Pulse or digital communications – Spread spectrum
Reexamination Certificate
1999-08-18
2001-10-30
Vo, Don N. (Department: 2631)
Pulse or digital communications
Spread spectrum
C375S239000, C329S313000, C332S112000
Reexamination Certificate
active
06310906
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns the field of communications. The present invention is especially useful in wireless communication systems and methods, but will provide additional privacy and reduced power consumption in systems using a wired communication medium as well. The description herein is directed to a preferred wireless medium communication systems and is applicable to optical communications using lasers, but artisans will appreciate the general applicability of the invention to be inclusive of wired communication systems and systems using other communication media as well.
BACKGROUND OF THE INVENTION
The modem trend is toward increased reliance on data communication. Data communication is an essential feature, for example, in commerce conducted over computer networks. Where sensitive information is communicated in personal or business transactions, privacy from interception of the information is an important aspect of the communication system relied upon for transmission of the information. This is especially true in wireless communication systems because the communication medium used by the wireless system, i.e., the atmosphere, is readily accessible by parties who are not intended recipients of the information. Wireless phone networks are another example of data communication systems in which privacy of communication is valued. Point-to-multipoint data systems, such as a cellular subscription television system, where a broadcast is provided to paid subscribers, are an additional example. Many other such systems which could benefit from increased privacy and from reduced power consumption will be apparent to artisans.
In particular, there is a growing concern over the privacy of wireless communication systems. Wireless systems place additional demands on the components of the systems. Personal communication devices, such as cell phones, and computers and personal organizers with wireless communication capability, form a primary component of the wireless systems. As the devices become smaller and lighter, there is a strong need to reduce power consumption as the available battery power life is reduced when smaller batteries are used. In addition, reduced power consumption is generally desirable even when battery life is maintained or increased because reduced power consumption leads to a longer period of device operation without replacement or recharging of the battery used for power. Particular applications which benefit greatly from reduced power consumption are military applications since many devices in military communication systems depend upon portable power sources. Military applications also have a particular need for privacy from both detection of communications and decoding of information transmitted during communications. Law enforcement applications also particularly benefit from such privacy.
Chaotic dynamical systems have been proposed to address the problem of communication privacy. Chaotic signals exhibit a broad continuous spectrum and have been studied in connection with spread spectrum applications. The irregular nature of a chaotic signal makes it difficult to intercept and decode. In many instances a chaotic signal will be indistinguishable from noise and interference to receivers not having knowledge of the chaotic signal used for transmission. An important development in the use of chaotic systems was the ability to synchronize coupled chaotic systems to produce identical chaotic oscillations. See,
Synchronization in Chaotic Systems
, L. M. Pecora and T. L. Carroll, Phys. Rev. Lett., 64:821-824, 1990
, A Simple Way to Synchronize Chaotic Systems with Applications to Secure Communication Systems, Int'l
J. of Bifurcation and Chaos, 3(6):1619-1627, 1993
, Synchronized Chaos in Electronic Circuits
, N. F. Rul'kov and A. R. Volkovskii, from
Chaos in Communications
, edited by Louis M. Pecora, pp. 132-140, SPIE—The International Society for Optical Engineering, Bellingham, Wash., 98227-0010, 1993, all three of which are incorporated by reference herein.
Various chaos based communication systems have been proposed. A difficulty with chaos based communications is their extreme sensitivity to phase distortions due to their nonlinear nature. Many of the prior art systems are therefore very sensitive to distortions, filtering and noise. The negative effect of filtering limits the ability of these types of systems to rely on filtering to improve performance, and makes them more susceptible to distortions that naturally occur in communication channels.
Accordingly, there is a need for an improved communication system. In particular, there is a need for an improved chaos based communication system which has reduced sensitivity to distortions and noise. It is an object of the invention to provide such an improved chaos based communication system and method.
It is a further object of the invention to provide such an improved communication system with a low power consumption for transmission and reception of data.
SUMMARY OF THE INVENTION
Those needs and objects are met by the present invention, which is a chaotic carrier pulse position modulation communication system and method. Filtering and noise concerns are eliminated by the use of chaotically timed pulse sequences instead of continuous chaotic waveforms. Each pulse has the same shape, but the time delay between pulses varies chaotically. Chaotically varying the spacing between pulses enhances spectral characteristics of the communication system by removing any periodicity from the transmitted signal. The chance of an unauthorized reception is reduced compared to non-chaotic carriers because chaotically positioned pulses are difficult to observe and detect by spectral and correlation methods. Even if a communication could be detected it is difficult to decode because synchronization requires an ability to reproduce the chaotic carrier pulse train. Data is encoded by selectively altering interpulse intervals in the carrier pulse train, and all information is therefore contained solely in the timing of pulses in the chaotic carrier pulse train. Any conventional data coding scheme can be used in addition to further increase privacy.
The system of the invention includes a transmitter and receiver having matched chaotic pulse regenerators. Driven by the received pulse train, the regenerator in the receiver produces a synchronized replica of a chaotic pulse train generated by the transmission chaotic pulse regenerator. The pulse train from the transmitter can therefore act as a carrier signal. The transmitter selectively alters interpulse timing between pulses in the chaotic pulse train. The selectively altered pulse train is transmitted as a pulse signal. The receiver uses a chaotic synchronization method which can synchronize to the transmission pulse regenerator using the pulse signal despite the modulation in the pulse signal. Accordingly, the receiver can detect whether a particular interpulse interval in the pulse signal has been altered based upon the synchronized replica it generates, and can therefore detect the data transmitted by the receiver.
Preferably, the receiver predicts the earliest moment in time when it can expect a next pulse after observation of a sample of the pulse signal including at least two consecutive pulses. Use of a sample may require transmission of some synchronization data to begin communication with a receiver. The receiver then decodes the pulse signal in a time window beginning at a short time before expected arrival of a pulse. The windowing process is repeated around the expected arrival of a next pulse and so on. This reduces the chance that the receiver will improperly decode noise or interference as data. In addition, it aids signal multiplexing by reducing the chance that the receiver will improperly decode data belonging to two or more data streams as belonging to a single data stream. The windowing operation provides the basis for a design of a multiplexer that permits a single user to detect the message intended for it from the sig
Abarbanel Henry D. I.
Larson Lawrence E.
Rulkov Nikolai F.
Sushchik Mikhail M.
Tsimring Lev S.
Greer Burns & Crain Ltd.
The Regents of the University of California
Vo Don N.
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