Walsh function signal scrambler

• US 4,052,565 A
• Filed: 05/28/1975
• Issued: 10/04/1977
• Est. Priority Date: 05/28/1975
• Status: Expired due to Term

• Current Assignee: Martin Marietta Corporation
• Original Assignee: Martin Marietta Corporation
• Inventors: Baxter, Denmer Dix, Reeves, Charles Michael
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/581,695
• Time in Patent Office: 860 Days
• Field of Search: 178/22, 179/1.5 R, 179/15 BC, 235/152, 235/156
• US Class Current: 380/28
• CPC Class Codes: H04K 1/02 by adding a second signal to make the desired signal unintelligible

Abstract

A digital speech scrambler system allowing for the transmission of scrambled speech over a narrow bandwidth by sequency limiting the analog speech in a low-pass sequency filter and thereafter multiplying the sequency limited speech with periodically cycling sets of Walsh functions at the transmitter. At the receiver, the Walsh scrambled speech is unscrambled by multiplying it with the same Walsh functions previously used to scramble the speech. The unscrambling Walsh functions are synchronized to the received scrambled signal so that, at the receiver multiplier, the unscrambling Walsh signal is the same as and in phase with the Walsh function which multiplied the speech signal at the transmitter multiplier. Synchronization may be accomplished by time division multiplexing sync signals with the Walsh scrambled speech. The addition of the sync signals in this manner further masks the transmitted speech and thus helps to prevent unauthorized deciphering of the transmitted speech.

Claims

1. An information signal scrambler comprising:

a. means for sampling an analog information signal to develop a series of amplitude samples of the information signal,

b. means for generating a plurality of Walsh function signals

c. sequencer means for causing the said means for generating a plurality of Walsh function signals to periodically and cyclically change the generated Walsh function signal, and

d. means for multiplying the said samples with each of the generated Walsh function signals.

2. The information scrambler of claim 1 further including, means for generating sync signals and means for time division multiplexing a sync signal between every n samples of the Walsh function scrambled signal, said time division multiplexing means comprising means for sampling the Walsh function scrambled information at a rate (n + 1)/n times the repetition rate of the sampled information signals, to thereby produce a blank interval in the sample stream and means for transferring the sync signal to the sample stream during the blank interval.

3. The information scrambler of claim 2 wherein:

a. said means for sampling the information signal comprises an integrating amplifier means receiving the analog information signal, first electronic switching means for periodically transferring the integrated signal from said integrating amplifier to said amplitude sample storage means, second electronic switching means for removing the integrated signal from said integrating amplifier means after the integrated signal is transferred to said amplitude sample storage means; and

b. said means for multiplying the Walsh function signals with the stored samples comprises polarity inversion means including a summing amplifier and third electronic switching means responsive to the Walsh function signals for causing the samples to be applied to the inverting input of said summing amplifier whenever the Walsh function is at -1 value and for causing the samples to be applied to the non-inverting input of said summing amplifier whenever the Walsh function is at +1 value.

4. A method for providing privacy in analog electric information signal transmission systems comprising the steps of:

a. sequency limiting the information signals,

b. generating a plurality of first electrical signals having the characteristics of Walsh functions,

c. multiplying the plurality of Walsh function electrical signals with the sequency limited information signals to produce a Walsh scrambled, sequency limited information signal,

d. transmitting said Walsh scrambled, sequency limited information signal,

e. receiving the transmitted Walsh scrambled signal,

f. generating a plurality of second electrical signals having the identical Walsh function characteristics as the Walsh function electrical signals multiplying the information signal, and

g. multiplying the Walsh scrambled, sequency limited information signals with the second electrical signals to produce the sequency limited information signal.

5. The method of claim 4 further including the step of passing the sequency limited information signal through a low-passing frequency filter.

6. The method of claim 4 further including the steps of:

a. generating sync pulses,

b. modulating said sync pulses with sync code words identifying said first electrical signals having the characteristics of Walsh functions, and

c. time division multiplexing said modulated sync pulses with said Walsh scrambled, sequency limited information signal prior to transmission.

7. The method of clam 6 further including the steps of:

a. recovering the modulated sync pulses from the received Walsh scrambled information signal,

b. synchronizing the said second electrical signals to the received Walsh scrambled information signal with the use of said recovered, modulated sync pulses, and

c. demultiplexing the received, time division multiplexed, Walsh scrambled information signal with modulated sync pulses to recover the Walsh scrambled information signal.

