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.
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Citations
1 Claim
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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.
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Specification