SOFT HANDOFF FOR OFDM
First Claim
1. A system adapted to schedule data for a mobile terminal during a soft handoff mode and deliver at least a portion of scheduled data to the mobile terminal from at least one of a plurality of base stations comprising each base station participating in the soft handoff being adapted to:
- a) process the scheduled data for delivery to the mobile terminal;
b) provide coding for the scheduled data to generate a plurality of spatially coded signals;
c) perform a transform on each of the plurality of spatially coded signals to generate a plurality of orthogonal frequency division multiplexed signals, each of the plurality of spatially coded signals configured to result in corresponding frequency division multiplexed orthogonal signals mapped into defined sub-bands in an orthogonal frequency division multiplexed spectrum of sub-bands, the defined sub-bands not used by other ones of the base stations participating in the soft handoff; and
d) transmit the plurality of orthogonal frequency division multiplexed signals with spatial diversity for reception by the mobile terminal.
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Accused Products
Abstract
The present invention relates to soft handoffs in an OFDM system. Each mobile terminal measures pilot signal strengths of transmissions from adjacent base stations. If the pilot signal strength for a base station exceeds the defined threshold, that base station is added to an active set list. Each mobile terminal notifies the base stations of their active set lists. By providing the set list to the base station controller and the servicing base station, the mobile terminal identifies the sole servicing base station or triggers a soft handoff mode when multiple base stations appear on the active set list. The soft handoff mode uses a combination of scheduling and space-time coding to affect efficient and reliable handoffs.
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Citations
6 Claims
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1. A system adapted to schedule data for a mobile terminal during a soft handoff mode and deliver at least a portion of scheduled data to the mobile terminal from at least one of a plurality of base stations comprising each base station participating in the soft handoff being adapted to:
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a) process the scheduled data for delivery to the mobile terminal; b) provide coding for the scheduled data to generate a plurality of spatially coded signals; c) perform a transform on each of the plurality of spatially coded signals to generate a plurality of orthogonal frequency division multiplexed signals, each of the plurality of spatially coded signals configured to result in corresponding frequency division multiplexed orthogonal signals mapped into defined sub-bands in an orthogonal frequency division multiplexed spectrum of sub-bands, the defined sub-bands not used by other ones of the base stations participating in the soft handoff; and d) transmit the plurality of orthogonal frequency division multiplexed signals with spatial diversity for reception by the mobile terminal. - View Dependent Claims (2, 3)
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4. A base station in an orthogonal frequency division multiplexing system comprising:
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a) encoding logic adapted to provide spatial coding of scheduled data to generate a plurality of spatially coded signals; b) transform logic adapted to provide a transform on each of the plurality of spatially coded signals to generate a plurality of orthogonal frequency division multiplexing signals, wherein during a soft handoff, each of the plurality of spatially coded signals is configured to result in corresponding orthogonal frequency division multiplexing signals mapped into defined sub-bands in an orthogonal frequency division multiplexing spectrum of sub-bands, the defined sub-bands not used by other base stations participating in the soft handoff; and c) transmit circuitry having a plurality of transmit paths to facilitate transmitting the plurality of orthogonal frequency division multiplexing signals with spatial diversity for reception by the mobile terminal.
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5. A method for facilitating soft handoffs in an orthogonal frequency division multiplexing system comprising:
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a) providing spatial coding of scheduled data to generate a plurality of spatially coded signals; b) generating a transform on each of the plurality of spatially coded signals to generate a plurality of orthogonal frequency division multiplexing signals, wherein during a soft handoff, each of the plurality of space-time coded signals is configured to result in corresponding orthogonal frequency division multiplexing signals mapped into defined sub-bands in an orthogonal frequency division multiplexing spectrum of sub-bands, the defined sub-bands not used by other base stations participating in the soft handoff; and c) transmitting the plurality of orthogonal frequency division multiplexing signals with spatial diversity for reception by the mobile terminal.
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6. A mobile terminal for facilitating soft handoffs in an orthogonal frequency division multiplexing system comprising:
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a) receive circuitry adapted to receive and downconvert a plurality of orthogonal frequency division multiplexing signals, which were encoded using spatial encoding and transmitted using spatial diversity; b) transform logic adapted to provide a transform on each of the plurality of orthogonal frequency division multiplexing signals to generate a plurality of spatially coded signals; c) decoder logic adapted to provide spatial decoding on the plurality of spatially coded signals to recover scheduled data from servicing base stations; d) processing logic adapted to; (i) monitor signal strength from a plurality of base stations; (ii) identify ones of the plurality of base stations having signal strength over a defined threshold; and (iii) enter a soft handoff mode when more than one of the plurality of base stations have a signal strength over the defined threshold; and e) transmit circuitry adapted to transmit information identifying the ones of the plurality of base stations having signal strength over the defined threshold.
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Specification