VBLAST-MC-CDMA系统自适应调制仿真分析

提出一种应用卷积码编码的VBLAST-MC-CDMA系统上行链路结构,并将自适应调制技术应用于上行链路结构中。自适应调制门限的设定采用试验法。先设定需要的误码率门限,并以此为依据通过仿真结果确定系统调制方式的转换门限。通过仿真,分别讨论了用户数固定和用户数变化时该自适应调制系统的误码率性能。仿真结果表明,两种情况下自适应调制都能在不牺牲期望误码率性能的情况下提高系统的频谱效率。     

Pragmatic Approach to Adaptive Turbo Coded Modulation

This paper presents a pragmatic adaptive scheme for TuCM over slowly fading channels. The adaptive scheme employs a single turbo coded modulator composed of a variable-rate turbo encoder and a variable-rate variable-power MQAM for all fading regions, so it has an acceptable complexity to implement. The optimal adaptive TuCM scheme is determined subject to various system constraints. Simulations have been performed to measure the performance of the scheme for different parameters. It is shown that adopting both the turbo coded modulator and the transmit power achieves a performance within 2.5 dB of the fading channel capacity.     

基于LDPC自适应编码调制的图像传输性能

研究了基于LDPC码的自适应编码调制技术及其在慢衰落无线信道图像传输中的应用,分析了确定最优信噪比转换门限集合的最小均方误差非线性曲线拟合法,进而得到基于LDPC码的自适应编码调制系统的最大平均吞吐量性能。仿真结果表明,在慢衰落无线信道图像传输中,系统能获得满意的图像传输质量和很高的频谱利用率。     

SCTCM及其在卫星移动通信信道下的性能分析

串行级联网格编码调制 (SCTCM)的主要构成部分是串行级联卷积码 (SCCC)和网格编码调制 (TCM)技术 ,在这两者的基础上给出了SCTCM基本编译码结构和设计原则。并结合具体的卫星移动通信信道的复杂时变特性 ,对SCTCM在该信道下的误码率 (BER)性能进行了理论分析 ,给出了误码率的一个上界。最后以 6 4状态的TCM为对照 ,进行了计算机仿真。仿真结果说明SCTCM在卫星移动通信中具有重要的应用价值     

UWB信道下的TH-PPM多径多址解调性能分析

分析了超宽带(ultra-wideband,UWB)通信系统在信道同时存在多径、多址干扰,及加性白噪声条件下的相干解调性能,给出了TH-PPM调制在高斯近似下的相干解调BER(biterrorrate)解析公式,分析了采用S-Rake接收下的BER性能,给出了解析表达式。为验证解析式的有效性,对比了系统仿真与解析数值计算的结果。并通过IEEE多径信道模型CM1~CM4、Rake插指数、不同的多址用户数等方面,详细分析和计算了TH-PPM的BER性能,给出了性能曲线。获得的结果为UWB室内高速多址通信系统的设计提供了依据。     

多入多出系统中的自适应比特交织编码调制

提出一种多入多出（M/MO）系统中的自适应空时比特编码调制方案（ST-ABICM）。本方案结合功率、比特分配及比特交织，在满足发射端吞吐量和总功率要求的条件下，使系统的误码率最小。为解决在快衰落信道中比特交织时延和可变速率编码之间的矛盾，提出与删除码结合的空时多层交织器，在实现比特交织的同时，不破坏编码比特位和删除位的位置。在接收端，我们提出一种比特连续干扰抵消（SIC）检测算法，这种算法相比最大似然算法大大降低了运算复杂度。     

基于AF的多相编码脉冲脉内调制参数估计

雷达信号脉内调制参数估计是电子对抗领域的一个重要问题。推导了P4编码脉冲信号模糊函数(ambiguity function, AF)的表达式,得出AF幅度图像上距离主脊线最近的脊线在时延轴和多普勒轴上截距分别等于编码时长和子码率这一结论。采用RAT(Radon ambiguity transform)和图像Radon变换估计信号参数,采用三次多项式插值方法提高估计精度。分析了估计方法应用于不同码型编码脉冲信号的输出信噪比,理论分析和仿真结果都说明,估计算法对P3和Frank编码脉冲比P1、P2和P4有更好的估计性能。     

Resource allocation for cooperative diversity systems based on quadrature modulation

To improve the error performance and the resource utilization of cooperative systems, the optimum resource allocation, i.e., power allocation and partner choice, for an adaptive decode-and-forward (DF) cooperative diversity system based on quadrature modulation is investigated. The closed-form expression of the bit error rate (BER) system performance is derived and an optimal power allocation (OPA) algorithm is proposed to optimize the power allocation between the local and relayed signals under the minimum BER criterion. Based on the OPA algorithm, a partner choice strategy is proposed to determine the partner locations specified by various cooperation gains. Simulation results show that the proposed resource optimization algorithms are superior to the unoptimized algorithms by significantly reducing the BER and improving the cooperative gain, which is useful to simplify the practical partner choice process.     

