High performance modem using pilot symbols for equalization and frame synchronization

Claim 1

Apparatus for demodulating an input signal that includes data symbols used to encode data and pilot symbols, said pilot symbols being a predetermined pseudo-random sequence of digital signals that are interspersed one at a time with said data symbols, so that each repeated sequence of said predetermined pseudo-random sequence of pilot symbols defines one data frame of a data message that is collectively established by said data symbols, said demodulator comprising: (a) signal sampling means for periodically sampling the input signal to provide a sequence of digital signal samples which includes signal samples that correspond to pilot symbols of said input signal and includes signal samples that correspond to data symbols of said input signal; (b) a quadrature converter for processing said sequence of digital signal samples to produce a complex baseband signal that corresponds to said sequence of digital signal samples; (c) synchronization means, said synchronization means including means for processing the complex baseband signal to determine a symbol timing error signal, said synchronization means further including means responsive to said symbol timing error signal for adjusting symbol sampling time to produce a synchronized signal in which signal samples corresponding to input data symbols and signal samples corresponding to pilot symbols are synchronized relative to the corresponding data symbols of said input signal and the corresponding pilot symbols of said input signal; (d) signal synchronization means for processing said synchronized signal to separate said signal samples representative of pilot symbols from signal samples representative of data symbols; (e) frame synchronization means for receiving the signal samples that correspond to said input pilot symbols and for comparing said data symbols that correspond to said pilot symbols with a sequence of digital signals that represent said predetermined pseudo-random sequence of said pilot symbols, said frame synchronization means detecting the end of one data frame and the beginning of a next data frame by determining processing by said frame synchronization means of the signal sample that corresponds to the last pilot symbol of said predetermined pseudo-random sequence of pilot symbols or the signal sample that corresponds to the first pilot symbol of said predetermined pseudo-random sequence of pilot symbols, said frame synchronization means supplying a signal to indicate detection of the end of one data frame and the start of a next data frame, said frame synchronization means processing said signal samples that correspond to said pilot symbols to determine an autocorrelation value and supplying said signal to indicate detection of the end of one data frame and the start of a next data frame when said autocorrelation value exceeds a predetermined threshold value. (f) decoding means for processing said signal samples that correspond to said data symbols, said decoding means supplying a digital signal representative of said data message.

Claim 7

A method for demodulating an input signal that includes data symbols used to encode data and pilot symbols, said pilot symbols being a predetermined pseudo-random sequence of digital signals that are interspersed one at a time with said data symbols so that each repeated sequence of said predetermined pseudo-random sequence of pilot symbols defines one data frame of a data message that is collectively established by the sequence of said data symbols, said method comprising the steps of: (a) sampling the input signal and converting it to a sequence of digital signal samples; (b) processing said digital signal samples to provide a complex baseband signal that corresponds to said sequence of digital signal samples and, further, corresponds to said input signal; (c) processing the complex baseband signal to determine a symbol timing error; (d) in response to said symbol timing error, adjusting a symbol sampling time to produce a synchronized signal in which the signals representative of data symbols are synchronized with the corresponding data symbols of said input signal; (e) processing said synchronized signal by: (i) separating said signals representative of the pilot symbols from said symbols representative of the data symbols; (ii) comparing said signals representative of said pilot symbols that have been separated from said signals representative of said data symbols with signals that correspond to said pseudo-random sequence of digital signals in said input signal to detect the final pilot symbol of a pseudo-random sequence of pilot symbols that is included in said input signal; (iii) generating a frame synchronization signal indicating that the final pilot symbol of a pseudo-random sequence of pilot symbols in said input signal has been detected; (iv) processing said frame synchronization signal to establish and maintain synchronization between the method for demodulating the input signal and the input signal on a frame-by-frame basis; and (f) decoding said signals representative of said data symbols to recover said data message that is collectively established by said data symbols of said input signal.

Claim 8

A method for demodulating an input signal that includes data symbols used to encode data and pilot symbols, said pilot symbols being a predetermined pseudo-random sequence of digital signals that are interspersed one at a time with said data symbols so that each repeated sequence of said predetermined pseudo-random sequence of pilot symbols defines one data frame of a data message that is collectively established by the sequence of said data symbols, said method comprising the steps of: (a) sampling the input signal and converting it to a sequence of digital signal samples; (b) processing said digital signal samples to provide a complex baseband signal that corresponds to said sequence of digital signal samples and, further, corresponds to said input signal; (c) processing the complex baseband signal to determine a symbol timing error; (d) in response to said symbol timing error, adjusting a symbol sampling time to produce a synchronized signal in which the signals representative of data symbols are synchronized with the corresponding data symbols of said input signal; (e) processing said synchronized signal by: (i) separating said signals representative of the pilot symbols from said symbols representative of the data symbols; (ii) comparing said signals representative of said pilot symbols that have been separated from said signals representative of said data symbols with signals that correspond to said pseudo-random sequence of digital signals in said input signal to detect the final pilot symbol of a pseudo-random sequence of pilot symbols that is included in said input signal; (iii) generating a frame synchronization signal indicating that the final pilot symbol of a pseudo-random sequence of pilot symbols in said input signal has been detected; (iv) processing said frame synchronization signal to establish and maintain synchronization between the method for demodulating the input signal and the input signal on a frame-by-frame basis; and (f) decoding said signals representative of said data symbols to recover said data message that is collectively established by said data symbols of said input signal.