1. All Photonic Analogue to Digital and Digital to Analogue Conversion Techniques
for Digital Radio over Fibre System Applications
S. R. Abdollahi, H.S. Al-Raweshidy, S. Mehdi Fakhraie*, and R. Nilavalan
WNCC Group, School of Eng. and Design, Brunel University, Uxbridge, Middlesex, UB8 3PH, UK, and *University College of Engineering, University of Tehran, North Kargar Ave., Tehran, 14395-515, Iran.
E-mail: {seyedreza.abdollahi, hamed al-raweshidy, rajagopal.nilavalan}@brunel.ac.uk, and fakhraie@ut.ac.ir
Radio over Fibre (RoF) Technique
RoF Features
Centralizing signal processing, performance and error
monitoring, share resources, and control and
management.
Cheaper, smaller size & simpler base stations.
Smaller cells: allocates higher bandwidth to end-users.
Future proof.
Green: Lower power radiated electromagnetic wave,
lower power consumption, fibre low attenuation and
loss.
Reduce the maintenance cost.
Could be accommodated with passive optical network
(PON) Infrastructures.
Can use wavelength division multiplexing (WDM)
technique for improving the network throughput.
Photonic Analogue-to-Digital and Digital-to-Analogue Conversions
Integration of wireless and fibre optic communication
technologies, and modulating wireless signals over
optical carrier for transporting over fibre optic cable.
Digital RoF & Integrated RoF System.
Digital RoF (DRoF) link can maintain the dynamic
range more independent than optical fibre link distance.
The analogue RF signal digitized by using the Photonic
Analogue-to-Digital Converter (PADC).
Generated digitized-RF data stream and RF analogue
signal are transported over optical fibre network by
using WDM technique. The photonic DAC of RF
system at the base station or access point converts
digital photonic signals to its analogue optical
modulated signal.
An 8-bits photonic sampling and quantization ADC is
designed by using 30 Gigasample/s mode-locked laser.
A photonic DAC converts photonic digital waveform to
analogue optical signal. By using the proposed PDAC, the
necessity of optical to electrical conversion will be fulfilled
by only a high-speed photo diode.
For reducing the cost and complexity of the system, the
optical sampling pulse has been reused at base-station for
sampling the uplink RF signal.
The SFDR and ENOB at 160 Gigasample/s sampling rate
are equal to 9.82 dB and 1.63, respectively.
Simulation Results and Conclusions
The performance of DRoF link is investigated and compared with ARoF system over 15 and 20
kilometres standard single mode fibre length. PADC’s performance is affected by the laser’s jitter, the
nonlinearity of MZM, photonic amplifier and other photonic devices performance. In the digital radio
over fibre, the dynamic range is independent of the fibre length.
Eye diagram of 1 Gbps ASK modulated signal with 10 GHz carrier over 15
km ( Left) 20 km (Right) length of single mode fibre: (top) ARoF system,
(bottom) DRoF system.
(Top) RF signal, (Bottom) Sampled optical signal.
ENOB variation versus sampling rate.
