, lost packets of different UEs are network coding (NC) combined at the AN by utilizing the XNCC strategy. The soft information of the lost packet at each UE can be recovered from the received network-coded retransmission packet by using the proposed xoring soft network decoder. The recovered soft information of the UEs lost packet is combined with the local undecodable soft information of the same packet to form a distributed turbo code. A Chase-combining-based distributed turbo decoder is proposed to perform turbo decoding, which introduces coding gain and improves packet-error-rate (PER) performance. Theoretical analyses and simulation results show that the average-number-of-transmission performance of the proposed NTC-HARQ protocol outperforms that of the XNCC-based type-I HARQ protocol, the traditional NC-based HARQ protocol, and the JNTD-based protocol.

Multi-Pair Two-Way Massive MIMO AF Full-Duplex Relaying With Imperfect CSI Over Ricean Fading Channels

This paper investigates a multi-pair two-way massive MIMO amplify-and-forward full-duplex relay (FDR) system over Ricean fading channels, where multiple pairs of full-duplex users exchange information within pair through a full-duplex relay with a very large number of antennas (M for transmission and M for reception). First, the zero-forcing reception/zero-forcing transmission and maximum-ratio combining/maximum-ratio transmission processing matrices with imperfect channel state information at the relay are presented. Then, the corresponding asymptotic expressions (in M) of the end-to-end signal-to-interference-plus-noise ratio are derived. Finally, the asymptotic spectral efficiency (SE) and energy efficiency (EE) at the general power scaling schemes when the number of the relay antennas tends to infinity is analyzed. Theoretical analyses and simulation results show that, when M → ∞, the effects of channel estimation error, the self-loop of each user as well as the relay, inter-user interferences, the noise at users and the relay can be eliminated, respectively, if the power scaling scheme is properly selected. Besides, the considered multi-pair two-way FDR outperforms the multi-pair two-way half-duplex relaying on SE and EE performances when M is large. Moreover, a low complexity power control scheme is proposed to optimize the SE and we analyze the impact of the number of user pairs on the SE.

On Max-SINR Receivers for HMT Systems Over a Doubly Dispersive Channel

In this paper, a novel receiver for hexagonal multicarrier transmission (HMT) systems based on a maximizing signal-to-interference-plus-noise ratio (Max-SINR) criterion is proposed. Theoretical analyses show that there is a timing offset between the prototype pulses of the proposed Max-SINR receiver and a traditional projection receiver. Meanwhile, the timing offset should be matched to the channel scattering factor of a doubly dispersive (DD) channel. The closed-form timing offset expressions of the prototype pulses for the Max-SINR HMT receiver over the DD channel with different channel scattering functions are derived. Simulation results show that the proposed Max-SINR receiver outperforms the traditional projection scheme and obtains an approximation to the theoretical upper bound SINR performance. Consistent with the SINR performance improvement, the bit error rate (BER) performance of the HMT system has been also further improved by using the proposed Max-SINR receiver. Meanwhile, the SINR performance of the proposed Max-SINR receiver is robust to the channel delay spread estimation errors.

Time and Frequency Synchronization for Multicarrier Transmission on Hexagonal Time-Frequency Lattice

In this paper, a novel synchronization acquisition approach, including preamble structure, time and frequency synchronization algorithms, is proposed for hexagonal multicarrier transmission (HMCT) system. Specifically, a novel signal acquisition scheme based on time-frequency subspace projection (TFSP) and its simplified form are proposed for reliable signal acquisition. Time and frequency synchronization is divided into three steps: 1) the coarse time offset (TO) and coarse fractional carrier frequency offset (CFO) estimation; 2) fine TO and integer CFO estimation; and 3) fine fractional CFO estimation. The closed-form Cramér-Rao lower bound of the proposed CFO estimation scheme is given. Theoretical analyses and simulation results show that the proposed preamble structure, time and frequency synchronization algorithms for HMCT system can obtain robust performance over doubly dispersive (DD) channel, and the simulation results show excellent agreement with theoretical analyses.

Carrier frequency offset estimation approach for multicarrier transmission on hexagonal time-frequency lattice

In this paper, a novel carrier frequency offset estimation approach, including preamble structure, carrier frequency offset estimation algorithm, is proposed for hexagonal multi-carrier transmission (HMCT) system. The closed-form Cramer-Rao lower bound of the proposed carrier frequency offset estimation scheme is given. Theoretical analyses and simulation results show that the proposed preamble structure and carrier frequency offset estimation algorithm for HMCT system obtains an approximation to the Cramer-Rao lower bound mean square error (MSE) performance over the doubly dispersive (DD) propagation channel.

Practical opportunistic full-/half-duplex relaying

The opportunistic full-/half-duplex relaying schemes are studied where the effects of imperfect channel state information (CSI) and transmit imperfection are taken into account. The opportunistic schemes with different levels of channel knowledge, that is, the scheme with CSI at the transmitter (CSIT), the scheme with CSI at the receiver (CSIR) and the scheme with only statistical CSI, are proposed. Power adaption (PA) schemes with different levels of channel knowledge are presented and combined with the opportunistic schemes to further improve the system performance. The opportunistic schemes are evaluated in the term of average capacity. The authors results show that the opportunistic scheme with CSIR achieves comparative performance to the scheme with CSIT when the PA is not used. Moreover, it is shown that the choice of full-duplex relaying becomes more attractive when the quality of estimation for desired channels degrades. However, the converse is true as the quality of estimation for echo interference channel degrading or the power of transmit noise increasing.