7
MSK application note
7.1 MSK send
The MSK transmission first frames the information data according to the frame structure, then maps
the data into the MSK modulation, and then transfers the modulated data to the 1.5KHz
intermediate frequency through the NCO. The MSK and spectrum shifting are performed in one
module. A continuous phase signal is generated and finally input to the FM modulation. Thus the
modulation process of the entire data is completed.
Figure 7.1 Transmitter system block diagram
7.2 MSK receiving
The MSK modulation proposed by MPT1327 contains an FM modulator, so the design of the
receiver is opposite to the modulation process, and the FM demodulation module is added, that is,
the non-coherent demodulation scheme is adopted. The receiver is divided into front-end data
acquisition and back-end baseband signal processing.
The front-end data collection part is similar to the second half of the sending end, and will not be
described here. In the back-end signal processing part, key steps such as arrival detection, timing
synchronization, and decision are all completed in this part. The flow of MSK baseband processing
is shown in Figure 7.2.
OMISSIS
Figure 7.2 Receive Baseband Processing Flowchart
The receiver design uses non-coherent demodulation, using the front-end data acquisition module to
obtain two baseband IQ signals, followed by differential phase discrimination, then sent to a low-
pass filter to eliminate out-of-band noise, and finally back-end signal processing.
7.3 MCU instructions
7.3.1 MCU workflow
7.3.1.1
Initialization
MCU initialization, configuration register TrainErrorThreshold is 5, DTBeforeTransAndRec is 160,
Channel_Delay is 20, NT is 103.
7.3.1.2
Send control
Control channel transmission
