（英）Orthogonal frequency division multiplexing for improving the performance of terahertz channel

Terahertz (THz) communication is considered to be one of the demanding technology for the upcoming 5G standards. The incredible demand for high rate through wireless channel necessitates the use of THz frequency for communication. The development of communication systems in this frequency band possess technical challenges as the characteristic of THz band is very much different from the present wireless channel. However, the advancements in the development of transceiver and antenna systems are rapidly bringing the THz communication into reality. The high path loss in THz band limits the communication range of this channel. Even, for a distance of few meters (>5m), the absorption coefficient is very high and hence the performance of the system is poor. Performance over this frequency channel can be enhanced by considering transmission windows over this band instead of the entire band. The transmission windows are the frequencies over which the absorption is relatively low. Though there is an improvement in the performance with this adaptive modulation scheme, but not sufficient for longer distance. Apart from path loss, the frequency selective nature of this high bandwidth channel is also a major reason for the poor performance of THz channel. Orthogonal Frequency Division Multiplexing (OFDM) is a promising solution to mitigate the effects of frequency selective nature of the wireless channel. OFDM has been exploited in this paper to improve the performance of terahertz channel. The results show that the Bit Error Rate (BER) of the terahertz channel is considerably improved with OFDM.     

THz wireless communication system based on wavelet transform

With a very wide frequency band not allocated at present, THz waves have many optimal characteristics such as high transmission rate, large capacity, and high security. The research of THz communication technology has become a hotspot in wireless communication. For THz wireless communications, it is crucial to study advanced electrical signal processing techniques. In this paper, in view of the shortcomings of traditional orthogonal frequency division multiplexing (OFDM) technology, we propose wavelet transform orthogonal multicarrier modulation method in THz system. In addition, we study THz channel coding technology to ensure that the THz wireless communication baseband system has better bit error rate (BER) performance and low computational complexity. Based on above, a THz wireless communication baseband system is conceived.     

MIMO系统空时特征波束性能分析

针对结合了发射与接收分集技术和空时编码技术的MIM0无线通信系统误比特率性能问题,提出了一种利用信道矩阵的最大奇异值平方的概率密度函数（pdf）,来推导相干接收条件下,基于M-PAM和M-QAM调制的MIM0系统最大比合并精确误比特率显式表达式的方法。以该误比特率表达式为依据,分析了天线数目为可配置资源条件下,发射天线和接收天线的不同配置方案对系统性能的影响。通过计算机的蒙特卡洛仿真验证了理论分析结论。     

基于DMT/QAM和STBC的室内MIMO光无线通信

针对室内漫射光无线通信问题,提出一种采用离散多音/正交幅度调制和空时块编码的多输入多输出(MIMO)光无线通信技术.基于离散多音/正交幅度调制技术,并通过考虑室内全光无线信道的脉冲响应和其噪声特性,建立起室内红外光无线链路的信道模型;再采用空时块编码技术,提出一种实现室内漫射光无线通信的MIMO无线通信系统,并通过分析...     

Combined turbo coding and unitary space-time modulation

Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases.     

Performance analysis of multi‐input multi‐output systems with maximum likelihood detection over shadowed fading channels

Multiple‐input multiple‐output (MIMO) transmission techniques constitute an important technology in modern wireless communication. Hence, performance analysis methods for such systems are of considerable interest. This paper considers first the average pairwise error probability for uncoded MIMO systems employing maximum likelihood detection over a composite Rayleigh‐Lognormal fading channel with spatial correlation. It provides general results, applicable also to a wider class of shadowing models, concerning asymptotical diversity gains and shows that they are not changed by such shadowing. Then, analytical evaluation techniques for bit‐error‐rate (BER) over composite Rayleigh‐Lognormal fading channels, based on the truncated union bound and the transfer function, are considered. Furthermore, these techniques are modified for applications over spatially correlated channels. This paper shows that such performance evaluation techniques provide good approximations to BER of spatially uncorrelated MIMO systems and also in the presence of moderate spatial correlation, over Rayleigh‐Lognormal fading channels. Copyright © 2013 John Wiley & Sons, Ltd.     

