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EP-4507216-B1 - SCRAMBLING AND DESCRAMBLING IN A PASSIVE OPTICAL NETWORK

EP4507216B1EP 4507216 B1EP4507216 B1EP 4507216B1EP-4507216-B1

Inventors

  • VAN DEN BERG, ERIC JOZEF DIANE
  • VERPLAETSE, Michiel

Dates

Publication Date
20260513
Application Date
20230807

Claims (15)

  1. An optical network unit (210), ONU, configured to transmit data (232) to an optical line terminal (110), OLT, during upstream timeslots (201, 204, 206) within a passive optical network; wherein the ONU comprises a scrambler circuitry (220) configured to scramble (226, 227) at least one data stream (222, 223) according to a periodic scrambling pattern (228), and a descrambler circuitry (240) configured to descramble (243, 244) the at least one scrambled data stream (230, 231) according to the periodic scrambling pattern; and wherein the ONU further comprises at least one data channel (251, 252) for exchanging the at least one scrambled data stream between the scrambler circuitry and the descrambler circuitry; and wherein the scrambler circuitry is further configured to perform, during a period (203, 205) between the upstream timeslots: - scrambling a predetermined reference sequence (221a, 221b) according to the periodic scrambling pattern, thereby obtaining a scrambled reference sequence; and - sending the scrambled reference sequence to the descrambler circuitry over the at least one data channel.
  2. The optical network unit, ONU, according to claim 1, wherein the predetermined reference sequence (221a, 221b) is a sequence of bits that have the same logical value.
  3. The optical network unit, ONU, according to any of the preceding claims, wherein the descrambler circuitry (240) is further configured to perform, determining the periodic scrambling pattern (228) for descrambling the at least one scrambled data stream (230, 231) based on the scrambled reference sequence and the predetermined reference sequence (221a, 221b).
  4. The optical network unit, ONU, according to any of the preceding claims, wherein the descrambler circuitry (240) is further configured to perform, capturing at least a portion of the scrambled reference sequence within at least one capture buffer (401, 403).
  5. The optical network unit, ONU, according to claim 3 and 4, wherein determining the periodic scrambling pattern (228) is based on the captured portion of the scrambled reference sequence and the predetermined reference sequence.
  6. The optical network unit, ONU, according to claim 4, wherein the periodic scrambling pattern (228) has a pattern length, and the at least one capture buffer (401, 403) has a buffer size; and wherein the buffer size is an integer multiple of the pattern length.
  7. The optical network unit, ONU, according to any of the preceding claims, wherein the scrambler circuitry (220) further comprises a controller (407) configured to perform, during the period (412, 417) between upstream timeslots, sending a control signal (305) to the descrambler circuitry indicative of that the scrambler circuitry is sending the scrambled reference sequence to the descrambler circuitry over the at least one data channel.
  8. The optical network unit, ONU, according to claim 7, wherein the scrambler circuitry is further configured to perform adjusting the periodic scrambling pattern (228) between (415, 419) the end of an upstream timeslot (411, 416) and the control signal (413, 418) that follows the upstream timeslot.
  9. The optical network unit, ONU, according to claim 8, wherein the adjusting is based on data expected to be transmitted from the ONU to the OLT within a next upstream timeslot (411, 416).
  10. The optical network unit, ONU, according to any of the preceding claims, wherein the descrambler circuitry (240) is further configured to perform detecting bit errors by comparing the determined periodic scrambling pattern with one or more previously determined periodic scrambling patterns.
  11. The optical network unit, ONU, according to claim 3, wherein the descrambler circuitry (240) is further configured to perform detecting bit errors by descrambling the scrambled reference sequence according to the periodic scrambling pattern determined by the descrambler circuitry.
  12. The optical network unit, ONU, according to any of the preceding claims, wherein the scrambler circuitry (220) is included in a first circuitry of the ONU configured to process the at least one data stream; and wherein the descrambling circuitry (240) is included in a second circuitry of the ONU configured to interface with an optical fibre of the passive optical network to transmit the data to the optical line terminal.
  13. An optical line terminal (300), OLT, configured to receive data (302) from one or more optical network units, ONUs (131, 132, 133, 134), during respective upstream timeslots (311, 312, 313, 314) within a passive optical network; wherein the OLT comprises a scrambler circuitry (220) configured to scramble (226, 227) at least one data stream (304, 305) according to a periodic scrambling pattern (228), and a descrambler circuitry (240) configured to descramble (243, 244) the at least one scrambled data stream (230, 231) according to the periodic scrambling pattern; and wherein the OLT further comprises at least one data channel (251, 252) for exchanging the at least one scrambled data stream between the scrambler circuitry and the descrambler circuitry; and wherein the scrambler circuitry is further configured to perform, during a period (315, 316, 317) between respective upstream timeslots (311, 312, 313, 314): - scrambling a predetermined reference sequence (221a, 221b) according to the periodic scrambling pattern, thereby obtaining a scrambled reference sequence; and - sending the scrambled reference sequence to the descrambler circuitry over the at least one data channel.
  14. A method comprising, during a period between upstream timeslots for transmitting data from an optical network unit, ONU, to an optical line terminal, OLT, within a passive optical network: - by a scrambler circuitry within the ONU, scrambling a predetermined reference sequence according to a periodic scrambling pattern, thereby obtaining a scrambled reference sequence; wherein the scrambler circuitry is configured to scramble at least one data stream according to the periodic scrambling pattern; and - sending the scrambled reference sequence to a descrambler circuitry within the ONU over at least one data channel for exchanging the at least one scrambled data stream between the scrambler circuitry and the descrambler circuitry; wherein the descrambler circuitry is configured to descramble the at least one data stream according to the periodic scrambling pattern.
  15. A method comprising, during a period between respective upstream timeslots for receiving data by an optical line terminal, OLT, from one or more optical network units, ONUs, within a passive optical network: - by a scrambler circuitry within the OLT, scrambling a predetermined reference sequence according to a periodic scrambling pattern, thereby obtaining a scrambled reference sequence; wherein the scrambler circuitry is configured to scramble at least one data stream according to the periodic scrambling pattern; and - sending the scrambled reference sequence to a descrambler circuitry within the OLT over at least one data channel for exchanging the at least one scrambled data stream between the scrambler circuitry and the descrambler circuitry; wherein the descrambler circuitry is configured to descramble the at least one data stream according to the periodic scrambling pattern.

