System approaches and technologies for satellite data microwave transmission approaching 8 gigabits per second

The paper describes a methodology for increasing digital satellite transmission throughput data rate by a factor of 2 over current practice (expanding from 1.5 to 3 bits per second per hertz of bandpass) and at the same time lessening the (E_b/N_o) penalty paid for higher order (3 and 4 bit per symbol) modulation waveforms by judicious application of forward error correction codes. This approach allows satellite transmitters to be driven into their high efficiency operating region at or near saturation. The high bandwidth efficiency is achieved by using higher order modulations (8-ary and 16-ary), precompensation of the signal to induce distortion complementary to that anticipated downstream in the channel, forward error correction coding, and adaptive equalization in the receiver. The recommended FEC, incurring about 10% overhead, can yield error rates on the order of 10 ^-8 for channel error rate between 8x10^-3. Error rates in the range of 10^-8 to 10^-9 are practical with channel error rates of 4xl0^-3. Operating at high error rates allows the channel to be operated in a region where small to medium distortions, which could be fatal at low error rates, are tolerable. This, along with precompensation for the nonlinear effects, allows the TWTA to be operated at or near saturation