正交M元码元移位键控扩频水声通信

M元和码元移位键控(CSK)扩频在水声通信中被广泛采用来克服扩频增益对通信速率的限制。为了获得更高的通信速率,文章基于Gold序列较大的码本数量、良好的自相关和互相关特性,提出正交双通道的M元和CSK相结合的水声通信方法。通过公式推导描述了正交M元CSK的调制和解调流程及影响其性能的因素。并且,通过与双通道M元CSK的仿真比较,得到正交M元CSK的误码率曲线。最后,通过实验验证了仿真的有效性。并实现了10 kbits数据量下1096.8 bps通信速率的无误码传输。通过推导、仿真和实验,可以得到这样的结论:正交M元CSK提供了优良的通信性能。      

M元码元移位键控扩频水声通信

针对传统直接序列扩频、M元扩频和码元移位键控扩频水声通信速率低的问题,基于小Kasami序列优良的自相关和互相关特性,提出了M元扩频和码元移位键控扩频两者相结合的水声扩频通信新方法.不仅利用了不同的序列信息,还利用了相同序列的扩频码相位信息.对于自相关和互相关函数在加性高斯白噪声和衰落信道下对M元码元移位键控扩频这种水声通信方法的影响进行了分析,并分别在两种信道下对其性能进行仿真,仿真结果表明在同等通信速率下M元码元移位键控扩频的抗噪声能力要高于直接序列扩频、M元扩频和码元移位键控扩频.在水池对M元扩频、码元移位键控扩频和M元码元移位键控这三种情况进行了比较性实验.在10~4比特的数据量下,实现了253.6 bps通信速率的M元码元移位键控无误码传输.     

正交多载波M元循环移位键控扩频水声通信

针对水声扩频通信中频带利用率低的问题, 提出了一种M元扩频技术和循环移位键控(CSK)技术相结合的多载波调制方式, 将M元扩频后选择的扩频码同时采用CSK调制, 并调制在多个正交的载波上, 显著提高了频带利用率. 在水声多途信道下, 采用相同的通信速率和带宽, m序列、Kasami小集合序列和Gold序列为扩频码时, 比较了系统的误码性能. 仿真结果和实验结果均表明, m序列为扩频码时性能最优, Gold序列性能最差. 由于m序列数量有限, 为了进一步提高通信速率, 并使其他序列的性能接近m序列性能, 提出了一种复合序列抑制载波间干扰的算法, 该算法能够很好抑制多途干扰, 使复合序列性能接近m序列的性能. 关键词： M元扩频')" href="#">M元扩频 循环移位键控 正交多载波 载波间干扰     

循环移位扩频水声通信

针对常规直接序列扩频水声通信数据传输速率低及M元扩频水声通信接收机复杂度高的问题,基于扩频序列优良的相关特性,提出循环移位扩频水声通信方法.在发射端,根据输入信息对基本波形进行循环移位编码;在接收端,利用快速相关技术进行时延估计及译码.进行了中远程湖上实验研究,在15 km距离,2 kHz带宽内,总数据传输速率可达438 bit/s, 误码率为10^-2—10^-5.实验结果表明该方法具有带宽利用率高、复杂度低的特点,适用于中远程及多用户水声通信. 关键词： 水声通信 扩频 循环移位 时延估计     

Pattern时延差编码四信道水声通信技术研究

本文所研究的是基于Pattern时延差编码（PDS）体制下的水声通信技术.PDS水声编码体制利用Pattern码片出现在码元窗的时延差值进行时延编码,通过码元分割,有效的降低了水声信道的多途干扰;通过频率分割划分四个通信信道,增加通信速率至1000bit/s.在接收端利用带通滤波器来实现通信信道分割,每个信道再应用拷贝相关器实现码元分割并估计出时延差值,完成译码.仿真实验表明,该系统适合于大量不同水声信道高可靠性工作,为水声通信网络化打下坚实基础.     

M元混沌扩频多通道Pattern时延差编码水声通信

Pattern时延差编码水声通信体制利用信息码元的时延值调制信息，他的抗多途扩展干扰能力与码型种类及码型脉宽有关. 扩频通信可获得扩频增益，可胜任远程水声通信，但其通信速率低是使用受限的重要原因. 提出将扩频通信与Pattern时延差编码水声通信体制相结合，并采用M元扩频、多通道工作方式，构成一种新的适用于水声环境的通信方案，既可获得扩频通信的优良性能，又可提高通信速率. 湖试结果验证了本文提出的M元混沌扩频多通道Pattern时延差编码水声通信方案的鲁棒性及可行性.     