多载波调制系统中的自适应调制方法

针对数字无线通信系统紧张的频率资源问题,提出了一种应用于多载波调制(multicarrier modula-tion,MCM)系统的自适应调制方法,该方法可提高系统频谱利用率,保证系统的目标BER性能和实现不同重要等级的数据传输。采用功率控制区技术,改善了系统的平均BER或BPS。理论分析与仿真结果均证明了该方法的良好性能。     

A Novel Concatenated Chaotic Communication System

A strategy for a novel concatenated chaotic communication system is presented. The transmitter system comprises chaotic turbo encoder and logistic CSK block in a serially concatenated form. Chaotic turbo code is capable of reducing bit error rate (BER) of the chaotic system in the AWGN channel. Through the chaotic turbo encoder, the coded sequence, which has quasi-chaotic properties, will be transmitted into the logistic CSK block. Having a very sensitive dependence on initial conditions of the map, the logistic CSK block can also be taken as the chaotic authentication method. The receiver, which has logistic demodulation block and chaotic decoder, is a linear asymptotic approximation to the inverse of the transmitter system. A chaotic iterative soft-decision decoding algorithm is also developed based on conventional maximum A posteriori decoding algorithm. At last, a two-step authentication method of this chaotic system is also presented.     

BICM-OFDM中基于ML算法的迭代信道估计

基于最大似然估计(ML),提出了一种新的联合译码的迭代信道估计算法。该算法利用比特交织编码调制(BICM)中迭代译码的硬判决信息,进行信道估计与译码之间的信息交换。在基于BICM的OFDM系统(BICM-OFDM)中,在短波宽带信道下的仿真结果表明,经过4次迭代,系统的误码率性能收敛。与传统ML算法相比,算法可有效的提高估计精度。     

Systematic design of single carrier overlap frequency domain equalization

<正> This paper proposes a systematic design method of overlap frequency domain equalization(FDE) for single carrier (SC) transmission without a guard interval (GI).Based on the analysis of signal-to-interference-plus-noise ratio (SINR) of the equalizer output for each symbol,the authors adaptivelydetermine the block of the overlap FDE,where the block is defined as a set of symbols at the equalizeroutput with sufficiently low error rate,for a certain fixed sliding window size,which corresponds toa fast Fourier transform (FFT) window size.The proposed method takes advantage of the fact thatthe utility part of the equalized signal is localized around the center of the FFT window.In addition,the authors also propose to adjust the block size in order to control the computational complexity ofthe equalization per processed sample associating with the average bit error rate (BER) of the system.Simulation results show that the proposed scheme can achieve comparable BER performance to theconventional SC-FDE scheme with sufficient GI insertion for both the coded and uncoded cases withvarious modulation levels,while requiring lower computational complexity compared to the SC overlapFDE transmission with the fixed block.     

一种极化分集制导雷达及低截获概率信号设计

研究了一种基于极化分集阵列的主动式弹载相控阵雷达及其信号设计问题。阐述了该制导雷达极化分集阵列的设计思想和雷达系统结构;设计的雷达发射信号为：在脉冲内部采用线性调频或者相位编码脉冲压缩信号、在脉冲组之间采用时域波形和极化状态的同时捷变,采用脉冲压缩技术以实现高距离分辨率和探测距离,综合采用脉冲压缩技术和极化编码技术有效提高雷达的低截获概率性能,采用极化估值与检测技术提高雷达的抗干扰能力。建立了双极化发射信号的数学模型,论述了双极化回波信号的处理方法,仿真分析了其抗干扰性能。研究结果表明,该新体制制导雷达具有良好的抗移频干扰和延时干扰的能力,电子战性能更为优良。     

多用户正交差分混沌键控通信系统

针对传统差分混沌移位键控(differential chaos shift keying, DCSK)传输速率较低的问题,提出一种多用户正交DCSK通信系统。该系统通过延迟不同时间区分不同信息时隙,每个信息时隙发送N个用户,有效提升其速率。同时采用正交混沌发生器产生两路正交的混沌信号,彻底消除其信号内干扰,提升系统误码性能。该系统从延迟线数目以及用户数两个方面分析了系统误码率和传输速率。推导在加性高斯白噪声和Rayleigh衰落信道下的误码率公式并进行仿真。仿真结果表明,该系统能够有效改善误码性能和提升速率,具有很好的实用价值。     

