Pulse or digital communications – Repeaters – Testing
Reexamination Certificate
1998-12-23
2002-06-18
Peeso, Thomas R. (Department: 2132)
Pulse or digital communications
Repeaters
Testing
C375S213000, C375S213000, C375S213000
Reexamination Certificate
active
06408019
ABSTRACT:
TECHNICAL FIELD
The present invention is generally related to the field of communications, and, more particularly, is related to a system and method for noise communication using noise modulation.
BACKGROUND OF THE INVENTION
In many circumstances regarding communications, it is desirable that the information transmitted from one point to the next be kept secret from outside parties. For example, in commercial communications, one may wish to communicate sensitive financial information without one's competitor being able to determine the information sent or to even be aware of the fact that a message was sent. As an alternative example, in military applications, one may wish to communicate without one's enemy being able to intercept and decode the message sent. In pursuit of a communications approach that would meet such demands, noise signaling has been pioneered. The concept of noise signaling has had a history that, much like the broader history of spread spectrum communications of which it is a part, has been superbly documented in, for example, Simon M. K., Omura J. K., Scholtz R. A., and Levitt B. K.,
Spread Spectrum Communications,
Vol. 1, Chapter 2, Computer Science Press, 1985.
Much of the earlier efforts in noise communications centered on the problem of generating the “randomness” that would be used to disguise, mask or scramble a transmitted communication signal. This same randomness would have to be faithfully reproduced at the receiving end of the communication link in order to achieve the complementary goal of revealing, unmasking or unscrambling the received signal for the intended listener. Historically, the process of randomization has taken many forms. In addition to the familiar pseudo-random sequences used in Direct Sequence Spread Spectrum (DSSS), frequency hopping, and time hopping, inventors have exploited less familiar techniques aspiring to communication security. There are a number of approaches, for example, that scramble temporal elements of the transmitted communication signal discussed in U.S. Pat. No. 3,824,467 issued to Charles, U.S. Pat. No. 3,978,288 issued to Bruckner, et al., and U.S. Pat. No. 3,921,151 issued to Guanella.
Historically, spread spectrum communications has made use of binary pseudorandom sequences. This initial focus was motivated by the need for simplicity in implementation and control. In those earlier years, the computational power and storage capabilities of small modern computers was unanticipated. The classic example of earlier attempts at noise communication is the famous noise wheel of DeRosa and Rogoff in U.S. Pat. Nos. 2,718,638 and 4,176,316 described at considerable length in Simon M. K., Omura J. K., Scholtz R. A., and Levitt B. K.,
Spread Spectrum Communications,
Vol. 1, Chapter 2, Computer Science Press, 1985. As one would expect from a mechanically rotating wheel, this device created a source of cyclically repetitive noise energy. To replicate randomness, Rogoff generated a radial plot of the middle digits of numbers randomly selected from the Manhattan phone directory. Later the plot was transferred to film and, once placed on the wheel, was rotated past a slot of light that intensity-modulated the light in accordance with the length of each radial slot. Information modulation was finally achieved through time-shift keying, i.e., switching between time wheels rotating at slightly different phase offsets. The system accomplished information transfer of approximately one bit per second over a distance of two hundred yards.
Another important contribution is that of Klund in U.S. Pat. No. 5,493,612. This invention uses two techniques to do the information modulation. The first can be thought of as M-ary Frequency Shift Keying (FSK) of the output from a single noise generator. It involves the transmitting of information by essentially changing the carrier frequency in accord with the data symbol by selecting from a very closely spaced set of M frequencies. Filter parameters are chosen so that bandpass filtering of the noise transmission forces the output spectrum to take on the same appearance in each case.
The second technique discussed in U.S. Pat. No. 5,493,612 includes a transmitter which uses a single carrier frequency and selects between noise generators to represent a particular data symbol. This transmitter makes use of analog waveforms which results in spectral splatter due to the discontinuities that occur when the information symbols are imposed on the noise, which this reference fails to discuss.
Another example that makes use of noise is the secret signaling system of Bitzer in U.S. Pat. No. 4,179,658 in which the basic information signal comprises a frequency modulated (FM) voice message. Through a balanced modulator the FM voice input is multiplied by an analog noise signal. Through a separate path the same noise signal is delayed then modulated onto the carrier. The two waveforms, the noise modulated FM voice and the delayed noise waveform (without information superimposed), are then linearly added, thus generating the transmitted signal. With the separate addition of an appropriate delay in the signal path at the receiver, one is able to obtain the reference noise waveform in the received transmission and, thus, demodulate the data. Schemes like this that include the reference noise waveform in the transmission are subject to intercept. In fact, the scheme just described has a very fundamental vulnerability; at just the right delay an interceptor will find that the received signal will correlate very strongly with a delayed version of itself. Additionally, it is not clear to what degree the slower variations of the information signal will affect the measurable statistics of the noise. Clearly, a very slow information signal would introduce a slow, most likely nonstationary, variation into the random noise.
Another secure communication approach is to randomize the transmitted signal by first sending it through a “random” filter. The device described in U.S. Pat. No. 4,393,276 issued to Steele, for example, scrambles the signal in the frequency domain by applying a mask to the Fourier transform of the signal. Because the mask parameters are shared with the receiver, the receiver is able to invert the mask at the other end of the communication link. Also, one signal processing scheme, for example, “randomizes” the power level to simulate fading (U.S. Pat. No. 4,658,436 to Hill) and thus gives the transmission a more natural appearance in the environment.
In contradistinction to the approaches made above, some systems directly radiate noise to mask the existence of an information-bearing signal. Motivated by the fact that directional antennas are subject to enemy sidelobe detection, we find in U.S. Pat. No. 4,397,034 to Cox, et al., for example, an omni antenna used to radiate noise into the sidelobes of a highly directional (one degree beamwidth) antenna. With the noise signal statistically related to the information transmission in order to aid in the masking, the goal of this scheme is to prevent the detection of the information transmission.
Although examples in the journal literature are sparse, the use of noise for communications has not been totally neglected by analysts. Bello, for example, has studied a communication system in which the information-bearing signal phase modulates a noise carrier. Bello, P. A., “Demodulation of a Phase-modulated Noise Carrier,”
IRE Transactions on Information Theory,
vol. IT-7, no. 1, pp. 19-27, January 1961. In this reference, the effect of additive Gaussian noise and linear filtering on the first-order statistics of the receiver output noise and some aspects of the output signal are presented along with some simplifications relative to modeling the distortion of the output signal.
Due for the most part to the state of technology of the time, the approaches described above suffer from a number of limitations. Of particular importance is the restrictive limit on availability of noise waveforms at both transmitter and receiver. This is seen, for e
Aaron Jeffrey A.
Pickering Leslie W.
Georgia Tech Research Corporation
Peeso Thomas R.
Thomas Kayden Horstemeyer & Risley LLP
LandOfFree
System and method for communication using noise does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for communication using noise, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for communication using noise will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2934874