LTE frequency selective scheduling performance and improvements assessed by measurements

In this paper the potential of downlink frequency selective scheduling (FSS) is addressed based on measurements in an experimental 3GPP Long Term Evolution (LTE) system setup. We find that scheduling on the best sub-band has the potential to improve channel conditions by up to 2 Channel Quality Indicator (CQI) units, which represents around 4 dB channel gain improvement. The time-frequency fading characteristics as a function of mobile speed is described and verified in measurements where instances of correlated time-frequency fading are observed. In stationary or semi-stationary scenarios CQI reporting delays are not limiting. However, at a mobile speed of 10 km/h the gain is lost when the reporting delay reaches 20 ms at the studied 2 GHz band. A simple prediction algorithm that utilizes how the best sub-band moves in frequency domain can improve the gain at 10 km/h around one CQI unit (2 dB) for the studied measurements indicating improvement potential for FSS at higher mobile speed.