SYNCHRONOUS RECEIVER FOR MINIMUM SHIFT KEYING TRANSMISSION

摘要

A receiver circuit recovers the phase of the carrier of a received MSK signal so that conventional synchronous detection techniques can be employed to demodulate the received signal. A quadrature receiver circuit (204-214) processes the received MSK signal to produce in-phase and quadrature phase baseband signals. These I-channel and Q-channel baseband signals are viewed as one signal which is expressed as a complex number; the I-channel forming the real part and the Q-channel forming the imaginary part. The baseband signal is multiplied (218 and 220) by odd and even orthogonal functions (222 and 224) and then integrated (226 and 227) over odd and even numbered two bit periods, respectively. The odd orthogonal function begins and ends on odd numbered two bit periods of the received MSK signal, while the even orthogonal function begins and ends on even numbered two bit periods. The result of the integration is a single complex number for each bit of the received signal. From each of these complex numbers, two supplementary angles are computed (228 and 229). A phase error algorithm (230) resolves which one of the two supplementary angles is the phase error between the carrier of the received MSK signal and the oscillator (208 or 302) of the quadrature circuit by selecting the angle that is closer to the phase error that was calculated for the previous bit.