基于切比雪夫-迹迭代的大规模MIMO系统软输出信号检测

在多用户大规模多输入多输出(MIMO)系统信号检测算法中,最小均方误差(MMSE)算法可取得近似最优性能,但MMSE算法中高维矩阵求逆的复杂度过高,导致在实际应用中难以快速有效地实现.同时,对于高阶正交幅度调制(HQAM),如果符号向比特的解映射采用硬判决,将会导致后续信道译码的性能明显下降.因此,该文针对采用格雷编码的HQAM的多用户大规模MIMO系统,提出一种基于切比雪夫-迹迭代(CTI)的低复杂度软输出信号检测算法.该算法不但有效地规避了信号检测所需的高维矩阵求逆,同时,利用格雷编码的调制信号的比特翻转特性和二叉树结构,给出了一种融合三叉链表搜索的比特对数似然比(LLR)简化计算方法.仿真结果表明,该文所提的软输出信号检测算法最多需要3次迭代就能收敛并可取得接近MMSE算法的性能,在复杂度和性能之间取得了很好的折中.     

LDPC编码调制系统中基于反馈LLR均值的迭代解调/译码算法

该文针对LDPC码编码的BICM系统,提出一种对LDPC码译码器输出外附信息的计算方法进行改进的迭代解调/译码算法。与传统的解调/译码算法不同在于,该算法对每次BP迭代中译码器输出的各编码比特的外附LLR分别求均值后,再将其作为先验信息反馈给软解调器开始下次的迭代解调/译码。采用该方法可有效地减轻LDPC码在BP迭代过程中某些比特LLR值的振荡现象,从而使得传递给软解调器的外附信息更准确。仿真结果表明,和传统的两种迭代解调/译码算法相比,该算法能进一步提高LDPC编码BICM迭代系统的译码性能,而复杂度并无明显增加。     

基于序列检测的块判决辅助Turbo均衡器

该文针对高斯分布假设条件下逐符号检测均衡器的不足,提出了一种基于序列检测的块判决辅助Turbo均衡器(Turbo-BDAE)。新算法利用译码全信息估计发送序列,提高了序列估计的可靠性,引入软判决可以降低硬判决引起的错误扩散,同时结合序列检测为均衡器输出的后验概率(APP)估计提供了更可靠的信息。仿真表明,该均衡器在保持相近复杂度的同时,进一步提升了均衡系统性能,优于逐符号LMMSE均衡器和硬反馈BDFE。     

基于软输出固定复杂度球形译码的高效迭代检测算法

该文在软输出固定复杂度球形译码(SFSD)算法的基础上,提出一种低复杂度高性能的MIMO迭代检测方法。该算法利用迭代过程中译码器的反馈信息更新SFSD检测算法的软输出,获得明显的迭代增益,并利用多级比特映射星座图的特点大大降低分支度量的运算次数。针对SFSD算法预处理复杂度较高的问题,该文将检测顺序调整和QR分解两个预处理步骤相结合,从而减少了矩阵求逆运算。在长期演进方案(LTE)下行链路环境中的仿真结果表明,该文提出的算法性能十分接近最优的最大后验概率(MAP)检测,并且实现复杂度相对于MAP有显著的下降。     

高阶QAM调制MIMO系统高斯逼近简化算法

针对多输入多输出(MIMO)高阶正交幅度调制(QAM)系统检测算法使用传统的高斯逼近算法检测复杂度高的问题,研究了其简化算法.MIMO系统高斯逼近算法通过采用树形搜索的办法,对符号后验概率影响大的符号序列加以保留,其算法复杂度与保留符号序列数目成线性,且与调制阶数成指数关系.针对高阶调制QAM符号的特点,用多级映射的方法来进行高斯逼近,新方法结合树形搜索算法的思想,通过将高阶调制QAM符号拆分成多个4-QAM符号,从而可以每次两个比特的计算序列权重,其算法复杂度与调制阶数成线性关系,从而使得高阶调制系统的检测复杂度大大降低.仿真结果表明,多级映射高斯逼近算法能取得接近传统高斯逼近算法的性能.     