8. An information signal scrambler comprising:

a. means for sampling an analog information signal to develop a series of amplitude samples of the information signal,

b. said means for sampling the information signal comprising an integrating amplifier means receiving the analog information signal, first electronic switching means for periodically transferring the integrated signal from said integrating amplifier to amplitude sample storage means, second electronic switching means for removing the integrated signal from said integrating amplifier means after the integrated signal is transferred to the amplitude sample storage means.

c. means for storing each amplitude sample for a time period substantially equal to the time interval between samples,

d. means for generating a plurality of Walsh function signals,

e. sequencer means for causing the said means for generating a plurality of Walsh function signals to periodically and cyclically change the generated Walsh function signals,

f. said sequencer means comprising N memory means each storing a code word representation for a particular Walsh function, each memory means including selectively enabled means for transferring its stored code word to said Walsh function signal generating means, and means for selectively enabling any one of said selectively enabled transfer means, said means for selectively enablng including means for periodically and cyclically enabling each of said selectively enabled transfer means,

g. said Walsh function signal generator means including binary counter means for generating electrical representations of inverted Walsh functions with indices 2ⁿ -1, logic means responsive to each of said code words stored in said N memory means for logically combining said electrical representations of said code words and electrical representations of inverted Walsh functions with indices 2ⁿ -1 to produce the particular Walsh function signal corresponding to the said code word applied to the logic means,

h. means for multiplying the stored samples with the Walsh function signal identified by the code word stored in the particular memory means whose transferring means has been enabled to provide Walsh scrambled signals,

i. said means for multiplying the Walsh function signals with the stored samples comprising polarity inversion means including a summing amplifier and third electronic switching means responsive to the Walsh function signal for causing the stored samples to be applied to the inverting input of said summing amplifier whenever the Walsh function signal is at -1 value and for causing the samples to be applied to the non-inverting input of said summing amplifier whenever the Walsh function signal is at +1 value.

j. means for generating sync signals and means for time division multiplexing a sync signal between every n samples of the Walsh function scrambled signal, said time division multiplexing means comprising means for sampling the Walsh function scrambled signal at a rate (n +

     1)/n times the repetition rate of the sampled signals, to thereby produce a blank interval in the sample stream and means for transferring the sync signal to the sample stream during the blank interval.

9. An information signal unscrambler for recovering information signals from Walsh function scrambled signals produced by multiplying the information signal by a plurality of different Walsh function signals, said scrambled signals being time division multiplexed with sync signals, comprising:

a. means for receiving Walsh function scrambled information signals, said means for receiving the Walsh function scrambled signals comprising integrating amplifier means and means for periodically sampling the integrated signal to thereby average the signal amplitude between sampling intervals and means for storing said averaged samples;

b. means for generating the Walsh functions used to produce the scrambled signals,

c. means for removing sync signals, time division multiplexed between n samples of the Walsh scrambled information signal samples, said sync signal removal means comprising sample and hold means receiving the sync signal multiplexed scrambled signal and means for generating sample pulses at a rate n/ (n+1) times the rate of the received scrambled information signal samples with sync signals,

d. means for multiplying the scrambled signal with the generated Walsh function signal said means for multiplying the scrambled signal with the unscrambler generated Walsh function signals comprising polarity inverter means, inverter by-pass means, and switch means responsive to the unscrambler generated Walsh function signals for causing the scrambled signal to pass through the inverter means when the value of the Walsh function signal is -1 and to pass through the by-pass means when the Walsh function signal value is +1.

10. A method for providing privacy in analog electric information signal transmission systems comprising the steps of:

a. sequency limiting the information signals,

b. selectively generating any of a plurality of first electrical signals each having the characteristic of a different Walsh function,

c. cyclically multiplying the sequency limited information signals with different Walsh function electrical signals to produce a sequency limited Walsh scrambled information signal,

d. generating sync pulses,

e. pulse amplitude modulating said sync pulses by a sync code word identifying the one of said first electrical signals multiplying said sequency limited information signal,

f. time division multiplexing said modulated sync pulses with said Walsh scrambled sequency limited speech prior to transmission,

g. transmitting said Walsh scrambed, sequency limited information signal,

h. receiving the transmitted Walsh scrambled signal,

i. recovering the modulated sync pulses from said received Walsh scrambled speech,

j. selectively generating any of a plurality of second electrical signals each having the Walsh function characteristics of one of first electrical signals,

k. synchronizing, in response to said recovered modulated sync pulses, the second electrical signals to the Walsh scrambled information signals so that the generated second electrical signal is the same as and in phase with the first electrical signal multiplying the sequency limited information signal, and

l. multiplying the Walsh scrambled information signal with the generated second electrical signal which is the same as and in phase with the first electrical signal multiplying the sequency limited information signal forming the Walsh scrambled speech.

