摘要:
A set of phases defining an `address` and a `spreading key` is selected. These are employed in determining a preamble waveform and a traffic waveform. The preamble carrier waveform is a sum of a set of tones each offset by its phase, whereas the traffic carrier waveform is the product of these same offset tones. The tones have frequencies which are geometrically increasing multiples of a fundamental frequency. The phases and magnitudes of the preamble and traffic carrier waveforms are determined and prestored in a transmit and receive unit storage device. An inverse discrete Fourier Transform unit (IDFT) in the transmit unit receives the phase preamble offsets and magnitudes from the storage unit and creates a preamble carrier signal transmitted to the receive unit which determines if the phases match those which it is to listen to. If not, the following message is ignored; if they are, the following message is despread and decoded. IDFT creates a traffic carrier waveform from the traffic phases and magnitudes. Binary information is encoded in the carrier, processed and transmitted to the receive unit. A discrete Fourier Transform unit converts the received signal into phases and magnitudes. A dot product unit determines a dot product of the phase and magnitudes of the received signal and the traffic carrier waveform over a number of frequencies. A decision unit determines a binary message from the dot product.
摘要:
The present invention provides a novel Geometric Harmonic Modulation (GHM) method. The GHM method functions in two modes, a preamble mode and a traffic mode. During the preamble mode, n+1 frequencies are each offset by a predetermined phase in a transmit unit and passed through a channel to a receive unit. The set of phases is used as the spreading code in the transmit unit, and also acts as an `address` of intended receive units. The receive unit monitors preamble signals to determine the phases. When it recognizes a set of phases, or `address`, which pertains to itself, the receive unit stores the phases and uses these phases to despread and decode the appended message. After the preamble mode is finished, the GHM modulator enters the traffic mode and requests the message to be transmitted from the message source. A traffic carrier waveform is created by multiplying tones, each having its specific phase. An analog or binary message is encoded by modulating the traffic carder waveform. The receive unit detects a preamble carrier and recovers the particular preamble phases to be used as the despreading `key`. The receive unit then employs the phases in despreading the received signal to recover the transmitted binary message.
摘要:
A traffic carrier waveform W.sub.n (.PHI.,R;t) being the product of a number of tones is employed in transmitting blocks of information from a transmit unit to a receive unit. The tones are geometrically increasing multiples of a frequency of a fundamental tone. Each tone incorporates a tone phase. The selection of these tone phases uniquely identifies each transmitted signal. The tone phases also is used as a `key` in converting a message signal into a direct wide spectrum signal for communication. To insure that third parties do not decode the transmitted message, the tone phases are transformed to seed phases by a method known to both the transmit and receive units, but not to third parties. The seed phases are then transmitted by intermittent preamble carrier waveform to the receive unit which transforms these into the tone phases and decodes the message signal. The seed phases may be dynamically changed according to a sequence known or generated by both the transmit unit and receive unit. In another embodiment, the tone phases may also be prestored in both the transmit and receive unit, and there is no need to calculate and transmit seed phases.
摘要:
The present invention provides a novel Geometric Harmonic Modulation (GHM) system. The GHM system operates in two modes, a preamble mode and a traffic mode. During the preamble mode, n+1 frequencies are each offset by a predetermined phase offset in the transmit unit and passed through a channel to a receive unit. The set of phase offsets is used as the spreading code in the transmit unit, and also acts as an `address` of receive units to transmit to. The receive unit monitors preamble signals to determine the phase offsets. When it recognizes a set of phase offsets, or `address`, which pertains to itself, the receive unit stores the phase offsets and uses these phase offsets to despread and decode the appended message. After the preamble mode is finished, the GHM modulator enters the traffic mode and requests the message to be transmitted from the message source. A traffic carrier waveform is created by multiplying tones, each having its specific phase offset. An analog or binary message is encoded by modulating the traffic carrier waveform. The receive unit detects a preamble carrier and recovers the particular preamble phase offsets to be used as the despreading `key`. The receive unit then employs the phase offsets in despreading the received signal to recover the transmitted message.
