Data processing apparatus and method
View Patent ↗A receiver for recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols. The receiver includes a signalling and guard detector, which includes a correlator comprising a first branch having a first moving averaging filter, which is arranged to form pre-amble average correlated samples by averaging a value of a plurality of pre-amble correlated samples within a moving window, the plurality of samples averaged within the moving window corresponding to a temporal length of the post-amble (Tb), a second branch having a second moving averaging filter, which forms post-amble average correlated samples by averaging a value of a plurality of post-amble correlated samples within a moving window, the plurality of samples averaged within the moving window corresponding to a temporal length of the pre-amble (Tc), a combiner, which combines the averaged pre-amble correlated samples and the averaged post-amble correlated samples to form output correlation samples.
1. A receiver for detecting and recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols, the OFDM symbols including within a repeating time frame a signalling OFDM symbol and one or more data bearing OFDM symbols, the signalling OFDM symbol including a pre-amble guard interval and a post-amble guard interval, the pre-amble and the post-amble guard intervals being formed by copying samples from a useful part of the signalling OFDM symbol in the time domain, the receiver comprising
a demodulator which is arranged in operation to detect a signal representing the OFDM symbols, and to generate a sampled version of the OFDM symbols in the time domain,
a signalling and guard detector, which includes a correlator comprising
a first branch which forms pre-amble correlated samples from the pre-amble of the signalling OFDM symbol, and includes a first moving averaging filter, which is arranged to form pre-amble average correlated samples by averaging a value of a plurality of the pre-amble correlated samples within a moving window, the plurality of pre-amble correlated samples averaged within the moving window corresponding to a temporal length of the post-amble (Tb),
a second branch which forms post-amble correlated samples from the post-amble of the signalling OFDM symbol, and includes a second moving averaging filter, which is arranged to form post-amble average correlated samples by averaging a value of a plurality of the post-amble correlated samples within a moving window, the plurality of post-amble correlated samples averaged within the moving window corresponding to a temporal length of the pre-amble (Tc),
a combiner, which is arranged to combine the averaged pre-amble correlated samples and the averaged post-amble correlated samples to form output correlation samples, and
a post processing detector which is arranged to detect the signalling OFDM symbol from the output correlation samples to identify a timing of the frame from which the data bearing OFDM symbols can be identified.
2. A receiver as claimed in claim 1 , wherein the post processing detector is arranged in operation to detect the signalling OFDM symbol by comparing the correlation output samples with a threshold value to identify a peak value of the output correlation value, and to adapt the value of the threshold in accordance with previously received output correlation samples.
3. A receiver as claimed in claim 2 , wherein the post processing detector includes a filter, which is arranged to form an average value of the output correlation samples for a predetermined duration to form the adaptive threshold.
4. A receiver as claimed in claim 3 , wherein the filter is a leaky bucket filter.
5. A receiver as claimed in claim 3 , wherein the post processing detector includes a third moving averaging filter, which is arranged to receive the output correlation samples and to form average samples, by averaging the value of the output correlation samples within a predetermined window of a plurality of the output correlation samples, the averaged samples produced by the third moving averaging window being fed to the filter for forming the adaptive threshold.
6. A receiver as claimed in claim 1 , wherein
the first and second branches of the correlator include a third and fourth moving averaging filter before the first and second moving averaging filters respectively, the third and fourth moving averaging filters each being arranged to form average samples from a plurality of the respective pre-amble and post-amble correlation samples within a moving window, the plurality of pre-amble and post-amble correlation samples corresponding to a temporal length of the window (TR) being such as to reduce continuous wave interference.
7. A receiver as claimed in claim 1 , wherein
the first branch includes a first delay element which is arranged to delay a version of the samples of the OFDM symbols by an amount corresponding to a temporal length of the pre-amble (Tc), and a first multiplier, which is arranged to multiply the samples of the received OFDM symbols with the delayed samples of the OFDM symbols received from the first delay element, one of the multiplied samples being conjugated, to form the pre-amble correlation output samples, and
the second branch includes a second delay element which is arranged to delay a version of the samples of the OFDM symbols by an amount corresponding to a temporal length of the post-amble (Tb), and a second multiplier, which is arranged to multiply the samples of the received OFDM symbols with the delayed samples of the OFDM symbols from the second delay element, one of the multiplied samples being conjugated, to form the post-amble correlated samples.
