US 8,605,843 B2 · Method and apparatus for signal acquisition in OFDM receivers

A method of signal acquisition in a communications receiver for receiving Orthogonal Frequency Division Multiplex (OFDM) signals comprising data packets each comprising a preamble training sequence having a periodic structure, the method comprising the steps of:

(i) sampling a received OFDM signal to obtain received-signal samples;
(ii) filtering said samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence;
(iii) detecting occurrence of one or several peaks, the highest peak representing a maximum amplitude, of the cross-correlation output from said FIR over a predetermined number of periods corresponding to at least part of said preamble training sequence;
and
(iv) using one or more of timing, magnitude and phase of said maximum amplitude, to determine one or more of time synchronization, carrier frequency offset and channel estimation.

2 more elements

A method of signal acquisition in an OFDM radio receiver having an array antenna comprising a plurality of antenna elements each for receiving an individual received signal comprising data packets each comprising a preamble training sequence having a periodic structure, the method comprising the steps of:

for each antenna element:
(i) sampling its individual received signal to obtain a series of received-signal samples;
(ii) filtering the preamble samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence;
(iii) detecting a series of peaks at the output of said filter, each peak corresponding to one received OFDM symbol of the preamble training sequence;
(iv) detecting a maximum amplitude of the cross-correlation output among said peaks from said FIR;
and
(v) providing the timing of said maximum amplitude on any given antenna, or any combined signal created by combining the filter outputs at all antennas, as a timing reference for demodulation of said received data;
(vi) determining magnitude and phase of said maximum amplitude;
and
(vii) using said magnitude and phase to weight corresponding data for that antenna element in a subsequent step of combining the individual received-signals of the antenna elements, respectively;
(viii)(a) extracting the phase difference between two peaks, where said two peaks can be two consecutive peaks or can be more widely separated;
(viii)(b) calculating from said phase difference the phase shift induced per sample by the carrier frequency offset, said phase difference being a multiple of said phase shift with the factor between the two being determined by the separation of the two peaks;
(ix) adjusting a phase shift estimate by adding such estimate for all antennas, each being previously weighted by the corresponding channel magnitude determined in step (vi);
and
(x) the adjusted phase shift estimate being used for carrier offset correction during subsequent processing steps, preferably after multiplying a signal sample by a complex coefficient of unit magnitude which is the inverse of said phase shift.

12 more elements

A method of estimating and correcting carrier frequency offset and estimating from received data in an OFDM radio receiver characteristics of a transmission channel whereby said received data was received, said OFDM radio receiver having an array antenna comprising a plurality of antenna elements each for receiving an individual received signal comprising data packets each comprising a preamble training sequence having a periodic structure, the method comprising the steps of:

for each antenna element:
(i) sampling a received OFDM radio signal to obtain a series of received-signal samples;
(ii) filtering the preamble samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence, said filter being preceded by a complex multiplication by a correction coefficient for dynamic carrier frequency offset compensation, said correction coefficient being initially equal to 1;
(iii) detecting the first two peaks at the output of said filter, each peak corresponding to one received short OFDM symbol;
(iv) determining magnitude and phase of the maximum amplitude out of the said two peaks, for each antenna, said magnitude and phase constituting the current estimate of the channel coefficient associated with each antenna;
(v)(a) extracting the phase difference between said two peaks on each antenna;
(v)(b) calculating from said phase difference the phase shift induced per sample by the carrier frequency offset, said phase difference being a multiple of said phase shift with the factor between the two being determined by the separation of the two peaks;
(vi) expressing said phase shift on each antenna by a complex coefficient of unit magnitude, computing the weighted normalized sum of all such coefficients for all antennas, where the weight associated with a specific coefficient is proportional to the current channel gain estimate on the same antenna;
(vii) multiplying the correction coefficient at the multiplier ahead of the matched filter by a complex value of unit amplitude whose phase is minus the phase shift found in the normalized sum operation of step (vi);
(viii) pursuant to the filtering operation, updating the current channel estimate and the correction coefficient for every received peak as a function of the last received two peaks according to steps (iii)-(vii)
(ix) detecting a maximum amplitude of the cross-correlation output among said peaks from said FIR;
and
(x) determining magnitude and phase of said maximum amplitude;
and
(xi) using said magnitude and phase to weight corresponding data for that antenna element in a subsequent step of combining the individual received-signals of the antenna elements, respectively;
(xii) providing the final value of the correction coefficient as a measure of the carrier frequency offset for compensation thereof in subsequent steps.

