SNR Threshold for Distributed Antenna Systems in Cloud Radio Access Networks

A distributed antenna system (DAS) architecture is a key enabler for Cloud Radio Access Networks (CRAN) where geographically separated base stations are connected to a centralized processing and decision making unit. Many schemes have been proposed to leverage Fractional Frequency Reuse (FFR) and co-ordinated joint transmission between base stations to improve cell-edge performance for static network deployments. In this paper, we investigate dynamic decision making that whether co-ordinated joint transmission should be selected in the downlink of a FFR-aided DAS. We derive the transmitting Signal-to-Noise-Ratio (SNR) threshold that co-ordinated joint transmission can provide better performance if the transmitting SNR is below this threshold. We simulated a three-cell cluster layout with FFR and the numerical results agree with our analytical results. We show that the transmitting SNR threshold is critical in the FFR-aided DAS analysis and can be used as a guide in the CRAN network planning and the evaluation of DAS performance.