一种改进的OvTDM检测算法

重叠时分复用(Overlapped Time Division Multiplexing,OvTDM)技术是一种通过人为引入符号间干扰的超奈奎斯特技术,其通过压缩时限信号的符号间间隔来进一步提升系统传输速率。因其存在的符号间干扰使得其信号检测变得非常复杂,如何开发设计适合OvTDM系统的检测算法是一项重要研究内容。对OvTDM的编码原理、系统模型及其符号特性进行了详细介绍,并结合互信息理论来分析OvTDM系统容量。此外,基于噪声相关性分析的基础上提出一种改进的MIMO相关检测算法。该算法利用符号相关性作为检测约束条件,采用迭代消除的方式对检测符号进行逐位检测,降低了信号的检测复杂度;同时该算法采用了串行干扰消除的思想进一步降低误差传播问题的影响,使之更加适合OvTDM系统的信号检测。数据仿真结果表明,所提算法相较于常规的ZF算法在检测性能方面具有优势。

Bidirectional Viterbi Decoding Algorithm for OvTDM

Overlapped time domain multiplexing(OvTDM)is an innovative encoding scheme that can obtain high spectral efficiency.However,the intentional inter-symbol interference(ISI)caused by OvTDM will make the decoding process more complex.The computational complexity of maximum likelihood sequence detection increases exponentially with the growth of spectral efficiency in OvTDM.As a consequence of high complexity,the decoding effort for a given spectral efficiency may occasionally exceed the physical limitations of the decoder,leading inevitably to buffer overflows and information erasures.In this paper,we propose a bidirectional Viterbi algorithm(BVA)based on the bidirectional sequence decoding for OvTDM.With the BVA,the decoding operation starts simultaneously from the both ends of the corresponding trellis and stops at the middle of trellis.The simulation results show that compared with Viterbi algorithm(VA),the decoding time of BVA can be reduced by about half.And the memory space of two decoders in BVA are about half of that in VA,which means that the BVA has lower memory requirements for decoder.And the decoding performance of BVA is almost the same as VA.

Performance of Gaussian waveform in OvTDM

Waveforms play a key role in overlapping time division multiplexing （OvTDM） system. The OvTDM has been proved to be a novel transmission technique that can utilize time diversity to improve the bit error ratio （BER） performance in Rayleigh channel. According to the resulted law, the BER performance of Gaussian waveform in OvTDM also improves with the increase in the waveform parameter monotonically, and the rectangular waveform is the worst case of Gaussian waveform. In contrast, the spectrum effectiveness of Gaussian waveform OvTDM decreases with the increase in the waveform parameter. In the study, it is obtained that waveforms can achieve the best performance when the smallest correlation coefficient between neighbor symbols is e^-1 .

Decoding OvTDM with sphere-decoding algorithm

Overlapped time division multiplexing （OvTDM） is a new type of transmission scheme with high spectrum efficiency and low threshold signal-to-noise ratio （SNR）. In this article, the structure of OvTDM is introduced and the sphere-decoding algorithm of complex domain is proposed for OvTDM. Simulations demonstrate that the proposed algorithm can achieve maximum likelihood （ML） decoding with lower complexity as compared to traditional maximum likelihood sequence demodulation （MLSD） or viterbi algorithm （VA）.

空地高速数据传输研究

针对高速空地数据传输时由于地面反射产生信号衰落、引起码间干扰的问题,阐述了空地数据传输的二径模型、信号衰落的模式及特点;在此基础上,对QPSK、QAM和OVTDM 3种调制体制进行了分析;使用MATLAB对3种调制方式在二径模型下信号的码间干扰进行了仿真、比较,并给出了一种2符号OVTDM的信号波形。仿真及分析结果表明,2符号OVTDM的码间干扰和波形畸变小,频谱利用率高,性能优于QPSK和16QAM。

