一种用于短波通信的新的频域差分解调器

在短波通信中,传输信号遭受延时、扩展、时变干扰以及接收机加性高斯噪声的影响。常规的差分解调器在恶劣的短波信道环境下性能很差。该文提出一种新的频域差分解调器,通过盲相位估计来消除延时扩展造成的相位误差的影响。仿真了常规差分解调器和新的差分解调器在恶劣短波信道环境下的性能对比。结果表明在快速衰落短波信道环境下,新的频域差分解调器的性能优于传统的差分解调器。     

短波环境中频域差分解调器误码率性能分析

在短波信道条件下,分析了正交频分复用系统中标准的频域差分解调和相位纠正的频域差分解调的误码率性能,并给出了频域差分解调的OFDM系统子载波数N的优化值.理论分析与仿真结果表明:对于典型短波信道,多径延迟扩展对系统优化的频域差分系统的误码率性能影响不大;对于快速衰落的短波信道,系统优化的频域差分系统仍然遭受多径延迟扩展和时变干扰的影响且有较大的误码平台.此外,在快速衰落短波信道环境下相位纠正的频域差分解调器性能优于常规的差分解调器性能.     

多径衰落信道下频域差分检测OFDM系统的误码率分析

在多径衰落信道条件下，分析了正交频分复用系统中频域差分检测的误码率性能，并进行了仿真验证。分析与仿真结果表明，信道相干时间和相干带宽均影响频域差分检测的误码率性能，信道相干带宽对频域差分检测的影响比信道相干时间的影响更大，频域差分检测适合于多径延迟扩展比较小的信道。     

基于正交频分复用的频域差分幅度相位调制

该文提出一种基于频域的幅度两电平的DAPSK+OFDM,并讨论该调制方式在频域的差分调制和解调,然后给出它在白高斯信道的误比特性能公式。最后在典型的调幅(AM)波段信道对它和基于时域的DAPSK+OFDM的误比特性能进行了仿真。结果表明:在短波信道,频域的DAPSK+OFDM比时域的DAPSK+OFDM性能好;在中波信道,时域的DAPSK+OFDM比频域的DAPSK+OFDM性能好。因此,数字调幅广播系统在短波信道可采用频域DAPSK+OFDM,在中长波信道可采用时域DAPSK+OFDM     

16DAPSK+OFDM及其在数字调幅广播中应用

本文提出一种新的频域16DAPSK＋OFDM。并讨论它的频域差分调制和解调,然后在白高斯信道分析它的误比特性能。同时域16DASK＋OFDM相比,频域16DAPSK＋OFDM可用于信道特性随时间变化更快的应用。最后,在典型的调幅（AM）波段信道对两者误比特性能进行了仿真。结果表明,时域和频域16DPSK＋OFDM都可用于中短波信道。在中波信道,时域16DAPSK比例域16DAPSK性能要好,在短波信道,频域16DAPSK比时域16DAPSK性能要好。另外,两者调制和解调的计算复杂度基本一样,且都不需要信息道均衡。     

频域差分和时域差分检测OFDM的误码率性能对比

在多径衰落信道条件下,分析了正交频分复用系统的频域差分检测和时域差分检测的误码率性能,得到了两种系统的误码率解析表达式,并进行了仿真验证.分析和仿真的结果表明:在保护时隙长度不小于最大多径时延长度的条件下,时域差分检测的误码率性能不受信道相干带宽变化的影响,时域差分检测的误码率性能主要受到信道相干时间变化的影响;频域差分检测的误码率性能同时受到信道相干时间和相干带宽变化的影响,并且相干带宽对频域差分检测的影响更大.     

