Power and Spectrum Efficient Access Services Using Adaptive Modulation and Coding

Existing satellite systems used QPSK modulation with concatenated Convolutional and Reed-Solomon error correction codes as per the DVB standard. In addition, the RF links are run using fixed margins with the size of the margin dependent upon the maximum rain attenuation predicted for the service area. One way to increase the system data throughput is to manage each user terminal separately and have each one use as high a level modulation in combination with as high a code rate as the instantaneous link conditions allow. As link conditions fade for each individual terminal, the modulation level and code rate is changed to maintain BER requirements. Since only a low percentage of user terminals in a beam will encounter large rain attenuation at any time, this technique, called Dynamic Link Assignment (DLA), significantly increases average information throughput per unit bandwidth. References 2 and 3 have shown this increase to be on the order of 250 to 400 percent for Ka-band geostationary satellite systems. The exact increase depends upon the rain rate region for the service location and the satellite configuration. In addition to these increases in capacity, the technique may lower satellite and user terminal EIRP requirements. These gains allow the service cost to be reduced to under $30 a month.