Pingyi Fan

Reliable relay assisted wireless multicast using network coding

We first consider a topology consisting of one source, two destinations and one relay. For such a topology, it is shown that a network coding based cooperative (NCBC) multicast scheme can achieve a diversity order of two. In this paper, we discuss and analyze NCBC in a systematic way as well as compare its performance with two other multicast protocols. The throughput, delay and queue length for each protocol are evaluated. In addition, we present an optimal scheme to maximize throughput subject to delay and queue length constraints. Numerical results will demonstrate that network coding can bring significant gains in terms of throughput.

Wireless Information and Energy Transfer for Two-Hop Non-Regenerative MIMO-OFDM Relay Networks

This paper investigates the simultaneous wireless information and energy transfer for the non-regenerative multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) relaying system. By considering two practical receiver architectures, we present two protocols, time switching-based relaying (TSR) and power splitting-based relaying (PSR). To explore the system performance limits, we formulate two optimization problems to maximize the end-to-end achievable information rate with the full channel state information (CSI) assumption. Since both problems are non-convex and have no known solution method, we firstly derive some explicit results by theoretical analysis and then design effective algorithms for them. Numerical results show that the performances of both protocols are greatly affected by the relay position. Specifically, PSR and TSR show very different behaviors to the variation of relay position. The achievable information rate of PSR monotonically decreases when the relay moves from the source towards the destination, but for TSR, the performance is relatively worse when the relay is placed in the middle of the source and the destination. This is the first time such a phenomenon has been observed. In addition, it is also shown that PSR always outperforms TSR in such a MIMO-OFDM relaying system. Moreover, the effects of the number of antennas and the number of subcarriers are also discussed.

A utility-based network selection scheme for multiple services in heterogeneous networks

It is a trend to integrate different wireless access networks into heterogeneous networks in next generation wireless networks. Network selection and QoS support for multiservices are two of the most significant issues in heterogeneous wireless networks (HWN). In this paper, we propose a utility-based network selection scheme for HWN, where the price mechanism acting as a lever system guides users to select the most efficient network and controls the allocation of network resources. Simulation results show that the proposed scheme can achieve more total utilities than traditional schemes for the whole networks. The proposed scheme can also balance traffic load between different networks and effectively avoid network congestion while still guarantees QoS for real-time users.

Spatial reuse in IEEE 802.16 based wireless mesh networks

The IEEE Standard 802.16 supports for creating wireless mesh networks. The primary advantage of mesh networks is an improvement of capacity by concurrent transmission in the wireless environment. Therefore, the degree of spatial reuse is very crucial to realize the full potential of such wireless mesh networks. In this paper, we investigate the spatial reuse in IEEE 802.16 mesh networks. We propose a scheduling mechanism and a routing algorithm taking into account the interference in wireless environment to achieve maximum spatial reuse hence to increase the overall network throughput. The simulation results show that the proposed schemes achieve significant improvement and are more effective.

Network Coding for Two-Way Relaying Networks Over Rayleigh Fading Channels

Wireless network coding is a useful technology that can increase the total throughput of wireless networks. There are, however, few works focusing on wireless network coding over fading channels, which is an important characteristic of many real wireless channels and may result in performance degradation. To investigate the fading channels impact on network coding, based on the constant transmission power scheme and the channel inversion-transmission scheme, we analyze network throughput over Rayleigh fading channels. It is shown that, when the difference between average channel gains over two broadcasting channels is very large, the throughput of network coding greatly decreases, and the advantage of network coding almost disappears. To address this issue and to maximize the throughput of network coding over fading channels, we formulate the fading compensation for network coding as optimization problems and present the optimal transmission data rate and transmission power level of the relay node. Furthermore, to consider the realization problem of network coding over fading channels, including unbalanced traffic load and asynchronization of packet arrivals, we present two opportunistic optimal network coding (OONC) schemes. Performance evaluation has shown that the proposed opportunistic schemes perform well in various scenarios.

Outage Probability of Energy Harvesting Relay-Aided Cooperative Networks Over Rayleigh Fading Channel

Energy harvesting technique is a potential way for relay node energy supply in cooperative networks with respect to deployment flexibility and maintenance charge reduction. However, unlike traditional power source, it is intuitive that the fluctuation of harvested energy flow can degrade the benefit resulted from relay-aided cooperative transmission. To this end, this paper focuses on the performance analysis of an energy harvesting relay-aided cooperative network under slow fading channel from a perspective of outage behavior and attempts deriving the closed-form expression of outage probability of the proposed cooperative protocol. Compared with simple direct transmission protocol, it is proved that a multiplicative gain for improving system performance in terms of minimizing outage probability can be obtained by energy harvesting relay-aided cooperative transmission. In particular, if there are multiple available relay nodes around the environment or the energy-exhausted probability of relay node is small, it is very profitable to employ relay-aided cooperative transmission protocol.

