【作者】 符桂英；

【导师】 张军；

【作者基本信息】 华南理工大学 ， 通信与信息系统， 2011， 硕士

【摘要】 水声信道是一种频谱资源非常受限的通信信道,这成为实现可靠、高速的水声通信的主要障碍之一。为了高效地利用水声通信中有限的频谱资源,需要合理地设计水声通信用户的信道接入方式。目前,常用的信道接入方式主要有固定分配方式和随机接入方式,但是这两种方式应用于水声通信都存在一定的不足:固定分配方式的各子信道由不同的用户所独占,造成了频谱资源的浪费,且网络的扩展性差;随机接入方式通常将整个信道给竞争胜出的用户使用,而水声信道传输时延大的特性会大大增加竞争冲突的概率,整个信道在冲突期间无法正常使用,同样造成了频谱资源的浪费。陆地通信中的认知无线电技术可以动态地使用最合适的频谱资源来完成无线传输,实现多用户高效的信道接入,显著地提高频谱利用率。因此,针对传统信道接入方式的不足,可以将认知通信技术应用到水声通信的信道接入过程中,以高效地利用水声信道有限的频谱资源。然而,认知技术应用于水下通信还存在诸多难点,其中,目前的认知通信网络一般采用专用控制信道进行信令的传输,会带来额外的带宽开销,因此专用控制信道并不适合在带宽很窄的水声信道中使用。鉴于水下认知通信中使用专用控制信道的局限性,本文对无需专用控制信道的水声信道动态接入方法进行了研究,并对传统的信令侦听算法进行了改进,以适应水声信道中较大的多普勒频移。本文先对传统的FFT能量检测和匹配滤波检测等信令侦听算法在水声通信网络中的性能进行了仿真与分析,结果表明它们的性能在多普勒频移较为严重的水声环境下明显下降。针对这一问题,本文提出了一种基于DTW的信令检测算法,并进行了仿真实验,结果表明,与匹配滤波检测和FFT能量检测算法相比,在无需对多普勒进行估计和补偿的前提下DTW检测算法具有更好的性能,它能有效克服多普勒效应的影响,从而降低水声通信网络的错误检测概率,有助于实现高效的信道接入,提高频谱利用率。更多还原

【Abstract】 Underwater acoustic channel is the most challenging channel in the world due to its time varying and frequency-selective characters. Especially, the extreme limited bandwidth obstructs the realization of most of intelligent and high bit rate underwater communication systems. Therefore, an underwater channel access method should cause little or no bandwidth overhead in order to take full advantage of the limited bandwidth available.Two kinds of traditional underwater channel access methods are fixed channel assignment and random access channel, but both of them will cause a waste of spectrum resources when used in underwater channel.In the terrestrial setting, cognitive radio has been of growing interest as it is able to increase spectrum efficiency and reduce collisions by opportunistically accessing a portion of free spectrum. But many cognitive radio techniques that have proven effective in the terrestrial setting can not simply be transplanted underwater. For instance a transmitter and receiver must agree on what frequency is going to be used before the data transmission begins. The classic approach is the use of a dedicated control channel, wherein all parameters can be negotiated before the data transfer begins. But this requires bandwidth overhead that is undesirable in the underwater setting.In this paper, we introduce a dynamic channel access method based on cognitive techniques, an approach for distributed channel allocation for the underwater acoustic environment that allows for dynamic control channel. This paper proposes the DTW signaling listening algorithm and studies its performance via simulations. The simulation results show that compared with FFT energy detecting algorithm and matched filter detecting algorithm, the DTW detecting algorithm is of much better performance in the underwater channel with doppler shift, which is beneficial to improve the channel utilization.更多还原