An ultra wide bandwidth, high speed, spread spectrum communications system uses short wavelets of electromagnetic energy to transmit information through objects such as walls or earth. The communication system uses baseband codes formed from time shifted and inverted wavelets to encode data on a RF signal. Typical wavelet pulse durations are on the order of 100 to 1000 picoseconds with a bandwidth of approximately 8 GHz to 1 GHz, respectively. The combination of short duration wavelets and encoding techniques are used to spread the signal energy over an ultra wide frequency band such that the energy is not concentrated in any particular narrow band (e.g. VHF: 30-300 MHz or UHF: 300-1000 MHz) and is not detected by conventional narrow band receivers so it does not interfere with those communication systems. The use of pulse codes composed of time shifted and inverted wavelets gives the system according to the present invention has a spatial resolution on the order of 1 foot which is sufficient to minimize the negative effects of multipath interference and permit time domain rake processing.

Ultra wide bandwidth spread-spectrum communications system

A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a transmitter transmitting information messages on a plurality of pseudo-random frequencies, comprising the steps of: scanning an available radio spectrum (517, 518); measuring (515) in a portion of the available radio spectrum, at least one of signal strength and quieting and signal lock quality, as a measurement, from an output of said frequency-agile receiver; identifying the portion of the available radio spectrum failing to provide a properly coded reception (508); generating (501) using the measurement and other system cues, a prediction of a level of undesired signal energy, within the portion of the available radio spectrum, present in a future scan of said frequency-agile receiver; and storing (505) the prediction of the level of undesired signal energy in memory location associated with the portion of the available radio spectrum.

Enhanced frequency agile radio

A waveform adaptive transmitter that conditions and/or modulates the phase, frequency, bandwidth, amplitude and/or attenuation of ultra-wideband (UWB) pulses. The transmitter confines or band-limits UWB signals within spectral limits for use in communication, positioning, and/or radar applications. One embodiment comprises a low-level UWB source (e.g., an impulse generator or time-gated oscillator (fixed or voltage-controlled)), a waveform adapter (e.g., digital or analog filter, pulse shaper, and/or voltage variable attenuator), a power amplifier, and an antenna to radiate a band-limited and/or modulated UWB or wideband signals. In a special case where the oscillator has zero frequency and outputs a DC bias, a low-level impulse generator impulse-excites a bandpass filter to produce an UWB signal having an adjustable center frequency and desired bandwidth based on a characteristic of the filter. In another embodiment, a low-level impulse signal is approximated by a time-gated continuous-wave oscillator to produce an extremely wide bandwidth pulse with deterministic center frequency and bandwidth characteristics. The UWB signal may be modulated to carry multi-megabit per second digital data, or may be used in object detection or for ranging applications. Activation of the power amplifier may be time-gated in cadence with the UWB source thereby to reduce inter-pulse power consumption. The UWB transmitter is capable of extremely high pulse repetition frequencies (PRFs) and data rates in the hundreds of megabits per second or more, frequency agility on a pulse-to-pulse basis allowing frequency hopping if desired, and extensibility from below HF to millimeter wave frequencies.

Waveform adaptive ultra-wideband transmitter

Synchronization is maintained among a plurality of network devices (102,...) having local clocks. A first packet including global time reference (606) derived from local clock is broadcast from a first network device to other devices. The clocks of the network devices are adjusted. The difference between a free running clock and a first network global time reference is determined (610). A first network offset is calculated (612). Similarly, a second network offset is calculated to account for the difference between the free running clock and the second network global time reference.

Maintaining a global time reference among a group of networked devices

Systems, methods and apparatus are provided for bridging data between different communication formats, or protocols. One embodiment of the present invention comprises a communication system that bridges data between a substantially continuous carrier wave format (see figure 4) and an ultra-wideband format (see numeral 100 in figure 4). The present invention may be used in wireless and wire communication networks such as hybrid fiber-coax networks. This Abstract is provided for the sole purpose of complying with the Abstract requirement rules that allow a reader to quickly ascertain the subject matter of the disclosure contained therein. This Abstract is submitted with the explicit understanding that it will not be used to interpret or to limit the scope or the meaning of the claims.

Bridged ultra-wideband communication method and apparatus

A predetermined radar pulse train is formed in space by transmitting individual spectral components thereof. Thus, a train of extremely short pulses is obtained without switching a radio frequency signal on and off at a high rate. A crystal oscillator is coupled to a harmonic generator such as a comb generator. A power divider distributes the output of the harmonic generator to a multiplicity of final filter amplifiers. Each final filter amplifier has a phase-locked VCO circuit that provides frequency accuracy, spectral purity, low noise and frequency stability. Thus, each final filter amplifier provides one of the spectral components of the predetermined radar pulse train. The final filter amplifiers are coupled by duplexers to a broadband multiplexing feed such as a nested cup dipole feed that illuminates a reflector. On receive, the broadband multiplexing feed separates all the spectral components of the incoming pulse train. Each spectral component is coupled to its own narrow band receiver by the duplexers. One receiver is used to amplify and detect each spectral component. The signals from the receivers are coherently combined in a signal processor in which the signals add coherently and the noise signals do not. This provides a processing gain in signal to noise ratio corresponding to the total number of receivers. The output of the signal processor is applied to a radar display.

Ultra wideband radar transmitter employing synthesized short pulses

An impulse radar that forms a predetermined radar pulse train in space by transmitting individual spectral components thereof. Thus, a train of extremely short pulses is obtained without switching a radio frequency signal on and off at a high rate. An oscillator is coupled to a harmonic generator, and a power divider distributes the output of the harmonic generator to a multiplicity of amplifiers. Each amplifier has a phase-locked VCO circuit that provides frequency accuracy, spectral purity, low noise and frequency stability. Thus, each amplifier provides one of the spectral components of the predetermined radar pulse train. The amplifiers are coupled to a multiplexing feed that illuminates a reflector. On receive, the multiplexing feed separates the spectral components of the incoming pulse train. Each spectral component is coupled to its own narrow band receiver, and one receiver is used to amplify and detect each spectral component. The signals from the receivers are coherently combined in a signal processor in which the signals add coherently and the noise signals do not. The output of the signal processor may be applied to a radar display. The short pulses produced by the radar provide very high resolution, and can map a target by sweeping across it, thus imaging it. The radar emits a wideband signal at a low power level; the signal is difficult to detect and intercept, and thus provides for a low probability of intercept radar. The radar may be used as a microwave link, wherein the oscillator may be frequency modulated to provide communications. It may also be used as a covert IFF system to identify friendly aircraft. The radar provides signals that penetrate sand and may be used for mapping and to locate land mines buried in the sand. It may also be used for clearing away land mines by detonating them. When the power is turned up, the radar provides for a directed energy beam. The radar may perform adaptive jamming, and is also a jam resistant radar. It is hard to jam because the receiver array is insensitive to noise at frequencies outside the narrow bandwidths of the individual receivers and also to noise which is not coherent across the multiplicity of receiver channels.

James G Small

Papers

Ultra wideband radar transmitter employing synthesized short pulses

Ultra wideband radar employing synthesized short pulses