Jinhong Yuan

Analysis of transmit antenna selection/maximal-ratio combining in Rayleigh fading channels

In this paper, we investigate a multiple-input-multiple-output (MIMO) scheme combining transmit antenna selection and receiver maximal-ratio combining (the TAS/MRC scheme). In this scheme, a single transmit antenna, which maximizes the total received signal power at the receiver, is selected for uncoded transmission. The closed-form outage probability of the system with transmit antenna selection is presented. The bit error rate (BER) of the TAS/MRC scheme is derived for binary phase-shift keying (BPSK) in flat Rayleigh fading channels. The BER analysis demonstrates that the TAS/MRC scheme can achieve a full diversity order at high signal-to-noise ratios (SNRs), as if all the transmit antennas were used. The average SNR gain of the TAS/MRC is quantified and compared with those of uncoded receiver MRC and space-time block codes (STBCs). The analytical results are verified by simulation. It is shown that the TAS/MRC scheme outperforms some more complex space-time codes of the same spectral efficiency. The cost of the improved performance is a low-rate feedback channel. We also show that channel estimation errors based on pilot symbols have no impact on the diversity order over quasi-static fading channels.

Safeguarding 5G wireless communication networks using physical layer security

The fifth generation (5G) network will serve as a key enabler in meeting the continuously increasing demands for future wireless applications, including an ultra-high data rate, an ultrawide radio coverage, an ultra-large number of devices, and an ultra-low latency. This article examines security, a pivotal issue in the 5G network where wireless transmissions are inherently vulnerable to security breaches. Specifically, we focus on physical layer security, which safeguards data confidentiality by exploiting the intrinsic randomness of the communications medium and reaping the benefits offered by the disruptive technologies to 5G. Among various technologies, the three most promising ones are discussed: heterogenous networks, massive multiple-input multiple-output, and millimeter wave. On the basis of the key principles of each technology, we identify the rich opportunities and the outstanding challenges that security designers must tackle. Such an identification is expected to decisively advance the understanding of future physical layer security.

Space-time TCM with improved performance on fast fading channels

New space-time trellis-coded modulation (STTC) which best satisfies the design criteria proposed by Tarokh, et al. (see IEEE Trans. Inform. Theory, vol.44, p.746-65, 1998) over fast fading channels are presented. STTC with a feedforward structure have been constructed by a systematic and exhaustive search. Simulation results and parameter comparison show that these codes offer a better performance on fast fading channels than other known codes while maintaining a comparable performance on slow fading channels.

Analysis of transmit antenna selection/ maximal-ratio combining in Rayleigh fading channels

In this paper, we investigate a scheme for combining transmit-antenna selection (TAS) and maximal-ratio combining (MRC) (TAS/MRC). In this scheme a single antenna is chosen for transmission among all available transmit antennas and MRC is performed at the receiver side. The bit error rate (BER) of the TAS/MRC scheme is derived for binary phase-shift-keying (BPSK) in flat Rayleigh fading channels. The analysis shows that the TAS/MRC scheme can achieve the full diversity as if all the transmit antennas were used. The simulation shows that this scheme significantly outperforms the space-time block codes (STBCs) of the same diversity order with the same spectral efficiency.

Performance and design of space-time coding in fading channels

The pairwise-error probability upper bounds of space-time codes (STCs) in independent Rician fading channels are derived. Based on the performance analysis, novel code design criteria for slow and fast Rayleigh fading channels are developed. It is found that, in fading channels, the STC design criteria depend on the value of the possible diversity gain of the system. In slow fading channels, when the diversity gain is smaller than four, the code error performance is dominated by the minimum rank and the minimum determinant of the codeword distance matrix. However, when the diversity gain is larger than, or equal to, four, the performance is dominated by the minimum squared Euclidean distance. Based on the proposed design criteria, new codes are designed and evaluated by simulation.

