Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 5 Interoperability of xPON and WiMAX 
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Figure 5-8: DFB bias current versus power (left) and RIN versus frequency (right)
After the circulator, the received signals in the OLT were converted to the electrical domain by 
APDs before their symbol detection in WiMAX receivers. In a similar manner to downstream, 
to determine the operating range of the direct modulated laser for optimum performance, the 
laser drive amplitude against EVM at the OLT was measured and displayed in Figure 5-9. This 
applied to upstream channels transmitted over the GPON only. EVMs below -27 dB were 
obtained for all wireless channels at drive currents in the range of 2.4-2.6 mA, matching closely 
the performance figures specified in the standard with 16-QAM modulation [2].
These figures 
confirm transparent transmission of WiMAX channels also in the upstream, without the need 
for complex dispersion compensation mechanisms. 

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Chapter 5 Interoperability of xPON and WiMAX 
106 
Figure 5-9: EVM versus laser drive amplitude in upstream
5.4 Transmission evaluation
Before transmission of the signal over a wireless channel, following the down-conversion in the 
ONU/BS, the system must provide sufficient received power to ensure that the minimum SNR 
is met at all times. Since the power level of the detected subcarriers after the APD is low, high 
gain power amplifiers are required prior to transmission over the wireless channel. A modified 
empirically based path loss model, accepted by the IEEE802.16 working group and expanded to 
cover higher frequencies [25], can then be used to predict coverage of the wireless network 
based on power budget analysis parameters as it will be extensively discussed in chapter 6. 
With typical parameters of WiMAX compliant equipment, 300m - 1km coverage for each 
sector is expected.
Furthermore, in order to consider multipath propagation, the standard SUI4 channel profile with 
a moderate delay spread, shown in chapter 4 and modelled in MATLAB with a single-input-
single-output antenna configuration, was utilised since it provided a satisfactory representation 
of the macro-cellular environments [26]. Finally, the RF switches after the amplifiers, which are 

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