回授量降低之多細胞合作式傳輸

Abstract

在下一代通信系統，為了去最大限度地提高頻譜效率而考慮使用頻率複用係數等於一，侵略性的細胞間干擾將嚴重的降低在細胞邊緣的效能。在多細胞的多輸入多輸出（MIMO）下行蜂巢式系統裡，為了細胞邊緣的用戶，我們提出協調波束形成（CB）的演算法去抑制細胞間嚴重的干擾。從實際系統的觀點，只需要對實際現存蜂巢式系統的演算法做些微的修正，就能夠分散地實現我們提出的協調波束形成演算法。雖然我們透過基地台之間的合作去對抗細胞間的干擾，但是在我們提出的協調波束形成演算法中並不需要基地台之間的後端交換傳輸，也不需要用戶端去估計干擾源的通道。主要設計的概念是，從用戶端獲得細胞間干擾的訊息，然後反覆地調整發送端/接收端的波束形成去避開彼此的細胞間干擾。此外，為了減少用戶的回授量，白化濾波器被用在用戶端去預先處理細胞間干擾，而且我們也已經證明，在用戶端新增白化濾波器並不會改變我們使用的性能指標。 除了提出協調波束形成演算法，我們還討論幾種方法藉由支付額外的代價去進一步提升性能。模擬結果驗證了多細胞協調傳輸的優勢和與其他現有的演算法做比較。

The cell-edge performance would be extremely degraded by the aggressive inter-cell interference when the frequency reuse factor of one is considered to maximize the spectral efficiency in next-generation communication systems. In multi-cell multi-input multi-output (MIMO) downlink cellular system, we propose the coordinated beamforming (CB) algorithms to suppress the serious inter-cell interference. Although we combat the out-of-cell interference through the cooperation between base stations (BSs), the backhaul-exchange between BSs and the estimation of interference-channels at user-end are not required in the proposed CB. From the viewpoint of practical systems, the proposed CB could be distributively implemented with only little revision to practical existing algorithms in cellular systems. The main idea is to obtain the inter-cell interference information at user-end and then iteratively adjust the transmit/receive beamformings to avoid the interference with one another. Besides, in order to reduce the feedback overhead of users, the whitening filter is considered to pre-process the inter-cell interference information at user-end, and we have proven that the adopted performance metric would not be changed by adding the whitening filter in user-end. In addition to proposed CB, we propose several methods to further improve the performance by paying additional costs. The simulation results verify the benefit of multi-cell coordinated transmission and compare the proposed schemes with other existing algorithms.