Preamble code structure and detection method and apparatus

• US 6,154,486 A
• Filed: 12/31/1998
• Issued: 11/28/2000
• Est. Priority Date: 06/05/1995
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Omnipoint Corp. (Deutsche Telekom AG)
• Inventors: Scott, Logan, Monroe, Robert
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): Corrielus, Jean B.
• Application Number:
  US09/224,481
• Time in Patent Office: 698 Days
• Field of Search: 375/200, 375/207, 375/206, 375/208, 375/343, 375/350, 375/209, 375/210, 375/356, 375/359, 375/366, 375/368, 375/219, 375/259, 370/515, 370/203, 370/208, 370/320, 370/335, 370/342, 370/347, 370/503, 370/507, 370/509, 370/511, 370/513, 370/516, 370/349, 370/474, 370/393, 370/471, 370/458, 455/422, 455/502
• US Class Current: 375/142
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 7/2681 Synchronisation of a mobile station with one base station
• CPC Class Codes: H04J 13/0022 PN, e.g. Kronecker
• CPC Class Codes: H04J 13/102 Combining codes
• CPC Class Codes: H04J 13/107 by concatenation
• CPC Class Codes: H04J 2013/0037 Multilevel codes
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04W 56/003 Arrangements to increase tolerance to errors in transmission or reception timing
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time
• CPC Class Codes: H04W 74/0891 for synchronized access
• CPC Class Codes: H04W 88/02 Terminal devices
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: H04W 92/10 between terminal device and access point, i.e. wireless air interface

Abstract

In a first embodiment of the invention, a concatenated preamble code is formed by a kronecker product between two subcodes of the same or different lengths. The subcodes have favorable correlation properties and may be Barker codes, minimum peak sidelobe codes, Gold codes, Kasami codes, Boztas codes, or other codes. At the receiver a two-stage processor is used to detect the concatenated preamble code. The two-stage processor comprises a series of two filters, one of which is preferably a mismatched filter. In another aspect of the invention, a repeated codeword preamble is formed from a series of the same repeated short subcode. The short subcode may be an augmented or truncated odd-length code. At the receiver a single matched filter is preferably used to generate a series of spikes separated by the period of the subcode. An alert/confirm detector non-coherently adds together individual correlation spikes and reject false alarms. The alert function measures total correlation energy and adjusts detection thresholds based thereon, while the confirm function ensures that the proper number of correlation spikes exceed a detection threshold at the correct times. The preamble codes and their means for detection are preferably employed in a TDMA spread spectrum communication system, wherein a plurality of user stations communicate with a base station, one in each time slot (or virtual time slot).

Claims

1. A method for communicating comprising the steps of:

transmitting a repeated codeword preamble code from a first station to a second station, said repeated codeword preamble code comprising a repeated series of the same subcode;

receiving said repeated codeword preamble code at said second station;

generating a plurality of correlation spikes in response to receiving said repeated codeword preamble code at said second station, each of said correlation spikes corresponding to a separate appearance of said subcode at said second station;

determining receipt of said repeated codeword preamble code upon simultaneous detection of more than one of said correlation spikes;

synchronizing a receiver at said second station in response to said repeated codeword preamble code;

transmitting a data message from said first station to said second station; and

receiving said data message at said second station.

2. The method of claim 1 wherein said step of receiving said repeated codeword preamble code at said second station comprises the step of detecting said repeated codeword preamble code by correlating to said subcode and generating a plurality of correlation spikes thereby, one correlation spike for each occurrence of said subcode in said repeated codeword preamble code.

3. The method of claim 2 wherein said step of detecting said repeated codeword preamble code comprises the steps of

detecting a predefined number of said plurality of correlation spikes, and

performing a verification of received data integrity of a data message following said repeated codeword preamble code.

4. The method of claim 2 wherein said step of correlating to said subcode comprises the step of inputting said repeated codeword preamble code to a matched filter configured to detect said subcode.

5. The method of claim 2 wherein said step of correlating to said subcode comprises the step of inputting said repeated codeword preamble code to a mismatched filter configured to detect said subcode.

