Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 7 Experimental Investigation of WiMAX Transmission over Multi-Wavelength PONs 
142 
architecture for smooth network migration, this could be achieved by utilising the free spectral 
range of the AWG allowing 1490/1310 nm to be transmitted. To demonstrate the fixed to 
mobile convergence, a baseband (e.g. GPON) channel at 1.25 Gbit/s was also introduced.
Also significant to mention is that an additional un-modulated wavelength at 
λ
d2
=1557.3 nm 
was connected at one of the unused AWG inputs to investigate interference at ONU/BSs.
Continuing downstream an optical attenuator was used after the fibre to account for various 
splitter loses. At the ONU/BS, a readily available add/drop multiplexer (ADM) was utilised 
prior to PIN detection as a substitute for a commercial 50 GHz optical band pass filter. The 
ADM drop port, at the wavelength of 1558.1 nm, produced a signal to interference ratio of 42 
dB (as displayed Figure 7-2). The resulting up-converted WiMAX electrical spectrum was then 
down-shifted in frequency to get the original WiMAX channels and subsequently amplified by 
a 30 dB gain amplifier to perform performance evaluation measurements. 
Figure 7-2: Output from the ADM
42 dB

---

Chapter 7 Experimental Investigation of WiMAX Transmission over Multi-Wavelength PONs 
143 
Complying with downstream, a single IEEE 802.16-2005, 3.5 GHz channel was generated in 
upstream to directly modulate a VCSEL at 
λ
u1
=1548.5 nm. An 8.3 mA bias was used producing 
-0.94 dBm output power prior to being transmitted over the SSMF. Since the experimental 
investigations involve no signal transmission over a wireless channel, the upstream WiMAX 
transmitter RCE was set to -25.8 dB [4] to conform to the figure expected to be received at the 
base station in a practical scenario. The resulting optical signal was then routed through the 
corresponding AWG output port to the destination receivers (Rx_Sect.X) in the OLT where 
individual EVMs are measured. 

---