mam1081 said:
I'm pretty sure Phase II P25 will all be 6.25 kHz bandwidth. I'm not sure, but I think it's supposed to be TDMA on trunked systems. The Phase I stuff is 12.5 kHz [C4FM], but can be 6.25 kHz [CQPSK], both in FDMA modulation.
Supposedly Phase II will require all new equipment. I don't know how true that is - seems like a lot of money for those big cities to go "Phase II". Phase III is supposed to follow II more quickly than II follows I. I think Phase III is to better integrate internet and data into the radios (probably will be all TDMA).
Maybe that helped?!
First, there is no Phase 3.
Phase 1 was everything completed in 1995, Phase 2 became the name for everything else.
This has caused much confusion.
Most refer to Phase 1 as the current Common Air Interface, 9600 bps, FDMA C4FM/CQPSK.
Most refer to Phase 2 as the upcoming (yet to be nailed down) TDMA scheme.
TDMA will be 2:1 TDMA (initially) on trunked systems.
ISSI, and other interface specifications are also often included in Phase 2.
The important thing to remember is that the whole body of individual specifications, whether they are in "Phase 1", Revisions of "Phase 1" documents, or in "Phase 2"; are all parts of a suite of standards that can be used in many configurations to build equipment and systems.
As for whether the TDMA scheme requires "all new equipment" will depend on a lot of things.
1) How the standard is finally decided
2) How the manufacturers decide to implement the finally decided standard
3) what equipment you have from those manufacturers.
There are provisions in the TDMA standards (Phase 2) to allow for FDMA (Phase 1) equipment backwards compatibility.