Extracting Multi-User Diversity in the Cellular Uplink, Where Transmission Grants Influence CSI Quality

Modern cellular communication systems facilitate fine-grained resource allocation that can opportunistically exploit the time variations and frequency selectivity of mobile channels by exploiting multi-user diversity. However, extracting such benefits requires the scheduler to have accurate channel state information (CSI). Channel estimation in the uplink direction requires all users to send unique reference signals. For resource allocation purposes, current standards have thus included sounding reference symbols (SRS), which allow simultaneous estimation, but are very sensitive to the channels´ frequency selectivity and the number of users. Also demodulation reference symbols (DMRS) are used which are always multiplexed with the data during transmission and yield more accurate CSI. However, the information that can be obtained in this way directly depends on the scheduling decisions. In this paper, we propose two new scheduling algorithms that are aware of the channel estimation quality and are thus able to make best use of the available estimation types. Furthermore, through their decisions, the algorithms inherently ensure the right CSI amount to achieve high spectral efficiency. We compare our approaches to the conventional scheduling algorithm that rely only on estimates from channel sounding based on SRS.