Error detection/correction and fault detection/recovery – Pulse or data error handling – Error count or rate
Reexamination Certificate
2000-03-02
2001-09-25
Chung, Phung M. (Department: 2784)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Error count or rate
C714S707000
Reexamination Certificate
active
06295614
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an apparatus for estimating bit error rate (BER). More particularly, the present invention is directed to a sampling circuit for estimating BER in a wavelength division multiplexing (WDM) communication system.
2. Technical Background
The performance of optical communication systems is generally determined by the bandwidth or data rate of information that can be carried by the communication system. As higher bandwidth optical fibers are developed and higher bandwidth optical communication systems are implemented, it becomes increasingly important to measure the bit error rate (BER) of the signals carried by the optical fiber or communication system. Wavelength division multiplexing (WDM) is one technique for increasing the bandwidth of an optical communication system.
Wavelength division multiplexing (WDM) is the practice of transmitting data streams at multiple wavelengths along a single optical fiber in order to increase the total rate of data transmission along that fiber. WDM also offers the possibility to preform operations upon each wavelength individually. These operations might include adding each wavelength to, or dropping each wavelength from the main data stream, or changing the particular wavelength's intensity or other properties, at locations intermediate to its point of origin and its point of termination. At present, the number of wavelengths used in optical communication systems is increasing, and the number and complexity of different operations performed on the signal, which may effect one or more signals differently than the others is also increasing. This motivates efforts to develop devices for optical monitoring of individual signal wavelengths.
Determining the bit error rate in a wavelength division multiplexing (WDM) channel in an optical fiber is essential for determining and maintaining the health of a WDM communication network. This capability for monitoring the system would ideally, measure channel capacity or bit error rate in a digital communication system independent of the type of modulation present through the channel. In an effort to determine BER in a WDM channel, it is desirable to employ low speed sampling for determining the statistics and/or histogram of the transmitted signals. It is further desirable to implement a sampling technique which offers independence from the transmitted format of the signal, and which can be implemented at low cost.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a sampling system for estimating the bit error rate of a signal carried by a communication system is disclosed. The sampling system includes an optical transmission medium for carrying an optical signal. A sampling circuit is connected to the optical transmission medium for receiving the optical signal and producing a digitized signal. A random trigger circuit is connected to the sampling circuit. The random trigger circuit provides a random drive signal to the sampling circuit. A threshold determination circuit is connected to the sampling circuit for comparing the digitized signal to a predetermined threshold value. The threshold determination circuit produces an indicator signal representing the logic value of the digitized signal. A histogram processor receives the digitized signal and the indicator signal and generates a histogram representing statistical information about the optical signal. The sampling system may also be configured for triggering off of the positive rising edge or the negative falling edge of the optical signal.
In another configuration, the sampling system includes an optical transmission medium for carrying an optical signal. A clock regenerator circuit is connected to the optical transmission medium. The clock regenerator circuit receives the optical signal and generates a synchronous clock signal. A clock divider circuit receives the synchronous clock signal and produces a divided clock signal. A sampling circuit receives a divided clock signal and produces a digitized signal. A threshold determination circuit compares the digitized circuit to a predetermined threshold value. The threshold determination circuit also produces an indicator signal representing the logic value of the digitized signal. In order to estimate the bit error rate, a histogram processor receives the digitized signal and the indicator signal, and generates a histogram representing statistical information about the optical signal.
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Peters Kurt
Wu Qi
Chung Phung M.
Corning Incorporated
Harness & Dickey & Pierce P.L.C.
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