11. In a system for providing privacy in information signal transmission system, transmitter means comprising:

means, responsive to an analog information signal, for sampling said analog information signal to develop a series of amplitude samples of said information signal,

means for generating different ones of a first plurality of Walsh function signals,

sequencer means including,

means for designating several of said plurality of Walsh function signals, said Walsh function signal generating means being responsive to said designator means to generate each of said designated Walsh function signals one at a time as commanded by said designator means, and means for controlling the order in which each of said several designated Walsh function signals are generated by said Walsh function signal generating means, and

means for multiplying the amplitude samples of the information signals by the Walsh function signals generated by said Walsh function signal generating means whereby different portions of said information signal after being converted into a pulse amplitude modulated signal are multiplied by different ones of selected Walsh function signals out of a plurality of Walsh function signals to produce Walsh scrambled signals.

12. The privacy system of claim 11 further including, means for generating a signal representative of the state of said order controlling means and sync code generator means responsive to said signal representative of the state of the order controlling means for generating a second pulse amplitude modulated signal indicative of the state of said order controlling means.

13. The privacy system of claim 12 further including means for interleaving the individual pulses of said second pulse amplitude modulated signal with the output of said multiplier means in a time division manner.

14. The privacy system of claim 13 wherein said designator means comprises a plurality of memory means equal in number to the several of said plurality of Walsh functions, each of said memory means storing a code word representing a particular Walsh function, each memory means including selectively enabled means for transferring its stored code word to said Walsh function signal generating means, said order controlling means comprising register means coupled to said selectively enabled means for periodically and cyclically enabling each of said selectively enabled transfer means.

15. In the privacy system of claim 14 further including, means operable on said designator means to change the selected ones of said plurality of Walsh function signals which can be generated by said Walsh function signal generator means and means operable on said order controlling means to alter the order in which the selected ones of said plurality of Walsh function signals are generated.

16. The privacy system of claim 15 wherein said Walsh function signal generator means comprises binary counter means for generating electrical representations of inverted Walsh functions with indices 2ⁿ -1, logic means responsive to each of said code words stored in said plurality of memory means for logically combining said electrical representations of said code words and electrical representations of inverted Walsh functions with indices 2ⁿ -1 to produce the particular Walsh function signal corresponding to the said code word applied to the logic means.

17. The privacy system of claim 11 further comprising means for receiving said Walsh function scrambled amplitude samples, said receiver means including:

means for generating a second plurality of Walsh function signals identical to said first plurality, sequencer means comprising;

means for designating several of said second plurality of Walsh function signals, said several Walsh functions being identical to the several designated Walsh function signals designated by said transmitter designator means, said receiver Walsh function signal generating means being responsive to said receiver designator means to generate each of said designated Walsh function signals one at a time,

means for controlling the order in which each of said several Walsh function signals are generated by said receiver Walsh function signal generating means, said receiver order controlling means operating to designate the several Walsh function signals at the receiver in the same order as they are designated at the transmitter, and

means for multiplying the Walsh scrambled samples with the Walsh function signals being generated.

18. The privacy system of claim 17 further including means operable on said receiver designator means to alter the selected ones of said plurality of Walsh function signals and means operable on said receiver order controlling means to alter the order in which the selected ones of said plurality of Walsh function signals are generated.

19. The privacy system of claim 18 further including means for generating signals representative of the state of the transmitter order controlling means and sync code generator means responsive to said signal representative of the state of the order controlling means for providing a second pulse amplitude modulating signal indicative of the state of the said order controlling means, and

means for interleaving the individual pulses of said second pulse amplitude modulated signal with the signal output from said multiplier means in a time division manner,

said receiver means further including means for extracting from the received signal the pulse amplitude modulated signals indicative of the state of the transmitter order controlling means and synchronization means responsive to said recovered second pulse amplitude modulated signal for synchronizing said receiver sequencer means to cause the Walsh function signal generated at the receiver to be in proper phase with the received Walsh scrambled samples when applied to said receiver multiplying means to thereby recover the amplitude samples of the analog information signal.