Combined turbo codes and interleaver design

The impact of the distance spectrum and interleaver structure on the bit error probability of turbo codes is considered. A new turbo code design method for Gaussian channels is presented. The proposed method combines a search for good component codes with interleaver design. The optimal distance spectrum is used as the design criterion to construct good turbo component codes at low signal-to-noise ratios (SNRs). In addition, an interleaver design method is proposed. This design improves the code performance at high SNR. Search for good component codes at low SNR is combined with a code matched interleaver design. This results in new turbo codes with a superior error performance relative to the best known codes at both low and high SNR. The performance is verified by both analysis and simulation.

Secrecy Sum-Rates for Multi-User MIMO Regularized Channel Inversion Precoding

In this paper, we propose a linear precoder for the downlink of a multi-user MIMO system with multiple users that potentially act as eavesdroppers. The proposed precoder is based on regularized channel inversion (RCI) with a regularization parameter α and power allocation vector chosen in such a way that the achievable secrecy sum-rate is maximized. We consider the worst-case scenario for the multi-user MIMO system, where the transmitter assumes users cooperate to eavesdrop on other users. We derive the achievable secrecy sum-rate and obtain the closed-form expression for the optimal regularization parameter αLS of the precoder using large-system analysis. We show that the RCI precoder with αLS outperforms several other linear precoding schemes, and it achieves a secrecy sum-rate that has same scaling factor as the sum-rate achieved by the optimum RCI precoder without secrecy requirements. We propose a power allocation algorithm to maximize the secrecy sum-rate for fixed α. We then extend our algorithm to maximize the secrecy sum-rate by jointly optimizing α and the power allocation vector. The jointly optimized precoder outperforms RCI with αLS and equal power allocation by up to 20 percent at practical values of the signal-to-noise ratio and for 4 users and 4 transmit antennas.

Space-time trellis codes for 4-PSK with three and four transmit antennas in quasi-static flat fading channels

It has been established that the appropriate design parameters for space-time trellis code (STTC) in quasi-static flat Rayleigh fading channels are the rank and determinant criteria or the Euclidean distance criterion, depending on the value of the overall diversity gain. We propose two groups of new STTCs with more than two transmit antennas based on these two design criteria, respectively. These new STTCs are shown to achieve large performance improvements over the ones with two transmit antennas.

Outage Probability of Multiuser Relay Networks in Nakagami-

We evaluate the performance of downlink multiuser relay networks (MRNs) equipped with a single amplify-and-forward (AaF) relay. A thorough and exact analysis is conducted to analyze the outage probability of MRNs under dissimilar Nakagami-m fading conditions. More specifically, we derive new closed-form expressions for the outage probability and the probability density function (pdf) of the highest end-to-end signal-to-noise ratio (SNR) associated with the strongest destination with the single user and Rayleigh fading as special cases. In particular, we provide new results for channel-state information (CSI)-based-gain relaying and fixed-gain relaying. We then demonstrate that the achievable diversity order is equal to either the first-hop fading parameter or the product of the second-hop fading parameter and the number of destinations. Furthermore, we derive compact closed-form expressions for the moments of the highest end-to-end SNR, from which other moment-based measures such as the average SNR and the amount of fading are deduced. Our results highlight the performance improvements offered by opportunistic scheduling and reveal the impact of the relay location with unbalanced hops on the overall performance. Various numerical examples illustrate the proposed analysis.

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In this paper, we study physical layer security for the downlink of cellular networks, where the confidential messages transmitted to each mobile user can be eavesdropped by both; 1) the other users in the same cell and 2) the users in the other cells. The locations of base stations and mobile users are modeled as two independent two-dimensional Poisson point processes. Using the proposed model, we analyze the secrecy rates achievable by regularized channel inversion (RCI) precoding by performing a large-system analysis that combines tools from stochastic geometry and random matrix theory. We obtain approximations for the probability of secrecy outage and the mean secrecy rate, and characterize regimes where RCI precoding achieves a non-zero secrecy rate. We find that unlike isolated cells, if one treats interference as noise, the secrecy rate in a cellular network does not grow monotonically with the transmit power, and the network tends to be in secrecy outage if the transmit power grows unbounded. Furthermore, we show that there is an optimal value for the base station deployment density that maximizes the secrecy rate, and this value is a decreasing function of the transmit power.