PDS structured optical subscriber system

A Passive Double Star (PDS) structured optical subscriber system, which comprises:

• at least one center unit;
• a plurality of optical subscriber units;
• a downbound transmission path for transmitting a downbound optical signal from said center unit to said plurality of optical subscriber units;
• an upbound transmission path for transmitting upbound optical signals from said plurality of optical subscriber units to said center unit;
• a downbound star coupler for branching the downbound optical signal to said plurality of optical subscriber units;
• and
• an upbound star coupler for multiplexing the upbound optical signals from said plurality of optical subscriber units,
• wherein said center unit comprises:
• an optical burst signal receiving portion for receiving an upbound optical burst signal from said upbound star coupler;
• an optical power/delay time period converting portion for inputting the upbound optical burst signal from said optical burst signal receiving portion and converting a power of the upbound optical burst signal into a first delay time period;
• a response frame detecting portion for inputting the first delay time period from said optical power/delay time period converting portion and detecting a response frame so as to generate a frame detection signal;
• a delay coarsely-adjusting portion for inputting the frame detection signal from said response frame detecting portion and the upbound optical burst signal from said optical burst signal receiving portion and coarsely-adjusting a second delay time period on the basis of the frame detection signal and the upbound optical burst signal;
• a delay finely-adjusting portion for inputting the second delay time period from said delay coarsely-adjusting portion and the upbound optical burst signal from said optical burst signal receiving portion and finely-adjusting the second delay time period;
• a delay time period comparing portion for inputting the first delay time period from said optical power/delay time period converting portion and the second delay time period from said delay finely-adjusting portion and comparing the first and second delay time periods so as to generate a third delay time period which is set to be equal to the second delay time period in case where a difference between said first and second delay time periods is within tolerable range and so as not to generate the third delay time period in the other case;
• a timing generating portion for inputting the third delay time period signal from said delay time period comparing portion and generating a response timing for each of said plurality of subscriber units;
• and
• an optical burst signal transmitting portion for transmitting a first downbound optical burst signal every two frames, and transmitting a second downbound burst signal containing an information on the response timing to each of said plurality of optical subscriber units when inputting the response timing from said timing generating portion, to each of said plurality of optical subscriber units through said downbound star coupler, and
• wherein each of said plurality of optical subscriber units comprises:
• an optical burst signal receiving portion for receiving the first and second downbound optical burst signals from said center unit through said downbound star coupler;
• a received-optical power calculating portion for inputting the first downbound optical burst signal from said burst signal receiving portion and estimating an installation distance corresponding to an optical power of the first downbound optical burst signal;
• a frame determining portion for inputting the estimated installation distance from said received optical power calculating portion and determining a frame in which inserted is the upbound optical burst signal to be transmitted to said center unit as a response to the first downbound optical burst signal;
• a timing generating portion for inputting the determined frame from said frame determining portion and generating a transmission timing when the upbound optical burst signal is transmitted from said optical subscriber unit;
• and
• an optical burst signal transmitting portion for inputting the transmission timing from said timing generating portion and outputting the upbound optical burst signal to said center unit through said upbound star coupler.