On the Joint V2I and V2V Scheduling for Cooperative VANETs With Network Coding

In the paper, we investigate the information spread problem in a joint vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communication system. A scene is considered where more information centers (or base stations) are allocated along the road so that the information centers are able to broadcast timely messages to vehicles within the range of the broadcast signal of each base station, which we shall refer to as broadcast zone . The seamless information spread is used to guarantee that messages are correctly received by each vehicle, regardless of whether it pulls into broadcast zones or not. We first derive the maximum throughput of the V2I downlink system for both additive white Gaussian noise (AWGN) channels and Rayleigh fading channels with Doppler effects. A measurement-based algorithm to estimate the throughput is also proposed. We then discuss the maximum achievable amount of information that can be relayed forward along a vehicular stream. A network coding technique will then be proposed to cancel the interference caused by relay signals to vehicles that are receiving messages from the corresponding information center. These theoretical results will give more insight into the vehicular communication system design.

High-Speed Railway Wireless Communications: Efficiency Versus Fairness

High-speed railways (HSRs) have been widely deployed all over the world in recent years. Different from traditional cellular communications, the high mobility of HSR communication makes it essential to implement power allocation (PA) along time. In the HSR case, the transmission rate greatly depends on the distance between the base station (BS) and the train. As a result, the train receives a time-varying data rate service when passing by a BS. It is clear that the most efficient PA will spend all the power when the train is nearest the BS, which will cause great unfairness along time. On the other hand, channel inversion allocation achieves the best fairness in terms of constant rate transmission. However, its power efficiency is much lower. Therefore, power efficiency and fairness along time are two incompatible objects. For the HSR cellular system considered in this paper, a tradeoff between the two is achieved by proposing a temporal proportional-fair PA scheme. In addition, a near-optimal closed-form solution and one algorithm finding ε-optimal allocation are presented.

AsOR: an energy efficient multi-hop opportunistic routing protocol for wireless sensor networks over Rayleigh fading channels

In this paper, we describe an efficient and energy conservative unicast routing technique for multi-hop wireless sensor networks over Rayleigh fading channels, which we shall refer to as assistant opportunistic routing (AsOR) protocol. In contrast to previous works, this protocol is presented from a systematic energy conservation perspective. During the source-destination transmission, the AsOR protocol forwards the data stream through a sequence of nodes, which are classified as three different node sets, namely, the frame node, the assistant node and the unselected node. The frame nodes are indispensable to decode-and-forward while the assistant nodes provide protections for unsuccessful opportunistic transmissions. Based on the AsOR protocol, each predetermined route can be divided into several disjoint segments, and we establish a mathematical model to characterize the energy consumptions for each node in one segment. Furthermore, we provide a method for selecting the optimal value N*, the number of nodes in one transmission segment, which can lead to the minimum average energy consumption. Numerical results will confirm that the proposed protocol is energy conservative compared with other two traditional routing protocols both in slow and fast Raleigh fading channels and that the method for searching the optimal value N* is efficient. Finally, robustness analysis for the theoretical results are presented.

Interference cancellation for OFDM systems in presence of overlapped narrow band transmission system

Narrowband interference (NBI) is one of the most important problems in an OFDM system, which not only degrades the signal performance on the overlapped subcarriers, but also affects the signal performance on the nearby subchannels due to the spectral leakage effect of DFT demodulation at the receiver. In this paper, we consider the NBI problem caused by narrow band digital communication systems, and propose a novel NBI cancellation method. We consider the NBI reconstruction problem including NBI central frequency and its bandwidth estimation. Simulation results show that this method can achieve about 6 dB signal to interference plus noise ratio (SINR) gain if the interference bandwidth is about twice of that OFDM bins and the system SINR is about 0 dB. As the bandwidth of NBI decreases, more SINR gain will be obtained. Meanwhile, we also consider the system implementation problem, it has shown that its implementation complexity is not high based on the current digital signal processing techniques. If zoom FFT is employed in our system, the calculation complexity can he reduced considerably.