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Question 4 (Total Marks: 26 marks) Due to the explosive growth of city Z, a few new suburbs surrounding the city have been setup to cope with the growing population. To ensure a long-term plan for the future telecommunication infrastructure, the local council has engaged your company to design a 4channel Time-Wavelength-Division-Multiplexed Passive Optical Network (TWDM-PON) to serve these new suburbs. Initial deployment is to cater for 32 users with each TWDM-PON channel operating at 10 Gb/s downlink. The proposed TWDM-PON architecture is shown in the figure below. In this configuration, a tunable bandpass filter (BPF) is needed in the ONU for the downlink direction. Here, you can assume that the optical frequency of the tunable BPF is fixed upon initialisation of the network and the loss of the BPF is uniform over the entire optical spectrum. To minimise the hardware cost of the ONU, only one uplink channel will be implemented and will be shared amongst the 32 users supporting a total bit-rate of 10 Gb/s. You are required to design this TWDM-PON system for a bit-error-rate (BER) of 10−15. Muuluomal injormation: Downlink: - Each downlink transmitter has an output power of 6dBm. - Each downlink transmitter has a slightly different wavelength, all located within the 1550 nm window (1550 nm,1552 nm,1554 nm,1556 nm). - Assume all downlink transmitters have the same characteristics. Uplink: - Each uplink transmitter has an output power of 0dBm. - The wavelength of single uplink channel is at 1300 nm. - Assume all uplink transmitters have the same characteristics.
Passive Device Parameters: - Fibre connector loss =0.5 dB - Fibre coupler loss =0.5 dB - Splitter loss = 15 dB - Tunable bandpass filter loss = 2 dB - Multiplexer (MUX) loss = 2 dB - Demultiplexer (DEMUX) loss =2 dB Fibre: - Single-mode fibre - Put aside 3 dB system margin for ageing, dispersion penalty, nonlinear effects, repair margin etc. a. What is the total downlink bit-rate of the designed TWDM-PON? (1 mark) b. Calculate the maximum bit-rate per user for uplink based on the specification for this architecture. (1 mark) c. Calculate the receiver sensitivity for PIN and Avalanche photodiode (APD) at a BER = 10−15 for a bit rate of 10 Gb/s. (2 marks) d. Determine the type of receiver you would use in the ONU and justify your choice. (7 marks) e. Determine the type of receiver you would use in the OLT and justify your choice. (7 marks) f. What type of transmitter would you use in the downlink and uplink? Justify your choice. (4 marks) g. After presenting your design to the local council, they are very happy with the final product. However, they have some concerns with regards to future upgradability. Provide an explanation on how you will upgrade your design (both downlink and uplink) if more users were to join later to convince the council that your design is robust and can be upgraded. (4 marks)