The Studies of Synchronization in Fading Channels

• Main Authors: Cheng, Tai-Yuan, 鄭泰源
• Other Authors: Chen Kwang-Cheng
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/07174496380382348617

博士 === 國立清華大學 === 電機工程學系 === 85 === The digital joint estimators for carrier phase, symbol timing,and the detection of data sequence with different modulations are proposed in this dissertation.In communication systems, the synchronization including both carrier phase andsymbol timing is important for data detection.Basically, the synchronization is an estimator which estimates carrier phase and/or symbol timing.In most systems, these functions are usually separated.However, it is expected that the receiver with joint estimation would be betterthan the one with separated estimations of parameters. Otherwise, it is the trend to use the digital circuit in applicationbecause it is usually more stable than its analog counter counterpartand can implement the complex algorithms.These estimators are derived from the maximum likelihood estimation (MLE)theorem. First, the scheme for BPSK modulation is derived.According to the derivation, a recursive scheme applying the decision directedmethod is proposed.In order to simplify the structure, the Sample- Correlate-Choose-Largest (SCCL)algorithm is used in the estimation of carrier phase.With the similar derivation, the proposed scheme is applied to the $\frac{\pi}{4}$-DQPSK modulation.Because the peculiarity of $\frac{\pi}{4}$-DQPSK, the estimation of carrierphase is omitted. The direct sequence spread spectrum (DSSS) communication systems have receiveda lot attention because many signals can be transmitted in the same frequencyband and in the same time.With the similar method, the similar scheme for DSSS systems can be obtained.However, the timing candidates are too many to implement.To solve this problem, the SCCL algorithm is also applied in timing estimation.The whole scheme becomes a modified two dimensional SCCL schemeand the two dimensional SCCL scheme also have efficient performance. The synchronization of DSSS systems includes two steps.The first step is acquisition and the second step is tracking.The mean acquisition time for single dwell and multi dwell scheme in slow Rayleighfading channels are analyzed. With some modifications in the proposed tracking scheme described above,A new acquisition scheme is obtained.Because the new acquisition scheme applies the same algorithm as the tracking scheme,the whole receiver scheme may be simpler than the traditional one.Simulation results have shown to prove its efficient performance.