【作者】 王彦波；

【导师】 李式巨；

【作者基本信息】 浙江大学 ， 通信与信息系统， 2008， 博士

【摘要】 随着信息化时代的到来,通信的发展有两个趋势:一是窄带通信向宽带通信发展,随着带宽增加,信道容量增加,信道中可传输信息的最大速率增大,从而满足人们对通信速率、质量的越来越多的要求。二是通信数字化,随着材料技术、集成电路技术和数字信号处理技术的成熟,通信系统正向数字时代迈进,基于数字处理的软件无线电概念的提出,为各种无线通信系统的融合提供了统一平台解决方案。IR-UWB技术顺应了通信发展的两个趋势,它采用超短脉冲发射信号,信号占用数吉赫兹带宽,信道容量大,可提供高速的数据传输。它易于数字化实现,直接发射脉冲,属于基带传输,接收机甚至可以实现除天线接收外的全数字处理。IR-UWB具有其它窄带系统、宽带系统所无法比拟的优势,但在实际应用时,尚有许多关键技术待解决。其中同步捕获是一大难点。超短脉冲,极低功率和复杂的室内多径信道,使得IR-UWB的同步捕获十分困难。传统的同步算法应用在IR-UWB中捕获时间太长,性能不是最优。如何找到适合脉冲信号传输特点的同步算法,是IR-UWB的研究热点。本文从减少同步捕获时间和减小实现复杂度角度分析研究IR-UWB的同步捕获问题,希望能获取一些有意义的启示。本文综合考虑了捕获时间,硬件复杂度和信道特性三个因素,运用检测理论,提出模板自适应的同步捕获算法,利用多径信道特征构造2个本地模板信号,分别与接收信号匹配相关,比较相关输出后,自适应改变模板信号,在新的搜索区域内继续重复相关、比较运算,以此迅速减小搜索区域,迭代过程结束后,在最后确定的搜索区域上采取串行全搜索方法捕获同步。本文推导出算法的平均捕获时间,并与现有搜索算法比较。运用假设检验理论,直接推导了检测概率,得到平均检测概率的解析表达式,为算法的性能评估提供理论依据;另外,本文用信号流程图方法推导算法平均捕获时间和平均检测概率,验证了直接推导的理论公式的正确。研究结果表明,该算法可以迅速捕获同步参数,有效提高检测概率。为解决信号传输过程波形失真情形下的IR-UWB接收问题,本文运用估计理论,提出有数据辅助的PPM-UWB同步捕获算法。首先推导出PPM调制下的互相关函数,发现互相关函数只与三个符号有关系,用穷举法得到互相关函数与发送信息序列的关系表。基于关系表,构造出相邻符号互相关函数的差值函数,设计训练序列来捕获同步。为有效平滑噪声,提高检测性能,提出两种噪声平滑方式,得到了两种同步捕获算法。本文运用估计理论,评估提出的两种同步捕获算法性能,证明同步参数估计是均方意义一致的。研究结果表明,该算法避开信道估计,简化了接收机结构,但对噪声的抑制能力较弱,适合在较高信噪比的信道环境中应用。IR-UWB接收机数字化实现时,A/D工作频率过高,为解决该问题,本文运用采样理论,提出低采样率的同步捕获接收方案。通过分析比较经典的香农采样定理和更新速率采样定理,对采样定理的本质做出物理解释,并理论分析评估了香农采样和更新速率采样的重构误差,继而将更新速率采样应用到IR-UWB中,提出了一种实际可行的数字接收方案,并在低速率IR-UWB通信环境下,给出一种新的符号同步方法,将信道多径时延估计转化为谱估计问题,利用子空间方法求解多径时延参数,根据相邻两径的距离做符号同步。在一定的误码率性能承受范围内,该算法具有一定实际应用意义。更多还原

【Abstract】 The coming information era promotes communication toward two ways. One is bringing the bandwidth from narrowband to wideband. With the bandwidth increasing, the channel capacity is improved, which consequently increases the maximum data rate to satisfy the demands for higher speed, longer distance and better communication quality; The other is from analog to digital. The development of material technology, integrated circuit and digital signal processing technology pave the way for the communication technology to step forward to digital age. In particular, the emergence of software defined radio concept is able to provide a uniform platform for various wireless communication systems utilizing programmable hardware modules.The impulse radio-based ultra wideband technology (IR-UWB) has the potential to fulfill the development trends mentioned above. It adopts ultra-short pulses to transmit information with duration of the order of nanoseconds. The extremely short pulses occupy the bandwidth of the order of several GHz and have a huge capacity to serve for high data rate. Meanwhile, only simple digital implementation is required as IR-UWB directly transmits pulse in baseband, eliminating the needs of carrier modulation and RF power amplifier, and almost all modules can be implemented in digital devices except for an ultra wideband antenna. IR-UWB, on the other side, has some critical problems to be solved. In particular, the design of fast and efficient synchronization, or acquisition scheme becomes more challenging due to ultra-short pulse, extremely low power, and dense multi-path channels. Traditional synchronization techniques result in prohibitively long acquisition time and a suboptimum performance. How to design a suitable algorithm for efficient synchronization is a key research point. In this dissertation, three algorithms are gradually proposed in view of mean acquisition time, implementation complexity to give inspirations to these challenges mentioned above.A novel acquisition algorithm based on adaptive templates is firstly proposed in this dissertation using detection theory, which takes acquisition time, implementation complexity and channel characteristics into account. Firstly two adaptive templates are generated using multi-path characteristics, and correlate with the received signal. The correlation results are compared to proceed the next iteration: the search region decreases gradually after each iteration is executed. The search region decreases to a certain small cell rapidly after a few iterations. Finally traditional serial search algorithm is applied to acquire the timing parameter. Mean acquisition time is analyzed and compared to other algorithms; and the mean detection probability is deduced to evaluate the algorithm performance. Both mean acquisition time and detection probability are analyzed utilizing signal flow graph. The theoretical deduction and simulation results show the proposed algorithm greatly reduces the acquisition time and effectively improves the detection probability.In order to resolve the synchronization of IR-UWB in the waveform distortion environment, a data-aided PPM-UWB acquisition algorithm using estimation theory is afterward proposed. Firstly the cross correlation function of PPM is deduced, which is found to be relative to three factors. The difference value of the cross-correlation function is constructed according to relative table between cross correlation and information symbol, then a simple training pattern is designed to expedited the synchronization. To remove the noise impact, we propose two noise suppression methods. We also prove that the two acquisition algorithms are mean square sense consistent.Traditional digital implementation of IR-UWB receiver adopts analog-to-digital converter with high sampling frequency which leads to high receiver manufacturing cost. From this point of view, a low sampling frequency based acquisition algorithm is finally proposed in this dissertation using sampling theory. Firstly the classical shannon sample theorem and innovative sample theorem are compared and some physical interpretations are given, then the reconstruction error is evaluated. Secondly the innovative sample theorem is applied to IR-UWB to propose a practical digital synchronization and receiver design method. A novel symbol synchronization algorithm under low data rate IR-UWB communication environment is also proposed, which translates the joint channel and timing estimation problem into a harmonic retrieval problem and utilizes subspace method to acquire the timing parameters. This proposed algorithm has practical meanings under certain affordable BER condition.更多还原