Secure communication by encryption/decryption of vector at PSK modulation/detection stage

A phase shift keying (PSK) transmitter comprising:

• a mapping circuit for mapping an N-bit symbol to a corresponding one of a predetermined number of vectors in a two-dimensional phase plane, where N is an integer equal to or greater than one;
• a pseudorandom number generator for producing a pseudorandom number varying in a range between 0 and 2.pi. radian;
• means for producing a sine-wave and a cosine-wave in accordance with said first pseudorandom number;
• a complex multiplier for complex-multiplying an output vector of said mapping circuit by the sine-wave and the cosine-wave;
• a lowpass filter circuit for lowpass-filtering an output vector of said complex multiplier;
• an oscillator for producing a carrier;
• and
• a quadrature modulator for quadrature-modulating said carrier with the lowpass-filtered vector for transmission.

A phase shift keying (PSK) receiver for receiving a quadrature-modulated PSK carrier containing a N-bit symbol vector which has been phase-rotated in a first direction in accordance with a first pseudorandom number varying in a range between 0 and 2.pi. radian, where N is an integer equal to or greater than one, comprising:

• a local oscillator for producing a local carrier having a same frequency as the quadrature-modulated PSK carrier;
• a quadrature detector for receiving the quadrature-modulated carrier and quasi-synchronously quadrature-detecting the received carrier with said local carrier;
• a lowpass filter circuit for lowpass-filtering an output vector of said quadrature detector;
• a sampling circuit for sampling the lowpass-filtered output vector in response to a sampling pulse;
• a pseudorandom number generator for producing a second pseudorandom number varying in a range between 0 and 2.pi. radian, said second pseudorandom number being identical in magnitude to but opposite in sign to said first pseudorandom number;
• means for producing a sine-wave and a cosine-wave in accordance with said second pseudorandom number;
• a complex multiplier for complex-multiplying an output vector of said sampling circuit by the sine-wave and the cosine-wave;
• a quadrature demodulator for detecting a phase error of said local carrier with respect to the quadrature-modulated PSK carrier and quadrature-demodulating an output vector of said complex multiplier with the detected phase error;
• and
• means for estimating a phase error of an output vector of said quadrature demodulator with respect to said N-bit symbol vector and producing therefrom a timing signal and applying the timing signal to said sampling circuit as said sampling pulse.

A method for securing privacy of communication, comprising the steps of:

• a) mapping an N-bit symbol to a corresponding one of a predetermined number of vectors in a two-dimensional phase plane, where N is an integer equal to or greater than one;
• b) producing a first pseudorandom number varying in a range between 0 and 2.pi. radian;
• c) producing a first sine-wave and a first cosine-wave in accordance with said first pseudorandom number;
• d) complex-multiplying the vector mapped by step (a) by the first sine-wave and the first cosine-wave;
• e) lowpass-filtering the vector complex-multiplied by step (d);
• f) quadrature-modulating a carrier with the lowpass-filtered vector;
• g) transmitting the quadrature-modulated carrier;
• h) receiving the quadrature-modulated carrier and quasi-synchronously quadrature-detecting the received carrier with a local carrier to produce a quadrature-detected vector;
• i) lowpass-filtering the quadrature-detected vector;
• j) sampling the lowpass-filtered vector in response to a sampling pulse;
• k) producing a second pseudorandom number varying in a range between 0 and 2.pi. radian, said second pseudorandom number being identical in magnitude to, but opposite in sign to said first pseudorandom number;
• l) producing a second sine-wave and a second cosine-wave in accordance with said second pseudorandom number;
• m) complex-multiplying the vector sampled by step (j) by the second sine-wave and the second cosine-wave;
• n) detecting a phase error of said local carrier with respect to the quadrature-modulated carrier and quadrature-demodulating the vector complex-multiplied by step (m) with the detected phase error;
• and
• o) estimating a phase error of the quadrature-demodulated vector with respect to said N-bit symbol and producing therefrom the sampling pulse of step (j).