数字集群通信中GMSK信号解调算法的研究

详细介绍了国内某数字集群系统中使用的解调算法,推导了GMSK信号的Laurent分解过程,重点分析简化最优接收机到单脉冲匹配滤波接收机的转换过程,比较了在不同频偏环境下解调算法的性能差异并给出相关仿真结果。     

一种GMSK数字解调算法的仿真与实现

GMSK调制因为其包络恒定、相对较窄的带宽、能进行相干解调、带外辐射低等优点而得到了广泛应用。本文提出了一种适用于DSP实现的改进型GMSK解调算法,利用仿真工具Matlab对其进行了仿真,并根据仿真结果在OMAP5910硬件平台上实现了该算法,取得了良好效果。     

递归SOQPSK-TG信号的两状态判决反馈解调算法

针对利用两状态网格图对递归部分响应成形偏移正交相移键控SOQPSK-TG信号进行解调时,网格图状态变量与累积相位不存在一一对应关系的问题,研究了解决此问题的判决反馈解调算法。该算法根据两状态网格图,在网格状态转移过程中,通过判决反馈,得到状态变量对应的累积相位。仿真结果表明,在信噪比大于0 dB时,SOQPSK-TG信号两状态判决反馈解调算法可以获得接近四状态解调的误比特性能。     

基于软件无线电的GMSK调制解调位同步算法

研究改进了一种基于软件无线电的GMSK调制解调全数字位同步算法.改进的位同步算法只需要简单的平方和累加运算,算法结构简单,能降低对硬件的要求,适合实现可重复软加载全数字解调.实验结果表明,此算法比数字锁相环方法实现起来更简单、更方便,同步效果也较好.     

用MATLAB实现GMSK信号的产生与解调

采用正交调制的方法,在MATLAB环境下用Simulink组件产生了射频GMSK信号。编写m文件实现1bit差分解调算法,对产生的信号进行解调,得到较好的结果。为验证该算法的正确性,还采集了信号源的射频GMSK信号数据,在已知采样速率、信息码速率的条件下进行解调,针对采样起始时刻的不确定性,还添加了判断信息数据跳变时刻的代码,也取得了满意的解调效果,说明该算法具有一定的实用性。     

一种新的GMSK数字解调算法

文章在原有的GMSK解调技术的基础上,提出了一种新的GMSK解调算法,并做了Matlab仿真。通过仿真可以看出,改进过的解调算法在性能上有较大的提升。     

一种面向DSP实现的GMSK位同步算法

本文针对于全数字GMSK差分解调接收机,提出了一种面向DSP(数字信号处理器)实现的位同步算法,使得解调算法和位同步算法结构简单,运算量小,便于全数字接收机的实现。然后作者经过了大量的软件仿真和最后的实际硬件实现证明了此算法简单可行。     

多进制GMSK频谱分析及解调算法

多进制GMSK具有较大的频谱效率优势,对提高通信的效能有十分重要的意义。首先在二进制GMSK信号频谱的基础上,对多进制GMSK信号的频谱进行简要介绍,并对其进行比较,其次借鉴二进制GMSK信号的产生和解调思路,研究了多进制GMSK的产生算法及解调方式,并提出了对多进制GMSK信号的准最佳最大似然比解调算法,并对该算法进行仿真,结果发现该算法能够取得较好的误码性能。     

一种低运算量的基于DDC的GMSK解调方案

在分析GMSK常用解调方案的基础上,提出了一种基于数字下变频器件(DDC)输出相位的差分负反馈解调方案,并给出其与常用解调方案的性能仿真分析和比较。分析结果表明,该方案在保证DDC晶振稳定度的条件下性能良好。同时该方案只需要在最佳抽判时刻进行运算,大大减小了运算量,降低了对处理器的速率要求的同时也降低了功耗,特别适合于便携式跳频通信系统。     

一种新的迭代判决反馈差分空时检测算法

针对快衰落信道,提出了Turbo码与块差分空时调制(BDSTM)串行级联的差分空时设计方案,并以该设计方案为基础,提出了一种新的迭代判决反馈差分空时检测(IDF-DSTD)算法.该算法实现了具有软输入软输出的判决反馈差分空时检测(SISO DF-DD),一方面在判决反馈线性滤波器中通过引入先验信息,提高了线性预测的准确性,另外,SISO DF-DD与外侧Turbo译码器之间通过边信息的交换实现了迭代检测与译码.仿真结果表明,在未知信道状态信息(CSI)的条件下,本文算法的误码性能接近已知CSI的相干检测,优于判决反馈块差分空时调制(DFBDSTM)约2dB.     

