RS编码非正交FSK系统性能的研究

本文首先介强了非正交频移键控(frequency shift keying,FSK)信号的设计方法,然后介绍加性高斯白噪声信道和平坦Rayleigh衰落信道中非正交2FSK和MFSK信号的设计和检测.为了提高非正交FSK信号的性能,将高效的Reed-Solomon(RS)编码用于系统设计.研究结果表明,RS编码的非正交FSK系统可以获得频带利用率和性能的良好折衷.本文同时给出了RS编码非正交FSK信号的性能分析和相应的数值仿真结果.     

Ka频段固定卫星通信Turbo码性能仿真

使用Ka频段是卫星通信系统解决信道拥挤和提高系统容量的有效途径.为了提高Ka频段卫星通信的传输性能,本文在对Ka频段固定卫星通信信道进行分析的基础上,提出了一种适合该信道的Turbo码编译码方案,译码时通过使用修正的信道可靠性常数极大地提高了译码性能.最后,利用Ka固定卫星通信信道模型对该Turbo码方案性能进行了仿真.仿真结果表明,本文采用的Turbo码方案与采用相同码率的卷积码和卷积级联码方案相比,所带来的增益大于1.5 dB.     

基于纠删码的海洋无线传感器网络丢包恢复方法

针对无线传感器网络在恶劣海洋环境下存在的严重丢包问题,设计并实现了一种低复杂度的基于里德-所罗门(RS)码 的丢包恢复方法。 具体而言,发送节点对信息数据包进行分析,进一步利用 RS 码编码生成并插入少量的冗余数据包,可以保 证数据包的顺序发送,同时利用较少的资源编码生成了冗余校验数据包。 接收节点基于接收的信息数据包与校验数据包,通过 RS 码对丢失的数据包进行纠删恢复。 在陆地和海洋两种复杂信道中测试提出的方法,以丢包率(packet loss rate, PLR)作为 RS 码丢包恢复方法性能的度量指标。 测试结果表明,采用低复杂度的 RS 码丢包恢复方法能降低信道衰落影响的丢包率,保证了 数据在严重丢包情况下的完整性,提高系统的可靠性。     

一种新的衰落信道自适应Turbo码调制方法

针对衰落信道下频谱资源利用率较低的问题,提出了一种自适应T urbo码调制方法。该方法在一定平均辐射功率和通信误码率的约束下,以优化平均频谱效率为目标,将衰落信道划分为 N个相邻的衰落区域,并利用拉格朗日函数法求得了最优的衰落区域边界值。仿真结果表明：与同等复杂度的自适应网格编码调制方案相比,本文方法的平均频谱效率获得了将近2～3 dB的性能增益,与香农极限仅相差3 dB ;与非最优4衰落区域相比,最优4衰落区域有将近1 dB的性能增益。本文方法可显著提高无线通信系统的平均频谱效率。     

基于QPSK图传链路信号的多径信道BER仿真

对于无线通信,衰落是影响系统性能的重要因素,而不同形式的衰落对于信号产生的影响也不相同。本文在分析移动多径信道特性的基础上,建立了不同信道模型下多径时延效应的计算机仿真模型。不仅针对不同信道衰落条件下多径衰落引起的多径效应进行仿真,而且进一步阐述了多径效应的影响,用Matlab对有3条固定路径的AWGN多径信道中的QPSK系统进行BER性能仿真。     

基于K-S检验的瑞利衰落信道统计特性评估

针对瑞利衰落信道的标准化评估问题,提出了一种基于K-S拟合优度检验的瑞利衰落信道统计特性评估方案。首先采用成形滤波器法产生瑞利衰落信道作为非参数假设检验模型;然后从瑞利衰落信道复序列中提取幅值序列和相位序列;最后采用K-S检验法,将经验累积分布函数和理论累积分布函数对比,验证幅值序列和相位序列是否分别服从瑞利分布和均匀分布。仿真结果表明,在样本长度为128 000,显著性水平小于0.01时,方案的正确识别概率达到95%以上,具有较高的性能,可以作为瑞利衰落信道标准化评估的重要依据。     

正交频分复用数字调制技术

介绍一种可较好地解决多径衰落所引起的信道选择性衰落 ,又可克服信道的瑞利衰落、性能优良的正交频分复用数字调制技术。它是通过多载波的并行传输方式将 N个单元码同时传输 ,来取代通常的串行码序列传送 ,使每个单元码所占的频带小于Δf ,从而有效地防止了因频率选择性衰落产生的码间干扰     

基于软件无线电的Turbo码编码通信系统实现

为保障和提高无线信道下的数据传输可靠性和灵活性,基于通用软件无线电外设（USRP）平台设计和实现了以Turbo码作为信道编码方案的通信系统.系统发射机可采用1/2或1/3码率的Turbo码对传输数据进行编码,接收机通过软解调方法和软输入软输出的Max-Log-MAP迭代译码算法获得编码增益.仿真与测试结果表明,采用Turbo码作为编码方案可有效对抗噪声和衰落,降低传输误比特率,进而提高无线通信系统的可靠性.此外,通过文件传输等应用,进一步验证了本系统的可行性.     

