多用户OFDM系统上行信号迭代接收技术研究

Since Orthogonal Frequency Division Multiplexing (OFDM) plays a key role in physical layer of the fourth-generation mobile communication system (4G), research on multiuser-OFDM systems which support high speed mobility is of great significance in both theoretical and application aspects.. Compared with the downlink situation of a multiuser-OFDM system, its uplink transmission is confronted with more challenging tasks. The received uplink waveform is a mixture of signals coming from different end-users and containing different parameters such as frequency/timing offsets and channel impulse responses, which increases difficulty in signal processing at the base station. Since turbo receiving has emerged from many signal processing technologies and showed better detection performance, this project focuses on turbo (iterative) detection for uplink transmission in multiuser-OFDM systems supporting high speed mobility. The detailed technical innovations are summarized as follows:. 1) Research on the multi-parameter estimation technology. A multi-parameter estimation algorithm for the uplink of multiuser-OFDM systems is proposed, in which carrier frequency offsets (CFO), symbol timing errors (STE) and channel impulse response (CIR) of all end-users can be estimated.. 2) Research on the iterative receiving technology for both CFO compensation and uplink signal detection. A turbo receiver based on the combination of CFO compensation and signal detection is proposed for uplink signals of multiuser-OFDM systems. The proposed receiver jointly performs soft interference cancellation based CFO compensation, frequency-domain equalization and maximum a posteriori (MAP) based decoding in an iterative fashion.. 3) Research on the performance of the proposed turbo receiver with the proposed multi-parameter estimation algorithm by using the two uplink models of 4G standards. Bit error rate (BER), convergence rate and computational complexity of the proposed receiver will be tested and verified by computer simulation, which demonstrates its feasibility, efficiency and performance superiority, compared with some existing turbo receivers..

正交频分复用(OFDM)被定为4G物理层核心技术，该背景下对支持用户高速移动的多用户OFDM系统开展研究具有一定理论意义和应用前景。该系统中各用户上行信号受到不同的时频误差和信道衰落影响，这使得基站在后4G时代如何实现更高性能的接收处理成为难题。鉴于近年来迭代接收被看作获取更高性能增益的检测手段，本项目拟针对多用户OFDM系统上行信号迭代接收技术开展研究：1）提出一套针对时频同步参数与均衡参数的联合估计方案，以获得各用户时频同步误差和信道冲激响应等估值；2）提出一套将时频同步误差补偿和频域Turbo均衡相结合的迭代接收处理方案，利用前述估值实现最小均方误差准则下上行信号时频同步、频域均衡和最大后验概率信道译码的最优化联合迭代接收；3）兼顾4G国际标准给出的升级版LTE和升级版WiMAX两套上行传输体制，测试该迭代接收机的误码率、收敛性和复杂度，论证其较之于现有迭代接收机的性能优势。

本项目计划针对支持高移动性的多用户OFDM系统上行同步、均衡和解码的联合接收技术开展研究。在本项目为期三年的研究过程中，项目组全体人员能够严格遵照原《申请书》中拟定的研究计划执行相应的研究任务，并紧跟这三年期间的5G最新研究趋势对原研究内容进行适当扩展。迄今为止，我们已顺利实现了本项目原定的研究目标。本项目的主要研究内容和取得的重要结果说明如下：. 一、同步参数与均衡参数的联合估计技术研究：提出了一套简单易行的多用户信号同步参数(CFO、STE)和均衡参数(CIR)的联合估计方案。. 二、时频同步、均衡与解码的联合迭代接收技术研究：提出了一套包含时频同步、频域均衡和解码的最优化联合迭代接收方案，可实现时频同步模块、频域均衡模块和信道解码模块在最小均方误差准则下的联合迭代。. 三、迭代接收机的性能评估：联合迭代接收方案较之于现有迭代接收方案的各项预期性能（复杂度、误码率和收敛性）优势均得到了仿真验证。. 四、面向5G新波形的峰均功率比参数降低方法研究：针对5G物理层备选技术——基于滤波器组的多载波(FBMC)系统，提出了一套将限幅法和部分序列传输方法相结合的PTS-Clipping峰均功率比降低方案。. 五、面向5G的广义频分复用(GFDM)接收技术研究：针对5G物理层备选技术——广义频分复用(GFDM)系统，设计出了一套完整的MIMO-GFDM发射接收方案，并完成了与OFDM系统的各性能指标对比。. 六、面向5G的D2D蜂窝异构网络物理层安全优化策略研究：针对D2D通信与蜂窝通信共存的蜂窝异构网络，提出了一套基于物理层安全机制的自适应功率控制和接入控制策略。. 七、信号迭代处理新方法和新应用：尝试利用当今流行的机器学习/深度学习模型解决信号处理问题，提出了一套基于自学习框架的传感信号迭代处理方法并应用于移动健康监测。. 本项目执行期间已公开发表学术论文14篇，其中SCI检索5篇、EI检索9篇，这些研究成果可用于优化现有4G蜂窝移动通信系统的底层信号接收处理算法性能，并为5G新空口物理层关键技术和协议的进一步完善提供理论指导。