In this paper, we study the joint allocation of three types of resources, namely, power, subcarriers and relay nodes, in multi-relay assisted dual-hop cooperative OFDM systems. All the relays adopt the amplify-and-forward protocol and assist the transmission from the source to destination simultaneously but on orthogonal subcarriers. The objective is to maximize the system transmission rate subject to individual power constraints on each node or a total network power constraint. We formulate such a problem as a subcarrier-pair based resource allocation that seeks the joint optimization of subcarrier pairing, subcarrier-pair-to-relay assignment, and power allocation. Using a dual approach, we solve this problem efficiently in an asymptotically optimal manner. Specifically, for the optimization problem with individual power constraints, the computational complexity is polynomial in the number of subcarriers and relay nodes, whereas the complexity of the problem with a total power constraint is polynomial in the number of subcarriers.We further propose two suboptimal algorithms for the former to trade off performance for complexity. Simulation studies are conducted to evaluate the average transmission rate and outage probability of the proposed algorithms. The impact of relay location is also discussed.

Subcarrier-pair based resource allocation for cooperative multi-relay OFDM systems

We study the joint allocation of three types of resources, namely, power, subcarriers and relay nodes, in cooperative two-hop multi-relay OFDM systems. Each relay adopts the amplify-and-forward (AF) protocol. The objective is to maximize the system transmission rate subject to individual power constraints on each node. We formulate such a problem as a subcarrier-pair based resource allocation that seeks the joint optimization of subcarrier pairing, subcarrier-pair-to-relay assignment, and power allocation. Using a dual decomposition method, we solve this problem efficiently in an asymptotically optimal manner. We further propose two suboptimal algorithms to trade off performance for complexity. Simulation results demonstrate that the proposed subcarrier-pair based resource allocation schemes significantly outperform the symbol based benchmark scheme. Moreover, it is shown that subcarrier pairing plays an important role in improving the system performance.

Subcarrier-Pair Based Resource Allocation for Cooperative AF Multi-Relay OFDM Systems

In this paper, a point-to-point orthogonal-frequency- division multiplexing (OFDM) system with a decode-and- forward (DF) relay is considered. The transmission consists of two hops. The source transmits in the first hop, and the relay transmits in the second hop. Each hop occupies one time slot. The relay is half-duplex, and capable of decoding the message on a particular subcarrier in one time slot, and re-encoding and forwarding it on a different subcarrier in the next time slot. Thus, each message is transmitted on a pair of subcarriers in two hops. It is assumed that the destination is capable of combining the signals from the source and the relay pertaining to the same message. The goal is to maximize the weighted sum rate of the system by jointly optimizing subcarrier pairing and power allocation on each subcarrier in each hop. The weighting of the rates is to take into account the fact that different subcarriers may carry signals for different services. Both total and individual power constraints for the source and the relay are investigated. For the situations where the relay does not transmit on some subcarriers because doing so does not improve the weighted sum rate, we further allow the source to transmit new messages on these idle subcarriers. To the best of our knowledge, such a joint optimization inclusive of the destination combining has not been discussed in the literature. The problem is first formulated as a mixed integer programming problem. It is then transformed to a convex optimization problem by continuous relaxation, and solved in the dual domain. Based on the optimization results, algorithms to achieve feasible solutions are also proposed. Simulation results show that the proposed algorithms almost achieve the optimal weighted sum rate and outperform the existing methods in various channel conditions.

Joint Subcarrier Pairing and Power Allocation for OFDM Transmission With Decode-and-Forward Relaying

The resource allocation problem is investigated for relay-based multi-user cooperative Orthogonal Frequency Division Multiple Access (OFDMA) uplink system, considering heterogeneous services. A quality of service (QoS) aware optimal relay selection, power allocation and subcarrier assignment scheme under a total power constraint is proposed. The relay selection, power allocation and subcarrier assignment problem is formulated as a joint optimization problem with the objective of maximizing the system throughput, which is solved by means of a two level dual decomposition and subgradient method. To further reduce the computational cost, two low-complexity suboptimal schemes are also proposed. The performance of the proposed schemes is demonstrated through computer simulations based on LTE-A network. Numerical results show that the proposed schemes support heterogeneous services while guaranteeing each user's QoS requirements with slight total system throughput degradation.

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Relay Selection and Resource Allocation for Multi-User Cooperative OFDMA Networks

In this paper, we consider cross-layer scheduling for the downlink of amplify-and-forward (AF) relay-assisted orthogonal frequency-division multiple-access (OFDMA) networks. The proposed cross-layer design takes into account the effects of imperfect channel-state information (CSI) at the transmitter (CSIT) in slow fading. The rate, power, and subcarrier allocation policies are optimized to maximize the system goodput (in bits per second per hertz successfully received by the users). The optimization problem is solved by using dual decomposition, resulting in a highly scalable distributed iterative resource-allocation algorithm. We also investigate the asymptotic performance of the proposed scheduler with respect to (w.r.t.) the numbers of users and relays. We find that the number of relays should grow faster than the number of users to fully exploit the multiuser diversity (MUD) gain. On the other hand, diversity from multiple relays can be exploited to enhance system performance when the MUD gain is saturated due to noise amplification at the AF relays. Furthermore, we introduce a feedback-reduction scheme to reduce the computational burden and the required amount of CSI feedback from the users to the relays. Simulation results confirm the derived analytical results for the growth of the system goodput and illustrate that the proposed distributed cross-layer scheduler only requires a small number of iterations to achieve practically the same performance as the optimal centralized scheduler, even if the information exchanged between the base station (BS) and the relays in each iteration is quantized, and the proposed CSI feedback reduction scheme is employed.

