Outage Performance Analysis of Underlay Cognitive Radio Networks with Decode‐and‐Forward Relaying

In this chapter, we evaluate the outage performance of decode‐and‐forward relaying in cognitive radio networks over Rayleigh fading channels, subject to the relay location for a secondary user. In particular, we obtain the optimal relay location in wireless communications systems for the cognitive radio networks, using differential evolution optimization algorithm. Then, we investigate the optimal transmission rate of the secondary user. We present the numerical results to validate the proposed theoretical analysis and to show the effects of the Rayleigh fading channel parameters for the whole system performance

Outage Capacity of Incremental Relaying at Low Signal-to-Noise Ratios

We present the \epsilon-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the \epsilon-outage capacity. It is shown that this location is independent of the outage probability and SNR but only depends on the channel conditions represented by a path-loss factor. We compare our results to the \epsilon-outage capacity of the cut-set bound and demonstrate that the ratio between the \epsilon-outage capacity of incremental relaying and the cut-set bound lies within 1/\sqrt{2} and 1. Furthermore, we derive lower bounds on the \epsilon-outage capacity for the case of K relays.Comment: 5 pages, 4 figures, to be presented at VTC Fall 2009 in Anchorage, Alask

Comparing the Outage Capacity of Transmit Diversity and Incremental Relaying

We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the e-outage capacity. It is shown that this location is independent of the outage probability and SNR but only depends on the channel conditions represented by a path-loss factor. We compare our results to the e-outage capacity of the cut-set bound and demonstrate that the ratio between the e-outage capacity of incremental relaying and the cut-set bound lies within 1/wurzel2 and 1. Furthermore, we derive lower bounds on the e-outage capacity for the case of K relays

Analysis of Coverage Region for MIMO Relay Network with Multiple Cooperative DF-Relays

We study and analyze coverage region in MIMO communication systems for a multiple-relay network with decode-and-forward (DF) strategy at the relays. Assuming that there is a line-of-sight (LOS) propagation environment for source-relay channels and channel state information is available at receivers (CSIR), we consider the objective of maximizing coverage region for a given transmission rate and show numerically the significant effect of propagation environment on capacity bounds, optimal relay location and coverage region. Also, we study the situation in which two adjacent relays cooperate in transmission signals to the destination and show analytically that the coverage region is extended compared to noncooperative scenario.Comment: Accepted for publication in International Symposium on Wireless Communication Systems (ISWCS) 201

Cooperative Symbol-Based Signaling for Networks with Multiple Relays

Wireless channels suffer from severe inherent impairments and hence reliable and high data rate wireless transmission is particularly challenging to achieve. Fortunately, using multiple antennae improves performance in wireless transmission by providing space diversity, spatial multiplexing, and power gains. However, in wireless ad-hoc networks multiple antennae may not be acceptable due to limitations in size, cost, and hardware complexity. As a result, cooperative relaying strategies have attracted considerable attention because of their abilities to take advantage of multi-antenna by using multiple single-antenna relays. This study is to explore cooperative signaling for different relay networks, such as multi-hop relay networks formed by multiple single-antenna relays and multi-stage relay networks formed by multiple relaying stages with each stage holding several single-antenna relays. The main contribution of this study is the development of a new relaying scheme for networks using symbol-level modulation, such as binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). We also analyze effects of this newly developed scheme when it is used with space-time coding in a multi-stage relay network. Simulation results demonstrate that the new scheme outperforms previously proposed schemes: amplify-and-forward (AF) scheme and decode-and-forward (DF) scheme

Optimal relay location and power allocation for low SNR broadcast relay channels

We consider the broadcast relay channel (BRC), where a single source transmits to multiple destinations with the help of a relay, in the limit of a large bandwidth. We address the problem of optimal relay positioning and power allocations at source and relay, to maximize the multicast rate from source to all destinations. To solve such a network planning problem, we develop a three-faceted approach based on an underlying information theoretic model, computational geometric aspects, and network optimization tools. Firstly, assuming superposition coding and frequency division between the source and the relay, the information theoretic framework yields a hypergraph model of the wideband BRC, which captures the dependency of achievable rate-tuples on the network topology. As the relay position varies, so does the set of hyperarcs constituting the hypergraph, rendering the combinatorial nature of optimization problem. We show that the convex hull C of all nodes in the 2-D plane can be divided into disjoint regions corresponding to distinct hyperarcs sets. These sets are obtained by superimposing all k-th order Voronoi tessellation of C. We propose an easy and efficient algorithm to compute all hyperarc sets, and prove they are polynomially bounded. Using the switched hypergraph approach, we model the original problem as a continuous yet non-convex network optimization program. Ultimately, availing on the techniques of geometric programming and $p$-norm surrogate approximation, we derive a good convex approximation. We provide a detailed characterization of the problem for collinearly located destinations, and then give a generalization for arbitrarily located destinations. Finally, we show strong gains for the optimal relay positioning compared to seemingly interesting positions.Comment: In Proceedings of INFOCOM 201