OFDMA Downlink Resource Allocation in User-Deployed Femtocells

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.

Outcomes of the project will have an impact on consumers, telecom industry, and other beneficiaries. Femtocells will offer consumers satisfying coverage and high-data-rate services in a cost-effective way. With a faster and more responsive network enabled by femtocells, ubiquitous indoor/outdoor wireless experience can be delivered to end users. Femtocells will offload a large amount of traffic from macrocells and increase the overall network capacity. The cost of backhauling traffic to the operator's core network will be handled by the consumer through IP broadband without any cost to the operator. Femtocell deployments will reduce both capital and operational expenditures, and raise average revenue per user for the operator. In moving to femtocells, operators will find themselves at advantages in network cost, breadth of services and user experience, which will enhance their competitiveness and profitability. Femtocells also offer a lower-risk technology platform for introducing next generation mobile networks, because femtocells are much smaller than macrocells and the high-speed backhaul will be readily available. Femtocells will also contribute to lowering carbon emissions, by improving power efficiency in mobile networks and enabling mobile services that can reduce the need for travel. FAPs are more power-efficient and greener than macro BSs. FAPs will be switched on/off according to user needs. Consumers can expect longer battery lives of mobile devices as they are connected to nearby FAPs. High data rates and good coverage of femtocells will enable video conferences and e-commerce that can reduce the energy required for travel and maintaining brick-and-mortar facilities. Project outputs may also contribute to standardisation activities, and aid government agencies and other bodies to know better about possible impacts of femtocells, e.g., on other radio services. The contribution to the research community, telecom industry, and standardisation bodies will lead to a subsequent impact on the economic success and the improvement in quality of life for the general public. In order to enhance knowledge exchange, a dedicated website and an email-distribution list will be established to report research progress and outcomes. Workshops will be held before each milestone for information dissemination and discussion. Research outputs will be published in peer-reviewed IEEE and IET journals and at international conferences on communications and associated subjects. The Centre for Wireless Network Design (CWiND) at the University of Bedfordshire and Alcatel-Lucent have expressed interest in collaboration on the project. We will explore opportunities for follow-on activities, such as joint publications and joint project proposals, to enable long-term sustainable collaborations. King's College London (KCL) has established strong links with the wireless industry through the Virtual Centre of Excellence in Mobile and Personal Communications (Mobile VCE), of which KCL is one of the 6 academic members together with 18 industrial members. The CWiND and Alcatel-Lucent both participate in Femto Forum activities and has interaction with other leading femtocell vendors. These provide excellent opportunities for timely dissemination of research advances. The Research Grants & Contracts Division at KCL will be consulted at an early stage for possible exploitations of project outcomes. Intellectual property protection will be administered through King's College London Business Ltd. Dr. Xiaoli Chu, as the PI, will manage the knowledge exchange and impact activities. She has given technical seminars at the IET and a number of universities. As Chair of the Graduates of the Last Decade affinity group of the IEEE UKRI Section, she has been organising technological seminars for engineering students and professionals. The RA needs to have experience in writing publications, website maintenance, and presentation at conferences.