What It Is
At its core, CATS is a packet radio standard primarily designed for autonomous position reports, but is versatile enough to support a much wider scope of communication. CATS packets are extremely versatile, consisting of multiple "Whiskers" which make up the packet. Whiskers come in several types. For example, a typical CATS position beacon would likely contain an Identification Whisker, GPS Whisker, and potentially a Comment Whisker and Timestamp Whisker. Different Whiskers can be mixed and matched to allow a wide range of data to be encoded. Detailed information on CATS can be found in the standard, linked below.
Comparison to APRS
CATS is ultimately meant to be a replacement to APRS. Although APRS was magnificent when it was first developed, current technology allows us to do better. APRS also suffers from decades of bloat, making the standard difficult to learn. Here are some of the ways CATS is better than APRS:
Raw FSK on the air - APRS is transmitted as AFSK over FM. This is an inefficient encoding technique which leaves a lot of performance on the table. In contrast, CATS uses raw FSK. This alone provides a significant coding advantage.
Shorter key-up/key-down times - APRS was designed to be used over standard FM radios. These have the disadvantage of very slow PTT times. It's not uncommon for an APRS packet transmission to take less time than keying up and keying down does. As a result, channel utilization suffers greatly. CATS is designed to use cheap FSK transmitters, allowing the standard to enforce very quick PTT times.
Faster data rate - APRS is typically used at 1200 baud. CATS sets the standard data rate to 9600 baud.
Forward Error Correction (FEC) - CATS uses LDPC encoding to ensure bit flips don't ruin the packet. Data whitening is used to provide a level of resiliency against burst errors.
70cm used by default - Whereas APRS typically uses 2m for RF transmission, CATS uses 70cm. The main advantage of this is that a single antenna can be used for a 2m voice radio and a 70cm CATS transceiver. This is especially useful in mobile installations.
Keep it simple. It should be possible to become a CATS expert in an afternoon.
Be efficient. CATS should use the airwaves as efficiently as possible. Nothing stands in our way besides the Shannon Limit.
FELINET is, roughly speaking, the APRS-IS equivalent for CATS. FELINET servers communicate with each other and with I-gates to provide a single unified network of CATS packets.
CATS is extremely work-in-progress. Most importantly, this means the standard can change in unpredictable ways that potentially aren't backwards compatible! Once things are solidified a bit more, the standard will be locked down and all new changes must be backwards compatible.
At the moment, there's a running FELINET server which gates to and from APRS-IS for backwards-compatibility, as well as an I-Gate and basic mobile transceiver. Packets are transmitted over the air to the I-Gate, then sent to FELINET and relayed onto APRS-IS.
CATS is entirely open, so contributing can be done the normal way by opening issues and PRs on any of the above projects. Another way to contribute is by setting up and playing with CATS hardware. Bug reports and feature requests are extremely important to allow the standard, and reference implementation, to mature.
If you're on Matrix, there is a space for CATS discussion: #cats:crabsin.space
If you have any questions, feel free to email me at cats (at) scd31.com . 73 and hope to catch you on CATS!