移动衰落信道特性分析和卷积编码π/4DQPSK的性能仿真

文中对移动衰落信道的统计特性进行了研究,建立了计算机仿真的信道模型,并在此基础上对卷积编码π/4DQPSK数字链路在衰落信道中的误码特性进行了仿真。     

Turbo码在电力线通信中的应用研究

在电力线通信(PLC)中采用具有较强纠错能力的Turbo码编译码方案，可以在电力线较为恶劣的通信环境下取得较好的通信质量。文中探讨了Turbo码在电力线通信噪声信道中采用几种不同交织器和分量码的性能，并给出了仿真结果。     

Multilevel code design for multistage and parallel decoding schemes for rayleigh fading channels

The objective is to design efficient coded modulation systems with sub-optimum but practical decoding schemes for Rayleigh fading channels. The well-known rate design rule is conventionally used for additive white Gaussian noise (AWGN) channels. In this paper its application is extended to the Rayleigh fading case by modelling the channel as a time-invariant additive non-Gaussian noise channel, and the equivalent channel capacity equations are evaluated. The sub-optimumbut practical decoding schemes of multistage decoding and parallel decoding on levels are considered. The fading channel is modelled as a time-invariant additive non-Gaussian noise channel by assuming that the channel state information is available at the receiver. The equivalent channel capacity equations for both decoding schemes and a code design example are presented. It is demonstrated that very good coding gains can be achieved if code rates are selected correctly.     

A novel rate-2 full diversity algebraic space-time code

Orthogonal space-time block codes (OSTBCs) have attracted considerable attention due to their low complexity linear decoding and full diversity in Rayleigh fading channels. However, OSTBCs exist only for certain numbers of transmit antennas and do not provide full code rate when more than two transmit antennas are used. In this paper, a novel rate-2 algebraic space-time code that combines coordinate-interleaving and group precoding is proposed. By properly choosing the designed parameters, the coding scheme can achieve full diversity order and high coding gain. The receiver adopts polynomial complexity sphere decoding algorithm to get maximum likelihood (ML) performance. Analysis and simulations illustrate that the new code exhibits significant performance gain over the conventional OSTBCs and diagonal algebraic space-time code.     

Noncoherent MT-CDMA system with post-detection diversity combining

This paper presents a theoretical analysis of a noncoherent multitone code division multiple access (MT-CDMA) system with diversity combining in terms of average bit error rate performance. The study is carried out for both slow Rayleigh and Ricean fading frequency-selective channels with differential binary phase-shift keying (DBPSK) modulation in the indoor environment. The investigation considers post-detection diversity with maximal ratio combining. Assuming a fixed bandwidth, bit rate and transmitter power, the effect of diversity order and number of tones on the systems performance is studied. Numerical results are presented to validate the analysis and to justify the approximations made.     

A new CDMA/SDMA structure with transmit diversity

Space division multiple access (SDMA) is a technique which can be used to increase the capacity of mobile communication systems by exploiting the spatial separation between different users. Space-time block codes can provide good performance in wireless fading channels through spatial diversity. Here these two techniques are combined to produce a new cooperative diversity architecture for code division multiple access (CDMA)/SDMA cellular systems using a space-time block code. An analysis of the system performance is given for a Rayleigh fading channel. This analysis can easily be generalized to similar systems. The bit error rate performance for this architecture with the Universal Mobile Telecommunications System, UMTS Terrestrial Radio Access, time-division duplex (UMTS UTRA TDD) and time-division synchronous CDMA (TD-SCDMA) systems is presented.     

统一测控系统下行信号仿真器设计与实现

通过对瑞利信道、莱斯信道与全阴影信道等特性研究,提出了适合统一测控系统下行信号模拟的设计方案。仿真设备利用对瑞利信道模块、莱斯信道模块与全阴影信道模块的切换可以有效地仿真实际测控环境,结果与经过实际信道传输后信号变化规律相吻合,验证了统一测控系统中频信号模拟方法的正确性和可行性。该系统的实现为分析评估接收机的工作状态、发现故障和查找事故的发生原因提供重要工具。     

On Reed–Solomon Coding for Data Communications Over Power-Line Channels

The problem of data communications through impulsive power-line channels using Reed–Solomon (RS) codes combined with $M$-ary modulation is treated. It is shown that under the influence of impulsive interference, the seemingly robust algebraic RS decoder can suffer drastic performance degradation even with the aid of an interleaver. We attempt to elucidate the mechanism that leads to the breakdown of such coding schemes. It is found that in impulse channels, excessive random and burst errors can occur prior to RS decoding mainly due to the deficiency of the Gaussian-based demodulator. An impulse mitigation strategy derived from the myriad filtering framework is incorporated into the demodulator for efficient baseband filtering and RS decoding. Even without an interleaver, the proposed solution leads to substantial performance improvements over the conventional interleaved scheme in impulsive channels. Consequently, the delay caused by interleaving can be avoided, which has significant benefits for future broadband power-line communication systems supporting interactive applications.      

A cross-layer adaptive transmission scheme over correlated fading channels

Conventional adaptive transmission schemes perform poorly in wireless correlated slow-fading channels. A cross-layer adaptive transmission scheme combined with selective repeat automatic repeat request (SR-ARQ) is proposed. We apply a multi-state Markov system model for analyzing the performance of systems and optimizing the selection of modulation levels and packet sizes in correlated fading channels, which is also described by a finite-state Markov chain. A general closed-form expression of the average throughput for our suggested scheme is presented. Numerical results show that our adaptive scheme combined with SR-ARQ can obtain good performance in correlated fading channels. Translated from Journal on Communications, 2006, 45(1): 35–41 [译自: 通信学报]