Vectored demodulation and frequency estimation apparatus and method

• US 6,218,896 B1
• Filed: 09/28/1999
• Issued: 04/17/2001
• Est. Priority Date: 08/27/1999
• Status: Expired due to Term

• Current Assignee: Tachyon, Inc. (Tachyon Networks Incorporated)
• Original Assignee: Tachyon, Inc. (Tachyon Networks Incorporated)
• Inventors: Becker, Donald W., Leigh, William E. L.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US09/407,642
• Time in Patent Office: 567 Days
• Field of Search: 329/304, 375/324, 375/329
• US Class Current: 329/304
• CPC Class Codes: G06F 11/0757 by exceeding a time limit, i.e. time-out, e.g. watchdogs
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: H03J 7/065 the counter or frequency divider being used in a phase locked loop
• CPC Class Codes: H04B 7/18582 Arrangements for data linking, i.e. for data framing, for error recovery, for multiple access
• CPC Class Codes: H04L 27/22 Demodulator circuits; Receiver circuits
• CPC Class Codes: H04L 27/2276 using frequency multiplication or harmonic tracking
• CPC Class Codes: H04L 69/08 Protocols for interworking; Protocol conversion
• CPC Class Codes: H04L 69/16 Implementation or adaptation of Internet protocol [IP], of transmission control protocol [TCP] or of user datagram protocol [UDP]
• CPC Class Codes: H04L 69/161 Implementation details of TCP/IP or UDP/IP stack architecture; Specification of modified or new header fields
• CPC Class Codes: H04L 69/163 In-band adaptation of TCP data exchange; In-band control procedures
• CPC Class Codes: H04L 69/166 IP fragmentation; TCP segmentation
• CPC Class Codes: H04L 69/168 specially adapted for link layer protocols, e.g. asynchronous transfer mode [ATM], synchronous optical network [SONET] or point-to-point protocol [PPP]
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04L 7/04 Speed or phase control by synchronisation signals H04L7/0075 takes precedence
• CPC Class Codes: H04L 9/40 Network security protocols
• CPC Class Codes: H04N 21/235 Processing of additional data, e.g. scrambling of additional data or processing content descriptors
• CPC Class Codes: H04N 21/23614 Multiplexing of additional data and video streams arrangements for simultaneous broadcast of plural pieces of information H04H20/28
• CPC Class Codes: H04N 21/2385 Channel allocation H04N21/266 takes precedence; Bandwidth allocation H04N21/24 takes precedence ; allocation of channels according to the instantaneous demands of the users in time-division multiplex systems H04J3/1682; admission control, resource allocation in open networks H04L12/5692; arrangements for maintenance or administration in data switching networks involving bandwidth and capacity management H04L41/0896; negotiating bandwidth in wireless networks H04W28/16
• CPC Class Codes: H04N 21/4348 Demultiplexing of additional data and video streams
• CPC Class Codes: H04N 21/435 Processing of additional data, e.g. decrypting of additional data, reconstructing software from modules extracted from the transport stream
• CPC Class Codes: H04N 21/4381 : Recovering the multiplex stream from a specific network, e.g. recovering MPEG packets from ATM cells transmission of MPEG streams over ATM H04L12/5601
• CPC Class Codes: H04N 21/6143 : involving transmission via a satellite
• CPC Class Codes: H04N 21/64322 : IP
• CPC Class Codes: H04W 80/06 : Transport layer protocols, e.g. TCP [Transport Control Protocol] over wireless transmission control protocol/Internet protocol [TCP/IP] or user datagram protocol [UDP] H04L69/16

Abstract

A method and apparatus for digitally demodulating QPSK signals includes a first portion in which the digitally sampled data burst is resampled with a plurality of predetermined timing hypotheses. The timing offset is determined according to an analysis of the resampled data. The digitally sampled data burst is then resampled according to the timing estimation. Modulation of the resampled data burst is then removed by twice squaring the complex I/Q pairs. The data with the modulation removed is then subjected to a Chirp-Z Transform to move the data into the frequency domain. The highest spectral power is used to determine the frequency offset. The phase offset is determined and the resampled data burst is derotated and dephased according to the phase offset and the frequency offset.

Claims

1. A demodulator for demodulating a digitally sampled data burst comprising:

a resampling section configured to resample the digitally sampled data burst at a plurality of timing offsets;

an evaluation section configured to evaluate the correlation of the resampling performed at the plurality of timing offsets by the resampling section and to determine a timing estimate;

a polyphase filter configured to resample the digitally sampled data burst according to the timing estimate determined by the evaluation section and generate resampled data;

a frequency estimation section configured to receive the resampled data from the polyphase filter and to determine a frequency offset;

a phase estimation section configured to receive the resampled data from the polyphase filter and to determine a phase offset; and

a phase/frequency correction section configured to receive the resampled data from the polyphase filter and to adjust the phase and frequency of the A resampled data according to the phase offset determined by the phase estimation section and the frequency offset determined by the frequency estimation section.

