GF(2p)LDPC编码的相位调制OFDM系统在瑞利衰落信道的性能

OFDM是一项能有效对抗高速无线通信中多径衰落的关键技术，为了进一步提高OFDM系统的误码性能，许多信道编码技术已被应用于OFDM系统中，二元域LDPC码以其近香农限的误码性能和较低的译码复杂度成为研究的热点。在AWGN信道下，多元域LDPC码比等效码长的二元域LDPC码有更好的纠错性能。本文提出了一种将多元域LDPC码经过MPSK调制后用于OFDM系统的新方法。仿真结果表明，在多径衰落信道下，通过合理选择多元LDPC码域的阶数和调制的方法，多元域LDPC编码的高阶调制OFDM系统比等效码长的二元域LDPC编码OFDM系统具有更好的性能，并且由于采用了多元域LDPC的快速BP译码，译码复杂度只是稍有增加。     

LDPC码在802.16a OFDM系统 衰落信道中的性能分析

本文通过对802.16a OFDM系统信道的分析,权衡估计的性能和算法复杂度两个因素,针对不同的传输环境,提出了动态的OFDM信道估计方案.另外我们找到了一组优秀的非正则LDPC码,将其应用于IEEE 802.16a OFDM环境中,仿真验证了它们在SUI-3和SUI-5多径衰落信道环境下具有良好的性能,并和协议中提出的卷积Turbo码进行了比较,结果证明在相同条件下,本文的LDPC码可以取得比协议提出的卷积Turbo码更优越的性能,具有更好的抗多径衰落的能力.     

具有低复杂度的 LDPC 已编码非相干酉空时调制系统设计简

提出一种克服无线信道瑞利衰落和高斯白噪声干扰的非相干编码调制MIMO系统方案。纠错码采用IEEE 802.16e中的非规则QC-LDPC码,非相干调制采用基于三角函数的酉空时调制(SC-USTM)。在接收端,推导出SC-USTM的最大后验概率（MAP）解调算法;为了降低复杂度,构造了SC-USTM的双解调器方案;为了改善双解调的性能,在置信传播（BP）迭代解码器和MAP解调器之间引入了迭代反馈机制。仿真实验表明LDPC已编码SC-USTM的MIMO系统比未编码USTM的MIMO系统在 误码率时,性能改善15~17 dB,并且整个系统具有较低的计算复杂度。     

基对称扩展信道极化算法及其在OFDM水声通信系统中的应用

针对水声通信系统中低密度校验 (Low Density Parity Check, LDPC) 码存在的译码复杂度高和译码错误平层问题,设计了基于极化码编码的水声通信系统,并针对水声信道的极化问题提出了新的基对称扩展极化权重 (Polarization Weight, PW)信道极化法。该算法通过PW高阶基计算各个子信道的极化权重,实现了独立于信道状态的信道极化,解决了传统Polar码编码稳健性差和依赖信道状态的问题。理论研究和仿真结果表明,与传统信道极化方法相比,改进的PW方法具有更稳定的信道极化结果。将该方法应用于正交频分复用 (Orthogonal Frequency Division Multiplexing, OFDM) 水声通信系统中,与现有的LDPC编码方法相比,基于改进的PW极化码具有更低的通信误码率和译码复杂度,且不存在译码错误平层。      

Pilot Based Channel Estimation in IEEE 802 16a OFDM System

1　Introdution　IEEE 802 16[1] is a specification for fixed broadbandwireless Metropolitan Access Networks (MAN). The stan dard is expected to bring low cost and more bandwidth prod ucts for broadband wireless access in the next years. Thisstandard specifies the physical (PHY) and Medium AccessControl layer (MAC) of the air interface of interoperablepoint to multipoint and optional Mesh topology broadbandwireless access system. The specification enables access todata, …     

Performance Analysis of Parallel Concatenation of LDPC Coded SISO-GFDM System for Distinctive Pulse Shaping Filters using USRP 2901 Device and its Application to WiMAX

