Method and apparatus for data encoding and communication over noisy media

• US 5,727,004 A
• Filed: 03/14/1995
• Issued: 03/10/1998
• Est. Priority Date: 03/14/1995
• Status: Expired due to Fees

• Current Assignee: Adaptive Networks, Inc.
• Original Assignee: Adaptive Networks, Inc.
• Inventors: Propp, Michael B., Propp, David L.
• Primary Examiner(s): Elmore, Reba I.
• Assistant Examiner(s): Brown, Thomas
• Application Number:
  US08/404,627
• Time in Patent Office: 1,092 Days
• Field of Search: 371/42, 371/43, 371/46, 371/47.1, 371/44, 371/45, 375/106, 375/108, 375/110, 375/114, 375/116, 375/117, 375/39, 375/60, 375/121, 375/296
• US Class Current: 714/798
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 2203/5408 using protocols
• CPC Class Codes: H04B 2203/5416 by adding signals to the wave form of the power source
• CPC Class Codes: H04B 2203/5425 improving S/N by matching impedance, noise reduction, gain control
• CPC Class Codes: H04B 2203/5441 Wireless systems or telephone
• CPC Class Codes: H04B 2203/5495 having measurements and testing channel
• CPC Class Codes: H04B 3/54 Systems for transmission via power distribution lines
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 1/1829 Arrangements specially adapted for the receiver end
• CPC Class Codes: H04L 2007/047 using a sine signal or unmodulated carrier
• CPC Class Codes: H04L 7/0337 Selecting between two or more discretely delayed clocks or selecting between two or more discretely delayed received code signals
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15
• CPC Class Codes: H04L 7/046 using a dotting sequence

Abstract

A novel apparatus and method are provided for data communication over noisy media. The apparatus includes one or both of a transmitter circuit located at a transmitting location and a receiver circuit located at a receiving location. The data is encoded to provide error correction capabilities. The encoded signal is further modified by performing one or more linear mathematical operations in order to further randomize the data signal. The transmitter circuit thus generates a wideband spread spectrum signal based on the data which is to be transmitted, which spreads the signal and improves its immunity to noise. The coding used to spread the data signal may or may not be a function of the data itself. The present invention provides enhanced noise immunity without any resulting degradation in the operation and efficiency of the error correction coding. A synchronization circuit and method are also provided for quickly achieving fast, accurate synchronization utilizing parallel synchronization and sub-bit correlation. The error correction is used to correct hard and soft errors, and dynamically adjust the combination of hard and soft errors corrected in order to improve the overall data error correction.

Claims

1. A method of detecting data signals containing a synchronization preamble to select proper bit timing, comprising the steps of:

generating a plurality of strings of said synchronization preamble, each string being sequentially offset in time by a fraction of a bit period of said synchronization preamble, said fraction being substantially proportional to said bit period divided by the number of said plurality;

correlating at least a first bit portion and a second bit portion of each bit period of the plurality of strings with a reference signal to produce at least a first correlation value and a second correlation value, each bit portion being less than said bit period;

for each first bit portion and second bit portion of each bit period, setting the value of each respective bit portion to one of a plurality of values based on the respective bit portion correlation value; and

selecting a string from among the plurality of strings of said synchronization preamble as the proper bit timing based on at least one of the fewest number of a particular value and an amount of matching to a predetermined pattern.

2. The method of claim 1, wherein the setting step comprises the further step of:

setting the value of the respective bit portion to a 1 if the respective correlation value exceeds a first threshold, setting the value of the respective bit portion to a 0 if the respective correlation value is less than a second threshold, otherwise setting the value of the respective bit portion to an unknown value.

3. The method of claim 1, wherein the selecting step comprises the further step of:

determining an overall value based on at least the first bit portion value and the second bit portion value.

4. The method of claim 1, wherein the plurality of values includes at least one strong value and at least one weak value, and the particular value is a weak value.

5. The method of claim 4, comprising the further step of:

discarding synchronization preamble strings having a bit period containing two weak values.

6. The method of claim 1, wherein the plurality of strings comprises sixteen strings.

7. The method of claim 1, comprising the further step of:

discarding synchronization preamble strings having a bit period containing inconsistent values.

8. The method of claim 7, wherein the inconsistent values include a first bit portion value of 1 and a second bit portion value of 0.

9. The method of claim 7, wherein the inconsistent values include a first bit portion value of 0 and a second bit portion value of 1.

10. The method of claim 1, wherein the correlating step is carried out in parallel.

11. The method of claim 1, wherein the correlating step is carried out serially.

12. The method of claim 4, wherein the selecting step comprises the further step of:

selecting the median synchronization preamble string from among a number of synchronization preamble strings having an identical number of weak values.