2. The demodulator according to claim 1, wherein said resampling section comprises a polyphase filter.

3. The demodulator according to claim 1, wherein said frequency estimation section comprises means for performing a Chirp-Z Transform of the resampled data from the polyphase filter.

4. The demodulator according to claim 1, wherein the evaluation section includes means for determining the power of the resampling performed at the plurality of timing offsets.

5. A demodulator for demodulating a digitally sampled data burst of QPSK data, the demodulator comprising:

a first resampling section configured to resample the digitally sampled data burst at a plurality of timing hypotheses;

a timing hypothesis correlation section configured to determine which of the plurality of timing hypotheses has the best correlation and to determine a timing estimate based thereon;

a second resampling section configured to resample the digitally sampled data burst according to the timing estimate, and thereby generate complex I/Q samples;

a data modulation removal section configured to receive the complex I/Q samples and move them all into the same quadrant, thereby generating Z data;

a Chirp-Z Transform section configured to transform the Z data into the frequency domain;

a frequency estimation section configured to estimate a frequency offset using the Chirp-Z transformed data;

a phase estimation section configured to receive the Z data and estimate a phase offset.

6. The demodulator according to claim 5, wherein said first resampling section comprises a polyphase filter.

7. The demodulator according to claim 6, wherein said first resampling section and said second resampling section comprise the same polyphase filter.

8. The demodulator according to claim 5, wherein said timing hypothesis correlation section is configured to determine the energy of each resampling of the data burst carried out by said first resampling section.

9. The demodulator according to claim 5, wherein said frequency estimation section is configured to determine the spectral power over the Chirp-Z-transformed data.

10. A method of demodulating a digitally sampled data burst comprising:

resampling the digitally sampled data burst with a plurality of timing hypotheses;

determining the total energy of each of the timing hypotheses;

determining a timing estimate based upon the energies of the timing hypotheses;

resampling the digitally sampled data burst according to the timing estimate;

determining the frequency offset by transforming the resampled data burst into the frequency domain, determining the spectral power over the data set of the transformed data and utilizing the highest spectral power to determine the frequency offset; and

determining the phase offset.

11. The method according to claim 10, wherein determining the frequency offset further comprises moving the transformed data into the same quadrant.

12. The method according to claim 11, wherein determining the frequency offset further comprises performing a Chirp-Z Transform on the data that has been moved to the same quadrant.

13. The method according to claim 10, wherein the digitally sampled data burst is resampled with a plurality of timing hypotheses using a polyphase filter.

14. The method according to claim 10, wherein the digitally sampled data burst is resampled according to the timing estimate using a polyphase filter.

15. The method according to claim 10, wherein determining the timing estimate further comprises determining the highest energy value over the data burst for each of the timing hypotheses.

16. A method of demodulating a digitally sampled data burst comprising:

resampling the digitally sampled data burst with a plurality of timing hypotheses to determine a timing estimate;

resampling the digitally sampled data burst based upon the timing estimate to obtain resampled data;

determining the frequency offset using the timing estimate;

determining the phase offset; and

adjusting the phase and frequency of the resampled data according to the determined phase offset and the determined frequency offset.

17. The method of claim 16 further comprising determining the total energy of each of the timing hypotheses.

18. The method of claim 16 further comprising transforming the resampled data into the frequency domain, determining the spectral power over the data set of the transformed data and utilizing the highest spectral power to determine the frequency offset.

19. A demodulator for demodulating a digitally sampled data burst of QPSK data, the demodulator comprising:

a first resampling means for resampling the digitally sampled data burst at a plurality of timing hypotheses;

a correlation means for determining which of the plurality of timing hypothesis has the best correlation and for determining a timing estimate based thereon;

a second resampling means for resampling the digitally sampled data burst according to the timing estimate, and thereby generating complex I/Q samples;

a modulation removal means, coupled to receive the complex I/Q samples, for moving the complex I/Q samples into the same quadrant, thereby generating Z data;

a means for receiving the Z data and transforming the Z data into the frequency domain;

a frequency estimation means estimating a frequency offset using the transformed Z data; and

a phase estimation means for receiving the Z data and estimating a phase offset.

20. The demodulator according to claim 19, wherein said first resampling means comprises a polyphase filter.

21. The demodulator according to claim 19, wherein said first resampling means and said second resampling means comprise the same polyphase filter.

22. The demodulator according to claim 19, wherein said correlation means comprises means for determining the energy of each resampling of the data burst carried out by said first resampling means.

23. The demodulator according to claim 22, wherein said frequency estimation means comprises means for determining the spectral power over the transformed Z data.