In this paper, we investigate the performance of a relay selection scheme in a buffer-aided multi-relay network with coded transmissions. We consider: (1) two different coding schemes, i.e., Turbo codes and distributed Turbo codes (DTC) and (2) quasi-static Rayleigh fading channels, where all the links are independent but asymmetric. For each of the aforementioned schemes, we analyze the performance of the system in terms of the average throughput and average delay. In addition, simple and explicit approximations of the asymptotic throughput for infinite buffer size and the high signal-to-noise ratio (SNR) regime are obtained. Our analysis of the asymptotic throughput provides the maximum achievable diversity gain of the system, and the accuracy of the derived analytical framework is assessed when compared to the Monte-Carlo simulations.

In this paper, a cross-layer-based sensor node selection scheme in a cooperative network with equally spatially correlated channels is proposed. The equally correlated model can be used as a worst-case benchmark or as a rough approximation by assuming equal correlation coefficients for all channels. By considering the physical and link layer characteristics, one or multiple sensor nodes are selected to maximize the link layer throughput. Based on the channel characteristics, the best performance is achieved by using one cooperative sensor node in poor links and multiple relays/sensors in high quality links. The performance of the proposed scheme is compared with the capacity-based scheme and considerable improvement in performance is achieved in both correlated and uncorrelated channels. The proposed scheme is examined for both decode-and-forward (DF) and amplify-and-forward (AF) relaying, and also for relay selection and subcarrier allocation in an orthogonal-frequency-division multiplexing (OFDM)-based systems. In all cases, the cross-layer technique is shown to offer significant improvement relative to physical-layer optimization techniques.

In this paper, an optimal algorithm is proposed for the joint power allocation and relay assignment problem in OFDM relay networks. The network model consists of single-source single-destination with N half-duplex decode-and-forward (DF) relays. The source node uses orthogonal frequency division multiplexing (OFDM) to transmit information to relays where each serves one subcarrier. Our objective is to find the best subcarrier-relay assignment and power allocation, that maximizes the minimum received signal-to-noise ratio (SNR). This non-convex optimization problem could be solved by exhaustive search with complexity order of O(N!). Suboptimal methods, that solve the relay assignment problem and power allocation separately, have less time complexity in the expense of performance degradation. We propose a simple algorithm to jointly solve the subcarrier-relay assignment and power allocation problem. It is shown that the proposed algorithm finds the optimal solution with complexity order of O(N4).