demodulate fsk

hi, all friends,

FSK or MSK modulation has been used in modern low data rate radio or burst communication, for example MDS's dsp remote transceiver, or some tactical radio. In the receiver, they use coherent demodulation.

i want to know how to do FSK demodulation in the receiver,including synchronization of timing, frequency and phase.

Use PLL? no , PLL can not capture the fsk signal rapidly in burst communication.

Use limiter + discriminator?, no, the demodulation performance may be poor.

Use two match filter type demodulator or other methods?

In addition, low data rate receiver's frequency synchronization may be a important. For example, a transceiver with data rate 9600bps, carrier stability 5ppm, carrier frequency 1GHz, So the frequency difference between Tx and Rx is 10KHz -- too large for the data rate.

I know some devices can do FSK, for example, philips's SA606 which use limiter + quadrature detector, I believe those devices are used mainly in low cost receiver, not high performance.

Any friends can give me some suggests?

thanks

the pll is enough

The simplest way to demodulate Low rate FSK is non-coherent method, such as a high pass filter and a everlope dector.

If you want high performance, you will have to have a receiver bandwidth wide enough to cover the TX and RX frequency errors plus the modulation bandwidth. Then bring this to baseband with a quadrature down converter feeding two ADCs. You will have to sample much faster than the Nyquist rate. Then do a DSP algorithm that looks for spectral lines that are separated by the shift of your signal.

A further refinement is that if there would be no other signals received when your desired one is, use a limiter in the IF so that your ADCs can be driven to nearly full scale. You can detect the absence of a signal by the signal power being high and equal over the whole frequency range. When a signal is present, the broad background noise out of the limiter will decrease and the signal spectral lines will appear.