差分GPS实时数据解调算法研究与实现

差分GPS实时数据传输格式依据RTCM-SC104标准,采用MSK调制而成。为了精确地获取MSK信号的码元信息,针对差分GPS实时数据提出一种基于加窗滑动的离散哈特莱变换解调算法。该算法首先采用窗口长度为码元宽度,移动步长为1的矩形窗滑动后求码元同步,获取同步信息后再对其进行离散哈特莱变换,最后通过幅值信息还原出数字码元。经Matlab仿真结果表明,该解调算法性能比对比算法更优,实用性及适用性更广,最后在VC++平台上实现了差分GPS实时数据的正确解调。     

Differential detection of GMSK using decision feedback

Differential detector structures that use decision feedback to partially remove the effect of destructive intersymbol interference from minimum-shift keying (MSK) are introduced. In comparison to the conventional two-bit differential detection of GMSK (Gaussian MSK), the proposed structures provide about 4-dB E_b/N ₀ improvement when the premodulation filter time-bandwidth product is 0.25. As the premodulation filter becomes narrower, the advantages of the proposed receivers are more pronounced. Thus the bit-error-rate performance of differential detection is brought closer to coherent detection while avoiding the problems associated with the carrier recovery     

SVD iterative decision feedback demodulation and detection of coded space-time unitary differential modulation

A new suboptimal demodulator based on iterative decision feedback demodulation (DFD), and a singular value decomposition (SVD) for estimation of unitary matrices, is introduced. Noncoherent communication over the Rayleigh flat-fading channel with multiple transmit and receive antennas, where no channel state information (CSI) is available at the receiver is investigated. With four transmit antennas, codes achieving bit-error rate (BER) lower than 10/sup -4/ at bit energy over the noise spectral density ratio (E/sub b//N/sub o/) of -0.25 dB up to 3.5 dB, with coding rates of 1.6875 to 5.06 bits per channel use were found. The performance is compared to the mutual information upper bound of the capacity attaining isotropically random (IR) unitary transmit matrices. The codes achieve BER lower than 10/sup -4/ at E/sub b//N/sub o/ of 3.2 dB to 5.8 dB from this bound. System performance including the iterative DFD algorithm is compared to the one using Euclidean distance, as a reliability measure for demodulation . The DFD system presents a performance gain of up to 1.5 dB. Uncoded systems doing iterative DFD demodulation and idealized pilot sequence assisted modulation (PSAM) detection are compared. Iterative DFD introduces a gain of more than 1.2 dB. The coded system comprises a serial concatenation of turbo code and a unitary matrix differential modulation code. The receiver employs the high-performance coupled iterative decoding of the turbo code and the modulation code. Information-theoretic arguments are harnessed to form guidelines for code design and to evaluate performance of the iterative decoder.     

Performance of offset receiver diversity for GMSK and spread spectrum GMSK with one-bit differential detection using decision feedback in fast Rayleigh channels

This paper introduces the application of three techniques to improve the performance of one-bit differential detection (DD). The Gaussian minimum shift keying (GMSK) modulation technique is employed. The proposed techniques are spread spectrum, offset receiver diversity and decision feedback (DF). A comparative study shows that when applying the direct sequence spread spectrum (DS-SS), the performance is improved by 9.3 dB at a bit error rate (BER) of 10^–3 and the processing gain is equal to 10 relative to that given by Elnoubi [IEEE Trans. Veh. Tech. VT-35(1986)162–167]. When using the offset receiver diversity technique, the corresponding relative improvement is 13 dB. When employing both SS and offset diversity at the same BER, 22 and 25.7 dB improvements are attained for DS and frequency hopping (FH), respectively. A further improvement of about 1 dB is obtained when DF is used.     

