Radio communication
AssigneeLinear Modulation Technology Limited
InventorsRichard A. Hillum, Ian S. Parry
Life of this patent
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Abstract
In a transparent tone-in-band (TTIB) single-sideband-modulated communication system used to communicate digital data; to compensate for variations due, eg, to doppler shift of the pilot tone in the received signal, during the sweep of the frequency of a local oscillator used to tune the receiver, the output of a narrow band filter is monitored for the presence of the expected pilot tone. When the pilot tone appears to be present, the sweep is interrupted and the error rate of the demodulated digital signal is tested, the sweep being resumed if an excessive error rate is encountered.
Claims12
A receiver apparatus for receiving a radio signal which comprises a modulated pilot tone signal and a modulated digital data signal whose digital data error rate when demodulated varies in dependence on the frequency error of the tuning of the receiver apparatus to the received signal, the digital signal having, prior to modulation, spectral components within a baseband spectrum and the pilot tone having, prior to modulation, a baseband predetermined frequency relative to said spectral components, the receiver apparatus having a demodulator and a local oscillator for producing an output signal, of controllable frequency, for demodulating the received signal, the demodulator being operative to demodulate the received digital data signal and pilot tone signal using the oscillator output signal by frequency translating the modulated pilot tone and modulated digital signal down to their baseband frequencies, means for controlling the local oscillator to sweep its output frequency and for interrupting the sweep and holding the frequency of the local oscillator signal when the demodulated signal comprises a signal component at said predetermined reference frequency of the pilot tone signal, means for testing the digital data error rate of the demodulated digital data signal and recommencing the sweep if that test yields an excessive error rate.
A method of receiving a radio signal which comprises a modulated pilot tone signal and a modulated digital data signal whose digital data error rate when demodulated varies in dependence on the frequency error of tuning of the receiver to the received signal, the digital signal having, prior to modulation, spectral components within a baseband spectrum and the pilot tone having, prior to modulation, a baseband predetermined frequency relative to said spectral components, said method comprising sweeping the frequency of a local oscillator which is used at the receiver to demodulate the received radio signal while monitoring a resulting demodulated signal for a frequency component at an expected frequency of the pilot tone, interrupting the sweeping and holding the frequency of the local oscillator signal when the demodulated signal comprises a signal component at said predetermined reference frequency of the pilot tone signal, testing the digital data error rate of the demodulated digital data signal and recommencing the sweep if that test yields an excessive error rate.
In a radio communication system in which a first transmission takes place in a designated channel of the radio frequency spectrum and may be subject to co-channel interference from a second transmission in that channel, the first and second transmissions comprising a respective modulated pilot tone and a respective associated modulated digital data signal, the pilot tone in the first transmission having, prior to modulation and within a baseband spectrum a predetermined frequency and the pilot tone in the second transmission having, prior to modulation and within that baseband spectrum a frequency which differs by a detectable amount from said predetermined frequency, a method of receiving the first transmission comprising:
- receiving and demodulating the first transmission with the steps:
- i) using a local oscillator to produce a local oscillator signal,
- ii) using the local oscillator signal to demodulate the received transmission,
- iii) sweeping the local oscillator frequency while monitoring the demodulated received signal,
- iv) interrupting the sweeping of the local oscillator frequency when the demodulated signal contains a signal component at said predetermined frequency, and
- v) while the sweeping of the local oscillator frequency is interrupted, testing the demodulated digital signal to determine a digital data error rate of the demodulated digital signal and recommencing the sweeping of step iii) if the testing determines if the digital data error rate is greater than a set value.
Dependencies are inferred from the claim text.