传感器信号的线性化处理与非线性补偿

介绍了两种对传感器输出信号进行线性化处理的方向；同时，对传感器不可避免的非线性提出了线性补偿的方法。     

一种用于补偿卫星通信信道记忆非线性的数字基带预失真技术

研究了卫星通信系统中记忆非线性信道的自适应数字基带预失真线性化技术,提出了一种基于记忆多项式的非直接学习结构的自适应基带预失真方案,给出了自适鹰算法。仿真结果表明,该方案能有效抑制带外频谱扩散,减小带内失真,降低误比特率,实现卫星通信系统中记忆非线性失真的自适应预失真。     

卫星信道中高阶APSK调制的非线性失真补偿算法

针对高阶APSK调制在卫星信道中存在有记忆非线性失真的现象,提出一种联合补偿算法,该算法充分利用APSK调制信号星座图的特点,在大幅度减小无记忆数据预失真计算量的基础上,联合非线性均衡实现对有记忆非线性卫星信道的自适应补偿.其优点是存储量和计算复杂度随调制阶数的增加变化很小.仿真结果表明,该算法能够达到有记忆数据预失真的补偿性能,且最佳工作点提高0.2 dB.     

外调制光发射机非线性补偿技术研究

讨论了外调制光传输系统中非线性补偿技术,分析了外调制光发射机存在的非线性失真问题:包括功率放大器引起的失真以及外调制器引起的失真。重点讨论了预失真补偿技术,寻找一种针对整个外调制发射机端非线性失真的补偿方案,设计出适用于外调制光发射机的预失真电路。     

改善放大器非线性失真的各种技术

本文介绍了改善放大器非线性失真指标的各种技术，包括功率回退、预失真、前馈和砷化镓等。指出了各种技术的应用场合。     

微波放大器的非线性失真分析及线性化技术

针对当前第三代通信技术对微波放大器的线性度的要求,分析了微波放大器的非线性失真特性,介绍了几种提高线性化特性的技术方案,并比较了各自的优缺点。最后,基于功率回退技术研制了一个W-CDMA(Wide-Code Division Multiple Access)线性功率放大器,并给出了实验测试结果。     

一种AM-VSB光发射机非线性失真补偿电路

本文提出一种相对简单的有线电视光发射机非线性预失真补偿电路网络,从理论分析得知,可以通过调节非线性元件的静态工作点和网络末端的放大器的增益,能使光发射机的二次失真和三次失真降低。实验测试结果表明该电路能改善CTB、CSO指标。     

射频信道非线性失真对多载波数字通信的影响及常用线性化技术分析

讨论了信道非线性特性引起的各种失真特性,利用仿真软件比较了信道非线性对单载波和多载波数字通信的影响,总结并分析了目前常用的信道线性化技术,对于高频段多载波数字通信系统射频信道的线性化设计具有一定的指导意义.     

FH-MCPFSK信号的数字接收机

讨论了在跳频方式下对多进制连续相位频移键控调制(CPFSK)载波偏差和位定时 联合估计的实现方法,对Caire等人的算法进行分析基础上做了优化,在保证精度的前提下,明 显减少了计算量。实际仿真结果表明每一跳需要传输20个码元就能够较好完成位定时与载 波同步,适用于跳频软件接收机。     

Holographic simulation of compensation for atmospheric wavefront distortion

An experiment is described which demonstrates the validity of the concept of compensating, by holographic techniques, for atmospheric distortions of wavefronts.     

Blind compensation of nonlinear distortion for bandlimited signals

Nonlinear distortion of bandlimited signals results in spectral spreading. This paper develops a blind nonlinear compensation method for bandlimited signals by suppressing the spectral content of the distorted signal above the original signal bandwidth by means of adaptive nonlinear filtering. The nonlinear compensator is constructed using a power series filter with adaptive coefficients. The adaptive coefficients are identified blindly by applying a least-squares criterion to the out-of-band spectral content of the nonlinear compensator output. The extraction of the out-of-band signal is efficiently performed by the discrete cosine transform. The effectiveness of the blind nonlinear compensation method is demonstrated by way of simulation examples involving periodic, colored noise, and bandlimited speech signals.     

A TECHNIQUE FOR MEASURING THE LINEARITY OF A LINEARLY FREQUENCY-MODULATED SIGNAL

A technique for measuring the linearity of a linearly frequency-modulated continuous wave (LFM-CW) signal is presented. It uses a delay-line and a mixer to sense the slope of the output of a sweep oscillator, so that the original form of frequency function deviated from idealized linear slope is retrieved by means of spectrum analysis. Consequently,the linearity of the LFM signal is determined. The formulation is performed based on the principle that an angle-modulated signal can be approximated by an amplitude-modulated signal if the modulation coefficient is sufficiently small. To examine the validity of the procedure and to study the effect of each parameter on the accuracy of measurement, a number of computer simulations has been made. The results of simulation show that the error of the measurement is less than 2%.     

