Hongyu Wang

An Energy-Efficient Relay Selection Strategy Based on Optimal Relay Location for AF Cooperative Transmission

In this paper, an energy-efficient optimal relay selection strategy which is jointly optimized with the energy-efficient optimal power allocation scheme for AF cooperative transmission is proposed. The relay selection criterion is the distance from the potential relay to the corresponding optimal relay locations where the minimum transmission power of the source, the relay or their total can be achieved. In order to determine the optimal relay locations, a universal algorithm with low computational complexity and easy implementation is also presented. Simulations are conducted to validate our theoretical analysis. The results show that with the relay selected by the proposed strategy, the cooperative transmission can achieve considerably high energy-efficiency.

How Network Coding Benefits Converge-Cast in Wireless Sensor Networks

Network coding is one of the most promising techniques to increase the reliability and reduce the energy consumption for wireless sensor networks (WSNs). However, most of the previous works mainly focus on the network coding for multi-cast or uni- cast in WSNs, in spite of the fact that the converge-cast is the most common communication style in WSNs. In this paper, we investigate, for the first time as far as we know, the feasibility of acquiring network coding benefits in converge-cast, and we present that with the ubiquitous convergent structures self-organized during converge-casting in the network, the reliability benefits can be obtained by applying linear network coding. We theoretically derive the network coding benefits obtained in a general convergent structure, and simulations are conducted to validate our theoretical analysis. The results reveal that the network coding can improve the network reliability considerably.

Cooperative Resource Allocation in Multicast Networks for Outage Probability Minimization

AbstractnIn this paper, we investigate the resource allocation issues in Orthogonal frequency division multiplexing access-based multicast systems that only allows average channel state information of users to be available at the resource manager. In this system, it is impossible to guarantee successful transmission of every data due to instant deep fading. Hence, in order to achieve efficient and reliable transmission, we exploit potential advantage provided by the cooperative diversity and propose a cooperative joint subcarrier and power allocation scheme that minimizes the probability of multicast transmission failure. This combinable allocation issue has high computational complexity, so we allocate subcarrier and power separately. We proposed cooperative proportional subcarrier allocation strategy to achieve tradeoff between throughput and fairness and iterative power (IP) allocation strategy to fully utilize the limited power. Simulation results show that system performance of the schemes with cooperation is significantly enhanced compared with that without cooperation and the schemes with IP remarkably outperform that without.n

A Conditioned Broadcasting Approach for On-Demand Ad Hoc Routing Protocols

Broadcasting is a common algorithm of on-demand ad hoc routing protocols for its simplicity and reliable accessibility. However, blind broadcasting often incurs collision, contention, and redundancy, which are called broadcast storms. As a countermeasure, we propose a conditioned broadcasting approach, by allowing each intermediate node decides whether to rebroadcast or not based on neighbourhood information when it first receives a route request (RREQ) message. The proposed scheme also takes account of node mobility speed as well as retry-times in route request process when making forwarding decisions. We demonstrate the effectiveness of the proposed scheme by applying it to Ad Hoc on-demand distance vector routing (AODV). Simulation results show that the proposed scheme outperforms original AODV in terms of several metrics, including the ratio of re-broadcasting transmitter to all mobile nodes in route discovery phase, average packet delivery ratio, and normalize routing overhead.

Network coding in convergecast of wireless sensor networks: Friend or foe?

Convergecast is probably the most common communication style in wireless sensor networks (WSNs). And network coding (NC) is a promising concept to improve throughput or reliability of convergecast. Most of the existing works have mainly focused on exploiting these benefits without considering its potential adverse effect. In this paper, we argue that network coding may not always benefit convergecast. This viewpoint is discussed within four scenarios: The network-coding-aided (NC-aided) and the none-network-coding (none-NC) convergecast schemes with or without automatic repeat request (ARQ) mechanisms. The most concerned performance metrics, including packet collection rate, energy consumption and end-to-end delay, are investigated. Theoretical analyses and simulation results show that the way network coding operates, i.e., conscious overhearing and the prerequisite of successfully decoding, could naturally diminish its advantages in convergecast. And NC-aided convergecast schemes may even be inferior to none-NC ones when the wireless link delivery ratio is high enough. The conclusion drawn in this paper casts a new light on how to effectively apply network coding to practical WSNs.

