PWM在几种模拟通信信号数字调制解调中的应用

面向控制领域的众多廉价的DSP和单片机均集成有PWM(脉冲宽度调制器)模块，在对PWM信号进行理论分析的基础上，分别得出了应用PWM来实现AM、FM和SSB三种模拟通信号的调制与解调方法，在解调时可以应用PWM和外接的LPF(低通滤波器)。实现对解调信号的D／A变换功能；在调制时则应用芯片CPU和PWM共同完成对信号的调制算法，其中的PWM和外接的BPF(带通滤波器)还具有实现D／A变换的功能。最后论文应用DSP56F803芯片对该方案进行了成功实现。     

AIS系统中NRZI编码及GMSK的调制与解调的仿真

该文介绍了AIS系统中的NRZI编码及GMSK的调制解调原理和特点,在详细分析了NRZI编码过程和GMSK调制解调算法的基础上,在Matlab平台上对AIS信号进行NRZI编码,并根据正交调制和1bit差分检测算法进行了GMSK的仿真实现。程序运行结果表明,程序设计方案能正确实现NRZI编码和GMSK的调制,较好地完成...     

GMSK信号的后解码相干解调

为提高现有通信系统中高斯最小频移键控(GMSK)信号的接收性能,提出了一种基于后解码的GMSK相干解调方法.对于接收到的GMSK基带信号,首先完成相位和载波的同步,将信号的初始相位补偿到零相位;然后通过交替抽取GMSK基带信号的虚部与实部幅度采样值完成信息提取;最后通过后续解码处理完成信号解调.仿真表明,在误码率为10-3时,基于后解码的GMSK解调性能仅比预编码GMSK相干解调差0.5 dB,与传统基于维特比迭代处理的GMSK相干解调性能基本相当,但算法实现更为简化,有利于在现有非相干解调GMSK通信系统中的性能提升实现.     

基于FPGA的GMSK调制解调实现

阐述了GMSK调制解调的原理与特点，并对其关键技术进行了分析；介绍了其在FPGA中的硬件实现方案，同时给出了GMSK信号调制解调的仿真图。     

GMSK数字化调制的FPGA设计与实现

针对GMSK调制的特点,提出了一种数字化的调制方法。使用matlab仿真工具对GMSK调制进行截断和量化,生成GMSK调制查找表,存入FPGA内部的存储器,通过查表实现GMSK调制的数字化,克服了传统GMSK模拟调制方法的相位不够准确,无法进行相干解调的缺点,提高系统设计的灵活性。最后分析了调制信号的频谱特性和接收端信号的基带波形,验证了GMSK数字化调制的正确性和可行性。     

基于e-Labsim平台的GMSK调制与相干解调研究

GMSK(高斯最小移频键控)是20世纪80年代提出的一种典型的连续相位调制方式,常应用在GSM、GPRS移动通信系统和WLN等多个领域。文章主要介绍了数字通信中GMSK调制与解调原理,采用e-Labsim仿真平台来实现GMSK调制与解调。     

基于FPGA的GMSK调制解调实现

本文阐述了GMSK调制解调的原理与特点,并对其关键技术进行了分析;介绍了其在FPGA中的硬件实现方案,同时给出了GMSK信号调制解调的仿真图。     

AIS系统中GMSK的调制解调

从AIS基带处理模块的研究出发，系统地介绍了GMSK调制解调的原理，在System View仿真平台上设计出一套GMSK调制解调的算法，效果良好，在AIS应答机中得到了充分的应用。     

慢符号速率低峰均比调制与信噪比关系的仿真研究

根据无线收发信机的工作原理,设计了慢符号速率调制信号经过各种环境的无线传输后误码率和信噪比变化的仿真原理结构,并应用理论公式和实际例子分析差分算法最适合慢符号速率低阶调制信号的解调.在时域同步和不同步的两种情况下,分别针对慢符号速率信号用GMSK和OQPSK低峰均比调制后经过4种不同的无线通信环境的仿真,详细分析了解调后信号误比特率和信噪比的关系,最后总结并比较了GMSK和OQPSK调制对信噪比的要求和对放大器工作效率的不同.     

GMSK的非相干解调与软判译码

本文提出了CPM的非相干解调与2状态格状译码的方法,并对GMSK信号进行了误码性能的模拟。结果表明:GMSK的2状态格状译码的比特差错性能,远远优于常规的1比特差分解码的GMSK的比特差错性能。     

基于数字正交方式实现的一种GMSK调制

从GMSK调制原理出发,分析了GMSK信号的特征,依据正交调制理论,由CPM调制的公式推导出GMSK调制的载波相位和正交I、Q分量运算公式,并提出以DSP、FPGA、DUC为平台的GMSK调制算法实现方案.文中方案成功用于某测试仪项目,根据用户需求选择码元类型、码元速率、BTb值、载波频率等参数实现了GMSK调制信号的产生.     

A multicarrier GMSK modulator with on-chip D/A converter for base stations

A multicarrier Gaussian minimum shift keying (GMSK) modulator with a 14-bit on-chip digital-to-analog (D/A) converter is presented. The design contains four GMSK modulators, which generate GMSK modulated carriers at the user-defined center frequencies. In wireless base stations, the modulated transmit signals are usually combined at the RF frequency after power amplification. The multicarrier modulator combines four GMSK modulated signals in the digital domain, thereby eliminating the need for an antenna microwave combiner. A new digital ramp generator and output power-level controller performs both the burst ramping and the dynamic power control in the digital domain. The maximum dynamic performance is obtained by multiplexing two D/A converters with output sampling switches. The digital multicarrier GMSK modulator is designed to fulfill the derived spectrum and phase-error specifications of the GSM 900/1800/1900 base stations for pico-, micro-, and macrocells. The die area of the chip is 26.8 mm/sup 2/ in 0.35-/spl mu/m CMOS (in BiCMOS) technology. Power consumption is 706 mW at 3.3 V with 52 MHz.     

