【作者】 汪晓宁；

【导师】 范平志；

【作者基本信息】 西南交通大学 ， 交通信息工程及控制， 2010， 博士

【摘要】 在码分多址跳频(FH-CDMA)通信系统中,跳频序列汉明自相关和互相关特性的好坏在很大程度上决定了系统自干扰(SI)、多址接入干扰(MAI)的大小,从而直接影响着系统性能的优劣和容量。无碰撞区(NHZ)跳频序列概念的提出,为进一步提高FH-CDMA系统抵制多址干扰能力、提高系统性能提供了一种新的选择。本文基于无碰撞区(NHZ)跳频序列的概念,对准同步组网跳频通信系统及系统收发同步相关技术进行分析与研究,得到了一些重要的结果。论文首先从已有的周期零相关区(ZCZ)二元扩频序列入手,寻找满足汉明相关函数具有无碰撞区特性且接近或达到理论界的跳频序列。通过对周期ZCZ二元扩频序列的特定状态字子集进行映射,构造出无碰撞区(NHZ)跳频序列集,文中列出了获取NHZ跳频序列的八个ZCZ二元扩频序列的子集,给出的映射规律揭示了ZCZ二元扩频序列集与NHZ跳频序列集的内在联系。在四种构造方法中,初始序列采用互补序列对的方法Ⅲ、Ⅳ在特定条件下达到NHZ跳频序列设计的理论界,即最佳NHZ跳频序列。其次,针对考虑频率碰撞边缘效应的四碰撞态Markov链多址干扰(MAI)分析模型特点,结合NHZ跳频序列的汉明互相关特性及NHZ准同步跳频通信系统多址接入的特点,获得了NHZ准同步跳频系统多址干扰的分析模型。同时分析并比较了NHZ准同步跳频通信系统与同步、异步跳频通信系统的多址干扰性能。研究结果表明,采用NHZ跳频序列的准同步跳频通信系统的MAI性能优于采用随机跳频序列的异步跳频通信系统。接着,论文通过分析BFSK调制的异步跳频通信系统K(K>1)个不同时延干扰用户干扰项的条件方差,从系统信噪干比(SINR)概率分布入手,导出异步跳频通信系统错误概率的准确闭合解。该表达式是系统所采用跳频模式的频率全碰撞概率、部分碰撞概率、异步干扰信号时延以及系统用户数的函数。在此基础上,针对NHZ跳频序列汉明互相关函数的特性,分析了NHZ准同步跳频通信系统的频率全碰撞概率和部分碰撞概率,以及NHZ准同步跳频系统多址干扰的条件方差,进而给出BFSK调制的NHZ准同步跳频通信系统错误概率闭合解。该表达式是系统用户数、异步干扰信号时延、系统所采用的NHZ跳频序列长度和无碰撞区长度的函数。论文基于准确闭合解,分析比较了异步、准同步和同步跳频通信系统在不同用户数的错误概率,以及干扰用户时延对系统错误概率的影响,并将分析闭合解与高斯近似解做了比较。数值计算结果表明,本文所给出的闭合解比高斯近似法更紧。然后,论文分析研究了在多径信道下,跳频通信系统存在收发时间和频率同步误差时,多径分量时延引起的相位变化对非相干FH/MFSK和SFH/MFSK系统信号正交性的影响。引入门函数表示跳频通信系统存在时间同步误差及多径时延时,一跳持续时间内传输信号的有效时间长度,推导出各种条件下的系统信号正交损失因子表达式,其中FH/MFSK系统的结果是SFH/MFSK系统的特例。结果显示,多径衰落信道下的跳频通信系统信号正交性损失不仅与多径时延、衰落信号强度、时间同步误差有关,而且和多径时延引起的相位变化也有关,进而会影响系统的BER特性。数值计算结果表明,多径衰落分量的相位变化对非相干解调FH/MFSK通信系统存在收发时间同步误差时的信号正交性会产生不同程度的影响,因而表明了非相干解调FH/MFSK系统的性能与多径衰落分量相位变化的关联性。最后论文研究了系统在全频带和部分频带噪声干扰下,多径分量时延引起的相位变化对非相干FH/MFSK系统时间同步和频率同步误差估计性能的影响,给出了不同情况下系统时间同步误差和频率同步误差谱估计值的均值和方差表达式。数值计算结果表明,多径分量的相位变化会影响时间同步误差谱估计均值的准确性。更多还原

