Reference signal communication method and system

• US 5,748,677 A
• Filed: 01/16/1996
• Issued: 05/05/1998
• Est. Priority Date: 01/16/1996
• Status: Expired due to Term

• Current Assignee: VuCast Media, Inc.
• Original Assignee: Derek D. Kumar
• Inventors: Kumar, Derek D.
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US08/586,214
• Time in Patent Office: 840 Days
• Field of Search: 375/260, 375/362, 375/363-366, 375/285, 375/296, 375/346, 375/326, 375/229, 375/355, 370/522, 370/525, 370/526, 370/527, 370/528
• US Class Current: 375/285
• CPC Class Codes: H04J 1/12 Arrangements for reducing cross-talk between channels in line transmission systems H04B3/32; in cables or lines H04B3/26 - H04B3/30
• CPC Class Codes: H04L 1/004 by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal

Abstract

A method and system are provided for the transmission and reception of a varying reference signal together with a data-modulated signal in a communication system. The reference signal is modulated by multiplying it by a predetermined reference value sequence and is summed together with the data-modulated signal in the transmitter system. The reference signal and reference value sequence generators are identically embodied in both the transmitter and receiver systems. The receiver system determines an estimate of the transmitted reference signal by canceling the effect of the reference signal modulation. The estimated reference signal may be removed from the received signal prior to demodulation of the data-modulated signal by subtracting the unmodulated reference signal estimate, which is multiplied in the receiver system with the known reference value sequence.

Claims

1. A communications system including a transmitter and a receiver which utilizes a modulated reference signal in order to reduce the effects of non-linearity and stationary interference on the recovery of the reference signal, the communications system comprising:

a transmitter including at least one subcarrier modulator for generating at least one data modulated signal;

said transmitter further including means for generating a modulated reference signal which varies from reference signal baud interval to reference signal baud interval in a predetermined manner based upon a sequence of reference values;

a summer in said transmitter for summing the modulated reference signal and the at least one data modulated signal to form an overall composite signal;

means for transmitting the overall composite signal from the transmitter to a receiver, the receiver including;

(i) means for cancelling the effect of the modulation of the reference signal thereby forming a substantially unmodulated reference signal;

(ii) a first accumulator for accumulating the unmodulated reference signal in order to determine a reference signal estimate; and

(iii) means for using said reference signal estimate for at least one of;

facilitating baud clock recovery;

facilitating carrier frequency recovery; and

equalization.

2. The system of claim 1, further comprising a second accumulator in the receiver for receiving an equalized input signal and outputting to a demodulator an equalized unmodulated reference signal estimate, said demodulator using the equalized unmodulated reference signal estimate in order to substantially cancel the effect of the reference signal in the subcarrier signal, said demodulator further including reference signal re-modulation means and scaling means for compensating for accumulation scale-factor gain.

12. The method of claim 1 further comprising the step of A method of receiving and processing a composite signal including a data modulated signal and a modulated reference signal, the reference signal being modulated in a corresponding transmitter, the method comprising the steps of:

receiving the composite signal including the data modulated signal and the modulated reference signal which varies in a predetermined manner;

substantially cancelling the effect of the modulation of the received reference signal thereby determining a first reference signal estimate;

using the first reference signal estimate for facilitating one of equalization and synchronization;

determining a re-modulated reference signal estimate;

using the re-modulated reference signal estimate in determining a subcarrier signal; and

scaling the re-modulated reference signal estimate before using the re-modulated estimate to determine the subcarrier signal.

13. The method of claim 12 further comprising the steps of A method of receiving and processing a composite signal including a data modulated signal and a modulated reference signal, the reference signal being modulated in a corresponding transmitter, the method comprising the steps of:

receiving the composite signal including the data modulated signal and the modulated reference signal which varies in a predetermined manner;

substantially cancelling the effect of the modulation of the received reference signal thereby determining a first reference signal estimate;

using the first reference signal estimate for facilitating one of equalization and synchronization;

equalizing the received composite signal so as to form an equalized signal; and

substantially cancelling the effect of the reference signal in the equalized signal by using one of (i) a stored replica of the reference signal; and

(ii) an equalized unmodulated reference signal estimate.

