2PSK调制解调的DSP实现

设计了以TMS3205402 DSP为数字信号处理平台,对语音信号的2PSK调制与解调系统.包括DSP硬件系统结构外围电路的设计以及软件的设计两大部分.所设计的系统通过音频接口芯片TLC320AD50C进行A/D和D/A转换,通过DSP的多通道缓冲串行接口McBSP实现TLC320AD50C与DSP芯片的通信,通过DSP软件完成2PSK调制解调功能.     

用FFT对8FSK信号进行解调方法的比较

随着DSP技术的发展,快速傅里叶变换(FFT)的应用越来越广泛。利用FFT算法对频移键控(FSK)信号进行频谱分布,通过比较FFT计算结果来确定信号的频率,可以实现对FSK信号的解调。采用MIL-STD-188-141A中的8FSK调制信号作为仿真信号,用MATLAB6.1对解调进行仿真。在提到的三种FFT的检测方案中,在没有频偏的情况下,第一种要较好;但当有频偏存在时,第二种方法较好。     

基于DSP的正交频分复用的实现

在理论上推导了采用快速傅里叶逆变换/傅里叶变换(IFFT/FFT)实现正交频分复用(OFDM)调制解调的可行性,分析了采用IFFT/FFT实现OFDM调制解调比传统方法更具优势;然后在数字信号处理器(DSP)硬件平台上对采用IFFT/FFT实现OFDM调制解调进行了验证。实验结果表明:采用IFFT/FFT不仅能正确实现OFDM信号的调制解调,而且还大大简化了OFDM系统结构,降低了系统实现难度,节约了成本。     

新一代业余无线电通信两用机

近几年来，由于数字电路半导体工艺的迅速发展，出现了DSP──数字信号处理电路，它具有滤波、调制、解调和频率变换等功能，这促使了制造厂商推出新一代高频收发两用机，例如；Kenwood的TS－950SDX和TS－8705等。其电路工作原理方框图如图1所示。电路接收过程分3步进行：（1）来自天线的模拟高频信号经低噪声放大器放大和混频器混频，变换成模拟中频信号；（2）中频信号经数字信号处理器中的解调电路和滤波电路处理，得到数字信号，并消除了干扰和噪声；（3）通过I／O信号处理器的D／A电路和放大电路把数字信号转换为模拟音频信号，…     

基于TMS320C5420的2FSK设计与实现

基于DSP的软件无线电技术在通信领域得到了广泛的应用。我们使用TI公司的TMS320C5420 DSP芯片成功设计了一种兼容2FSK，DPSK，QAM等多种调制解调方式的JH5001通信原理实验系统，在系统硬件不变的情况下只要修改DSP的软件处理部分就能实现无线参数的改变和增加新的功能。详细介绍了用DSP实现2FSK调制解调的算法，并就解调中所应用的数字滤波器做了具体分析。     

一维小波变换在时域光学相干层析成像中的应用

时域光学相干层析(OCT)系统通常采用短时傅里叶变换(STFT)完成干涉信号的解调和图像重构。短时傅里叶变换算法简单,但是在干涉信号解调时难以获得好的去噪效果,通常还需在二维(2D)图像域对重构图像进行去噪。该方法数据运算量大,集成度不高。将一维(1D)小波变换(WT)应用于时域光学相干层析成像技术,同时实现干涉信号解调、去噪和图像重构。算法将时域光学相干层析的干涉信号分解到各个不同的频率空间,保留包含调制频率的频率空间的小波系数,对保留的小波系数进行滤波去噪后进行逆变换即可实现对干涉信号的解调和去噪,对解调信号等间距采样实现图像重构。该方法数据运算量小,集成度高,结合先进的小波去噪技术可以大大提高重构图像的分辨率,具有良好的应用前景。     

基于A/D和DSP技术实现混频的实验方法

本文介绍采用A／D转换器和DSP技术实现混频的一种实验方法,文章从频域角度分析与研究A／D转换器的频率变换功能,并采用欠抽样技术（带通采样技术）对高频带通信号进行采样,然后通过DSP软件编程对采样信号进行实时处理与滤波,便得到低频带通信号。与常规电子线路组成的混频器比较,这种基于A／D和DSP技术实现混频的实验结果表明：对一些固定频率的带通信号是可以实现下混频的。     

基于CPLD和DSP的雷达信号数字采集接口模块设计

介绍了一种采用CPLD复杂可编程逻辑器件M4A5-128／64和DSP数字信号处理器TMS320VC5402实现的雷达信号数字采集接口模块,对所用主要器件的功能和特性进行了简要说明;讨论了雷达触发信号、船首信号的电平变换电路及视频信号的A／D变换电路,并重点讨论了实现雷达信号数字采集接口设计中CPLD逻辑设计和DSP软件设计。     

用PWM实现廉价隔离型标准电流输出D/A转换器

分析了将脉宽调制(PWM)波形转换为模拟电压输出的D／A转换器基本理论，指出通过一个低通滤波器可以把经PWM的数模信号解调出来，给出了滤波器设计的参数选择方法，分析了D／A转换器分辨率和PWM参数的关系。在此基础上设计出简单的电压输出D／A转换器，该电路适合精度要求比较低的场合。在进一步分析该电路的基础上，设计了光电隔离、基准电压、I-V变换和功率放大等电路，得到了0mA～10mA和4mA～20mA模拟电流输出电路，该电路具有较高的精度和较大的负载驱动能力，可以应用于工业过程仪表的设计中。     

