OFDMA Downlink Resource Allocation in User-Deployed Femtocells

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One option for mobile operators to improve coverage and provide high-data-rate services in a cost-effective way is the emerging femtocell network, where low-power femtocell access points (FAPs), each being able to provide high-data-rate wireless connections to users within a short range, are overlaid on macro/micro cellular networks. Indoor deployments of femtocells can solve the problem of weak macrocell signal inside a building and offload a large amount of traffic from macrocells, leading to a promising solution for ubiquitous indoor/outdoor coverage with a single radio-access technology, such as the orthogonal frequency division multiple access (OFDMA) that has been considered in the downlink by major candidate technologies for next generation wireless networks. OFDMA combined with femtocells is widely expected to deliver massive improvements of coverage and capacity for wireless networks. Inter-cell interference management is among the most urgent challenges that operators must face before femtocells can be widely deployed. As plug-and-play devices, most FAPs will be deployed by end users and could be moved or switched on/off at any time. The number and locations of active FAPs are by no means known to operators. Therefore, inter-cell interference in femtocells cannot be managed using conventional network planning methods. An FAP has to be able to integrate itself into the cellular network with least interference caused. Most existing work on interference avoidance in femtocell deployments is for wideband code division multiple access (WCDMA) networks, while little work has been done for OFDMA-based femtocells, where interference avoidance can be implemented from a perspective of temporal and spectral reuse of OFDMA radio resources across different cells. This project aims to develop solutions for inter-cell interference avoidance through OFDMA downlink resource allocation in a network that has femtocells overlaid on macrocells. We will focus our work on the following two tasks: a) the development of a low-complexity interference-avoidance solution based on partial temporal and spectral reuse of OFDMA radio resources between femtocells, and b) the development of a dynamic time-frequency resource allocation algorithm for the OFDMA downlink to provide inter-cell interference avoidance and achieve a frequency reuse factor of 1 across macro and femto cells of the network. These cutting-edge topics cover some of the key aspects of future wireless networks and may lay the foundation to attain ubiquitous indoor/outdoor coverage.