Method and system for decoding multilevel signals
First Claim
1. An optical receiver for receiving and decoding a multilevel optical communication signal, comprising:
- a plurality of first comparators for estimating a transmitted level based on the received multilevel signal;
a decoder coupled to the first comparators;
a second comparator connected in parallel with the first comparators, for indicating when the received signal exceeds a voltage;
a filter coupled to the second comparator, for calculating a cumulative distribution function for the received multilevel signal;
an analog-to-digital converter coupled to the filter for sampling a cumulative distribution function; and
a microcontroller for processing the cumulative distribution function to determine threshold voltage values, for feeding the threshold voltage values to the first comparators for decoding the multilevel signal.
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Abstract
A multilevel optical receiver can comprise a plurality of comparators that generally correspond with the number of levels in a multilevel data stream. Each comparator can be individually controlled and fed a decision threshold in order to decode a multilevel signal. The multilevel optical receiver can generate a statistical characterization of the received symbols in the form of a marginal cumulative distribution function (CDF) or probability density function (pdf). This characterization can be used to produce a set of ε-support estimates from which conditional pdfs are derived for each of the transmission symbols. These conditional pdfs may then be used to determine decision thresholds for decoding the received signal. The conditional pdfs may further be used to continuously estimate the fidelity or error rate of the received signal without the transmission of a testing sequence. The ε-supports may further be used to automatically control the gain on the receiver.
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Citations
61 Claims
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1. An optical receiver for receiving and decoding a multilevel optical communication signal, comprising:
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a plurality of first comparators for estimating a transmitted level based on the received multilevel signal; a decoder coupled to the first comparators; a second comparator connected in parallel with the first comparators, for indicating when the received signal exceeds a voltage; a filter coupled to the second comparator, for calculating a cumulative distribution function for the received multilevel signal; an analog-to-digital converter coupled to the filter for sampling a cumulative distribution function; and a microcontroller for processing the cumulative distribution function to determine threshold voltage values, for feeding the threshold voltage values to the first comparators for decoding the multilevel signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An optical receiver for receiving and decoding a multilevel optical communication signal, comprising:
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a plurality of first comparators for estimating a transmitted level based on the received multilevel signal; a decoder coupled to the first comparators; a pair of second comparators connected in parallel with the first comparators, to indicate when the received signal falls within controlled voltage ranges; a logic circuit coupled to the second comparators, to indicate when the received signal is in the intersection of the two controlled voltage ranges; a filter coupled to the logic circuit, for calculating a probability density function for the received multilevel signal; an analog-to-digital converter coupled to the filter for sampling a probability density function; and a microcontroller for processing the probability density function to determine threshold voltage values, for feeding the threshold voltage values to the first comparators for decoding the multilevel signal. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 61)
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21. A desymbolizer for receiving and decoding a multilevel optical communication signal, comprising:
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an analog-to-digital converter for receiving and decoding the multilevel signal; a signal integrity unit coupled to the analog-to-digital converter for calculating and controlling one or more threshold voltages supplied to the analog-to-digital converter, for calculating at least one of a cumulative distribution function and a probability density function derived from the multilevel signal and associated with the one or more threshold voltages; wherein the analog-to-digital converter is a first analog-digital converter, and the signal integrity unit further comprises; a digital-to-analog controller coupled to inputs of respective comparators located in the first analog-to-digital converter; a microcontroller coupled to the digital-to-analog controller for controlling a threshold voltage of each comparator located in the first analog-to-digital controller; a second analog-to-digital converter coupled to the first analog-to-digital controller and microcontroller of the signal integrity unit, for converting the signals received from the first digital-to-analog controller and for feeding the converted signals to the microcontroller for statistical analysis. - View Dependent Claims (22, 23, 24, 26)
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25. A desymbolizer for receiving and decoding a multilevel optical communication signal, comprising:
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an analog-to-digital converter for receiving and decoding the multilevel signal; a signal integrity unit coupled to the analog-to-digital converter for calculating and controlling one or more threshold voltages supplied to the analog-to-digital converter, for calculating at least one of a cumulative distribution function and a probability density function derived from the multilevel signal and associated with the one or more threshold voltages, wherein the analog-to-digital converter comprises a holding circuit for sampling the multilevel signal in response to control signals generated by the signal integrity unit, and wherein the holding circuit samples the multilevel signal at random intervals.
