Channel Quality Estimation and Adaptive Transmission of an OFDM System for Spaceborne SAR Data links

In this paper, we consider an OFDM system design with channel quality estimation and adaptive transmission for spaceborne SAR data links. A channel quality metric based on noise covariance matrix and channel gains is introduced into the design. We developed a link adaptation technique by maximizing the transmission throughput subject to the constraints on the transmitter power, the signal bandwidth, the bit error rate (BER) as well as the channel quality metric. A re-transmission protocol is also considered based on Automatic Repeat Request (ARQ) and packet combining. If the transmitter has the knowledge on channel quality estimation, it may adjust modulation constellation, channel coding rate and transmitting powers of each subcarrier to maximize the total transmission throughput. Both performance analysis and computer simulation demonstrate that OFDM system link adaption is efficient to channel utilization and this may provide very high throughput to satellite communications, which are preferred properties to SAR data links.