Radio Resource Virtualization in Cellular Networks

Virtualization of wireless networks holds the promise of major gains in resource usage efficiency through spectrum/radio resources sharing between multiple service providers (SPs). Radio resources however are not like a simple orthogonal resource such as time slots on a wire and its shared quantity is a function of geography and signal strength, rather than orthogonal slices. To better exploit the radio resource usage, we propose a novel scheme - radio resource virtualization (RRV) that allows SPs to access overlapping spectrum slices both in time and in space considering the transmit power, the interference, and the usage scenario (capabilities/needs of devices). We first investigate the system capacity of a simple two-cell network and show that RRV often leads to better efficiency than the well-known separate spectrum virtualization (SSV) scheme. However, the use of RRV requires careful air-interface configuration due to interference in the overlapping slices of spectrum. Therefore we next examine scenarios of a multi-cell network with fractional frequency reuse (FFR) implementing five radio resources configuration cases. From the evaluation of capacity data obtained from simulations, a variety of tradeoffs exist between SPs if RRV is applied. One example shows that capacity of the SP that operates smaller cells almost doubles while capacity of the SP deployed in larger cells may drop by 20% per subscriber. Based on these tradeoffs, we suggest configuration maps in which a network resource manager can locate specific configurations according to the demand and capabilities of SPs and their subscribers. Finally, we consider a case study on top of LTE. A system-level simulator is developed following 3GPP standards and extensive simulations are conducted. We propose and test 3 schemes that integrate RRV into the LTE radio resource management (RRM) -- unconditional RRV, time domain muting (TDM) RRV and major-interferer time domain muting (MI-TDM) RRV. Along the same line as the capacity analysis, we compare those schemes with the traditional SSV and suggest configuration maps based on the produced tradeoffs. Our investigation of RRV provides a framework that evaluates the resource efficiency, and potentially the ability of customization and isolation of spectrum sharing in virtualized cellular networks