Spectrum Sharing for Next Generation Mobile Communication Networks

The International Telecommunications Union (ITU) is currently working on specifying the system requirements towards next generation mobile communication systems called International Mobile Telecommunications - Advanced (IMT-A). 3G mobile communication systems including their evolution are in this respect part of the ITU IMT-2000 systems. The deployment of IMT-A is believed to take place around year 2015 at mass market level and will facilitate what has been a buzzword for almost a decade, namely "4G". IMT-A systems are expected to provide peak-data-rates in the order of 1Gbit/s in local areas. Such high data rates require both usage of advanced MIMO (Multiple Input Multiple Output) antenna technology to achieve high spectral efficiency and also extremely high spectrum allocation in the range of 100MHz.

Despite that new frequency bands are expected to be allocated for IMT-A, the high system bandwidth requirements will likely demand spectrum sharing between operators. This is a very different situation from today's IMT-2000 systems (e.g. GSM/UMTS), where each network operator operates its network in a dedicated licensed band.  The research goal of this project is to investigate the feasibility of spectrum sharing in IMT-A from both technological and performance point of view.

Traditionally, cellular mobile network operators (e.g. GSM/UMTS) have obtained dedicated spectrum resources from their national telecommunication regulators. The dedicated radio resources can be utilized independently by each operator without any interference coordination. As today the operators are assigned different frequency bands, they do not need any radio resource coordination. On the other hand the obvious drawback of dedicated spectrum allocation is reduced spectrum trunking efficiency and reduced peak data-rates by restricting the system bandwidth to each operator. This has, however, not been a severe problem for IMT-2000 cellular systems since the system bandwidth has been relatively small (lower than 5 MHz). 

Next generation IMT-A systems are predicted to facilitate flexible bandwidths of up to 100 MHz. Even with new spectrum allocated to IMT-A by the World Radio Congress in 2007, It will become impossible to allocate such high bandwidth to several operators operating in the same geographical area. Hence, new approaches for spectrum sharing among operators are required.

Sharing of spectrum could, for example, be accomplished by means of contention based methods as is the case in WLAN systems. However, contention based method becomes very inefficient for cellular systems. The approach of this project is to make research on new non-contention based methods, where different operators use resources in a way that services of other operators are not interfered.

The working assumption is that IMT-A systems will use a multiple access technique, which facilitate radio channel multiplexing in frequency, time and spatial domains. New cellular systems, currently under standardization, such as the UTRA Long Term Evolution (LTE) and WiMAX also fulfill this kind of multiplexing.

The objective of this project is to investigate the technologies, and their feasibility, required for efficient non-contention based spectrum sharing for IMT-A systems, and compare the shared network performance to that of traditional dedicated spectrum allocation.