Pulse or digital communications – Systems using alternating or pulsating current
Reexamination Certificate
1998-01-09
2001-04-03
Chin, Stephen (Department: 2734)
Pulse or digital communications
Systems using alternating or pulsating current
C375S227000, C375S377000
Reexamination Certificate
active
06212239
ABSTRACT:
DESCRIPTION
1. Field of the Invention
This invention generally relates to the field of symbol communication and, more particularly, to the field of symbol communication with an encoding scheme for a receiver to reconstruct symbols occurring during periods in which the received signal is too weak or corrupted by noise to be accurately detected.
2. Description of the Related Art
The ideal case in any communication system is for the receiver to detect and identify, with perfect and uninterrupted accuracy, the sequence of symbols sent out by the transmitter. However, as is well known in the prior art, this level of detection is not generally possible in an actual communication system due to, for example, channel fading and in-band noise. Conventional communication systems are therefore designed to only attain a selected performance level in terms of bit error rate. The available system architectures, design methodologies, and hardware selection criteria used by designers to achieve a workable communication system meeting a given bit error rate are well known and are thoroughly described in various treatises.
There are certain issues, though, which generally govern the design and performance of prior art communication systems. More particularly, the parameters that determine the bit error rate include the transmitter power, the channel bandwidth, the symbol or bit rate, the channel physical length, the channel quality, and the in-band noise power. The term “bit error rate”, as used above, means the error rate by the receiver on a bit-by-bit basis. As is well known in the art, transmitter power and channel bandwidth are generally fixed. Therefore, to attain a desired bit error rate at the required bit rate, the transmitted bit or symbol sequence is frequently encoded by any of the various well-known redundancy codes prior to transmission. This allows error detection and correction by the receiver.
However, these codes have known drawbacks. One of the drawbacks is that extra bits or symbols must be added to convey the redundancy information, and the extra bits use valuable channel capacity. Another drawback is that the encoding and decoding schemes are generally computationally intensive. Still another, particularly serious drawback is that channel fading, or path loss, often results in the loss of several bits in sequence. These are generally termed “block drop outs” and, as is known in the art, the number of bits in the lost block frequently exceeds the maximum number that the redundancy code can correct, or even detect. The prior art therefore generally employs interleaved coding schemes, in addition to the redundancy coding schemes. These methods, however, generally fail to provide complete immunity to the block drop outs and, in addition, further increase the computation and related hardware burden.
A previous patent disclosure by the present inventor proposes the use of a dynamically generated chaos signal for information transmission. As described therein, a dynamically generated signal is analog in nature but has a state progression which carries digital information. However, that previous disclosure does not provide a means or method for a receiver to correct or recover the transmitted signal during dropouts nor does it preview this idea.
SUMMARY OF THE INVENTION
The present invention is directed to solving the above-identified problems, and to providing further substantial advantages over the prior art methods and apparatus of signal dropout correction. A general embodiment of the invention comprises an apparatus and method for controlling chaotic oscillations of a transmitter-based physical oscillator in such a way that the resulting oscillator signal has a trajectory which carries a desired symbolic (digital) information, and for transmitting the oscillator signal, and for coupling a received version of the transmitter signal to a receiver-based chaotic oscillator which is substantially identical in its dynamical motion to the transmitter oscillator. If the received signal has, for even a very short time period, a signal-to-noise ratio greater than a certain threshold the receiver-based chaotic oscillator automatically and quickly synchronizes with the transmitter-based oscillator due to the coupling effect of the received signal. This allows the receiver described herein to continue generating the signal through dropouts even when the incoming signal may be completely absent.
According to known chaos theory the state trajectory of a chaotic oscillator is deterministic over infinite time. The method and apparatus of the present invention exploit this theory to transmit and recover symbol information by a fundamentally new approach. A basis of the invention is that if a signal is transmitted carrying information defining the state vector of a first chaotic oscillator with infinite precision, and sent through a noiseless channel, then a receiver having a-priori knowledge of, or a means to duplicate, the first chaotic oscillator's trajectory can predict the signal for all future time based only an instantaneous sample of the received signal. Further, if a first and a second region of a state space defining the first oscillator's trajectory are assigned respective first and second symbol values, then the receiver having the a-prior knowledge can predict the symbol sequence it will receive for infinite time given only one instantaneous point of the transmitted state signal with infinite precision.
In the practical world, though, the state information of the chaotic oscillator cannot be measured with infinite precision. Instead, the oscillator state, or point on its motion trajectory, can be determined only to the accuracy limit of the physical measuring unit, i.e., voltmeter or current meter, that is used. Therefore, an estimate or predictor of a first oscillator's future motion based on a duplicate or model of that oscillator, with the duplicate using an initial state equal to the (inaccurately) measured starting point at t=0, will start with an initial error and the error will progressively increase over time with respect to the first oscillator. However, the estimated future motion of the first oscillator based on the model or duplicate will be accurate within a known maximum error for a finite duration of time, with that duration being a function of the accuracy that the oscillator state information can be measured.
The present invention achieves this predictive receiver function with a receiver oscillator or model oscillator which when coupled with a signal from the transmitter representing the transmitter's state, for a duration sufficient to synchronize with that transmitter oscillator, will lock to and will remain synchronized with it for a determinable length of time, even after the transmitter signal is lost. The lock will be to a precision substantially matching the accuracy by which received transmitter signal represents the transmitter oscillator state. That accuracy depends on the particular hardware in the transmitter that detects its oscillator state, and on the integrity of the transmitter signal when received at the receiver oscillator. As will be understood from the detailed description below, the length of time that the receiver oscillator will remain synchronized to the transmitter oscillator depends on the accuracy of the lock at the time the transmitter signal is lost. The invention thereby uses the receiver oscillator as a predictor of the transmitter signal, for at least that determinable length of time.
Accordingly, the present invention is a fundamentally new method and apparatus for recovering an uninterrupted symbol stream at a receiver, notwithstanding limited periods in which the received signal is either too weak or corrupted for conventional carrier demodulation, or during periods in which the transmitter or the channel, or both, are temporarily shut off. This invention achieves these and other objectives without conventional error correction bits, and without the related mathematical operations generally required fo
Chin Stephen
Rupert Paul N
Stein, Esq. Laurence E.
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