Dithering scheme using multiple antennas for OFDM systems
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United States of America Patent
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-
Dec 11, 2012
Grant Date -
Jul 16, 2009
app pub date -
Mar 27, 2009
filing date -
Aug 28, 2002
priority date (Note) -
In Force
status (Latency Note)
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Abstract
A ground- or roof-top-based repeater in an OFDM system uses multiple transmission antennas to transmit multiple identical OFDM signals. Dithering is performed by introducing a slight variable-frequency phase offset to all but one of the multiple identical transmitted OFDM signals. 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 (i) in a line-of-site position with the receiver and (ii) approximately the same distance from the receiver, a delay is deliberately introduced to make the delayed signals 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.
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