基于天底点的二相编码解调算法及实现

针对雷达高度表二相编码回波信号受多普勒和回波相位差双重调制问题,在深入分析雷达高度表回波信号模型及回波功率分布特征的基础上,提出了基于天底点的二相编码解调算法。该算法通过检测天底点回波中的多普勒和相位差信息,进行相应补偿从而实现码解调。仿真和实验表明:该算法多普勒频率检测误差小于20 Hz,相位检测误差小于2°,可有效实现码解调。     

极小BTb参数GMSK信号的非相干解调

针对高斯滤波器与码元间隔乘积极小（BTb≤1/6）的最小高斯频移键控（GMSK）信号解调,研究了基于1比特相位差分、2比特相位差分和基于维特比（Viterbi）检测算法的相位差分的解调方法,给出了不同了BTb下维特比检测的状态转移计算方法,有效的克服了极小BTb参数引入的码间串扰对解调误比特率的影响。仿真结果表明,在BTb=0.15的情况下,采用基于2比特相位差分的维特比检测（截断长度为4Tb）是较好的解调方案。     

基于相位变化率的三维定位技术

传统的无源定位方法定位时间长、定位精度较低。文中针对该问题,提出了一种基于相位差变化率的三维定位方法,该方法通过三单元天线阵获取相位差变化率,实现了辐射源定位,其定位精度高、定位速度快。同时分析了定位误差与测量误差的关系,给出了定位误差表达式。通过仿真分析了相位差测量误差以及相位差变化率测量误差对于定位精度的影响,仿真结果表明,相位差变化率误差对定位精度的影响最大,是制约精度提高的主要因素。     

使用偏振盘的角度位置传感器

本专利阐述一种使用带码道偏振盘的角位置传感器。大部分角位置编码器由一个或多个圆形码道组成的,包含相当大数量的线,通过探测系统可以获得码盘的编码信息。通     

脉冲激光测距机靶标调向光轴平行性检测方法研究

提出一种基于靶标调向装置的脉冲激光测距机光轴平行性检测方法。靶标十字分划中心分别与脉冲激光测距机白光瞄准光轴十字分划中心和激光发射光轴光斑中心对准,通过读取码盘数据计算光轴平行性误差。该方法操作简单,能够实时定量地检测光轴平行性误差,有效地提升了检测精度,实现了光轴平行性检测的数字化、自动化。     

基于曲线拟合的单脉冲跟踪系统校相方法

针对目前单通道单脉冲跟踪系统传统校相方式的不足,提出了一种基于曲线拟合理论的校相方法.阐述了单通道单脉冲跟踪系统的工作原理,分析了跟踪过程中误差电压收敛曲线特性与和差通道相位差之间的对应关系,并以仿真曲线为例,讨论了和差通道相位差对误差电压收敛曲线及跟踪效果的影响;基于曲线拟合理论,提出了利用对星跟踪过程中的误差电压数据进行相位差校准的算法,并设计了校相实现方案;最后通过仿真验证了该方法的有效性.     

改进相位差分法实现步进频雷达测速研究

目前利用相位差分法实现调频步进雷达测量目标径向速度的研究,针对目标相邻回波信号建立了模型,并利用回波信号的相位差分信息估算目标速度.首先对原算法所建信号模型和公式推导进行分析,论证了原算法在相位差分运算方面和测距误差评估方面的不足,然后提出一种在一级脉压后进行相位差分的改进算法.并进一步分析了测距误差对该算法得到的估计速度的影响,最后提出利用最小波形熵法减小估计速度误差的方法.通过仿真试验证明了该方法的有效性.     

直接序列扩频通信系统中PN码相位的精确测量方法

本文提出了一种精确测量本地PN码和输入PN码相位差的方法,这种方法结合了数值分析算法和数字信号处理技术,通过对鉴相单元输出值的处理得到很高的测量精度,并且由于这种方法为全数字方法,可以用FPGA、DSP等处理芯片方便地实现。文中给出了计算机仿真的结果,并根据仿真结果分析了此方法的准确度和抗噪声性能。这种方法在伪码测距、高精度伪码捕获跟踪、差分定位等领域中有很大的应用价值。     

一种高精度求解入射角的新方法

提出了通过相位差计算入射角的方法。不再将正弦函数作为相位差与入射角的关系,而是通过数据拟合的方法求出两者的函数关系,从而减小了相位差斜率线性度差带来的测向误差。通过综合分析不同基线的多个模糊角的相互关系解决了测向模糊的问题,使布阵更具灵活性。仿真和实测结果显示,该方法能解模糊,并提高测向精度。     