The increasing demand for high data rates requires channel error control codes for the upcoming fifth generation. This article presents an investigation of the parallel concatenation of low-density parity-check codes (PC-LDPC) in the fifth generation proposed waveform candidate called generalized frequency division multiplexing (GFDM). PC-LDPC codes are obtained by dividing the long and high complexity single LDPC codes into small two lower complexity codes, and these designed codes are applied to the 5G-GFDM waveform. Since the GFDM signal transmits data in both the time and frequency domain, these PC-LDPC codes can deal with two-dimensional errors. This channel coded GFDM system is integrated into Universal software radio peripheral (USRP) device for real-time implementation. The Attainment of the proposed transceiver is verified by computation of BER under distinctive channel coding techniques like convolutional, Golay, Bose-Chaudhuri-Hochquenghem (BCH), extended length single LDPC code. The different pulse shaping filters such as Raised Cosine (RC), Root Raised Cosine (RRC), Gaussian, and Xia 4th order filter are applied to the GFDM under the Gaussian noise and Rayleigh fading channel to compute Out of band (OOB) power. The PC-LDPC coded GFDM outperforms LDPC by 6.5 dB in the RRC filter for roll-off factor rate 0.5 under the Rayleigh fading channel. PC-LDPC code outperforms LDPC code with a coding gain of 2 dB was observed in IEEE 802.16 Transceiver.

     

Low complexity channel estimation for space-time coded wideband OFDM systems

In this article, channel estimation for space-time coded orthogonal-frequency division multiplexing (OFDM) systems is considered. By assuming that the channel frequency response is quasi-static over two consecutive OFDM symbols, we develop channel parameter estimators based on the use of space-time block coded (STBC) training blocks. Using an STBC training pattern, a low-rank Wiener filter-based channel estimator with a significant complexity reduction is proposed. A simplified approach for the optimal low-rank estimator is also proposed to further reduce the estimator complexity while retaining an accurate frequency domain channel estimation. Numerical results are provided to demonstrate the performance of the proposed low complexity channel estimators for space-time trellis coded OFDM systems.     

非正则LDPC码在DSP上的实现

首先简单介绍了非正则LDPC码的结构,给出了一种基于IEEE802.16e直接编码法生成的(576,288)非正则LDPC码的编译码原理。然后详细论述了其在TI定点DSP(TMS320C5510)上的定点化算法实现方式,并在经过C和部分汇编优化后将算法效率提高了70%以上,达到了实时系统要求。最后给出了该LDPC码与(2,1,7)卷积码在AWGN信道下的性能对比,表明这种中短码长的非正则LDPC码较卷积码有较大的纠错性能优势。     

Comb type pilot aided channel estimation in OFDM systems with transmit diversity

Transmit diversity can be applied to OFDM systems by adopting space time code. Since the received signal is the overlapped signals transmitted from different transmit antennas, channel estimation is a rather challenging task for space time coded OFDM (ST-OFDM) systems. Pilot structure can help the receiver to effectively separate the overlapped signals and perform accurate channel estimation. In this paper, we propose three different channel estimation algorithms based on specially designed comb type pilots inserted in frequency domain. One of our proposed algorithms is performed in frequency domain and the other two are performed in time domain. Such comb type pilot based algorithms can provide higher bandwidth efficiency than common significant-tap-catching algorithm using training block pilots. Numerical analyzes and computational simulation show that our proposed estimation schemes have the same good performance while the time domain methods have relatively simple structure.     

IEEE802.16e标准LDPC译码器设计与实现

LDPC码自在上个世纪90年代被重新发现以来,以其接近香农极限的差错控制性能,以及译码复杂度低、吞吐率高的优点引起了人们的关注,成为继Turbo码之后信道编码界的又一研究热点。利用FPGA设计并实现了一种基于IEEE802.16e标准的LDPC码译码器。该译码器采用偏移最小和（Offset Min-Sum）算法,其偏移因子β取值为0.125,具有接近置信传播（Belief Propagation）算法浮点的性能。译码器在结构上采用了部分并行结构,可以灵活支持标准中定义的所有码率和码长的LDPC码的译码。此外,该译码器还支持对连续输入的数据块进行处理,并具有动态停止迭代功能。硬件综合结果表明,该译码器工作频率为150MHz时,固定15次迭代,最低可达到95Mb/s的译码吞吐率,完全满足802.16e标准的要求。     

OFDM接收机及其在BLAOKFIN561上的实现

本文借鉴IEEE802．16d的参数，介绍了正交频分复用（OFOM）的基本原理，主要研究了同步技术如符号定时、频偏估计、信道估计。然后以BLACKFIN561评估板为平台，实现并评估了整个系统。     

MIMO-OFDM系统中信道估计技术的性能评估

本文给出了MIMO-OFDM系统中的三种信道估计算法,详细的分析与比较了这几种算法在估计均方误差、实现复杂度、跟踪速度以及频带效率等方面的性能,最后通过MATLAB仿真试验对其进行了验证.     

