Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1997-04-03
2001-08-28
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Transceivers
Modems
C375S295000, C375S303000, C375S308000, C455S086000
Reexamination Certificate
active
06282236
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates the field of data transmission, and in particular to modems that reduce the cost and/or complexity of data transmission and a system using the improved modems.
BACKGROUND OF THE INVENTION
The development and evolution of communications equipment in recent years has altered the manner in which business is conducted. Functions previously performed manually, such as the collection and processing of data, are now performed automatically using computers and sophisticated communications equipment. As the ability to transmit and receive data reliably, efficiently and over long distances has become more and more a part of everyday business, the need for cost efficient communications equipment, and in particular modems, has increased greatly.
For example, such a need is readily apparent in circumstances where data is collected at a number of remote locations and is subsequently transmitted to a central location for processing. In such a situation, it is often necessary to install hundreds or even thousands of modems at the remote locations. Because prior art modems are typically not designed to optimize total system cost savings and, as a result, often incorporate expensive components, the need for such a large number of modems can make the cost of any such system prohibitive. Thus, it has become increasingly important to provide low cost modems that are tailored to a specific task.
SUMMARY OF THE INVENTION
The present invention features modems that reduce the costs and/or complexity of data transmission and a system using the improved modems. For example, the system can gather and transmit data from a large number of remote locations back to one or more central locations.
In one aspect, the invention features a transmitter which converts a data stream into a modulated signal including a memory for storing a plurality of digital waveform signals, a state machine for receiving the data stream, and for choosing an appropriate one of the digital waveform signals based upon the data stream and a digital-to-analog converter for converting the digital waveform signal into an analog signal. In the transmitter, the modulated signal can be represented as a sequence of possible transitions wherein each of the digital waveform signals is a particular one of the possible transitions. In preferred embodiments, the modulated signal is a bipolar coded frequency shift keyed signal and the state machine chooses the appropriate digital waveform signals according to a set of rules for bipolar coding.
In another aspect, the invention features a receiver which converts a differential bipolar phase shift keyed signal into an output data stream including a sampling circuit for sampling the differential bipolar phase shift keyed signal at a predetermined sampling rate, a serial to parallel converter for converting the sampled signal into a plurality of parallel signals, a counter for cycling the parallel signals through a predetermined number of memory locations of a memory, a parallel to serial converter for converting the plurality of parallel signals into a serial signal, and an exclusive OR gate which takes as inputs the sampled signal and the serial signal and outputs a data stream.
In a preferred embodiment, the receiver further includes at least one shift register coupled to the parallel to serial converter. Also, in other preferred embodiments, the parallel signals are cycled through the memory locations at a predetermined cycling rate that is equal to the predetermined sampling rate divided by the number of parallel signals, and the number of memory locations is chosen such that a time elapsed in cycling the parallel signals through the memory locations and receiving the serial signal in the shift register and subsequently outputting the serial signal is equal to a time corresponding to one data bit of the differential bipolar phase shift key to signal.
In still another aspect, the invention features a method of converting a data stream into a modulated signal including the steps of storing a plurality of digital waveform signals, choosing an appropriate one of the digital waveform signals based upon the data stream, and converting the appropriate one of the digital waveform signals into an analog signal. In this method, the modulated signal can be represented as a sequence of possible transitions and each digital waveform signal is a particular one of the possible transitions. In preferred embodiments of the method, the modulated signal is a bipolar, coded frequency shift keyed signal and the appropriate one of the digital waveform signals is chosen according to a set of rules for bipolar coding.
In yet another aspect, the invention features a method of converting a differential bipolar phase shift keyed signal into an output data stream, including the steps of sampling the differential bipolar phase shift keyed signal at a predetermined sampling rate, converting the sampled the signal into a plurality of parallel signals, cycling the parallel signals through a predetermined number of memory locations, converting the parallel signals into a serial signal, and inputting the sampled signal and the serial signal into an exclusive OR gate wherein a data stream is output by the exclusive OR gate. In a preferred embodiment, the method includes cycling the serial signal through at least one shift register after the step of converting the parallel signals into a serial signal. In other preferred embodiments, the parallel signals are cycled through the memory locations at a cycling rate that is equal to the predetermined sampling rate divided by the number of parallel signals and the number of memory locations is chosen such that a time elapsed in cycling the parallel signals through the memory locations and the shift register is equal to a time corresponding to one data bit of the differential bipolar phase shift keyed signal.
In yet a further aspect, the invention features a modem including modulator circuitry for modulating an input data stream with a carrier signal generated by an oscillator circuit, an amplifier for amplifying the modulated signal and outputting a second modulated signal, and a protection circuit coupled to the amplifier and the oscillator circuit having a timer triggered by receipt of the monitor signal. The amplifier outputs a monitor signal when the amplifier is outputting the second modulated signal and the protection circuit outputs first and second signals when the amplifier outputs the monitor signal for a time longer than the duration of the timer. The first signal disables the amplifier and the second signal disables the oscillator circuit. In preferred embodiments, a differential bipolar phase shift keyed modulation scheme is used to modulate the input data and the modulator circuitry comprises a BPSK based and generator coupled to a double balanced modulator.
In still another aspect, the invention features a modem including an oscillator circuit for producing a carrier signal and modulator circuitry for modulating an input data stream with the carrier signal. The oscillator circuit includes a frequency synthesizer coupled to a voltage controlled oscillator and a divide by two circuit coupled to the voltage controlled oscillator. The voltage controlled oscillator outputs a second carrier signal which is input into the divide by two circuit. The carrier signal is output by the divide by two signal. In preferred embodiments, the frequency synthesizer uses a frequency reference provided by a voltage controlled crystal oscillator and the modem further includes a receiver which receives a downlink signal, wherein the downlink signal is used in a feedback loop as an input into the voltage controlled crystal oscillator.
In another aspect, the invention features a modem including an oscillator circuit for producing a mixing signal, a mixer for mixing the mixing signal with the modulated signal, and a detector for converting the mixed modulated signal into a data stream. The oscillator circuit comprises a frequency synthesizer coupl
Ghebretinsae Temesghen
Lucent Technologies - Inc.
Morgan & Finnegan , LLP
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