Anti-jam communications system

• US 4,231,113 A
• Filed: 03/11/1968
• Issued: 10/28/1980
• Est. Priority Date: 03/11/1968
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Blasbalg, Herman L.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US04/713,564
• Time in Patent Office: 4,614 Days
• Field of Search: 325/32, 325/34, 178/22, 179/1.5 R, 179/1.5 FS
• US Class Current: 380/34
• CPC Class Codes: H04K 1/003 by varying carrier frequency at or within predetermined or random intervals H04K1/04 takes precedence

Abstract

Binary information signals which are to be transmitted are combined with a pseudo-random signal wave form such as a pseudo-random sequence of binary bits. Each binary message element, whether a binary "1" or a binary "0", alters successive portions of the pseudo-random binary sequence to thereby create a modified pseudo-random binary bit sequence, successive portions of which represent the binary information. The successive portions of the modified pseudo-random binary sequence are converted to an analog quantity which will be similarly varying in a pseudo-random manner.

Claims

1. In an anti-jam communications system wherein binary message signal representations are to be transmitted, the combination comprising:

a source for producing an oscillating electrical signal;

a source of binary message bits;

a source of pseudo-random signals for producing a pseudo-random sequence of bits, each bit 1/N the length of said binary message bit where N is greater than one;

a modulo-two adder responsive to said binary message bits and said pseudo-random sequence of bits for producing a pseudo-random sequence of bits modified by said binary message bits;

digital to analog conversion means responsive to said modified pseudo-random sequence of bits for producing a pseudo-randomly varying series of analog values; and

means responsive to said analog values for varying the oscillating electrical signal in accordance with said analog values.

2. In an anti-jam communication system wherein binary message signal representations are to be transmitted, the combination comprising:

a source of binary message signals;

transmitter means including,

a source for producing an oscillating electrical signal;

a first source of pseudo-random signals for producing a pseudo-random sequence of bits;

a modulo-two adder responsive to said sequence of bits and said binary message signal for producing a first sub-sequence of binary bits when said binary message signal is a binary "1," and for producing a second sub-sequence of binary bits when said binary message signal is a binary "0," whereby said adder produces pseudo-random sub-sequences for each binary message bit;

first digital to analog conversion means responsive to the sub-sequences produced by said adder means for converting the digital value thereof to an analog value, whereby, over the cource of a number of binary message bits, said conversion means produces a pseudo-randomly varying analog value; and

means responsive to said pseudo-randomly varying analog values for pseudo-randomly varying said oscillating electrical signal in accordance with said analog value to produce said binary message signal representation; and

receiver means including,

a second source of pseudo-random signals for producing a second pseudo-random sequence of binary bits, said second source being synchronized with said first pseudo-random source;

second digital to analog conversion means responsive to said second pseudo-random sequence of binary bits for generating the two analog values corresponding both to the digital value of a sub-sequence and the complement thereof; and

means responsive to said two analog values generated by said second digital to analog conversion means for detecting the transmitted binary message signal representations.

3. In an anti-jam communication system wherein binary message signal representations are to be transmitted, the combination comprising:

a source of binary message signals;

transmitter means including,

a source for producing an oscillating electrical signal;

a first source of pseudo-random signals for producing a pseudo-random sequence of bits;

a modulo-two adder responsive to said sequence of bits and said binary message signal for producing, for each message bit, either one of two sub-sequences according to their said message bit in a binary "1," or a binary "0," said two sub-sequences being complementary with respect to each other, whereby said modulo-two adder produces a different sub-sequence of a fixed number of bits for each message bit;

first digital to analog conversion means responsive to said sub-sequences for converting the digital value thereof to an analog value, whereby said conversion means produces a pseudo-randomly varying set of analog values; and

means responsive to said analog values for varying the oscillating electrical signal in accordance with said analog values to produce said binary message signal representations; and

receiver means including,

a second source of pseudo-random signals for producing a second pseudo-random sequence of bits, said second source being synchronized with said first source, whereby said second generates a pseudo-random sequence identical to that produced by said first source;

second digital to analog conversion means responsive to said second pseudo-random sequence of binary bits for generating the two analog values corresponding both to the digital value of a sub-sequence and the complement thereof; and

means responsive to said two analog values generated by said second digital to analog conversion means for detecting the transmitted binary message signal representations.