摘要:
The present invention provides a novel Geometric Harmonic Modulation (GHM) system. The GHM system operates in two modes, a preamble mode and a traffic mode. During the preamble mode, n+1 frequencies are each offset by a predetermined phase offset in a transmit unit and passed through a channel to a receive unit. The set of phase offsets is used as the spreading code in the transmit unit, and also acts as an `address` of receive units to transmit to. The receive unit monitors preamble signals to determine the phase offsets. When it recognizes a set of phase offsets, or `address`, which pertains to itself, the receive unit stores the phase offsets and uses these phase offsets to despread and decode the appended message. After the preamble mode is finished, the transmit unit enters the traffic mode and requests the message to be transmitted from the message source. A traffic carrier waveform is created by multiplying tones, each having its specific phase offset. Both analog or binary message are provided by a switching device in interleaved fashion to an appropriate modulator which encode the messages in the traffic carrier waveform. The receive unit detects a preamble carrier and recovers the particular preamble phase offsets to be used as the despreading `key`. The receive unit then senses then separates the binary from analog message signals and employs the phase offsets in despreading the received signal to recover the transmitted analog and binary messages in an interleaved fashion.
摘要:
A countermeasure to a partial-band follower jammer for frequency hopping spread spectrum communication systems employs an M-ary orthogonal frequency shift keyed (FSK) signaling system having q frequency channels available for hopping. During each signaling interval, the transmitter and receiver operate in either a conventional or unconventional mode. The conventional mode is selected by the transmitter and the receiver with a pseudorandom probability p.sub.c. In this mode, the transmitter transmits one of r tones within the corresponding hop (i.e., within one of q channels), and log.sub.2 r information bits are conveyed, while the receiver comprises a dehopper followed by noncoherent matched filters. The unconventional mode is selected with probability 1-p.sub.c. In this mode, the transmitter randomly chooses one of the r tones and transmits it in one of r channels within each hop, where the r channels are selected pseudorandomly. In the unconventional mode, log.sub.2 r information bits are transmitted and the receiver comprises a bank of r radiometers.
摘要:
A protocol and mechanism which provide for centralized asset tracking communications from a central station are based on a control/polling forward channel; i.e., a narrow band channel from the central station to tracking units affixed to the assets. A narrow band service channel is used by the asset tracking units to transmit to the central station to aid the central station in efficient scheduling of asset reporting, and a plurality of narrow band channels that are appropriately multiplexed are used for conveyance of data from the asset tracking units to the central station.
摘要:
Characteristics of the radio channel are used to establish key sequences for use in encrypting communicated information. These characteristics are the short-term reciprocity and rapid spatial decorrelation of phase of the radio channel. The keys can be established with computations equivalent to a bounded distance decoding procedure, and the decoder used to establish a key may be used for processing the subsequent data transmission. Compared to classical and public-key systems, an alternative mechanism for establishing and sharing key sequences that depends on a physical process is provided in which each party need not generate a pseudorandom quantity because the necessary randomness is provided by the temporal and spatial non-stationarity of the communication channel itself. By using a channel decoder, the probability of two users establishing the same secret key is substantially unity, and the probability of an eavesdropper establishing the same key is substantially zero. Also, the number of possible keys is large enough that finding the correct one by exhaustive search is impractical.
摘要:
Apparatus for monitoring the health and response of critical electromechanical control valves to detect the likelihood of future valve malfunction includes the use of Fourier transform decomposition and time-domain wavelets to selectively enhance portions of the valve response signal for comparison with a normal valve response signal.
摘要:
A spatial synchronization method for an optical communications system includes the step of transmitting from a transmit aperture a pyramidal synchronizing profile so as to sequentially spatially register a user identification speckle pattern at a receive aperture. The iterative patterns in the pyramidal synchronizing profile detected by the receive array are processed and correlated with a library of respective user pyramidal synchronizing profiles so as to match and register the speckle pattern for a particular user. Registration of the user speckle pattern provides an offset value representing the spatial relation of a reference point of the user's pattern to a corresponding reference point of the receive aperture, which offset information is applied to a receive pattern processor so that the receive aperture is aligned with the transmitted speckle patterns.