Apparatus for receiving and correlating a spread spectrum signal

• US 5,953,370 A
• Filed: 09/12/1997
• Issued: 09/14/1999
• Est. Priority Date: 09/09/1994
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Omnipoint Corp. (Deutsche Telekom AG)
• Inventors: Durrant, Randolph L., Burbach, Mark
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US08/928,846
• Time in Patent Office: 732 Days
• Field of Search: 375/200, 375/206, 375/207, 375/208, 375/209, 375/210, 375/343, 375/274, 375/336
• US Class Current: 375/150
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04J 14/005 Optical Code Multiplex
• CPC Class Codes: H04L 27/2014 in which the phase changes in a piecewise linear manner during each symbol period, e.g. minimum shift keying, fast frequency shift keying H04L27/201 takes precedence
• CPC Class Codes: H04L 27/2278 using correlation techniques, e.g. for spread spectrum signals
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

A spread spectrum receiver for demodulating a CPM spread spectrum signal receives burst comprising a preamble and a data message that have been transmitted by M-ary encoding of a data signal into a single chip stream, dividing the chip stream into I and Q signal streams, independently modulating the I and Q signal streams, and superposing the resultants for transmission. The receiver detects the preamble using a non-coherent parallel correlator, and from the preamble correlation peak generates a series of integration periods for serial non-coherent correlation. A bank of non-coherent, serial correlators operate in parallel to recover the spread spectrum encoded information. For each of M spread spectrum codes, the receiver simultaneously attempts to correlate the non-preamble portion of the received spread spectrum signal by separating, the received signal into real and imaginary parts, correlating both real and imaginary parts for I and Q sequences, and combining the real I, real Q, imaginary I, and imaginary Q correlation signals into a unified correlation signal. The maximum of the unified correlation signals from the non-coherent, serial correlators dictates the content of the data stream for each integration period. The local clock reference signal in the receiver need not be frequency or phase matched with the clock of the transmitter in order to carry out the integration and recovery of the data stream.

Claims

1. An apparatus comprising:

means for receiving a spread spectrum signal transmitted from a transmitter, said spread spectrum signal comprising a plurality of symbol codes and a preamble, each one of said symbol codes corresponding to a set of data bits,

a non-coherent parallel correlator for correlating said preamble, said parallel correlator outputting a synchronizing signal when said preamble is received,

a serial correlator clock responsive to said synchronizing signal, said serial correlator clock establishing a plurality of consecutive serial integration time intervals each corresponding to a symbol code period,

a plurality of non-coherent serial correlators responsive to said serial correlator clock, each of said non-coherent serial correlators programmed to respond to a different one of said symbol codes, and each of said non-coherent serial correlators generating, without deriving further timing information from said spread spectrum signal for maintaining synchronization, a correlation signal upon matching said spread spectrum signal to a predetermined degree with said one symbol code and being periodically reset by said serial correlator clock at the end of each serial integration time interval, said correlation signal being generated in the presence of an arbitrary phase difference between a clock of said transmitter and said serial correlator clock, and

means connected to said non-coherent serial correlators for generating a data stream.

2. The apparatus of claim 1 wherein said means for generating said data stream comprises a best-of-M device for selecting the largest of said correlation signals generated by said non-coherent serial correlators.

3. The apparatus of claim 1 further comprising a counter for maintaining timed synchronicity within a time division multiple access system.

4. The apparatus of claim 1 wherein said spread spectrum signal comprises a continuous phase modulated signal.

5. The apparatus of claim 1, wherein a frequency difference between the clock of said transmitter and said serial correlator clock is less than 1/4 of a symbol code rate corresponding to the symbol code period.

6. The apparatus of claim 1, further comprising a mobile handset unit containing said means for receiving said spread spectrum signal, said non-coherent parallel correlator, and said plurality of non-coherent serial correlators.

7. An apparatus comprising:

means for receiving a spread spectrum signal, said spread spectrum signal comprising a plurality of symbol codes and a preamble, each one of said symbol codes corresponding to set of data bits, wherein said symbol codes comprise the following hexadecimal codes;

0544D65E, 0E4424A1, 5B118E0B, 5B1171F4, 3D77E66D, 3D771792, 6822BD36, 682242C7, 014BD451, 014B2BAE, 541E8104, 541E7EFB, 3278E762, 3278189D, 672DB237, 672D4DC8, 0EBBDBA1, 0EBB245E, 5BEE8EF4, 5BEE710B, 3D88E892, 3D86176D, 68DDBDC7, 68DD4238, 01B4D4AE, 01B42B51, 54E181FB, 54E17ED4, 3287E79D, 32671862, 67D2B2C8, and 67D24D37,

a parallel correlator for correlating said preamble, said parallel correlator outputting a synchronizing signal,

a serial correlator clock responsive to said synchronizing signal,

a plurality of serial correlators responsive to said serial correlator clock, each of said serial correlators programmed to respond to a different one of said symbol codes, and each of said serial correlators generating a correlation signal upon matching said spread spectrum signal to a predetermined degree with said one symbol code, and

means connected to said serial correlators for generating a data stream.

