3GPP毫微基地台之負載平衡研究

Abstract

不像大型基地台能夠使用很寬的頻帶，毫微基地台能使用的頻帶有所限制，因此可達到的總傳輸速度會比大型基地台還小；另外，毫微基地台有可能與其他裝置共用後端的實體線路頻寬，例如桌上型電腦。因此，相較於大型基地台，毫微基地台可同時服務的行動裝置數量將會有所限制。 大多數負載平衡的方法只考慮單一參數。雖然考慮的參數所影響的效能能夠表現的不錯，但是卻造成其它沒考慮到的效能有較為低落的情形。為了克服此項缺點，我們提出的負載平衡方法考慮了行動裝置的移動、服務品質的要求以及毫微基地台間的負載係數，藉此讓更多的使用者能夠同時進行資料傳輸，並且維持較高的傳輸速度和毫微基地台間的平衡。 假設鄰近毫微基地台間的涵蓋範圍有部分重疊，並且有許多的行動裝置位在重疊範圍內。針對那些行動裝置，首先我們利用訊雜比的大小和變化來估計各個行動裝置停留在涵蓋範圍內的時間係數。接著利用毫微基地台剩餘的資源，我們計算出毫微基地台能提供的頻寬，並藉此得知毫微基地台能夠提供的服務品質係數。再來，我們根據毫微基地台的負載狀況來計算它們之間的平衡係數。我們利用以上三個係數進行行動裝置的挑選並將之換手到其他毫微基地台，以達到負載平衡的目的。而我們也提出了兩種方法，以便用來挑選被換手的行動裝置。最後我們列出模擬結果並且說明之。

The usable frequency bandwidth of femto-cells is narrower than macro BSs’. Hence, the total data rate of femto-cells is lower than macro BSs’; besides, the backhaul of femto-cells may be shared by other devices, such as PC. The number of concurrently connecting users is restricted by those reasons mentioned above. Many load balance methods consider one parameter only. Although the evaluated performance affected by that parameter works well, other performance affected by non-considered parameters may not work well. In order to overcome the weakness mentioned above, we propose a load balance method that considers the movement of user equipment (UE), QoS requirement and the load balance index between femto-cells. Assume that the coverage area of a femto-cell is partially overlapped with another femto-cell, and there are many UEs within the partially overlapping area. Firstly, we use the magnitude and variation of signal to noise ratio (SNR) to estimate the remaining time index of a UE within the overlapping area. Secondly, we make use of the remaining resource of a femto-cell to calculate the remaining bandwidth, and then we use the acquired remaining bandwidth to calculate the satisfaction index of a UE. Thirdly, we use the loading of those femto-cells to calculate the load balance index. Finally, based on those three indexes mentioned above, we choose a UE to handover for the purpose of load balance, and we propose two strategies to select the UE. We describe the performance evaluation and explain it in chapter 5.