6. The method of claim 1 wherein said subcode comprises a member of a code family selected from the group of code families consisting of:

Barker codes, Boztas codes, minimum peak sidelobe codes, Kasami codes, Gold codes, and Matsufuji codes.

7. The method of claim 1 wherein said subcode comprises a quadriphase code.

8. A method of communicating among a plurality of stations comprising the steps of:

selecting a first subcode and a second subcode having low cross-correlation properties;

generating a first repeated codeword preamble code from a repeated series of said first subcode, said first repeated codeword preamble code comprising a first single continuous code;

generating a second repeated codeword preamble code from a repeated series of said second subcode said second repeated codeword preamble code comprising a second single continuous code; and

communicating among the plurality of stations using said first repeated codeword preamble code and said second repeated codeword preamble code as preambles preceding data messages;

generating a first odd-length code;

modifying a length of said first odd-length code by one chip to form said first subcode,

generating a second odd-length code; and

modifying a length of said second odd-length code by one chip to form said second subcode.

9. The method of claim 8 wherein said step of communicating among a plurality of stations using said first repeated codeword preamble code and said second repeated codeword preamble code comprises the step of modulating said first repeated codeword preamble code and said second repeated codeword preamble code using an I and Q modulation format.

10. The method of claim 8 wherein said step of modifying a length of said first odd-length code by one chip comprises the step of truncating said first odd-length code by one chip to form said first subcode, and wherein said step of modifying a length of said second odd-length code by one chip comprises the step of truncating said second odd-length code by one chip to form said second subcode.

11. The method of claim 8 wherein said step of modifying a length of said first odd-length code by one chip comprises the step of adding one chip to said first odd-length code to form said first subcode, and wherein said step of modifying a length of said second odd-length code by one chip comprises the step of adding one chip to said second odd-length code to form said second subcode.

12. A communication system, comprising:

a first station, said first station comprising a transmitter for transmitting a preamble code and a data message, said preamble code comprising a kronecker product of a first subcode and a second subcode; and

a second station, said second station comprising a receiver for receiving said preamble code, synchronizing in response to said preamble code, and receiving said data message;

wherein said receiver of said second station comprises

a first correlator for correlating said preamble signal against said first subcode and generating a first correlation output signal in response thereto, said first correlation output signal comprising a first correlator correlation pulse corresponding to each occurrence of said first subcode or its inverse in said preamble code; and

a second correlator for correlating said first correlation output signal against said second subcode and generating a second correlation output signal in response thereto, said second correlation output signal comprising a second correlator correlation pulse when said preamble code is fully received.

13. A station for communication, comprising:

a receiver for receiving a repeated codeword preamble code and a data message, said repeated codeword preamble code comprising a repeated series of the same subcode;

a correlator for generating a plurality of correlation spikes in response to receiving said repeated codeword preamble code, each of said correlation spikes corresponding to a separate appearance of said subcode;

means for detecting receipt of said repeated codeword preamble code upon simultaneous detection of more than one of said correlation spikes; and

means for synchronizing the receiver in response to said repeated codeword preamble code.

14. The station for communication of claim 13, wherein said means for detecting receipt of said repeated codeword preamble code upon simultaneous detection of more than one of said correlation spikes comprises

an alert signal generator for generating an alert signal based on a maximum received correlation energy for said plurality of correlation spikes, and

a confirm signal generator for generating a confirm signal based on a minimum energy level of each of said plurality of correlation spikes.

15. The station for communication of claim 13, wherein said means for detecting receipt of said repeated codeword preamble code upon simultaneous detection of more than one of said correlation spikes detects a predefined number of said plurality of correlation spikes.

16. The station for communication of claim 13, further comprising means for performing a verification of received data integrity of said data message following said repeated codeword preamble code.

17. The station for communication of claim 13, wherein said correlator comprises a mismatched filter for receiving said repeated codeword preamble code, said mismatched filter configured to detect said subcode.