符号间干扰对频域差分OFDM误码率性能的影响

在多径衰落信道条件下,分析了符号间干扰对频域差分正交频分复用系统误码率性能的影响,得到了误码率的解析表达式,分析和仿真的结果表明,频域差分的误码率性能受到符号间干扰的影响,但在不同的信道条件下,符号间干扰对系统性能的影响程度也有不同。     

短波通信中MIMO单载波频域均衡算法研究

短波信道是一个典型的频率选择性衰落信道,需要在接收端采用均衡技术来补偿信道衰落的影响。针对短波信道的特性,介绍了能有效对抗多径干扰的MIMO单载波频域均衡的系统结构,并研究了传统的线性均衡。在此基础上提出了一种改进的频域均衡算法,对信号进行两次均衡,进一步消除了多径分量造成的干扰,并在中度短波信道下验证了改进算法的性能。Matlab仿真结果表明,提出的改进算法降低了误码率,提高了系统性能。     

基于谐波叠加的短波信道模拟器设计

在基于Watterson模型的短波信道模拟器设计中,常采用滤波法实现短波信道的多普勒扩展和衰落,其运算复杂度较高。给出一种新的短波信道模拟器实现方法,采用谐波叠加法设计抽头增益函数,模拟短波信道的多普勒扩展和衰落,有效降低了运算复杂度。最后,采用单音信号对信道模拟器多径？多普勒扩展和多普勒频移等性能进行了仿真,仿真结果证明了用谐波叠加法设计短波信道模拟器的有效性。     

差分跳频通信系统的特点及性能

文章介绍了一种新型的短波跳频通信技术——差分跳频,分析了差分跳频技术区别于常规跳频技术的主要特点。针对按序列检测的信号接收方法,对差分跳频通信系统在AWGN信道下的性能进行了理论分析,同时做出相应的计算机仿真,证实了差分跳频通信技术和按序列检测方法的结合,使通信系统在AWGN信道下的性能得到了比较显著的提升。     

Joint data detection and channel estimation for coded and uncoded continuous phase modulation signals

The performance of decision‐directed approach for joint data detection and channel estimation for continuous phase modulation (CPM) signal is limited because of an inevitable decision delay, which results in a trade‐off between data detection and channel estimation. In this paper, a novel hard output demodulation that solves the conflict requirement on the decision delay by predicting the channel coefficients over a given observation interval through a Kalman filter is proposed for uncoded CPM signal. The prediction guarantees high channel tracking capability and meanwhile maintains the accuracy of data detection. The proposed hard output demodulator is further extended to design a soft‐input soft‐output demodulator for serially concatenated CPM signal, which allows iterative processing. The convergence behavior of the proposed iterative receiver is presented. Simulation results show that the proposed demodulators provide improved performance in terms of bit error rate over some existing algorithms. Copyright © 2014 John Wiley & Sons, Ltd.     

非相干解扩解调器频偏影响分析

频偏的存在相当于对带限信号的频谱进行了搬移，使解扩信号经过带限滤波器后能量受到损失，从而降低了系统的误码性能。本文首先详细分析了零中频非相干解扩解调器误码性能的影响，推导出误码率表达式，然后提出了改进型非相干解扩解调器，并分析了它的误码性能，最后对这两种解扩解调器误码特性进行了比较。     

A comparative study of higher-order differential phase shift keying schemes over AWGN and Rayleigh fading channels

Double differential phase shift keying (DDPSK) is known to be immune to Doppler shift, a property that is valuable in mobile communication systems. The present paper is about DDPSK and analyzes its two variations, the adjacent DDPSK and the nonadjacent DDPSK. The performance is evaluated for the case of slow Rayleigh fading with and without frequency offset using the three receiver structures: the IQ demodulator, the autocorrelation demodulator, and the multiphase autocorrelation demodulator. In additive white Gaussian noise channels (AWGN), the performance of both schemes is evaluated in the presence of a frequency offset with the above demodulators. The obtained analytical results are verified via Monte Carlo simulations. The obvious disadvantage of DDPSK is its power requirements when compared to the conventional DPSK. In order to overcome this shortcoming, a demodulator structure is proposed in this paper. The performance of this demodulator is found to yield a lower probability of error when compared to the other demodulators for DDPSK as well as for DPSK. Results obtained using computer simulation of the proposed demodulator was found to be in good agreement with the analytical results derived in this paper.     

