This is a FSK transreceiver based on SDR.
I use a DSP from TI, which is called F28335, a series of C2000 DSP.
The IQ modulator/demodulator is SX1255, a very cheap chip originally used in LORA.
Due to the limit of CPU load and the ugly performance of the SX1255,the system can only achieved 9600bps at 433.9M ± 9K(FSK).
Maybe it can do a little bit better when using a better MCU such as RT1052 or F28388D.
The reference version, designed by my mother, powered by RT1052, AIC23 and CMX973, easily achieved 284kbps(OFDM).Σ(⊙▽⊙"a
Square root rasied cosine filter is used both in tx and rx to reduce side lobe leakage and maxim the SNR.
Both phy and link layer are provided, while the phy provide a payload of 36 bytes per frame.
The link layer, uses the 6 bytes as link encapsulation, remaining 32 bytes for upper layer(the same as NRF905).
The struct looks like:
(Preamble ->( PHY Payload )-> EOF)
(Address -> Type -> Link Payload -> CRC)
At burst mode, the signal in frequency domain looks like this:
Besides FSK version, QPSK(DSSS) and OFDM(QAM) versions are also in progress.
After THE BIG exam, the version of QPSK may be released if there are few bugs.