【作者】 赵永丽；

【导师】 彭代渊；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2011， 硕士

【摘要】 跳频通信技术是扩频通信技术之一,是一种多址接入技术,允许多个用户在相同频段上同时传输信息。跳频多址技术有以下优点：不需要连续的频谱,可以回避被干扰的频带；对远近效应不敏感,可以不使用功控,所以被广泛应用于军事、商用等领域。但同直接扩频多址(DS-CDMA)通信一样,跳频多址通信也面临着多址干扰(MAI)问题,在跳频系统中克服干扰的办法主要有两种：一是设计汉明相关性尽可能低的码型,二是使用消除或减少MAI的多用户检测技术。本文试图结合这两种方法,以期获得更好的抗多址干扰能力。首先本文采用一类无碰撞区(NHZ)跳频码,该类码在特定区间不会发生频点重合,并根据该类码的特点采用多级快速跳频多频移键控(FFH/MFSK)准同步系统,系统中将总的活动用户分组,组内用户和组间用户分别采用最优地址码和NHZ码区分,并使各用户时延不超过NHZ,故组间用户无干扰。然后,为进一步降低误比特率(BER),在接收端使用多用户检测算法,即基于最大行的最小均方误差(MMSE)异步快跳频多址干扰消除算法,并针对此算法进行了研究。最后,本文作者还研究了多级迭代干扰消除(MS-IIC)算法。本论文作者主要完成了以下工作：一、详细介绍了NHZ跳频序列,在有限域GF(p)和GF(pm)上分别构造了该序列,并分析了其性能。二、搭建基于NHZ序列的两级FFH/MFSK系统模型,包括发送端模型和接收端模型。详解了最优地址码的构造和编码方案,然后分析了组内用户多址干扰,根据干扰模型推导了符号干扰公式,最后在MATLAB平台上对系统各功能模块进行了仿真。三、深入研究了异步FFH/MFSK系统的MMSE多用户检测算法,并针对算法的效率和检测性能以及系统的复杂度作了改进,分别在AWGN和Rayleigh信道下对这两种算法进行了仿真。仿真结果表明改进的算法在信噪比较低时BER也较低,且较适用于多用户情况。本文作者又通过举例的方式,证明了改进的MMSE算法与MMSE算法相比检测效率高且复杂度低。作者还研究了门限阀值对系统容量的影响,在迭代一次时,改进的算法受门限值的影响较小；另外通过仿真还验证了部分条件一定时,会存在一个最佳的参数组合尽可能地降低BER。四、研究和改进了MS-IIC算法,根据仿真分析和实例比较可知,改进的MS-IIC算法能提高检测效率,改善系统性能以及减小算法复杂度。五、指出算法仍存在的不足之处和后序的改进方案,并给出了未来的研究方向。更多还原

【Abstract】 Frequency hopping communication is one of the spread spectrum communication technologies, which is a multiple access technology. Frequency hopping coded division multiple access (FH-CDMA) communication can allow multiuser to transfer information in the same bandwidth at the same time. FH-CDMA technology has some important advantages, first, the frequency usage does not have to contiguous, frequency bands interfered by another system can be avoided; second, FH-CDMA systems are less susceptible in general to the near-far problem and do not request power control. So FH-CDMA technology has been widely used in many fields, such as military, commerce and so on. Whereas, as the same as DS-CDMA, FH-CDMA systems have been confronted with multiple access interference (MAI). There are two important methods to overcome interference, one is to design frequency hopping sequence with a hamming correlation as low as possible; the other is to improve the system performance by using the multiuser detection (MUD) technology of eliminate or reduce MAI.The thesis combines both methods to improve the performance of anti-MAI. First of all, a class of FH sequence with no hit in a certain correlation zone (NHZ) is chose, and according to the characteristic of NHZ hopping code, we exploit quasi-synchronous multistage fast FH/multiple level shift keying (FFH/MFSK) system. The active users are divided into a number of groups here, a unique NHZ FH sequence is assigned to each group, and the optimum address codes are assigned to the users in the same group. The MAI among users of different groups can be eliminated as long as their relative delays do not exceed NHZ. Then, to obtain better bit error rate (BER) performance, MUD algorithm is exploited in the receiver, such as a based-MMSE multiple access interference cancellation algorithm of asynchronous fast FH communication system. At last, the multistage iterative interference cancellation (MS-IIC) algorithm is studied.The main studying results of this thesis are provided as follows:First, a class of NHZ FH sequences are introduced and constructed based on finite field GF(p) and GF(p’"). Some properties of NHZ FH sequence are also analyzed.Second, the multistage FFH/MFSK system model based on NHZ frequency sequence is established, including the models of transmitter and receiver. The construction and coding scheme of the optimum address is introduced particularly. Then the MAI among users belonging to the same group is analyzed, and symbol interference formula is derived. Finally, the function models simulation of FFH/MFSK system are carried out on MATLAB simulation platform.Third, a MMSE multiuser detection algorithm of asynchronous FFH/MFSK system is studied deeply, according to the detection performance and complication of the MMSE algorithm, the algorithm is improved. In the AWGN channel and Rayleigh fading channel, the author does a simulation study on these two detectors. Simulation results show that the improved detector improves the integral BER performance of system, even if the signal-to-noise ratio (SNR) is low. The author proves that the improved detector has higher detection efficiency and lower complication by illustration. And the effect of the threshold on system capacity is also studied. Simulation results show that the influence of the threshold on the improved algorithm is small. Otherwise, there exist the parameters combination can obtain the best BER performance.Forth, MS-IIC algorithm is studied and improved. Simulation analysis and illustration comparison show that the improved MS-IIC algorithm has higher detection efficiency, better performance and lower complication.Fifth, the deficiencies of MUD algorithm are pointed out. The improved methods and the vision for the future are given at last.更多还原