Decomposed LT Codes for Cooperative Communications

In order to reduce computation complexity and latency in cooperative communication system based on fountain code, a decomposed LT codes (DLT) based cooperative transmission scheme was proposed. The scheme comprises of two layers of random encoding but only a single layer of decoding. A general decomposition technique for the decomposed LT codes construction is developed. The transmission latency for the proposed scheme was analyzed. Simulation results show that the total time consumed under the proposed scheme can be significantly reduced compared to direct transmission and conventional cooperative transmission based on LT codes in the medium to high packet erasure rate regimes. Moreover, With the increase of packet erasure rate, the advantage of the proposed scheme is more evident.

An energy-efficient relay selection strategy based on optimal relay location for AF cooperative transmission

In this paper, an energy-efficient optimal relay selection strategy which is jointly optimized with the energy-efficient optimal power allocation solution for AF cooperative transmission is proposed. The relay selection criterion is the distance to the optimal relay locations where the minimum transmission power of the source, the relay or their total can be achieved. To determine those most energy-efficient relay locations, a universal algorithm with low computational complexity and easy implementation is also presented in this paper. The simulations are conducted to validate our theoretical analysis. The results show that with the relay selected by the proposed strategy, the cooperative transmission can achieve considerably high energy-efficiency.

Incentive Pricing Mechanism for Hybrid Access in Femtocell Networks

In this letter, we propose a novel incentive pricing mechanism, where wireless service provider (WSP) offers additional benefits (called bonus) to motivate the adoption of hybrid access in femtocells. The problem is formulated as a two-stage Stackelberg game to reach a win–win situation, where WSP determines the pricing policy as the leader and FOs respond as the followers. The optimal proportion of shared resources for each FO and the optimal pricing factor for WSP are decided independently. Furthermore, a Quality of Service (QoS) based admission control scheme is also designed to admit or reject macro users access. Numerical simulations have been conducted and the results show that the utilities of both WSP and FOs are significantly improved due to the exploitation of incentive pricing mechanism.

Study on Protocol Design and Performance Analysis for Cognitive Relay Networks

This paper investigates the cooperative transmission in the downlink of a large-coverage secondary system which opportunistically accesses the licensed spectrum of some small-coverage primary systems scattered inside. We propose a cognitive-relay-based selection cooperation protocol under which cognitive relays help forward information in an opportunistic fashion by acquiring spectrum holes. We also present two cognitive relay selection strategies and analyze the performance in terms of the outage probability and the system throughput. Compared to the optimal instantaneous channel state information (ICSI) based strategy, the partial CSI (PCSI) based one can provide a close-to-optimal performance with no additional channel estimation. Simulation results indicate that the scenario where relays have to opportunistically access spectrum holes incurs a cooperative diversity order penalty, and the performance advantage of our proposed protocol depends on conditions of spectrum acquisition and spectrum quality of cognitive relays.

Performance Analysis of Multi-User Multi-Round Linear Network Coded Cooperation

This letter presents a novel linear network coded cooperation (LNCC) scheme, called multi-user multi-round LNCC (M2-LNCC), for many-to-one communications in wireless networks. The scheme involves multiple users, each of which has an independent message destined to a common base station (BS). The peculiarity of the M2-LNCC is that, not only the native messages, but also the codewords generated via linear network coding (LNC) in the previous time slots participate in the subsequent LNCC operations. Thus, the LNCC operation is performed for multiple rounds and the benefits of LNCC are further exploited. The closed-form expression for the tight approximation of the outage probability is derived in this letter, and the analyses on the asymptotic outage probability and diversity order are also presented. The analysis results show that the M2-LNCC scheme with M(M ≥ 2) users and N + 1(N ≥ 1) time slots is able to achieve the diversity order MN + 1. Monte Carlo simulations are conducted to verify the correctness of our theoretical analyses.