基于二维格星座对SCMA码本的一种设计方法

现有的SCMA(稀疏码分多址)码本采用高维复数星座和映射矩阵相结合的设计方法,存在高维复数星座设计过程复杂,且任意时频资源星座图星座点间的最小欧式距离难以控制的问题。针对上述问题提出了一种基于时频资源星座的码本设计方法。首先设计一个二维格星座,然后通过星座优化和扩频得到特定用户的码本。所提方法不仅可以获得最大成形增益和最大最小欧式距离的合成星座图,还能使SCMA系统性能随着码本维度的增加而提升。仿真结果表明:在高斯信道下,提出的码本较现有的码本有效提升了系统性能。     

一种稀疏码本多址接入码本优化设计方法

稀疏码多址接入(SCMA)作为一种具有竞争力的非正交多址接入(NOMA)技术,该技术通过高维调制与稀疏扩频的结合,有效地提升了系统的频谱效率。该文针对现有SCMA码本设计中存在的问题,提出一种同时适用于高斯信道和瑞利衰落信道的SCMA码本优化设计方法。在该方法中,首先通过旋转基准星座和母星座,实现母星座在各个维度上投影点间的最小欧氏距离以及叠加在单个资源块上的总星座中与各用户对应的星座图上星座点间的最小欧氏距离的最大化,以提升SCMA码本在高斯信道下的性能;进而在保持总星座上星座点间最小欧氏距离不变的条件下,通过旋转叠加在单个资源块上多个用户的星座,优化叠加在单个资源块上的与各用户对应的星座图中星座点间最小乘积距离和信号空间分集(SSD)阶数,最后结合Q路坐标交织技术获得额外的分集增益,以提升系统抗信道衰落的能力。仿真结果显示:在高斯信道和瑞利衰落信道下,该文设计的SCMA码本的性能均明显优于华为公司提出的SCMA码本和低密度扩频多址接入(LDS-MA)技术。     

基于Anti-Gray映射的4D-QPSK星座设计

多维映射通过增加星座的维度数而使得符号间的平均欧式距离大大增加,这可以大程度地提高数字通信系统的可靠性。然而已有的基于Gray映射的4D-QPSK星座在设计上,并没有充分利用四维星座的空间优势,对于相邻星座点的汉明距离并未达到最大。提出一种基于Anti-Gray映射的4D-QPSK星座设计方案,该方案中的比特映射方式按照相邻星座点汉明距离最大,汉明距离为1的星座点欧式距离最大的设计原则,使星座点间具有最大的分集度。仿真结果表明,该方案可以提高抵抗衰落信道的能力。     

SER‐Based Relay Selection for Two‐Way Relaying with Physical Layer Network Coding

To enhance the symbol error rate (SER) performance of the two‐way relay channels with physical layer network coding, this letter proposes a relay selection scheme, in which the relay with the maximal minimum distance between different points in its constellation among all relays is selected to assist two‐way transmissions. We give the closed‐form expression of minimum distance for binary phase‐shift keying and quadrature phase‐shift keying. Additionally, we design a low‐complexity method for higher‐order modulations based on look‐up tables. Simulation results show that the proposed scheme improves the SER performance for two‐way relay networks.     

Multilevel codes for unequal error protection

Two combined unequal error protection (UEP) coding and modulation schemes are proposed. The first method multiplexes different coded signal constellations, with each coded constellation providing a different level of error protection. In this method, a codeword specifies the multiplexing rule and the choice of the codeword from a fixed codebook is used to convey additional important information. The decoder determines the multiplexing rule before decoding the rest of the data. The second method is based on partitioning a signal constellation into disjoint subsets in which the most important data sequence is encoded, using most of the available redundancy, to specify a sequence of subsets. The partitioning and code construction is done to maximize the minimum Euclidean distance between two different valid subset sequences. This leads to ways of partitioning the signal constellations into subsets. The less important data selects a sequence of signal points to be transmitted from the subsets. A side benefit of the proposed set partitioning procedure is a reduction in the number of nearest neighbors, sometimes even over the uncoded signal constellation     

