【作者】 黄仰博；

【导师】 欧钢；

【作者基本信息】 国防科学技术大学 ， 信息与通信工程， 2011， 博士

【摘要】 随着全球卫星导航系统的广泛应用,各个领域对导航接收机在捕获性能、多径抑制及实现复杂度等方面提出了更高的要求。现有研究主要在捕获算法、多径抑制算法等计算方法层面来开展优化研究,而本文结合电路实现约束来开展量化分析与优化方法研究,为导航接收机基带芯片设计提供更具指导性的优化设计方法。论文主要针对制约导航接收机基带芯片关键性能的四个方面开展了研究工作:1、信号捕获是导航接收机基带处理中计算复杂度最大、实时性要求最高的环节,其性能直接决定接收机的首次定位时间、接收灵敏度等关键指标。已有研究对捕获方法硬件实现复杂度缺乏准确和系统的定量分析,本文在统一的信号捕获模型下,系统地比较了时域、频域、时频域等信号捕获方法的硬件复杂度和实现约束条件,给出了量化的分析结论,为基带芯片设计的实现复杂度评估提供了系统性的量化分析方法。2、伪码相位误差、载波频偏以及伪码频偏均会导致捕获性能严重恶化,而已有的捕获方法通常没有对它们的影响进行处理或补偿。针对伪码相位误差和载波频偏引起的相干处理损耗,提出了基于相邻检测量组合判决的检测方法,可显著提高系统的检测概率,在常规搜索步进条件下,最大可使检测器的等效信噪比提高3.8dB。针对伪码频偏问题,提出了一种基于信号采样分数抽取的伪码频偏补偿技术,避免了因修改本地码采样频率而带来的工程实现难题,在5倍码率的采样率条件下最大伪码频偏损耗小于0.5dB、峰值偏移小于0.1个码元宽度,可以满足大多数高动态捕获系统的要求。在此基础上,提出了一种基于匹配滤波频域并行FFT捕获的改进捕获方案,并优化了匹配滤波器的设计和频率搜索策略。3、多径效应是影响导航接收机定位精度的主要因素之一,在一些高精度测量应用中甚至是最主要的误差源,多径问题也是当前高性能导航接收机的一个研究热点。针对导航接收机中多径抑制算法性能和资源占用量之间的矛盾,提出了一种基于FIR滤波器模型的多径抑制方法,其性能与基于最大似然估计的MEDLL算法相当,但优点是计算量与多径信号数量无关,可大大减小存在多个路径信号时的硬件实现复杂性。针对高分辨率多相关器的实现问题,提出一种基于本地伪码差分的实现结构,在相关器间隔为1/16码元宽度条件下,其计算量只有传统结构的1/32,硬件规模只有传统结构的1/8。4、通过建立多任务划分的导航接收机基带处理模型,提出了一种基于多处理器协同工作的芯片架构,用多个协处理器对多任务进行并行处理,克服了传统基带接收机集中式单一处理器的资源占用高、调度复杂、计算实时性要求高等缺点,简化了基带芯片设计,同时兼顾了基带处理的灵活性和处理效率。针对芯片开发过程中仿真验证耗时长、工作量大等问题,研究了基于Palladium仿真加速器仿真流程和基于FPGA的芯片原型验证方法,直接应用于导航基带芯片开发,并通过实际样片测试,在功耗、处理性能方面充分验证了上述技术研究的有效性。论文的研究成果已经应用于我国自主卫星导航系统接收机和基带芯片的设计中,并取得了良好的应用效果。相关方法和结论也可应用于其他扩频系统的测距接收机设计。更多还原

【Abstract】 As GNSS (Global Navigation Satellite System) is widely used all around the world, various fields have more requirements for navigation receiver, such as acquisition performance and multipath mitigation. Existing researches mainly pay attention to the algorithm for acquition and multipath mitigation. But quantitative analysis and optimized method combined with the restrictions of hardware implementation are developed in this dissertation, which is more directive for the design of navigation baseband chip.This dissertation is mainly focused on four crucial topics which restrict the promotion of the receiver’s performance:1. Signal acquisition has the most computational complexity and maxim requirements for realtime processing in the navigation baseband processing, and its performance has direct influence on time to first fix, receiver sensitivity and some other key indexes. There is a lack of quantitative analysis of hardware complexity of acquisition methods in existing researches. Based on the uniform signal acquisition model, the hardware complexity and restrictions are compared between different aqutition methods, and quantitative analysis is presented. The systemic method of quantitative analysis is afforded to evaluate the implementation complexity of baseband chip.2. Pseudo-code phase error, carrier frequency offset and pseudo-code frequency offset will all give rise to serious deterioration of performance of acquisition, while traditional acquisition methods usually haven’t dealt with the effects or compensated. Considering the coherent processing loss caused by pseudo-code phase error and carrier frequency offset, detection based on combinatory and judgment of adjacent detection limit is proposed, which can dramatically increase the probability of detection of system. Under the general conditions for the search step, equivalent signal to noise ratio of detectors can be maximally increased by 3.8dB. In view of pseudo-code frequency offset, an approach to compensating pseudo-code frequency offset based on decimation of signal fractional sampling is presented, so some engineering implementation problems caused by modification of frequency of sampling local codes are avoided. In the condition that the sampling rate is 5 times of code rate, the maximum pseudo-code frequency offset loss is less than 0.5dB and peak shift is also less than one tenth of chip width, being able to satisfy the requirements of most high dynamic capture systems. Based on this, a revised acquisition proposal on the basis of frequency domain of matched filter and FFT acquisition in parallel is put forward, and the design of matched filter and strategy of frequency search is also improved.3. Multipath effect is one of the main factors that affect the accuracy of position of navigation receivers. It is even the most primary error source in some application of high-accuracy survey. In consideration of the contradiction between performance of multi-path mitigation algorithm and resource consumption in navigation receivers with high performance, a multipath mitigation technique based on FIR model is put forward. Its performance is similar to that of MEDLL based on maximum likelihood estimate, but it has advantages that its computation complexity is independent of the amount of multipaths and hardware complexity can be reduced in the existence of multiple paths. As for implementation of high resolution multi-correlator, an implement architecture based on local pseudo-code differential is presented. Under the condition that correlator interval is one sixteenth of chip width, the computation and hardware scale is only one thirty-second and one eighth of traditional architectures respectively.4. A chip architecture based on the cooperation of multi-correlator is put forward, by establishing the multiple tasks model of navigation baseband processing. The conventional receivers which use single processor request a mass of resources, complicated scheduling and high realtime processing. Using the proposed architecture, multiple tasks are performed by multiple processors, so the shortcoming of the conventional receivers is conquered and the design of baseband chip is simplified. Also the chip is flexible and efficient simultaneity. In the view of some problems as the long consuming time and the heavy workload of simulation verification in chip development, simulation process based on Palladium simulation accelerator and prototype chip verification method based on FPGA is researched. These techniques are directly applied to developing the baseband chip. The above-mentioned reserchs are fully verified by actual tests in the aspects of power and performance.The researches have been used in Chinese autonomous satellite navigation system receiver and design of baseband chip and have obtained favorable effects in engineering application. Related methods and conclusions can also be applied in design of ranging receiver in other spread spectrum systems.更多还原