Wei Jibo

Throughput analysis of IEEE 802.11 DCF over correlated fading channel in MANET

The throughput of 802.11 DCF over correlated fading channel in MANET are investigated in this paper. By obtaining the analytical representation of saturation throughput of 802.11 DCF over correlated fading channel, we get the impact of frame length and the mobile speed on throughput. Study shows the throughput decreases with the increase of mobile velocity and there exists an optimal frame length to maximize throughput under a certain velocity. Moreover, the optimal length is independent of the number of nodes.

Traffic-aware channelization medium access control for wireless ad hoc networks

Existing multi-channel Medium Access Control (MAC) protocols have been demonstrated to significantly increase wireless network performance compared to single channel MAC protocols. Traditionally, the channelization structure in IEEE 802.11 based wireless networks is pre-configured, and the entire available spectrum is divided into subchannels and equal channel widths. In contrast, this paper presents a Traffic-Aware Channelization MAC (TAC-MAC) protocol for wireless ad hoc networks, where each node is equipped with a single half duplex transceiver. TAC-MAC works in a distributed, fine-grained manner, which dynamically divides variable-width subchannels and allocates subchannel width based on the Orthogonal Frequency Division Multiplexing (OFDM) technique according to the traffic demands of nodes. Simulations show that the TAC-MAC can significantly improve network throughput and reduce packet delay compared with both fixed-width multi-channel MAC and single channel 802.11 protocols, which illustrates a new paradigm for high-efficient multi-channel MAC design in wireless ad hoc networks.

Outage probability of composite microscopic and macroscopic diversity over correlated shadowed fading channels

The outage probability of a composite microscopic and macroscopic diversity system is evaluated over correlated shadowed fading channels. The correlations on both a microlevel and macrolevel are taken into account for the evaluations. The expression of the desired outage probability is explicitly presented, and two evaluation approaches, i.e. a compact Gaussian-Hermite quadrature method and an effective iterative algorithm, are proposed. The accuracy and efficiency of the proposed approaches are analysed, and a guideline is provided for their application. By employing the proposed evaluation approaches, results and demonstrations are presented, which display the implied effects of the corresponding parameters on the system outage performance, and reveal the potential to facilitate the design and analysis of such composite diversity systems.

Optimizing the performance of OFDM-based cooperative networks by relay selection, power allocation and relay localization

We investigate the outage probability for amplify-and-forward (AF) and decode-and-forward (DF) relaying in OFDM-based cooperative networks. To minimize the outage probability, the relay which has the maximum received SNR is selected as the cooperative relay. Based on the relay selection, the problems of optimal power allocation and placing relays in the optimal position are discussed. And the expressions of optimal power allocation and optimal position are finally achieved. The analysis and simulation results show that through the proposed relay selection scheme, M orders of diversity is achieved, where M is the number of potential relays. It also shows that optimal power allocation and optimal position to placing relays achieve much better performance.

The expected complexity of sphere decoding algorithm in spatial correlated MIMO channels

The sphere decoding (SD) algorithm is widely considered to be an efficient approach to obtain maximum likelihood (ML) performance in MIMO detection. At present, almost all of the research about the SD algorithm is based on the assumption of independent and identically distributed channel coefficients. However, the channel coefficients are often correlated in practice, which cause the complexity of the SD algorithm to vary. In this paper, we give a theoretical analysis of the complexity of Fincke and Pohsts(FP) SD algorithm in spatial correlated MIMO channels; the exact expression of the expected complexity is derived. We present simulation results obtained from this expression to show the effect of spatial correlation on the complexity of the algorithm, for different Signal-to-Noise Ratios (SNR) and level of spatial correlations.

A novel method to improve spatial resolution of acousto-optic deflector

In this paper, a novel method of laser beam deflecting is introduced to improve the spatial resolution of an acoustic-optic deflector (AOD). We use double AOD (DAOD) to control laser beam. Compared with single AOD, the double AOD can improve speed and precision of target tracking and pointing significantly. Finally, a method of calculating the static and dynamic number of resolvable poins (NRP) is and it is supported by the experimental data excellently.

A low complexity residual frequency offset compensation algorithm for coherent QPSK/16QAM OFDM systems

In this paper, the effects of residual frequency offset on OFDM systems are analyzed, and incorrect decision will be made due to the introduced signal constellation rotation. Kobayashi and Nikitopoulos present a method of estimating the phase rotation caused by residual frequency offset. In their work, phase error is obtained by comparing signals after frequency equalization with signals after decision, then compensates the following signals by using the estimated value of the phase rotation. The method involves two decision operations and the calculation of the quantity of every signals phase rotation, consequently its computational complexity is high. Considering that in estimation what we need is only the phase information, we propose a method which obtains the phase rotation information from data directly by using such operations as sign inversion, real and imaginary part exchanging, accumulation and avoids two decision operations. The proposed method reduce the computational complexity without degrading the performance of the original algorithm, which is more suitable for hardware implementation. Simulation results show that the degradation of SNR caused by the residual frequency offset is not more than 0.2 dB after employing the proposed algorithm on the AWGN or SUI-2 channel.