适用于WMSN的联合信源信道迭代译码

提出了一种适用于WMSN的联合信源信道迭代译码(ISCD)方案,基于一种软输入软输出(SISO)后验概率的变长译码算法,不仅可以得到最大似然(ML)变长序列估计,而且可以计算ISCD所必需的比特级的置信信息.此外,把缩放外信息技术引入到ISCD领域,提出了利用外信息交换特性来获得最优常数缩放因子的方法,这可以在几乎不增加运算复杂度的前提下提高ISCD的性能.这种方案的显著特点是运算复杂度低,所需存储空间小,可以被应用于WMSN节点上.仿真结果表明,提出的ISCD方案显著地提高了变长度编码数据在WMSN中传输的抗差错能力.     

LDPC码译码算法及性能分析

为了进一步降低低密度奇偶校验(LDPC)码译码算法的复杂度,基于经典置信传播(BP)译码算法,给出了对数域迭代后验概率对数似然比(APP LLR)算法。通过概率域的和积算法(SPA)和对数域的迭代APP LLR算法的性能仿真及分析可见,迭代APP LLR算法能以较小的性能损失换取复杂度的大幅降低。进一步选用迭代APP LLR算法,结合不同地形条件下的VHF频段信道模型,仿真了LDPC码编译码系统的性能。理论分析及仿真结果均表明,基于迭代APP LLR算法的LDPC码,实现简单,性能优异,具有良好的工程应用前景。     

基于LDPC编码的MIM0系统迭代接收机研究

研究了基于LDPC编码无线MIMO通信系统中的软输出最小均方误差干扰抵消迭代(MMSE PIC)检测算法.针对初次迭代检测时PIC输出的后验比特对数似然比(LLR)不可靠的问题,利用MMSE滤波器输出的高斯近似表示,给出了基于后验概率估计的迭代干扰抵消检测算法,以提高检测器输出的编码比特对数似然比的可靠性.仿真结果表明:改进的检测算法优于现有算法.     

基于LDPC编码的MIM0系统迭代接收机研究

研究了基于LDPC编码无线MIMO通信系统中的软输出最小均方误差干扰抵消迭代(MMSE PIC)检测算法.针对初次迭代检测时PIC输出的后验比特对数似然比(LLR)不可靠的问题,利用MMSE滤波器输出的高斯近似表示,给出了基于后验概率估计的迭代干扰抵消检测算法,以提高检测器输出的编码比特对数似然比的可靠性.仿真结果表明...     

OFDM系统中基于软干扰抵消的Turbo均衡算法研究

针对OFDM系统中子载波间干扰带来的性能恶化问题,在最优Turbo均衡的基础上,提出了基于软干扰对消技术的MAP均衡算法。Turbo均衡部分首先利用先验信息进行干扰抵消,然后通过干扰抵消输出结果计算编码比特后验概率;同时对信道矩阵进行带状近似,提出简化算法,运算复杂度进一步降低。通过仿真分析表明,相比于传统turbo均衡算法,该算法在工程应用中更具有可行性。     

On the optimality of bit detection of certain digital modulations

In this paper, we study the optimality of bit detection for coherent M-ary phase-shift keying (PSK) and M-ary quadrature amplitude modulation (QAM), and noncoherent M-ary frequency-shift keying (FSK) signal sets. For M-PSK and M-QAM signal constellations, we employ Gray mapping, consider 8-PSK and 16-QAM signal sets as representative of the general results, and derive the log-likelihood ratio (LLR) for each bit forming the symbol. Using the LLRs, we derive the average bit-error probability (BEP) for the individual bits, and show that the decision regions and the corresponding average BEP for the case of M-PSK coincide with those obtained with the optimal symbol-based detector, whereas, in general, this is not the case for both M-QAM and M-FSK.     

