宽带分布式协作频谱感知与协作传输机理研究

Aiming at the scenario that the terminal for future wireless communication systems is a multi-mode one, and in order to solve the problems of low detection probability and long detection time as well as large interference to authorized users and low transmission efficiency for cognitive users, a distributed broadband cooperative spectrum sensing and transmission system based on the joint use of network coding and transform domain processing is proposed. In this proposed method, Chirp signals with different parameters are used for cognitive users, and conventional communication system is used for authorized users, and then, in the receiver end, by utilizing the energy concentration property of Chirp signals in the fractional Fourier transform domain, cognitive users with different parameters and authorized users can then be separated, and hence, the interference to authorized users can be reduced. In addition, network coding is used by different cognitive users to improve the transmission efficiency of cognitive frequency bands and at the same time, decrease the detection time to authorized users and improve detection probability. Moreover, by analyzing the optimization design of transmitted waveforms to cognitive users, multi-user network coding method, receiver design and channel estimation algorithm in complex channel condition, the detection probability of broadband spectrum sensing can be further increased and the detection time as well as interference to authorized users can be further reduced, and at the same time, the signal transmission of cognitive users can also be performed when conducting spectrum sensing, which can improve the transmission efficiency of cognitive users significantly.

本项目针对未来无线通信终端是多模终端这一场景，考虑现有频谱感知方法存在的检测概率低、检测时间长、对授权用户干扰大以及认知用户传输效率下降等问题，提出联合网络编码和变换域处理的分布式宽带协作频谱感知及信息传输方法。通过认知用户采用Chirp化的信号，而授权用户采用传统正弦信号的传输方式，在接收时利用认知用户信号在分数域的能量聚集特性可以实现认知用户之间以及授权用户同认知用户的信号分离，以降低对授权用户的干扰；在此基础上协作认知用户使用网络编码来提高认知用户的传输效率，同时还可以降低对授权用户的检测时间，提高检测概率。此外，通过研究认知用户发射波形的设计方法、多认知用户条件下的网络编码、复杂信道条件下的接收方法和信道估计方法，可以进一步提高宽带频谱感知的检测概率，降低检测时间和对授权用户的干扰，同时还可以在频谱感知的同时进行认知用户的信息传输，有效提高认知用户的信息传输效率。

针对现有频谱感知方法存在的检测概率低、检测时间长、对授权用户干扰大以及认知用户传输效率低等问题，提出联合网络编码和变换域处理的分布式宽带协作频谱感知方法。利用Chirp信号在分数域优良的能量聚集特性与多协作用户网络编码带来的增益，提出了高检测概率、低虚警概率、低检测时间以及低用户间干扰的基于中继的分布式协作频谱感知模型；设计得到易于分离的认知用户波形和对应的信道估计方法，进一步提升了系统性能。在此基础上，对上述提出的分布式协作频谱感知模型进行优化设计，提出了基于分布式协作频谱感知的协作传输方法，实现了认知用户传输速率的大幅度提升和检测概率的提高；同时，为了在满足用户需求的同时，进一步提升系统吞吐量和保证公平性，提出了联合用户分组和资源分配的波束赋形算法优化。最后，针对5G网络的研究现状，在频谱感知的基础上研究了联合变换域处理技术和协作通信的频谱共享策略，在通过协作传输保证授权用户通信性能的前提下，显著地提升了系统的频谱利用率和认知用户的吞吐量；为了进一步提升频谱利用率，提出了基于资源利用率的时延优先调度算法，有效提高了系统的吞吐量。本项目的研究为高效的频谱感知、信息传输与协作频谱共享的深入研究奠定了基础。