Shangzhi Xu

Novel Relay Scheme Based on Traffic Type in Vehicular Networks

Emergency message propagated in vehicular networks is delay intolerance and crucial for safety management. While the non-real-time traffic can highly improves the quality and comfortable of everyday. However, due to the limited transmission coverage and the poor quality of time-varying wireless environment, the two type traffic need relay to assist in the completion of communication. So this paper is dedicated to present novel relay scheme for the transmission of the two type traffic. We propose an effective broadcast scheme (PCC) which adopts primary and candidate relaypsilas cooperative work for emergency message propagation. Also we present a novel relay scheme (RCS) in which relay vehicle is replaced by relay cluster for the transmission of non-real-time traffic. Simulation results help to prove that our schemes gain better performance.

Relay Enhanced Architecture for Broadband Wireless Access Networks

Services based on the broadband wireless access (BWA) technology are fast developing, yet the applications are limited by the radio spectrum resource. Due to the high frequency bands allocated, the conventional cellular (single-hop) BWA network can not promise both coverage and throughput achievements in the metropolitan environment This paper proposes a MAC layer simulator architecture introducing cross-layer design to enhance the radio resource management in the BWA networks. Then relay concept is transferred into the BWA networks where relay station (RS) pads the shadowing area between directional antennas. The results show that the proposed relay enhanced BWA system outperforms the single-hop one on both spectrum efficiency and throughput.

A Novel Queue Priority Algorithm for Real-Time Message in VANETs

Without any doubt the research of VANETs plays an important role in ITS. This paper focuses on reducing the end-to-end delay and the packet loss ratio of the real-time message in VANETs. In this paper, a novel real-time message data packet queue priority algorithm which takes full advantage of the parameters (such as the relative distance, the relative velocity, the relative driving direction between the current packet forwarding node and the next hop node) of the VANETs and the real-time messages internal parameter(real-time message packet timestamp left from the deadline) is proposed. In the end, the performance of the algorithm in the two-lane highway scenario is simulated, the results show that this algorithm decreases the average end-to-end packet delay and the packet loss ratio compared to the FIFO queue scheme.

Performance Analysis of Multi-Hop MIMO Relay Network

Without any doubt MIMO techniques count to the few emerging key technologies for wireless communications. It is obviously that MIMO techniques can improve the system capacity and performance. On the other hand, there has been an upsurge of interest in multi-hop infrastructure-based networks in both industry and academia. In this article, multi-hop MIMO relay network is studied and different channel models are analyzed. At first, 2-hop relay network is worked on within both SISO and MIMO systems. Three channel models are applied into the system and different value of signal-to-noise ratio (SNR) of direct link between BS and MS are observed. Results show that when meeting 100% system efficiency, the required relay SNR gain of 2-antenna system can be reduced to half of that with only one transceiver antenna. After that, multi-hop network is researched. Statistics figures out that when passing through ideal channel, 4-hop relays is possible with given SNR of more than 10 dB whereas, 5-hop communication can be realized in 4times4 MIMO under the assumption of 0 dB of SNR of direct link between BS and MS and 100% system efficiency. With respect to Rayleigh frequency-selective fading channel, SISO system can only ensure 2-hop relays whereas one more hop is supported in 4times4 MIMO network. Furthermore, in 4times4 MIMO, with the increase of hop, extra 3 dB is needed.

Improved Balanced Power Allocation in Uplink MIMO System

This paper studies a balanced power allocation scheme to approach the capacity limits and power consumption reduce simultaneously of orthogonal-frequency- division-multiplexing multiple-input multiple-output (OFDM-MIMO) channels under the assumption that perfect channel state information (CSI) is available at both the transmitter and the receiver. In this paper, we build a function to describe the coordinate performance of capacity and total power, and use convex optimization method to solve this question, and an adaptive power allocation scheme is proposed according to the interior-point method. By numerical example we verify our analysis and show that proposed approach, compared to the optimal water-filling algorithm, actually achieves significantly lower total power consumption with similar performance in capacity.

An Enhanced Scheduling Solution to Support Quality of Service for Broadband Wireless Access Networks

This paper proposes an enhanced scheduling solution to support different quality of service (QoS) for IEEE 802.16e broadband wireless access network. Based on the existing scheduling algorithm M-LWDF, we do deeper research into how to integrate it into IEEE 802.16e. The proposed scheduling solution combines the key service flow parameters defined by IEEE 802.16e standard with M-LWDF scheme. Simulation results show that the delay character is improved for real-time services using the proposed method.