平坦快速衰落信道预测方法的研究
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摘要
无线移动通信的信道非常复杂,使无线通信系统的性能有很大的局限性。
    发射机和接收机之间的多径问题,以及快速运动的移动终端在接收信号时产
    生的多普勒效应,引起接收信号的幅度和相位都有很大的变化,就是通常所
    说的衰落。也正是由于深度衰落的影响,严重的限制了通信系统的性能,需
    要出现更好的调制、编码、功率控制等方法,更有效的应用于衰落信道。A.J.
    Glodsmith 和 S.G..Chua 等人研究了一些新的自适应传输技术,例如自适应调
    制、自适应编码、自适应功率控制,自适应天线阵列系统等。这些自适应传
    输方法,都是通过瞬时监视信道条件,来调整调制水平、符号率、码率、传
    输功率等级、传输天线增益或者与这些参数相关的一些方面。它们都是尽量
    在不牺牲误码率性能的同时,更有效的利用功率和频谱,来实现更高的信息
    传输速率。
     实际中,为了实现自适应传输方法,传输过程中的信道状态信息(CSI)
    必须是可知的。通过接收机一端,可以获得的过去一段时间衰落信道系数的
    采样,用信道预测算法来预测未来的一段时间间隔内,衰落信道系数将会怎
    样的变化,然后通过反馈信道传输给发射机,发射机根据数据传输时将会出
    现的信道状态信息,来确定发射功率,调制方法,编码方法和传输天线等一
    些问题,来适应当时的传输条件。这样,发射机就可以优化的进行传输,随
    之而来也就提高了通信的质量。
     本文首先介绍了课题的意义,发展现状和一些基础理论知识。主体部分
    以及主要工作,就是对当前的信道预测算法的改进。主要分成两大部份:第
    一部分就是对常用信道预测算法 ESPRIT 算法的改进部分,第二部分是自适
    应子空间追踪算法的研究。改进算法有
    1. 基于采样数据共轭重排的 C-ESPRIT 算法
     这种方法的基本思想是:原 ESPRIT 算法仅仅利用了采样数据本身,忽
    略了采样数据是复数的事实,再次利用采样数据的共轭数据,来参与自相关
    函数的运算,保证计算量不变的同时提高算法的准确度和精确度。
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    吉林大学硕士学位论文
    2. 基于数据预处理的 SS-ESPRIT 和 MSS-ESPRIT 算法
     基本 ESPRIT 算法是目前常用的几种算法(例如最大熵算法(MEM),
    长距离预测(LRP)算法)中性能最好的一种算法,它的主要缺点是进行奇
    异值分解(SVD)或特征值分解时运算量较大,限制了算法的实时应用。针
    对基本 ESPRIT 的这一不足,可以想办法减少奇异值或特征值分解的阶数,
    提出了 SS-ESPRIT 和 MSS-ESPRIT 算法。其中 SS-ESPRIT 是应用空间平滑
    技术的 ESPRIT 方法,空间平滑的基本思想是将用Rcc = CCH 方法估计的采
     ?
    样数据自相关矩阵进行重新分块并且组合,得到阶数较少的采样数据自相关
    矩阵的估计,再对其进行特征值分解。显然这种算法能够减少特征值分解时
    候的运算量,但是要以牺牲运算精度为代价;而 MSS-ESPRIT 算法实质上是
    利用了前两个改进方法的优点,它将采样数据共轭重排和空间平滑技术相结
    合,形成了双向平滑技术,仿真实验证明,MSS-ESPRIT 算法的性能非常好,
    在减少了运算量(特征值分解的阶数)的同时,也提高了预测的预测性能。
    3. 子空间追踪算法
     在以往的所有信道预测方法中,都是采用标准的平稳杰克模型,它由几
    个复数正弦信号的和组成。重要的是假定模型中的参数幅度 An、多普勒频移
    fn 和相位φn 都是固定不变的。然而实际中,这些参数都是缓慢变化着的,这
    些非平稳的变化会严重的恶化信道预测性能,为了克服这一不足,采用了自
    适应子空间追踪同 ESPRIT 算法相结合的方法。这种算法的优点是:首先,
    子空间追踪算法解决了标准杰克衰落模型中,多普勒频移 fn 的变化带给传
    统信道预测算法性能的恶化问题,这样信道预测算法能够适合更多的应用场
    合;其次,它采用的是一种自适应的方法,而基本 ESPRIT 算法是批处理的
    算法,运算量很大,子空间追踪算法和基本 ESPRIT 算法比起来,在准确度
    和精度基本相当的情况下,运算量会减少很多,更有利于进行实时应用;再
    次,还对现有的子空间追踪算法 FAST 和 FAST2 进行了改进,提出了 MFAST
    和 MFAST2 算法,仿真实验和统计数字表明,它们比原有的子空间追踪算法
    FAST 和 FAST2 算法不仅减少了运算量,同时也提高了预测的准确性和精确
    性,加快了收敛速度,更适合于多普勒频移 fn变化严重的场合,是两种非常
    好的算法。
     还给出了信道预测算法在自适应传输技术中自适应调制的应用。自适应
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    摘 要
    调制的基本思想就是:预测传输时刻的信道状态信息,根据信道将要发生的
    条件来选择调制的具体方法。这样,总体来说在保证了误码率要求的同时,
    提高了带宽效率,是一种很好的自适应传输方法。
    最后总结了本次论文的全部工作内容,指出了本次论文中信道预测算法
    的成绩和不足之处,对今后的信道预测算法工作重点进行了展望。
The wireless mobile communication channel is very complex. It limits the
    performance of the wireless communication system a lot. The multipath problem
    between the transmitter and the receiver and the fast moving terminal which cause
    the Doppler affect result in the amplitude and phase of the receive signal vary
    fastly. We call it “feeding”. It is the influence of the deep feeding that limit the
    performance of the communication system very much. We need the better
    modulation, coding and power control methods to be used in the feeding channel
    efficiently. A.J. Glodsmith and S.G..Chua have investigated some new adaptive
    transmitter technique, for example adaptive modulation, adaptive coding, adaptive
    power control and adaptive transmitter antenna diversity and so on. These
    adaptive transmitter schemes all vary the constellation size, symbol rate, coding
