多用户MIMO技术因其能够充分挖掘空域资源来大幅提升频谱利用效率和区域吞吐量的优势，成为下一代无线局域网的一项关键技术。然而，多用户MIMO技术在带来多用户增益的同时，引入了用户间共信道干扰，为了减少共道干扰，提升系统性能，需要合理地进行空域资源分配。对于基于OFDMA机制的下一代无线局域网，系统整个频带资源被划分为多个资源块，某一个时隙内用户只工作在一个资源块上，由于严重的反馈开销和探测时延，发射端想要获得每个用户在每个频域资源块上理想实时的信道状态信息（CSI）以实现多用户在多资源块上的空域资源分配是不可能的。而统计CSI具有长时缓变性并且可以较为容易地在发送端准确获取，所以本文基于统计信道信息对下一代无线局域网的空域资源分配技术进行研究。论文具体研究工作如下：

    （1）对下一代无线局域网的特征及关键技术进行了综述，重点讨论了多用户MIMO系统下基于实时CSI的线性预编码和基于统计CSI的预编码技术，并通过仿真验证了强相关信道下用户在空域资源上匹配的重要性。

     （2）对下一代无线局域网中迫零（ZF）传输下的多用户多子信道上的空域资源分配问题进行研究。针对下一代无线局域网中用户与接入点（AP）工作带宽不对等，多个用户在多个子信道上实时CSI反馈开销过大，探测时延过长的问题，考虑到统计CSI的长时缓变性，给出一种统计与实时CSI联合的空域资源分配方案。该分配方案首先根据统计CSI进行用户分组，然后再在各用户分组内进行实时CSI探测反馈和ZF预编码。仿真表明，本文给出的统计与实时CSI联合的空域资源分配方案，在降低了系统反馈开销的同时，保证了系统的性能。      

    （3）对下一代无线局域网中完全基于统计CSI传输下的多用户多子信道的空域资源分配问题进行研究。考虑到下一代无线局域网中用户配对间干扰严重，用户分组和速率可能低于单用户传输速率的情况，针对现有的基于统计CSI的快速分配算法求得的最优解中存在不合理用户对的问题，给出了一种改进的传输模式自适应切换的空域资源分配算法。该算法首先根据传输模式切换判决准则剔除不合理的用户组合，然后再从剩余的所有可能的用户组中找出最佳用户匹配进行多用户统计特征模式传输，而剩下未匹配的用户则进行单用户统计特征模式传输，仿真表明改进的传输模式自适应切换的资源分配算法所达到的系统和速率高于其他空域资源分配算法。

With the advantage of improving the spectrum efficiency and system capacity significantly by fully exploiting the spatial resource, multi-user MIMO has become a key technology of the next generation WLAN. However, multi-user MIMO will bring co-channel interference while introducing multi-user gain. In order to reduce co-channel interference and improve system performance, it is necessary to allocate reasonably spatial resource. For the next generation WLAN based on OFDMA, the whole frequency band is divided into multiple resource units. In a certain time slot, the user only works on a resource unit. Due to serious feedback overhead and sounding latency, it is essentially impossible for the transmitter to get the perfect and instantaneous channel state information (CSI) of each user on each frequency resource unit to implement the spatial resource allocation over multiple resource units. On the contrary, statistical CSI varies at a much slower rate than the instantaneous CSI and it can be more easily and accurately obtained at the transmitter. For this reason, based on statistical CSI at the transmitter, this dissertation investigates the spatial resource allocation of the next generation WLAN. The specific research work of this paper can be summarized as follows.

 

Firstly, the acteristics and key technologies of the next generation WLAN are introduced, followed by the analysis of the linear precoding based on instantaneous CSI and statistical precoding technology under multi-user MIMO system. After that, the necessity of the spatial resource allocation under strong correlation channel is verified by simulation.

 

Secondly, the spatial resource allocation on multi-user multi-subchannel under zero-forcing (ZF) transmission in the next generation WLAN is studied. To solve the problem that the work bandwidth of users and access point (AP) is not equal in the next generation WLAN and that the feedback overhead and sounding delay of instantaneous CSI of each user on each frequency resource unit is serious, taking into ac that statistical CSI varies at a much slower rate than the instantaneous CSI, a spatial resource allocation scheme of joint statistics and instantaneous CSI is put forward. In the proposed scheme, users are grouped based on statistical CSI firstly, and then instantaneous CSI feedback is performed for the intra-group users according to the allocation result to complete the ZF precoding. The simulation results show that the proposed spatial resource allocation algorithm can reduces the system feedback cost while ensuring the system performance.

 

Finally, the spatial resource allocation on multi-user multi-subchannel based on statistical eigen-mode transmission in the next generation WLAN is studied. To solve the problem that there are unreasonable user pairs in the optimal solution obtained by the fast resource allocation algorithm based on statistical CSI, considering that the sum rate of user groups may be lower than the single-user transmission rate with the serious interference between users in the next generation WLAN, an improved adaptive spatial resource allocation algorithm is proposed. In the proposed algorithm, we first remove the unreasonable user pairs by the transmission mode switching criterion, and then find out the optimal user matches with the multi-user statistical eigen-mode transmission while the other unpaired users perform the single-user statistical eigen-mode transmission. Simulation results show that the improved adaptive resource allocation algorithm achieves higher system rate than other spatial resource allocation algorithms.

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