Femtocells at PIMRC in Istanbul

Femtocells were discussed in a multitude of ways at the 21th PIMRC conference in Istanbul September 26-29. A full-day workshop (IOFC) was organized before the conference, and there were one specific femtocell paper session and one panel session. In addition, a number of femtocell papers were presented at sessions on interference control and radio resource management.

KTH had three contributions: one cost&capacity analysis paper, one on the use of femtocells in the GSM band and one paper on interference and implications for spectrum allocation.

 The big technical issue discussed is the interference introduced by femtocells. This includes interference between femtocells and with the macro network. There seems to be an agreement among researchers that the usage of the same bands for both femtocells and the macro layer is a necessity. Even is operators in some countries may have many 10th of MHz of bandwidth they seem to be reluctant to allocate separate bands to femtocells. In other countries operators may have 5-10 MHz of spectrum and in these countries the operators CAN not allocate separate bands.

 However, there is some interesting research going on that may be a way forward to solve the interference problem. The underlying idea is that the femtocell and macrocell users are treated fairly in terms of resources. With the traditional approach “few” users ( 2 – 8) are allocated to a femtocell with a bandwidth of 5 MHz. At the same time “many” macrocell users ( 20 -100 ) have to share a bandwidth of 5 – 20 MHz. The fairness means that the femtocell users “get less resources” than the technology would allow. But at the same time the decreased usage means that less interference is introduced.

Related papers at the PIMRC are e.g. “Capacity of Closed-Access Femtocell Networks with Dynamic Spectrum Reuse Resource Allocation Analysis in OFDMA” by Demirdögen, Guvenc and Arslan, “Resource Allocation Analysis in OFDMA Femtocells Using Fractional Frequency Reuse” by Lee, Yoon and Shin and the IOFC workshop paper by Guvenc et al “Interference Avoidance in 3GPP Femtocell Networks Using Resource Partitioning and Sensing”

 Business aspects of femtocells were also discussed, mainly at the panel session. The panelists represented the vendors NEC and Alcatel Lucent, the operator Turkcell and the Turkish regulator.

On interesting aspect was the different view when it comes to deployment scenarios. NEC presented a number of business scenarios for small and large companies to public access. Turkcell presented their strategy with a strong focus on homes and small enterprises. Femtocells were not considered to be an option for large enterprises, shopping malls and public access, “other” solutions were to prefer.

At the Q&A session it was clarified that the use of femtocells for offloading of macrocell traffic had been considered, but not needed at this stage. It can be noted that Turkcell launched the 3G services june 2009 and has had a very large growth in number of users and traffic. Within a year around 5000 new 3G base stations have been deployed.

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