以DMT為調變方法的xDSL系統之同步

Abstract

離散多重頻調(Discrete Multitone, DMT)系統為一種在有限頻帶上能夠高速傳輸的多重載波技巧。藉由它的高速傳輸，已應用在各類數位用戶迴路(x digital subscriber line, xDSL)家族上，如非對稱數位用戶迴路系統(asymmetric digital subscriber line, ADSL)和非常快速數位用戶迴路系統(very-high speed digital subscriber line, VDSL)。 本論文將對符號元同步(symbol synchronization)和取樣元素同步(sample synchronization)在非常快速數位用戶迴路系統上進行討論。在符號元同步方面，以一近似最大概似法(maximum likelihood, ML)的方法來找出符號元的位置； 在取樣元素同步方面，以線性內差器(linear interpolator)來做頻率偏移量偵測(frequency offset detector)。基於上述兩大部分，並以規格上提出的通道模型，再加入種種雜訊所模擬出的結果，與文獻上的方法作比較。

The transmission of high-speed data over band-limited channels may be accomplished through the use of discrete multitone (DMT) modulation. Because of its high-speed data transmission, it is applied in xDSL such as ADSL (asymmetric digital subscriber line) systems and VDSL (very high-speed digital subscriber line) systems. The data cannot be recovered correctly if the synchronization of DMT system is not maintained because of the effect of ISI (intersymbol interference) and ICI (intercarrier interference). This thesis study the symbol synchronization and sample synchronization for VDSL systems. In symbol synchronization, we use near ML (maximum likelihood) approach to find correct symbol allocation. In sample synchronization, we use linear interpolator to detect the frequency offset. The simulations are also conducted under the standard channels and simulation results are compared with those obtained in terms of techniques proposed in existing literature. Since DMT system is almost similar to orthogonal frequency division multiplexed (OFDM) system, the technique developed in this thesis can be applied for the synchronization of OFDM system.