8. A method of detecting and recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols, the OFDM symbols including within a repeating time frame a signalling OFDM symbol and one or more data bearing OFDM symbols, the signalling OFDM symbol including a pre-amble guard interval and a post-amble guard interval, the pre-amble and the post-amble guard intervals being formed by copying samples from a useful part of the signalling OFDM symbol in the time domain, the method comprising
detecting a signal representing the OFDM symbols,
generating a sampled version of the OFDM symbols in the time domain,
forming pre-amble correlated samples from the pre-amble of the signalling OFDM symbol,
forming pre-amble average correlated samples by averaging a value of a plurality of the pre-amble correlated samples within a moving window, the plurality of pre-amble correlated samples averaged within the moving window corresponding to a temporal length of the post-amble (Tb),
forming post-amble correlated samples from the post-amble of the signalling OFDM symbol,
forming post-amble average correlated samples by averaging a value of a plurality of the post-amble correlated samples within a moving window, the plurality of post-amble correlated samples averaged within the moving window corresponding to a temporal length of the pre-amble (Tc),
combining the averaged pre-amble correlated samples and the averaged post-amble correlated samples to form output correlation samples, and
detecting the signalling OFDM symbol from the output correlation samples to identify a timing of the frame from which the data bearing OFDM symbols can be identified.
9. A method as claimed in claim 8 , wherein the detecting includes
comparing the correlation output samples with a threshold value to identify a peak value of the output correlation value, and
adapting the value of the threshold in accordance with previously received output correlation samples.
10. A method as claimed in claim 9 , wherein the detecting includes
filtering with a filter, which is arranged to form an average value of the output correlation samples for a predetermined duration to form the adaptive threshold.
11. A method as claimed in claim 10 , wherein the filter is a leaky bucket filter.
12. A method as claimed in claim 10 , wherein the detecting includes
receiving the output correlation samples and
forming averaged samples of the output correlation samples, by averaging the value of the output correlation samples within a predetermined window of a plurality of the output correlation samples, the averaged output correlation samples produced by being filtered by the filter to form the adaptive threshold.
13. A method as claimed in claim 8 , wherein the forming the pre-amble correlation samples includes filtering the pre-amble correlation samples before the forming the pre-amble average correlated samples, and the forming the post-amble correlation samples includes filtering the post-amble correlation samples before the forming the post-amble average correlated samples, the filtering each being arranged to form average samples from a plurality of the respective pre-amble and post-amble correlation samples within a moving window, the plurality of pre-amble and post-amble correlation samples corresponding to a temporal length of the window (TR) being such as to reduce continuous wave interference.
14. A receiving apparatus comprising
a demodulator which is arranged in operation to detect a signal representing OFDM symbols, and to generate a sampled version of the OFDM symbols in the time domain, the OFDM symbols including within a repeating time frame a signalling OFDM symbol and one or more data bearing OFDM symbols, the signalling OFDM symbol including a pre-amble guard interval and a post-amble guard interval, the pre-amble and the post-amble guard intervals being formed by copying samples from a useful part of the signalling OFDM symbol in the time domain,
a signalling and guard detector, which includes a correlator comprising
a first branch which forms pre-amble correlated samples from the pre-amble of the signalling OFDM symbol, and includes a first moving averaging filter, which is arranged to form pre-amble average correlated samples by averaging a value of a plurality of the pre-amble correlated samples within a moving window, the plurality of pre-amble correlated samples averaged within the moving window corresponding to a temporal length of the post-amble (Tb),
a second branch which forms post-amble correlated samples from the post-amble of the signalling OFDM symbol, and includes a second moving averaging filter, which is arranged to form post-amble average correlated samples by averaging a value of a plurality of the post-amble correlated samples within a moving window, the plurality of post-amble correlated samples averaged within the moving window corresponding to a temporal length of the pre-amble (Tc),
a combiner, which is arranged to combine the averaged pre-amble correlated samples and the averaged post-amble correlated samples to form output correlation samples, and
a post processing detector which is arranged to detect the signalling OFDM symbol from the output correlation samples to identify a timing of the frame from which the data bearing OFDM symbols can be identified.
15. A receiver as claimed in claim 14 , wherein the combiner includes a delay element for delaying the pre-amble averaged correlated samples by an amount corresponding to the useful part of the signalling OFDM symbol and a multiplier, which multiplies the delayed pre-amble averaged correlated sampled and the post-amble averaged correlated samples.
16. A receiver as claimed in claim 14 , wherein the OFDM symbols are formed in accordance with the DVB-T2 standard and the signalling OFDM symbol is a P1 symbol.
17. A receiver as claimed in claim 14 , wherein the OFDM symbols are formed in accordance with the DVB-T2 standard and the signalling OFDM symbol is a P1 symbol.
18. A receiver as claimed in claim 14 , wherein the receiver is a television receiver.
19. A receiver as claimed in claim 1 , wherein the OFDM symbols are formed in accordance with the DVB-T2 standard and the signalling OFDM symbol is a P1 symbol.
20. A receiver as claimed in claim 1 , wherein the receiver is a television receiver.