Candidate plans for adaptive digital transmission are briefly reviewed. It is suggested that adaptive format transmission with asynchronous multiplexing capability is attractive and promising from the standpoint of practical application. Feasibility and efficiency of this new transmission plan are investigated. A formula for predicting the minimum required transmission rate is derived. Upper and lower bounds of transmission efficiencies are analysed. A signal distributing technique for improving transmission efficiency is also developed. Investigation of memory requirements anticipates the possibility of simple implementations for format conversion and reconversion. Results of simulations prove the reliability of theoretical predictions. Fiber optic transmission is expected to be suitable for realizing this new communications concept.

Application of multipled block codes (MBCs) for realizing new flexible and efficient transmission systems that feature in hunting-free reframing and asynchronous multiplexing is investigated. First, the principles of MBC are overviewed to show the capacities of filterless clock recovery. Then it is shown that modification of simple frame structure of MBC line code can be used for attaining hunting-free reframing for multiplexing systems. Two types of MBCs are developed to this end. While the one uses header blocks for hunting-free reframing, the other uses distributed frame patterns. Header design of multipled block codes (MBC) for hunting-free reframing (HFR) is investigated for frame patterns with and without violation compensation. The feasibility of hunting-free reframing is tested in an experimental system. Application of hunting-free reframing to asynchronous multiplexing is also investigated and tested in an experimental system. Finally, advantages of hunting-free multiplexing systems are discussed.

It is shown that significant accumulation of alignment jitter can result if there exists any delay difference between signal and timing paths in respective regenerators in a chain. This phenomenon of extra alignment jitter accumulation is analyzed by using Chapman model. Dependence of accumulation on timing extrator Q and delay difference is predicted through the theoretical analyses. Results of computer simulation are found to be in good agreement with theory. It is also revealed by the simulation that additional accumulation can be entailed, which is explained in terms of jitter fine structures. Methods for alleviating extraaccumulations and desigh considerations for time cross hair budget are also discussed.

Generalized expressions for variable transfer functions (VIFs) , v(f,x) , for approximating real transmission chracteristic y0(f)u are investigated, which results in several new VTFs that provide error reductions and/or realizations superior to conventional ones. Error reduction is attained through zero forcing (ZF) of errors in terms of u and/or x parameters (ZF- U, ZF-X). It is shown that error reduction for first order VTFs (Linear and bilinear VTFs) depends only on ZF-U. On the other hand, second order VTFs (quadratic and biquadratic VTFs) utilize both ZF-U and ZF-X to attain drastic error reductions. The concept of x range modification is also introduced to contribute design flexibility.

Transmission and distribution systems are investigated for application in future fiber optic super-broadband and super-multi-channel subscriber loops. Gradual upgrading is considered so that future systems can keep compatibility with existing systems. First, time frame and strategies for subscriber loop upgrade are overviewed and assumptions for evolution of broadband multimedia distribution systems are discussed. It is suggested that upgrading to super-high definition (SHD) quality multimedia is desirable. Next, some examples of extra-auxiliary picture (EAP) formats are discussed to show the possibility of improving upgradability and compatibility by using extra-channels. Then multiplexing and channel selecting systems are investigated for economical realization of super-multi-channel distribution and flexible channel selection, and hybrid multiplexing (HMUX) and a trans-selector (T-SEL) are proposed. Finally, the efficiencies of HMUX and T-SEL are discussed by using numerical examples. Although broadband down streams are mainly considered, other streams such as IP traffics can be accommodated in the distribution systems investigated in this paper.

This letter proposes an improved polarization diversity method for heterodyne/coherent optical transmission systems. It is theoretically clarified that this method can reduce the noise caused by polarization fiuctuations and can receive a binary FSK or PSK modulated signal with high sensitivity.