DITHERING SCHEME USING MULTIPLE ANTENNAS FOR OFDM SYSTEMS
First Claim
1. A method for transmitting an information stream over a wireless communication medium to one or more receivers, the method comprising:
- (a) applying both orthogonal-frequency division multiplexed (OFDM) modulation and splitting to the information stream to generate a first copy and M−
1 other copies of an OFDM signal;
(b) applying M−
1 variable-frequency phase offsets to the M−
1 other copies to generate M−
1 phase-offset copies; and
(c) transmitting the first copy and the M−
1 phase-offset copies via M respective antennas over the wireless communication medium, where M is an integer value greater than 1.
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Accused Products
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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Citations
14 Claims
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1. A method for transmitting an information stream over a wireless communication medium to one or more receivers, the method comprising:
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(a) applying both orthogonal-frequency division multiplexed (OFDM) modulation and splitting to the information stream to generate a first copy and M−
1 other copies of an OFDM signal;(b) applying M−
1 variable-frequency phase offsets to the M−
1 other copies to generate M−
1 phase-offset copies; and(c) transmitting the first copy and the M−
1 phase-offset copies via M respective antennas over the wireless communication medium, where M is an integer value greater than 1. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for transmitting an information stream over a wireless communication medium to one or more receivers, the apparatus comprising:
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both an orthogonal-frequency division multiplexing (OFDM) modulator and a splitter adapted to apply OFDM modulation and splitting, respectively, to the information stream to generate a first copy and M−
1 other copies of an OFDM signal;a first multiplier adapted to apply M−
1 variable-frequency phase offsets to the M−
1 other copies to generate M−
1 phase-offset copies; anda transmission device adapted to transmit the first copy and the M−
1 phase-offset copies via M respective antennas over the wireless communication medium. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification