Soft handoff for OFDM

A base station in an orthogonal frequency division multiplexing (OFDM) system comprising:

• 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.

A method for facilitating soft handoffs in an orthogonal frequency division multiplexing (OFDM) system comprising:

• 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.

A mobile terminal facilitating soft handoffs in an orthogonal frequency division multiplexing (OFDM) system comprising:

• 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.

A method for determining channel responses for OFDM transmissions comprising:

• 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.