Abstract
Joint linear beamforming and scheduling are performed in a system where limited feedback is present
at the transmitter side. The feedback conveyed by each user to the base station consists of channel
direction information (CDI) based on a predetermined codebook and a scalar metric with channel quality
information (CQI) used to perform user scheduling. In this paper, we present a design framework for
scalar feedback in MIMO broadcast channels with limited feedback. An approximation on the sum
rate is provided for the proposed family of metrics, which is validated through simulations. For a given
number of active users and average SNR conditions, the base station is able to update certain transmission
parameters in order to maximize the sum-rate function. On the other hand, the proposed sum-rate function
provides a means of simple comparison between transmission schemes and scalar feedback techniques.
Particularly, the sum rate of SDMA and time division multiple access (TDMA) is compared in the
following extreme regimes: large number of users, high SNR, and low SNR. Simulations are provided to
illustrate the performance of various scalar feedback techniques based on the proposed design framework.