	US 7,512,341 B2
	Passive optical network system and ranging system thereof
Tohru Kazawa, Kokubunji (Japan); Masaki Ohira, Yokohama (Japan); Yusuke Yajima, Fujisawa (Japan); and Norihiro Sakamoto, Yokohama (Japan)
Assigned to Hitachi Communication Technologies, Ltd., Tokyo (Japan)
Filed on Aug. 04, 2008, as Appl. No. 12/185,560.
Application 12/185560 is a continuation of application No. 11/729974, filed on Mar. 30, 2007.
Claims priority of application No. 2006-279446 (JP), filed on Oct. 13, 2006.
Prior Publication US 2008/0317469 A1, Dec. 25, 2008
Int. Cl. H04J 14/00 (2006.01)

U.S. Cl. 398—71

3 Claims

1. A station-side communication device connected to a plurality of subscriber-side communication devices via an optical combining device; sending, to said plurality of subscriber-side communication devices, a distance measurement request signal for measuring the distances to respective ones of said subscriber-side communication devices; computing transmission delay times of optical signals from individual ones of said subscriber-side communication devices by receiving distance measurement signals which are replies from said plurality of subscriber-side communication devices with respect to said distance measurement request signal, and comprising:

a threshold control part identifying the voltage level of said distance measurement signals converted from optical signals into electrical signals;

a signal detection part detecting breaks in said distance measurement signals from said threshold control part;

a transmission granting part determining the timing at which transmission of optical signals is granted, with respect to an individual subscriber-side communication device;

a reset timing generation part that, while it is being notified from said transmission granting part that distance measurement is carried out to and from said subscriber-side communication devices, sends a plurality of reset signals, indicating that said voltage level is reset, to said threshold control part; and

a serial number mask generation part designating at least a part of the serial number allocated dedicatedly in said subscriber-side communication device, said serial number mask generation part limiting, by notifying said plurality of subscriber-side communication devices of the serial numbers designated by said serial number mask generation part, said subscriber-side communication devices transmitting said distance measurement signals to said subscriber-side communication devices that include said designated serial numbers.