Advanced modulation technology development for earth station demodulator applications. Coded modulation system development

A jointly optimized coded modulation system is described which was designed, built, and tested by COMSAT Laboratories for NASA LeRC which provides a bandwidth efficiency of 2 bits/s/Hz at an information rate of 160 Mbit/s. A high speed rate 8/9 encoder with a Viterbi decoder and an Octal PSK modem are used to achieve this. The BER performance is approximately 1 dB from the theoretically calculated value for this system at a BER of 5 E-7 under nominal conditions. The system operates in burst mode for downlink applications and tests have demonstrated very little degradation in performance with frequency and level offset. Unique word miss rate measurements were conducted which demonstrate reliable acquisition at low values of Eb/No. Codec self tests have verified the performance of this subsystem in a stand alone mode. The codec is capable of operation at a 200 Mbit/s information rate as demonstrated using a codec test set which introduces noise digitally. The measured performance is within 0.2 dB of the computer simulated predictions. A gate array implementation of the most time critical element of the high speed Viterbi decoder was completed. This gate array add-compare-select chip significantly reduces the power consumption and improves the manufacturability of the decoder. This chip has general application in the implementation of high speed Viterbi decoders

Ubiquitous antisense transcription in eukaryotes: novel regulatory mechanism or byproduct of opportunistic RNA polymerase?

One of the more notable observations made in the last few years in gene regulation is that eukaryotic genomes appear to be pervasively transcribed. Recent transcriptome mapping studies have shown that much of the genome is transcribed, and in some instances transcripts from both strands of specific genomic loci are detectable. While some of these transcripts map to known RNA polymerase II transcription units [that is, protein encoding open reading frames (ORFs)], many are derived from regions of DNA thought to be non-genic. Parallel chromatin immunoprecipitation studies of template-bound RNA polymerase II have shown that it is indeed resident on those regions found to be transcribed, both ORF and non-ORF. However, the strandedness of these pervasive transcripts has never been measured on a genome-wide basis. Four recent reports have addressed this question and, in the process, have made the startling discovery that many loci of mRNA sense gene transcription are associated with very active antisense or divergent transcription that begins at mapped transcription start sites and proceeds in an upstream direction