13 more elements

A method of jointly A—estimating and correcting carrier frequency offset, B—recovering timing (synchronizing) and C—estimating from received data in an OFDM radio receiver characteristics of a transmission channel whereby said received data was received, said OFDM radio receiver having an array antenna comprising a plurality of antenna elements each for receiving an individual received signal comprising data packets each comprising a preamble training sequence having a periodic structure, the method comprising the steps of:

for each antenna element:
(i) sampling its individual received OFDM radio signal to obtain a series of received-signal samples;
(ii) filtering the preamble samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence, said filtering being preceded by a complex multiplication by a correction coefficient for dynamic carrier frequency offset compensation, said correction coefficient being initially equal to 1;
(iii) detecting the first two peaks at the output of said filter, each peak corresponding to one received OFDM symbol of the training sequence;
(iv) determining magnitude and phase of the maximum amplitude out of the said two peaks, for each antenna, said magnitude and phase constituting the current estimate of the channel coefficient associated with each antenna;
(v)(a) extracting the phase difference between said two peaks on each antenna;
(v)(b) calculating from said phase difference the phase shift induced per sample by the carrier frequency offset, said phase difference being a multiple of said phase shift with the factor between the two being determined by the separation of the two peaks;
(vi) expressing said phase shift on each antenna by a complex coefficient of unit magnitude, computing the weighted normalized sum of all such coefficients for all antennas, where the weight associated with a specific coefficient is proportional to the current channel gain estimate on the same antenna;
(vii) multiplying the correction coefficient at the multiplier ahead of the matched filter by a complex value of unit amplitude whose phase is minus the phase found in the normalized sum operation of step (vi);
(viii) pursuant to the filtering operation, updating the current channel estimate and the correction coefficient for every received peak as a function of the last received two peaks according to steps (iii)-(vii)
(ix) detecting a maximum amplitude of the cross-correlation output among said peaks from said FIR;
and
(xi) determining magnitude and phase of said maximum amplitude;
(xii) using said magnitude and phase to weight corresponding data for that antenna element in a subsequent step of combining the individual received-signals of the antenna elements, respectively;
(xiii) providing the timing of said maximum amplitude on any given antenna, or any combined signal created by combining the filter outputs at all antennas, as a timing reference for demodulation of said received data;
and
(xiv) providing the final value of the correction coefficient as a measure of the carrier frequency offset for its compensation in subsequent steps.

14 more elements

An OFDM receiver for receiving Orthogonal Frequency Division Multiplex (OFDM) signals comprising data packets each comprising a preamble training sequence having a periodic structure, the receiver having signal acquisition means comprising:

(i) means for sampling a received OFDM signal to obtain received-signal samples;
(ii) means for filtering said samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence;
(iii) means for detecting occurrence of one or several peaks, the highest representing a maximum amplitude, of the cross-correlation output from said FIR over a predetermined number of periods corresponding to at least part of said training sequence;
and
(iv) means for using one or more of timing, magnitude and phase of said maximum amplitude, to determine one or more of time synchronization, carrier frequency offset and channel estimation.

2 more elements

An OFDM receiver having an array antenna comprising a plurality of antenna elements each for receiving an individual received signal comprising data packets each comprising a preamble training sequence having a periodic structure, and signal acquisition means operable, for each antenna element, for:

(i) sampling its individual received signal to obtain a series of received-signal samples;
(ii) filtering the preamble samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence;
(iii) detecting a series of peaks at the output of said filter, each peak corresponding to one received OFDM symbol of the preamble training sequence;
(iv) detecting a maximum amplitude of the cross-correlation output among said peaks from said FIR;
and
(v) providing the timing of said maximum amplitude on any given antenna, or any combined signal created by combining the filter outputs at all antennas, as a timing reference for demodulation of said received data;
(vi) determining magnitude and phase of said maximum amplitude;
and
(vii) using said magnitude and phase to weight corresponding data for that antenna element in a subsequent step of combining the individual received-signals of the antenna elements, respectively;
(viii)(a) extracting the phase difference between two peaks, where said two peaks can be two consecutive peaks or can be more widely separated;
(viii)(b) calculating from said phase difference the phase shift induced per sample by the carrier frequency offset, said phase difference being a multiple of said phase shift with the factor between the two being determined by the separation of the two peaks;
(ix) adjusting a phase shift estimate by adding such estimate for all antennas, each being previously weighted by the corresponding channel magnitude determined in step (vi);
and
(x) the adjusted phase shift estimate being used for carrier offset correction during subsequent processing steps.