4. In an anti-jam communicating system wherein binary message signal representations are to be transmitted, the combination comprising:

means for transmitting a pseudo-randomly varying information signal;

receiver means for receiving said information signal, said receiver means including,

a source of pseudo-random signals for producing a pseudo-random sequence of bits;

digital to analog conversion means responsive to said pseudo-random sequence of bits for simultaneously generating the corresponding analog values of the actual and complemented value of successive pseudo-random subsequences, whereby said conversion means generates two series of complementarily varying analog values; and

means responsive to said two series of analog values for detecting said pseudo-randomly varying information signal.

5. An anti-jam communication system in which binary message signal representations are to be transmitted to a receiver, the combination comprising:

a source of binary message signals;

transmitter means including,

a source for producing an oscillating electrical signal;

a first source of pseudo-random signals for producing a pseudo-random sequence of bits;

mod-2 addition means responsive to said message signals and said sequence of bits for producing a sequence of bits complementary to the sequence produced by said source when said binary message contains a binary "1," and, for producing a sequence of bits identical to the sequence produced by said source when said binary message contains a binary "0," whereby said means produces a pattern of sub-sequences with each sub-sequence corresponding either to the unaltered or the complemented version of the corresponding portion of the pseudo-random sequence produced by said source;

first digital to analog conversion means responsive to said sub-sequences of bits for converting the value thereof to a corresponding analog value, whereby said conversion means produces a pseudo-random pattern of analog values;

means responsive to said analog values for varying the oscillating electrical signal in accordance with said analog values, said means including means for shifting the frequency spectrum of said oscillating electrical signal in accordance with said pattern of analog values, whereby the position in the spectrum occupied by said oscillating electrical signal changes for each bit of the message signal to produce said binary message signal representations; and

receiver means including,

a second source of pseudo-random signals for producing a second pseudo-random sequence of bits, said second source being synchronized with said first source, whereby said first and said second sources produce synchronized and identical pseudo-random binary sequences;

second digital to analog conversion means responsive to the pseudo-random binary sequence produced by said second source for producing the corresponding analog value of both a sub-sequence and the complement thereof, whereby said second conversion means produces two pseudo-random patterns of analog values; and

means responsive to said two pseudo-random patterns of analog values for detecting said binary message signal representations, said means including a first detection means responsive to one of said two pseudo-random patterns for sensing signals present in a first portion of the frequency spectrum, and a second detection means responsive to the other of said two pseudo-random patterns for sensing signals present in a second portion of the frequency spectrum.

6. Apparatus according to claim 5 wherein said detection means each include at least one voltage controlled oscillator.

7. Apparatus according to claim 5 wherein said transmitter means includes buffer storage means interposed between said mod-2 addition means and said first digital to analog conversion means, and said receiver means includes buffer storage means interposed between said second source and said second digital to analog conversion means.

8. Apparatus according to claim 5 wherein said receiver means further include:

means for comparing the relative magnitude of signals sensed in said first and said second portions of the frequency spectrum of the transmission channel, whereby said comparison means indicates the reception of a binary "1" or "0" according to whether said first or said second portion contained the larger signal.

9. An anti-jam communication system in which binary message signal representations are to be transmitted to a receiver, the combination comprising:

a source of binary message signals;

transmitter means, including,

a first source of pseudo-random signals for producing a first pseudo-random sequence of bits;

means responsive to said message signals and said sequence of bits for producing a sequence of bits complementary to the sequence produced by said source when said binary message contains a binary "1", and, for producing a sequence of bits identical to the sequence produced by said source when said binary message contains a binary "0", whereby said means produces a pattern of sub-sequences with each sub-sequence corresponding either to the unaltered or the complemented version of the corresponding portion of the pseudo-random sequence produced by said first source;

first digital to analog conversion means responsive to said sub-sequences of bits for converting the value thereof to a corresponding analog value, whereby said conversion means produces a pseudo-random pattern of analog values;

means responsive to said analog values for varying the transmitted signal representations in accordance with said analog values, said means including means for shifting the time position of said transmitted signal representations in accordance with said pattern of analog values, whereby the respective time positions occupied by said transmitted signal representations changes for each bit of the message signal; and

receiver means including,

a second source of pseudo-random signals for producing a second pseudo-random sequence of binary bits, said second source being synchronized with said first source, whereby said first and second sources produce synchronized and identical pseudo-random binary sequences;

second digital to analog conversion means responsive to said second pseudo-random sequence for producing the corresponding analog values of both a sub-sequence and the complement thereof, whereby said second conversion means produces two pseudo-random patterns of analog values; and

means responsive to said two pseudo-random patterns of analog values for detecting said transmitted signal representations, said means including a first detection means responsive to one of said two pseudo-random patterns for sensing signals present in a first time position, and a second detection means resposive to the other of said two pseudo-random patterns for sensing signals present in the other of said two time positions.

