Abstract: A technique for deriving a phase reference for PSK demodulation uses the absolute values of phase vectors as they are received to establish a reference with which the individual phase vectors are compared for data demodulation. Over some span of N successively received signals (phase vectors), the received phase vectors are successively analyzed to derive a hypothetical reference phase vector with which the vector symbols are to subsequently compared for data demodulation. The symbol values are temporarily buffered as they are received. As each phase vector is received, all possible (i.e. M-ary) phase values, referenced to the value of the received phase vector, are compared to a stored reference. Each of these M-ary possible phase values is vector-summed with the stored reference and the resulting vector sum having the largest magnitude is then substituted for the stored reference and is used by the next received vector symbol to further refine the reference vector.

Abstract: In a communication system, a signal detection and acquisition system, which is capable of locating and phase-locking onto a narrow-band signal in a large frequency uncertainty region in a short period of time, employs the following series of operations:(a) sequentially search for signal power in adjacent frequency bins into which the frequency uncertainty region is divided,(b) find the widest loop filter bandwidth at which the receiver phase lock loop can lock onto a transmitted signal,(c) sweep the loop carrier reference oscillator and phase lock onto the transmitted signal,(d) convert the bandwidth of the loop filter at which phase lock was acquired to the bit rate bandwidth, and(e) bit synchronize and begin data recovery.

Abstract: A carrier recovery scheme for a PSK demodulator through which side locking onto an interference-created sideband is avoided includes a hard-limited upstream of a phase-locked loop which removes jammer-induced AM from the input signal. As the loop sweeps through the frequency range of interest, a lock detector, coupled to the phase-locked loop will lock onto or acquire only the true carrier and thereby enable demodulation of the PSK information signal.In a digital implementation of the invention, received PSK input signals are converted into digital format by a multi-level quantizer, after being down-converted to an IF signal and subjected to gain control. The output of the quantizer may be a multi-bit, parallel word indicative of the changing amplitude of the IF signal which is to be sampled at the receiver sampling rate and converted into a digitally encoded representation of a received IF signal sample.

Abstract: A digital demodulator for recovering a baseband signal from a selectable bit rate PSK modulated signal. Carrier recovery and bit timing recovery are accomplished by using the digital equivalent of an analog in phase-quadrature (I/Q) phase locked loop. The recovered I and Q components are directed through matched filters to remove unwanted out-of-band signal components. A normalization loop responds to the output of the filters to provide normalized signals whose amplitudes do not significantly vary with changes in data rate or signal to noise ratio. Circuitry is provided for tailoring the parameters of a loop filter used in the carrier recovery loop in accordance with the data rate of the incoming signal. A lock detector is provided for determining the signal-lock status of the demodulator, and for controlling the operation of a carrier sweep control. Several numerically controlled oscillators are disclosed for use in the carrier recovery and bit timing recovery loops.