Interference Mitigation by Practical Transmit Beamforming Methods in Closed Femtocells
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Research Article Interference Mitigation by Practical Transmit Beamforming Methods in Closed Femtocells Mika Husso,1 Jyri H¨am¨al¨ainen,1 Riku J¨antti,1 Juan Li,1 Edward Mutafungwa,1 Risto Wichman,1 Zhong Zheng,1 and Alexander M. Wyglinski2 1 Department 2 Department
of Communications and Networking, Helsinki University of Technology, P.O. Box 3000, 02015 TKK, Espoo, Finland of Electrical and Computer Engineering, Worcester Polytechnic Institute, Worcester, MA 01609-2280, USA
Correspondence should be addressed to Mika Husso, [email protected] Received 21 December 2009; Accepted 3 April 2010 Academic Editor: Ismail Guvenc Copyright © 2010 Mika Husso et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We present an analysis of a femtocellular communications network and the impact of cochannel interference on link performance. Furthermore, we propose a method whereby user terminals can maintain a controlonly connection to an adjacent femtocell for interference mitigation purposes. Specifically, we provide an emphasis on suboptimal but practical methods that rely on transmit beamforming. Our numerical results demonstrate that even simple multiantenna methods can be effectively used to suppress co-channel interference provided that control channel connection between interfering femto-base station and user terminal is allowed.
1. Introduction The emergence of new data-intensive wireless services coupled with an increase in the number of multimedia-enabled user equipments, such as smartphones, has forced mobile operators to examine new ways for increasing coverage, achieve requested data rates, and to lower the capital and operating costs (CAPEX and OPEX) of their mobile networks. One approach for filling-in coverage holes and increasing data rates has been the utilization of relatively small cellular access sites. Femtocells provide a practical solution that has recently been generating considerable interest among both academic and industrial communities. The potential cost reduction of up to 70 percent per annum in operator’s network functions [1], combined with the prediction of 95 percent annual market growth in the following years [2], makes the femtocell concept a particularly lucrative option for most mobile operators. The standardization process of femtocells launched in August 2007 via the 3rd Generation Partnership Project (3GPP) is still under way. Until now, 3GPP has published both technical reports [3] and technical specifications [4, 5] focusing on end-to-end and UTRAN architectures, respectively. Simultaneously with the 3GPP activities, the IEEE
802.16 standardization group has discussed femtocellular networking and related products. More recently, in June 2009, the Femto Forum and the WiMAX Forum agreed on collaborating with respect the development of a WiMAX Femtocell Access Point (WFAP) specifications addressing a wide range of topics
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