卫星测控侦察中相位编码信号的调制识别

针对卫星测控链路中常用的数字调相信号BPSK、QPSK、OQPSK（偏移QPSK）和UQPSK（非平衡QPSK）的调制识别问题，提出了基于二阶矩和相位差统计特性的分类算法。该方法首先以二倍码速率对复基带信号进行采样，然后利用能量归一化的二阶矩的模和相邻样点相位差绝对值的统计特性，分两个等级实现对这四种信号的分类。分析了载频偏移、相位误差以及成形脉冲对分类算法性能的影响，并通过计算机仿真验证了算法的有效性。     

Optimal resource allocation for wireless video over CDMA networks

We present a multiple-channel video transmission scheme in wireless CDMA networks over multipath fading channels. We map an embedded video bitstream, which is encoded into multiple independently decodable layers by 3D-ESCOT video coding technique, to multiple CDMA channels. One video source layer is transmitted over one CDMA channel. Each video source layer is protected by a product channel code structure. A product channel code is obtained by the combination of a row code based on rate compatible punctured convolutional code (RCPC) with cyclic redundancy check (CRC) error detection and a source-channel column code, i.e., systematic rate-compatible Reed-Solomon (RS) style erasure code. For a given budget on the available bandwidth and total transmit power, the transmitter determines the optimal power allocations and the optimal transmission rates among multiple CDMA channels, as well as the optimal product channel code rate allocation, i.e., the optimal unequal Reed-Solomon code source/parity rate allocations and the optimal RCPC rate protection for each channel. In formulating such an optimization problem, we make use of results on the large-system CDMA performance for various multiuser receivers in multipath fading channels. The channel is modeled as the concatenation of wireless BER channel and a wireline packet erasure channel with a fixed packet loss probability. By solving the optimization problem, we obtain the optimal power level allocation and the optimal transmission rate allocation over multiple CDMA channels. For each CDMA channel, we also employ a fast joint source-channel coding algorithm to obtain the optimal product channel code structure. Simulation results show that the proposed framework allows the video quality to degrade gracefully as the fading worsens or the bandwidth decreases, and it offers improved video quality at the receiver.     

基于相位调制技术的可见光通信系统码间干扰识别研究

室内可见光通信系统的传输信道易受到多径效应产生严重码间干扰,降低通信质量,为此提出了相位调制技术的可见光通信系统码间干扰识别方法.通过构建可见光通信系统信道模型,针对信道光源之间在时域和频域上形成的重叠光信号在多径效应作用下,产生的码间干扰,利用位调制技术对系统信道展开均衡设计,并依照多径扩展统计限定码元速率均值,实现...     

Erasure decoding in burst-error channels

Burst-error channels have been used to model a large class of modern communication media, and the problem of communicating reliably through such media has received much study [1]-[9]. Existing techniques include two-way communication schemes that involve error detection and retransmission, and schemes that utilize error correcting codes in code interleaving. The error-detection and retransmission scheme is simple, but its applicability has been restricted to limited environments. On the other hand, the concept of code interleaving has proved to be versatile and effective. Code interleaving distributes the error detection and correction burden among the component codes and thus lowers the overall redundancy requirement. However, the memory characteristics of the burst-error channel have not been used. This omission has prompted the investigation presented in this paper to utilize the inherent information embedded in the code interleaving scheme when used with burst-error channels. The concept of erasure decoding is introduced, leading to some useful coding and decoding strategies. Theoretical formulations are devised to predict code performance, and their validity is verified with computer simulations.     

Performance Analysis of a Complex Multicode Tracking Loop in Bandlimited Rayleigh Fading Channels

This paper presents the root-mean-squared tracking error performance analysis of a class of coherent digital delay-locked loops for multicode direct sequence spread spectrum signals in bandlimited correlated Rayleigh fading channels. In the transmit side, multiple independent PSK-modulated data streams in the in-phase and qudrature phase branches are spread by short mutually orthogonal codes before being further complex spread by a long complex PN code. We assume that the system employs a pilot code channel to assist the receiver’s synchronization and channel estimation. The proposed code tracking loop incorporates the pilot-aided channel estimator and derives the timing error from all short-code-spread subchannels. Our analysis takes into account the effects of imperfect channel estimate, correlated frequency selective Rayleigh fading and band-limiting. Numerical results are presented to quantify the impact of the resulting multipath interference within the same code channel and amongst different code channels.     

