【作者】 周军；

【导师】 任俊彦； 叶凡；

【作者基本信息】 复旦大学 ， 微电子学与固体电子学， 2010， 硕士

【摘要】 超宽带(Ultra Wide Band, UWB)是一种适用于短距离、高速、无线数据传输的技术。它能够在2米的室内多径环境中,提供最高480Mbps的传输速率。超宽带技术在下一代无线个域网、无线家庭互联等领域拥有广泛的应用前景。目前,WiMedia联盟倡导的基于正交频分多路复用(MB-OFDM)技术的超宽带架构被国际标准组织(ISO)采纳为超宽带国际标准。在中国,一种基于双载波正交频分复用(DC-OFDM)技术的超宽带技术被采纳为中国超宽带标准草案。这种双载波正交频分复用超宽带系统具有更多的频谱资源、较低的硬件要求等优点,同时它兼容了MB-OFDM传输标准,具有较高的灵活性。同步(Synchronization)处于接收机数字基带最前端,是任何无线通信系统中不可或缺的过程。它的性能好坏直接决定了接收机能否正确接收射频信号,基带模块能否有效完成数字信号处理功能。在基于OFDM技术的无线通信系统中,同步过程大致分为两个部分：符号同步和频率同步。符号同步完成对经过多径信道衰落影响的OFDM符号起始位置的判断。频率同步完成对模拟前端诸多非理想因素干扰的估计和补偿。本文围绕DC-OFDM超宽带系统中同步问题展开系统研究,首次分析了适用于DC-OFDM超宽带系统的同步算法与硬件实现方法,并给出了同步模块的VLSI设计结果。论文整体分为符号同步和频率同步两个部分。在符号同步方面,我们分析了多种同步误差对OFDM系统造成的性能影响。然后,我们将整个符号同步过程按照功能划分为包检测、粗同步、时频码检测和精细同步四个部分,并通过系统仿真确认每一部分的参数设置。算法设计方面,我们采用了相关检测和能量检测相结合的方法来满足超宽带系统对于室内多径环境下的要求,实现了较好的鲁棒性。硬件实现方面,我们重点介绍了符号同步模块中重要的信号处理单元的结构和VLSI实现结果,如自相关器、互相关器、实数除法器等。在频率同步方面,我们首先分析了OFDM系统中多种模拟前端非理想因素的影响,如载波频偏,采样频偏和I/Q失配,并给出了他们在DC-OFDM超宽带系统中的数学模型。然后,我们采纳误差矢量幅度(Error Vector Magnitude,EVM)作为参考,分析讨论了这些非理想因素对于OFDM系统性能的损失。射频工程师可以通过本文的理论分析在失配参数与性能损失之间建立关联,从而指导工程师在硬件设计的早期完成系统规划。算法设计方面,本文分析了I/Q失配引入镜像频率干扰的特点,继而设计了一种基于相位旋转的训练序列并给出了相应的失配估计算法。仿真结果表明,新的训练序列能够获得I/Q失配过程中引入的分集信息,从而使系统在解调过程中得到额外的分集增益。然后,我们针对多种模拟前端非理想因素共存的复杂情形提出了一种联合估计和补偿算法。硬件实现方面,我们给出了适合于DC-OFDM超宽带系统中载波频偏估计和补偿模块的设计方法,并着重介绍了负责三角函数运算的CORDIC单元。VLSI实现结果表明,本文所设计的频率同步模块满足DC-OFDM超宽带系统的时序和资源要求。论文最后给出了未来的工作计划。在60GHz无线应用中将包括更多非理想因素的影响,如相位噪声、非线性功率放大、直流偏移、ADC偏差等。对于这些非理想因素的联合估计和补偿将更具挑战性。更多还原

【Abstract】 UWB is a promising technology for short-range high-rate wireless applications. It is able to provide maximal 480Mbps data-rate at a distance of 2 meters in realistic indoor multi-path environments. UWB technology is widely applied to the next generation WPAN as well as the wireless access of consumer electronics at home. Recently, Multi-Band OFDM based UWB technology proposed by WiMedia has been selected as the international standard by ISO. In China, a new transmission architecture based on Dual-Carrier OFDM technology is adopted as UWB standard draft. Comparing to MB-OFDM based UWB system, DC-OFDM based UWB system has multiple advantages, like more spectrum resource, lower requirements on devices, etc. Besides, it is compatible with existing MB-OFDM based UWB technology. Therefore, DC-OFDM based UWB is more flexible.Synchronization is the first step at the receiver digital baseband, which is of tremendous importance in any wireless communication systems. The performance of synchronization directly determines whether the receiver can pick up radio signals correctly or not, whether the baseband modules can fulfill the digital signal processing effectively or not. The synchronization process in OFDM system can be briefly divided into two parts:symbol timing and frequency synchronization. Symbol timing serves to judge the starting position of OFDM symbols after considering the impact of multi-path fading channel. While the frequency synchronization estimates the multiple imperfections in analog front-end signal processing and make proper compensation.This thesis puts the emphasis on synchronization issues in DC-OFDM based UWB systems. We are the first to analyze the synchronization algorithm as well as the hardware implementation method tailored for DC-OFDM based UWB system. We also present the VLSI implementation result for synchronization module. The thesis consists of symbol timing and frequency synchronization.Regarding on the symbol timing, we analyze the impact of several synchronization errors in OFDM system. After that, we divide the synchronization process into four modules by functionality:packet detection, coarse timing, TFC detection and fine timing. The internal parameters in each module are determined by system simulations. In the aspect of algorithm development, we adopt the joint auto-correlation and cross-correlation method to meet the requirements of UWB system in different indoor multi-path environments, and therefore achieve the robustness. In the aspect of hardware implementation, we put the attention on the structure of some key modules in symbol timing and their VLSI implementation result, such as auto-correlator, cross-correlator, real-number divider, etc.Regarding on the frequency synchronization, we first investigate the multiple analog front-end imperfections in OFDM system, like CFO, SFO and I/Q imbalance, and present their mathematics models respectively in DC-OFDM based UWB system. After that, we analyze the performance degradation in OFDM system due to these non-ideal effects by the metric of EVM. RF designer can build the connection between mismatching parameters and performance degradation by referring to the analysis. Hence, the RF designer is able to trace out the outline of system design. In the aspect of algorithm development, we explore the intrinsic character of I/Q imbalance which causes the image interference. Then, we design a set of new training sequences based on phase rotation and give the corresponding estimation algorithm. The simulation result shows that the new training sequence is able to obtain the diversity message introduced by I/Q imbalance and therefore achieve the diversity gain during demodulation process. In order to deal with the challenging situation where multiple analog front-end imperfections co-exist, we propose a joint estimation and compensation scheme. In the aspect of hardware implementation, we present the hardware structure of CFO estimation and compensation module catered for DC-OFDM based UWB system, with the emphasis on CORDIC unit that is responsible for triangle calculations. The VLSI implementation result shows that the proposed CFO estimation and compensation module satisfies the timing and resource requirements in DC-OFDM based UWB system.In the last, we present the prospective research area in 60-GHz applications. It includes multiple non-ideal impairments, like phase noise, non-linear power amplification, DC offset, ADCs mismatch, etc. It is even more challenging to develop joint estimation and compensation scheme for these non-ideal effects.更多还原