8DPSK传真信号解调/再调制的DSP实现

介绍了数字电路倍增设备(DCME)中8DPSK传真信号的解调／再调制技术。提出了一种适于DSP实现的非相干基带差分解调算法,采用该算法不需恢复相干载波即可实现8DPSK传真信号的全数字解调。另外根据8DPSK调制信号的空间矢量图的特点,提出了采用相位旋转的抽样判决方法,大大降低了抽样判决的运算量。最后简要介绍了利用基带信号的包络特征实现8DPSK传真信号解调位同步技术的原理和DSP软件的实现方法。     

Cross-phase modulation in multispan WDM systems with arbitrary modulation formats

Cross-phase modulation (XPM) is a major performance-limiting effect in high bit-rate wavelength-division-multiplexed (WDM) networks with narrow channel spacing. In this paper, we present closed expressions for fast and accurate calculation of both XPM-induced amplitude and phase distortions of WDM channels. This is of particular importance for network optimization and examination of advanced modulation formats. By comparison with simulations, we demonstrate the wide application range of the novel method.     

Frequency modulation and variable-slope delta modulation in SCPC satellite transmission

This paper analyzes and presents subjective assessments of the performance that can be expected with FM, companded FM, and vaniable-slope delta modulation in single-channel-per-carrier (SCPC) service to small earth stations. In addition, it points out some of the problems that may be encountered in applying FM and digital techniques to an operational system.     

Noncoherent-coded modulation constructed from conventionaltrellis-coded modulation

We propose a method to construct noncoherent-coded modulation (NCM) by modifying the conventional trellis-coded modulation (TCM) as proposed by Ungerboeck (1982). The error performance of the modified TCM using noncoherent decoding can approach that of the conventional TCM using coherent decoding for additive white Gaussian noise     

Second-order theory for self-phase modulation and cross-phase modulation in optical fibers

The authors develop a second-order perturbation technique for the study of self-phase modulation (SPM) and cross-phase modulation (XPM) effects in optical fibers. When the dispersion distance is much shorter than the nonlinear length, it is found that the difference between the first- and second-order solution is negligible. However, as the dispersion distance increases, nonlinearity becomes a stronger perturbation, and the first-order theory is not adequate to describe the SPM effects. However, the results obtained using the second-order perturbation technique is in good agreement with numerical simulations even when the dispersion distance is longer than the nonlinear length. When pulses of different channels are copropagating in a fiber, they undergo amplitude distortion and timing shift due to XPM. The perturbation technique presented in this paper accounts for both amplitude distortion and timing shift of a pulse due to XPM.     

Cross-phase modulation induced modulation instability in single-mode optical fibers with saturable nonlinearity

Taking into account the saturable nonlinearity of the single-mode optical fibers, condition and gain spectra of scalar modulation instability induced by cross-phase modulation of two optical waves of different frequencies with the same polarizations are investigated. In both of the normal and anomalous dispersion regions, the contour plots of gain spectra of modulation instability with gray levels, the critical perturbation frequency (or instability domain), and the peak perturbation gain versus the input powers of the two waves are analyzed and discussed. The results show that, the critical perturbation frequency (or instability domain) and the peak perturbation gain increase with the input power, reaching a maximum value, and then decrease. This leads to a unique value of peak perturbation gain and critical perturbation frequency for two different input powers.     

光通信中基于脉冲调制的联合编码调制研究

为了研究无线光通信中数字脉冲调制与信道编码的联合编码调制问题,在给出调制时域结构的基础上,采用理论推导和数值仿真相结合的方法,分析了基于二进制线性分组码的开关键控、数字脉冲位置调制和数字脉冲间隔调制系统的差错性能,得出了信道编码纠错能力与调制阶数的结合关系。结果表明,采用开关键控调制的系统,其汉明距离与欧式距离等价,故不存在调制与信道编码参量匹配问题;脉冲位置调制系统在纠错个数大于调制阶数时,可取得较明显的编码调制增益,当纠错个数能被调制阶数整除时,编码和调制达到匹配;由于数字脉冲间隔调制的符号时隙不固定,存在错误传播现象,不宜与差错编码联合使用。所得结果可为无线光通信链路的设计提供参考。     

The 'inverted' gain-levered semiconductor laser-direct modulation with enhanced frequency modulation and suppressed intensity modulation

A gain-levered semiconductor laser has enhanced efficiencies in both intensity modulation (IM) and frequency modulation (FM). It is shown that by inverting the bias points of the gain and modulation sections, a mode of operation referred to as 'inverted' gain-lever, the FM efficiency is suppressed. The large FM-to-FM ratio makes it a desirable source for an FM optical transmitter.<>     

Delay modulation

The definition of the encoding procedure known as delay modulation is given, along with the autocorrelation function and the spectral density. It is shown that the procedure generates a waveform for magnetic recording which is superior to presently used encoding processes.     

Permutation modulation

A class of codes and decoders is described for transmitting digital information by means of bandlimited signals in the presence of additive white Gaussiau noise. The system, called permutation modulation, has many desirable features. Each code word requires the same energy for transmission. The receiver, which is maximum likelihood, is algebraic in nature, relatively easy to instrument, and does not require local generation of the possible sent messages. The probability of incorrect decoding is the same for each sent message. Certain of the permutation modulation codes are more efficient (in a sense described precisely) than any other known digital modulation scheme. PCM, ppm, orthogonal and biorthogonal codes are included as special cases of permutation modulation.     

Delta modulation

The idea of coding the human voice into digital pulses was conceived more than three decades ago; exploitation had to await the ushering in of the transistor era. Since then, coding systems gradually have improved. One of the latest and most efficient schemes is delta modulation. Compared with earlier analog-to-digital-pulse conversion systems, an increase in the voice-handling capacity of telephone equipment by a factor of two or more has been made possible. At the same time, equipment requirements have become less stringent.