A Self-Organizing Approach to Inter-Cell Interference Avoidance for OFDMA Femtocells Sharing Spectrum with Macro Underlay

Visiting researcher: Dr Xiaoli Chu (KCL)
Host researcher: Prof. Xiaofeng Tao (BUPT)
Duration: 3 months
Status: Ongoing

Biography of the visiting researcher

Xiaoli Chu received the BEng degree with first class honors in Electronic and Information Engineering from Xi’an Jiao Tong University, China, in July 2001, and the PhD degree in Electrical and Electronic Engineering from the Hong Kong University of Science and Technology, Hong Kong, in August 2005. She has been a Lecturer with the Centre for Telecommunications Research (CTR) in the Division of Engineering at King’s College London, UK, since January 2007. From September 2005 to December 2006, she was a Postdoctoral Research Associate with the Division of Engineering at King’s College London. She received the UK EPSRC Cooperative Awards in Science and Engineering for New Academics in June 2008, and the UK EPSRC First Grant on “OFDMA Downlink Resource Allocation in User-Deployed Femtocells” in December 2009.
Xiaoli conducted her PhD study focusing on physical-layer designs for power-efficient ultra-wideband (UWB) communications and narrow-band interference mitigation techniques for UWB communications. Her current research extends to advanced technologies for link performance improvement and capacity enhancement, such as adaptive/dynamic radio resource management algorithms, cooperative communications, and cognitive communications, especially in heterogeneous networks for next generation mobile communications.
Xiaoli is a Key Member of the Interest Group (IG) on Wireless Technology for Multimedia Communications of IEEE Multimedia Communication Technical Committee, Editorial Board Member of the International Journal of UWB Communications and Systems, and Editorial Committee Member of the International Journal of Wireless Networks and Broadcasting Technologies (IGI-Global). She is currently Chair of the Graduates of the Last Decade (GOLD) Affinity Group and Secretary of the Computer Chapter within the IEEE United Kingdom and Republic of Ireland (UKRI) Section.

Background and Motivation

One cost-effective solution for mobile operators to improve network coverage is the emerging femtocell network, where femtocell access points (FAP) are overlaid on existing macrocells and provide high-data-rate connections to user equipments (UE) within a short rangeusing the same radio-access technology as the macro underlay. An FAP is connected to the operator’s network through the user’s broadband connection. Moreover, femtocells also fit perfectly in the context of Green Radio, as shrinking cells is the most effective way to increase energy efficiency.
Given that most femtocells will be deployed within coverage of macrocells, inter-cell interference is among the most urgent challenges that must be tackled for successful deployments of femtocells. When operating in the same spectrum with the macro underlay, closed-access femtocells, each serving its authorized UEs only, may intensify femto-to-macro interference. Although open-access femtocells that allow passing UEs to connect to them may mitigate the femto-to-macro interference, due to the nomadic nature of outdoor mobile UEs, it is likely that their connections will be frequently switched between neighboring femtocells or between femtocells and the macro underlay. Thus, the network signaling overhead would be significantly increased due to the elevated number of handovers. As plug-and-play devices, FAPs are likely to be deployed by end users. Hence, interference caused by femtocells cannot be managed using conventional network planning methods. Nevertheless, because no signaling interface between eHNodeBs has been standardized by LTE and the IP backhaul of femtocells may not be owned by the same operator, inter-cell interference avoidance can hardly rely on the exchange of messages between femtocells (and macrocells). Therefore, more research activities are in demand to develop distributed dynamic radio resource allocation algorithms for OFDMA-based femtocells operating in the same spectrum as the macro underlay, so that interference avoidance can be achieved in a self-organizing manner.

Research Activities

The aim of the proposed research is to provide solutions for avoidance of inter-cell interference in the OFDMA downlinks of collocated spectrum-sharing macrocells and closed-access femtocells, through the development of distributed dynamic radio resource management algorithms to be implemented in femtocells, in a way that the cellular network can self-organize into an efficient and stable frequency reuse pattern.
The visiting fellowship is planned for three months. In April and May 2011, Dr. Xiaoli Chu visited Prof. Xiaofeng Tao at Beijing University of Posts and Telecommunications for two months. Dr. Chu will visit Prof. Tao for another month in December 2011 or April 2012. The visiting fellowship so far has led to the following journal paper submission and conference paper acceptance.


  1.  X. Chu, Y. Wu, D. López-Pérez and X. Tao, “On providing downlink services in collocated spectrum-sharing macro and femto networks,” IEEE Trans. Wireless Commun., under review.
  2.  X. Chu, Y. Wu, D. López-Pérez and H. Wang, “Decentralized femtocell transmission regulation in spectrum-sharing macro and femto networks,” IEEE VTC 2011-Fall, San Francisco, US, Sep 2011, to appear.
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