多速率直接序列-分碼多工擷取蜂巢式系統之軟性遞移機制

Abstract

在本論文中，我們在直接序列-分碼多工擷取蜂巢式系統環境下，首先提出一個「改進式的負載均衡軟性遞移 (enhanced soft handoff with transmission power balancing (SHXPB) ) 」機制。在此方法在訊號品質可以接受的情況下，將軟性遞移用戶之現役集個數減到最小，並且根據細胞 (cell) 負載的反比來分配功率給此軟性遞移的使用者。在這樣的機制下，細胞的負載可以更平均。並且系統的容量可以增加，尤其是在過熱點細胞 (hot spot cell)容量的改進更為顯著。再來我們提出一個乏晰現役集控制器，其內包含了一個乏晰現役集成本估計器跟一個決策器。乏晰現役集成本估計器的輸入是使用者與基地台之間的連節增益 (link gain) 以及接受了一個軟性遞移的使用者後的剩餘細胞負載 (remaining cell loading)。藉由乏晰現役集控制器來估計來估測現役子集 (active subset) 接受一個軟遞移使用者所需要的成本，並且挑選出一個成本最少的現役子集來當乏晰現役集 (fuzzy active set)。由模擬的結果中可以知道乏晰現役集控制器方法可以在過熱點細胞內有良好的表現。

In this thesis, we study the effects of soft handoff to the system in a Direct Sequence-Code Division Multiple Access (DS-CDMA) cellular system. Traditionally, soft handoff algorithm only takes the pilot channel quality into consideration as the active set decision parameter. But this is not enough for multirate service. We first propose an enhanced soft handoff with transmission power balancing (SHXPB) algorithm for DS-CDMA wireless systems. In this method, the member of active set is reduced to a minimum with an acceptable signal quality and the cell loading is balanced by allocating power to soft handoff users by inversely proportional to the cell load. It is shown that SHXPB can increase system capacity, especially for hot spot cell. Secondly, we design a fuzzy active set controller (FASC) to decide a more effective active set. FASC is constituted by a fuzzy active set cost estimator (FASCE) and a decision maker. The input to the FASCE is the link gain and the remaining cell load after accepting the soft handoff user. Use FASC to estimate the cost for each active subset to accept a soft handoff user and choose the active subset with minimum cost to be the fuzzy active set. The simulation results show that FASC method can have good performance in the hot spot cell.