BER for optical heterodyne DPSK receivers using delay demodulationand integration detection

Previous work on the bit error rate (BER) performance of differential phase-shift keying (DPSK) including the effects of additive white Gaussian noise (AWGN) and phase noise has concentrated on the delay demodulator with narrow-band intermediate frequency (IF) bandpass filtering (BPF) and sampling detection. No similar analysis has yet been performed for the delay demodulator with wideband IF bandpass filtering and integration detection. Phase noise is an important consideration in coherent optical communication systems and the most widely accepted model is a Brownian motion process. A closed-form BER expression along with detailed Monte Carlo simulation results are presented for the DPSK delay demodulator with wideband IF bandpass filtering and integration detection filtering including phase noise effects using the Brownian motion model. Analytic expressions are also obtained for the moments of the phase noise component of the decision variable. Using these moments, estimates of the phase noise BER floor are produced. It is found that this receiver has noise performance comparable to receivers with narrowband IF bandpass filtering and sampling detectors for signal-to-noise ratio (SNR) and phase noise in the range of practical interest, but with potentially less degradation due to intersymbol interference (ISI)     

基于Watterson模型的短波航空移动信道建模与仿真

信道建模与仿真是短波航空通信系统性能分析评估的基础,该文通过分析研究飞行器最大移动速度、加速度、机动频率、运动轨迹等机动状态参数对短波航空移动信道时变多普勒频移的影响,提出一种基于Watter-son模型的短波航空移动信道模型.该模型能够充分描述由收发两端相对运动引入的信道多普勒频移与扩展,适用于短波超视距航空移动通信...     

“Turbo DPSK”: iterative differential PSK demodulationand channel decoding

Multiple symbol differential detection is known to fill the gap between conventional differential detection of MPSK (M-DPSK) and coherent detection of M-PSK with differential encoding (M-DEPSK). Emphasis has been so far on soft-input/hard-output detectors applied in uncoded systems. In this paper, we investigate a receiver structure suitable for coded DPSK signals on static and time-varying channels. The kernel is an a posteriori probability (APP) DPSK demodulator. This demodulator accepts a priori information and produces reliability outputs. Due to the availability of reliability outputs, an outer soft-decision channel decoder can be applied. Due to the acceptance of a priori information, if the outer channel decoder also outputs reliability information, iterative (“turbo”) processing can be done. The proposed “APP DPSK demodulator” uses linear prediction and per-survivor processing to estimate the channel response. The overall transmission scheme represents a type of serial “turbo code,” with a differential encoder concatenated with a convolutional code, separated by interleaving. The investigated system has the potential to improve the performance of coherent PSK without differential encoding and perfect channel estimation for fading cases! Only a small number of iterations are required. The receiver under investigation can be applied to several existing standards without changing the transmission format. Results are presented for uncoded and convolutionally coded 4-DPSK modulation transmitted over the Gaussian channel and the Rayleigh flat-fading channel, respectively     

基于OFDM的短波多天线分集接收技术性能仿真

研究了短波OFDM调制下多天线分集合并接收技术。针对短波信道存在多径干扰、深衰落、多普勒频移等特点,采用ITU-R建议的中纬度恶劣信道条件下的短波信道参数,应用短波Watterson信道模型,运用最大比值合并的多天线分集合并算法,进行了短波OFDM系统下误码率性能仿真。仿真结果表明：设计的算法,在不加大发射功率的情况下,有效地降低了OFDM系统的误码率,减轻了信道衰落的影响,提高了通信的可靠性。     

改进Watterson模型的无人机短波信道仿真

Watterson模型是多年来仿真短波信道的标准表示方法,其对短波信道多径时延、多普勒扩展、多径增益等特性都有全面的描述。针对无人机短波通信信道的特点,结合无人机的各种不同飞行状态,提出一种改进的Watterson模型,并在Simulink软件平台上对改进模型进行了仿真验证,仿真结果主要分析了不同飞行状态对短波通信性能的影响。在当前没有权威实测数据的情况下,对无人机等高速移动通信的信道衰落研究具有重大意义。     

Optical DPSK demodulator based on /spl pi/-phase-shifted fiber Bragg grating with an optically tunable phase shifter

We propose and demonstrate a novel optical differential phase-shift keying (DPSK) demodulator with an optically tunable phase shifter. The proposed DPSK demodulator is implemented by using a /spl pi/-phase-shifted fiber Bragg grating and an Yb/sup 3+/-Al/sup 3+/ codoped optical fiber. A 10-Gb/s DPSK signal was successfully demodulated by the proposed demodulator, showing clearly open eye diagrams as well as bit-error-free performance. Moreover, the phase of delayed optical signal can be tuned by the phase shifter that is controlled by a pumping light at around 980nm.