3. A method of transmitting an overall composite signal to a receiver including a data modulated signal and a varying reference signal, the method comprising the steps of:

modulating source message bits so as to generate the data modulated subcarrier signal;

generating a modulated reference signal which varies from reference signal baud interval to reference signal baud interval in a predetermined manner as a function of a sequence of reference values thereby reducing the effects of non-linearity and stationary interference on the recovery of the reference signal in the receiver;

summing the data modulated signal and the modulated reference signal to form an overall composite signal; and

transmitting the overall composite signal to the receiver.

4. The method of claim 3, wherein said modulating step further includes generating a plurality of data modulated subcarrier signals and said summing step includes summing the plurality of data modulated subcarrier signals and the modulated reference signal to form the overall composite signal.

5. A method of receiving an overall composite signal including a modulated reference signal and a data modulated signal, the reference signal having been modulated in a corresponding transmitter, the method comprising the steps of:

receiving the overall composite signal including the data modulated signal, and the modulated reference signal which varies from reference signal baud interval to reference signal baud interval in a predetermined manner;

substantially cancelling the effect of the modulation in the reference signal so as to form a substantially unmodulated reference signal;

accumulating the unmodulated reference signal in order to determine a reference signal estimate; and

using the reference signal estimate to facilitate at least one of equalization, carrier recovery, and baud clock recovery thereby reducing the effects of at least one of non-linearity and stationary interference on the recovery of the reference signal in the receiver.

6. The method of claim 5 further comprising the steps of:

using the reference signal estimate in equalizing the received signal thereby forming an equalized signal;

cancelling the effect of the reference modulation in the equalized signal to form an equalized substantially unmodulated reference signal; and

accumulating the equalized unmodulated reference signal so as to determine an equalized reference signal estimate.

7. The method of claim 6 further comprising the steps of:

re-modulating the equalized reference signal estimate to form a re-modulated reference signal estimate;

scaling the re-modulated reference signal estimate in order to compensate for accumulation scale factor gain thereby determining a scaled re-modulated reference signal estimate;

determining a subcarrier signal using the scaled re-modulated reference signal estimate to substantially cancel the effect of the reference signal in the equalized signal; and

demodulating the subcarrier signal in order to determine a bit estimate.

8. A receiver for receiving an overall composite signal including a varying reference signal and at least one data modulated signal, the reference signal varying from reference signal baud interval to reference signal baud interval in a predetermined manner as determined by a sequence of reference values in a corresponding transmitter, the receiver comprising:

means for receiving the overall composite signal including the varying reference signal and a data modulated signal;

means for cancelling the effect of the sequence of references values in the reference signal so as to form a non-varying reference signal;

an accumulator for accumulating the non-varying reference signal in order to determine a reference signal estimate; and

means for using the reference signal estimate for one of clock synchronization and equalization.

9. The receiver of claim 8 further comprising:

an equalizer for equalizing the received signal using the reference signal estimate thereby forming an equalized signal;

means for canceling the effect of the reference sequence in the equalized signal thereby forming an equalized substantially non-varying reference signal; and

a secondary accumulator for accumulating the equalized non-varying reference signal thereby forming an equalized reference signal estimate.

10. The receiver of claim 9 further comprising a subcarrier demodulator for determining data bit estimates from the data modulated signal, said subcarrier demodulator including a re-varying device for re-varying the equalized reference signal estimate using the sequence of reference values thereby forming a varying equalized reference signal estimate.

11. The receiver of claim 10 wherein said subcarrier demodulator includes means for scaling the varying equalized reference signal estimate and determining a subcarrier signal from the equalized signal and the varying equalized reference signal estimate, said demodulator further comprising means for determining the bit estimates from the determined subcarrier signal.

14. A method of receiving and processing a modulated reference signal from a transmitter, the method comprising the steps of:

receiving the modulated reference signal which varies from reference signal baud interval to reference signal baud interval as determined by a sequence of reference values in the transmitter;

substantially cancelling the effect of the modulation of the reference signal so as to form a substantially unmodulated reference signal;

accumulating the substantially unmodulated reference signal in order to determine a reference signal estimate thereby reducing the effect of non-linearity on the recovery of the reference signal; and

using the determined reference signal estimate for at least one of equalization, synchronization, and channel characteristic determination.