Generalized polynomial-based receiver for the flat fading channel

This letter presents a simple polynomial predictor-based sequence detector for the Rayleigh nonselective fading channel. Unlike the polynomial predictor-based sequence detector proposed by Borah and Hart, the new receiver is not restricted to constant envelope modulation schemes. Analytical and simulated results are presented. In some instances, the proposed receiver performs within 6 dB of the equivalent maximum-likelihood sequence estimation receiver.     

大气光通信信道特性及相位补偿技术研究

大气湍流使光载波的强度和相位在空间和时间上都呈现随机起伏,从而极大地降低了激光通信系统的性能.基于大气湍流信道的特点,分析了各种湍流效应对大气激光通信系统性能的影响,介绍了自适应光学相位补偿技术在大气激光通信系统中的应用进展,特别指出基于随机并行梯度下降(SPGD)算法的自适应光学技术由于具有诸多优点,在未来的大气激光通信系统中可能有较为广阔的应用前景.     

Extended MLSE diversity receiver for the time- andfrequency-selective channel

This paper develops a maximum-likelihood sequence estimation (MLSE) diversity receiver for the time- and frequency-selective channel corrupted by additive Gaussian noise when linear constellations (M-ASK, M-PSK, M-QAM) are employed. The paper extends Ungerboeck's derivation of the extended MLSE receiver for the purely frequency-selective channel to the more general channel. Although the new receiver structure and metric assume ideal channel-state information (CSI), the receiver can be used wherever high-quality CSI is available, such as a comb of pilot tones or time-isolated symbols. The major contributions of this paper are as follows: (1) the derivation of a finite-complexity diversity receiver that is maximum likelihood (ML) for all linear channel models and sources of diversity, as long as ideal CSI is available; (2) a benchmark, in that the new receiver's performance is a lower bound on the performance of practical systems, which either lack ideal CSI or are not ML; (3) insight into matched filtering and ML diversity receiver processing for the time- and frequency-selective channels; and (4) bounds on the new receiver's bit-error rate (BER) for ideal CSI and pilot tone CSI, in a fast Rayleigh-fading channel with multiple independently faded paths. The new receiver can seamlessly tolerate square-root Nyquist pulses without a fading-induced ISI error floor     

Code and receiver design for the noncoherent fast-fading channel

This paper deals with the design of coding/modulation and demodulation/decoding schemes for single- or multiple-antenna systems with focus on fast-fading channels, where channel state information (CSI) is not available at the transmitter and the receiver. We explore two possible solutions for this channel with increasing degree of sophistication. The first one utilizes pilots at the transmitter and a simple and explicit noniterative channel estimation algorithm at the receiver. We show that this pilot-assisted system is exactly equivalent, in terms of performance analysis and design, to an appropriately "degraded" system having perfect CSI at the receiver. The second scheme utilizes pilots and a family of well-justified and simple suboptimal iterative detection/estimation algorithms. It is shown that when turbo-like codes are considered in conjunction with this pilot-assisted transmission scheme and the proposed receiver algorithm, the unitary constellations investigated in the literature are inferior to simple pilot-assisted constellations in both complexity and performance. Specific instances of the proposed systems (that use optimized irregular low-density parity-check outer codes) are designed. The design examples provided show that the proposed systems can achieve a good tradeoff between complexity and performance and can be used to bridge the gap between the high complexity/high-performance optimal scheme and low-complexity/mediocre performance noniterative estimation/coherent detection scheme.     

Extended MLSE receiver for the frequency-flat, fast-fading channel

This paper develops a maximum likelihood sequence estimation (MLSE) receiver for the frequency-flat, fast-fading channel corrupted by additive Gaussian noise when linear modulations (M-ASK, M-PSK, and M-QAM) are employed. This paper extends Ungerboeck's derivation of the extended MLSE receiver for the purely frequency-selective channel to the time-selective channel. Although the new receiver's structure and metric assume ideal channel state information (CSI) at the receiver, the receiver structure can be used wherever high-quality CSI is available. The receiver is maximum likelihood for a variety of channels, including Ricean, Rayleigh, lognormal, and additive white Gaussian noise (AWGN) channels. Bounds on the receiver's bit error rate (BER) are deduced for ideal and pilot tone CSI for fast Rayleigh fading. A crude lower bound is developed on the BER of predictor-based receivers for the same channel. This paper offers insight into matched filtering and receiver processing for the fast-fading channel and shows how pilot symbols and tones should be exploited     

直序扩频信号RAKE接收机的改进与实现

对抗移动通信中的衰落效应的措施之一是信号的多径分集接收,多径分集在直序扩频系统中的实现方法就是RAKE接收机技术.为了解决传统RAKE接收机相关器消耗大的问题,给出了一种改进的直序扩频信号RAKE接收机的实现方法,最后给出了部分实测结果.