Abstract
非堅持性載波偵測多重存取協定對無線網路而言, 是非常吸引人的, 尤其是當做無線區域網路的介質存取控制協定. 由於無線網路的通道具有強且變化衰退的特性以致於無法完美地偵測到載波, 所以隱藏使用者是非常有仍能存在的. 另外, 傳統的分析都僅考慮在單一細胞的環境而實際上無線網路的操作環境是多細胞的環境, 且為了提供服務給移動的使用者, 細胞間須有適當的重疊. 我們用機率來模型化使用者的移動性及通道的特性而得到了一個機率的模型. 用通道狀態的觀念及更新定理的方法, 我們分析了非堅持性載波偵測多重存取協定在多細胞有重疊及隱藏使用者情況下的效果. 除了分析以外, 我們做了模擬來驗證由推導而得的結果並且將條件 為與以前的分析相同, 即單一細胞且無隱藏使用者的情況, 來驗證我們的推導.從分析而得的數值結果得知細胞有重疊會使效果變差而且隱藏使用者的存在會嚴重地降低協定的效果. 為了避免碰撞的發生以改善非堅持性載波偵測多重存取協定在無線網路中多細胞有重疊及隱藏使用者情況下的效果,載波偵測多存取碰撞避免型態的協定被考慮用來當做無線網路的多重存取協定. 在這篇論文中, 我們分析了一個碰撞避免的載波偵測多重存取協定, 請求傳送/允許傳送+載波偵測多重存取碰撞避免協定, 在無線網路中多細胞有重疊及隱藏使用者情況下的效果, 並做比較.Nonpersistent CSMA is recognized as an attractive member inCSMA family for wireless networks, especially as the mediumaccess control protocol for wireless LANs. As the wirelesschannels us- ually result in strong and changeable fadingcharacteristics, it is very possible to exist imperfect carriersensing and thus hidden terminals. Futhermore, the traditionalanalysis is basedsingle-cell coberage while wireless networkstypically ing due to frequency reuse and necessary services tomobile users. Introducing the stochastic modeling of dynamicfading and mobility effects on nodes within the coverage ofvarious base stations, we analyzed the performance ofnonpersistent CSMA in multi-cell coverage with hidden terminalsby the channel statecept and renewel theory approach. Ournumerical results from asympototical cases and simultions showthat the nonpersistent CSMA clearly suffers from performancedegradation if we take hidden terminals into consideration. Inorder to prevent from the occurring of collsions CSMA/CA-typeprotocols are considered to be the methods of multiple accesscontrol in wireless local area networks. In this paper, we alsoanalyzed the performance of the RTS/CTS+CSMA/CA protocol underthe same conditions. From the numercial results, we find thethroughput of RTS/CTS+CSMA/CA protocol occurs in the higherload than that of nonpersistent CSMA.