协作通信中高效鲁棒的分布式空时编码技术研究

As an important approach to exploit the spatial resources in wireless communications, the cooperative communication technique faces different kinds of challenges that arise from the distributed feature of the multiple collaborating nodes. One of the most important is the inherent multiple timing errors and frequency offsets among the distributed nodes. Most existing distributed space-time coding schemes only considered the timing errors or frequency offsets. However, the existence of both the above two factors not only increases the receiver design complexity at the destination, but also may lead to the loss of diversity gain or even severe performance degradation in existing coding systems. To deal with this problem, this project proposes designing high efficient and robust distributed space-time code based on the concept of equivalent local oscillator frequency synchronization. Specifically, this project will aim at designing distributed space-time codes which are robust to both timing errors and frequency offsets by exploiting the following two ideas. One is based on the convolution and amplify forwarding at the relay nodes, and the other one is based on the frequency domain orthogonal space-time coding. By doing so, the forwarded signals from the multiple distributed relay nodes can automatically achieve an equivalent local oscillator frequency synchronization. For mobile scenarios, based on the array signal processing, this project will further convert the original complicated problem with multipath and multiple Doppler shifts into the simplified situation with only one Doppler shift between each transceiver pair, and will then study the design theory of the distributed space-time codes which are also robust to the Doppler shifts. In addition to the above theoretical research, this project will also evaluate the proposed studies based on the existing hardware experimental platform for cooperative communication.

作为无线通信中发掘空域资源的重要手段，协作通信技术面临着由节点分布式特性带来的诸多挑战，首当其冲的便是节点间固有的多个时偏和频偏。现有的分布式空时编码往往仅考虑节点间的时偏或频偏。时频偏的同时出现不仅会增大目标节点接收机的设计复杂度，而且可能会给现有编码设计带来分集增益的丧失甚至性能的严重下降。针对此问题，本申请提出利用中继节点等效本振频率同步的思想来设计高效鲁棒的分布式空时编码。拟分别基于中继节点卷积放大转发和频域正交空时编码两个思路来设计对时频偏同时鲁棒的分布式空时编码，同时使得各中继节点无需调整本振频率便可自动实现等效的本振频率同步。拟进一步针对移动场景，基于阵列信号处理技术将复杂的多径多普勒频偏问题分解为节点间仅具有单多普勒频偏的简化场景，并以此为基础研究对多普勒频偏鲁棒的分布式空时编码设计。在理论方法研究的同时，拟使用已有的协作通信硬件实验平台对提出的理论方法进行实测验证和评估。

与传统集中式多天线不同，协作通信系统面临着由节点分布式特性带来的诸多挑战。首当其冲的便是多个中继节点间的时频异步问题。据此，本项目针对协作通信系统中高效鲁棒的分布式空时编码技术展开了深入研究，着力设计对节点间固有的时偏和本振频偏同时鲁棒，且能避免目标节点复杂接收机设计的分布式空时编码。具体研究进展包括：..1）针对分布式的协作节点，提出了一种简单高效的分布式卷积延迟空时编码方案。各中继节点无需调整本振频率便会自动获得等效的本振频率同步。目标节点接收端可基于最小均方误差准则设计频域判决反馈均衡器来获取满分集增益。..2）在分布式频域正交空时编码设计方面，项目组提出了适用于任意多个节点的分布式频域正交空时编码方案。项目组通过理论分析和仿真结果表明，当节点间的时频异步限定在某个范围之内时，所提方案在时频异步场景中仍然能够获得空域分集增益。..3）针对移动场景中的分布式空时编码系统，项目组提出了基于阵列信号处理空域多径分离的分布式空时编码方案。所提方案可以从根本上消除移动场景中多径多普勒频偏对分布式空时编码系统的影响。..4）在理论方法研究的同时，项目组基于微软SORA软件无线电平台搭建了分布式空时编码实验平台。项目组还基于软件无线电思想研制了一套通用阵列信号处理实验平台。项目组进一步基于硬件平台测试评估了空时编码系统对异步的鲁棒性。..以上研究充分表明了中继节点等效本振频率同步思路在鲁棒分布式空时编码设计中的可行性。另外，项目组还结合自身在无线通信信号处理方面的研究经验，针对目标节点分别设计了一系列基于接收端多天线的载频偏和频选信道的盲估计方法。本项目已按计划顺利开展，在上述几个方面获得了一定的理论突破和技术创新，取得了丰富的研究成果，预期将对促进相关学科的研究起到积极的推动作用。