基于空间分集的太赫兹光子计数系统

由大气湍流引起的闪烁效应是影响太赫兹无线通信系统性能的重要因素,为此提出了使用空间分集技术来改善受强大气湍流和噪声影响的太赫兹光子计数无线通信系统性能的方案,并分别推导了在开关键控(OOK)调制下基于Laguerre模型采用发射分集、接收分集以及多输入多输出技术(MIMO)的系统在强大气湍流下的误码率表达式。数值分析结果表明,在自由空间使用分集技术可以有效对抗强大气湍流,降低通信系统的误码率,是一种在不利天气条件下提升太赫兹无线通信性能的简单而有效的方法。     

瑞利衰落信道下的网格酉空时调制的研究

酉空时是一种多天线系统信号调制方案,可以在不知道信道状态下进行解调。文中将网格编码与酉空时星座结合运用,性能仿真证明了网格酉空时调制系统非常适合无信道状态信息的无线通信系统,网格编码在一定程度上改进了系统的比特误码率性能。将网格编码下的酉空时调制与未编码的酉空时调制进行对比,结果显示在10^-4的比特误码率下可以得到10～15dB的编码增益。     

FSO中分层空时编码的误码性能

分层空时编码(BLAST)虽然具有极高的频谱效率,能成倍提高光通信系统的信息传输速率,但BLAST系统的误码率较大,严重影响了光通信系统的可靠性。在描述了湍流信道中多输入多输出(MIMO)系统的信道模型后,针对多进制脉冲位置调制(Q-PPM)技术,推导出了采用线性译码算法时分层空时码的极大似然判决准则及其误码率公式,并比较了最大似然译码算法、线性译码算法、串行干扰消除译码算法的误码性能。最后,利用仿真实验进行了验证。结果表明:在自由空间光通信(FSO)中,串行干扰消除译码算法的误码性能更接近最大似然译码算法的性能,明显优于线性译码算法。在4×4系统中,当误比特率为2×10-2时,相对于最小均方误差(MMSE)译码算法,最大似然译码算法和MMSE-SIC译码算法的信噪比分别改善了约14.5 dB和7 dB。理论分析与实验结果相一致。     

嵌入式实时操作系统在MIMO无线通信中的应用

多输入多输出（Muhiple Input Muhiple Output，MIMO）无线传输技术可以在不增加带宽和天线发射功率的情况下，成倍地提高无线通信系统的信道容量。文中基于嵌入式实时操作系统，实现了MIMO传输系统中的协议处理、业务汇聚和高速数据传输。采用VxWorks操作系统为平台，以TCP／IP协议为基础，提出了实现MIMO系统中高层协议的总体方案。实验表明，采用的高层协议可以很好地支持话音、图像和数据传输，也可以为未来移动通信高速数据传输、无线资源管理、无线网络协议及规划提供良好的支持。     

虚拟多天线无线传感器网络

提出一种基于虚拟多天线技术的分布式和协作的无线传感器网络,分析了该虚拟多天线无线传感器网络的性能。同点到点的无线传感器网络相比较,在天线传输信号能量相同的情况下,虚拟多天线无线传感器网络的误比特概率(BER)更小;或者在同样误比特概率情况下,虚拟多天线无线传感器网络的天线传输信号能量更低。这些特性能够提高无线传感器网络的性能或延长无线传感器网络的使用寿命。     

水下复合信道对GMSK无线光通信系统性能的影响

The absorption and scattering of light in seawater channel cause signal attenuation, and the turbulence of seawater causes signal amplitude fluctuation, both of which will reduce the bit error rate (BER) performance of underwater wireless optical communication (UWOC) system. The effects of the two channel characteristics on the signal performance were considered comprehensively, and a method was proposed to equate the transmission distance and turbulence probability density function to the system signal-to-noise ratio (SNR) and turbulence noise, and then the signal attenuation and turbulence noise were combined into the signal waveform to establish the underwater composite channel signal transmission model. According to the experimental system parameters, the signal transmission waveforms of Gaussian minimum frequency shift keying (GMSK) modulation under composite channel were simulated, and the one-bit difference demodulation algorithm was used to compare the demodulated waveforms with the original waveform, and the influence relationships of composite channel on the system BER performance was analyzed. The simulation experiment results show that, compared with on-off keying modulation (OOK), pulse position modulation (PPM), GMSK system can obtain the SNR gain of 3.3 dB, 4.8 dB respectively only in the attenuation channel with seawater attenuation coefficient of 0.151 m?1. Under the composite channel, GMSK modulation performance is superior to OOK modulation and PPM modulation. When the water attenuation coefficient is 0.151 m?1, and turbulence intensity variance is smaller than 0.16, GMSK modulation system has no error rate limit, the system BER is decided by signal attenuation and turbulence noise and Gaussian noise together, GMSK modulation achieves SNR gain of 4.35 dB compared with PPM modulation. Furthermore, turbulence intensity variance is greater than 0.16, system BER arrives limit, which value is determined by the turbulence intensity, and the limit value of BER increases nonlinearly with the increase of turbulence intensity.     