M元混沌扩频多通道Pattern时延差编码水声通信

Pattern时延差编码水声通信体制利用信息码元的时延值调制信息,他的抗多途扩展干扰能力与码型种类及码型脉宽有关.扩频通信可获得扩频增益,可胜任远程水声通信,但其通信速率低是使用受限的重要原因.提出将扩频通信与Pattern时延差编码水声通信体制相结合,并采用M元扩频、多通道工作方式,构成一种新的适用于水声环境的通信方案,既可获得扩频通信的优良性能,又可提高通信速率.湖试结果验证了本文提出的M元混沌扩频多通道Pattern时延差编码水声通信方案的鲁棒性及可行性.     

猝发混合扩频水声隐蔽通信技术

针对常规的连续载波调制扩频通信方式容易通过能量检测的方法被截获的问题,提出了一种猝发的混合扩频水声隐蔽通信方式,该方法通过在时间上随机的发送脉冲混合调制扩频信号来降低截获概率,而且可以比较灵活的通过调整平均占空比来满足不同隐蔽性的要求,但是该隐蔽性是以牺牲通信速率为代价的。猝发信号中混合了二进制相位键控(BPSK)、循环移位键控(CSK)和多进制频移键控(MFSK)扩频调制方式,采用自同步和时频二维搜索算法实现码元和载波同步。通过仿真分析了猝发通信系统的隐蔽性能和多途信道下的误码性能,并且通过了南海海试验证了算法的性能,在5 km的通信距离上,4 kHz的带宽内,单个脉冲信号的通信速率可以达到317 bps,误码率达到10-3以下。      

基于差分Pattern时延差编码和海豚whistles信号的仿生水声通信技术研究

为解决传统的隐蔽水声通信方法带来的通信性能降低问题, 提出了一种将差分 Pattern 时延差编码通信体制与海豚whistles信号相结合的仿生水声通信技术. 海豚whistles信号频带较窄且各信息码元间隔不等、码元之间互相关性较弱, 选取whistles信号作同步码和Pattern 码, 并以相邻whistles信号之间的时延差值携带信息. 这种仿生的水声通信信号不易被敌方探测、截获, 且差分Pattern时延差特殊的编码方式也不易使信息被破译, 因此该水声通信技术具有较强的隐蔽性和保密性, 且在抗码间干扰以及抗多普勒效应方面具有优异性能. 本文对系统进行了水池实验, 在信噪比为0 dB、存在相对运动时实现了通信速率为67 bit/s的低误码数据传输, 验证了系统的有效性、稳健性和隐蔽性. 关键词： 仿生水声通信 差分Pattern时延差编码 海豚whistles信号 隐蔽性     

基于扩频码的单载波迭代频域均衡水声通信

单载波时域均衡在长时延扩展水声信道中计算量大,并对接收机参数的选择较为敏感,可靠性低,而正交频分复用信号峰均功率比高、对频率偏移敏感. 针对这些问题,提出基于扩频码的单载波块传输高速率水声通信方法和基于T/4分数间隔迭代频域均衡的接收机算法. 该接收机利用已知扩频码进行信道估计以及对由多普勒偏移引起的旋转相位进行估计,并通过一种低复杂度迭代频域均衡算法改善系统性能. 开展了湖上实验研究,结果表明在浅水1.8 km距离且复杂多径干扰条件下,利用BPSK/QPSK调制可实现10^-2–10^-4的误码率并达到1500–3000 bit/s的有效数据率. 关键词： 水声通信 单载波 频域均衡 迭代处理     

Orthogonal M-ary code shift keying spread spectrum underwater acoustic communication

M-ary and code shift keying（CSK）spread spectrum is generally applied to overcoming the spreading gain versus data rate limitation in underwater acoustic（UWA）communications.In addition,the concept of orthogonal M-ary CSK is introduced to UWA communication to gain higher rates.We propose a scheme employing dual-orthogonal-channel M-ary and CSK spread spectrum UWA communication based on Gold sequences owing large code set and good self and cross correlation.The modulation and demodulation scheme of the orthogonal M-ary CSK is derived algebraically and the factors critical to its performance are discussed.Furthermore,its bit error rate（BER）curve is evaluated via simulations and compared with the dual-channel M-ary CSK.Finally,the validity of the simulations is verified in tank experiments.1096.8 bps data rate of the proposed communication scheme is realized for 10 kbits data volume with no error.Overall through deduction,numerical simulation,and experiment,it is shown that the proposed method offers significantly improved performance.     

