Call-by-Call Activation Technique for Fiber-Optic Subscriber Transmission Units

A call-by-call activation technique for fiber-optic subscriber systems has been developed to reduce electric power consumed in transmission units installed on subscriber premises. The major part of the transmission unit is supplied power call-by-call. The technique has been applied for a fiber-optic subscriber system in the INS Model System (NTT project) for which the PFM technique is used to transmit a frequency division multiplexed signal containing video, audio, and digital signals bidirectionally. This paper describes the control procedure and hardware implementation for this call-by-call activation. Discussion is made on methods of achieving optical carrier sensing. A unique technique is proposed which enables rapid and accurate indication of frame synchronization together with no considerable bit error occurrence for the digital signal just after activation. Experimental results which reveal validity of control procedure, carrier sensing, and frame synchronization methods are also shown together with the effect of power saving and assessment of build-up time required for activation.