稀疏码分多址系统一种改进的检测算法

稀疏码分多址(SCMA)系统中基于球形译码算法(SD)由于具有优良的性能受到越来越多的关注,然而现有基于SD的算法只能用于某些特定星座结构的检测,导致其应用受限。该文提出一种适用于任意星座且性能达到最大似然(ML)算法性能的改进球形译码(ISD)算法。该算法将用户星座图拆分,并将用户星座图转换为多层树结构,利用对树结构的搜索完成译码操作,并且对树的搜索是从高层向低层进行的。因此,可以将SCMA检测转换成最小化树结构部分度量问题;同时,所提出的改进算法对星座图的结构无任何限制,所以该算法适用于任意类型的星座图。此外,由于SCMA的稀疏性,每一层的部分度量均与分配给每个资源元素的用户无关,从而进一步降低了计算复杂度。     

Trellis-coded vector quantisation based on modified set partitionmethod and partial vector search scheme

An efficient trellis-coded vector quantisation (TCVQ) algorithm based on the modified set partition method and partial distance search scheme is presented. Using the modified set partition method, the minimum distance within a subset can be maximised as much as possible, thus improving the performance of the TCVQ. A novel partial distance search method based on the codebook structure of TCVQ is also proposed to reduce the computational complexity of the minimum distortion encoding for TCVQ. Experimental results show that it can reduce the computational complexity by ~60-90% depending on the codebook size     

A coding and Modulation scheme for HDTV services in DMB-T

In this paper a channel coding and modulation scheme for providing HDTV broadcasting services is presented, which adopts BICM structure as inner code in connection with 64QAM constellation and OFDM transmission. A new mapping method is designed to maximize the minimum Euclidean distance between signal points divided by feedback bits, thus an iterative algorithm between demodulator and decoder can be performed to acquire performance improvement. Analysis, simulation and laboratory test results have proved that the proposed system has good SNR performance in both AWGN and multipath channels.     

On block-coded modulation with interblock memory

Block-coded modulation with interblock memory (BCMIM) is a variation of block-coded modulation (BCM) which is designed for multilevel coding. By providing interblock memory between adjacent blocks, the coding rate of a BCMIM scheme can be increased without decreasing the minimum squared Euclidean distance (MSED) as compared to the original BCM. In an early version of BCMIM, interblock coding is provided only between the first two coding levels of adjacent blocks. In this paper, we design BCMIM with a more general form for which interblock coding can be introduced among many coding levels. In this way, we can further increase the coding rate of BCMIM without decreasing the MSED. We provide many examples to show the advantages of BCMIM with the general form. Most of the examples are designed based on multidimensional signal sets, since a multidimensional signal set can provide more coding levels than a two-dimensional (2-D) signal set     

一种多符号网格码与差分空时分组码级连方法

我们提出了一种多符号网格码(MTCM)与差分空时分组码级连的传输方法,研究了在传输信道是慢时变平坦瑞利衰变的条件下,并采用理想交织时系统的性能。导出了这个级连系统的成对错误概率上限表达式,分析表明,系统的性能主要受到不同信号序列间的最小汉明矩离和信号星座间的平方欧几里德矩离的影响。仿真结果表明,在相同的频谱有效性和信号星座条件下,这种级连的系统比非级连差分空时编码系统有更好的性能。     

上行SCMA系统的动态子图检测算法

面对未来网络需求量的爆炸性增长,稀疏码多址接入（Sparse Code Multiple Access,SCMA）作为一种基于码本的非正交多址技术,在用户连接数、频谱效率和低时延都有很大的提升。由于码字的稀疏性,SCMA采用消息传递算法（Message Passing Algorithm,MPA）实现多用户检测,但是复杂度还是相对较高,以至于很难应用于实际系统。为了解决上述问题,提出了一种动态子图消息传递算法（Dynamic Sub-graph Message Passing Algorithm,DS-MPA）进行信号检测。DS-MPA利用剩余值来确定下一次迭代的子图,减少了资源节点的更新用户数量,达到了降低复杂度的目的。仿真结果显示算法性能几乎无损并且降低了1/3左右的复杂度。     

