Global Broadcast System (GBS)

The Global Broadcast System (GBS) is a military satellite broadcast capability designed to provide high-rate, one-to-many dissemination of data, imagery, and video to deployed forces. The first operational GBS payload was launched aboard UHF Follow-On-8, and GBS payloads are also hosted on the Wideband Global Satellite (WGS) constellation.

The GBS payload replaced the earlier SHF X-band broadcast payload with four Ka-band transponders, each capable of transmitting data at rates of up to 24 Mbps using approximately 130 W of radio-frequency output power. Data is received by the satellite via a fixed uplink antenna from a Broadcast Management Center (primary injection point), as well as via a steerable uplink antenna from a theatre injection point. Each of the four transponders can be accessed through either uplink path.

Downlink transmission is provided through three steerable spot beams. Two of the spot beams each cover an area approximately 500 nautical miles in diameter and support data rates of up to 24 Mbps for reception by terminals with antennas as small as 56 cm. The third spot beam provides wider coverage of approximately 2,000 nautical miles in diameter, supporting a reduced data rate of about 1.5 Mbps. One of the four transponders can be switched between the narrow-area (500 nm) and wide-area (2,000 nm) spot beams to provide operational flexibility.

GBS is optimized for asymmetric traffic, providing high-rate downlink capacity with relatively low uplink bandwidth requirements. The system is particularly suited to dissemination of intelligence products, software updates, and situational awareness data to large numbers of users simultaneously.