A multicarrier GMSK modulator

A multicarrier Gaussian minimum shift keying (GMSK) modulator has been developed and implemented. The design contains four GMSK modulators, which generate GMSK modulated carriers at the specified center frequencies. Utilization of the redundancy in the stored waveforms reduces the size of the GMSK trajectory look-up table to less than one-quarter of the original size in the modulator. Conventionally, the power ramping and output power level controlling are performed in the analog domain. A novel digital ramp generator and output power level controller perform both the burst ramping and the dynamic power control in the digital domain. The power control is realized by scaling the ramp curve, which follows a raised cosine/sine curve. The four GMSK modulated signals are combined together in the digital domain. The digital multicarrier GMSK modulator is designed to fulfil the spectrum and phase error specifications of the GSM 900 and DCS 1800 base stations     

Nonobvious correlation properties of quadrature GMSK, a modulationtechnique adopted worldwide

GMSK is the world's most widely used modulation technique for mobile digital telephony and digital wireless applications. We describe two GMSK modulator structures, the voltage controlled oscillator (VCO) and the quadrature modulator structure. The tremendous advantages of the quadrature modulator structure for practical GMSK modulator implementations are emphasized. We present the results of computer simulations and hardware experimental measurements performed on GSM-standardized IC chips which are used by several million subscribers in order to illustrate the operation of a GMSK modulator. Since quadrature modulator structures are used in nearly all practical GMSK chipsets, the properties of this structure are of wide interest. In this paper we highlight the crosscorrelation properties of the GMSK in-phase and quadrature-phase baseband signals, which are part of the quadrature modulator structure. While uncorrelated in-phase and quadrature-phase baseband signals are used in traditional QPSK and OQPSK modulated systems, we demonstrate that there is strong crosscorrelation between the in-phase and quadrature-phase baseband signals. The crosscorrelation is stronger if the observation interval is shorter. Nonobvious quadrature modulator/radio crosscorrelation advantages were patented by Kato/Feher (1986). Design with crosscorrelated quadrature transmitter is “contrary to the wisdom of classical linear communications theory”. Crosscorrelated quadrature modulated systems include FQPSK-KF and GMSK     

GMSK中频数字化非相干接收机的设计与实现

针对突发模式下的GMSK信号,设计并实现了一种非相干数字化接收机,并且提出了一种更容易硬件实现而且频谱更好的GMSK信号产生方式。该接收机为了降低系统的复杂度,接收机采用2bit差分的方式按样点先进行信号解调,然后利用提出的基于引导码的位定时算法,在8个符号之内实现了位定时的快速捕获。最后在FPGA上的实现证明了接收机的可行性和优越性。     

GMSK混合信号的PSP盲分离算法

针对GMSK混合信号的单通道盲分离问题进行了研究。由于不能直接采用逐幸存路径处理(PSP)算法对GMSK混合信号进行分离,考虑对GMSK信号作线性近似处理,使得GMSK混合信号适用于PSP算法。该算法通过在符号序列和信道参数组成的联合空间进行最大似然估计,保留最优路径,输出符号对,从而获得分离信号。仿真结果表明,使用PSP算法对GMSK混合信号进行分离的误码率性能略优于粒子滤波算法误码率性能,但复杂度远低于粒子滤波算法。     

A Novel Serially Concatenated GMSK System for Satellite Communications

A novel serially concatenated GMSK system is proposed for satellite communications subject to low SNR, limited power and spectrum resources. First, we design a Nonrecursive continuous-phase encoder (NRCPE) based GMSK based on the Rimoldi's decomposition. Then, a corresponding pilot-aided quasi-coherent demodulation algorithm is developed, whose basic principle is that a modified BCJR-based detection performs on the received signals with initial and ending trellisstates being determined using the very limited pilot overhead. Finally, we choose proper modulation parameters for the NRCPE based Gaussian minimum shift keying GMSK signaling according to the trade-offs between the power and spectral efficiency. The simulation results show that the LDPC coded GMSK system using the proposed algorithm can achieve excellent performance and can also work well in the presence of the large Doppler shifts and some burst errors.     

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。     

Differential detection of GMSK signals with low BtTusing the SOVA

A noncoherent Gaussian minimum phase-shift keying (GMSK) detector using differential phase detection combined with the soft-output Viterbi algorithm (SOVA) is presented. This approach overcomes the severe intersymbol interference (ISI) of GMSK signals with low B_tT. Unlike conventional detectors the SOVA produces soft-decision bits resulting in larger coding gains in subsequent convolutional decoders     

A high-performance reduced-complexity GMSK demodulator

A four-state adaptive maximum-likelihood sequence estimation (MLSE) Gaussian minimum-shift keying (GMSK) demodulator for modulation (BT=0.3) on AWGN channels is analyzed and simulated. This demodulator uses the linear representation of GMSK signals and achieves near-optimum BER performance. The channel-impulse response used in the MLSE demodulator is initialized to the highest energy component in the linear representation, and then adapted in a decision-directed mode to offset any performance losses incurred by initially ignoring other lower energy (and time-varying) components in the linear representation. The number of MLSE states is reduced to two, at about 0.1-dB performance loss, by implementing a whitening matched filter which concentrates most of the GMSK pulse energy in its two leading samples