Abstract
本論文將提出數個全數位的共同估計接收器應用在不同的調變信號上，它同時估計相位(Phase)、時序(Timing)、以及資料串的偵測(DataSequence Detection)。在通訊系統裡，同步主要包括了載波相位以及信號時序的同步，是很重要的部份。而同步器基本上是一個可估計相位及時序的估計器。在大多數地系統裡，這些功能多是分開來完成的，然而一般說來，一個共同估計器 (Joint Estimator) 的效能會比分開估計再合併地估計器要來地好；此外，因為數位電路比其對應地類比電路要來地穩定，且可以完成複雜地運算法則，目前地趨勢就是利用數位電路來設計應用電路。這些共同估計器皆是由最相似估計理論(Maximum LikelihoodEstimation Theory)推導而來。 首先，先推導對應於BPSK調變信號地結構，根據推導地結果，我們得到一個利用決定-導向 (decision-directed) 的方法地替迴 (recursive) 結構。為了使結構能簡化，我們使用Sample-Correlate-Choose-Largest (SCCL) 的法則來估計相位。利用相似地推導，我們可以得到對應於p/4-DQPSK的類似結構，同時因為p/4-DQPSK的特性，不需要載波相位的估計，使結構簡化。 因為直接序列(Direct Sequence)展頻(Spread Spectrum)通訊 (DSSS)系統可以同一時間在同一頻道上傳送資料，近來受到很多的重視。利用與前面相似的推導方法，可以得到類似但運用於DSSS上的結構，但是結構太複雜；為了簡化結構，將估計時序的部份也改用SCCL的方式，如此，整個的結構變成是二維的 SCCL可同時估計相位及時序。 在DSSS的同步包括有兩部份，第一部份是搜尋 (Acquisition)，第二部份是追蹤 (Tracking)，前面提到二維 SCCL 的結構主要用於追蹤的功能。我們對一般單井(Single-Dwell)和多井(Multi-Dwell)的搜尋結構在衰退通道中的效能將有所分析。此外我們將前述用於追蹤的二維 SCCL 結構加以小幅的修改，即可用於搜尋上；因為搜尋與追蹤皆使用類似的結構，可大幅降低接收器的複雜度。The digital joint estimators for carrier phase, symboltiming,and the detection of data sequence with differentmodulations are proposed in this dissertation.In communicationsystems, the synchronization including both carrier phaseandsymbol timing is important for data detection.Basically, thesynchronization is an estimator which estimates carrier phaseand/or symbol timing.In most systems, these functions areusually separated.However, it is expected that the receiver withjoint estimation would be betterthan the one with separatedestimations of parameters. Otherwise, it is the trend to usethe digital circuit in applicationbecause it is usually morestable than its analog counter counterpartand can implement thecomplex algorithms.These estimators are derived from the maximumlikelihood estimation (MLE)theorem. First, the scheme forBPSK modulation is derived.According to the derivation, arecursive scheme applying the decision directedmethod isproposed.In order to simplify the structure, the Sample-Correlate-Choose-Largest (SCCL)algorithm is used in theestimation of carrier phase.With the similar derivation, theproposed scheme is applied to the $\frac{\pi}{4}$-DQPSKmodulation.Because the peculiarity of $\frac{\pi}{4}$-DQPSK, theestimation of carrierphase is omitted. The direct sequencespread spectrum (DSSS) communication systems have receiveda lotattention because many signals can be transmitted in the samefrequencyband and in the same time.With the similar method, thesimilar scheme for DSSS systems can be obtained.However, thetiming candidates are too many to implement.To solve thisproblem, the SCCL algorithm is also applied in timingestimation.The whole scheme becomes a modified two dimensionalSCCL schemeand the two dimensional SCCL scheme also haveefficient performance. The synchronization of DSSS systemsincludes two steps.The first step is acquisition and the secondstep is tracking.The mean acquisition time for single dwell andmulti dwell scheme in slow Rayleighfading channels are analyzed.With some modifications in the proposed tracking schemedescribed above,A new acquisition scheme is obtained.Because thenew acquisition scheme applies the same algorithm as thetracking scheme,the whole receiver scheme may be simpler thanthe traditional one.Simulation results have shown to prove itsefficient performance.