Dian-Wu Yue

Outage Performance of Cooperative Communication Systems Using Opportunistic Relaying and Selection Combining Receiver

We analyze the performance of cooperative communication systems with opportunistic decode-and-forward for relaying and selection combining receiver at the destination. We derive an exact closed-form expression for the outage of the system over dissimilar Nakagami fading channels. Also, we study its asymptotic outage performance, based on which the optimum power allocations for the source and the relays are determined. Finally, we verify the theoretical results by simulations.

Diversity order for amplify-and-forward dual-hop systems with fixed-gain relay under Nakagami fading channels

Dual-hop transmission systems employing fixed-gain amplify-and-forward (AF) relaying have been studied recently over Nakagami fading channels. These analyses, however, either have imposed certain constraints on the fading parameters or have not been totally accurate when evaluating the diversity order of the systems. In this letter, we will develop a methodology for evaluating the diversity order of such systems. The methodology can be easily extended to analyze fixed-gain AF relaying with multiple relays.

A General Parameterization Quantifying Performance in Energy Detection

This letter presents a new look at the problem of energy detection with and without diversity schemes. The impact of channel fading and/or diversity scheme on the probability of missing detection is quantified and then the definition, sensing gain, is proposed based on the analytical result. The sensing gain proposed in this letter determines the slope of the probability of missing detection versus average signal-to-noise ratio (SNR) curve, at high SNR, in a log-log scale. Our result shows that the sensing gain just has a relationship with the type of channel fading and/or diversity scheme and is totally irrelevant with the false alarm probability which is preset.

Orthogonal DF cooperative relay networks with multiple-SNR thresholds and multiple hard-decision detections

AbstractsThis paper investigates a wireless cooperative relay network with multiple relays communicating with the destination over orthogonal channels. Proposed is a cooperative transmission scheme that employs two signal-to-noise ratio (SNR) thresholds and multiple hard-decision detections (HDD) at the destination. One SNR threshold is used to select transmitting relays, and the other threshold is used at the destination for detection. Then the destination simply combines all the hard-decision results and makes the final binary decision based on majority voting. Focusing on the decode-and-forward (DF) relaying protocol, the average bit error probability is derived and diversity analysis is carried out. It is shown that the full diversity order can be achieved by setting appropriate thresholds even when the destination does not know the exact or average SNRs of the source-relay links. The performance analysis is further extended to multi-hop cooperation and/or with the presence of a direct link where multiple thresholds are needed. By combining the multiple-SNR threshold method with a selection of the best relaying link, a high spectral-efficiency cooperative transmission scheme is further presented. Simulation results verify the theoretical analysis and demonstrate performance advantage of our proposed schemes over the existing ones.

Unified scaling factor approach for turbo decoding algorithms

Turbo (iterative) decoding can be implemented with a large family of soft-input soft-output (SISO) algorithms, including suboptimal but practical algorithms such as the soft-output Viterbi algorithm (SOVA) and max-log-MAP algorithm. The performance with these practical algorithms can be improved with simple scaling factor methods. However, their theoretical analysis was mainly based on the relaxed assumption proposed by Papke et al. that the extrinsic information is Gaussian distributed. This study proposes a novel scaling factor approach for reducing both the overestimation of reliability values and the correlation between the intrinsic and extrinsic information. Explicit formulae for computing the scaling factors are derived based on mathematical statistics. A key difference compared to the scaling factor method of Papke et al. is that the proposed scaling factors can be computed off-line. The numerical results show that when implemented in the decoding algorithm of block component codes, the proposed scaling factor approach improves the performance of turbo decoding over additive white Gaussian noise and Rayleigh fading channels. It is superior than the method by Papke et al. in both performance and complexity.

