A digital audio communication system includes a digital modulation and demodulation scheme which efficiently uses the bandwidth and channel spacing of a cable television system. A 30 channel digital bit stream is demultiplexed into six groups of five channels. Each group of channels thereafter modulates...http://www.google.es/patents/US5271041?utm_source=gb-gplus-sharePatente US5271041 - Method and apparatus for QPR carrier recovery