Discovering long lifetime routes in mobile ad hoc networks

In mobile ad hoc networks, node mobility causes frequent link failures, thus invalidating the routes containing those links. Once a link is detected broken, an alternate route has to be discovered, incurring extra route discovery overhead and packet latency. The traffic is also interrupted at the transport layer, and proper traffic recovery schemes have to be applied. To reduce the frequency of costly route re-discovery procedures and to maintain continuous traffic flow for reliable transport layer protocols, we suggest discovering long lifetime routes (LLR). In this paper, we first propose g-LLR, a global LLR discovery algorithm, that discovers LLRs of different route lengths for any given pair of nodes. We then propose a distributed LLR discovery scheme (d-LLR) that discovers two of the most desirable LLRs through one best-effort route discovery procedure. Simulations show that the lifetimes of the routes discovered by d-LLR are very close to those discovered by g-LLR. Simulations also show that the performance of different transport layer protocols is greatly improved by using LLRs. More importantly, traffic can remain continuous using the provided LLRs. D-LLR can be implemented as an extension to existing ad hoc routing protocols, and it improves the performance of transport layer protocols without modifications on them.     

一种利用软信息网络编码在双向中继网络进行估计转发的方法

 在本文中,我们为双向中继网络(Two-way Relay Networks)设计了一种崭新的估计-转发(EF:Estimate-and-Forward)方法.在中继端信道解码后首先得到每一比特的对数似然比(LLR:Log-Likelihood Ratio),然后利用两个方向的比特LLR进行软信息网络编码,并借此构造出中继端的发送信号.因为此方法保留了两端比特信息的软信息并抑制了噪声,所以在任何条件下它的性能都要优于传统的放大-转发(AF:Amplify-and-Forward)方式和解码-转发(DF:Decode-and-Forward)方式,文中详细推导了三种转发方式的最大可达速率,得到EF方式下最大可达速率的上界和下界,还证明了EF方式较其它两种方式节省功率消耗,并通过仿真得到了速率曲线与误码率曲线,明确的验证了EF的优势.     

Maximum-likelihood symbol synchronization and detection of OPPMsequences

For an optical Poisson channel, we consider the problem of symbol synchronization and detection of chip-synchronized, random overlapping pulse-position modulation (OPPM) sequences. Maximum-likelihood algorithms are derived for both synchronization and detection and for soft and hard data, and their performances are evaluated through simulations and an upper bound on the symbol detection and symbol synchronization probabilities. As for the case of pulse-position modulation previously studied, it is seen that a performance ceiling exists when only chip synchronization is present, which can be removed through the periodic insertion of synchronizable symbols in the random data stream     

A low-complexity SISO multiuser detector for iterative decoding of asynchronous CDMA systems with convolutional codes

The optimal decoding scheme for asynchronous code-division multiple-access (CDMA) systems that employ convolutional codes results in a prohibitive computational complexity. To reduce the computational complexity, an iterative receiver structure was proposed for decoding multiuser data in a convolutional coded CDMA system. At each iteration, extrinsic information is exchanged between a soft-input soft-output (SISO) multiuser detector and a bank of single-user SISO channel decoders. A direct implementation of the optimal SISO multiuser detector, however, has exponential computational complexity in terms of the number of users which is still prohibitive for channels with a medium to large number of users. This paper presents a low-complexity SISO multiuser detector using the decision-feedback scheme, of which tentative hard decisions are made and fed back to the SISO multiuser from the previous decoding output. In the proposed scheme, the log-likelihood ratios (LLR) as well as the tentative hard decisions of code bits are fed back from the SISO decoders. The hard decisions are used to constrain the trellis of the SISO multiuser detector and the LLRs are used to provide a priori information on the code bits. The detector provides good performance/complexity tradeoffs. The computational complexity of the detector can be set to be as low as linear in the number of users. Simulations show that the performance of the low-complexity SISO multiuser detector approaches that of the single-user system for moderate to high signal-to-noise ratios even for a large number of users.     

