Soft handoff for OFDM
First Claim
1. An orthogonal frequency division multiplexing (OFDM) system comprising:
- a) a base station controller adapted to schedule data for a mobile terminal during a soft handoff mode and deliver at least a portion of scheduled data for the mobile terminal to at least one of a plurality of base stations; and
b) the plurality of base stations operatively associated with the base station controller, each base station participating in the soft handoff adapted to;
i) receive the scheduled data for delivery to the mobile terminal;
ii) provide space-time coding for the scheduled data to generate a plurality of space-time coded signals;
iii) perform an Inverse Fourier Transform (IFT) on each of the plurality of space-time coded signals to generate a plurality of OFDM signals, each of the plurality of space-time coded signals configured to result in corresponding OFDM signals mapped into defined sub-bands in an OFDM spectrum of sub-bands, the defined sub-bands not used by other ones of the base stations participating in the soft handoff; and
iv) transmit the plurality of OFDM 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.
257 Citations
50 Claims
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1. An orthogonal frequency division multiplexing (OFDM) system comprising:
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a) a base station controller adapted to schedule data for a mobile terminal during a soft handoff mode and deliver at least a portion of scheduled data for the mobile terminal to at least one of a plurality of base stations; and b) the plurality of base stations operatively associated with the base station controller, each base station participating in the soft handoff adapted to; i) receive the scheduled data for delivery to the mobile terminal; ii) provide space-time coding for the scheduled data to generate a plurality of space-time coded signals; iii) perform an Inverse Fourier Transform (IFT) on each of the plurality of space-time coded signals to generate a plurality of OFDM signals, each of the plurality of space-time coded signals configured to result in corresponding OFDM signals mapped into defined sub-bands in an OFDM spectrum of sub-bands, the defined sub-bands not used by other ones of the base stations participating in the soft handoff; and iv) transmit the plurality of OFDM signals with spatial diversity for reception by the mobile terminal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A base station in an orthogonal frequency division multiplexing (OFDM) system comprising:
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a) space-time encoding logic adapted to provide space-time coding of scheduled data to generate a plurality of space-time coded signals; b) Inverse Fourier Transform (IFT) logic adapted to provide an IFT on each of the plurality of space-time coded signals to generate a plurality of OFDM signals, wherein during a soft handoff, each of the plurality of space-time coded signals is configured to result in corresponding OFDM signals mapped into defined sub-bands in an OFDM 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 OFDM signals with spatial diversity for reception by the mobile terminal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A method for facilitating soft handoffs in an orthogonal frequency division multiplexing (OFDM) system comprising:
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a) providing space-time coding of scheduled data to generate a plurality of space-time coded signals; b) generating an Inverse Fourier Transform (IFT) on each of the plurality of space-time coded signals to generate a plurality of OFDM signals, wherein during a soft handoff, each of the plurality of space-time coded signals is configured to result in corresponding OFDM signals mapped into defined sub-bands in an OFDM 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 OFDM signals with spatial diversity for reception by the mobile terminal. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42)
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43. A mobile terminal facilitating soft handoffs in an orthogonal frequency division multiplexing (OFDM) system comprising:
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a) receive circuitry adapted to receive and downconvert a plurality of OFDM signals, which were encoded using space-time encoding and transmitted using spatial diversity; b) Fourier Transform (FT) logic adapted to provide a FT on each of the plurality of OFDM signals to generate a plurality of space-time coded signals, c) space-time decoder logic adapted to provide space-time decoding on the plurality of space-time 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. - View Dependent Claims (44, 45, 46, 47, 48, 49)
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50. A method for determining channel responses for OFDM transmissions comprising:
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a) determining relative transmission delays from a plurality of base stations participating in an OFDM soft handoff; b) extracting scattered pilot signals in a frequency domain for OFDM signals; c) estimating first channel responses for each scattered pilot signal for each transmit channel; d) removing additional phase rotation caused by the transmission delays from the first channel responses; e) interpolating the first channel responses to estimated second channel responses for each OFDM data sub-carrier; and f) adding phase rotation caused by transmission delays to the second channel responses to estimate final channel responses for each of the OFDM data sub-carriers.
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Specification