Pulse or digital communications – Spread spectrum
Reexamination Certificate
1998-03-10
2002-08-06
Tse, Young T. (Department: 2634)
Pulse or digital communications
Spread spectrum
C375S146000, C370S342000
Reexamination Certificate
active
06430208
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of communications, and more particularly, the present invention relates to ultrawide-band impulse communication systems and methods employing subcarriers.
2. Related Art
Designers of radio technology for personal communications devices, medical and military devices, and the like, are currently faced with several development challenges. Low power consumption, reuse of available spectrum, channelization and cost are four of the main issues.
These issues are addressed in part by an emerging, revolutionary technology called impulse radio communications (hereafter called impulse radio). Impulse radio was first fully described in a series of patents, including U.S. Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989) and U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990) and U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994), all to Larry W. Fullerton. These patent documents are incorporated herein by reference.
Basic impulse radio transmitters emit short Gaussian monocycle pulses with tightly controlled average pulse-to-pulse interval. Impulse radio systems use pulse position modulation. Pulse position modulation is a form of time modulation in which the value of each instantaneous sample of a modulating signal is caused to modulate the position in time of a pulse.
For impulse radio communications, the pulse-to-pulse interval is varied on a pulse-by-pulse basis by two components: an information component and a pseudo-random code component. Spread spectrum systems make use of pseudo-random codes to spread the normally narrowband information signal over a relatively wide band of frequencies. A spread spectrum receiver correlates these signals to retrieve the original information signal. Unlike spread spectrum systems, the pseudo-random code for impulse radio communications is not necessary for energy spreading because the monocycle pulses themselves have an inherently wide information bandwidth (information bandwidth, hereafter called bandwidth, is the range of frequencies within which performance, with respect to some characteristics, falls within specific limits). Instead, the pseudo-random code is used for channelization, energy smoothing in the frequency domain, and jamming resistance.
The impulse radio receiver is a homodyne receiver with a cross correlator front end. The front end coherently converts an electromagnetic pulse train of monocycle pulses to a baseband signal in a single stage. (The baseband signal is the basic information channel for the basic impulse radio communications system, and is also referred to as the information bandwidth.) The data rate of the impulse radio transmission is only a fraction of the periodic timing signal used as a time base. Each data bit time position modulates many pulses of the periodic timing signal. This yields a modulated, coded timing signal that comprises a train of identical pulses for each single data bit. The cross correlator of the impulse radio receiver integrates multiple pulses to recover the transmitted information.
As with all aspects of the electronics field, what is desired are still smaller, lower power and more flexible systems. However, generally accepted principles in continuous wave (CW) radio technology do not readily lend themselves to time domain systems, such as impulse radio.
Descriptions of some of the basic concepts discussed below are found in a number of references, including Robert C. Dixon,
Spread Spectrum Systems
(John Wiley & Sons, Inc., New York, 1984, 2nd ed.); and Don J. Torrieri,
Principles of Military Communication Systems
(Artech House, Inc., Dedham Mass., 1982, 3rd ed.).
SUMMARY OF THE INVENTION
The impulse radio communications system according to the present invention uses one or more subcarriers to communicate information from an impulse radio transmitter to an impulse radio receiver. Three impulse radio communications system embodiments are described, including: a one channel system, a two channel system and a three or more channel system. Typical radio frequency impulse radio communications system applications include cellular telephones, wireless telephones, wireless PBXs/Local area networks, and the like. The impulse radio communication system is an ultrawide-band time domain system. Operation in the time domain is in accordance with general impulse radio theories discussed below in section II. The use of subcarriers provides impulse radio transmissions added channelization, smoothing and fidelity. Subcarriers of different frequencies or waveforms can be used (simultaneously) to add channelization of impulse radio signals. Thus, an impulse radio link can communicate many independent channels simultaneously by employing different subcarriers for each channel.
There are three impulse radio transmitter embodiments. The first and second transmitter embodiments comprise a subcarrier generator and modulator that uses one or more information signals to modulate a periodic timing signal.
According to the first embodiment, coding of the impulse radio signals is achieved by coding the periodic timing signal before it is time modulated by the modulated subcarrier signal.
According to the second embodiment, coding of the impulse radio signals is achieved by coding a modulated subcarrier signal before it is used to time modulate the periodic timing signal.
The third transmitter embodiment comprises a subcarrier generator and modulator that uses one or more information signals to modulate a periodic timing signal in combination with direct digital modulation of a digital data signal. In this embodiment, the modulated subcarrier signal is used to time modulate the direct digitally modulated signal.
The impulse radio transmitter generally comprises a time base that generates a periodic timing signal. The time base comprises a voltage controlled oscillator, or the like, having sub-nanosecond timing requirements. The periodic timing signal is supplied to a code source and to a code time modulator. The code source comprises a storage device for storing nearly orthogonal pseudo-random noise (PN) codes and means for outputting the PN codes as a code signal. The code source monitors the periodic timing signal to permit the code signal to be synchronized to the code time modulator. In one embodiment, the code time modulator uses the code signal to modulate the periodic timing signal for channelization and smoothing of a final emitted impulse radio signal. The output of the code time modulator is called the coded timing signal.
The coded timing signal is supplied to a subcarrier time modulator for information modulation thereof. Prior impulse systems used non-subcarrier, baseband modulation. In other words, the information itself was used for modulation. In the present invention, however, an information source supplies an information signal to a subcarrier generator and modulator. The information signal can be any type of intelligence, including digital bits representing voice, data, imagery, or the like, analog signals, or complex signals.
The subcarrier generator and modulator of the present invention generates a modulated subcarrier signal that is modulated by the information signal, and supplies the modulated subcarrier signal to the subcarrier time modulator. Thus, the modulated subcarrier signal is used by the subcarrier time modulator to modulate the carrier, which in this case is the coded timing signal. Modulation of the coded timing signal by the subcarrier time modulator generates a modulated, coded timing signal that is sent to an output stage.
The output stage uses the modulated, coded timing signal as a trigger to generate monocycle pulses. In a radio frequency embodiment, the monocycle pulses are sent to a transmit antenna via a transmission line coupled thereto. The monocycle pulses are converted into propagating electromagnetic pulses by the transmit antenna. The emitted signal propagates to an impulse radio receiver through a propagation medium, such as air in a radio fr
Cowie Ivan A.
Fullerton Larry W.
Sterne Kessler Goldstein & Fox P.L.L.C.
Time Domain Corporation
Tse Young T.
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