Abstract: A QPSK modulation scheme uses a data spreading mechanism to rob a relatively limited portion of available transmitter power, and inject into the QPSK waveform a prescribed amount of carrier signal power, through which detection and non-regenerative extraction of the carrier at the receiver may be achieved without incurring a signal-to-noise degradation penalty. In addition, the injected carrier-based modulation scheme of the invention may employ high performance forward error correction coding, to significantly reduce the signal power required for achieving a very low energy per bit-to-noise density ratio (Eb/N0)—on the order of one to zero dB.

Abstract: A satellite communications scheme for enhancing the communications system with existing satellites is disclosed. The existing satellites include a transponder having a phase locked loop phase demodulator at the front end thereof. The present invention discloses a technique wherein the phase demodulator is locked by transmitting a relatively high-power carrier from the ground to the satellite transponder. Once the demodulator has been locked, remote ground terminals operating at much lower power levels can access the satellite transponder by transmitting at carrier frequencies spaced apart from the primary high-power carrier. These are down-converted by the transponder phase demodulator and then typically amplitude and frequency limited before being remodulated and retransmitted.

Abstract: A code tracking loop for a spread spectrum receiver includes a pair of mixer circuits to which phase offset or relatively delayed pseudo noise code signals are applied and combined with an incoming IF spread spectrum signal. The output of the mixers are coupled to a sum and difference hybrid. The hybrid produces a sum signal corresponding to the sum of the mixer outputs and a difference signal corresponding to the difference between the mixer outputs. These sum and difference signals are separately filtered, amplified and then coupled to a further mixer or phase detector. Appropriate AGC circuitry is controlled by the envelope of the sum signal to adjust the gains of the respective amplifiers. The output of the phase detector is proportional to the difference between the squares of the outputs of the hybrid and represents the phase of the sum signal relative to the difference signal.

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 QPSK modulation scheme uses a data spreading mechanism to rob a relatively limited portion of available transmitter power, and inject into the QPSK waveform a prescribed amount of carrier signal power, through which detection and non-regenerative extraction of the carrier at the receiver may be achieved without incurring a signal-to-noise degradation penalty. In addition, the injected carrier-based modulation scheme of the invention may employ high performance forward error correction coding, to significantly reduce the signal power required for achieving a very low energy per bit-to-noise density ratio (Eb/N0)—on the order of one to zero dB.