10. Apparatus according to claim 9 wherein said shifting means include a pulse position modulator.

11. Apparatus according to claim 9 wherein said transmitter means includes buffer storage means interposed between said modulo means and said digital to analog conversion means, and said receiver means include buffer storage means interposed between said second source and said second digital to analog conversion means.

12. Apparatus according to claim 9 wherein said receiver means further include comparison means responsive to the signals detected by said first and said second detection means for indicating which of said two time positions contained the larger signal.

13. An anti-jam communication system in which binary message signal representations are to be transmitted to a receiver, the combination comprising:

a source of binary message signal representations;

transmitter means including,

a first source of pseudo-random signals for producing a first pseudo-random sequence of bits;

means responsive to said message signals and said sequence of bits for producing a sequence of bits complementary to the sequence produced by said source when said binary message contains a binary "1", and, for producing a sequence of bits identical to the sequence produced by said source when said binary message contains a binary "0", whereby said modulo means produces a pattern of sub-sequences with each sub-sequence corresponding either to the ulaltered or the complemented version of the corresponding portion of the pseudo-random sequence produced by said source;

first and second digital to analog conversion means each responsive to a different predetermined portion of consecutive sub-sequences of said sequence for converting the digital value thereof to a corresponding analog value, whereby said first and said second digital to analog conversion means each produce a pseudo-random pattern of analog values;

means responsive to said analog values for varying the transmitted signal representations in accordance with said pseudo-random analog values, said means including first means for varying the time position of the transmitted signal representations in response to the analog values produced by said first conversion means, and second means for shifting the frequency spectrum of said transmitted signal representations in response to the analog values produced by said second conversion means, whereby both the time and the frequency position of said transmitted signal representations is caused to be different for the transmission of each message bit; and

receiver means including,

a second source of pseudo-random signals for producing a second pseudo-random sequence of bits, said second source being synchronized with said first source whereby said first and said second sources produce synchronized and identical pseudo-random binary sequences;

third and fourth digital to analog conversion means each responsive to portions of successive sub-sequences of said second pseudo-random sequence thereof for each producing two pseudo-random patterns of analog values, one for a sub-sequence and one for the complement thereof; and

means responsive to said pseudo-random patterns of analog values for detecting said transmitted signal representations, said means including first means responsive to the analog values produced by said third conversion means for sensing signals present in the two portions of the frequency spectrum specified by said analog values, and including second means responsive to the two analog values produced by said fourth conversion means for sensing signals present in the two time positions specified by said two analog values.

14. Apparatus according to claim 13 wherein said transmitter means include buffer storage means interposed between said modulo means and said first and second to analog conversion means and wherein said receiver means include buffer storage means interposed between said second source of pseudo-random bits and said third and fourth digital to analog conversion means.

15. Apparatus according to claim 13 wherein the first means included in said receiver means comprise first and second voltage controlled oscillators.

16. Apparatus according to claim 13 wherein the second means included in said receiver means comprise first and second pulse position modulators.

17. Apparatus according to claim 16 wherein said receiver means further includes:

first and second voltage controlled oscillators included within said first means;

a first and second receiver channel, each responsive to one of said voltage controlled oscillators and one of said pulse positioned modulators, with each channel including frequency mixing means for tuning the receiver to a predetermined portion of the frequency spectrum and also including gating means for rendering said receiver means capable of detecting signals during one of a predetermined number of time periods; and

comparing means connected to both of said channels for determining which of said two channels contained the larger signal.

18. A method for transmitting binary data in the form of transmitted electrical signals comprising the steps of:

generating a pseudo-random binary sequence composed of bits each bit 1/N the length of a binary message bit where N is greater than one;

modulating said pseudo-random sequence with binary message bits; and

successively controlling at least one parameter of the transmitted signals in response to the analog values of successive portions of said modulated pseudo-random sequence.

19. In a communication system in which the transmitted signal is adapted to be placed within an F-T checkerboard matrix, the method of causing pseudo-random variations of the locatin of said transmitted signal within said matrix, comprising the steps of:

producing a pseudo-random sequence of binary bits, each of said bits 1/N the length of a binary message bit where N is greater than one;

modulo-2 adding to successive portions of said sequence the value of successive binary message bits;

converting successive portions of said binary message sequence to which said binary message bits have been added into successive analog values; and

controlling the successive values of at least one of the parameters of said transmitted signal in response to said successive analog values.

20. A method according to claim 19 wherein the frequency of the transmitted signal is successively varied in response to said successive analog values.

21. A method according to claim 19 wherein the time position of the transmitted signal is successively varied in response to said successive analog values.