US 5,604,768 A · Frequency synchronized bidirectional radio system

Abstract

A bidirectional radio system for low-cost high-throughput accumulation of data from a large number of site units. Frequency synchronization is achieved at low cost by transmitting a high accuracy carrier and clock signal at a base station, and using receiving circuitry at remote stations to extract the base clock signal and base carrier frequency and a phase-lock loop to stabilize the remote station carriers. A burst demodulator at a base station receiver can decode a short remote station response by scaling the response with the phase and amplitude of an initial segment of the response. The burst demodulator may continuously update the decoding threshold based on a comparison of the signal amplitude and the current value of the decoding threshold. In an alternate embodiment, the carrier synthesizer is not part of a phase-lock loop, but the transmitted signal is rotated by a phase proportional to a frequency error to provide an accurate carrier frequency. In yet another alternate embodiment only a frequency-control loop is implemented, and again the transmitted signal is rotated by a phase ramp proportional to a frequency error to provide an accurate carrier frequency. In this embodiment separate rotators may be used on both the transmission and reception sides of the circuit, or a single rotator may be switched between the transmission and reception sides of the circuit for half-duplex operation.

Claims8

Dependent claims

An apparatus for decoding an encoded analog signal suffering from amplitude modulation to determine discrete output values, said discrete output values including a first nonzero value and a zero value, comprising:

a first means for comparing a first component of said encoded analog signal to a threshold value, if said first component is greater than said threshold value then said first means for comparing sets a first one of said discrete output values equal to said first nonzero value, and if said first component of said encoded analog signal is less than said threshold value then said first means for comparing sets said first one of said discrete output values equal to one of a set of discrete values, said set of discrete values including a zero value;
and
a first means for modifying said threshold value by adding a first error signal multiplied by a first reduction factor thereto, if said first one of said discrete output values is said zero value then said first means for modifying sets said first error signal equal to zero, and if said first one of said discrete output values is said first nonzero value then said first means for modifying sets said first error signal equal to a difference between said first component of said encoded analog signal and twice said threshold value.

A bidirectional radio communication system comprised of at least one communication cell, said cell having a base station and at least one remote station, said remote station operating in half-duplex mode, said remote station receiving a polling signal at a base clock rate on a base carrier frequency from said base station during a reception, said remote station transmitting a response signal carrying a baseband response signal with a remote clock rate to said base station during a transmission, said remote station being comprised of:

a first frequency synthesizer generating a remote carrier frequency, and utilizing a frequency error signal in a frequency-control loop;
a first frequency heterodyne, said first heterodyne heterodyning said remote carrier frequency and said polling signal to generate an intermediate frequency signal;
a second frequency synthesizer generating an intermediate frequency sinusoid, said intermediate frequency sinusoid being stabilized by a first frequency stabilization signal;
a second frequency heterodyne, said second heterodyne heterodyning said intermediate frequency sinusoid and said intermediate frequency signal to generate a received baseband signal;
a first recovery circuit, said first recovery circuit including
a rotator for frequency-translating an input signal at a rotator input to provide a frequency-translated rotator output signal at a rotator output,
a phase detector for producing a phase detector output proportional to a phase of a phase detector input,
a ramp estimator for providing a rotator control signal to said rotator and producing said frequency error signal, said frequency error signal being related to a difference between said base carrier frequency and said remote carrier frequency,
a rotator input switch for directing said received baseband signal to said rotator input during said reception, and directing said baseband response signal to said rotator input during said transmission,
a rotator output switch for directing said rotator output to said phase detector input and a clock estimator input during said reception, and directing said rotator output to a modulator for modulating said rotator output onto said remote carrier frequency to provide said response signal during said transmission,
a ramp estimator input switch for connecting said phase detector output to said ramp estimator during said reception, and disconnecting said ramp estimator during said transmission so that said rotator control signal and said frequency error signal are unchanged, and
a clock estimator for determining an estimate of said base clock rate from said clock estimator input;
and
a second recovery circuit, said second recovery circuit generating said first frequency stabilization signal and said remote clock rate from said estimate of said base clock rate.

11 more elements

Dependencies are inferred from the claim text.

Frequency synchronized bidirectional radio system

Life of this patent

Frequency synchronized bidirectional radio system

Life of this patent

Abstract

Claims8