Outage Performance and Cooperative Diversity Under Amplify and Forward Relaying in Cognitive Radio Networks

This paper investigates the outage and diversity performance in a cognitive radio (CR) network, in which data are transmitted through amplify-and-forward protocol. A fixed CR node is selected as relay to combat fading effect. The CR user transmits or relays data when the result of cooperative spectrum sensing indicates that primary user (PU) channel is free and the relay node stops performing the protocol as soon as the PU is detected to be active. A closed-form expression of outage probability for the CR network is calculated based on which diversity order is derived. The results show that the proposed scheme suffers a loss in diversity order. To compensate for this loss, a repetition-based scheme is proposed in a delay-insensitive system at the cost of the challenge in implementation. In this case, we evaluate the outage performance and the average transmit duration and then compare them with the ones in the delay-sensitive system. Asymptotic analysis is also presented to show the outage performance advantage of using a relay over the one without using it. The numerical results presented in the paper verify our analysis.

Performance Analysis of Orthogonal Space-Time Block codes over Nakagami-q (Hoyt) Fading channels

In this paper, we investigate the orthogonal space-time block codes communication systems with various M-ary modulation schemes over independent identically distributed (i.i.d) Nakagami-q (Hoyt) fading channels. We derive exact closed-form expressions of the system performances in terms of symbol error rate (SER). These expressions are composed of Lauricellas multivariate hypergeometric functions, which are easily evaluated numerically.

On the Diversity Order of a General Cooperative Relaying Communication System

Cooperative communication technology exploiting distributed spatial diversity is a promising solution for the future high data-rate cellular and ad-hoc wireless communications. To characterize the performance of a cooperative network, the cooperative diversity is commonly used. In this paper, we revisit the concept of diversity and look into the essence of cooperative diversity. We analyze the diversity performance of a general cooperative relaying system with multiple branches. Moreover, each branch consists of one or more hops. Unlike in other analyses, the assumptions that each node being only equipped with a single antenna and that all channel characteristics belonging to the same family are NOT required in our study. Using the decode-and-forward (DF) relaying protocol as an illustration, we provide analytical results on the diversity gain and the coding gain. The results also encompass most of the existing results as special cases. We further show the relationship between the diversity order of a branch and those of the constituent links; and the relationship between the diversity order of the network and those of the constituent branches. In particular, we show that for the uncoded DF protocol, the full diversity order can be achieved by using simple hard-decision detection at the destination. The requirement is to set appropriate signal-to-noise-ratio (SNR) thresholds for the multi-hop branches. To improve the bandwidth efficiency, we also randomly select one branch, among those branches satisfying the SNR-threshold requirement, for the transmission. We show that such a scheme accomplishes the full diversity order and produces a good error performance.

Performance of cooperative spectrum sensing over fading channels with low signal-to-noise ratio

Transmission error because of fading in the cognitive radio–fusion centre (CR–FC) links can severely degrade the performance of cooperative spectrum sensing. In this study, the upper and lower bounds of the overall false alarm probability and overall detection probability are derived as functions of the bit-error probabilities (BERs) of the CR–FC links. Based on these bounds, the constraints that the BERs of the CR–FC links should satisfy are addressed given the target overall false alarm probability or overall detection probability. Furthermore, channel coding schemes and cooperative schemes that provide reliable transmissions in the CR–FC links are studied. Particularly, inspired by the cluster-based cooperative spectrum sensing, a multi-user cooperative scheme is proposed. Finally, the relationship between the overall detection probability and the overall false alarm probability is investigated when the SNR of the primary user signal at each CR node is small.

Performance analysis of serial cooperative communications with decode-and-forward relaying and blind-EGC reception under nakagami fading channels

We analyze a serial cooperative transmission system with DF relaying over Nakagami fading channels. We consider a system in which the simple receivers will not estimate the amplitude of the received signals. Hence, signals are combined with equal gain before decoding. Moreover, the relays use a simple protocol when relaying the messages - they re-transmit the message if they can decode the received message correctly; otherwise, they do not transmit anything and remain idle. We will derive an exact expression for the asymptotic symbol error rate of the system and evaluate the diversity properties.