Design and implementation of the 155 Mbps adaptive modem for broadband satellite communications

We present the design and implementation of a 155 Mbps satellite modem adaptively compensated against rain attenuation. In order to compensate rain attenuation over a high-speed satellite link, adaptive coding schemes with variable coding rates and pragmatic TCM, that can decode both QPSK and TC-8PSK using the same Viterbi decoder, are studied and analyzed. The pragmatic TCM with rate 2/3, selected as the optimal parameters for implementation, is modeled by VHDL. The key design issues are how to achieve a high data rate and how to integrate into a single ASIC chip various functions such as different data rates, scrambler/descrambler, interleaver, encoder/decoder, and BPSK/QPSK/8PSK modulator/demodulator. The implemented 155 Mbps adaptive modem has simplified interface circuits among the many functional blocks, and parallel processing architecture to achieve the high data rate. This 155 Mbps adaptive modem was designed and implemented by a single ASIC chip with the 0.25 μm CMOS standard cell technology.