Abstract
分碼多重擷取技術因其應用在無線通訊上的優點，已獲得廣泛的注意。在分碼多重擷取技術中，每一位使用者皆被指定一特殊的碼用來展頻以及聚頻，然而，暨有好的自相關函數且享有特別的交互相關函數的碼組的數目，實為有限。因此，如要簡化系統且維持良好的性能，碼組的分配便得慎行其事。取而代之的，分碼多工技術便被選用來運作在一個基架型無線區域網路中的各個不同的侍服區，所有經由同一個擷取點服侍的遠端單元皆使用相同的上傳碼來完成向上傳送，其方式乃採用時槽式ALOHA協定(slotted-ALOHA)做為向上傳輸的介質擷取控制方式。然而，擷取點的基本服務範圍之間的重疊現象是維持服務連續不中斷的前題下，無可避免的安排。任何遠端單元皆可能坐落在其他非其註冊的擷取點以外的擷取點涵蓋之服侍範圍，因此可能對這些擷取點封包的接收產生影響。這種由註冊於其他擷取點，且坐落在本擷取點之服侍範圍內的遠端單元所產生的干擾，稱為重合服侍區之干擾，雖然重合服侍區之干擾可利用分碼多工技術來降低錯誤率至某些程度，但在無線區域網路的應用上，其作用因來自多數同時正進行傳送所累加起來、強烈的重合服侍區之干擾訊號而變得不可忽視。在本論文中，我們主要探索重合服侍區之干擾對建構於分碼多工技術之時槽式 ALOHA 協定操作的性能所造成的影響。Code-division multiple access (CDMA) techniques have beenreceiving great attention especially in wirelesscommunications due to some promising good advantages ofusing them. In CDMA, each user is assigned a unique code tospread and despread signals. However, the number of codes whichhave good autocorrelation as well as crosscorrelationproperties is limited. As a result, in order to simplifythe implementation of real systems while maintaining goodperformance, the assignment of a set of codes with goodcrosscorrelation properties should be properly managed. Insteadof CDMA, code-division multiplexing (CDM) is considered tooperate among different cells in an infrastructured wirelesslocal area network (LAN). All remote units served by the sameaccess point use the same preassigned code for uplinktransmission. And each cell operates with slotted ALOHA as itsuplink transmission medium access control. Nonetheless, thebasic service areas of access points are inevitable to overlapone another for the sake of continuation in service. A remoteunit registered to some certain cell may possibly lie in thecoverage areas of other access points and has some influence onthe packet reception in these other access points. Theinterference produced by remote units which lie in the jointregion of two cells is called joint-cell interference. Althoughjoint-cell interference can be suppressed with CDM to somedegree, it can not be totally neglected in a wireless LANapplication because of the strong summing signal transmittedfrom a large number of active remote units simultaneously in aperiod of time. In this thesis, we investigate the effects ofthe joint-cell interference on the performance of slotted ALOHAprotocol with CDM.