Outdated Uplink Adaptation Due to Changes in the Scheduling Decisions in Interfering Cells

Abstract

The major difference between a non-cellular system, i.e. a single isolated cell, and a cellular system is the intercell interference (ICI). In the uplink, the base station can measure the users' signal to noise and interference ratio (SINR) and through a feedforward channel it can inform the users which coding and modulation scheme to apply in order to perform link adaptation (LA). However, a user's SINR observed in the uplink by the base station when determining the link adaptation decision might no longer be the same when the link adaptation is effected by the user due to fluctuations of the intercell interference. By then, the intercell interference could have greatly changed even if the users are static, due to changes in the scheduling decisions in the interfering cells. Hence, the uplink transmission would no longer have the correct link adaptation for the current SINR, since we are to some extent blind with respect to the ICI. In this work, we quantify this degree of ICI blindness by the correlation between the measured ICI and the actual experienced ICI. Furthermore, we analyze the degradation in throughput for different degrees of ICI correlation which depends on the scheduling in the interfering cells. Additionally, we show how much benefit correct link adaptation provides in a cellular environment over outdated link adaptation. In this work, we assume that there is no intracell interference as a consequence of an orthogonal multiple access scheme.

Fast Distributed Multi-Cell Scheduling with Delayed Limited-Capacity Backhaul Links

“…However, we assume that average CSI is available to all base stations. Multi-cell scheduling is a very active field of research [16]- [21], as is the analysis of limitations in the backhaul network connecting the base stations [22]- [27]. Our simulations show that the algorithm preserves most of the per cell sum-rate of the beamforming and dirty-paper coding approaches that require unlimited-capacity backhaul links and even outperforms them when out-of-cell information is outdated.…”