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。     

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。     

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。     

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。     

频域扩频码片级差分检测的误码率性能分析

该文提出了一种频域扩频系统中的差分检测方法:频域扩频码片级差分检测.通过利用判决变量的矩生成函数,并采用鞍点近似的分析方法,得到了频域扩频码片级差分检测的误码率性能的解析表达式,同时进行了仿真验证.分析和仿真结果表明,频域扩频码片级差分检测具有抵抗频率选择性衰落的能力,在信道的相干带宽不小于两个码片对应的频带宽度的前提下,随着信道多径时延扩展的增加,其误码率性能有进一步的提高.     

Nakagami-m衰落信道下差分跳频接收机性能分析

目前差分跳频系统的性能研究主要集中在无衰落信道和Rayleigh衰落信道,但短波信道是一种典型的多径衰落信道,采用Nakagami-m信道衰落模型能够更好地描述短波信道的特性.研究了Nakagami-m衰落信道下序列检测线性合并差分跳频接收机的误符号性能,给出了误符号率的闭式表达式,并证明了在m=1时所得结果与已有的瑞...     

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。     

时变衰落信道中同步时间扩展信号的分集接收技术

扩频通信可以区分多径信号进行RAKE分集接收,是一种有效处理多径效应的手段。与此对应,时间扩展通信也可以在频域上进行类似RAKE的分集接收,有效处理时变衰落带来的影响。时间扩展会带来严重的符号间干扰,同步时间扩展可以有效控制和处理符号间干扰。基于信道分解的分集接收技术保证了同步时间扩展在时变衰落信道下的性能。获得10-4误码率,本文分集算法(扩展长度1024)在时变衰落信道中所需的信噪比与AWGN信道不分集处理所需的信噪比只相差1.4dB。     

BER Performance of Frequency Domain Differential Demodulation OFDM in Flat Fading Channel

A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter.     

Multicarrier transmission using quadrature frequency/phasemodulation

Multicarrier (MC) systems using quadrature frequency and phase modulation (QFPM) schemes called MC-QFPM are described. In MC-QFPM systems, the power efficiency and resistance to delay spread can be increased for the price of reduced bandwidth efficiency. M-ary orthogonal frequency-shift-keying with M=1, 2 and 4 are considered along with MC modulation. The BER performance of MC-QFPM schemes in frequency selective delay spread environments is examined and compared     

基于ITS信道模型的HF信道模拟器的实现

提出了一种基于ITS短波信道模型的HF信道模拟器的实现方法,并给出了线性调频信号通过HF信道模拟器后频域的MATLAB仿真结果。信号通过信道后产生的时延展宽、多普勒频移和多普勒展宽都是利用现场可编程逻辑门阵列来实现。电离层参数是利用三维射线追踪技术根据选定的电离层模型得到。这种HF信道模拟器适用于高达500kHz带宽的信号。利用这种HF信道模拟器,实现了在实验室研究探测信号经过HF信道传输的特性的可能。     

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。     

Frequency domain equalization for single-carrier broadband wirelesssystems

Broadband wireless access systems deployed in residential and business environments are likely to face hostile radio propagation environments, with multipath delay spread extending over tens or hundreds of bit intervals. Orthogonal frequency-division multiplex (OFDM) is a recognized multicarrier solution to combat the effects of such multipath conditions. This article surveys frequency domain equalization (FDE) applied to single-carrier (SC) modulation solutions. SC radio modems with frequency domain equalization have similar performance, efficiency, and low signal processing complexity advantages as OFDM, and in addition are less sensitive than OFDM to RF impairments such as power amplifier nonlinearities. We discuss similarities and differences of SC and OFDM systems and coexistence possibilities, and present examples of SC-FDE performance capabilities     

Analysis of HF pulse reflection from a randomly varying ionosphere

The reflection of high-frequency (HF) pulses by a randomly inhomogeneous, dispersive, and absorbing ionosphere is considered. The distortion of the transmitted pulses due to the intrinsic ionosphere dispersion, multipath effects, and frequency incoherence is related to the spatial, temporal, and frequency dependent characteristics of both the ionosphere and the troposphere. The envelope broadening of a constant-carrier pulse due to the dispersion (delay distortion) and randomness of the media (diffuse multipath) is seen to be small compared to the discrete mulfipath spread resulting from variations of the ionosphere's index of refraction with height. In the case of chirp-pulse transmission, pulse compression in the range of 20-30 dB may be achieved provided the frequency sweep of the transmitted pulse is matched to the slope of the delay of the channel and the bandwidth of the chirp pulse is large enough (0.1-10% of the center frequency).     

Multipath propagation model for line-of-sight street microcells inurban area

This paper proposes a multipath propagation model for line-of-sight (LOS) street microcells with building roof base sites (BS) in urban areas, Multipath propagation characteristics are of great importance in evaluating the performance of digital systems and designing wireless links. Typical delay profiles are measured to clarify their statistical characteristics in LOS street microcells. The channel sounder used is a sliding correlator with 30-Mb/s PN code and a center frequency of 2.6 GHz. The measurements clarify the features of delay profile and mean RMS delay spread. The proposed delay profile model explains one plausible mechanism of multipath propagation. The delay profiles calculated using the model agreed well with the measured profiles. Furthermore, the factors influencing the RMSs delay spread are investigated, and the regression equation of medium RMS delay spread on a sidewalk is established. The proposed model can evaluate the transmission characteristics of wireless digital communication systems in multipath propagation environments