Modem performance characterization for satellite communications on the move

One of the crucial goals of the US Army is to have location information and access to continuous communication for all personnel and equipment in the battlefield. Unfortunately, most tactical command and control vehicles only have line of sight (LOS) tactical radios that are severely range-limited. These tactical radios, without the assistance of radio relays, do not provide coverage over the needed 10's of kilometers of the battlefield. One alternative to provide beyond LOS communications is to use satellite technology. In the past, this was an expensive alternative for continuous communications, and ground terminals capable of supporting medium data rate (MDR) satellite communications (SATCOM) service on-the-move were not available. However, the competition in this market over the past few years has significantly decreased the cost of both the satellite equipment and satellite time. The MITRE Corporation is investigating the technology of SA TCOM on-the-move (SOTM) for the US Army Ground Mobile Forces. The focus of the project is to develop the capability using current Ku-band commercial satellites and eventually migrate to future DOD-owned Ka-band satellites that will support high bandwidth on demand type services (i.e., Wideband Gapfiller Satellite). The primary effort of the project is to develop a low-cost integrated terminal capable of providing MDR performance (256 kbps target). There are several technological hurdles to overcome in the design and building of a SOTM terminal designed for operation over commercial Ku-band satellites. This paper focuses on the modem performance in this system including the background analysis done, determining the need for a spread modem, the parameters required for the modem and the methodology and results of both lab testing and field testing of the modem. The performance of the modem was evaluated in an environment with noise, multipath, changing Doppler and frequent signal loss. Finally, the satellite channel was validated through signal and delay spread testing.