Receiver and method

A method of detecting and recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols, the OFDM symbols including pilot data arranged in accordance with a pilot pattern which have been modulated with a unique random sequence, and a guard interval, the guard interval being formed by copying samples from a useful part of the OFDM symbol in the time domain, a length of the guard interval for each OFDM symbol corresponding to one of a plurality of predetermined lengths, the method comprising

• detecting a signal representing the OFDM symbols;
• generating a sampled version of the OFDM symbols in the time domain;
• concurrently auto correlating each OFDM symbol using a plurality of correlation processes, each correlation process auto correlating the same OFDM symbol between a length of samples corresponding to one of the plurality of predetermined guard interval lengths and determining a time domain start point of each OFDM symbol based on a point at which one of the correlation processes detects a correlation;
• performing a frequency transform on the sampled OFDM symbols to form a frequency domain version of the OFDM symbols starting at the time domain start point determined by the correlation detect processor, and
• detecting a coarse frequency offset of the frequency domain OFDM symbols by monitoring the output of a filter which filters each frequency domain OFDM symbol, the filter having taps which correspond to a value of the unique random sequence and a spacing of the pilot pattern of the OFDM symbols.

A non-transitory computer readable recording medium storing a computer program which when executed on a computer is arranged to carry out a method of detecting and recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols, the OFDM symbols including pilot data arranged in accordance with a pilot pattern which have been modulated with a unique random sequence, and a guard interval, the guard interval being formed by copying samples from a useful part of the OFDM symbol in the time domain, a length of the guard interval for each OFDM symbol corresponding to one of a plurality of predetermined lengths, the method comprising:

• detecting a signal representing the OFDM symbols;
• generating a sampled version of the OFDM symbols in the time domain;
• concurrently auto correlating each OFDM symbol using a plurality of correlation processes, each correlation process auto correlating the same OFDM symbol between a length of samples corresponding to one of the plurality of predetermined guard interval lengths and determining a time domain start point of each OFDM symbol based on a point at which one of the correlation processes detects a correlation;
• performing a frequency transform on the sampled OFDM symbols to form a frequency domain version of the OFDM symbols starting at the time domain start point determined by the correlation detect processor, and
• detecting a coarse frequency offset of the frequency domain OFDM symbols by monitoring the output of a filter which filters each frequency domain OFDM symbol, the filter having taps which correspond to a value of the unique random sequence and a spacing of the pilot pattern of the OFDM symbols.

A receiver comprising:

• a demodulator operable to detect a signal representing OFDM symbols including pilot data arranged in accordance with a pilot pattern which has been modulated with a unique random sequence, and a guard interval formed by copying samples from a useful part of the OFDM symbol in the time domain, a length of the guard interval for each OFDM symbol corresponding to one of a plurality of predetermined lengths, the demodulator being operable to generate a sampled version of the OFDM symbols in the time domain,
• a symbol synchronisation unit comprising a plurality of correlators into each of which a same sampled OFDM symbol is concurrently input and a correlation detect processor, each correlator being operable to auto correlate each sampled OFDM symbol with a length of samples corresponding to one of the plurality of predetermined lengths, the correlation detection processor being operable to determine a time domain start point of each OFDM symbol based on a point at which one correlator from the plurality of correlators detects a correlation,
• a frequency transform processor operable to receive the sampled version of the OFDM symbols and to perform a frequency transform on the OFDM symbol to form a frequency domain version of the OFDM symbols starting at the time domain start point determined by the correlation detect processor, and
• a coarse frequency offset detector including a pilot data filter and a coarse frequency offset detection processor, the pilot data filter including taps corresponding to a value of the unique random sequence and a spacing of the pilot pattern of the OFDM symbols and arranged to receive as an input the frequency domain OFDM symbols from the frequency transform processor and the coarse frequency detection processor being arranged to detect a coarse frequency offset from an output of the pilot data filter.

An apparatus for detecting and recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols, the OFDM symbols including pilot data arranged in accordance with a pilot pattern which has been modulated with a unique random sequence, and a guard interval, the guard interval being formed by copying samples from a useful part of the OFDM symbol in the time domain, a length of the guard interval for each OFDM symbol corresponding to one of a plurality of predetermined lengths, the apparatus comprising

• means for detecting a signal representing the OFDM symbols;
• means for generating a sampled version of the OFDM symbols in the time domain;
• means for concurrently auto correlating each OFDM symbol using a plurality of correlation processes, each correlation process auto correlating the same OFDM symbol between a length of samples corresponding to one of the plurality of predetermined guard interval lengths and determining a time domain start point of each OFDM symbol based on a point at which one of the correlation processes detects a correlation;
• means for performing a frequency transform on the sampled OFDM symbols to form a frequency domain version of the OFDM symbols starting at the time domain start point determined by the correlation detect processor, and
• means for detecting a coarse frequency offset of the frequency domain OFDM symbols by monitoring the output of a filter which filters each frequency domain OFDM symbol, the filter having taps which correspond to a value of the unique random sequence and a spacing of the pilot pattern of the OFDM symbols.