Dynamic Spectrum Refarming of GSM Spectrum for LTE Small Cells

Small cells, involving isolated or clustered deployment of low power base stations in the foot print of macro cellular networks, is emerging as an effective approach to address high capacity demand in traffic hot spots. Small cells may be deployed in the same spectrum as the macro cell or in separate spectrum. Deploying Long Term Evolution (LTE) small cells in the same spectrum requires careful handling of the interference between the small cell and the macro cell while deploying it in separate spectrum requires additional dedicated spectrum for small cells. Refarming of the spectrum used by older technologies such as Global System for Mobile (GSM), the demand for which is diminishing, offers the possibility to make additional spectrum available for use by LTE. We propose a novel solution called dynamic spectrum refarming (DSR) for deploying small cells systems based on orthogonal frequency division multiplexing (OFDM) technology such as LTE small cells using the same spectrum as existing GSM networks. The basic idea of DSR is that LTE small cells are deployed in the GSM spectrum but suppress transmission of all signals including the reference signals in some specific physical resource blocks corresponding to a portion of the GSM carriers to ensure full GSM coverage. Our study shows that the proposed solution can provide LTE mobile terminals with high speed data services when they are in the coverage of the LTE small cells while minimally impacting the service provided to GSM terminals located within the LTE small cell coverage area. Thus, the proposal allows the normal operation of the existing GSM networks even with LTE small cells deployed in that spectrum. The proposed approach is superior to an approach based on partitioning the band between GSM macro and LTE small cell since it can maximize LTE small cell capacity and maintain macro GSM capacity while enabling high speed data services within the small cell. Though the focus of this paper is about GSM networks, an analogous approach can be applied to reuse code division multiple access (CDMA) spectrum for LTE small cells.