Technique for generating sets of binary spreading-code sequences for a high data-rate spread-spectrum network

• US 5,452,328 A
• Filed: 07/30/1993
• Issued: 09/19/1995
• Est. Priority Date: 09/27/1991
• Status: Expired due to Term

• Current Assignee: CommWorks Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Lockheed Missiles and Space Co Inc (Martin Marietta Corporation)
• Inventors: Rice, Bart F.
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US08/100,334
• Time in Patent Office: 781 Days
• Field of Search: 364/717, 380/46, 380/50, 375/201-210
• US Class Current: 375/142
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04J 13/0074 Code shifting or hopping
• CPC Class Codes: H04J 13/0077 Multicode, e.g. multiple codes assigned to one user
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04J 13/102 Combining codes
• CPC Class Codes: H04J 13/16 Code allocation

Abstract

A method and apparatus for electrically generating sets of binary spreading-code sequences for use in a multi-node communication network are disclosed. A method for assigning disjoint sets of binary spreading-code sequences to different nodes of such a network is also disclosed. Each set of binary spreading-code sequences consists of multiple sequences, which are generated using two binary shift registers. The sequences can be generated simultaneously, or sequence segments can be generated sequentially. To generate sequences simultaneously, the contents of multiple pairs of stages of two linear-feedback binary shift registers are combined by modulo-2 addition, where each pair of stages consists of one stage from each of the two binary shift registers. To generate sequence segments sequentially, the contents of a single stage of a first binary shift register are combined by modulo-2 addition with the contents of a single stage of a second binary shift register, where new fills are switched into each of the registers at the beginning of each period. To assign disjoint sets of binary spreading-code sequences to different nodes of the network, the initial fill of the first binary shift register is fixed and different initial fills are specified for the second binary shift register.

Claims

1. A method for electrically generating a set of binary spreading-code sequences for use in transmitting information in a multi-node communication network, said set of binary spreading-code sequences consisting of more than one binary spreading-code sequence, said method comprising the steps of simultaneously:

a) combining contents of a single stage of a first multi-stage binary shift register with contents of each stage of a plurality of stages of a second multi-stage binary shift register, the contents of each stage of each of said first and second binary shift registers having a period of (2"-1), where n is a fixed integer having the same value for each of said first and second binary shift registers, the contents of said stages of said first and second binary shift registers being combined by modulo-2 addition to produce a first subset of combined spreading-code sequences, and

b) combining contents of a single stage of said second binary shift register with contents of each stage of a plurality of stages of said first binary shift register by modulo-2 addition to produce a second subset of combined spreading-code sequences,

said first and second subsets of combined spreading-code sequences having cross-correlation properties as follows;

(i) a cross-correlation between any two of said combined binary spreading-code sequences over any contiguous (2ⁿ -1) bits has a magnitude

space="preserve" listing-type="equation">≦

(2.sup.[n+1)/2] +1),

where [(n+1)/2] denotes the greatest integer ≦

(n+1)/2; and

(ii) a cross-correlation at zero offset between any two of said combined binary spreading-code sequences in either one of said first and second subsets has a magnitude equal to 1.

2. A method for electrically generating a set of binary spreading-code sequences for use in transmitting information in a multi-node communication network, said set of binary spreading-code sequences consisting of more than one binary spreading-code sequence, said method comprising:

a) specifying a switching interval consisting of a fixed number of steps for each of a first multi-stage binary shift register and a second multi-stage binary shift register, contents of each stage of each of said first and second binary shift registers having a period of (2ⁿ -1), where n is an integer having the same value for each of said first and second binary shift registers;

b) inserting contents into each stage of said first and second multi-stage binary shift registers once per said switching interval; and

c) combining the contents of a single stage of said first binary shift register with the contents of a single stage of said second binary shift register by modulo-2 addition at each step of said first and second binary shift registers to produce binary spreading-code sequences such that any two of said binary spreading-code sequences have cross-correlation properties as follows;

