差分酉空时协作系统的多符号裁减自动球形译码

鉴于差分协作系统中多符号差分检测(multiple-symbol differential detection,MSDD)算法计算复杂度高的缺点,引入裁减自动球形译码(pruning automation sphere detection,PASD)算法来降低差分酉空时协作系统的检测复杂度.PASD算法是在球形译码的基础上,结合自动球形译码和裁减球形译码的思想而提出的.通过对扩展节点所消耗的复杂度和系统的误码率两方面来分析译码算法的性能.仿真分析表明,在差分酉空时协作系统中,PASD算法在误码性能几乎不变的情况下,复杂度曲线比球形译码(sphere detection,SD)算法收敛迅速.其中在分组长度N=5、信噪比SNR=15dB的情况下,PASD、SD算法的扩展点数分别为14.138 6、78.950 5,大大降低了系统的复杂度;同时,当SNR>16dB时,协作节点的增加有利于提高系统的误码性能,系统的复杂度性能并没有很大的损失.     

协作系统中DMPSK查表调制的译码方案研究

采用一种新的查表差分算法,理论分析得出,此差分算法不仅能降低硬件实现难度,而且在调制端避免了传统差分的数学运算.随后又在检测端针对多符号差分检测(MSDD)复杂度高的问题,提出结合自更新半径的球形译码(Auto-Updating Radius Sphere Detection,AUR-SD)算法的检测策略.仿真表明,结合了此两种算法的方案不仅使得复杂度得到了明显的改善,也使得在性能上相比传统宽度优先球形译码检测算法更加逼近ML算法.因此,可以作为一种较好的方案应用在差分协作系统中.     

空间调制系统下基于硬限制球形译码检测算法的研究

为了解决空间调制系统(spatial modulation,SM)下传统球形译码检测算法(SD)复杂度高的问题,提出了一种将矩阵重组、硬限制算法与球形译码算法结合的低复杂度检测算法(MR-HL-SD).矩阵重组的引入减少了算法的计算量,与硬限制算法的结合进一步降低了算法的复杂度.仿真结果表明,MR-HL-SD算法相对于最大似然检测算法(ML)与球形译码检测算法在保证一定性能的情况下,大大降低了复杂度.     

基于协同优化算法的Reed-Solomon码迭代软判决译码

基于协同优化算法推导出一种Reed-Solomon(RS)码的迭代软判决译码(SDD)算法。该算法属于消息传递算法,具有严格的理论基础。仿真结果表明,该算法相对于硬判决译码(HDD)能够获得有效的软判决译码增益,对于(15,9)RS码在误帧率(FER)为4×10-4时有0.3~1.3dB的增益;同时译码复杂度低,具有很好的工程实用性。此外该算法是一类软输入软输出(SISO)译码算法,能够应用于以RS码为子码的复合码,如级连码和乘积码的迭代译码。     

基于硬判决的BICM-ID系统的迭代载波相位同步算法

在基于迭代译码的比特交织编码调制(BICM-ID)系统中,提出了一种利用译码产生的硬判决信息作引导的迭代载波相位同步的算法.该算法等效于期望最大化(EM)算法,收敛于最大似然(ML)估计,利用Viterbi译码过程中产生的数据比特硬判决信息,通过迭代地在同步和解码之间交换信息来完成联合解码和载波相位同步,实现了联合解码同步.仿真结果验证了该算法的有效性.在相偏θ∈[-20°,20°]时,其误码率性能最佳;在迭代次数达到5次时,误码率性能基本接近理想同步性能,较传统的相位同步算法具有更优的性能.随着信噪比的增大,能更快地逼近理想同步性能.     

比特排序的低复杂度K-best检测算法

为了降低多输入多输出(multiple-input multiple-output,MIMO)系统中K-best检测算法的计算复杂度,提出一种基于硬件操作中比特计数思想的比特排序(bit-sort,BS)K-best算法和一种进一步简化BS K-best算法的动态比特排序(dynamic bit-sort,DBS)K-best算法.这两种算法都是通过依次查找和计数每条路径的累积权重值的对应比特位,从而快速地找出所需的K条最短路径.此外,DBS K-best算法根据路径累积权重的大小只找出不大于K条的最短路径,因此,它比需要找出固定K条最短路径的BS K-best算法更加简便.仿真结果表明,BS K-best算法和DBS K-best算法均可以在逼近次优的球形译码(SD)算法的误码率性能的同时又大大降低了K-best检测算法的计算复杂度,且DBS K-best算法又进一步简化了BS K-best算法的计算.     