    rate, transmitted power level weights of transmission antennas or any combination
    of these parameters by instantaneously monitoring channel conditions. They are
    trying to use both power and spectrum more efficiently without sacrificing the bit
    error rate performance to realize the higher information transmitter rate.
     To implement adaptive transmission methods in practice, the channel state
    (CSI) must be available at the transmitter. With the sampling data of the receiver
    samples in the past interval, we use the arithmetic of channel predictions to
    predict the fading channel coefficient. Afterwards, transmit the fading channel
    coefficient to transmitter in the feedback channel. The transmitter will decide the
    transmission power, modulation methods, coding methods and the transmission
    antennas, to fit the transmission conditions of the time. Thus, transmitter is
    optimized, and the communication performance is improved at the same time.
     The thesis first introduces the significance of this subject, development status
    and some basic theory knowledge. The important part and mostly task of this
    thesis are the modification of the current channel prediction arithmetic. It has two
    parts: the first part is the improvement of basic ESPRIT arithmetic. It is a channel
    prediction method in common use. The second part is the investigation of the
    adaptive subspace tracing. These modified arithmetic is
    1. The C-ESPRIT arithmetic based on sampling data conjugation recomposition
     The basic idea is: the sampling data itself is used in the basic ESPRIT
    arithmetic but the data are complex numbers is ignored. The conjugation data of
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    ABSTRACT
    the sampling is reused to compute the self-correlation matrix in C-ESPRIT
    arithmetic. The veracity and precision of the arithmetic are improved and the
    operation quantity does not changed much at the same time.
    2. The SS-ESPRIT and MSSESPRIT arithmetic based on data pretreatment
     The basic ESPRIT arithmetic is the best in the current prediction arithmetic
    (such as the Maximum Entropy Method (MEM) and the Long-range Prediction
    method (LRP)). Its’ serious shortcoming is that the operation quantity is great
    when the singular value decomposition (SVD) or eigenvalue decomposition is
    computed. It limits the real time application. To overcome the shortcoming of the
    arithmetic, the dimensions of singular value decomposition or eigenvalue
    decomposition must be reduced. SS-ESPRIT and MSS-ESPRIT arithmetic are
    given. The SS-ESPRIT is formed by the basic ESPRIT method combined with the
    space smooth techniques. The basic idea of the space smooth techniques is that
    the self-correlation matrix is disparted and assembled again, which is estimated by
    the Rcc = CCH method. Then the eigenvalue decomposition is computed. It is
     ?
    apparent that the operation quantity is reduced by reducing the dimensions of
    eigenvalue decomposition but the prediction precision is decreased. Well the
    virtues of the two arithmetics are utilized by the MSS-ESPRIT arithmetic
    substantially. The sampling data conjugation recomposition and space smoothing
    techniques are com
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