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US 6,310,926 B1Granted
Adjustment of the sampling frequency in a multicarrier receiver
AssigneeTelefonaktiebolaget LM Ericsson (publ)
InventorMikael André Tore
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Abstract
In a multicarrier QAM system, a receiver comprises a data directed phase error estimator which determines a phase rotation direction of each received complex QAM data value (Yk) with respect to the complex default QAM data value C(k) used by a quantizer/decoder for decoding. The data directed phase error estimator averages the phase rotation directions for all carriers and adjusts the phase of a sample frequency (fsampR) output by a numerically-controlled oscillator on the basis of this overall average phase rotation direction value (D). Thus, an overall estimate of the missing phase synchronization to the sample frequency used in the transmitter can be obtained such that the data symbols can be more accurately decoded.
Claims37
A receiver of a multicarrier QAM system for receiving and demodulating an analog multicarrier QAM signal TM into a digital output signal (Rx) consisting of successive bits, comprising:
- a) analog/digital conversion means (7, 8) for converting said analog multicarrier QAM signal TM into a digital time-domain multicarrier QAM signal (DS) using a predetermined sample frequency (fsampR) from a receiver clock generator (NCO, 15);
- b) time-domain/frequency-domain conversion means (10) for converting said digital time-domain multicarrier QAM signal (DS) into a digital frequency-domain multicarrier QAM signal consisting of a plurality of complex QAM data values (Y1, Y2 . . . Yk;
- Y00, Y01, Y10, Y11);
- c) decoding means (11, 12) for respectively selecting a complex default QAM data value (Ck, C00, C01, C10, C11) representing a known digital data symbol (00, 01, 10, 11) on the basis of said complex default QAM data values and for decoding said complex default QAM data values into said digital output signal;
- and
- d) timing recovery means (14, 16, 19-21) for adjusting a phase of said receiver clock generator (NCO, 15) such that the sample timing in said analog/digital conversion means (7, 8) coincides with that (fsampT) used in a transmitter (1-6) which generates said analog multicarrier signal;
- characterized in that
- e) said timing recovery means (14, 16, 19-21) comprises:
- e1) phase rotation direction determining means (221-224) for determining a plurality of phase rotation direction values (−1, +1, 0;
- d1, d2, d3, dk) of a respective complex QAM data value (Yk) with respect to a corresponding complex default QAM data value;
- and
- e2) average phase rotation direction determining means (219) for determining an average phase rotation direction value (dk′) by averaging all respective rotation direction values;
- and wherein
- f) said phase of said sample frequency (fsampR) is adjusted on the basis of said average phase rotation direction value (dk).
11 more elements
A multicarrier QAM communication system for transmitting information using a multicarrier QAM between a transmitter and a receiver, comprising at said transmitter:
- a) coding means (1, 3) for coding an input bit stream (Tx) into a digital frequency-domain multicarrier QAM signal consisting of a number (NcT) of complex QAM data values using a multicarrier QAM technique;
- b) frequency-domain/time-domain conversion means (4) for converting said digital frequency-domain multicarrier QAM signal into a digital time-domain multicarrier QAM signal consisting of number of separate QAM samples;
- and
- c) digital/analog conversion means (5, 6) for converting said samples of said digital time-domain multicarrier QAM signal into an analog multicarrier QAM signal (TM) using a predetermined transmitter sample frequency (fsampT) from a transmitter clock generator;
- and at said receiver:
- d) analog/digital conversion means (7, 8) for converting said analog multicarrier QAM signal (TM) into a digital time-domain multicarrier QAM signal (DS) using a predetermined sample frequency (fsampR) from a receiver clock generator (NCO, 15);
- e) time-domain/frequency-domain conversion means (10) for converting said digital time-domain multicarrier QAM signal (DS) into a digital frequency-domain multicarrier QAM signal consisting of a plurality of complex QAM data values ((Y1, Y2 . . . Yk;
- Y00, Y01, Y10, Y11);
- f) decoding means (11, 12) for respectively selecting a complex default QAM data value (Ck, C00, C01, C10, C11) representing a known digital data symbol (00, 01, 10, 11) on the basis of said complex default QAM data values and for decoding said complex default QAM data values into a digital output signal;
- and
- g) timing recovery means (14, 16, 19-21) for adjusting a phase of said receiver clock generator (NCO, 15) such that the sample timing in said analog/digital conversion means (7, 8) coincides with that (fsampT) used by said digital/analog conversion means (5) in said transmitter (1-6);
- characterized in that
- h) said timing recovery means (14, 16, 19-21) comprises:
- h1) phase rotation direction determining means (221-224) for determining a plurality of phase rotation direction values (−1, +1, 0;
- d1, d2, d3, dk) of a respective complex QAM data value (Yk) with respect to a corresponding complex default QAM data value;
- and
- h2) average phase rotation direction determining means (219) for determining an average phase rotation direction value (dk) by averaging all respective rotation directions;
- and wherein
- i) said phase of said sample frequency (fsampR) is adjusted on the basis of said average phase rotation direction value (dk).
16 more elements
A method in a multicarrier QAM system for receiving and demodulating an analog multicarrier QAM signal (TM) into a digital output signal (Rx) consisting of successive digital data symbols, comprising the following steps:
- a) converting said analog multicarrier QAM signal (TM) into a digital time-domain multicarrier QAM signal (DS) using a predetermined sample frequency (fsampR) from a receiver clock generator (NCO, 15);
- b) converting said digital time-domain multicarrier QAM signal (DS) into a digital frequency-domain multicarrier QAM signal consisting of a plurality of complex QAM data values (Y1, Y2 . . . Yk;
- Y00, Y01, Y10, Y11);
- c) selecting respectively a complex default QAM data value (Ck, C00, C01, C10, C11) representing a known digital data symbol (00, 01, 10, 11) on the basis of said complex default QAM data values said complex default QAM data values and decoding said complex default QAM data values into said digital output signal;
- and
- d) adjusting a phase of said receiver clock generator (NCO, 15) such that the sample timing used in said analog/digital conversion step coincides with that (fsampT) used in a transmitter (1-6) which generates said multicarrier QAM signal;
- characterized by the following steps:
- e1) determining respectively a plurality of phase rotation direction values (−1, +1, 0;
- di, d2, d3, dk) of a respective complex QAM data value (Yk) with respect to a corresponding complex default QAM data value;
- and
- e2) determining an average phase rotation direction value (dk) by averaging all respective phase rotation direction values;
- and
- f) adjusting said phase of said sample frequency (fsampR) on the basis of said average phase rotation direction value (dk).
10 more elements
Dependencies are inferred from the claim text.