由於移動通訊服務需要某些服務品質(QoS)，其中呼叫允入控制 (Call Admission Control, CAC)是在無線網路上提供滿意的服務品質的重要機制。以往的允入控制著重在如何分配換手和新呼叫阻絕率，卻無法解決因為大量使用者造成的壅塞問題，如此就會造成QoS降低，這個現象可以用外部性來解釋。 在本論文中，我們提出一種結合使用者進入壅塞控制(User-level Burst Control, UBC)和呼叫允入控制機制來解決此問題。此機制定期地偵測網路壅塞，並且當發生壅塞時可以即時地控制進入的使用者。此外，此機制能夠提供使用者壅塞的資訊，例如預計等待時間，而使用者依據此資訊來決定是否繼續等待或是放棄。因此在壅塞發生時，此機制除了能夠控制進入的使用者，還可以抑制使用者對於無線網路資源的需求。 經過模擬證實此機制有相當大的改善。此機制減少了70%至80%加權阻絕率 (weighted blocking probability)；而總使用者效用(total user utility)更增加了2至3倍。因此，我們的機制確實能夠解決壅塞的問題並且提供使用者希望的服務品質保證。 As mobile communication services require some sort of Quality of Service (QoS), Call Admission Control (CAC) plays a significant role in providing desired QoS in wireless networks. Traditional CAC that mainly focus on the tradeoff between new call blocking probability and handoff call dropping probability cannot guarantee QoS requirements to users when the network is congested with too many users. This phenomenon can be explained by externality. In this thesis, we propose an integrated scheme which combines user-level burst control (UBC) with CAC to solve the problem of congestion and provide desired QoS to users. Our proposed scheme periodically detects the network congestion, and control input user traffic in a real-time fashion when the congestion occurs. Besides, it notifies users of the congestion information, such as expected waiting time, so that users can make decisions to leave or keep waiting according to this information. Specially, our scheme not only control user traffic but also restrains user’s demand to resource when the network is congested. The simulations showed that our scheme achieves considerable improvement than conventional systems where UBC is not taken consideration in the call admission control process. Pb (weighted blocking probability) of our scheme decreases 70~80% than conventional systems (CAC only) and achievable total user utility increases 2~3 times. Therefore, our proposed scheme indeed solves the problem of congestion and provides desirable QoS to users.
