Conference Paper

WLC41-1: An Optimized User Selection Method for Cooperative Diversity Systems

Dept. of Electr. & Comput. Eng., Aristotle Univ. of Thessaloniki, Thessaloniki
DOI: 10.1109/GLOCOM.2006.853 Conference: Proceedings of the Global Telecommunications Conference, 2006. GLOBECOM '06, San Francisco, CA, USA, 27 November - 1 December 2006
Source: IEEE Xplore


Multi-user cooperative diversity is a recent techni- que promising great improvement of the performance of wireless communication systems operating in fading environments. Based on combinatorial optimization theory and specifically on the so-called knapsack problem, this paper presents a method of optimizing the selection among the potential cooperating users, when amplify-and-forward relays are used. In particular, two optimization problems are studied: the error probability mini- mization subject to total energy consumption constraints, and the dual one, the energy consumption minimization under error performance constraints. Depending on the frequency of repea- ting this selection, the above problems are categorized into short- term and long-term node selection. Numerical examples verify the expected knapsack scheme's advantage of adapting the number of cooperating users, depending on the desired performance- consumption tradeoff. Moreover, long-term node selection seems to lead to similar error or consumption performance compared to the short-term one, despite its simplicity. I. INTRODUCTION In the last few years, a new concept that is being acti- vely studied in multihop-augmented networks is multi-user cooperative diversity, where several terminals form a kind of coalition to assist each other with the transmission of their messages. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version to the intended destination node. The destination node combines the signal received from the relays, taking into account the source's original signal (1)- (4).

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    • "For the multirelay selection strategies, most existing work assumes orthogonal transmission in the relay-to-destination stage, making the bandwidth efficiency an important factor for the selection of relays [20], [21]. In [20], Michalopoulos et al. modeled the relay selection with total energy consumption constraints as a knapsack problem by mapping the instantaneous SNR performance and energy consumption metric of a node to the profit and weight coefficients , respectively. A buyer/seller game approach is adopted in [21], which jointly considers the multirelay selection and power allocation problem. "
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    ABSTRACT: For clustered wireless networks, the conventional dual-hop cooperation technique is inefficient since relays with imbalanced channels to the source and the destination may become the bottleneck of the overall transmission. In this paper, a novel cooperative framework called the three-stage relaying (TSR) scheme is proposed to address this problem. In TSR, relays are divided into two clusters/groups, and a virtual multiple-input–multiple-output (MIMO) antenna array is formed by introducing the transmission between the two relay groups. This “relay-to-relay” communication enables transmissions over shorter distances, which naturally breaks the bottleneck emerging in the dual-hop cooperation scheme. An optimization problem is formulated to deal with the relay selection for these two groups, aiming at maximizing the received signal-to-noise ratio (SNR) at the destination, subject to the number-of-relay constraint. This problem turns out to be nontrivial due to the coupling of the relays between two groups. We tackle this challenging problem by decomposing it into two subproblems: One deals with the selection of transmitting relays, and the other deals with the selection of receiving relays. We then propose two heuristic algorithms that achieve the tradeoff between the optimality of the solution and the computational complexity. Through extensive numerical simulations, we show the superiority of TSR over the dual-hop cooperation schemes in both the clustered and centered wireless networks in terms of symbol error rate and throughput.
    Full-text · Article · Jan 2014 · IEEE Transactions on Vehicular Technology
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    • "Later works have generalized the single relay selection concept to multiple relay selection in an effort to find optimal relay selection methods under various assumptions [8]–[16]. Most of these works consider AF relaying (e.g., [8]–[12]). The DF two-hop relaying technique is considered in [14]– [16]. "
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    ABSTRACT: In this paper, the utilization of mobile devices (MDs) as decode-and-forward relays in a device-to-device assisted virtual MIMO (VMIMO) system is studied. Single antenna MDs are randomly distributed on a 2D plane according to a Poisson point process, and only a subset of them are sources leaving other idle MDs available to assist them (relays). Our goal is to develop an efficient algorithm to cluster each source with a subset of available relays to form a VMIMO system under a limited feedback assumption. We first show that the NP- hard optimization problem of precoding in our scenario can be approximately solved by semidefinite relaxation. We investigate a special case with a single source and analytically derive an upper bound on the average spectral efficiency of the VMIMO system. Then, we propose an optimal greedy algorithm that achieves this bound. We further exploit these results to obtain a polynomial time clustering algorithm for the general case with multiple sources. Finally, numerical simulations are performed to compare the performance of our algorithm with that of an exhaustive clustering algorithm, and it shown that these numerical results corroborate the efficiency of our algorithm.
    Preview · Article · Dec 2013 · IEEE Transactions on Wireless Communications
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    • "Although SRS schemes achieve higher spectral efficiencies than APR, their error rates and outages are higher. The complexity of the optimal MRS schemes proposed in [11] and [13] exponentially increases with the available number of relays. Although the GSCbased MRS scheme [14] achieves considerable performance gains, it requires channel estimation of all the relayed paths. "
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    ABSTRACT: An output-threshold multiple-relay-selection (OT-MRS) scheme for dual-hop multibranch cooperative wireless networks is proposed. In this scheme, the first Lc (nonordered) relays are sequentially selected out of L relays such that the SNR of the maximal ratio combined Lc relayed paths and the direct path exceeds a preset threshold. Analytical results for the performance bounds are derived. The numerical results verify the analyses and show that OT-MRS outperforms optimal single-relay selection and generalized-selection-combining-based multiple relay-selection for low to moderately high SNRs. The proposed scheme provides more flexibility in utilizing bandwidth and spatial diversity in cooperative wireless networks.
    Full-text · Article · Aug 2010 · IEEE Transactions on Vehicular Technology
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