11 more elements

An OFDM receiver having an array antenna comprising a plurality of antenna elements each for receiving an individual received signal comprising data packets each comprising a preamble training sequence having a periodic structure, the receiver having signal acquisition means for estimating and correcting carrier frequency offset and estimating from each of said individual received signals characteristics of a transmission channel whereby said individual received signal was received, the signal acquisition means being operable, for each antenna element, for:

(i) sampling a received OFDM radio signal to obtain a series of received-signal samples;
(ii) filtering the preamble samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence, said filter being preceded by a complex multiplication by a correction coefficient for dynamic carrier frequency offset compensation, said correction coefficient being initially equal to 1;
(iii) detecting the first two peaks at the output of said filter, each peak corresponding to one received short OFDM symbol;
(iv) determining magnitude and phase of the maximum amplitude out of the said two peaks, for each antenna, said magnitude and phase constituting the current estimate of the channel coefficient associated with each antenna;
(v)(a) extracting the phase difference between said two peaks on each antenna;
(v)(b) calculating from said phase difference the phase shift induced per sample by the carrier frequency offset, said phase difference being a multiple of said phase shift with the factor between the two being determined by the separation of the two peaks;
(vi) expressing said phase shift on each antenna by a complex coefficient of unit magnitude, computing the weighted normalized sum of all such coefficients for all antennas, where the weight associated with a specific coefficient is proportional to the current channel gain estimate on the same antenna;
(vii) multiplying the correction coefficient at the multiplier ahead of the matched filter by a complex value of unit amplitude whose phase is minus the phase shift found in the normalized sum operation of step (vi);
(viii) pursuant to the filtering operation, updating the current channel estimate and the correction coefficient for every received peak as a function of the last received two peaks according to steps (iii)-(vii)
(ix) detecting a maximum amplitude of the cross-correlation output among said peaks from said FIR;
and
(x) determining magnitude and phase of said maximum amplitude;
and
(xi) using said magnitude and phase to weight corresponding data for that antenna element in a subsequent step of combining the individual received-signals of the antenna elements, respectively;
(xii) providing the final value of the correction coefficient as a measure of the carrier frequency offset for compensation therefor in subsequent steps.

12 more elements

An OFDM receiver having an array antenna comprising a plurality of antenna elements each for receiving an individual received signal comprising data packets each comprising a preamble training sequence having a periodic structure, the receiver having signal acquisition means for jointly (A) estimating and correcting carrier frequency offset, (B) recovering timing (synchronizing) and (C) estimating from received signals characteristics of a transmission channel whereby said received signal was received, the signal acquisition means being operable, for each antenna element, for:

(i) sampling its individual received OFDM radio signal to obtain a series of received-signal samples;
(ii) filtering the preamble samples using a matched finite impulse response (FIR) filter having an impulse response matched to said periodic structure of said preamble training sequence, said filtering being preceded by a complex multiplication by a correction coefficient for dynamic carrier frequency offset compensation, said correction coefficient being initially equal to 1;
(iii) detecting the first two peaks at the output of said filter, each peak corresponding to one received OFDM symbol of the training sequence;
(iv) determining magnitude and phase of the maximum amplitude out of the said two peaks, for each antenna, said magnitude and phase constituting the current estimate of the channel coefficient associated with each antenna;
(v)(a) extracting the phase difference between said two peaks on each antenna;
(v)(b) calculating from said phase difference the phase shift induced per sample by the carrier frequency offset, said phase difference being a multiple of said phase shift with the factor between the two being determined by the separation of the two peaks;
(vi) expressing said phase shift on each antenna by a complex coefficient of unit magnitude, computing the weighted normalized sum of all such coefficients for all antennas, where the weight associated with a specific coefficient is proportional to the current channel gain estimate on the same antenna;
(vii) multiplying the correction coefficient at the multiplier ahead of the matched filter by a complex value of unit amplitude whose phase is minus the phase found in the normalized sum operation of step (vi);
(viii) pursuant to the filtering operation, updating the current channel estimate and the correction coefficient for every received peak as a function of the last received two peaks according to steps (iii)-(vii)
(ix) detecting a maximum amplitude of the cross-correlation output among said peaks from said FIR;
and
(xi) determining magnitude and phase of said maximum amplitude;
(xii) using said magnitude and phase to weight corresponding data for that antenna element in a subsequent step of combining the individual received-signals of the antenna elements, respectively;
(xiii) providing the timing of said maximum amplitude on any given antenna, or any combined signal created by combining the filter outputs at all antennas, as a timing reference for demodulation of said received data;
and
(xiv) providing the final value of the correction coefficient as a measure of the carrier frequency offset for its compensation in subsequent steps.

13 more elements

Method and apparatus for signal acquisition in OFDM receivers

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Method and apparatus for signal acquisition in OFDM receivers

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Abstract

Claims30