Dithering scheme using multiple antennas for ofdm systems

Abstract

A ground-or roof-top-based repeater in an OFDM system uses multiple transmission antennas to retransmit satellite signals. By using multiple transmission antennas, multiple identical OFDM signals are transmitted. Dithering is performed by, using a phase of Rayleigh process generator, introducing a slight variable-frequency phase offset to all but one of the multiple identical transmitted OFDM signals, and thus the effective overall channel is more dynamic and provides spatial diversity to minimize long periods of fading in fading subchannels of the OFDM signals when the receiver is in a slow moving or stationary situation. To overcome the additional cancellation problem that can occur when two or more of the transmitting antennas are in a line-of-site position with the receiver and approximately the same distance from the receiver, a delay is deliberately introduced to make the delayed signal(s) appear to be reflected signals. This delay will not negatively impact the OFDM receiver performance as long as the delay is within the guard interval used in the OFDM process.