一种改进基于门限的稀疏码多址接入低复杂度多用户检测算法

稀疏码多址接入(Sparse Code Multiple Access, SCMA)作为一种基于多维码本的非正交多址技术,能有效满足5G的巨连接、高频谱效率和毫秒级时延需求。针对基于门限的消息传递算法(Message Passing Algorithm, MPA)存在低门限时误比特率(Bit Error Rate, BER)较高的问题,该文提出一种改进的SCMA多用户检测算法。所提出的算法在基于门限MPA的基础上,增加了对用户节点稳定性必要条件的判决,即只有符合门限条件并通过用户节点稳定性必要条件判决的用户才能被提前解码。这提高了提前判决码字的可靠性并减少了因变相硬判的检测机制造成的后验软信息损失。与基于门限的MPA相比,所提出的算法可使消息在低门限时迭代得更加充分,从而在低门限时仍然能够使SCMA用户获得较好的BER性能。仿真结果表明,在低门限时采用该文所提出的算法SCMA用户BER性能明显好于仅采用基于门限的MPA的BER性能。     

Joint optimization of VQ codebooks and QAM signal constellationsfor AWGN channels

A joint design scheme has been proposed to optimize the source encoder and the modulation signal constellation based on the minimization of the end-to-end distortion including both the quantization error and channel distortion. The proposed scheme first optimizes the vector quantization (VQ) codebook for a fixed modulation signal set, and then the modulation signals for the fixed VQ codebook. These two steps are iteratively repeated until they reach a local optimum solution. It has been shown that the performance of the proposed system can be enhanced by employing a new efficient mapping scheme between codevectors and modulation signals. Simulation results show that a jointly optimized system based on the proposed algorithms outperforms the conventional system based on a conventional quadrature amplitude modulation signal set and the VQ codebook designed for a noiseless channel     

On space-time code design

It is shown that the separation between space-time code matrices can be described in terms of a metric of Euclidean type, which is defined via the singular values of difference code matrices, and arises naturally from a minimization of the pairwise error probability. Essentially, the distance between complex space-time code matrices is the Euclidean distance between the respective - demultiplexed and concatenated - transmit antenna streams, expressed in terms of the structure inherent to the multiple antenna arrangement. It is further shown that the determinant criterion can be strengthened, in a manner that not only suggests an optimum space-time code matrix structure, but also outlines the central role played by the Euclidean distance in quasi-static fading. Theorem 5 - which claims that in order to optimize the product distance one must optimize the Euclidean distance -establishes a close interdependence between product and Euclidean distances; it thereby links the performance determining factors in quasi-static and independent fading, and rigorously establishes the relevance of combining space-time coding and modulation in fading environments. A multidimensional space-time constellation for two transmit antennas, and its coset partitioning-based on traces of differences between constellation matrices-are described. Example codes constitute the first reporting of a space-time coded modulation scheme for fading channels, whereby a space-time constellation is partitioned in cosets.     

Interlevel‐correlated orthogonal space–time block codes based on the expanded signal constellation

Orthogonal space–time block codes provide full diversity with a very simple decoding scheme. However, they do not provide much coding gain. For a given space–time block code, we combine several component codes in conjunction with set partitioning of the expanded signal constellation according to the coding gain distance (CGD) criterion. By providing proper interlevel coding between adjacent blocks, we can design an orthogonal space–time block code with high rate, large coding gain, and low decoding complexity. The error performance of an example code is compared with some codes in computer simulation. These codes are compared based on the situation of the same transmission rate, space diversity order, and state complexity of decoding trellis. Copyright © 2010 John Wiley & Sons, Ltd.     

