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Seyed Reza Abdollahi

Email: seyedreza.abdollahi@brunel.ac.uk

Supervisor: Prof. Hamed Al-Raweshidy

PhD Research: All-Photonic Digital Radio over Fibre

Digital systems are more flexible, more conveniently interface with other systems, are more reliable and robust against additive noise from devices and channels, and achieve a better dynamic range than analogue systems. Analogue to digital and digital to analogue converters (ADC and DAC, respectively) are the link between the analogue world and the digital world of signal processing and data handling. In an analogue system the bandwidth is limited by devices performance and parasitic components are introduced.

In a Digital RoF (DRoF) system, an electrical RF signal is digitized by using an Electronic ADC (EADC). Then, the generated digital data is modulated with a continuous coherent optical carrier wave either using a direct modulation technique or by using an external electro-optical modulator as shown in Fig. 1. The modulated optical carrier is transmitted through the fibre. At the base station, after detecting the optical signal using a photo diode, the detected digital data is converted back to the analogue domain using an EDAC. Finally, the analogue electrical signal is fed to an antenna. Current EDAC systems experience problems such as jitter in the sampling clock, the settling time of the sample and hold circuit, the speed of the comparator, mismatches in the transistor thresholds and passive component values. The limitations imposed by all of these factors become more severe at higher frequencies. Wideband analogue to digital conversion is a critical problem encountered in broadband communication and radar systems. For the future beyond Gigabit/s mobile and wireless end-user traffic rates due to the limitations of electronic technology for implementing ultra high-speed, high performance EADC, and the resolution of existing EDAC, the deployment of conventional DRoF links is not simply achievable.

Seyed reza Abdollahi Research

Figure 1. Conventional DRoF architecture using EADC (downlink)

Moreover, if a conventional DRoF link could be achieved for Gigabit/s traffic rates the generated digital traffic creates a new challenge, namely, for this architecture to use more electro-optical modulators and photo diodes to implement the wavelength division multiplexing (WDM) technique to diminish the chromatic dispersion caused by the restrictions on the modulation bandwidth for super broadband access by RoF.

All-Photonic Digital Radio over Fiber

An all-photonic DRoF architecture has been proposed and is depicted in Fig. 2. This architecture uses an electro-optical modulator, which is simultaneously shared as an optical sampling and modulating device at the CS. A photonic ADC (PADC) by using a mode-locked laser (MLL) and an electro-optical modulator is able to scale the timing jitter of the laser sources to the femtosecond level, which allows designers to push the resolution bandwidth by many orders of magnitude beyond what electronic sampling systems can currently achieve. The proposed system includes an all-photonic signal processing block for optical quantization and wavelength conversion of the sampled and symmetrically split signal’s power. By using the WDM technique to distribute the generated traffic over different wavelengths exceeding the modulation bandwidth of the fiber on a particular wavelength is prevented.

Seyed reza Abdollahi Research

Figure 2. All-photonic DRoF architecture, (downlink).

Publications

Journals:

S. R. Abdollahi, and H.S. Al-Raweshidy, and Thomas Owens, “Digital Pulse Regeneration in Optical Networks”, IEEE Journal of Optical Communications and Networking (Under Review).
S. R. Abdollahi, S. M. Fakhraie, M. Kamarei, " A Crystal-Based Low-Voltage All-Digital Programmable Ring Oscillator," International Journal, Analog Integrated Circuits and Signal Processing, Vol. 43, N0.4, P. 147-157, Springer Publication, April 2005.
S. R. Abdollahi, B. Bakkalglue, S. E. Abdollahi, “A Fully Digital Numerical-Controlled-Oscillator,” Integrated Circuit and System Design, Vol. 2799, P. 389-398, Springer Publication, September 2003.

Conferences:

