Yonglan Zhu

Non-Coherent Detection for Amplify-and-Forward Relay Systems in a Rayleigh Fading Environment

We consider about a multiple relay system operating under amplify-and-forward (AF) protocol and non-coherent modulation and demodulation. When the relays are under long-term power constraints, a near-maximum likelihood (ML) receiver and a diversity combining receiver are proposed. Both the near- ML receiver and the diversity combining receiver are expressed in simple closed forms and only rely on the second order statistics of the fading coefficients. Moreover, both of the proposed detectors outperform a non-cooperative system which only has a direct link with non-coherent ML detection in a Rayleigh fading environment. However, when the relay output is under a short-term power constraint, the ML detector derived here for the non-coherent AF relay performs the same as the non-cooperative system.

Optimal transmission strategies for rayleigh fading relay channels

In this paper, a decode-and-forward (DF) single relay model in a Rayleigh fading environment is considered. The outage probability and ergodic rate for this model are derived. With the objective of either minimizing the outage probability or maximizing the ergodic rate, optimal and approximately optimal transmission strategies are developed through selecting appropriate transmit signaling and/or spatial power allocation. The derived transmission strategies only require the knowledge of the second-order statistics of the channels at the transmitters, which can be readily acquired in practice. Simulation results demonstrate that the optimal transmit signaling and/or spatial power allocation can offer considerable performance improvements over the equal power allocation strategy.

Differential modulation for decode-and-forward multiple relay systems

In this paper, differential modulation and demodulation in a multiple relay system using either the decode-and-forward (DF) protocol or the selection relaying (SR) protocol, are investigated. For the DF protocol, the detectors at the destination take the average bit error probabilities (BEPs) of all the source-relay transmissions into account. For a DF single relay system, the exact BEP and its approximation at high signal-to-noise ratio (SNR) are obtained. The approximation of the BEP at high SNR shows explicitly the diversity order and the different effects of the source-relay link and the relay-destination link on the end-to-end error performance. For a DF multiple relay system, a Chernoff upper bound on the BEP and a high SNR approximation for the BEP are obtained. For the SR protocol, some computational complexity is shifted from the destination to all the relays. Each relay computes the instantaneous BEPs of the source-relay transmissions, and uses the instantaneous BEPs to decide whether to transmit or remain silent. The destination performs simple maximal ratio combining (MRC) reception whose error performance is analyzed at high SNR. It shows from an error probability perspective that the SR protocol offers a space diversity order equal to the number of all the potential cooperating nodes.

On the Mutual Information Distribution of MIMO Rician Fading Channels

In a fading environment, the statistical distribution of the mutual information of a multiple-input multiple-output (MIMO) system depends on the joint distribution of the eigenvalues of a Wishart matrix, and is quite complex in general. We obtain here simple expressions for the distributions of the determinant and the trace of a Wishart matrix. Based on the obtained distributions, we derive some simple and tight bounds on the complementary cumulative distribution function (CCDF) of the mutual information of a MIMO system in Rician fading environments. The bounds obtained on the CCDF of mutual information provide further insights into the channel mutual information, and show the effects of the system parameters on the mutual information distribution explicitly. In addition, results for the Rayleigh channels are obtained as a special case.

Outage Probability of Rician Fading Relay Channels

In this paper, we consider the decode-and-forward (DF) relay network system over Rician fading channels. We derive an analytical expression for the outage probability of the highest achievable information rate of the system, which can be evaluated by employing standard numerical techniques. We also obtain some simple but tight lower and upper bounds on the derived outage probability by using the geometrical representation of the distribution of the Hermitian quadratic form. Furthermore, we investigate the impact of the correlation coefficient between the transmitted signals from the source and relay. We disclose that when the Rice factors are relatively large, the optimal correlation coefficient that minimizes the outage probability is not necessarily zero, and instead it generally depends on the signal-to-noise ratios (SNRs), Rice factors, as well as the rate threshold

WLC11-1: A New Approach to the Capacity Distribution of MIMO Rayleigh Fading Channels

The distribution of the capacity of multiple input multiple output (MIMO) fading depends on the joint distribution of the eigenvalues of a Wishart matrix, and is quite complex in general. We obtain here simple expressions for the distributions of the determinant of a Wishart matrix. Based on the distributions of the determinant and the trace of the Wishart matrix, we derive some simple and tight bounds on the complementary cumulative distribution function (CCDF) of the capacity of MIMO Rayleigh fading channels. The new bounds on capacity CCDF provide further insights into the channel capacity, and show the effects of the system parameters on the capacity distribution explicitly. These bounds can be used to evaluate the mean capacity as well.

Outage-Optimal Transmission Strategies for Rayleigh Fading Relay Channels

We investigate optimal transmission strategies for Rayleigh fading relay channels, which minimize the outage probability of the achievable rate. We consider two cases depending upon whether spatial power allocation at the source and relay is available. We disclose that when no spatial power allocation is available, the optimal transmit signals are not necessarily independent, and their correlation depends on the signal-to-noise ratios of the links and the transmission rate. Moreover, we derive optimal spatial power allocation strategies in a small outage scenario. Our results show that it is not always beneficial to utilize a relay, and the optimal spatial power allocation depends on the total transmit power, the transmission rate, and the variances of the channels. Simulation results validate our theoretical findings.

A Decision-Feedback Channel Estimation Receiver for Independent Nonidentical Rayleigh Fading Channels

We derive a decision-feedback channel estimation receiver for independent and non-identically distributed (i.n.d.) Rayleigh fading channels. The receiver has memory to store signals received over the past several symbol intervals, and then use them to adaptively estimate instantaneous channel gains. The receiver adapts its decision rule based on estimates of the varying channel gains, and hence it is partially coherent. We also obtain the bit error rate (BER) of the channel estimation receiver for binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulations. The BER results are obtained in simple forms which explicitly show the effects of system parameters on the BER. In addition, our results are applicable to the cases where all the branches have arbitrary fade rates.

Differential Modulation and Demodulation for Decode-and-Forward Multiple Relay Systems

We consider differential modulation and demodulation in a decode-and-forward (DF) multiple relay system when channel state information (CSI) is unknown to any node. This paper first derives the maximum likelihood (ML) detector and proposes a low complexity pairwise-linear (PL) detector to well approximate the nonlinear ML detector. In both the ML and PL detectors, the receive signals at the destination from the source and all the relays are combined with different weights, since the transmission links in the relay system have different statistics. Then, the bit error rate (BER) for the PL detector is analyzed. For single relay systems, the exact BER is obtained as a simple function of signal-to-noise ratios (SNRs), the variances, and the fading rates of the transmission links. Based on the exact BER, a BER approximation at high SNR is derived, and explicitly shows the diversity order and the asymmetry between the source-relay link and the relay-destination link. For multiple relay systems, a Cherenoff upper bound on the BER is obtained. In addition, our results are applicable to the cases where all the transmission links have arbitrary fading rates.

On the Outage Performance of Single-Relay Transmissions over Quasi-Static Fading Channels

In this paper, we study the outage performance of single relay transmissions over quasi-static fading channels. We derive closed-form expressions of the outage probability of the achievable rate for two different power allocation policies. We show that a simple on-off power allocation policy, which relies on the quality of the link from the source to the relay, can improve the outage performance considerably for a relatively large transmission rate.