Description

Field of the Invention Various example embodiments relate to passive optical networks. In particular, to scrambling and descrambling of upstream data in passive optical networks. Background of the Invention In a passive optical network, PON, at least one optical line terminal, OLT, at the network side connects to one or more optical network units, ONUs, at the user side. It can be desirable to physically separate some signal processing functions of the ONUs and/or the OLT by providing the signal processing functions on distinct circuitries that are interconnected. This allows implementing or incorporating the distinct circuitries in advantageous physical locations according to the signal processing functions they include. For some emerging PON systems with an increased line rate, e.g. 50G-PON according to the ITU-T G.9804 standard, such a physical separation of signal processing functions is a challenge as the increased line rate requires a connection between the distinct circuitries with a high bandwidth, thereby increasing cost substantially. To this end, a demultiplexed interface can be used to exchange data streams between the interconnected circuitries at a lower baud rate compared to the full-rate PON signal. The characteristics of these demultiplexed data streams, e.g. allowable consecutive identical bits and DC-balancing, are uncontrolled as demultiplexed data streams of full-rate PON signals are not standardized. For some full-rate data sequences, the corresponding demultiplexed data streams can therefore comprise undesirable bit sequences which can result in failure or suboptimal performance of the signal processing functions included in the circuitry that receives the demultiplexed data streams, e.g. long bit sequences of consecutive identical bits can induce failure of clock recovery at the receiving circuitry. CN104168124A discloses a distributed Optical Terminal Line for a PON. Summary of the Invention The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments and features described in this specification that do not fall within the scope of the independent claims, if any, are to be interpreted as examples useful for understanding various embodiments of the invention. Amongst others, it is an object of embodiments of the invention to limit the probability of occurrence of undesirable bit sequences that impact signal processing functions when exchanging upstream data between distinct circuitries of an optical network unit or an optical line terminal. This object is achieved, according to a first example aspect of the present disclosure, by an optical network unit, ONU, configured to transmit data to an optical line terminal, OLT, during upstream timeslots within a passive optical network. The ONU comprises a scrambler circuitry configured to scramble at least one data stream according to a periodic scrambling pattern, and a descrambler circuitry configured to descramble the at least one scrambled data stream according to the periodic scrambling pattern. The ONU further comprises at least one data channel for exchanging the at least one scrambled data stream between the scrambler circuitry and the descrambler circuitry. The scrambler circuitry is further configured to perform, during a period between the upstream timeslots: scrambling a predetermined reference sequence according to the periodic scrambling pattern, thereby obtaining a scrambled reference sequence; and sending the scrambled reference sequence to the descrambler circuitry over the at least one data channel. The scrambler circuitry may be included in a first circuitry of the ONU, and the descrambler circuitry may be included in a second circuitry of the ONU. This first and second circuitry may each perform a portion of the signal processing functions of the ONU, e.g. electro-optical conversion of signals, clock and data recovery, equalization, and data processing. The first and second circuitry may further be located at different physical locations. The scrambler circuitry and the descrambler circuitry, and hence the first and second circuitry, are interconnected by means of the at least one data channel which provides an interface between the circuitries. The baud rate of the at least one data stream exchanged over the at least one data channel may be substantially lower than the baud rate of data transmitted from the ONU to the OLT, i.e. the upstream line rate of the PON. For example, a 50G non-return-to-zero, NRZ, upstream signal can be exchanged between the circuitries as two demultiplexed 25G NRZ data streams over two data channels; as five demultiplexed 10G NRZ data streams over five data channels; or as a single 50G pulse amplitude modulation 4-level, PAM4, data stream over one data channel. Alternatively, the baud rate of the at least one data stream exchanged over the at least one data channel may have substantially the same baud rate as the data transmitted