8. A method for communication comprising the steps of:

receiving a spread spectrum signal from a transmitter, said spread spectrum signal comprising a preamble portion and a non-preamble portion, said non-preamble portion comprising a series of symbol codes,

non-coherently correlating said preamble portion and generating a preamble correlation signal thereby,

establishing a series of symbol code periods using said preamble correlation signal as a reference,

for each symbol code period, and in the presence of an arbitrary difference between a clock of said transmitter and a receiver chip clock, simultaneously correlating said non-preamble portion for each symbol code using non-coherent serial correlation and generating a plurality of serial correlation signals thereby, and

detecting the largest of said serial correlation signals for each symbol code period and generating a data signal in response thereto.

9. The method of claim 8, wherein a frequency difference between the clock of said transmitter and said receiver chip clock is less than 1/4 of a symbol code rate corresponding to the symbol code period.

10. The method of claim 8, wherein said step of receiving said spread spectrum signal from said transmitter comprises the step of receiving said spread spectrum signal at a mobile handset.

11. An apparatus comprising

a demodulator connected to an input signal,

a plurality of correlators connected to the output of said demodulator, each correlator configured to detect a different one of a plurality of symbol codes,

a plurality of correlation signals, one correlation signal output from each of said plurality of correlators, and

a selector connected to each of said plurality of correlation signals, whereby one of said correlation signals is selected in each symbol code period,

wherein said symbol codes are drawn from the following group of hexadecimal codes:

0544D65E, 0E4424A1, 5B118E0B, 5B1171F4, 3D77E66D, 3D771792, 6822BD36, 682242C7, 014BD451, 014B2BAE, 541E8104, 541E7EFB, 3278E762, 3278189D, 672DB237, 672D4DC8, 0EBBDBA1, 0EBB245E, 5BEE8EF4, 5BEE710B, 3D88E892, 3D86176D, 68DDBDC7, 68DD4238, 01B4D4AE, 01B42B51, 54E181FB, 54E17ED4, 3287E79D, 32671862, 67D2B2C8, and 67D24D37.

12. The apparatus of claim 11 wherein said plurality of correlators are serial, non-coherent correlators.

13. The apparatus of claim 12 wherein each of said correlators separately correlates for a real I signal portion, a real Q signal portion, an imaginary I signal portion, and an imaginary Q signal portion, and combines the separate correlation signals generated thereby into a unified correlation signal.

14. The apparatus of claim 11 wherein said selector comprises a best-of-M device.

15. The apparatus of claim 11 further comprising a preamble matched filter configured to detect a preamble distinct from said symbol codes, said preamble matched filter connected to a non-coherent clock.

16. A method for communication comprising the steps of:

receiving a spread spectrum signal, said spread spectrum signal comprising a preamble portion and a non-preamble portion, said non-preamble portion comprising a series of symbol codes selected from the following hexadecimal codes;

0544D65E, 0E4424A1, 5B118E0B, 5B1171F4, 3D77E66D, 3D771792, 6822BD36, 682242C7, 014BD451, 014B2BAE, 541E8104, 541E7EFB, 3278E762, 3278189D, 672DB237, 672D4DC8, 0EBBDBA1, 0EBB245E, 5BEE8EF4, 5BEE710B, 3D88E892, 3D86176D, 68DDBDC7, 68DD4238, 01B4D4AE, 01B42B51, 54E181FB, 54E17ED4, 3287E79D, 32671862, 67D2B2C8, and 67D24D37.,

non-coherently correlating said preamble portion and generating a preamble correlation signal thereby,

synchronizing a receiver clock to said preamble correlation signal,

establishing a series of symbol code periods using said receiver clock as a reference,

for each symbol code period, simultaneously correlating said non-preamble portion for each symbol code using serial correlation and generating a plurality of serial correlation signals thereby, and

detecting the largest of said serial correlation signals for each symbol code period and generating a data signal in response thereto.

17. A method for communication, comprising the steps of:

receiving at a receiver, a signal sent from a transmitter, said signal comprising a preamble and a data message in a spread spectrum format,

synchronizing said receiver, using said preamble to obtain a series of integration periods for serial correlation,

serially correlating said data message over each integration period simultaneously for a plurality of spread spectrum codes, without deriving further timing information from said signal for synchronizing a receiver chip clock to a clock of said transmitter, and generating a plurality of correlation signals thereby, and

generating a data signal in response to a maximum one of said correlation signals each integration period.