群时延失真对QPSK系统误码性能影响的仿真与分析

群时延失真是影响卫星通信误码性能的重要因素之一.首先介绍了群时延的概念和表达式以及卫星信道群时延失真模型,然后根据最小相位系统的系数和复倒谱系数之间的关系,设计了线性群时延和抛物线群时延滤波器,利用MATLAB/SIMULINK仿真软件包,建立了两种群时延失真信道模型,对QPSK调制信号在群时延失真信道特性下进行了仿真,得出了两种群时延失真对系统误码性能的影响.     

Lattice-reduction-aided MMSE precoding for correlated MIMO channels and performance analysis

The lattice-reduction (LR) has been developed to improve the performance of the zero-forcing (ZF) precoder in multiple input multiple output (MIMO) systems. Under the assumptions of uncorrelated flat fading channel model and perfect channel state information at the transmitter (CSIT), an LR-aided ZF precoder is able to collect the full transmit diversity. With the complex LenstraLenstra-Lova′sz (LLL) algorithm and limited feedforward structure, an LR-aided linear minimum-mean-square-error (LMMSE) precoder for spatial correlated MIMO channels and imperfect CSIT is proposed to achieve lower bit error rate (BER). Assuming a time division duplexing (TDD) MIMO system, correlated block flat fading channel and LMMSE uplink channel estimator, it is proved that the proposed LR-aided LMMSE precoder can also obtain the full transmit diversity through an analytical approach. Furthermore, the simulation results show that with the quadrature phase shift keying (QPSK) modulation at the transmitter, the uncoded and coded BERs of the LR-aided LMMSE precoder are lower than that of the traditional LMMSE precoder respectively when E b / N0 is greater than 10 dB and 12 dB at all correlation coefficients.     

Study of adaptive modulation and LDPC coding in multicarrier systems

An adaptive modulation （AM） algorithm is proposed and the application of the adapting algorithm together with low-density parity-check （LDPC） codes in multicarrier systems is investigated. The AM algorithm is based on minimizing the average bit error rate （BER） of systems, the combination of AM algorithm and LDPC codes with different code rates （half and three-fourths） are studied. The proposed AM algorithm with that of Fischer et al is compared. Simulation results show that the performance of the proposed AM algorithm is better than that of the Fischer＇s algorithm. The results also show that application of the proposed AM algorithm together with LDPC codes can greatly improve the performance of multicarrier systems. Results also show that the performance of the proposed algorithm is degraded with an increase in code rate when code length is the same.     

时频栅格误差条件下的双基地MIMO雷达角度估计

研究了时频栅格误差引起的匹配滤波器失配下双基地多输入多输出(multiple-input multiple-output,MIMO)雷达的角度估计问题。首先,建立了存在时延和多普勒频率栅格误差条件下的双基地MIMO雷达信号模型;其次,推导了正交频分复用线性调频信号和相位编码信号的栅格误差失配矩阵,并分析了其对目标收发角度估计的影响;再次,针对正交频分复用线性调频信号,提出了平行因子和最小二乘相结合的发射角度估计算法,该方法能够有效减小栅格误差失配矩阵对发射角度估计的影响;最后,仿真实验表明,栅格误差失配矩阵对相位编码信号的角度估计影响较小,但对正交频分复用线性调频信号的发射角度估计则会产生较大的影响,从而进一步验证了理论分析的正确性。     

New blind adaptive approach to multiuser detection in CDMA systems

Due to a number of advantages, blind adaptive multiuser detector has become a research hotspot in recent years. But low convergence rate problem occurs to many blind adaptive algorithms. A new blind adaptive approach to multiuser detection is presented. The simulation results show that by reasonably choosing time varying step size, the proposed detector can not only improve the convergence rate, but also reduce the bit error rate (BER) of the system, and so it can effectively improve the system performance with less computational cost.     

稀疏码分多址收发端改进方案的设计

为降低传统稀疏码分多址接入(sparse code multiple access,SCMA)系统的译码复杂度,同时保证系统误比特率(bit error ratio,BER)性能,考虑信道质量因素提出SCMA系统收发端改进方案.在接收端,提出基于信道质量动态选择节点改进消息传递算法(message passing al...