时间选择性衰落信道DS-CDMA系统的联合时空频3D-Rake

针对Rake接收结构由于快衰落导致多普勒散布，导致系统性能下降的问题，在时频Rake、时空Rake接收机设计基础上，提出一种联合时空频3D-Rake接收结构。利用自适应天线在空间形成定向波束和利用联合时频处理技术，将频域多普勒频率分集的分析方法应用到时空二维处理中，实现基于天线阵列的时空频三维信号处理。通过接收合并具有不同时延、多普勒频移和来自不同方向的信号，实现最大信噪比准则下的最优接收，提高系统分集增益，和时频Rake、时空Rake相比，其系统性能得到进一步提高，数值仿真表明，联合时空频3D-Rake比时空Rake平均信干噪比提高了3dB。

Joint space-time-frequency (3D) Rake in DS-CDMA systems over time-selective fading channel

According to the Doppler induced by rapid channel variations, the performance of the Rake receiver degrades under time-selective channels, and the conventional receiving structure cannot satisfy the acquirement. After analyzing the multipath-Doppler Rake (TF-Rake) and the space-time Rake (ST-Rake), a joint 3D-Rake receiver is proposed for achieving diversity in spatial, temporal and frequency domains. It combines the Doppler diversity technology with the space-time processing, and utilizes the powerful tools of time-frequency analysis and adaptive beamforming. The diversity idea behind the Rake receiver is now extending from time domain to frequency (Doppler shift) and space (antenna array beamforming) domain. It can provide maximum SINR estimation of signal by optimally combining desired signals from different paths, different antenna elements and with different Doppler frequency. Compared with TF-Rake and ST-Rake, it provides substantial performance improvement. The numerical simulations show that the 3D-Rake receiver has a 3dB improvement than ST-Rake.