GMSK frequency detection using decision feedback equalisation

Frequency detection of GMSK signals using one-bit decision feedback equalisation (DFE) in conjunction with offset decision instant is presented. Experiments on a 16kbit/GMSK signal reception with a premodulation filter bandwidth-bit duration product (Bb T) of 0-25 (typical for mobile radio applications) show that, compared to MSK signal reception, a bit error rate (BER) of 10-2 is obtained with a loss of about 4dB in the signal energy per bit/noise power density ratio (Eb/N0) in the additive white Gaussian noise (AWGN) channels. In the cochannel interference limited channels, a BER of 10-2 is obtainable at a signal/interference power ratio (SIR) about 5-5 dB larger than in the case of MSK signal reception.     

CCK demodulation via symbol decision feedback equalizer

A symbol decision feedback equalization (DFE) technique is developed for demodulating complementary code keying (CCK) signals. The efficacy of the proposed receiver is demonstrated on the physical layer (PHY) specified in the IEEE 802.11b wireless local area network (WLAN) standard. Packet error rate (PER) performance is compared with that of the conventional RAKE receiver. The proposed receiver structure and its low complexity variations demonstrate significant performance advantages over the RAKE receiver, especially in severe multipath channels. While a large delay spread can limit the performance of two low-complexity variations discussed here, performance of the optimal symbol DFE receiver is not limited by delay spread as long as the channel signal-to-noise ratio (SNR) is sufficiently high.     

BER analysis of a GMSK system using decision feedback

There are considerable literatures on the Bit Error Rate（BER）evaluation of Differential Detection of Gaussian Minimum Shift Keying（DDGMSK）system using Decision Feedback（DF）,but most of them give the performance based on the Monte Carlo Error Counting（MCEC）technique.From the probability distribution of the phase angle between two vectors perturbed by Gaussian noises,the formulae of BER are derived for the performance analysis of DDGMSK system with DF in this letter.Considering the m-bit dock-tailed sequence,the new formulae of Gaussian Minimum Shift Keying（GMSK）modulated phase and the Time-Varying Signal to Noise Ratio（TVSNR）of the demodulated signal are presented,and it is proved that the relationship between the TVSNR of the demodulated signal and the size of eye opening is not inevitable.Simulation results show that the theoretical investigation gives analogous results with the MCEC technique.The formulae presented are useful for the performance analysis of systems using GMSK as modulating and demodulating method,for instance,the analysis of synchronous performance of frequency-hopping communication system.     

Turbo编码GMSK信号准相干解调时的迭代信道估计和译码研究

针对准相干解调Turbo编码GMSK信号,提出了一种简便的迭代信道估计算法。该方法基于Turbo码的迭代译码原理,将信道估计和译码联合考虑,利用译码器输出反馈进行迭代信道估计,从而提高了估计精度。仿真结果表明,该方法能显著地改善系统误码率性能。     

一种高动态弱GNSS信号跟踪解调算法研究与实现

在某些高动态弱信号场景中,载波相位难以锁定。为实现对高动态弱全球导航卫星系统(GNSS)信号的跟踪,考虑锁频环较锁相环更为鲁棒,提出了一种基于锁频环(FLL)+差分解调的算法,实现对GNSS信号的跟踪和解调。该算法采用二阶FLL实现对卫星信号的频率进行跟踪,差分解调算法实现对比特数据的解调。工程应用上,算法采用现场可编程门阵列和数字信号处理器(FPGA+DSP)的架构实现,在FPGA中实现信号的跟踪信号的前处理,在DSP中实现跟踪环路算法、位同步和差分解调。本文在Matlab平台中实现算法的仿真,通过模拟器平台和对天接收真实的GNSS信号对算法进行验证。仿真结果与实验结果表明,该算法在高动态弱信号条件下能实现对卫星信号的稳定跟踪和数据的解调,克服了锁相环难以锁定导致数据无法解调的难题,最终实现GNSS信号在该条件下的位置、速度和时间(PVT)解算。