紫外分离双脉冲位置调制误码性能分析

基于紫外非视距(NLOS)单次散射信道传输模型,分析了用于无线紫外光通信的分离双脉冲位置调制(SDPPM)方案的误码性能.介绍了SDPPM调制方案的符号结构,将该调制方案与开关键控调制(OOK)、脉冲位置调制(PPM)和双脉冲位置调制(D-PPM)在带宽需求、功率需求方面进行比较.利用光子计数方法,研究了无背景辐射噪声条件下SDPPM的误符率(SER).对PPM、D-PPM和SDPPM紫外通信系统的误码性能进行仿真,分析路径损耗对其影响.结果表明,SDPPM在信源比特分组长度n为5和6 bit时获得了带宽需求与功率需求的较好平衡.当SER达到10-4时,有效通信距离比D-PPM长20 m左右.同时,SDPPM调制方案降低了紫外光散射通信中因多径色散造成的码间串扰(ISI).     

基于LDPC码的无线光通信副载波误码性能分析

为了研究信道编码技术对无线光通信副载波系统差错性能的影响,基于无线光通信链路噪声特性,建立了大气信道等效数学模型。采用低密度奇偶校验(LDPC)码作为信道编码方式引入无线光通信,在不同光强闪烁指数下对基于副载波相移键控调制无线光通信系统进行了差错性能仿真,比较分析了LDPC编码前后副载波调制系统的误比特率,并对二相相移键控及四相相移键控两种系统进行了对比。结果表明,副载波二相相移键控调制系统的差错性能优于四相相移键控系统,同时LDPC码在弱湍流信道具有优越的纠错能力,可以获得比未编码系统较高的编码增益,在无线光通信领域具有一定的应用价值。     

太赫兹频段星地通信信道建模与仿真

太赫兹频段作为至今尚未被完全开发的超高通信频段,具有超大带宽等优点,将其应用于第五代（the 5th Generation,5G）、后五代（Beyond 5G,B5G）移动通信系统,除实现更高速率传输外,还可实现地面移动网络与卫星网络频谱资源的共享,有利于推动新一代空天地一体化通信网络建设.文章提出了一种适用于星地通信系统的太赫兹信道建模与仿真方法,分析了自由空间损耗、分子吸收损耗、云雾衰减、雨衰减及多普勒频移等太赫兹信道的影响因素,构建了星地太赫兹通信信道建模流程,并给出了分步骤信道参数的生成方法.通过数值仿真,对不同天气状况下传输距离和频率对传输信号的影响进行了分析,并基于所生成的信道响应对误码率进行评估,从而验证了所提出模型和方法的可用性.所提建模方法能够提供不同传输条件下的动态太赫兹信道响应数据,从而为今后太赫兹频段无线通信系统的设计与开发提供评估与测试依据.     

Quality of Service Aware Inter Carrier Interference Mitigation and Antenna Selection Schemes for Beyond 4G Systems

Future broadband wireless communication systems demand high quality of service (QoS) for anytime anywhere multimedia applications. The standards which use orthogonal frequency division multiplexing (OFDM) coupled with multi input multi output (MIMO) are expected to rule the future wireless world. Time selective nature of the channel introduces inter carrier interference (ICI), which is the major performance limiting parameter in OFDM based systems. ICI causes loss in spectral efficiency and results in poor bit error rate (BER) performance, affecting the QoS of MIMO-OFDM systems. The conventional single input single output (SISO)-OFDM-flexible subcarrier spacing (FSS) system offers better performance than the fixed subcarrier spacing systems in terms of ICI mitigation. But BER and spectral efficiency performance of SISO-OFDM-FSS is not good enough to satisfy the requirements of future wireless broadband services. To improve the BER performance, SISO-OFDM system is replaced by space frequency block coded (SFBC)-OFDM system, which adds spatial and frequency diversity benefits to the conventional system. More number of antennas in the MIMO scheme increases the hardware cost, computational complexity and percentage of overhead. In the present study, to improve the spectral efficiency and to reduce the complexity and cost, optimal transmit antenna selection (OTAS) is combined with the SFBC-OFDM-FSS scheme. The simulation results prove that the proposed SFBC-OFDM-FSS-OTAS scheme offers better QoS than the conventional SISO-OFDM-FSS scheme.     