13. A circuit for detecting data signals containing a synchronization preamble to select proper bit timing, comprising:

a delay circuit which generates a plurality of strings of said synchronization preamble, each string being sequentially offset in time by a fraction of a bit period of said synchronization preamble, said fraction being substantially proportional to said bit period divided by the number of said plurality;

a correlator which correlates at least a first bit portion and a second bit portion of each bit period of the plurality of strings with a reference signal to produce at least a first correlation value and a second correlation value, each bit portion being less than said bit period;

a decision circuit which for each first bit portion and second bit portion of each bit period, sets the value of each respective bit portion to one of a plurality of values based on the respective bit portion correlation value; and

an evaluation circuit which selects a string from among the plurality of strings of said synchronization preamble as the proper bit timing based on at least one of the fewest number of a particular value and an amount of matching to a predetermined pattern.

14. The circuit of claim 13, wherein the decision circuit further comprises:

a specific value circuit which sets the value of the respective bit portion to a 1 if the respective correlation value exceeds a first threshold, which sets the value of the respective bit portion to a 0 if the respective correlation value is less than a second threshold, otherwise which sets the value of the respective bit portion to an unknown value.

15. The circuit of claim 13, wherein the evaluation circuit further comprises:

a circuit which determines an overall value based on at least the first bit portion value and the second bit portion value.

16. The circuit of claim 13, wherein the plurality of values includes at least one strong value and at least one weak value, and the particular value is a weak value.

17. The circuit of claim 16, further comprising:

a circuit which discards synchronization preamble strings having a bit period containing two weak values.

18. The circuit of claim 13, wherein the plurality of strings comprises sixteen strings.

19. The circuit of claim 13, further comprising:

a circuit which discards synchronization preamble strings having a bit period containing inconsistent values.

20. The circuit of claim 19, wherein the inconsistent values include a first bit portion value of 1 and a second bit portion value of 0.

21. The circuit of claim 19, wherein the inconsistent values include a first bit portion value of 0 and a second bit portion value of 1.

22. The circuit of claim 13, wherein the correlator is a parallel correlator.

23. The circuit of claim 13, wherein the correlator is a serial correlator.

24. The circuit of claim 16, wherein the evaluation circuit includes a median selector which selects the median synchronization preamble string from among a number of synchronization preamble strings having an identical number of weak values.

25. A method of data communication comprising the steps of:

encoding error correcting data signals, said encoding step comprising the step of;

randomizing the error correcting data signals using at least one linear operator to increase the randomness of the data signals without decreasing error correcting capabilities and effective signal bandwidth; and

detecting data signals containing a synchronization preamble to select proper bit timing, said synchronizing step comprising the steps of;

generating a plurality of strings of said synchronization preamble, each string being sequentially offset in time by a fraction of a bit period of said synchronization preamble, said fraction being substantially equivalent to said bit period divided by the number of said plurality;

correlating at least a first bit portion and a second bit portion of each bit period of the plurality of strings with a reference signal to produce at least a first correlation value and a second correlation value, each bit portion being less than said bit period;

for each first bit portion and second bit portion of each bit period, setting the value of each respective bit portion to one of a plurality of values based on the respective bit portion correlation value; and

selecting a string from among the plurality of strings of said synchronization preamble as the proper bit timing based on at least one of the fewest number of a particular value and a match to a predetermined pattern.

26. A data communication apparatus comprising:

a data encoder circuit for encoding error correcting data signals, said data encoder comprising;

a randomizer which performs at least one linear operation on said error correcting data signals to increase the randomness of the data signals without decreasing error correcting capabilities and effective signal bandwidth; and

a circuit for detecting data signals containing a synchronization preamble to select proper bit timing, comprising;

a delay circuit which generates a plurality of strings of said synchronization preamble, each string being sequentially offset in time by a fraction of a bit period of said synchronization preamble, said fraction being substantially equivalent to said bit period divided by the number of said plurality;

a correlator which correlates at least a first bit portion and a second bit portion of each bit period of the plurality of strings with a reference signal to produce at least a first correlation value and a second correlation value, each bit portion being less than said bit period;

a decision circuit which for each first bit portion and second bit portion of each bit period, sets the value of each respective bit portion to one of a plurality of values based on the respective bit portion correlation value; and

an evaluation circuit which selects a string from among the plurality of strings of said synchronization preamble as the proper bit timing based on at least one of the fewest number of a particular value and a match to a predetermined pattern.