(i) a cross-correlation between any two of said binary spreading-code sequences over any contiguous (2ⁿ -1) bits has a magnitude

space="preserve" listing-type="equation">≦

(2.sup.[(n+1)/2 +1),

where [(n+1)/2] denotes the greatest integer ≦

(n+1)/2;

(ii) a cross-correlation at zero offset over any contiguous (2ⁿ -1) bits between any two of said binary spreading-code sequences for which the initial contents of said first binary shift register are identical has a magnitude equal to 1; and

(iii) a cross-correlation at zero offset over any contiguous (2ⁿ -1) bits between any two of said binary spreading-code sequences for which the initial contents of said second binary shift register are identical has a magnitude equal to 1.

3. The method of claim 2 wherein said specified switching interval has a length equal to an integral multiple of said period.

4. A method for assigning disjoint sets of binary spreading-code sequences to corresponding nodes of a multi-node digital communication network, each of said binary spreading-code sequences being a modulo-2 addition of a first maximal length linear recursive sequence and a second maximal length linear recursive sequence, each of said first and second maximal length linear recursive sequences having a period of (2ⁿ -1), said first maximal length linear recursive sequence being generated by a first primitive polynomial of degree n, said second maximal length linear recursive sequence being generated by a second primitive polynomial also of degree n, said method comprising:

a) specifying an initial fill for a first multi-stage binary shift register, contents of each stage of said first binary shift register having a period of (2ⁿ -1), where n is an integer, said first binary shift register being driven by said first primitive polynomial;

b) specifying a first plurality of distinct initial fills for a second multi-stage binary shift register, contents of each stage of said second binary shift register also having a period of (2ⁿ -1), where n is an integer that is the same for each of said first and second binary shift registers, said second binary shift register being driven by said second primitive polynomial, said first plurality of initial fills for said second binary shift register being identified with a first node of said network; and

c) specifying a second plurality of distinct initial fills for said second binary shift register, each initial fill of said second plurality of initial fills for said second binary shift register being different from any initial fill of said first plurality of initial fills for said second binary shift register, said second plurality of initial fills for said second binary shift register being identified with a second node of said network.

5. A method for electrically generating a plurality of disjoint sets of binary spreading-code sequences for use in a multi-node communication network, each of said disjoint sets consisting of more than one binary spreading-code sequence, individual binary spreading-code sequences of each set being generated by combining contents of specified stages of a first multi-stage binary shift register with contents of specified stages of a second multi-stage binary shift register, contents of each stage of each of said first and second binary shift registers having a period of (2ⁿ -1), where n is an integer having the same value for each of said first and second binary shift registers, said method for generating said plurality of disjoint sets comprising:

a) selecting a non-zero first initial fill for said second binary shift register, said first initial fill for said second binary shift register being identified with a first node of said network;

b) stepping said second binary shift register to produce a second initial fill for said second binary shift register, said second initial fill for said second binary shift register also being identified with said first node of said network;

c) selecting a non-zero first initial fill for said second binary shift register that is identified with a second node of said network, said first initial fill that is identified with said second node of said network being different from any initial fill for said second binary shift register that is identified with said first node of said network; and

d) stepping said second binary shift register as many times as necessary to a maximum of (2ⁿ -1) times to produce a second initial fill for said second binary shift register that is identified with said second node of said network, said second initial fill for said second binary shift register that is identified with said second node of said network being different from any second initial fill for said second binary shift register that is identified with said first node of said network.

6. The method of claim 5 wherein said first initial fill for said second binary shift;

register that is identified with said second node of said network is obtained by stepping said

second binary shift register when the fill for said second binary shift register is one of said initial fills for said second binary shift register identified with said first node of said network.