大规模MIMO系统多用户PSK调制方案的优化

针对超可靠低时延通信短包传输特征,在大规模多输入多输出( Multiple-Input Multiple-Output,MIMO)上行链路系统中,利用较低导频开销来设计相移键控( Phase Shift Keying,PSK)调制方案,并对该方案进行优化兼顾无线链路传输的可靠性.首先,在接收端构建基于最小欧式距离的非相...     

Optimal precoding for orthogonalized spatial multiplexing in closed-loop MIMO systems

In this paper, we propose a new precoding algorithm for orthogonalized spatial multiplexing (OSM) systems over flat-fading multiple-input multiple-output (MIMO) channels. The OSM scheme was recently introduced for closed-loop MIMO systems which allows single symbol decodable maximum likelihood detection. To further improve the performance of the OSM system, we propose a new precoding method by maximizing the minimum Euclidean distance between constellation points in the effective channel. In order to efficiently identify the parameters of a precoder which maximizes the minimum distance, we introduce a partitioning approach. Through analysis, it is shown that one real value parameter and two bits are required for feedback information for precoding in 16-QAM systems. Simulation results demonstrate that our algorithm provides 9 dB and 7.5 dB gains at a bit error rate (BER) of 10^-4 over the conventional OSM systems for 4-QAM and 16-QAM, respectively. We also confirm that the performance of the proposed scheme is the same as that of the optimum closed-loop MIMO systems in terms of the minimum distance. Consequently, our precoding algorithm significantly improves the system performance with a small increase of feedback amount.     

基于星座图对射频指纹识别方法的研究

针对星座图的射频(RF)指纹识别方案中,低信噪比环境下识别准确率低的问题,提出一种基于欧式距离与幅度距离的二维识别算法来进行RF指纹识别。该方案通过对星座图进行优化处理,可从优化后的星座图中提取识别性能更好的RF指纹,再通过二维识别算法来提高识别准确率。仿真结果表明:与仅用欧式距离作为判断依据的方法相比,所提出的二维识别算法的识别准确率最高可提升8%,在设备容量为50组的情况下识别准确率为77.8%,并且从优化后的星座图中所提取的RF指纹具有更好的唯一性和稳定性。     

Trellis-coded differential unitary space-time modulation over flat fading channels

Coding and modulation for multiple-antenna systems have gained much attention in wireless communications. This paper investigates a noncoherent trellis-coded scheme based on differential unitary space-time modulation when neither the transmitter nor the receiver know the channel. In a time-varying flat Rayleigh fading environment, we derive differentially noncoherent decision metrics and obtain performance measures for systems with either an ideal interleaver or no interleaver. We demonstrate that with an ideal interleaver, the system performance is dominated by the minimum Hamming distance of the trellis code, while without an interleaver, the performance is dominated by the minimum free squared determinant distance (a novel generalization of the Euclidean distance) of the code. For both cases, code construction is described for Ungerboeck-type codes. Several examples that are based on diagonal cyclic group constellations and offer a good tradeoff between the coding advantage and trellis complexity are provided. Simulation results show that, by applying the soft-decision Viterbi decoder, the proposed scheme can achieve very good performance even with few receive antennas. Extensions to trellis-coded differential space-time block codes are also discussed.     

A Coding Algorithm for Constant Weight Vectors: A Geometric Approach Based on Dissections

We present a novel technique for encoding and decoding constant weight binary vectors that uses a geometric interpretation of the codebook. Our technique is based on embedding the codebook in a Euclidean space of dimension equal to the weight of the code. The encoder and decoder mappings are then interpreted as a bijection between a certain hyper-rectangle and a polytope in this Euclidean space. An inductive dissection algorithm is developed for constructing such a bijection. We prove that the algorithm is correct and then analyze its complexity. The complexity depends on the weight of the vector, rather than on the block length as in other algorithms. This approach is advantageous when the weight is smaller than the square root of the block length.