扩展空间调制技术的低复杂度检测算法

针对发射天线数可变的扩展空间调制技术(Extended Spatial Modulation,ESM)提出了相应的低复杂度检测算法。传统的空间调制技术(Spatial Modulation,SM)将信息调制在发射的天线上,但是在一个符号周期内活跃的天线数为常数。而ESM允许在不同符号周期以不同数目的发射天线进行组合,不仅能够承载更多信息,同时对发射的天线也有了更多优选的空间,但是传统的检测算法在发射天线数固定时才能正常使用,针对ESM的特殊情况提出了阈值法检测天线,并通过数值实验给出了性能分析。     

Efficient Hybrid Modulation/Demodulation Scheme Using Differential Encoding/Decoding for UWB-IR

An efficient hybrid modulation/demodulation scheme using a short duration pulse in the time-domain for ultra wideband-impulse radio (UWB-IR) systems is proposed. The proposed modulation scheme is pulse position modulation (PPM) of the UWB-IR standard modulation combined with differential encoding, and non-coherent energy detection (ED) adopting differential decoding is proposed for demodulation. Differential encoding makes a pulse that can transfer additive information bit into bits assigned in one symbol without increasing the symbol period. The BER performance is evaluated for 2-PPM, 4-PPM and the proposed HD-2PPM (which has the same symbol duration as BPPM and includes two information bits per symbol). The error performance indicates that the proposed scheme is an outstanding 0.5 dB over existing schemes of UWB-IR, and the data-rate performance shows that the proposed method has higher spectral efficiency than conventional methods that occupy the same duration as the proposed scheme.

     

Novel decoding of square QAM modulated mimo systems based on turbo multiuser detection

By introducing the bit-level multi-stream coded Layered Space-Time （LST） transmitter along with a novel iterative MultiStage Decoding （MSD） at the receiver, the paper shows how to achieve the near-capacity performance of the Multiple-Input Multiple-Output （MIMO） systems with square Quadrature Amplitude Modulation （QAM）. In the proposed iterative MSD scheme, the detection at each stage is equivalent to multiuser detection of synchronous Code Division Multiple Access （CDMA） multiuser systems with the aid of the binary representation of the transmitted symbols. Therefore, the optimal Soft-Input Soft-Output （SISO） multiuser detection and low-complexity SISO multiuser detection can be utilized herein. And the proposed scheme with low-complexity SISO multiuser detection has polynomial complexity in the number of transmit antennas M, the number of receive antennas N, and the number of bits per constellation point Me. Simulation results demonstrate that the proposed scheme has similar Bit Error Rate （BER） performance to that of the known Iterative Tree Search （ITS） detection.     

Linear LLR approximation for iterative decoding on wireless channels

On a fading channel with no channel state information at the receiver, true log-likelihood ratios (LLR) are complicated functions of the channel output. It is assumed in the literature that the power of the additive noise is known and the expected value of the fading gain is used in a linear function of the channel output to find approximate LLRs. This approach, however, is not optimal in the sense of bit error rate performance. In this paper, we introduce a measure of accuracy for the approximate LLRs based on their probability density function and we show that this measure provides a very convenient tool for finding good approximate LLRs. Assuming that the power of the additive noise is known, and using the proposed measure, we find a linear LLR approximation whose performance is extremely close to that of the true LLR calculation on an uncorrelated Rayleigh fading channel. These results are then extended to the case that the noise power is also unknown and a performance almost identical to the previous case is obtained.     

基于极化码的可见光通信自适应调光方法研究

针对在可见光通信的闪烁问题,提出了一种通过曼彻斯特编码级联极化码进行调光控制的自适应打孔方法.极化码与曼彻斯特编码级联以便于在可见光系通信统系统中提供50％的调光,并且通过打孔和插入补偿比特的方式可以实现不等于50％的调光值.常规打孔方案应将曼彻斯特编码符号的所有比特都打孔,本文提出的方法可以根据选定的极化码的预定冻结...