Performance analysis of two‐hop decode‐amplify‐forward relayed system in different fading conditions

Recent advances in the field of wireless communication have proven the importance of diversity in combating channel fading and improving the bit error rates (BERs). In this report, a dual‐hop decode‐amplify‐forward (DAF) transmission system over Nakagami‐m fading channel is studied. The DAF relay system is a hybrid of decode‐and‐forward and amplify‐and‐forward relay systems that shows the benefits of both decode‐and‐forward and amplify‐and‐forward relay systems and is also called hybrid relay system or hybrid DAF relay system. Signal‐to‐noise ratios and BERs for various system models with varying number of transmit and receive antennas have been discussed. The diversity is achieved in two ways: firstly, by the use of relay and secondly, by the use of multiple antennas at both the transmitter and the receiver. Dual‐hop relaying gives better trunking efficiency and with single antenna at the relay site acquisition and antenna structures are much less expensive. The variations in the performance levels when the relay is moved to different locations within the line of sight of the transmitter and the receiver have also been analyzed. BERs with respect to variations in the fading parameter ‘m’ have also been presented and discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

A two‐hop equalize‐and‐forward relay scheme in OFDM‐based wireless networks over multipath channels

Relay communications have attracted increasing research attentions as a cost‐effective technique to improve spatial diversity, service coverage, and energy efficiency in wireless networks. However, existing relay schemes (e.g., amplify‐and‐forward and decode‐and‐forward (DF) schemes) still face several major challenges, particularly the accumulation of multipath channels effect in AF and long processing latency in DF. To address these issues, we propose a novel equalize‐and‐forward (EF) relay scheme to enhance the retransmission reliability while maintaining low processing delay at the relay node. In particular, the proposed EF relay estimates and equalizes the channel between source and relay to eliminate the channel accumulation effect without signal regeneration. To further reduce the relay processing time, the channel estimation and equalization in the proposed EF design are performed in parallel. The proposed equalization is realized by presetting the equalizer coefficients with the current channel response that is predicted in parallel using multiple past channel responses. Numerical results show that the proposed EF relay scheme can achieve comparable symbol error rate performance as the DF relay with much less relay latency. In addition, the EF relay exhibits low outage probability at the same data rate as compared with traditional amplify‐and‐forward and DF schemes. schemes. Copyright © 2015 John Wiley & Sons, Ltd     

“电力系统继电保护”混合教学探索与实践

“电力系统继电保护”是电气工程专业的重要专业课程之一,但传统的教学实施过程中仍然存在“教师为主学生为辅”、“学生先修课程不牢”、“学习劲头不足”及“理论联系实际不紧密”等问题。本文基于“新工科”思想及工程认证的OBE理念,对电力系统继电保护的线上线下相结合的混合教学模式进行探索,充分利用“雨课堂”、“微课”及“慕课”等教学手段,有效改善教学效果,并通过调整考核方式进行课程目标达成情况的全方位评估,并持续改进。     

Exact analysis of maximal ratio transmission-based decode-and-forward relaying with arbitrary number of co-channel interferers

This paper analyzes the performance of maximal ratio transmission (MRT)-based cooperative communication system over Nakagami- $m$ fading channels in the existence of co-channel interference which is becoming a critical factor since the limited spectrum bands are shared by growing number of devices. In particular, a dual-hop decode-and-forward relaying is investigated when multiple interferers affect the relay and the destination nodes. Firstly, the cumulative distribution function (CDF) and the probability density function (PDF) of the signal-to-interference-plus-noise ratio (SINR) are derived. Then, the exact expressions for the outage probability (OP), average bit error probability (ABEP), and ergodic capacity are obtained. Furthermore, asymptotic expressions for OP and ABEP are provided to find the diversity and coding gains. Finally, simulation results are presented to validate our theoretical findings.     

Bit error rate performance of orthogonal frequency‐division multiplexing relaying systems with high power amplifiers and Doppler effects

This paper analyzes the bit error rate performance of orthogonal frequency‐division multiplexing systems in mobile multihop relaying channels. We considered the uplink scenario and quantified the effects of mobile channel impairments such as Doppler shift due to user mobility per hop, high power amplifier distortions when amplifying the transmitted/relayed orthogonal frequency‐division multiplexing symbol per hop, and the cumulative effects of these impairments on multihop relaying channels. It was shown that the resulting intercarrier interference due to the cumulative effects of the phase noise generated by these impairments per hop becomes very significant in a multihop relaying communication system and severely degrades the bit error rate performance of the system. Simulation results agree well with and validate the analysis. Copyright © 2011 John Wiley & Sons, Ltd.