Constant envelope offset QPSK modulator

Claim 1

Apparatus for transforming a serial input data signal into a substantially constant envelope offset phase shift keying modulated signal vector, comprising: first means for generating a baud clock having a repetition rate that is one-half that of the data signal; second means for directing alternate data bits in the input data signal into in-phase and quadrature-phase I and Q pulse trains, with the present data bit that is entered into a pulse train being held constant for the time interval 2T of the present and next data bits which have a symbol interval T; storage means for storing a present and past bit for each of the I and Q pulse trains; a quadrature-phase modulator for combining quadrature-phase sinusoidal carrier signals with associated ones of first and second input signals for generating the phase modulated signal vector; and third means responsive to the baud clock and the present and a prior bit from each of the I and Q pulse trains during each symbol interval for generating associated series of analog voltages which are said first and second input signals and which cause the rate of change w of the phase of the signal vector during each symbol interval to satisfy the criteria: ______________________________________ I(t) = I(t - nT) Q(t) = Q(t - nT) |w| ______________________________________ yes yes O yes no W no yes W no no 2W ______________________________________ where W and 2W are constant phase velocities that rotate the signal vector a total of 45° and 90°, respectively, in a symbol interval; n is an integer; t is time; I(t) and Q(t) are the present bits; and I(t-nT) and Q(t-nT) are prior bits in the I and Q pulse trains; wherein n=2 and I(t-2T) and Q(t-2T) are the bits immediately preceeding the present bits in the I and Q pulse trains; and wherein said series of voltages from said third means cause rotation of the signal vector either clockwise or counterclockwise when the baud clock is one of a binary 1 and 0 and the bit I(t-2T) is not equal to and is equal to the bit Q(t), respectively; and rotation of the signal vector either counterclockwise or clockwise when the baud clock is the other of a binary 1 and 0 and the the bit I(t) is not equal to and is equal to the bit Q(t-2T), respectively.

Claim 4

A method of generating a constant envelope offset phase shift keying modulated signal vector from a digital input data signal in which alternate bits are directed into in-phase I and quadrature-phase Q channels, with the current bit that is entered into each channel being held constant for a time interval 2T of the current and next data bits, and wherein the phase of the signal vector varies by prescribed amounts and in prescribed directions during a symbol interval T of each data bit, comprising the steps of: causing the rate of change w of phase to be determined as follows: ______________________________________ I(t) = I(t - 2T) Q(t) = Q(t - 2T) |w| ______________________________________ yes yes O yes no W no yes W no no 2W ______________________________________ where I(t) and Q(t) represent the current data bits in the in-phase and quarature-phase channels, respectively; I(t-2T) and Q(t-2T) represent the immediate past data bits in the in-pase and quadrature-phase channels, respectively; I(t)=I(t-2T) and Q(t)=Q(t-2T) are identities; w is the phase velocity or rate of change of phase; and W and 2W are constant phase velocities that will rotate the signal vector a total of 45° and 90°, respectively, in one bit time T; generating a baud clock signal having a repetition rate which is one-half that of the input data signal; and performing one of the steps of: rotating the signal vector either counterclockwise or clockwise when the baud clock is one of a binary 1 and 0 and the identity I(t-2T)=Q(t) is satisfied and not satisfied, respectively; and rotating the signal vector either clockwise or counterclockwise when the baud clock is the other of a binary 1 and 0 and the identity I(t)=Q(t-2T) is satisfied and not satisfied, respectively.

Claim 5

A method of generating a constant envelope offset phase shift keying modulated signal vector from a digital input data signal in which alternate bits are directed into in-phase I and quadrature-phase Q channels, with the current bit that is entered into each channel being held constant for a time interval 2T of the current and next data bits, and wherein the phase of the signal vector varies by prescribed amounts and in prescribed directions during a symbol interval T of each data bit, comprising the steps of: causing the rate of change w of phase to be determined as follows: ______________________________________ I(t) = I(t - 2T) Q(t) = Q(t - 2T) |w| ______________________________________ yes yes O yes no W no yes W no no 2W ______________________________________ where I(t) and Q(t) represent the current data bits in the in-phase and quarature-phase channels, respectively; I(t-2T) and Q(t-2T) represent the immediate past data bits in the in-pase and quadrature-phase channels, respectively; I(t)=I(t-2T) and Q(t)=Q(t-2T) are identities; w is the phase velocity or rate of change of phase; and W and 2W are constant phase velocities that will rotate the signal vector a total of 45° and 90°, respectively, in one bit time T; generating a baud clock signal having a repetition rate which is one-half that of the input data signal; and performing one of the steps of: rotating the signal vector either counterclockwise or clockwise when the baud clock is one of a binary 1 and 0 and the identity I(t-2T)=Q(t) is satisfied and not satisfied, respectively; and rotating the signal vector either clockwise or counterclockwise when the baud clock is the other of a binary 1 and 0 and the identity I(t)=Q(t-2T) is satisfied and not satisfied, respectively.