18. The station for communication of claim 13, wherein said subcode comprises a Gold code.

19. The station for communication of claim 13, wherein said subcode comprises a member of a code family selected from the group of code families consisting of:

Barker codes, Boztas codes, minimum peak sidelobe codes, and Kasami codes.

20. The station for communication of claim 13, wherein said subcode comprises a quadriphase code.

21. A communication system, comprising:

first station, said first station comprising a first transmitter for transmitting a first concatenated code generated from a kronecker product of a first subcode and a second subcode;

a second station, said second station comprising a second transmitter for transmitting a second concatenated code generated from a kronecker product of a third subcode and a fourth subcode, said second concatenated code having the same length as said first concatenated code;

a first receiver, said first receiver configured to receive said first concatenated code; and

a second receiver, said second receiver configured to receive said second concatenated code.

22. The communication system of claim 21, wherein said first subcode and said third subcode are both Barker codes.

23. The communication system of claim 21, wherein said first subcode and said third subcode comprise the same code.

24. The communication system of claim 21, wherein each of said first subcode and said second subcode have a cross-correlation of no more than -10 dB with respect to each of said third subcode and said fourth subcode.

25. A communication system, comprising:

a first station, said first station comprising a first transmitter for transmitting a first concatenated code generated from a kronecker product of a first subcode and a second subcode, said first subcode being an inner code in said kronecker product and said second subcode being an outer code in said kronecker product;

a second station, said second station comprising a second transmitter for transmitting a second concatenated code generated from a kronecker product of said first subcode and said second subcode, said first subcode being the outer code in said second kronecker product and said second subcode being the inner code in said second kronecker product, said second concatenated code having the same length as the first concatenated code;

a first receiver, said first receiver configured to detect said first concatenated code; and

a second receiver, said second receiver configured to detect said second concatenated code.

26. A communication system, comprising:

a first station, said first station comprising a first transmitter for transmitting a first concatenated code generated from a product of a first subcode and a first Barker code;

a second station, said second station comprising a second transmitter for transmitting a second concatenated code having the same length as said first concatenated code, said second concatenated code generated from a product of a second subcode and a second Barker code;

a first receiver, said first receiver configured to detect said first concatenated code; and

a second receiver, said second receiver configured to detect said second concatenated code.

27. The communication system of claim 26 wherein said first Barker code and said second Barker code comprise the same code.

28. The communication system of claim 26 wherein said first subcode and said second subcode have a cross-correlation of no more than -10 dB.

29. A communication system, comprising:

first station, said first station comprising a first transmitter for transmitting a first repeated codeword preamble code generated from a repeated series of a first subcode;

a second station, said second station comprising a second transmitter for transmitting a second repeated codeword preamble code generated from a repeated series of a second subcode, said second subcode having relatively low cross-correlation properties with respect to said first subcode;

a first receiver, said first receiver configured to detect said first repeated codeword preamble code; and

a second receiver, said second receiver configured to detect said second repeated codeword preamble code.

30. The communication system of claim 29, wherein said first subcode and said second subcode each comprises a quadriphase code.

31. The communication system of claim 30, wherein each quadriphase code comprises a Boztas code.

32. The communication system of claim 29, wherein said first subcode comprises a first odd-length code modified in length by one chip, and wherein said second subcode comprises a second odd-length code modified in length by one chip.

33. The communication system of claim 32, wherein said first transmitter and said second transmitter each comprise means for modulating said first repeated codeword preamble code and said second repeated codeword preamble code, respectively, using an I and Q modulation format.

34. A communication system, comprising:

first station, said first station comprising a first transmitter for transmitting a first preamble code and a first data message, said first preamble code generated from a series of a first subcode;

a second station, said second station comprising a second transmitter for transmitting a second preamble code and a second data message, said second preamble code generated from a series of a second subcode, wherein said second subcode has the same length as said first subcode and a low cross-correlation level with respect said first subcode, and wherein said first preamble code and said second preamble code have the same length;

a first receiver for receiving said first preamble code and said first data message, and for synchronizing to said first preamble code; and

a second receiver for receiving said second preamble code and said second data message, and for synchronizing to said second preamble.