Frame synchronization of an OFDM signal
View Patent ↗Frame synchronization of a received OFDM signal (such as that used in a hybrid FM DAB system) is provided by filtering out significant outer frequency portions of the digital channels, and then using cyclic extension and correlation of the cyclically extended bits (or samples). The received OFDM signal is passed through a bandpass filter to remove outer digital subcarriers (i.e., those farthest from a center frequency) from a received OFDM signal before correlating to locate the OFDM frame boundaries. By filtering out digital subcarriers within each of the digital channels, particularly those closest to adjacent channels and thus most likely to be interfered with by an adjacent first channel OFDM (or FM) signal, correlation between cyclically extended bit (or sample) patterns and thus frame synchronization of OFDM signals can be improved significantly.
1. An orthogonal frequency division multiplexing (OFDM) signal frame sync signal generator, comprising:
a bandpass filter adapted to remove a portion but not all of a signal corresponding to at least one digital channel from a received OFDM signal; and
an OFDM frame synchronizing correlator adapted to generate a frame sync signal based on a detected correlation of a cyclically extended portion of a data frame in said received OFDM signal after processing by said bandpass filter;
wherein said bandpass filter is adapted to remove a significant portion of each of two digital channels from said received OFDM signal, said portion of said two digital channels being respective portions in a frequency domain farthest from a center frequency of an analog channel contained in said received OFDM signal.
2. The OFDM signal frame sync signal generator according to claim 1 , wherein:
said portion of said at least one digital channel is a portion in a frequency domain farthest from a center frequency of an analog channel contained in said received OFDM signal.
3. An orthogonal frequency division multiplexing (OFDM) signal frame sync signal generator, comprising:
a bandpass filter adapted to remove a portion of a signal corresponding to at least one digital channel from a received OFDM signal; and
an OFDM frame synchronizing correlator adapted to generate a frame sync signal based on a detected correlation of a cyclically extended portion of a data frame in said received OFDM signal after processing by said bandpass filter;
wherein said bandpass filter is adapted to remove a significant portion of each of two digital channels from said received OFDM signal, said portion of said two digital channels being respective portions in a frequency domain farthest from a center frequency of an analog channel contained in said received OFDM signal.
4. The OFDM signal frame sync signal generator according to claim 1 , wherein:
said bandpass filter is a digital bandpass filter.
5. The OFDM signal frame sync signal generator according to claim 1 , wherein:
said OFDM frame synchronizing correlator generates said frame sync signal based on an integrated detection of respectively correlated cyclically extended portions of a plurality of data frames.
6. A method of detecting a timing of a data frame in a received orthogonal frequency division multiplexing (OFDM) signal, comprising:
filtering out a portion but not all of a signal corresponding to at least one digital channel from said received OFDM signal to provide a bandpass filtered OFDM signal, said portion being in a frequency domain farthest from a center frequency of an analog channel contained in said received OFDM signal;
correlating a cyclically extended portion of a data frame in said bandpass filtered OFDM signal; and
generating a frame sync signal based on a correlation of said cyclically extended portion of said data frame.
7. The method of detecting a timing of a data frame in a received OFDM signal according to claim 6 , wherein said filtering comprises:
digitally filtering.
8. The method of detecting a timing of a data frame in a received OFDM signal according to claim 6 , wherein:
said correlating correlates respective cyclically extended portions of a plurality of data frames in said bandpass filtered OFDM signal.
9. Apparatus for detecting a timing of a data frame in a received orthogonal frequency division multiplexing (OFDM) signal, comprising:
means for filtering out a portion but not all of a signal corresponding to at least one digital channel from said received OFDM signal to provide a bandpass filtered OFDM signal, said portion being in a frequency domain farthest from a center frequency of an analog channel contained in said received OFDM signal;
means for correlating a cyclically extended portion of a data frame in said bandpass filtered OFDM signal; and
means for generating a frame sync signal based on a correlation of said cyclically extended portion of said data frame.
10. The apparatus for detecting a timing of a data frame in a received OFDM signal according to claim 9 , wherein said means for filtering comprises:
means for digitally filtering said received OFDM signal.
11. The apparatus for detecting a timing of a data frame in a received OFDM signal according to claim 9 , wherein:
said means for correlating correlates respective cyclically extended portions of a plurality of data frames in said bandpass filtered OFDM signal.