Relay-aided Cellular Networks Research Articles

Joint User Association and Power Allocation for Hybrid Half-Duplex/Full-Duplex Relaying in Cellular Networks

For hybrid half-duplex/full-duplex relaying in a relay-aided cellular network, a joint user association, relay mode selection, and power allocation scheme is proposed to maximize the energy efficiency under the minimum spectral efficiency requirement and transmission power constraints. This combinatorial optimization problem is a mixed-integer nonconvex one, which is difficult to be solved in its original form. To circumvent this issue, the problem is first transformed into an equivalent one whose objective function is in a parametric subtractive form. Then, the equivalent problem is reformulated as a convex one by relaxing index variables, converting the nonconvexity by the successive convex approximation, and constructing auxiliary variables. In this way, the equivalent nonconvex problem is approximated by a convex one in each iteration, and the dual decomposition technique is employed to solve the convex one. An iterative algorithm is further developed to reach the solution to the primal problem. Simulation results show that the performance of the iterative algorithm can be very close to the optimal solution obtained by the exclusive searching within only a few number of iterations. Moreover, the proposed scheme outperforms existing ones, which only adhere to either the user association or the relay mode selection but not both.

Cooperative Interference Neutralization in Multi-Hop Wireless Networks

Interference neutralization (IN) is regarded as a promising interference management techniques for multi-hop wireless networks. Yet most existing results of IN are limited to two-hop networks such as the relay-aided cellular network. Little progress has been made so far in the exploration of IN in generic multi-hop (more than two hops) networks. This paper aims to bridge this gap by developing an optimization framework for IN in a generic multi-hop network with the objective of maximizing the end-to-end throughput of multiple coexisting communication sessions. We first derive a mathematical model for IN in a special one-hop network to characterize the capability of IN, and then generalize this model to a multi-hop network. Based on the IN model, we develop a cross-layer optimization framework for a multi-hop network with the objective of fully translating the benefits of IN to the end-to-end throughput of the multi-hop sessions. To evaluate the performance of IN in multi-hop networks, we compare its performance against the case where IN is not employed. Simulation results show that the use of IN can significantly (more than 50%) increase the session throughput and, more notably, the throughput gain of IN increases with the node density and traffic intensity in the network.

On the Feasibility of Full-Duplex Relaying in Multiple-Antenna Cellular Networks

In this paper, we perform a system-level feasibility analysis of full-duplex (FD) relay-aided cellular networks that are equipped with multiple antennas at the base stations (BSs) and the relay nodes (RNs). The aim is to understand whether FD relaying is capable of enhancing the rate of cellular networks. With the aid of tools from stochastic geometry, we develop a tractable approach for computing the percentile rate, which allows us to gain insights on the impact of FD relaying for both the cell-edge and the cell-median mobile terminals subject to network interference. Contrary to previous works that do not consider the network interference, the framework reveals that even in the absence of self-interference at the FD RNs, a network with half-duplex (HD) RNs can outperform its FD counterpart for a moderate number of antennas at the BSs and RNs. On the other hand, the FD-based network can substantially outperform both the HD-based one and the one without RNs for a sufficiently large number of antennas at the BSs and RNs and substantially small self-interference power effect at the RNs. Finally, the aforementioned analytical insights are validated by means of Monte Carlo simulations.

A hybrid half-duplex/full-duplex transmission scheme in relay-aided cellular networks

In two-hop relay-aided cellular networks, both half-duplex (HD) and full-duplex (FD) transmission have been extensively studied. FD transmission can achieve twice throughput of HD transmission, but suffers from strong self-interference (SI), which may not be perfectly cancelled. In this paper, a hybrid HD/FD transmission scheme in a relay-aided cellular network is proposed, which not only utilizes the throughput advantage of FD but also weakens the negative effect of SI. The key idea is that a relay station (RS) switches between the HD and the FD modes based on the received signal-to-interference-plus-noise ratio (SINR). If the information rate of the base station (BS)-to-RS link is lower than a preset threshold, the RSs adopt the FD mode to guarantee the throughput; otherwise, the RSs adopt the HD mode to reduce the negative effect of SI. As FD transmission consumes more power than HD transmission, we try to maximize the system energy efficiency under the system spectral efficiency constraint and the transmit power constraints. It is difficult to solve this optimization problem directly, so the alternate optimization method is adopted to solve it, i.e., optimizing the transmit power of the BS and the transmit power of RSs in turn. Simulation results show that under perfect SI cancellation, the hybrid scheme can achieve higher energy efficiency than the HD mode by taking the throughput advantage of FD; while under poor SI cancellation, the hybrid scheme can greatly weaken the negative effect of SI and achieve higher energy efficiency than the FD mode.