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27. A desymbolizer for receiving and decoding a multilevel optical communication signal, comprising:
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an analog-to-digital converter for receiving and decoding the multilevel signal; a signal integrity unit coupled to the analog-to-digital converter for calculating and controlling one or more threshold voltages supplied to the analog-to-digital converter, for calculating at least one of a cumulative distribution function and a probability density function derived from the multilevel signal and associated with the one or more threshold voltages, wherein the analog-to-digital converter comprises a holding circuit for sampling the multilevel signal in response to control signals generated by the signal integrity unit and wherein the holding circuit samples the multilevel signal at a periodic sample rate that is not harmonically related to a data rate of the multilevel signal.
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28. A desymbolizer for receiving and decoding a multilevel optical communication signal, comprising:
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an analog-to-digital converter for receiving and decoding the multilevel signal; a signal integrity unit coupled to the analog-to-digital converter for calculating and controlling one or more threshold voltages supplied to the analog-to-digital converter, for calculating at least one of a cumulative distribution function and a probability density function derived from the multilevel signal and associated with the one or more threshold voltages, wherein the signal integrity unit further calculates a conditional probability density function for each symbol of the multilevel signal based ε
-support estimates, wherein each ε
-support estimate comprises one or more values in which a marginal probability density function is positive. - View Dependent Claims (29)
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30. A desymbolizer for receiving and decoding a multilevel optical communication signal, comprising:
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an analog-to-digital converter for receiving and decoding the multilevel signal; a signal integrity unit counted to the analog-to-digital converter for calculating and controlling one or more threshold voltages supplied to the analog-to-digital converter, for calculating at least one of a cumulative distribution function and a probability density function derived from the multilevel signal and associated with the one or more threshold voltages; and programmable analog signal processing modules that equalizes and optimally filters the multilevel signal prior to the analog-to-digital converter, where the signal integrity unit selects an operating point of the programmable analog signal processing modules based upon the determination of the fidelity of the multilevel signal. - View Dependent Claims (31, 32)
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33. A method for receiving and converting a multilevel signal into a plurality of data streams, comprising the steps of:
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receiving a multilevel signal; calculating one of a cumulative distribution function and a probability density function based on the received multilevel signal; determining one or more decision thresholds based upon one of the cumulative distribution function and probability density function; associating one or more threshold voltage levels based on the decision thresholds; comparing the multilevel signal with the threshold voltage levels; estimating a conditional probability density function for each symbol of the multilevel signal; determining a probability of error for the multilevel signal based upon the conditional probability density function of each symbol and the decision levels; and decoding the multilevel symbol into one or more bits based on the comparison of the multilevel signal with the threshold voltage levels. - View Dependent Claims (34, 35, 36, 37, 38)
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39. A method for determining threshold voltages of comparators in a multilevel signal receiver system, comprising the steps of:
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estimating a probability density function, wherein the step of estimating the probability density function comprises directly computing the probability density function from the received multilevel signal by collecting sampling voltage levels of the multilevel signal at random time intervals; determining one or more statistical centers positioned on local minima that are present in the probability density function; and associating one or more threshold voltage levels based on the one or more statistical centers positioned according to the local minima. - View Dependent Claims (40, 41)
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42. A method for receiving and converting a multilevel signal into a plurality of data streams, comprising the steps of:
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receiving a multilevel signal; determining one or more decision thresholds by calculating an initial set of ε
-support estimates, wherein determining one or more decision thresholds further comprises combining ε
-supports, wherein each ε
-support estimate comprises one or more values in which a marginal probability density function is positive;associating one or more threshold voltage levels based on the decision thresholds; comparing the multilevel signal with the threshold voltage levels; and decoding the multilevel symbol into one or more bits based on the comparison of the multilevel signal with the threshold voltage levels. - View Dependent Claims (43, 44)
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45. A method for determining a set of decoding thresholds from a marginal probability density function comprising the steps of:
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thresholding the probability density function to obtain an initial set of intervals conveying regions of significant probability for received signal; calculating ε
-support regions by merging intervals until the number of regions is substantially equal to the number of candidate symbol transmission levels;associating each ε
-support region with a mode of a conditional probability density function corresponding to a transmission level, wherein each ε
-support region comprises one or more values in which a marginal probability density function is positive; andcomputing a decision threshold based on the conditional probability density functions. - View Dependent Claims (46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56)
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57. A system for receiving and converting a multilevel signal into a plurality of data streams comprising:
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means for determining one or more decision thresholds by calculating an initial set of ε
-support estimates, wherein each ε
-support estimate comprises one or more values in which a marginal probability density function is positive;means for associating one or more threshold voltage levels based on the decision thresholds; means for comparing the multilevel signal with the threshold voltage levels; and means for decoding the multilevel symbol into one or more bits based on the comparison of the multilevel signal with the threshold voltage levels. - View Dependent Claims (58, 59, 60)
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Specification