User Profiling: A Method for Limited Feedback in OFDMA Systems

In the OFDMA downlink, obtaining channel state information (CSI) from users is necessary for the base station (BS) to optimize network performance by intelligently allocating resources and scheduling mobile stations (MS). However, the overhead of obtaining CSI is a large burden and therefore, schemes to reduce CSI are necessary for a realizable system. By considering a MS´s coherence time Deltat_coh and coherence bandwidth B_coh, and exploiting this redundancy in the MS´s CSI, the amount of feedback can be tailored to the specific user´s profile and greatly decreased. Typically, reducing feedback results in more uncertainty in CSIT and performance degradation. However, in the proposed scheme, the CSIT´s deviation from the true channel state is bounded, and thus can provide robust scheduling. Specifically, two BS schemes are suggested that either fix the average BER or the average outage probability regardless of user mobility or delay spread.