Broadband digital transmission over passive optical networks

The authors propose a low-cost digital technique for broadband transport which is capable of transparently carrying distribution quality video, data, and digital audio services economically over a passive optical network. Two possible upgrade routes from unidirectional to bidirectional services are discussed, one using optical technology, the other using electrical techniques. The use of digital transmission, with its inherent scrambling abilities, enables access to switched services to be controlled and generates an architecture suitable for a bidirectional service with no switching necessary at the head end. By locating shared transcoders at the head end, low-cost, high-bit-rate transmission can be used in the access network where the onus is on cheap terminal equipment, and an economic gateway to low-bit-rate transmission in the core network can be provided. The authors also discuss a video coding technique implemented in field programmable gate array technologies that encodes PAL at around 57 Mb/s, should be capable of encoding NTSC at around 45 Mb/s, and delivers video at a weighted SNR (signal-to-noise ratio) of 52 dB