Stochastic Geometry Modeling and System-Level Analysis & Optimization of Relay-Aided Downlink Cellular Networks

In this paper, a tractable mathematical framework for the analysis and optimization of two-hop relay-aided cellular networks is introduced. The proposed approach leverages stochastic geometry for system-level analysis, by modeling the locations of base stations, relay nodes and mobile terminals as points of homogeneous Poisson point processes. A flexible cell association and relay-aided transmission protocol based on the best biased average received power are considered. Computationally tractable integrals and closed-form expressions for coverage and rate are provided, and the performance trends of relay-aided cellular networks are identified. It is shown that coverage and rate highly depend on the path-loss exponents of one- and two-hop links. In the interference-limited regime, in particular, it is shown that, if the system is not adequately designed, the presence of relay nodes may provide negligible performance gains. By capitalizing on the proposed mathematical framework, a system-level and interference-aware optimization criterion of the bias coefficients is proposed. Numerical results confirm the effectiveness of the proposed system-level optimization to enhance the coverage probability in the interference-limited regime. The presence of relays, on the other hand, is shown to have a limited impact on average/coverage rate under the same assumptions.

A Distributed Algorithm for Bandwidth Resource Sharing in Relay-Aided Wireless Cellular Networks: From the Perspective of Economic Equilibrium Theory

Relay selection, power control and bandwidth allocation for relay nodes are the key issues in exploiting the advantage of cooperative relaying in wireless networks. In this paper, an effective bandwidth resource sharing scheme is proposed for relay-aided cellular networks. Considering a user equipment (UE) can act as a data source as well as a potential relay for other UEs, and a selfish UE is willing to share its resource for relaying purpose only if the cost can be recovered by the payment of the source UEs, we can formulate this cooperative resource sharing problem as an economic market model. Then, the demand-and-supply theory is employed to derive the equilibrium point (EP, i.e., the optimal price charged by the relay UE and the optimal resource purchased by the source) of the market. To assist the UEs to achieve the EP in decentralized network environments, an effective distributed algorithm, based on the excess demand theory, is developed to approach the EP in an iterative manner. Simulation results show that the proposed algorithm is stability as it can converge to the EP after several ($$<$$<15) times iterative computations.

Spectral-Energy Efficiency Tradeoff in Relay-Aided Cellular Networks

A relay cooperation scheme is proposed for the downlink of multicell multiple-input-multiple-output cellular networks. The relay stations (RSs) will cooperatively transmit the signal replicas of all the user equipments obtained during the broadcast phase. We consider different RS decoding strategies during the broadcast phase and joint relay transmission with different degrees of channel state information (CSI) sharing during the relay phase. We also propose the partial semi-orthogonal user selection (PSUS) method designed specifically for relay cooperation. The spectral and energy efficiencies are then evaluated for the relay cooperation scheme. Its cooperative costs for different cooperation levels are also investigated. Simulation results indicate that joint RS decoding outperforms independent RS decoding but a cooperative link with a bit rate of an order of magnitude greater than that achievable by the relay network is required. Compared to the competing user selection methods that require global CSI, the proposed PSUS method utilized for relay phase joint transmission operates at less than half of the cooperative cost while introduces only a slight degradation in system performance.

Network coding-aware cooperative relaying for downlink cellular relay networks

In this paper, we first overview some traditional relaying technologies, and then present a Network Coding-Aware Cooperative Relaying (NC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> R) scheme to improve the performance of downlink transmission for relay-aided cellular networks. Moreover, systematic performance analysis and extensive simulations are performed for the proposed NC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> R and traditional relaying and non-relaying schemes. The results show that NC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> R outperforms conventional relaying and non-relaying schemes in terms of blocking probability and spectral efficiency, especially for cell-edge users. Additionally, the location selections for relays with NC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> R are also discussed. These results will provide some insights for incorporating network coding into next-generation broadband cellular relay mobile systems.