Experimental demonstration of underwater acoustic communication using bionic signals

This paper applies dolphin whistles to covert underwater acoustic (UWA) communication and proposes a UWA communication scheme based on M-ary bionic signal coding. At the transmitter end, the scheme maps multiple information bits into a dolphin whistle through a signal selector. At the receiver end, passive time reversal mirror (PTRM) is used for channel equalization and source information is restored according to the decision of which whistle is transmitted. The scheme has high spread spectrum gain. The anti multi-path performance is greatly improved when using PTRM. Different from traditional covert UWA communication methods, this mimicked signal is unlikely to alert an adversary even in high SNRs because of its real existence in marine environment. A tank experiment is conducted for the scheme, at communication rate of 50 bit/s with SNR −5 dB user information is recovered at a very low bit error rate. The results of tank experiment demonstrate the feasibility of this covert UWA communication scheme.     

Chaotic direct sequence spread spectrum for secure underwater acoustic communication

Direct sequence spread spectrum (DSSS) has been widely used in underwater acoustic (UWA) communications. In DSSS communications, spreading sequence’s period and chip rate are important characteristic parameters. However, these characteristic parameters may be detected in hostile environments due to the periodic nature of spreading sequence and their well-known construction process. In this paper, a novel chaotic direct sequence spread spectrum (CD3S) method is proposed for secure UWA communications. In the CD3S communications, chaotic sequences acting as encryption keys are used to encrypt the phases of transmitted signals. Consequently, the application of chaotic sequences disguises these obvious characteristic parameters of spread spectrum (SS) signals. It is difficult for unauthorized users to detect or intercept CD3S signal without knowledge of corresponding chaotic sequences. Hence, CD3S signal has a lower probability of detection and interception. Moreover, CD3S can achieve similar bit error ratio (BER) performance compared with DSSS in actual UWA communications. Also, the receivers that are suitable for DSSS communication can also be applied to CD3S communication. Numerical simulations demonstrate its excellent performance and potential applications in confidential UWA communications.     

OFDM-based visible light communication with rotated polarity modulation aided complex color shift keying

High-rate techniques, such as optical orthogonal frequency division multiplexing(OFDM) and color shift keying(CSK), have been proposed for visible light communication(VLC). To fully exploit their advantages,in this Letter, we design a modulation scheme called rotated polarity modulation(RPM) aided complex CSK(CCSK) for OFDM-based VLC systems and derive its theoretical bit error rate and an optimal scaling factor. Analytical and simulation results show that in comparison to the existing schemes, the new RPM-CCSK-OFDM system offers an improved link performance and data rate under a modest complexity.It can also be applied to VLC systems equipped with different types of LED devices, thus enabling flexible deployments.     

基于单矢量差分能量检测器的扩频水声通信

通过获得扩频处理增益, 直接序列扩频水声通信系统具有较高的稳定性, 是高质量水声通信及远程水声通信的首选通信方式. 但复杂的海洋环境使得直扩系统在解扩时受到载波相位跳变的影响, 这将导致直扩系统的扩频处理增益下降. 为此, 本文针对直扩系统提出了差分能量检测器算法, 通过比较接收端相关器输出能量完成解码, 并与有源平均声强器算法相结合, 提出单矢量差分能量检测器算法. 该算法具有很好的抗载波相位跳变和多途扩展干扰的能力, 并可对信号方位信息实时跟踪估计, 利用估计方位进行矢量组合可获得矢量处理增益, 从而保证直扩系统可以在低信噪比、时变信道条件下稳定工作. 通过仿真分析和大连海试试验, 验证了本文提出的单矢量差分能量检测器算法的有效性和稳健性.     

Channel temporal correlation-based optimization method for imperfect underwater acoustic channel state information

The rapid time variations and large channel estimation errors in underwater acoustic (UWA) channels mean that transmitters for adaptive resource allocation quickly become outdated and provide inaccurate channel state information (CSI). This results in poor resource allocation efficiency. To address this issue, this paper proposes an optimization approach for imperfect CSI based on a Gauss–Markov model and the per-subcarrier channel temporal correlation (PSCTC) factor. The proposed scheme is applicable to downlink UWA orthogonal frequency division multiple access systems. The proposed PSCTC factors are measured, and their long-term stability is verified using data recorded in real-world sea tests. Simulation and experimental results show that the optimized CSI effectively mitigates the effects of the temporal variability of UWA channels. It demonstrates that the resource allocation scheme using optimized CSI achieves a higher effective throughput and a lower bit error rate than both imperfect CSI and the CSI predicted by the recursive least-squares (RLS) algorithm.