Performance of LDPC coded FMT systems over frequency selective fading channel

This paper proposes the Low Density Parity Check （LDPC） coded Filtered MultiTone （FMT） systems with high-order modulation for the high data rate reliable transmission over frequency selective fading channel. For the purpose of accomplishing soft input soft output iterative decoding of LDPC codes, a new soft decision metric generation method is proposed, which obviates the need of the noise variance estimation, for M-PSK/M-QAM-type high-order modulation over frequency selective fading channel. Computer simulation indicates that, there is no performance loss with our new metric, but the complexity of implementation is reduced, and that the LDPC codes are effective to improve the Bit Error Rate （BER） of FMT in frequency selective fading channel.     

一种用于IEEE802.16d的联合信道估计算法

针对IEEE802.16d帧结构提出一种结合前导训练序列和导频的信道估计算法。算法通过前导完成初始精确的信道估计,再使用判决反馈方式提高导频估计准确度,并根据前后符号导频估计结果得到反映信道变化的时变因子,利用它来调整前导估计和导频估计比例,联合完成信道估计。仿真结果表明,与传统的信道估计方法相比,此算法能够更有效的对抗频率选择性衰落和更大的多普勒频移,改善系统的性能。     

基于IEEE802.16d系统的简易信道估计算法

提出了基于IEEE802.16d标准的当信道的响应大于循环前缀(CP)时一种简易的信道估计算法。利用系统前导的特殊时域结构,在不增加系统实现复杂度的基础上就可以很好地消除由于循环前缀不足而带来的ICI和ISI的干扰。仿真结果表明该方法可以满足IEEE802.16d在高速非视距环境下对信道估计的性能要求,该研究结果对高传输速率的信道信息估计有较大的参考价值。     

LDPC码在802.16a协议中的应用

基于LDPC码的优越性能，找出一组优秀的非正则LDPC码应用于IEEE802．16a OFDM环境中，并对其性能进行仿真。仿真结果表明，LDPC码在衰落信道下具有良好的纠错能力，适用于WMAN等采用OFDM的无线通信系统。     

使用准循环LDPC码的OFDM系统性能分析

参照IEEE802．16e标准中的准循环LDPC码校验矩阵结构,设计了一种新的校验矩阵,并将其应用于OFDM系统中。同时,将该设计方案与RS和卷积编码级联方案进行比较,仿真显示,该方案与级联编码方案有几乎相同的编码增益。OFDM调制之前采用BPSK映射比采用QPSK映射有2dB的增益。出于对比的目的,在BPSK调制模式下,对该设计方案与级联编码方案也做了仿真比较,结果显示,前者比后者有大约3dB的编码增益。     

Implementation of a Flexible LDPC Decoder

Low-density parity-check codes (LDPC) are among the most powerful error correcting tools today available. For this reason they became very popular in several applications such as the digital satellite broadcasting system (DVB-S2), wireless local area network (IEEE 802.11n) and metropolitan area network (802.16e). Whereas several code-specific decoders have been proposed in the literature, the implementation of a high performance yet flexible LDPC decoder still is a challenging topic. This work presents a novel formulation of the decoding algorithm that strongly simplifies internal communication requirements and enables the development of decoders supporting generally defined LDPC codes. The resulting architecture is tailored to decode both IEEE 802.11n and IEEE 802.16e LDPC codes, as well as any other code of comparable complexity. The implementation cost deriving from the full flexibility offered by the proposed approach is also evaluated.     

状态网格图的LDPC码在OFDM系统中的应用

介绍了LDPC码的编译码技术,提出了一种新颖的2状态网格图译码算法,研究了该码在OFDM系统中的性能,对不同的译码算法进行了比较.仿真结果表明,LDPC码在OFDM基带传输系统中用2状态网格图对其译码能够更好的对错误码进行纠错,提高码字性能,信息传输速率会大大提高.     

基于IEEE802.16d标准的信道估计分析

分析了基于IEEE802.16d标准的正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统在SUI-3信道下的误码性能,并对发射端的帧结构以及组帧方式作了详细说明.通过实验仿真发现利用帧前导做信道估计得出的误码性能要优于没有信道估计的情况.