Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 4 FDM Simulation Platform with Wireless Compatibility 
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Figure 4-2: Example of a mobile WiMAX OFDMA frame [6]
 
In downlink QPSK, 16QAM and 64 QAM can be used (as shown in Table 4-1), in uplink only 
QPSK and 16QAM are available to modulate the subcarriers. For the sake of channel estimation 
and synchronization, pilots are placed regularly within the sub-frames (the actual placements 
depend on the applied allocation scheme [6]). To ensure multipath robustness a CP is added to 
every OFDM symbol. 
The main PHY difference between the mobile and fixed WiMAX standards is that in the latter 
the subcarrier spacing is fixed and is typically 256. Also, mobile WiMAX data transmissions to 
individual users can be multiplexed in both time and frequency, due to the much higher number 
of available sub-channels. For this reason, this form of data transmission is referred to as 
OFDMA. 
Taking into account all of the above and due to the high resemblance among the modulation 
techniques used in both IEEE802.16d [4] and IEEE802.16e [6] standards, the feasibility 
investigations to be conducted will be based on fixed WiMAX. This would be sufficient to 

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Chapter 4 FDM Simulation Platform with Wireless Compatibility 
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demonstrate optical network transparency to wireless signals delivered to remote base station 
antennas and wireless users bidirectionally. 
4.3 VPI/MATLAB Elements for the WiMAX Transceiver 
To initially establish accurate WiMAX signal routing over the xPON, the OFDM transmitter 
and receiver are devised in VPI in co-simulation with MATLAB utilising the functional blocks 
outlined in the previous chapter.
Figure 4-3 displays the OFDM transmitter with the pseudo random binary sequence (PRBS) fed 
from VPI to the input MATLAB interface (i.e. OFDM coding block).