Half-duplex Cooperative System Research Articles

Power allocation and relay selection for AF two-path successive relaying networks

Two-path or successive relaying, which aims to establish two relay links transmitting different information symbols in adjacent time slots, has recently emerged as an attractive wireless communication protocol to improve the spectral efficiency in half-duplex cooperative systems. In this paper, we investigate power allocation and relay selection techniques for amplify-and-forward two-path successive relaying networks. Our approach is based on the maximization of the received SNR subject to a total power budget consumed by the source and the relay assisting this specific transmission. Two scenarios including with and without direct link are considered here. We show that the main problem has a closed-form solution and only requires a few amounts of feedback bits to be broadcasted. Numerical results reveal that the proposed approaches are more insensitive to the inter-relay interference and robust to channel estimation errors; meanwhile, they perform better than the existing schemes. Copyright © 2013 John Wiley & Sons, Ltd.

Weighted-Sum-Rate Maximization in Certain Half-Duplex Cooperative Systems

In half-duplex cooperative systems the problem of finding the jointly optimal power and channel resource allocation that maximizes the weighted sum rate (WSR) can be difficult to solve. Algorithms to solve that problem are provided herein for two classes of orthogonal half-duplex systems. For a class of systems in which the set of rates that can be achieved without time sharing is convex, the WSR problem is decomposed into a direct search in which a target rate problem is solved at each step. The target rate problem involves maximizing one of the rates subject to target values for the others, and can often be efficiently solved. For a subclass of those systems, the notion of perspective is used to transform the WSR problem into an efficiently-solvable convex optimization problem. Numerical examples involving a multiple access relay system and a pairwise cooperation scheme show that joint optimization can result in significantly larger weighted sum rates than optimization over the powers alone with a fixed channel resource allocation.

Ergodic Channel Capacities for the Amplify-and-Forward Half-Duplex Cooperative Systems

In this paper, the ergodic channel capacities are established for the amplify-and-forward (AF) half-duplex cooperative systems, which consist of a source node, a destination, and multiple-relay nodes. The relay nodes assist the transmission from the source node to the destination. Since the channel matrices for the cooperative systems involve product of Gaussian random variables, which are no longer Gaussian, the approach in obtaining the ergodic channel capacity for conventional multiple-input-multiple-output (MIMO) Gaussian channels (Telatar, 1999) is not applicable. By using a novel approach, we have arrived at the following conclusions about the ergodic channel capacities for the AF cooperative systems. For the single antenna AF relay systems in which all nodes are equipped with one antenna, the optimal covariance matrix of the input signals to achieve the ergodic channel capacity is diagonal, and the diagonal elements are obtained by solving optimization problems of multidimensional integrals. These diagonal entries are not all equal even if all the channel gains in the cooperative systems are independent and identically distributed (i.i.d.) Gaussian with unit variance. Therefore, a white input signal for the AF cooperative system may not achieve the ergodic channel capacity of the system. This is in direct contrast to the case of conventional multiple-input-single-output (MISO) systems having i.i.d. Gaussian channel gains of unit variance, in which case, the ergodic capacity is achieved if the input covariance matrix is a scaled identity matrix. For the MIMO relay system in which the nodes have multiple antennas, the input covariance matrix to achieve the ergodic capacity is block diagonal and each block diagonalizes the autocorrelation of channel matrix from the source to the destination. This is different from the case of conventional MIMO systems, where the input covariance matrix to achieve the ergodic channel capacity diagonalizes the channel autocorrelation matrix of the MIMO system (Tulina, Lozano, and Verdu, 2006). If the channel gains in conventional MIMO systems are correlated Gaussian random variables, the input covariance matrix is a full matrix, not block diagonal; and if the channel gains are i.i.d. Gaussians, the optimal input covariance matrix is a scaled identity. The observations obtained in this paper reveal useful insights of how the AF cooperative systems ldquomimicrdquo the conventional MISO and MIMO systems from the ergodic channel capacity perspective.

The Amplify-and-Forward Half-Duplex Cooperative System: Pairwise Error Probability and Precoder Design

In this paper, an exact asymptotic pairwise error probability (PEP) is derived for a half-duplex cooperative system employing an amplify-and-forward (AF) protocol. When compared with the PEP of a traditional multiple-input multiple-output (MIMO) system, the for the cooperative system is no longer just a simple exponential function of the signal-to-noise ratio (SNR), rather, it involves the logarithm of the SNR. The term diversity gain function is used to designate this characteristic of the PEP. The coding gain, on the other hand, is found similar to that for the MIMO system and is proportional to the determinant of the autocorrelation of the error matrix. Based on our analysis and observations, we propose a design of unitary precoder for the cooperative system to achieve the full diversity gain function. For the case of a 4-QAM signal being transmitted, we further optimize the coding gain and arrive at a closed-form optimum precoder. Simulations indicate that our proposed precoder designs greatly improve the performance of the cooperative system