有中斷機率限制之毫微微蜂巢網路下鏈干擾管理

Abstract

近年來，鑒於能夠有效提高通道容量(Capacity)以及提高室內覆蓋率(Coverage)，毫微微細胞(Femtocell)日漸受到重視。為了能夠有效利用頻譜效率(Spectrum efficiency)，毫微微細胞蜂巢網路使用與現存之無線通訊網路(Macrocell)相同頻帶。因此，如何有效控制毫微微細胞網路與現存網路之相互干擾成為目前急需克服的難題。

本文的主旨在於基於中斷機率限制之下控管網路下鍊之毫微微蜂巢網路與現存網路之間相互干擾，透過中斷機率管制毫微微細胞對於現存網路所造成的影響。換言之，當某毫微微細胞之中斷機率符合標準，此毫微微細胞方可與其服務之用戶通訊。反之，鑒於此毫微微細胞會對現存網路造成過大干擾，此毫微微細胞不允許服務其用戶。此外，由於採用中斷機率限制條件，毫微微細胞無須知曉現存網路用戶確切位置，此能有效降低毫微微網路與現存網路之間資料交換量。

為了能夠滿足中斷機率限制，毫微微細胞必須控制其資源分配。本文中，資源分配最佳化問題被切割成兩個下鍊資源分配問題：次載波分配問題，與傳輸功率分配問題。於本文中，筆者藉由半定放寬(Semidefinite Relaxation)將原問題簡化成半定規劃(Semidefinite Programming)，並且利用主偶型內點法(primal-dual interior-point method)解決此資源分配問題。透過數值結果，我們證明基於有中斷機率限制之資源分配可以在保證現存網路之通道容量之下，有效提高毫微微細胞之通道容量。

The femtocell technology is an attractive alternative to solve the capacity and coverage problems of the existing macrocellular networks. To fully exploit and realize the promised potentials, it has toovercome the interference issue when femtocells are to be deployed over a macrocell system sharing the same spectrum.

In this thesis, we adopt a resource allocation based interference control approach. We consider downlink transmissions of an orthogonal frequency division multiple access (OFDMA) based femtocell network. The interference constraint is manifested in the form of (average) outage probability requirement. In other words, a femto base station (BS) is allowed to use a certain spectrum only if such an use does not cause the outage of a macrocellular user within the coverage neighborhood. The advantage of using the outage probability constraint is that the knowledge of the locations of the primary (macrocellular) users is not needed.

To satisfy the average outage probability constraint, a femtocell BS has to allocates the downlink resource (subcarriers and power) properly. We divide the resource allocation problem into two subproblems. The semidefinete relaxation (SDR) is used to convert the non-convex subcarrier assignment problem into a convex semidefinete programming (SDP) which is then solved by the primal-dual interior-point method. Given the subcarrier assignment, we suggest an iterative water-filling method by solving the KKT conditions for the power allocation problem.