Pulse or digital communications – Receivers
Reexamination Certificate
2001-06-13
2004-04-06
Fan, Chieh M. (Department: 2634)
Pulse or digital communications
Receivers
C375S136000, C375S325000, C375S340000
Reexamination Certificate
active
06717992
ABSTRACT:
CROSS-REFERENCE TO OTHER APPLICATIONS
The following applications of common assignee may contain common disclosure with the present application:
U.S. patent application Ser. No. 09/638,192 entitled “A METHOD FOR SPECIFYING NON-TEMPORAL PULSE CHARACTERISTICS”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/638,046 entitled “A METHOD AND APPARATUS FOR APPLYING CODES HAVE PREDEFINED PROPERTIES”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/637,878 entitled “A METHOD AND APPARATUS FOR POSITIONING PULSES USING A LA YOUT HAVING NON-ALLOWABLE REGIONS”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/638,150 entitled “A METHOD AND APPARATUS FOR POSITIONING PULSES IN TIME”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/638,151 entitled “A METHOD AND APPARATUS FOR MAPPING PULSES TOA NON-FIXED LAYOUT”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/638,152 entitled “A METHOD AND APPARATUS FOR SPECIFYING PULSE CHARACTERISTICS USING CODE THAT SATISFIES PREDEFINED CRITERIA”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/638,153 entitled “A METHOD FOR SPECIFYING PULSE CHARACTERISTICS USING CODES”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/638,154 entitled “A METHOD FOR SPECIFYING NON-ALLOWABLE PULSE CHARACTERISTICS”, filed on Aug. 15, 2000.
U.S. patent application Ser. No. 09/708,025 entitled “A METHOD AND APPARATUS FOR GENERATING A PULSE TRAIN WITH SPECIFIABLE SPECTRAL RESPONSE CHARACTERISTICS”, filed on Nov. 8, 2000.
The above-listed applications are incorporated herein by reference in their entireties.
TECHNICAL FIELD
The present invention relates to impulse radio systems and, more particularly, to a method and apparatus for receiving time spaced signals.
BACKGROUND OF THE INVENTION
As the availability of communication bandwidth in the increasingly crowded frequency spectrum is becoming a scarce and valuable commodity, Ultra Wideband (IWB) technology provides an excellent alternative for offering significant communication bandwidth, particularly, for various wireless communications applications. Because UWB communication systems are based on communicating extremely short-duration pulses (e.g., pico-seconds in duration), such systems are also known as impulse radio systems. Impulse radio systems are described in a series of patents, including U.S. Pat. Nos. 4,641,317 (issued Feb. 3, 1987), 4,813,057 (issued Mar. 14, 1989), 4,979,186 (issued Dec. 18, 1990), and 5,363,057 (issued Nov. 8, 1994) to Larry W. Fullerton, and U.S. Pat. Nos. 5,677,927 (issued Oct. 14, 1997), 5,687,169 (issued Nov. 11, 1997), and 5,832,035 (issued Nov. 3, 1998) to Larry W. Fullerton, et al. These patents are incorporated herein by reference.
Multiple access impulse radio systems are radically different from conventional Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) systems. Unlike such systems, which use continuous sinusoidal waveforms for transmitting information, a conventional impulse radio transmitter emits a low power electromagnetic train of short pulses, which are shaped to approach a Gaussian monocycle. As a result, the impulse radio transmitter uses very little power to generate noise-like communication signals for use in multiple-access communications, radar and positioning applications, among other things. In the multi-access communication applications, the impulse radio systems depend, in part, on processing gain to achieve rejection of unwanted signals. Because of the extremely high achievable processing gains, the impulse radio systems are relatively immune to unwanted signals and interference, which limit the performance of systems that use continuous sinusoidal waveforms. The high processing gains of the impulse radio systems also provide much higher dynamic ranges than those commonly achieved by the processing gains of other known spread-spectrum systems.
Impulse radio communication systems transmit and receive the pulses at precisely controlled time intervals, in accordance with a time-hopping code. As such, the time-hopping code defines a communication channel that can be considered as a unidirectional data path for communicating information at high speed. In order to communicate the information over such channels, impulse radio transmitters may use position modulation, which is a form of time modulation, to position the pulses in time, based on instantaneous samples of a modulating information signal. The modulating information signal may for example be a multi-state information signal, such as a binary signal. Under this arrangement, a modulator varies relative positions of a plurality of pulses on a pulse-by-pulse basis, in accordance with the modulating information signal and a specific time-hopping code that defines the communication channel.
In applications where the modulating information signal is a binary information signal, each binary state may modulate the time position of more than one pulse to generate a modulated, coded timing signal that comprises a train of identically shaped pulses that represent a single data bit. The impulse transmitter applies the generated pulses to a specified transmission medium, via a coupler, such as an antenna, which electromagnetically radiates the pulses for reception by an impulse radio receiver. The impulse radio receiver typically includes a single direct conversion stage. Using a correlator, the conversion stage coherently converts the received pulses to a baseband signal, based on a priori knowledge of the time-hopping code. Because of the correlation properties of the selected time-hopping codes, the correlator integrates the desired received pulses coherently, while the undesired noise signals are integrated non-coherently such that by comparing the coherent and non-coherent integration results, the impulse receiver can recover the communicated information.
Conventional spread-spectrum code division multiple access (SS-CDMA) techniques accommodate multiple users by permitting them to use the same frequency bandwidth at the same time. Direct sequence CDMA systems employ pseudo-noise (PN) codewords generated at a transmitter to “spread” the bandwidth occupied by transmitted data beyond the minimum required by the data. The conventional SS-CDMA systems employ a family of orthogonal or quasi-orthogonal spreading codes, with a pilot spreading code sequence synchronized to the family of codes. Each user is assigned one of the spreading codes as a spreading function. One such spread-spectrum system is described in U.S. Pat. No. 4,901,307 entitled “SPREAD-SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS” by Gilhousen et al.
Unlike direct sequence spread-spectrum systems, impulse radio communications systems have not employed time-hopping codes for energy spreading, because the monocycle pulses themselves have an inherently wide bandwidth. Instead, the impulse radio systems use the time-hoping codes for channelization, energy smoothing in the frequency domain, and interference suppression. The time-hoping code defines a relative position of each pulse within a group of pulses, or pulse train, such that the combination of pulse positions defines the communications channel. In order to convey information on such communication channel, each state of a multi-state information signal may vary a relative pulse position by a predefined time shift such that a modulated, coded timing signal is generated comprising a train of pulses, each with timing corresponding to the combination of the time position coding and the multi-state modulation. Alternative modulation schemes may also be used instead of time modulation or in combination with it.
In one conventional binary approach, pulses are time-modulated forward or backward about a nominal position. More specifically, each pulse is time modulated by adjusting its position within a time frame to one of two or more possible times. For example, in order to send a “0” binary bit during the time frame, the pulse
Cowie Ivan A.
Roberts Mark D.
Babayi, Esq. Robert
Time Domain Corporation
Venable LLP
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