TETRA Air Interface
If you are interested in how the air interface and the lower levels of TETRA
work, you should have a look at the
My contribution so far was to search for a suitable demodulator (TETRA uses
PI/4-DQPSK) which I found at the
OP25 project (the
author of the demodulator is KA1RBI).
I also implemented some "proof of concept" code which allows decoding
speech traffic and converting it to raw audio using the TETRA reference
codec. Please note that this cannot be used to listen to encrypted
TETRA traffic, it only works if no encryption is used.
Microsoft Research and SDR
I wasn't aware of it, but Microsoft Research is doing SDR
(Software Defined Radio):
Their approach is interesting, all the raw samples are transferred between
the PC memory and the ADC/DAC of the Radio Front-end by a PCIe card and
all the signal processing is done by the CPU of a PC. There is no DDC
(Digital Down Converter) or DUC (Digital Up Converter) in an FPGA
involved. They already implemented 802.11a/b/g and an LTE receiver
The price of the hardware does not sound too expensive. The
software only runs on Windows and I have not yet checked the
license terms in detail.
I could imagine that combining this approach with the power of
a GPU can be quite interesting.