Monday, July 02, 2012
It is sometimes confused with TETRAPOL. Tetrapol uses Gaussian Minimum Shift Keying (GMSK) modulation instead of the Quadrature Differential Phase Shift Keying (QDPSK) used by TETRA. This is where most people say "huh?" GMSK is a type of digital modulation that uses spectrum efficiently. Efficiently in these case refers to its needed bandwidth. Other forms of phase shift keying have sidebands that extend outwards from the main carrier and cause interference to other signals. QDPSK is less efficient and uses two encoded BPSK carrier waves. The two carrier waves are out of phase with each other by 180°. So it's highly noise resistant. If that's getting too complicated just remember that TETRAPOL is the one based on an FDMA multiplex using a narrow-band channel.
There are more than a hundred nations using TETRA systems: China, India, Pakistan, Germany, Ireland, Italy, Poland, Sweden, Australia, Mexico, Israel and the UK. (Notice that the USA isn't on that list. The FCC has not officially allocated any frequencies for the use of any TETRA-based standards. TETRA is a European Telecommunications Standards Institute (ETSI) standard. The first version published 1995 and it's fully endorsed by the European Radio Communications Committee (ERC.) So why don't we have it here?
You might think that maybe the FCC doesn't like open standards, or maybe just not European ones. But that's not the case. Motorola cock-blocked all that technology. Motorola, having invented the walkie-talkie owns a lot of valid US patents.They just refused to license them to the ETSI. More here. They tried to petition the FCC to intervene, but they did nothing since ETSI has no standing as a broadcaster in the US.