Dynamic Access and Coverage Optimization Scheme for Cross-tier Interference Mitigation in Femtocell Networks

Abstract

펨토셀은 사용자가 설치하고 인터넷을 백본망으로 사용하는 초소형 기지국으로 제한적인 기능과 저렴한 가격을 가진다. 많은 수의 펨토셀이 설치될 미래 펨토셀 네트워크가 원활히 동작하기 위해서 여러 기술적인 문제를 해결해야 한다. 그 중에 가장 중요한 문제 중 하나는 매크로셀과 펨토셀 간의 간섭 문제이다. 이 교차 간섭 문제를 해결하기 위해 본 논문은 액세스 타입과 전송 파워 조절 기법을 제안한다. 또한 간섭을 일으키는 사용자가 존재하는 지와 얼마나 심각한 간섭을 주는지 자가 구성을 통하여 파악할 수 있는 기법도 제안한다. 본 논문의 목표는 매크로 사용자를 보호하면서 셀 내에 있는 모든 사용자 용량 합을 최대화시키는 것이다. 시물레이션을 통하여 제안하는 기법이 다른 기법들보다 높은 용량을 가지는 것을 보였다.

Femtocell network is a low power, consumer installed small base station and uses internet as its backhaul. Femtocell coexists with macrocell to exploit spatial reuse gain, but to realize it, interference mitigation is very important. The mass deployment of femto base stations (FBSs) will create different technical challenges among which cross-tier interference between femtocell and macrocell is more subtle and needs an effective solution. To solve cross-tier interference problem, a joint access and power control scheme is proposed which also overcomes the low performance of earlier schemes. We have limited information about neighboring macro users (MUEs) to take proper measure to solve the problem which forces us to take a centralized approach and this is not suitable for femtocell case. To make our algorithm work in a distributive manner, we introduced a self-organizing scheme to detect the presence of interferes and how much they are affecting the victims. Our objective is to maximize the sum capacity of whole network while protecting the neighboring macro users (MUEs). We achieve this goal by optimizing transmit power for all the FBSs and making dynamic decision on access mode of FBS based on resources and femto users (FUE) capacity requirements. We formulated optimization problem with two control variables for controlling power and access to femtocell and solved it by using local search algorithm to ii get an initial solution. The problem is reformulated by defining objective function separately for the power control and separately for access control and solved them by using well known meta-heuristic algorithms (Knapsack and Interior Point method) to get near optimal solution. In results section we analyzed both uplink and downlink interference scenarios comprehensively. Through extensive simulations we have shown that our proposed scheme out performs earlier works.