A simplified exact expression of SEP for cross QAM in AWGN channel from M × N rectangular QAM and its usefulness in Nakagami-m fading channel

This paper derives a simple exact expression of symbol error probability (SEP) for general order cross QAM constellation in the presence of additive white Gaussian noise (AWGN) channel. The key idea is to obtain this novel expression from a simple analysis of the corresponding rectangular QAM. The analysis of the expression involves simple one dimensional Gaussian Q functions unlike other complex SEP expressions. A simple tight bound approximation of the proposed exact SEP is also given, which provides performance improvement over the existing SEP approximations, particularly for low signal to noise ratios (SNRs). Also, with the help of simulation results, we show that the proposed approximation is in excellent agreement with the exact SEP curve. Moreover, the proposed expressions prove to be useful for accurate estimation of the SEP in Nakagami-m fading channel, including the special case of Rayleigh fading (m = 1).     

Signal Space Diversity Augmented Space Time Block Coded Communication System

In this paper we propose the combination of space-time diversity techniques and signal space diversity, in order to improve communication system performance. Specifically, we use prior knowledge of the channel behavior to design a mapping algorithm to generate a two-dimensional constellation with the same number of symbols as MPSK constellations currently used in coherent space time block coding applications, to demonstrate that superior performance can be achieved. This is accomplished by constructing a two-dimensional map that results from the minimization of the estimated symbol error probability when transmission occurs in a fading environment. System performance for each each mapping is assessed in quasi-static Rayleigh fading channels.     

Optical and morphological properties of InGaAs/AIGaAs self-assembled quantum dot nanostructures for 980 nm room temperature emission

This work deals with the study of optical and morphological properties of InGaAs/AlGaAs quantum dot （QD） structures grown by molecular beam epitaxy （MBE）. Photoluminescence （PL） emission energies, activation energies of PL quenching and QD sizes are studied as functions of the Al content in the AlyGal-yAs confining layers （CL）. We show that the PL emission energy of In（Ga）As/AlyGal-yAs QD structures increases with increasing y and that the sizes of InAs/AlyGal-yAs QDs decrease with increasing y. By the comparison of the experimental results with those of an effective-mass model developed to calculate the QD fundamental transition energies, we show that the blueshift of emission energy has to be ascribed not only to the increase in barrier discontinuities that confine the carriers into QDs but even to effects related to changes of the QD morphology dependent on CL composition. Moreover, we show that the Al content in the barriers determines also the activation energy of thermal quenching of PL, which depends on the thermal escape of carriers from QD levels. These studies resulted in the preparation of structures with efficient light-emission in the 980 nm spectral window of interest for lightwave communications.     

DVB—C多载波QAM系统中的PAPR问题研究

峰值平均功率比（PAPR）是制约DVB-C多载波QAM系统集成度的关键问题之一。本文从理论出发分析了DVB—C多载波QAM系统中的PAPR问题的特殊性,并在此基础上研究了限幅法在不同剪波比情况下引起的信号失真程度。可为实际系统设计提供参考。对于无失真传输,文中给出了一种简化的初始相位优化序列的方法．该方法无需额外资源,不影响系统BER性能。同时又能够对PAPR起到一定的抑制作用。     

OFDM信号的盲侦察技术分析

正交频分复用传输系统,以其可对抗频率选择性衰落,高频谱利用率等优点,得到了广泛的应用。论述了正交频分复用(OFDM)信号非协作接收中的某些关键算法,研究了基于循环前缀的符号同步算法及最大联合似然估计(ML)算法、基于高阶累量的OFDM信号调制样式识别算法,解决了OFDM信号和常规通信信号之间的类间信号识别问题。仿真结果进一步说明了该方法的有效性。     

一种改进的QAM载波恢复方法

文中提出了一种新的QAM载波恢复环路结构。在此结构中频率检测和相位检测同时进行,在鉴相阶段引入了改进的加权直接判决（MWDD）算法。经仿真实验验证此方法提高了整个载波恢复环路的捕获速度,并使载波环路的相位抖动有所减小,16-QAM载波环路最大可以捕获11%符号率的频偏。     

数字视频传输中的数字调制技术

介绍了QPSK和QAM两种数字调制技术，对这两种数字调制技术的工作原理进行分析，并给出了二者比较结果。     

CDMA 2000 1xEV-DO前向链路调制与编码技术

1xEV-DO是CDMA 2000针对数据业务的增强系统.为提高数据传输速率,1xEV-DO前向链路引入了8PSK和16QAM这样的高阶调制以及Turbo码.本文在简要介绍CDMA 2000 1xEV-DO系统前向链路的基础上,着重研究了相应的调制与编码技术.文中以16QAM为例推导了MAP,Log-MAP及Max-Log-MAP软解调算法,另外还说明了Turbo解码器如何针对软信息输入做必要的修改,最后通过在不同信道下1xEV-DO系统前向链路仿真分析了解调和解码算法的性能.     

自适应MQAM调制性能分析

本文首先分析了自适应MQAM调制的原理,它以频谱效率最高为准则,在恒定功率约束条件下对接收信噪比优化来选择不同调制阶数。然后引入时变多径信道模型,通过仿真给出了自适应QAM在此信道条件下的性能,并分析了信道估计误差对其性能的影响。     

LTE中密钥生成算法SFHA-256的优化

详细介绍了LTE中基于3C结构的密钥生成算法SFHA-256(SHA-256的改进),并针对由于计算分支f'包括f的一个分支,存在部分算法重复的嫌疑,对SFHA-256进行了优化,最后通过仿真验证优化的SFHA-256在抗冲突性和均匀分布方面都得到了改善。