无线紫外光MIMO直升机助降ALOS链路性能分析

无线紫外光通信具有高速率高可靠性的特点,可以满足复杂环境下的通信。通过直升机助降的过程提出近似直视通信方式,并研究了无线紫外光MIMO系统的ALOS通信链路模型,同时计算了弱湍流条件下ALOS链路中MIMO系统的误码性能,并仿真分析其信噪比、发射功率、发射（接收仰角）以及通信距离对误码率的影响。计算分析当发射（接收）仰角小于35时,误码率随着发射（接收）仰角的增大,其增长趋势比较明显,当大于35时,误码率随着发射（接收）仰角的增大,其增长趋势变缓。结果表明,在无线紫外光ALOS链路中,采用天线阵列和多探测器的MIMO技术能够较好地降低误码率和抑制大气湍流,并提高抗衰弱能力。     

不完美反馈自适应多天线跨层系统的性能分析

为提高网络无线通信的频谱利用率,提出一种自适应闭环多输入多输出(MIMO)跨层设计方案。该方案是融合物理层的自适应调制技术(AM)和数据链路层的自动重传技术(ARQ);发射端利用反馈信息,自适应选择调制模式和发射权矢量,并自动重传数据,形成三重反馈的闭环MIMO跨层系统。推导了不完美反馈下的系统频谱效率和中断概率闭合表达式,分析了时延对跨层系统性能的影响。仿真结果表明:对比单发/单收(SISO)跨层系统以及开环MIMO跨层系统,自适应闭环MIMO跨层系统的性能有明显提高。     

Performance analysis of hybrid transmit antenna selection/maximal‐ratio transmission in Nakagami‐m fading channels

Hybrid diversity systems have been of great importance because they provide better diversity orders and robustness to the fading effects of wireless communication systems. This paper focuses on the performance analysis of multiple‐input gle‐output systems that employ combined transmit antenna selection (TAS)/maximal‐ratio transmission (MRT) techniques (i.e., hybrid TAS/MRT). The probability density function, the moment generating function and the n ^th order moments of the output signal‐to‐noise ratio of the investigated diversity scheme are derived for independent identically distributed flat Nakagami‐m fading channels. The system capacity of the hybrid TAS/MRT scheme is examined from the outage probability perspective. Exact bit/symbol error rate (BER/SER) expressions for binary frequency shift keying, M‐ary phase shift keying and square M‐ary quadrature amplitude modulation signals are derived by using the moment generating function‐based analysis method. By deriving the upper bounds for BER/SER expressions, it is also shown that the investigated systems achieve full diversity orders at high signal‐to‐noise ratios. Also, by Monte Carlo simulations, analytical performance results are validated and the effect of feedback delay, channel estimation error and feedback quantization error on BER/SER performances are examined. Copyright © 2011 John Wiley & Sons, Ltd.     

PERFORMANCE OF THE ZERO FORCING PRECODING MIMO BROADCAST SYSTEMS WITH CHANNEL ESTIMATION ERRORS

In this paper, the effect of channel estimation errors upon the Zero Forcing (ZF) precoding Multiple Input Multiple Output Broadcast (MIMO BC) systems was studied. Based on the two kinds of Gaussian estimation error models, the performance analysis is conducted under different power allocation strategies. Analysis and simulation show that if the covariance of channel estimation errors is independent of the received Signal to Noise Ratio (SNR), imperfect channel knowledge deteriorates the sum capacity and the Bit Error Rate (BER) performance severely. However, under the situation of orthogonal training and the Minimum Mean Square Error (MMSE) channel estimation, the sum ca- pacity and BER performance are consistent with those of the perfect Channel State Information (CSI) with only a performance degradation.