Xiaowen Tian

Iterative Hybrid Precoder and Combiner Design for mmWave Multiuser MIMO Systems

This letter investigates analog/digital hybrid precoder and combiner design for millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems. We propose a novel iterative algorithm for the joint hybrid precoder and combiner design by exploiting the duality of the uplink and downlink MU-MIMO channels. For the initialization stage, the proposed algorithm selects the analog precoder-combiner pair based on the orthogonal matching pursuit (OMP) algorithm to enhance the channel gain, while mitigating the multiple access interference, and obtains the digital combiner via minimum mean square error criterion. Then, the proposed algorithm enhances the performance gradually at each iteration via joint design of the uplink and downlink precoders/combiners. Simulation results demonstrate the significant performance advantages of the proposed precoder and combiner design compared with existing hybrid beamforming algorithms.

Fast Detection of Orthogonal Space-Time Block Codes With Unknown Channel

This letter investigates the problem of blind detection of orthogonal space-time block codes (OSTBCs) over a quasi-static flat multiple-input multiple-output Rayleigh fading channel. We first introduce a core iterative least-squares (ILS) algorithm to blindly detect OSTBC signals without the knowledge of channel state information (CSI) at the receiver. This ILS algorithm has low computational complexity but may converge to local optimum, which offers unreliable detection result. Then, in order to improve the detection performance, we propose an enhanced ILS (E-ILS) approach, which is based on statistical analysis of repeated independent ILS procedures on received data. Extensive simulation studies prove the efficiency of the proposed E-ILS algorithm with blind detection performance approaching the optimal maximum-likelihood detector with known CSI.

Transmit filter and artificial noise aided physical layer security for OFDM systems

This paper considers the problem of physical layer security of a wireless orthogonal frequency division multiplexing (OFDM) communication system. We first develop a transmit filter-aided secure OFDM system scheme which can disturb eavesdroppers receptions by destroying the orthogonality of OFDM signals at the eavesdropper, while the quality of legitimate transmission is maintained. Then, in an effort to further improve the security performance, we also propose an artificial noise (AN)-aided secure OFDM system associated with the transmit filter-aided approach. AN is generated in the null space of the legitimate channel by making use of residual power after power allocation for subcarriers. Therefore, AN can only disrupt eavesdroppers receptions but not affect legitimate receiver. Simulation results are presented to illustrate the efficiency of the proposed transmit filter and AN-aided physical layer security designs in the OFDM wiretap system.

Random-training-aided pilot spoofing detection

The pilot spoofing attack is considered as an active eavesdropping activity launched by an adversary during the reverse channel training phase. By transmitting the identical pilot signal as that of the legitimate user, the pilot spoofing attack can degrade legitimate transmission and, more severely, facilitate eavesdropping. This paper considers the problem of detecting pilot spoofing attack for a typical multi-input single-output (MISO) wiretap system. We slightly modify the conventional training mechanism and divide the procedure into pilot phase and random phase. By examining the difference of estimated legitimate channels during these two phases, a novel random-training-aided (RTA) detection algorithm is proposed to identify the existence of the pilot spoofing attack. Extensive simulation results illustrate that our proposed RTA scheme can achieve accurate pilot spoofing detection.

Iterative hybrid precoder and combiner design for mmWave MIMO-OFDM systems

AbstractThis paper investigates the problem of hybrid precoder and combiner design for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems operating in millimeter-wave (mmWave) bands. We propose a novel iterative scheme to design the codebook-based analog precoder and combiner in forward and reverse channels. During each iteration, we apply compressive sensing technology to efficiently estimate the equivalent MIMO-OFDM mmWave channel. Then, based on the effective channel, we designed the analog precoder and combiner to alleviate the interference between different data streams as well as maximize the spectral efficiency. The digital precoder and combiner are finally obtained based on the effective baseband channel to further enhance the spectral efficiency. Simulation results demonstrate that the proposed iterative hybrid precoder and combiner algorithm has significant performance advantages.

Joint hybrid precoder and combiner design for multi-stream transmission in mmWave MIMO systems

Millimeter wave (mmWave) communications have been considered as a key technology for future 5G wireless networks since it can provide orders-of-magnitude wider bandwidth than current cellular bands. To overcome the severe propagation loss of the mmWave channel, an economic and energy-efficient analogue/digital hybrid precoding and combining transceiver architecture is widely used in mmWave massive multiple-input multiple-output (MIMO) systems. The digital precoding/combining layer offers more freedom than pure analogue one and enables multi-stream transmission. In this study, the authors consider the problem of codebook-based joint hybrid precoder and combiner design for multi-stream transmission in mmWave MIMO systems. The authors propose to jointly select an analogue precoder and combiner pair for each data stream successively, which can maximise the channel gain as well as suppress the interference between different data streams. Then, the digital precoder and combiner are computed based on the obtained effective baseband channel to further mitigate the interference and maximise the sum-rate. Both fully-connected and partially-connected hybrid beamforming structures are investigated. Simulation results demonstrate that the proposed algorithms exhibit prominent advantages in combating interference between different data streams and offer satisfactory performance improvements compared with the existing codebook-based hybrid beamforming schemes.

QoS-Based Binary Signature Design for Secure CDMA Systems

Physical layer security, aiming at preventing the confidential information from eavesdroppers, has drawn significant attentions in recent years. In this paper, we address the problem of securing downlink single-user and multiuser transmissions in code division multiple-access systems. Particularly, we propose a novel binary signature design method to minimize the reception of the confidential messages at the eavesdropper. The popular signal-to-interference-plus-noise ratio (SINR) metric is adopted as a pragmatic security performance measurement. Specifically, for securing the single-user transmission, we aim to design a binary signature to minimize the eavesdroppers SINR while maintain the legitimate users SINR at a desired level. However, the optimal exhaustive searching method has complexity growing exponentially with the signature length. Thus, we propose two suboptimal low-complexity semi-definite relaxation (SDR)-based and Rayleigh-quotient-based binary signature design algorithms, which have near optimal performance with much lower computational complexity. Furthermore, we extend the findings in the single-user case to multiuser scenario. Particularly, we propose to design a set of quasi-orthogonal signatures based on eavesdropping channel and select the conditionally optimal binary signature for each user iteratively until convergence. Simulation studies confirm our analytical performance predictions and demonstrate the benefits of the proposed secure signature design algorithms.