Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 6 Multi-Wavelength WiMAX-PONs with Overlapping Cells 
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6.1 Extended wavelength band overlay over wireless-enabled PON 
The WiMAX-GPON architecture [1-3] presented in the previous chapter, utilised a single 
wavelength to address multiple ONU/BSs bidirectionally based on FDM. In that architecture, 
the ONU/BSs received in upstream time-interleaved WiMAX channels, avoiding at the optical 
receiver in the OLT any potential optical beat interference. To that extent, each wireless 
subscriber station transmits its signal in predetermined time slots dictated centrally from the 
OLT. This could however result in restricting the bandwidth utilisation efficiency for the 
wireless users. Also, a single wavelength approach could impose high dispersion penalties 
across the fibre as the number of frequency subcarriers in the FDM window is increased, to 
address larger number of ONU/BSs. As a result, increased network penetration would require 
sophisticated, high bandwidth optical and electrical components.
The application of extended wavelength band overlay [3, 4] reduces optical beat interference in 
upstream while allowing for low component cost with high scalability and dynamicity. This has 
been achieved in the current architecture over a typical splitter PON, requiring the slightest 
modification in network hardware. Subsequently, each ONU/BS’s allocated FDM subcarrier 
downstream could be dynamically multiplexed on different wavelengths. The low-cost long-
wavelength VCSEL arrays [5] and tuneable optical band-pass filters (BPF) [6, 7] are universally 
employed in the ONUs to demonstrate colourless wireless-PONs with no requirement of 
wavelength-specific optical sources. 
In addition, the network resilience is demonstrated through the drop of multiple wavelengths, to 
users terminated to ONU/BSs exhibiting overlapping cells to potentially double their spectrum 
efficiency. These extended features of the wireless network, compared to traditional 
deployments, are justified through the significant reduction in the WiMAX base station 
deployment cost by the application of the proposed RoF transmission.

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