Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 3 Optical and Wireless PHY Integration
55 
EVM
∑ I
I
Q
Q
∑ I
Q
3.1
where 
I
and 
I
are the transmitted and receiver 
I
components of the complex symbols 
respectively. The same notation applies for the 
Q
and 
Q
components. 
Figure 3-12: EVM against RF drive power for different fiber lengths
As expected, the EVM characteristics increase with the optical link noise for low RF drive 
powers (i.e. for power levels in the range of -27 dBm the EVM is 14%). With the power levels 
in the range of 2.5 dBm the EVM below 5% is observed. Further degradation of the system 
performance can also be seen for increasing fibre lengths due to chromatic dispersion. Taking 
into consideration the stringent requirements, as they are dictated by emerging broadband 
wireless standards, EVM figures in the range of 2-5% [34, 35] will be typically required at 
antenna inputs. Therefore, RF drive power inside the optical modulator and fibre link lengths 
are important factors in designing a RoF transmission link for these wireless signals.
Finally, the obtained constellation diagrams at -3 dBm RF drive power for back-to-back and 23 
km fibre transmission links are shown in Figure 3-13. 
EVM (all carriers)
0
5
10
15
20
25
30
-30
-25
-20
-15
-10
-5
0
RF drive (dBm)
E
V
M
 (
%
)
0 km
2 km
4 km
8 km
17 km
23 km

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Chapter 3
Figure 
The pilot tones were not considered by the OFDM transmitter therefore only data points are
visible on the constellation
resulting unavoidably to more points 
to the relatively high, -3dBm
would be required in order to 
effects and consequently more symbols in error.