7. An apparatus for generating a set of binary spreading-code sequences for use in transmitting information in a multi-node communication network, said set of binary spreading-code sequences consisting of more than one binary spreading-code sequence, said apparatus comprising:

a) a first multi-stage binary shift register;

b) a second multi-stage binary shift register; and

c) means for simultaneously;

(i) combining contents of a single stage of said first binary shift register with contents of each stage of a plurality of stages of said second binary shift register by modulo-2 addition, the contents of each stage of each of said first and second binary shift registers having a period of (2ⁿ -1), where n is a fixed integer having the same value for each of said first and second binary shift registers, so as to produce a first subset of combined spreading-code sequences; and

(ii) combining contents of a single stage of said second binary shift register with contents of each stage of a plurality of stages of said first binary shift register by modulo-2 addition to produce a second subset of combined spreading-code sequences;

said first and second subsets of combined spreading-code sequences having cross-correlation properties as follows;

(A) a cross-correlation between any two of said binary spreading-code sequences over any contiguous (2^n-

     1) bits has a magnitude

space="preserve" listing-type="equation">≦

(2.sup.[(n+1/2] +1)

where [(n+1)/2] denotes the greatest integer ≦

(n+1)/2; and

(B) a cross-correlation at zero offset between any two of said binary spreading-code sequences in either one of said first and second subsets has a magnitude equal to 1.

8. An apparatus for electrically generating a set of binary spreading-code sequences for use in transmitting information in a multi-node communication network, said set of binary spreading-code sequences consisting of more than one binary spreading-code sequence, said apparatus comprising:

a) means for specifying a switching interval consisting of fixed number of steps for each of a first multi-stage binary shift register, contents of each stage of each of said first and second binary shift registers having a period of (2ⁿ -1), where n is an integer having the same value for each of said first and second binary shift registers;

b) means for inserting contents into each stage of said first and second binary shift registers once per said switching interval; and

(c) means for combining the contents of a single stage of said first binary shift register with the contents of a single stage of said second binary shift register by modulo-2 addition at each step of said first and second binary shift registers to produce binary spreading-code sequences such that any two of said binary spreading-code sequences have cross-correlation properties as follows;

(i) a cross-correlation between any two of said binary spreading-code sequences over any contiguous (2ⁿ -1) bits has a magnitude

space="preserve" listing-type="equation">≦

(2.sup.[(n+1)/2] +1).

where [(n+1)/2] denotes the greatest integer ≦

(n+1)/2;

(ii) a cross-correlation at zero offset over any contiguous (2ⁿ -1) bits between any two of said binary spreading-code sequences for which the initial contents of said first binary shift register are identical has a magnitude equal to 1; and

(iii) a cross-correlation at zero offset over any contiguous (2ⁿ -1) bits between any two of said binary spreading-code sequences for which the initial contents of said second binary shift register are identical has a magnitude equal to 1.

9. An apparatus for electrically generating a plurality of disjoint sets of binary .spreading-code sequences for use in transmitting information in a multi-node communication network, each of said disjoint sets consisting of more than one binary spreading-code sequence, individual binary spreading-code sequences of each set being generated by combining contents of specified stages of a first multi-stage binary shift register with contents of specified stages of a second multi-stage binary shift register, contents of each stage of each of said first and second binary shift registers having a period of (2ⁿ -1), where n is a fixed integer having the same value for each of said first and second binary shift registers, said apparatus comprising:

a) means for inserting a non-zero first initial fill into said second binary shift register corresponding to a first node of said network;

b) means for stepping said second binary shift register to produce a second initial fill for said second binary shift register corresponding to said first node of said network;

d) means for inserting a non-zero first initial fill into said second binary shift register corresponding to said second node of said network, said first initial fill corresponding to said second node of said network being different from any initial fill corresponding to said first node of said network; and

e) means for stepping said second binary shift register as many times as necessary to a maximum of (2ⁿ -1) times to produce a second initial fill for said second binary shift register corresponding to said second node of said network that is different from said second initial fill for said second binary shift register corresponding to said first node of said network.

10. The apparatus of claim 9 wherein said specified switching interval has a length equal to an integral multiple of said period.