Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 5 Interoperability of xPON and WiMAX 
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manage resources across multiple ONU/BSs from the OLT according to traffic penetration and 
requirement in bandwidth. This chapter presents a complete transparent optical/wireless access 
network architecture based on RoF and FDM. 
 
Figure 5-1: WiMAX over xPON architectural platform 
The network architecture, depicted in Figure 5-1 [1], consists of a standard GPON with novel 
wireless-enabled OLT and ONUs. As outlined in the previous chapter, the ONU/BSs are 
relatively simple in their design since they are only responsible for down-conversion and 
filtering of the received downstream radio channels. Each WiMAX transmitter at the OLT is 
serving a single radio cell at an ONU/BS that is divided into small parts called sectors, 
operating on the same or different frequencies, in order to make the cell more efficient in terms 
of reduced co-channel interference and increased capacity. In some current deployment 
scenarios all sectors are operating on the same frequency to reduce the cost of BSs, however in 
the novel proposed architecture frequency reuse patterns of higher order could be considered 
due to the deployment cost reduction enabled by the centralised processing in the OLT. 

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Chapter 5 Interoperability of xPON and WiMAX 
90 
A different RF subcarrier was dedicated to each ONU/BS in downstream to enable concurrent 
transmission of multiple WiMAX channels to each ONU antenna. Within the OLT, standard 
microwave OFDM WiMAX symbols [2], generated by Transmitter (Tx) for BS
n
, for different 
sectors in each ONU/BS were up-converted to the predetermined RF subcarriers spectrum 
before they were combined with the packets for wired users and subsequently modulated onto 
the optical carrier for 20 km fibre downstream transmission.
Figure 5-2 illustrates how this technique addresses each individual ONU/BS. The microwave 
RF wireless channels are shifted in frequency using a predetermined LO and BPFs in the OLT 
prior to being combined and modulated onto an optical carrier. At an ONU/BS a single LO is 
only required operating on the same frequency for the specific ONU/BS to downshift the 
WiMAX channels. Multiple band pass filters (BPFs) are needed to select each channel prior to 
transmission over the air. This approach would significantly simplify the BS design, compared 
to traditional base-band or IF FDM over fibre approaches [3]. This is expected since only a 
single LO and multiple electrical filters required. The LO leakage and higher order IMDs of the 
non-linear mixer inside the OLT and ONU/BSs will not degrade the system performance since 
in the deployed scenario the unwanted products fall outside the band of interest and are filtered 
by the BPF.

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