/pdf/cross-layer-scheduling-for-ofdma-amplify-and-forward-relay-3jf14q44tr.pdf

Cross-Layer Scheduling for OFDMA Amplify-and-Forward Relay Networks

We consider a two-hop relay link in which orthogonal frequency division multiplexing (OFDM) is used on both hops. Under a joint sum-power constraint, our aim is to allocate power over subcarriers on the two hops such that the instantaneous rate of the relay link is maximized. Ordered subcarrier pairing (OSP) has been proposed in the literature to further improve the relay link rate; however, the optimality of OSP has been proven only for equal power allocation and the proof of its optimality under optimal power allocation has not been available yet. In this letter, we will provide our proof which verifies that OSP is optimal for both amplify-and-forward (AF) and decode-and-forward (DF) relay links when optimal power allocation is applied.

Subcarrier pairing for amplify-and-forward and decode-and-forward OFDM relay links

We consider a two-hop relaying network in which orthogonal frequency division multiplexing (OFDM) is employed for the source-to-destination, the source-to-relay and the relay- to-destination links. Amplify-and-forward (AF) and decode-and- forward (DF) policies are both discussed with or without two-hop diversity, respectively, for the relaying network with a sum-power constraint. An unified approach is used for optimal power allocation in the four different relaying scenarios. First, equivalent channel gains are developed for any given subcarrier pair in each scenario, and then optimal power allocation can be obtained by applying the classic water-filling method. Moreover, we provide the proof to the optimality of sorted subcarrier pairing for AF and DF relaying without diversity, which, combined with optimal power allocation, can offer further performance gain.

Power Allocation and Subcarrier Pairing in OFDM-Based Relaying Networks

The invention discloses two starting methods of a hybrid automatic repeat request (HARQ) process, wherein one method comprises the following steps: a base station and a user terminal select a regulation to each new data according to a set identification ID, and the HARQ process corresponding to the ID is started synchronously in the current idle HARQ process. The technical scheme of the starting methods can realize that the HARQ process is started correctly, and the data is stored in an HS-SCCH less technology.

Starting methods of hybrid automatic repeat request process

Although the established capacity results for the classic three-node relay channel rely on the assumption of fullduplex relay nodes, it's practically difficult for radio transceivers to support simultaneous signal transmission and reception. Timedivision half-duplex relay strategies have thus been proposed to address this limitation. Amplify-and-forward (AF) and decode-and-forward (DF) are two well-known half-duplex relay strategies in the literature. Later, DF approach was extended by the so-called variable-rate two-phase relay strategy, in which the transmission rates for both phases are not necessarily the same. More recently, a novel half-duplex relay strategy based on the information theoretical concepts of broadcast channel (BC) and multiple access channel (MAC) models is proposed. In this approach, the source broadcasts distinct data flows to the destination and the relay respectively during the first phase, and in the second phase the relay forwards the received information whereas the source sends another data flow to the destination. In this paper, we will first develop optimal resource allocation, in terms of power and time, for these half- duplex relay strategies, and then compare their performance under various link conditions.

Optimal Resource Allocation and Performance Comparison of Half-Duplex Relay Strategies

We consider a multi-hop wireless sensor network in which a large number of sensor nodes are grouped into cooperative clusters. Multi-hop transmission is carried out between the source and the destination nodes by concatenating consecutive cluster-to-cluster hops. For each hop, both the transmit and the receive clusters can exploit node cooperation such that cooperative distributed multiple-input multiple-output (MIMO) channels can be formed. As proposed in [1], a time-division protocol is employed for transmissions within a cluster and between clusters, i.e., the intra-cluster slot is used for broadcasting within the transmit cluster, and the inter-cluster slot is used for transmissions between clusters. Distinguished from the scheme in [1] that space-time codes (STC) are utilized for inter-cluster transmissions, random beamforming is proposed in this paper, which is shown to outperform STC in term of energy efficiency provided that the number of nodes within receive cluster is adequately large. We demonstrate that even with moderate number of nodes within receive cluster, e.g., 10 nodes, random beamforming can offer higher energy efficiency for inter-cluster links, at 5% outage rate. The "random" nature incorporated in random beamforming scheme assigns the clusterhead node within receive cluster in an alternate manner, thus balancing energy consumption within receive cluster.

Jia Kong

Papers

Subcarrier pairing for amplify-and-forward and decode-and-forward OFDM relay links

Power Allocation and Subcarrier Pairing in OFDM-Based Relaying Networks

Starting methods of hybrid automatic repeat request process

Optimal Resource Allocation and Performance Comparison of Half-Duplex Relay Strategies

Space-Time Codes Versus Random Beamforming in Cooperative Multi-Hop Wireless Networks