Hybrid ARQ schemes for point-to-multipoint communication overnonstationary broadcast channels

Hybrid automatic-repeat-request (ARQ) error control schemes make use of both error detection and error correction in order to achieve high throughput and low undetected error probabilities on two way channels. Two hybrid ARQ schemes, termed hybrid go-back-N (HGB- N) and hybrid selective-repeat (HSR), are proposed for point-to-multipoint communications over broadcast channels. Both schemes incorporate a concatenated code for error correction and error detection. The performance study of the hybrid schemes is based on a two-state Markov model of a burst noise channel. An analytic solution is derived for the throughput efficiency of the HSR scheme, while approximations and computer simulation are used to evaluate the throughput efficiency of the HGB-N scheme. It is shown that the schemes perform considerably better than the corresponding pure ARQ schemes in which a block code is used for error detection only, especially in environments with a large number of receivers and large channel roundtrip delays, such as satellite broadcast links     

The design of joint source and channel trellis waveform coders

The generalized Lloyd algorithm is applied to the design of joint source and channel trellis waveform coders to encode discrete-time continuous-amplitude stationary and ergodic sources operating over discrete memoryless noisy channels. Experimental results are provided for independent and autoregressive Gaussian sources, binary symmetric channels, and absolute error and squared error distortion measures. Performance of the joint codes is compared with the tandem combination of a trellis source code and a trellis channel code on the independent Gaussian source using the squared error distortion measure operating over an additive white Gaussian noise channel. It is observed that the jointly optimized codes achieve performance close to or better than that of separately optimized tandem codes of the same constraint length. Performance improvement via a predictive joint source and channel trellis code is demonstrated for the autoregressive Gaussian source using the squared error distortion measure.     

准分布式光纤振动传感系统信号增益均衡及稳定技术

针对准分布式光纤振动传感系统的各传感通道的增益差异,提出一种基于PI算法的多路信号增益均衡及稳定技术。通过合理设置算法的调节时间,确保传感系统正常工作的同时,消除了因光波偏振、相位等参数缓慢变化引起的增益变化。实验结果表明,四通道的复用系统,不同通道的最大增益差是1.6V;每个通道增益波动幅度最大是2.3V,波动周期是0.23h。选取合适的PI控制器参数K_P=0.01,K_I=0.1,此时,PI算法的调节时间大约为4s,增益波动幅度小于0.2V。     

A moment-based blind method for identification of FIR down-linkDS-CDMA channels

In order to achieve lower bit error rates (BERs), multiuser detection techniques have been proposed. Generally, multiuser detectors can provide excellent performance only when channel parameters are precisely known. In this paper, we propose a moment-based blind method to estimate down-link channels precisely. The mean square error (MSE) expression of the channel vector estimate has been derived. Through simulations, we show the effect of the channel estimation error on the performance of a multiuser detector. In this paper, we also show that finite impulse response (FIR) channels can be blindly identified by using the proposed method and the spreading operation. Since the spreading operation of the code division multiple access (CDMA) can induce cyclostationarity, any FIR channel can be identified by the proposed method. Of course, in order to guarantee identifiability, some conditions on the spreading codes will be satisfied. In this paper, these conditions are also found     

Error probability of coded STBC systems in block fading environments

In this letter, a union bound on the error probability of coded multi-antenna systems over block fading channels is derived. The bound is based on uniform interleaving of the coded sequence prior to transmission over the channel. Using this argument the distribution of error bits over the fading blocks is computed and the corresponding pair wise error probability (PEP) is derived. We consider coded systems that concatenate a binary code with a space-time block code (STBC). Coherent detection is assumed with perfect and imperfect channel state information (CSI) at the receiver, where imperfect CSI is obtained using pilot-aided estimation. Under channel estimation environments, the tradeoff between channel diversity and channel estimation is investigated and the optimal channel memory is approximated analytically. Results show that the performance degradation due to channel memory decreases as the number of transmit antennas is increased. Moreover, the optimal channel memory increases with increasing the number of transmit antennas.     

Maximum-likelihood differential detection of uncoded and trelliscoded amplitude phase modulation over AWGN and fading channels-metricsand performance

This paper derives metrics for maximum-likelihood differential detection of uncoded and trellis coded MPSK and QAM transmitted over Rayleigh and Rician fading channels. Receiver structures based on these metrics are proposed and their error probability performance analyzed and/or simulated. The results represent a generalization of the notion of multiple symbol differential detection, previously introduced by the authors for MPSK over an AWGN, to the fading channel and other modulations. For the coded cases, ideal interleaving/deinterleaving is assumed and furthermore the presence or absence of channel state information. An interesting side result is that for a constant envelope modulation transmitted over a fading channel with unknown but rapidly-varying phase error (the other extreme to the slowly-varying phase error case normally assumed for differential detection), under certain practical assumptions, it is shown that the optimum receiver is of the limiter-discriminator type