For fixed installation of a wireless ICS I can recommend the system from Telephonics", which is also used on some Navy helicopters.
It consists of:
- Access Point Transceiver (installed in the helicopter)
- Portable Transceiver(s)
- Headset adaptor (for the Portable Transceiver)
- fixed installed antenna
Power consumption of the Access Point Transceiver is approx. 2 Watt.