One of the new navigation signal type introduced with the Block III GPS are a protocol called M-Code, which is designed for direct military use and warzone conditions. It is designed to further enhance the high anti-jamming capability and secure access of military GPS signals. This signal is broadcast with a high-gain directional antenna, in addition to a wide angle antenna. The directional antenna's signal, termed a spot beam, is intended to be aimed at a specific region and increase the local signal strength.
M-code also includes: Satellites will transmit two distinct signals from two antennas. Binary offset carrier modulation. Occupies 24 MHz of bandwidth. It uses a new MNAV navigational message, which is packetized instead of framed, allowing for flexible data payloads. There are four effective data channels; different data can be sent on each frequency and on each antenna. It can include FEC and error detection. The spot beam is ~20 dB more powerful than the whole Earth coverage beam. M-code signal at Earth's surface: –158 dBW for whole Earth antenna, –138 dBW for spot beam antennas.
The features in these open sources are also summarized on the relevant wiki page. This new block system also envisages significant innovations in the GPS operational control segment (OCS), and those interested can take a look at this page:
https://en.wikipedia.org/wiki/GPS_Block_III In short, significant advances are emerging not only in life safety and civilian use, but also and predomnantly in non-civilian use. This makes access to this technology to some extent essential for armed forces with very specific requirements, such as the TAF. Probably the global positioning constellation satellites project will also be a very large and comprehensive aerospace program that cannot be limited to a few individual aerospace companies. To the best of my limited knowledge, what appears for some just to be a passive signal broadcasting satellite will have to be backed up by a very powerful infrastructure.
forum.nasaspaceflight.com
