High Rate Ka-band Downlink Digital Receiver for MUOS

The Mobile User Objective System (MUOS) will provide global SATCOM for the DOD using WCDMA technology. A key to achieving this is the "virtual" location of the radio base station (RBS) antennas on 4 geosynchronous satellites. The transport of the user-to-base (U2B) and base-to-user (B2U) signals between these antennas and the RBSs located on the ground is provided by Ka-band uplink/downlinks. Each Ka-band downlink transports samples for 32 WCDMA beam-carriers via three 8-PSK signals at a rate of 2457 Mbits/sec. This downlink is processed on the ground by an FPGA-based digital receiver to recover the samples and reconstruct the WCDMA uplink signals. The high data rate of this demodulator coupled with the constraints of cost, BER, availability and power consumption drives a challenging design solution. This paper discusses a number of features of this design including high speed processing architecture, hybrid analog/digital timing recovery loop, carrier recovery loop (CRL), equalizer, adaptive cross-pol interference canceller (AXPIC), frame synchronizer and turbo decoder.