基于比特可靠性的LDPC码编译码算法

提出了一种基于比特可靠性的低密度奇偶校验(LDPC)码编码算法和一种加权置信传播(BP)译码算法.该编码算法首先利用蒙特卡罗仿真得到LDPC码各个比特节点的出错概率,然后用已知信息替换易出错比特节点进行编码;该译码算法根据比特节点可靠性的差异,在译码时为每个比特节点赋予相应的权值,以调整它们对译码的影响程度.仿真表明,新的编译码算法使得系统性能大大提高,同时加快了译码迭代收敛速度.     

一种基于极化码APC-SCL的译码算法

极化码在CRC-SCL译码方面需要逐层判决逐比特取值的比特依赖,是整个译码系统复杂度与延迟的主要来源.所以,本文在CRC-SCL译码的基础上提出一种新型的译码算法,即APC-SCL译码算法,并通过理论分析和MATLAB仿真,验证了在码长为1 024情况下译码的性能,在列表长度相同的条件下,APC-SCL译码算法相比CRC-SCL译码平均搜索宽度减少了26.5%,降低了系统复杂度,该算法在低信噪比区间效果更加明显.     

适用于编码MIMO系统的软输出估计算法

提出了适用于检测与译码相级联的编码MIMO系统次最优接收机的软输出估计算法。它利用基于均值软输出估计算法的似然比输出，为译码器组提供软输入信息，使接收机运算量与发射天线的数目呈线性关系。瑞利平衰落环境的仿真结果表明，本文提出的算法与VVA相比，性能虽有一定的损失，但运算量大幅度减少；与采用最大似然检测(MIMO)的次最优接收机相比，其在运算量减少的同时还获得了一定的软输入增益。     

一种新颖的水声相干通信接收算法

为了克服水声信道的多径衰落,消除码间干扰,获得可靠的数据传输,提出了一种新颖的水声相干通信接收算法。该新型算法有两个优点:一是将自适应判决反馈均衡器和迭代译码技术相结合,二是译码采用Turbo译码原理,整个译码系统可以看作是串联迭代译码器,只是其中的内部译码器被编码比特对数似然率(LLR)计算器所取代,有效地降低了运算复杂度。同时,自适应判决反馈均衡器采用了变步长因子算法,改善了均衡器的收敛速度。仿真实验验证了该组合接收算法的性能     

Performance of differential pulse-position modulation (DPPM) with concatenated coding over optical wireless communications [optical wireless communications]

The concatenation of marker and Reed-Solomon codes in order to correct insertion/ deletion errors in differential pulse-position modulation (DPPM) over optical wireless communications is presented. The concatenated code decoding algorithms with hard-decision and soft-decision detection are presented. The performance of the hard-decision coded DPPM system is evaluated over both nondispersive and dispersive channels via analysis and simulation. It is shown that the coding gain provided by the concatenated code is approximately 4 dB when the code rate is about 0.7 and the channel is nondispersive. Over a dispersive channel, the coded system performs better than the uncoded system when the ratio of delay spread to bit duration is not high. A soft-decision detector is employed to combat intersymbol interference. The soft- decision decoding algorithm, which has low complexity and can be practically implemented, is described. The performance over nondispersive and dispersive channels is evaluated by analysis and simulation. It is shown that the soft-decision system requires approximately 2 dB less transmit power than the hard-decision system for additive white Gaussian noise and low-dispersive channels. Soft decoding also provides a performance improvement in high-dispersive channels.     

克隆选择算法在多用户信号检测中的应用

为了减少计算复杂度,改善CDMA(Code Division Multiple Access)系统性能．将具有解决复杂组合优化问题能力的克隆选择算法(CLONALG)应用于码分多址系统多用户信号检测中．确定每一个用户传输的符号位．仿真结果表明,基于克隆选择算法的多用户检测器不仅具有克服多址干扰,抗“远-近效应”的能力,而且通过调整算法参数可以在检测时间和系统平均误码性能间进行均衡,与最佳多用户检测器相比明显地降低了计算复杂度．     

Modified sum-product algorithms for decoding low-density parity-check codes

The authors deal with the sum-product algorithm (SPA) based on the hyperbolic tangent (tanh) rule when it is applied for decoding low-density parity-check (LDPC) codes. Motivated by the finding that, because of the large number of multiplications required by the algorithm, an overflow in the decoder may occur, two novel modifications of the tanh function (and its inverse) are proposed. By means of computer simulations, both methods are evaluated using random-based LDPC codes with binary phase shift keying (BPSK) signals transmitted over the additive white Gaussian noise (AWGN) channel. It is shown that the proposed modifications improve the bit error rate (BER) performance up to 1 dB with respect to the conventional SPA. These results have also shown that the error floor is removed at BER lower than 10^-6. Furthermore, two novel approximations are presented to reduce the computational complexity of the tanh function (and its inverse), based on either a piecewise linear function or a quantisation table. It is shown that the proposed approximations can slightly improve the BER performance (up to 0.13 dB) in the former case, whereas small BER performance degradation is observed (<0.25 dB) in the latter case. In both cases, however, the decoding complexity is reduced significantly     

