【作者】 周先军；

【导师】 胡修林；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2005， 博士

【摘要】 在3G 及beyond 3G 无线通信中,信号的捕获始终是一个关键问题,制约着无线通信的质量和效率。3G 通信使用直扩(直接序列扩频),这一通信方式具有强抗窄带干扰性能、隐蔽性良好、大容量多址接入等优越性能。直扩方式下的接收信号相位捕获问题,从扩频通信产生到现在,一直都被予以高度重视,处在不断的探索和性能改进中。对直扩,本论文提出了如下两种快速捕获算法: 1.通过分析辅助信号特性,以相位预估器的输出概率为基础,首先获得输入信号相位的一高概率调整区间,再运用滑动相关法对该区间进行捕获,从而形成一贝努利概型。2.以辅助信号与输入信号互相关结果的特征为基础,通过二分搜索,大幅缩小PN 码调整范围,形成一二叉树搜索模型。与传统滑动相关算法相比,这两种捕获算法在硬件复杂度折中下,都有效改善了对长码的捕获性能。作为个域网的一种信息高速传送方式,超宽带(UWB)凭借其优良性能,已经引起了世界范围科研领域和实业界的广泛关注,其快速捕获算法是超宽带关键技术之一,对经典的无载波超宽带,本论文提出如下四种快速捕获方案: 1.引入周期锯齿形脉冲作为辅助信号,将其与导频信号的相关,获得导频信号的时延估计,然后依据该估计值,延展形成一小探测区间,对此小区间运用比特反转法搜索发射对齐位置,从而实现超宽带信号的快速捕获,对这一方案与其它搜索算法进行了比较,显示性能有了较大改进。2.基于TH-PPM UWB 的多径和多址特性,提出一种基于协议的超宽带快速捕获算法,按照协议,预置有关参数,把复杂的捕获问题分解成两步,依次进行初始捕获和跳时捕获,从而保证超宽带系统信息有效传输。3.通过分析超宽带信号多径特征,提出一种基于数字滤波器的超宽带捕获算法,该方案依据探测概率Pd 和虚警概率Pf a选择合适的滤波器窗口宽度,依据跳时码设置更多还原

【Abstract】 The study on acquisition is a key technology to affect the quantity and effect in the wireless communication. The direct sequence spread spectrum (DSSS) is widely used in the third generation (3G) for many attractive performances, for instance, excellently anti-interference, well covert, numerously multi-access and effective far and near resistance. The acquisition of phase of received signal is explored to approve the speed and capability that accompanied with the development of this communication mode. Based the analyses of an auxiliary, the acquisition process in the DSSS communications is regarded as a Bernoulli Model, in which the auxiliary sequence generator and a pre-loop estimator can be utilized to adjust the local pseudo-noise (PN) phase in some range centered the estimator phase. According to relevant results of the Model, the means and its variances of the acquisition time under this scheme are computed and compared with the conventional coherent serial search receiver. It shows that the receiver presented here can improve the acquisition performance through this novel tactics. Besides, the wide cross-correlation function about the input signal and an auxiliary sequence, which can be used to adjust the local PN phase range to be halved the search range last time. It’s obvious that method for big scale adjustment can reduce the time to acquisition. The ratios about the means and variances of the acquisition time are analyzed with the conventional coherent serial search receiver and the other coherent system brought forward in the literature. The evaluation also shows that the receiver presented here can improve the acquisition performance under this scheme. Under the high transmission speed from the reality urgent requirement of wireless personal area network (WPAN), the ultrawideband (UWB) technology has brought broad interesting in the world. The UWB is classified to two kinds: one is baseband signal mode; the other is carrier wave one. The fast acquisition algorithm of them is studying now by many scholars around the world. An efficient acquisition scheme is proposed in which a type of auxiliary pulse sequence is used to estimate delay phase between the received signal and the assistant one in the UWB communications. A small search bins range whose number is a power of 2 is selected according to the estimated results. By the bit reversal search, the alignment position is sought under an alterative order. In addition, the simulation evaluation shows that the receiver presented here can improve the acquisition performance under this scheme. A second efficient acquisition scheme is proposed in which some parameters are pre-decided. Under advanced strategy, the transmission and receive parts attain the coarse synchronization state through two steps, which are named clock initialization and time-hopping (TH) acquisition. Owing to resolving the difficulties into two simple tasks, this scheme can improve the acquisition performance in assuring TH-PPM UWB signal transmission to a large degree. A third coarse synchronization scheme is proposed through introducing a digital matched filter combining diversity according to the same TH as the expected user. By analyzing the signal characteristic, the filter window parameters are set to utilize sufficient energy from the receiving signal in a multipath environment. The receiver can spend about one bit duration in achieving acquisition, which indicates the receiver presented here can efficiently improve the acquisition performance. Aside, utilizing the received signal itself that is a “dirty”template for containing thermal noise and multiple access interference as an auxiliary tool, a synchronization algorithm is suggested for the receiving process. In the initiation phase, a pilot symbol sequence designed is capitalized to assure frame-level acquisition and pulse-level tracking. During the conveying information, the transceiver synchronization is monitored. With a small number of pilot signal, the scheme show good performance by simulations. Based on the research of channel characteristic and optimal receiver principle, a transmission signal scheme is proposed by the designed process to attain a satisfying performance, in which multiband access is decided for multiuser, adaptive data subcarrier is considered for different dada velocity, a hopping frequency coded by a Costas sequence is utilized to take advantage of the multipath diversity provided by the channel, and the parameters choice of preamble and pilot sub-carrier is optimized for synchronization requirement. Otherwise, a symbol synchronization scheme based the preamble is proposed. Contrasting to the traditionally OFDM system, the cyclic prefix (CP) is replaced with the zero padding (ZP), which behaves natural resist multipath and decrease the power consumption. The special preamble is designed, and the performance during the symbol synchronization is analyzed. In the end, the scheme is observed in the simulation. The typical application about the acquisition algorithm is to implement the distance measure. In this case, a scheme about the radio altimeter is analyzed and compared with other algorithm in theory.The application process about OCOG (Offset Center Of Gravity) algorithm, which had functioned to achieve the task under high precision on the current spaceborne altimeters, is provided in detail to indicate its character. It is taking the whole return waveform into account, not only leading edge as the conventional tracking algorithm. Its performance is contrasted with the other tracking algorithm, WSG (Wave splitting Gate), through the simulation research. It is obvious that the error signal obtained by OCOG algorithm possess wider linear range that will be used to lock the waveform leading edge in the observation window. Moreover, there are bigger Signal Noise Ratio (SNR) and smaller value of mean square error in this algorithm. These results show that algorithm is an excellent robust performance-tracking algorithm. For complicated region, such as land surface, an algorithm to acquire its average height is suggested based the return waveform. Through the origin analyse about each point of return, it scattering from assured distance reflects the corresponding information of incident scope. In the difficult situation of how to decide the single characteristic point, the technique built in the theory can be handled easy in practice. Otherwise, we validate our model by simulation in a very good way. In addition, a ranging scheme with multi-band orthogonal frequency division multiplexing (MB-OFDM) is proposed to decide the range between two nodes in ultra-wideband communication. The transmission part emits the radio wave in a hopping frequency fashion controlled by a PN sequence, but the receiver process the received signal to form a big wideband. Through this scheme, the ranging resolution can be improved efficient. In the end, we validate our scheme by simulation. Through studying the fast acquisition algorithm and their application, several schemes were proposed to facilitate the progress in the field of 3G and beyond 3G for national wireless communication.更多还原