System and method for transmitting auxiliary information on a subcarrier of a broadcast transmission

A communication system (100) is provided for transmitting data to mobile receivers utilizing a subcarrier within a commercial FM channel of a radio station (55). The data transmitted is first encoded in encoder (112), utilizing a forward error correction code. The sequence of the encoded data is altered in interleaver (116), subdivided into a plurality of subframes, in framing and synchronization circuit (120), which also adds channel state bits to each subframe. The framed data is modulated onto the subcarrier in the differential quadrature phased shift keying modulator (130), the output of which is coupled to the FM modulator (52) of radio station transmitter (50). The transmitted radio frequency signals may be received by a vehicle antenna (12) for coupling to the vehicle's FM receiver (80). The modulated subcarrier is recovered from the FM demodulator (84) of the receiver (80), the modulated subcarrier being demodulated to recover the encoded digital data therefrom. The channel state bits included with the data are extracted from the digital data and utilized to form a data reliability factor for each bit of the encoded data. The data reliability factors thus obtained are associated with each bit of the data in a deinterleaver (360). Deinterleaver (360) provides each data bit in proper sequence, with its associated data reliability factor to decoder (370). The decoded digital data is provided to a vehicle traffic computer (90) for processing and presentation of traffic information to a user on a display (92).