This document discusses network architectures for rural broadband access. It summarizes several proposed architectures: 1. Using GPON extenders and amplifiers can increase reach to 60km and serve up to 128 users. Multiple branching allows flexible expansion. 2. Placing Raman amplifiers or SOAs at the OLT and using a dual wavelength system achieved a 60km reach with a 1:32 split ratio in Tasmania. 3. A dual-fiber system using EDFAs in the feeder and passive distribution achieved a reach of over 15km with a 1:64 split ratio. The document also outlines open problems remaining around using amplifiers at different stages, applying OFDM and dual-fiber architectures,

1. Saptadeep Pal
CTVR, Trinity College Dublin.

2. Key Features:
• Sparse Population. User density is usually very
low.
 Cost of Deployment per user is High
• User premises are distributed over a larger
geographical area. Fiber length per user is
high
• Generally far from the urban regions.  More
fiber required to connect to the metro/core
node as well
• OSNR problem due to longer fiber portions in
feeder and distribution part.

3. Standard network architectures:
Fig: GPON architecture (ITU-T G.984 standard)
With this architecture we cannot reach many users in rural areas as
the span of reach is constrained within 20 Km. Suitable for denser
URBAN regions.
Courtesy: TELNET

4. A Step forward towards a Long-Reach
Using GPON Extender (typically an 1:1 Amplifier or regenerator)
the span of the network can be increased to 60 Km and can serve
as many as 128 users per OLT. Suitable for less dense and sparsely
distributed population.
Courtesy: TELNET

5. A Better and Flexible Architecture:
GPON extender with multiple branching allows adding splitters and ONUs at a
later stage without affecting the total reach or the OSNR at the other ONUs. 256
users can be reached.
Courtesy: TELNET

6. Proposed Network architectures:
Proposals about
architecture and
network elements
Advantages and
discussions on the
Results
University of
Melbourne.
(R.S. Tucker)*
• Raman Amplifier & SOA at OLT
• Dual wavelength (US-DS)
• 1:32 split ratio
• Passive Long-Reach Field
• 60 Km.
• Implementation in Tasmania
resulted in decrease of CO
numbers from 96 to 27
University of
Melbourne.
(R.S. Tucker)**
• Dual-Fiber
• EDFA at the CO keeping the feeder
and distribution section passive
• 1:64 split
• About 15% less power required in
transmission
• Reach can be increased by
increasing signal power
• Simple upgradability
• High bandwidth in upstream and
downstream
University of
California, Davis.
Lei Shi, Avishek Nag #
• BER-aware wavelength allocation
in WDM PON
• Remote Nodes in the Network
which contains AWG & EDFA
• Average BER per ONU increases
• Suitable for LR-PON architecture
as BER is one of the mainstream
issues in design of such a
network
K. Kanonakis et. al.
(IEEE members)
(ACCORDANCE FP7) ++
• OFDM-over-WDM/TDM
• Use of Back-to-Back Amplifiers
• No-amplification required for
transmission of 78 km
• Upgradability is easier
• Less power, more bandwidth, less
BER

7. Proposals about
architecture and
network elements
Advantages and
discussions on the
Results
Darren P. Shea et. al.
(BT networks) ^^
• 1024-split architecture
• Use of EDFAs in the backhaul
section of 90 Km
• 3-stage splitting in the
distribution section
• Very long reach of about 100
km
• Multi-stage amplification
required
• Addition of noise and
degradation of OSNR
• Non-passive field
ITM, KTH & Atellus
AB(Sweden)
H.E. Sandstrom et. al.
• 3 access nodes in the network
• Splice points and splitters for
end-users
• Using amplifiers and regenerators
instead of increasing Cos
• Economically possible to
distribute access networks in
areas with <1 person/km
• Laying of fiber besides main-
stream roads only for access
networks is a better option
C.H. Chang et. al.
National University of
Taiwan
• OFDM and AWG
• BTB amplifiers
• Less BER with less Power as
compared to non-OFDM
architectures
• Reach can be increased using
such BTB techniques

8. Key points of these architectures:
 Amplifiers at the central office
 Remote node in a network: Upgradability and further reach
 Back to Back amplifiers
 OFDM (over WDM/TDM)
 Fiber deployment along Primary/Main Roads

9. Genetic Algorithm Based Network Planning:
GU Rentao et. al., Beijing, China
Evolutionary 2-stage method
The best locations of splitters are chosen
With the splitter location, the optimal solution for best connection
arrangement is found out
Losses have been considered alongside maximum reach
Gives very good results with error of less than 0.5% even with 256 ONUs

10. Open Problems:
o Use of amplifiers in various stages
o Using OFDM in rural areas with fiber deployment alongside Roads only
o Using Back to back amplifiers in the feeder
o Dual-fiber architecture
o Genetic algorithm approach