Scaling Laws of Multiple Antenna Group-Broadcast Channels

Broadcast (or point to multipoint) communication has attracted a lot of research recently. In this talk, we consider the multiple antenna group broadcast channel where a base station is to transmit to a group of users and where the users' pool is divided into K groups, each group of which is interested in common information. Such a situation occurs for example in digital audio and video broadcast where the users are divided into various groups according to the shows they are interested in. When each group consists of exactly one user, group broadcast simplifies to the familiar broadcast problem. When there is exactly one group of users (interested in common information), the scenario simplifies to the unicast problem.

Finding the sum-rate capacity for the group broadcast is very challenging. As such, we study the scaling laws of the sum-rate in the large number of users and/or large number of antennas regimes. In the talk, we quantify the effect of spatial correlation on the system capacity and the sum-rate achieved by various scheduling schemes. Intuitively, the group broadcast capacity should decrease with the number of users. The talk thus shows that in order to achieve a constant rate per user, the number of transmit antennas should scale at least logarithmically with the number of users.

This is a joint work with Amir Dana (Qualcomm Corporation) and Babak Hassibi (California Institute of Technology)