扇形多工二維耙狀接收器之效能評估

Abstract

在蜂巢式無線分碼多工通訊環境中，由於每位使用者均利用相同之通 道進行通訊，因此在接收端所接收到之干擾量亦隨著使用者個數之增加而 增大。傳統之耙狀接收器並不能有效地消除這些干擾，因此系統容量並不 能有效地增加。近年來，結合陣列天線之空間自由度和耙狀接收器之時間 自由度所衍生而來的二維耙狀接收器受到漸多的重視。不同於傳統之串接 式分開處理法，此二維耙狀接收器將時間和空間兩種不同之自由度結合成 單一之空時聯合自由度，再經由最小均方誤差或其他演算法推導出空時聯 合最佳處理法。由於空時聯合處理之自由度為空間之自由度與時間之自由 度之積，其遠大於此兩種自由度之和，故相對於空時分開處理法，二維耙 狀接收器具有極佳之表現。在本論文中，吾人同時探討了非盲蔽式和盲蔽 式之空時聯合或分開處理法，經由電腦模擬，吾人可以驗證此二維耙狀接 收器之表現。但由於空時聯合處理需要大量之運算，當天線個數增加時， 系統即時處理之能力會降低，針對此問題，吾人利用扇形多工之觀念，先 藉由陣列天線在一特定區域內產生數個少於天線數目之波束，在此一區域 內，目標信號被加強性地接收，而在此一區域外，干擾被有效地壓低。因 此雖然可利用之自由度大幅地減少，但系統整體之表現亦不會太差，且由 於自由度之大幅降低，運算量因此亦大幅減小，而即時處理之目的即可達 到。最後，吾人將以電腦模擬之結果來驗證以上之各種方法。 In the cellular code division multiple access (CDMA) communication environment, each user communicate via the same radio channel such that interference increases with the number of subscribers. Traditional RAKE receivers cannot handle the co- channel interference (CCI) well, and this prompts the use of extra sptial degree of freedom (array), leading to the space- time RAKE receiver. In particular, a 2-D RAKE receiver takes the spatial and temporal domains into consideration. Since the degree of freedom of joint processing is the product of the spatial and temporal degrees of freedom, the performance of the joint processor will be superior to the separate processor. In the thesis, we will discuss the performance of the nonblind and blind space-time separate/joint RAKE receivers. In despite ofthe superior performance of the space-time joint processor, it needs more complex computations and real-time processing is hard to achieve when the joint degree of freedom is large. To remedy this, we make use of the concept of sector division multiple access, in which a few mainbeams (less than numberof antennas) are formed encompassing a specified sector in the cell. In sodoing, the in-sector desired signal is received, and the CCI's are suppressed outside the sector. By beamspace sectorization, the total degree of freedom ofthe 2-D RAKE receiver can be reduced without degrading the system capacity much. This will be demonstrated via a complete set of numerical examples.