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In digital modulation, minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying that was developed in the late 1950s by Collins Radio employees Melvin L. Doelz and Earl T. Heald. [1] Similar to OQPSK, MSK is encoded with bits alternating between quadrature components, with the Q component delayed by half the symbol period.
Minimum frequency-shift keying or minimum-shift keying (MSK) is a particular spectrally efficient form of coherent FSK. In MSK, the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms that represent a 0 and a 1 bit differ by exactly half a carrier period.
Notable variants of CPM include minimum shift keying (MSK) and Gaussian minimum shift keying (GMSK), which uses a Gaussian filter to smooth out phase shifts. [7] [8] Since the underwater environment is highly scattered, it can cause multipath propagation and signal degradation.
ASK (amplitude-shift keying): a finite number of amplitudes are used. QAM (quadrature amplitude modulation) : a finite number of at least two phases and at least two amplitudes are used. In QAM, an in-phase signal (or I, with one example being a cosine waveform) and a quadrature phase signal (or Q, with an example being a sine wave) are ...
In addition to Gaussian minimum-shift keying (GMSK), EDGE uses higher-order PSK/8 phase-shift keying (8PSK) for the upper five of its nine modulation and coding schemes. EDGE produces a 3-bit word for every change in carrier phase.
Although most transmit specifications are classified, it is known that the radio uses Gaussian Minimum Shift Keying and M-ary encoding. It can also be used in an analog FM mode, in which it is compatible with other radios like AN/PRC-77 and civilian radios.
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AIS messages are transmitted using Gaussian minimum-shift keying (GMSK) modulation. The GMSK modulator BT-product used for transmission of data should be 0.4 maximum (highest nominal value). The GMSK coded data should frequency modulate the VHF transmitter. The modulation index should be 0.5. The transmission bit rate is 9600 bit/s