Apparatus and method for measuring the quality of burst signals and performing optical line diagnostics
View Patent ↗Apparatus and method to measure the quality of burst signals and to perform optical line diagnostics in and optical passive optical network (PON). Statistical information about phase noise (jitter), signal distortion, clock distortions, and any other effects present in burst signals is generated. The statistics are based on phase and bit-length distortions, direction and length of the effect as detected by a phase error detector integrated in a burst mode clock and data recovery (BCDR) circuit. The invention can be further adapted to perform optical line diagnostics to detect the root cause performance degradation and failures in the PON, thereby providing an optical layer supervision tool for monitoring the PON. The statistical information can be used to estimate the quality of service (QoS) per customer connected to the PON. In addition, the generated statistic information can be used to calibrate transmission parameters of optical network unit (ONU) transmitters.
1. An apparatus for performing optical line diagnostics of a transmission line between optical network units (ONUs) and an optical line terminal (OLT) in a passive optical network (PON), the apparatus comprising:
a phase error unit (PEU) for generating initial quality indicators and quality measures respective of input burst signals received at the OLT;
a statistical accumulation block (SAB) coupled to the PEU and capable of performing statistical analysis on the quality measures by computing for each quality measure an average value, an absolute value, a minimum value, a swing value, and a maximum value, the SAB aggregates quality measures computed for each ONU in different times within a burst signal sent from the ONU, the quality measures include at least one of: an average sampling point (ASP), a number of detected narrow bits (NB), an average wave form (AWF), a jitter indication, and a duty cycle indication;
a memory unit for storing statistics generated by the SAB; and
a processor for processing statistics stored in the memory unit to generate a plurality of failure indications related to the optical line diagnostics.
2. The apparatus of claim 1 , further comprising:
an over-sampler capable of over-sampling input burst signals and being further capable of generating over-sampled bit streams;
a phase interpolator capable of generating sampling clock signals using a reference clock and phase information; and
a digital filter capable of selecting from the over-sampled bit streams a single data stream representing recovered data.
3. The apparatus of claim 2 , wherein the PEU generates initial quality indicators by recognizing patterns in the over-sampled bit streams.
4. The apparatus of claim 3 , wherein the initial quality indicators provide an indication about distortions present in the input burst signals and include at least one of: a sampling point, a narrow bit indication, a number of consecutive high logic values in the input bit stream, and a valid bit indication.
5. The apparatus of claim 1 , wherein the statistics generated by the SAB are stored per ONU in the memory unit.
6. The apparatus of claim 5 , wherein the processor further processes PON parameters to generate the plurality of failure indications.
7. The apparatus of claim 6 , wherein the PON parameters comprise at least one of:
a modulated signal amplitude indication (RSSI); a bias current, a modulation current, an error rate, a locking indication, forward error correction information; an external temperature, and a physical distance from the OLT to the ONUs.
8. The apparatus of claim 1 , wherein the plurality of failure indications comprise at least one of: an end-of-life (EOL) of an ONU transmitter, an EOL of an OLT transmitter, a clock drift, a broken fiber channel, high noise in the PON, an OLT with unstable phase-lock-loop (PLL), and a shot noise.
9. The apparatus of claim 7 , wherein the processor is further adapted to estimate the quality of service per customer coupled to an ONU by correlating PON parameters with statistics stored in the memory unit.