Efficient pilot transmission schemes for multi-antenna communication
systems are described. In general, MISO receivers prefer a pilot
transmitted in one spatial direction, and MIMO receivers typically
require a pilot transmitted in different spatial directions. In one pilot
transmission scheme, a first set of T scaled pilot symbols is generated
with a first training vector and transmitted (e.g., continuously) from T
transmit antennas, where T>1. If MIMO receiver(s) are to be supported
by the system, then at least T-1 additional sets of T scaled pilot
symbols are generated with at least T-1 additional training vectors and
transmitted from the T transmit antennas. The training vectors are for
different (e.g., orthogonal) spatial directions. Each MISO receiver can
estimate its MISO channel based on the first set of scaled pilot symbols.
Each MIMO receiver can estimate its MIMO channel based on the first and
additional sets of scaled pilot symbols.