Method and apparatus for symbol boundary synchronization
View Patent ↗The apparatus for symbol boundary synchronization in one embodiment includes on the receive path of a multi-tone modem a window synchronizer, a converter and a symbol boundary component. The window synchronizer obtains windowed portions of the received datastream which includes symbols each expressed with a corresponding set of tones in a time domain. The windowed portions obtained in the training phase exhibit varying degrees of misalignment with the corresponding symbol boundaries. The window synchronizer is responsive to an alignment signal to obtain succeeding windowed portions of the incoming datastream aligned with the corresponding symbol boundaries therein. The converter couples to the window synchronizer to convert the set of tones from each windowed portion from the time domain to a frequency domain. The symbol boundary module couples to the converter to evaluate a phasor angle characteristic of selected tones from each windowed portion converted by the converter and to convert the phasor angle characteristic of the selected tones from a selected one of the windowed portions to the alignment signal to align the window synchronizer with the symbol boundaries in the received datastream. In an alternate embodiment of the invention the symbol boundary component couples to the window synchronizer to correlate sign values of the selected tones with a reference set and to output the alignment signal identifying the corresponding windowed portion which exhibits maximum correlation with the reference set to align the window synchronizer.
1. An apparatus for symbol boundary synchronization in a multi-tone modem with a plurality of components forming a transmit path and a receive path: and the receive path components of the multi-tone modem comprising:
a window synchronizer to obtain windowed portions of a received datastream with symbols each expressed with a corresponding set of tones in a time domain and with the windowed portions obtained in a training phase exhibiting varying degrees of misalignment with corresponding symbol boundaries and with the window synchronizer responsive to an alignment signal to obtain succeeding windowed portions of the incoming datastream aligned with the corresponding symbol boundaries therein;
a converter coupled to the window synchronizer to convert the set of tones from each windowed portion from the time domain to a frequency domain; and
a symbol boundary component coupled to the converter to evaluate a phasor angle characteristic of selected tones from each windowed portion converted by the converter and to convert the phasor angle characteristic of the selected tones from a selected one of the windowed portions to the alignment signal to align the window synchronizer with the symbol boundaries in the received datastream and the symbol boundary component including:
a calculator for selecting at least one set of adjacent pilot tones within each successive windowed portion and for determining for each adjacent pair of tones in the at least one set a corresponding phasor resulting from multiplying a one tone of each adjacent pair by a complex conjugate of an other;
a peak detector for detecting from among the phasors of successive windowed portions from the calculator, a peak phasor which exhibits a peak magnitude; and
a converter for converting the phasor angle of the peak phasor detected in the peak detector to the alignment signal with a tone offset required to align the windowed portion obtained by the window synchronizer with the corresponding symbol boundaries.
2. An apparatus for symbol boundary synchronization in a multi-tone modem with a plurality of components forming a transmit path and a receive path; and the receive path components of the multi-tone modem comprising:
a window synchronizer to obtain windowed portions of a received datastream with symbols each expressed with a corresponding set of tones in a time domain and with the windowed portions obtained in a training phase exhibiting varying degrees of misalignment with corresponding symbol boundaries and with the window synchronizer responsive to an alignment signal to obtain succeeding windowed portions of the incoming datastream aligned with the corresponding symbol boundaries therein, and a number of windowed portions ‘W #f ’ obtained by the window synchronizer during the training phase substantially corresponding with:
W
#
f
=
S
+
Xp
+
Xs
Xp
+
Xs
where ‘S’ corresponds with a number of samples per symbol, ‘Xp’ corresponds with a number of samples per cyclic prefix, and ‘Xs’ corresponds with a number of samples per cyclic suffix;
a converter coupled to the window synchronizer to convert the set of tones from each windowed portion from the time domain to a frequency domain; and
a symbol boundary component coupled to the converter to evaluate a phasor angle characteristic of selected tones from each windowed portion converted by the converter and to convert the phasor angle characteristic of the selected tones from a selected one of the windowed portions to the alignment signal to align the window synchronizer with the symbol boundaries in the received datastream.
3. A method for demodulating data received over a communication medium with a communication channel with multiple pilot tones with pilot data modulated thereon; and the method for demodulating comprising;
obtaining in a time domain windowed portions of a received datastream with symbols each expressed with a corresponding set of tones and with the windowed portions obtained in a training phase exhibiting varying degrees of misalignment with corresponding symbol boundaries;
transforming the set of tones from each windowed portion from the time domain to a corresponding set of tones in a frequency domain; and
correcting misalignment of the windowed portions obtained in the time domain using phasor-angle parameters derived in the frequency domain from at least two tones from the set of tones for a selected windowed portion transformed in the transforming act;
deriving phasors from the combination of the at least two selected tones within each set of tones transformed in the transforming act;
determining a peak phasor, among the phasors derived in the deriving act with the peak phasor exhibiting a peak magnitude relative to phasors; and
converting a phasor-angle of the peak phasor to a tone offset required to correct misalignment of the windowed portions obtained in the time domain; and wherein a number of phasors W #f derived in the deriving act substantially corresponds with:
W
#
f
=
S
+
Xp
+
Xs
Xp
+
Xs
where ‘S’ corresponds with a number of samples per symbol, ‘Xp’ corresponds with a number of samples per cyclic prefix, and ‘Xs’ corresponds with a number of samples per cyclic suffix.
4. A method for symbol boundary synchronization of a received datastream of a multi-tone modulated communication channel; and the method comprising:
obtaining in a time domain successive windowed portions of the received datastream with symbols each expressed with a corresponding set of tones and with the windowed portions obtained in a training phase exhibiting varying degrees of misalignment with corresponding symbol boundaries;
transforming the set of tones from each windowed portion from the time domain to a corresponding set of tones in a frequency domain; and
correcting symbol boundary misalignment of the successive windowed portions by:
selecting at least one set of adjacent pilot tones within each successive windowed portion;
determining for each adjacent pair of tones in the at least one set a corresponding phasor by multiplying a one pilot tones of each adjacent pair times a complex conjugate of an other;
detecting from among the phasors of successive windowed portions from the calculator, a peak phasor which exhibits a peak magnitude; and
converting a phasor-angle of the peak phasor detected in the detecting act to a tone offset required to correct symbol boundary misalignment of the windowed portions obtained in the time domain.
5. The method of claim 4 , further comprising the act prior to the multiplying act of:
de-scrambling the pilot tones selected in the selecting act.