Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Optical and Wireless PHY Integration 
53 
frequencies. The number of subcarriers in the network could thus be limited not only by the 
of optical and electrical components but also by the fibre chromatic dispersion. 
-10: Amplitude variations due to fibre chromatic dispersion
OFDM Transmission Evaluation
Having previously established the key characteristics of RoF transmission, it is 
important to evaluate the impact of optical fibres this time on RF OFDM signals
all emerging broadband wireless standards [34, 35]
performance evaluation in view of its compatibility with optical 
architectures enabling wireless/optical integration is paramount. In that direction
error vector magnitude (EVM) is one of the most important test parameter to ensure 
to produce more power and yet maintain signal quality. 
Optical and Wireless PHY Integration
frequencies. The number of subcarriers in the network could thus be limited not only by the 
of optical and electrical components but also by the fibre chromatic dispersion.
: Amplitude variations due to fibre chromatic dispersion
transmission, it is equally 
on RF OFDM signals. OFDM 
[34, 35]
and as a result its 
performance evaluation in view of its compatibility with optical transmission links in 
In that direction, for the 
rtant test parameter to ensure the 
signal quality.

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Chapter 3 Optical and Wireless PHY Integration
54 
Figure 3-11: OFDM transmission investigation setup
Figure 3-11 displays a point-to-point RoF link devised in VPI, demonstrating external optical 
modulation of an FDM multiplexed, OFDM channel, to estimate the EVM of the received 
signal after transmission over various lengths of the optical fibre. 
The OFDM transmitter comprises of 64 subcarriers with 16-QAM modulation each, at a 3.5 
GHz carrier. This carrier is up-converted to 4 GHz and filtered in order to avoid unwanted 
sidebands. The resulting signal is then fed, via a power control unit, to a MZM RF input biased 
at its quadrature point. The power control circuit of Figure 3-11 is utilised to adjust the input RF 
power inside the MZM.
The second MZM arm was fed by a 1550nm optical carrier at 0 dBm output power ending up 
supplying the SSMF with -6 dBm. The modulated output is then transmitted over various 
lengths of the fibre before being received by a PIN photo-detector and demodulated in the 
OFDM receiver. The receiver parameters comply with the transmitter parameters to achieve 
accurate demodulation.
Figure 3-12 presents the obtained EVM figures at the OFDM receiver with respect to the MZM 
RF drive power for varying fibre lengths. The relative constellation root-mean-square error, or 
EVM, is calculated at the receiver as proposed in [35], 

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