Integrated Wireless-pon access Network Architectures Milos Milosavljevic

4.1 Principle of RoF Approach in the Integrated Architecture
The cost-effectiveness and scalability of RoF techniques [1], to supply fixed to mobile 
convergence by means of FDM constitute powerful properties in enhancing broadband wireless 
networks and TDM-PON operation [2, 3]. Although extensive proposals of hybrid 
optical/wireless architectures have been investigated, as presented in previous chapters, the 

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Chapter 4 FDM Simulation Platform with Wireless Compatibility 
68 
application of WiMAX over legacy PONs have not been collectively examined, by means of 
enhancing their operation features with respect to aggregate capacities, reach and number of 
supported users. Figure 4-1 demonstrates an architecture accounting for these features. Even 
though the figure in particular portrays a basic overview of the architecture, for the benefit of 
building an argument in this chapter, its enhancements and corresponding modes of operation 
fully embrace the properties outlined above supported by scalability and dynamicity. 
Figure 4-1: FDM approach for the proposed optical/wireless integration 
The topology consists of one OLT located at the CO and several ONU/BSs located either at the 
user premises or at remote antenna posts which will be used for providing connectivity to 
mobile terminals. One single feeder optical fibre from the OLT is used to carry all upstream and 
downstream signals up to a passive splitter which broadcasts them to multiple network 
segments.
Inside the OLT, multiple RF broadband wireless channels are frequency multiplexed in a given 
spectral window, avoiding interference with legacy PONs in downstream. The combined 

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Chapter 4 FDM Simulation Platform with Wireless Compatibility 
69 
spectrum is then modulated onto an optical carrier and broadcasted to each remote ONU/BS. 
This approach provides for transparency to any wireless signal formats as radio frequency sub-
carriers are transmitted over the optical fibre completely independent to xPON functionalities. 
The remote base station solutions are therefore simplified since all the wireless processing and 
subcarrier allocation are performed centrally at the OLT. Consequently, densely populated base 
stations could be deployed providing for high spectral efficiency across an area as well as 
increased frequency reuse pattern.
To that extent, the OLT manages the assignment of traffic to a large number of sub-carriers 
which travel all along the optical distribution network (ODN), to be de-multiplexed only at the 
user side and vice versa. Therefore, the CO can generally be thought of as a PON OLT but 
combining the additional functionalities of a wireless base transceiver station (BTS).
In addition, upstream transmission could be either based on a TDMA approach, as in standard 
xPONs and shown in the current architecture, or dedicated wavelengths could be assigned to 
each ONU/BS to avoid optical beat interference and further reduce deployment cost as sub-
carrier multiplexing is not required.
Finally, since RoF could impose various impairments on the standard wireless signal formats 
further investigations would be required to examine the efficiency of the network with regards 
to signal routing. 

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