时频二维重叠复用系统

基于时域重叠复用和频域重叠复用的思想,该文提出了时频二维重叠复用系统——OvHDM系统。研究了OvHDM系统的最佳检测、频谱效率、复杂度、性能以及峰均比。OvHDM系统模型是向量卷积编码约束模型。为了检测OvHDM信号,提出了向量空间上的最大似然序列检测算法,MU-MLSD。计算机仿真证明:频谱效率为6bit/(s?Hz)时,OvHDM较64QAM具有4.5dB的功率增益,较OvTDM也有1.5dB的功率增益;同时,OvHDM的峰均比较128个子载波的OFDM有2dB的增益,较1024个子载波的OFDM有2.6dB的增益。

波形对重叠时分复用符号差错率的影响

为了深入研究重叠时分复用系统,通过已有的理论界推导了影响系统符号差错概率的关键因素,由此解析地研究了指数波形、高斯波形和矩形波形对重叠时分复用符号差错概率的性能影响。在加性白高斯噪声信道和瑞利信道的仿真分别验证了这种分析。结果表明:无论是在加性白高斯噪声信道还是在瑞利信道,重叠时分复用系统的符号差错率随着波形参数的增加而单调减小。因此采用截断指数波形和高斯波形的重叠时分复用系统比采用矩形波形的重叠时分复用系统更灵活,性能更好。

A Novel High Spectral Efficiency Waveform Coding-OVFDM

Based on the Overlapped Multiplexing Principle[12],a frequency domain OVFDM(Overlapped Frequency Domain Multiplexing) Coding is proposed.By the data weighted shift overlapped version of any band-limited Multiplexing Transfer Function H(f) the coding gain and spectral efficiency are both achieved.The heavier the overlap of the data weighted Multiplexing Transfer Function H(f),the higher the coding gain and spectral efficiency as well as the closer the output to the optimum complex Gaussian distribution.The bit error probability performance is estimated.The time domain OVTDM(Overlapped Time Domain Multiplexing) Coding,the dual of OVFDM in time domain is incidentally proposed as well.Both theoretical analysis and testified simulations show that OVFDM(OVTDM) is suitable for high spectral efficiency application and its spectral efficiency is only roughly linear to SNR rather than the well-known logarithm to SNR.

残余频偏对重叠复用信号接收性能的影响分析

主要研究AWGN信道下,残余频偏对重叠时分复用(OvTDM)信号接收的性能影响;同传统的QAM技术相比,OvTDM是一种可以获得高频谱效率的传输技术,它通过引入符号码间串扰,并利用符号间互扰的约束特性来实现更高传输速率。在一个实际通信系统中,接收信号不可避免的会受到系统载波频偏的影响,从而影响信号的接收性能。因此,分析了系统残余频偏对OvTDM的性能影响,对比了相同条件下QAM信号性能,研究结果表明,在相同的信噪比和残余频偏条件下,OvTDM信号具有更好的误码性能。

一种基于消息传递的时域重叠复用译码算法

时域重叠复用(Overlapped Time Division Multiplexing,OvTDM)技术作为一种非正交的传输技术,人为地引入了符号间干扰来实现高传输速率,但这也使得OvTDM系统在进行最大似然序列检测时面临着极高的运算复杂度。为解决这一问题,研究了OvTDM系统的卷积编码方式,利用发送序列和接收信号之间的关系构建了对应的因子图模型,结合消息传递的原理,提出了一种基于消息传递的OvTDM系统译码算法。该算法通过节点之间信息的不断迭代更新来实现信号的检测。最后,对该算法的性能进行了仿真和分析,并与Fano算法进行比较,仿真结果表明该算法的译码性能优于Fano算法并且具有很低的计算复杂度。

Semidefinite programming detection for OvHDM signal

Non-orthogonal time-frequency division multiplexing （NTFDM） transmission scheme has been proposed to further improve the bandwidth efficiency and overcome the drawbacks of the conventional orthogonal frequency division multiplexing （OFDM） method. Based on such approach, the fast signal detection algorithm, semidefinite programming （SDP） detection, has been studied. As the coefficient matrix tends to be ill conditioned, the modified SDP algorithm combined with successive interference cancellation （SIC） has been developed. The improved algorithm is a good tradeoff between performance and detection complexity. Simulation results show that the proposed algorithm can achieve better performance than cutting plane aided SDP method.