Bell Telephone Laboratories

Lucent Technologies Inc.

Gerald L Frazer

James Russell Blodgett

Michael W Goodwin

James P Moffatt

Karen E Leonard

Fan Zhang

An adaptive controller generates a sequence of dither signals for each of a plurality of control parameters. Each dither signal sequence is uncorrelated with every other dither signal sequence. Each nominal control signal has the first of its respective dither signal values simultaneously summed with it to form the control parameter values used by the controller. Updated control signals are applied in parallel to the controller outputs and a performance measure is taken and stored. The second signals in the dither control sequences are then summed with their respective nominal controls and applied in parallel to the controller and a second performance measure is taken and stored. This process is repeated for the length of the dither control signal sequence to yield a sequence of performance measurements. The sequence of performance measurements is correlated with each of the dither sequences, forming sequences of correlator outputs, one for each control signal. Each correlator output sequence is integrated and, depending upon the value of a correlator's integration output, the corresponding nominal signal has it's dither value added to or subtracted from it to form the respective, updated control values.

Apparatus and method for adaptive control

The adaptive threshold circuit (FIG. 1) senses the amplitude of a digital signal relative to a threshold and generates a corresponding output signal therefrom. Feedback circuitry generates a correction signal which drives the threshold toward a predetermined level in the signal-eye pattern. This predetermined level passes only through the region of intersymbol interferene in the signal-eye pattern.

Adaptive threshold circuit

Digital transmission systems operating over microwave radio generally employ phase modulation rather than amplitude modulation because phase modulation is less sensitive to non-linearities in the transmitter. Coherent demodulation is typically employed in the receiver to ensure maximum immunity to the thermal noise of the radio receiver. This, in turn, requires that the receiver include circuitry to recover an unmodulated carrier from the incoming digital signal for use as a phase reference in the demodulation process. Unfortunately, the phase of the recovered carrier is subject to ambiguities which may result in the demodulated digital signal being transposed and/or inverted, resulting in gross transmission errors. Differential encoding of the digital signal, prior to modulation, overcomes this problem but may create additional problems, such as the inability of the receiver to monitor transmission errors by means of the parity bits which are included in the digital signal to be transmitted. The instant invention comprises an encoding algorithm which encodes the digital signal prior to modulation so that phase ambiguities in the recovered carrier signal become unimportant, yet at the same time preserves the ability of the receiver to check for transmission errors. The algorithm comprises two separate but complementary encoding rules, one of which is employed if the last three outputs of the encoder are logical equivalents and the other if they are not. A similar decoding algorithm is employed at the receiver.

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Atkinson, NH, United States of America

Gerald L Frazer