無線下行資料服務網路的訊號比允入控制

Abstract

在無線網路中，服務需求很容易受到嚴重的時間和空間隨機的變動下而有不同，因此為確保在此環境中的服務品質 (QoS)，適當的允入控制是必須的，我們為探討更完整性的網路系統，在 CDMA/TDM 架構下研究一維空間的訊號比允入控制，初步先設想在個數允入控制的環境中，利用使用者可以接收多個天線而進行移動的現象，以騰出細胞格的允入個數，增加系統的效能，然而在個數允入控制的環境中所作的訊號比允入控制所能提昇的效能有限，因此進一步的將個數允入控制環境的前提拿掉，而單純的針對細胞格的服務品質條件，設想利用封包延遲時間(packet delay)來作為品質需求，及採用指數法則(exponential rule)的方式以訊號比 (SINR)來當作允入控制之機制，以達到系統的效能提昇之目的，並透過系統的阻塞率及服務率來觀察訊號比允入控制與個數允入控制之不同點，以及分析各個細胞格允入人數及延遲率的狀況，最後希望能透過適性調整使用者在細胞格移動的方式下達到效能提昇之目的。Wireless traffics tend to vary temporally and spatially. In order to support QoS guarantee in such environments, an admission control is necessary. We propose SINR-based admission control schemes for CDMA/TDM networks. The first scheme attempts to move the service of one accepted user to a neighbor cell, in order to accommodate a new service request into a full loaded cell. The user chosen for reallocation is essentially based on relative SINR values. This scheme is, however, number-based, which does not wholly exploit disparate received SINR values for reducing block probabilities. To release the “number” constraint, the second scheme attempts to use “packet delay” as an admission criterion which is designed to involve the use of the exponential rule. The performance of proposed schemes is evaluated in terms of blocking rate, effective service rate, and packet delay, all obtained by computer simulation.