An application of multiple block codes (MBC) for realizing new digital transmission schemes that features in hunting-free reframing is investigated. First, the principles of MBC are overviewed to show the capability of filterless clock recovery. Then it is shown that modification of the simple frame structure of MBC line code can be used for attaining hunting-free refraining for multiplexing systems. Two types of MBC are developed to this end. While the one uses header blocks for hunting-free refraining, the other uses no headers. Finally, systematic design of MBC format for hunting-free refraining is investigated. It is shown that variable frame lengths can be accommodated by MBC with header type framing blocks.

The technical feasibility of applying a fiber-optic multilevel QAM (quadrature amplitude modulation) subcarrier multiplexing scheme to a multichannel conventional TV signal transport is explored. This transport scheme has some advantageous features. Because a digital subcarrier modulation scheme is used, a high-quality transmission performance is expected to be achieved, if the bit error is sufficiently small over a transmission line and the required carrier-to-noise ratio (CNR) is relatively small among the many candidates of subcarrier modulation schemes. The use of multilevel modulation allows the bandwidth to be efficiently utilized; consequently, up to 40-channel uncompressed digital TV signals are estimated to be accommodated in the frequency region of the VHF and UHF bands, where well-developed and inexpensive electronics can be easily applied.>