Iterative reduced-state decoding for coded partial-response channels

The conventional iterative decoding based on the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm rises exponentially in terms of channel memory length. In this paper, we propose a low-complexity soft-input/soft-output (SISO) channel detector based on tentative hard estimates fed back from the outer decoder in the previous iteration. The computational complexity of the proposed detector is polynomial in terms of the channel memory length. To demonstrate the performance/complexity tradeoff of the proposed detector, we present simulation results for 9-tap, 11-tap, and 12-tap channels. We show that the proposed detector significantly reduces the computational complexity with only slight performance degradation compared to the full-complexity BCJR algorithm.     

A hybrid multiuser detector for DS-UWB systems with matched filter and error-bit recognizer

In this article, we propose a hybrid algorithm of multiuser detection (MUD) for direct sequence ultra-wideband (UWB) communication systems, based on matched filters (MF) and error-bit recognizers (ER). The ER embraces three steps: bit mapping, K-means clustering, and sign judgment. In this detector, we construct a mapping function and map the output base-band bits from MFs into a one-dimensional feature space to get the amplitude information. After that, we set an initial value and classify the bits into right bits and wrong ones by K-means clustering. Finally, we make the sign judgment to prevent some right bits being picked out as wrong bits and correct the wrong bits to reduce the bit error rate (BER) of the system. Compared to a conventional detector based on MFs and minimum mean square error detector, to a large extent, our detector can improve the BER performance of a system because of high recognition probability of the wrong bits in K-means clustering. What is more, the simulation results show that the proposed hybrid MUD is not sensitive to the number of users. It can achieve a good BER performance and low computational complexity when there are 20 UWB transmitters in the channel.     

Multilevel spatial modulation

In this paper, a new Multilevel Spatial Modulation technique is proposed. It combines computationally efficient multilevel oding and spatial modulation based on trellis codes to increase coding gain, diversity gain, and bandwidth efficiency. The trellis complexity of the single-stage system increases exponentially, whereas in the proposed multilevel system the complexity increases linearly. The proposed system is analyzed with optimal Viterbi and suboptimal sequential decoding algorithms. The results show that sequential decoding saves 75% of the computational power with a loss of 2 dB SNR approximately, when compared with optimal Viterbi decoding, over both fast- and slow-fading channel conditions. Since the antenna index is used as a source of information in spatial modulation, the number of antennae required increases with the throughput and packing a large number of antennas make cross-correlation unavoidable. In this paper, a low complexity modified decoding technique is also proposed for the multilevel spatial modulation system, in which the correlated received signals are equally combined and decoded by the multistage decoder using the Viterbi algorithm. This technique exploits the receiver antenna correlation and makes the decoding complexity independent of number of antennas. The simulation results indicate that the proposed low complexity algorithm gives approximately 8–10 dB gain when compared with optimal Viterbi decoder with equivalent computational complexity when the eight highly correlated signals are equally combined. This may be a suitable solution for mobile handsets where size and computational complexity are the major issues.     

Internally coded TH?UWB?CDMA system and its performance evaluation

A new time-hopping ultrawideband (TH-UWB) CDMA scheme for indoor wireless communications is presented. In the proposed method, the duration of each bit is divided into Ns₁ frames, each one containing Ns₂ subframes. Two pseudorandom sequences are assigned to each user. During each bit interval, based on the output of a super-orthogonal encoder and the user's first dedicated pseudorandom sequence, the transmitter selects one of the Ns₁ frames and then transmits Ns₂ narrow pulses in that frame, one in each of the Ns₂ subframes. The location of the pulse in each subframe is determined by the user's second dedicated PN sequence. Four different detection techniques are considered at the receiver front end, namely thresholded hard decision, strict hard decision, soft decision and chip-based decision. Their performances are analysed and the results are compared with those of the previously introduced coded and uncoded TH-UWB systems. The results indicate that the proposed scheme has the best performance without requiring any extra bandwidth. It is also shown that the chip-based decoding technique works better in moderate and high SNRs while the soft decision method has better performance in low SNRs.