DEMOD/decoder integration

Abstract : This report considers the benefits to be gained by an integrated coding and modulation approach for high speed digital communications over line-of-sight (LOS) and troposcatter links. While the importance of coding on tropo links has been previously established, this work indicates that error correction coding also plays an important role in the design of high bit packing density LOS modems. This result was not known apriori and, in fact, conventional rate-1/2 codes were shown to be ineffective for LOS modems operating with packing densities in excess of 2 bits/sec/Hz. However, an efficient 2 bits/sec/Hz and a 4 bits/sec/Hz modem, utilizing a rate-8/9 block code, were shown to yield superior performance to uncoded modems at this same packing density.