【Abstract】 In frequency hopping code-division multiple-access (FH-CDMA) communication systems, the Hamming autocorrelation and cross-correlation properties of the frequency hopping sequences employed play an important role on the level of the self-interference (SI), multiple access interference (MAI), therefore directly influence the performance and capacity of the FH-CDMA systems. The idea of no hit zone (NHZ) for frequency hopping sequence gives a new choice to enhance the multiple access performance. In this thesis, some beneficial results are obtained by investigating on the techniques of quasi-synchronization and synchronization for frequency hopping system based on the concept of NHZ frequency hopping sequences.Firstly, by employing the periodic zero correlation zone(ZCZ) binary spread spectrum sequences obtained, this thesis generates a new class of frequency hopping sequence sets which not only have no hit zone Hamming correlation performance but also approach or achieve the theoretic bound. There are eight subsets that can be mapped to NHZ frequency hopping sequences and these mapping shows up the relationshp between NHZ sequences and ZCZ sequences. The proposed four methods where methods III and IV with complementary sequences as starter are optimal NHZ sequences which achieve the theoretical bound under some conditions.Secondly, based on the four hit states Markov model which takes into account the marginal effect of the multiple access interferences (MAI) in frequency-hopping communication systems, combining the Hamming cross-correlation performance of NHZ frequency hopping sequences and the multiple access characteristic of quasi-synchronous (QS) FH-CDMA system, the MAI performance analyses model for NHZ QS-FH-CDMA system is given. The thesis analysis and compares the multiple access interference performances for NHZ QS-FH-CDMA system, synchronious FH-CDMA system and asynchronious FH-CDMA system. The results shown that the MAI performance of NHZ quasi-synchronous system used NHZ sequences outperforms the asynchronous system employing random hopping frequency sequences.Thirdly, the conditional deviation of multiple access interferences of K(K>1) users which have different time delays in the asynchronious FH system and the probability distribution function(PDF) of signal noise plus interference ratio(SINR) are analyzed, then the exact closed form expressions of error probability of asynchronious FH system are obtained, which is the function of frequency full hit probability, frequency partial hit probability, time delay of interference signal and the number of user. Based on the Hamming cross-correlation performance of NHZ frequency hopping sequences, the frequency full hit probability and frequency partial hit probability of NHZ-QS-FH-CDMA system and the conditional deviation of multiple access interference for NHZ-QS-FH-CDMA system are analyzed, and then the exact closed form expressions of error probability of NHZ-QS-FH-CDMA system are also obtained. Besides the above variables, the expression involves also the length of sequences and the size of no hit zone. Compared with Gaussian approximate method, the obtained closed form expression is much tight.Then, the effect of multipath fading on orthogonality of signal tones in FH/MFSK and in SFH/MFSK with non-coherent demodulation and time and frequency synchronization error are analyzed. By using the gate function to represent the valid length of signal in time synchronization error and multipath time delay, a general expression of orthogonality loss factor Djnl which is appropriate in various conditions is derived. The results shown that the Djn is determined not only by the multipath delays, signal strength fading and synchronization time error, but also by the phase variations caused by multipath time delays. Further, the scenario of FH/MFSK is the special case of SFH/MFSK system. Numerical results demonstrate that the effects vary with different phase variations. This result will further affect BER performance of FH/MFSK systems. Thus it is no longer appropriate to consider that the MFSK non-coherent demodulation is independent of the phase variations in the case of multipath fading for frequency hopping system.Finally, the effect of phase variations caused by multipath time delays on the estimation performance of time and frequency synchronization errors for FH/MFSK system with non-coherent demodulation in full-band and partial-band noise jamming are analyzed. The expressions for mean and deviation of time and frequency synchronization errer spectral estimation are derived under various conditions. Numerical results demonstrate that the phase variations caused by multipath time delays may influence accuracy of the mean of time synchronization error spectral estimation.更多还原