Maximum-likelihood frame synchronization algorithms for OFDM systems

A method, in a communication signal with frames containing symbols at least one of the symbols being a preamble symbol, for synchronizing the frames and for determining a segment index of the communication signal, the method comprising:

• estimating and compensating for a carrier frequency offset;
• obtaining a signal-to-noise ratio;
• sampling a time domain version of the communication signal to obtain a plurality of samples;
• for each of the samples:
• forming a group of samples from the plurality of samples, the group of samples having a length of a preamble symbol,
• dividing the group into a plurality of portions;
• and
• calculating a likelihood value representing a correlation between the portions in the group;
• and
• identifying a first sample of the plurality of samples as a start of the preamble symbol, wherein the first sample is associated with a maximum likelihood value among each of the calculated likelihood values;
• determining both a frame timing delay and a segment index;
• and
• using the frame timing delay to synchronize the frames.

A method, in a communication signal containing frames with symbols at least one of the symbols being a preamble symbol, for synchronizing frames and for estimating a fractional carrier frequency offset of a communication signal, the method comprising:

• obtaining a signal-to-noise ratio;
• sampling a time domain version of the communication signal to obtain a plurality of samples;
• for each of the samples:
• forming a group of samples from the plurality of samples, the group of samples having a length of a preamble symbol,
• dividing the group into a plurality of portions;
• and
• calculating a likelihood value representing a correlation between the portions in the group;
• and
• identifying a first sample of the plurality of samples as a start of the preamble symbol, wherein the first sample is associated with a maximum likelihood value among each of the calculated likelihood values;
• determining frame timing delay and fractional carrier frequency offset;
• and
• using the frame timing delay to synchronize the frames.

A method for synchronizing frames of a communication signal containing symbols at least one of the symbols being a preamble symbol, without knowing a-priori a signal-to-noise ratio, the method comprising:

• sampling a time domain version of the communication signal to obtain a plurality of samples;
• for each of the samples:
• forming a group of samples from the plurality of samples, the group of samples having a length of a preamble symbol,
• dividing the group into a plurality of portions;
• and
• calculating a likelihood value representing a correlation between the portions in the group;
• and
• identifying a first sample of the plurality of samples as a start of the preamble symbol, wherein the first sample is associated with a maximum likelihood value among each of the calculated likelihood values;
• determining a frame timing delay;
• and
• using the frame timing delay to synchronize frames of the communication signal.