International Business Machines Corporation

Gary M Warchocki

William O Camp, Jr

Arthur E Fleek

Michael J Bracco

Ralph Yeager

A phase shift modulator at the transmitter has a control input connected to a binary signal source. A high frequency carrier signal is applied to a carrier signal input of the modulator. The modulated carrier signal is transmitted to a receiver where it is mixed with a local oscillator frequency. At the receiver, a modulated signal is amplified by a limit amplifier to form the received signal into square wave pulses of a uniform height. The demodulator detects when the spacing between the edges of the square wave signal change in response to the phase shift modulation at the transmitter. When the spacing between the edges of the square wave IF signal is detected to be shorter than the normal spacing for a steady IF signal with no modulation, this signifies a first binary value. A longer than normal spacing between the edges of the square wave IF signal signifies a second binary value. Frequency drift compensation circuits are disclosed to overcome frequency variations in the carrier and the local oscillator.

Phase demodulation method and apparatus for a wireless LAN, by counting

The oscillator at the sending node of a wireless digital network, generates a carrier signal, starting at a first instant. A modulator coupled to the oscillator performs phase shift modulating of the carrier signal with an input signal. A spoiler signal generator is coupled to the modulator, for providing a spoiler signal as the input signal, starting at the first instant and continuing for a first duration which is longer than a period needed for the oscillator to achieve stable characteristics. A transmitter is coupled to the modulator at the sending node, for transmitting a wireless radio signal representation of the carrier signal phase shift modulated with the spoiler signal to a receiver at a receiving node. The spoiler signal in the modulated carrier signal interrupts the periodic characteristic of the pulses, and thereby prevents the carrier sensor from detecting the carrier signal. Further, the spoiler signal ceases to modulate the carrier signal after the first duration when the oscillator has achieved stable characteristics, thereby enabling the carrier sensor to detect the carrier signal.

Method and apparatus for digital carrier detection in a wireless lan

A carrier sensing circuit coupled to a receiving amplifier, measures the frequency of a phase shift modulated carrier signal by counting a predetermined number of the pulses for a measured interval whose duration is determined by counting a first clock count value. A demodulator coupled to the amplifier, detects when the spacing between the edges of the square wave pulses changes in response to the phase shift modulation. The demodulator measures first intervals between consecutive rising edges of the received signal, by counting clock pulses for a second selected interval whose duration is determined by a second selected count value. The demodulator further measures second intervals between consecutive falling edges of the received signal by counting clock pulses for a third selected interval whose duration is determined by a third selected count value. A compensating circuit coupled to the carrier sensing circuit and to the demodulator, compensates for frequency drift in the carrier signal or in the local oscillator by adjusting the second selected count value and the third selected count value, using the first clock count value.

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Owego, NY, United States of America

Gary M Warchocki