S. R. Abdollahi, H.S. Al-Raweshidy, and Thomas Owens, “Data Regeneration in Communication Networks” IEEE International Conference on Ubiquitous and Future Networks, ICUFN 2012.
S. R. Abdollahi, H.S. Al-Raweshidy, and R. Nilavalan, “Wavelength Allocation Schemes Impact on All-Photonic Digitized-Radio over Fibre Access Network”, 2011 Advanced Photonics Congress, Optical Socity America, June 2011 Toronto, Canada.
S. R. Abdollahi, H.S. Al-Raweshidy, and R. Nilavalan, “An Integrated Transportation System for Baseband Data, Digital and Analogue Radio Signals over Fibre Network”, IEEE IWCMC 2011, Turkey, July 2011.
S. R. Abdollahi, H.S. Al-Raweshidy, and R. Nilavalan, “An Integrated Transportation System for Baseband Data, Digital and Analogue Radio Signals over Fibre Network”, RESCON 2011, Brunel Univ. UK, June 2011.
S. R. Abdollahi, H.S. Al-Raweshidy, and R. Nilavalan, “Fully-Photonic Analogue-to-Digital Conversion Technique for Super-Broadband Digitized-Radio over Fibre Link”, NOC2011, UK, July.
S. R. Abdollahi, H.S. Al-Raweshidy, and R. Nilavalan “Non-Uniform Wavelength Allocation in All-Photonic Digitized-Radio over Fibre Access Network”, IEEE WPMC11 France, Sep 2011.
S. R. Abdollahi, H.S. Al-Raweshidy, and R. Nilavalan, “Pipeline Time-Interleaved All-photonic Sampling and Quantization Analogue-to-Digital Converter”, IEEE International Congress on Ultra Modern Telecommunications and Control Systems (ICUMT), 2011.
M. Behjati, S. R. Abdollahi, and H.S. Al-Raweshidy, “Photonic Sampled and Electronically Quantized Analogue to Digital Conversion in Access Networks”, IEEE International Congress on Ultra Modern Telecommunications and Control Systems (ICUMT), 2011.
S. R. Abdollahi, H.S. Al-Raweshidy, A. Ahmadinia, and R. Nilavalan, “An All-photonic Digital Radio over Fiber architecture,” IEEE Swedish Communication Technologies Workshop (Swe-CTW), 2011.
S. R. Abdollahi, H.S. Al-Raweshidy, S. Mehdi Fakhraie, and R. Nilavalan, “Full Duplex 60 GHz Millimeter Wave Transmission over Multi-Mode Fiber ”, IEEE ICUFN 2010, South Korea, June 2010.
S. R. Abdollahi, H.S. Al-Raweshidy, S. Mehdi Fakhraie, and R. Nilavalan, “ Digital Radio over Fibre for Future Broadband Wireless Access Network Solution ”, IEEE ICWMC 2010, Spain, Sep. 2010.
S. R. Abdollahi, H.S. Al-Raweshidy, R. Nilavalan, and Abolgasem Darzi, “ Future Broadband Access Network Challenges ”, IEEE WOCN 2010, Sri Lanka, Sep. 2010.
S. R. Abdollahi, H.S. Al-Raweshidy, S. Mehdi Fakhraie, and R. Nilavalan, “All Photonic Analogue to Digital and Digital to analogue conversion techniques for digital Radio over Fiber system applications”, ITU-T Kaleidoscope Event, Beyond the Internet ?: Innovation for future networks and services, India, Dec 2010.
S. R. Abdollahi, R. Anvari, " Dff-based Programmable Digital Controlled Oscillator," Proc. The IEEE Wireless Personal Multimedia Communication,” pp 298-300, Jaipour, India, December 2007, (WPMC07).
S. R. Abdollahi, S. M. Fakhraie, M. Kamrei, “A Low Power 1.5 GHz Crystal–Based Digital Ring Oscillator,” Proc. The IEEE Midwest Circuit and System Symposium 2003.
S. R. Abdollahi, S. M. Fakhraie, M. Kamarei, “A Crystal-Based Digital Ring Oscillator,” Proc. The IEEE International Conference of Field Programmable Technology, FPT 2003, Tokyo, Japan.
S. R. Abdollahi, M. Kamarei, S. M. Fakhraie, “Semi-Coherent GFSK Receiver For DECT Standard," Proc. IEEE International Conference of Electronic Circuits and Systems, Sharjah, UAE, December, 2003.
S. R. Abdollahi, S.Kiaei, B. Bakkalglue, S. M. Fakhraie, “An All –Digital Programmable Digitally-Controlled-Oscillator (DCO) For Digital Wireless Applications,” Proc. IEEE International Symposium on Circuits and Systems, vol IV. , PP.101-104 -, Phoenix, Arizona, May 2002.USA (ISCAS2002).

Book Chapter:

Book Chapter “Super-Broadband Wireless Access Network” @ Wireless Communication Network, Recent Advances, appeared in http://www.intechopen.com/books/wireless-communications-and-networks-recent-advances/super-broadband-wireless-access-network-
Radio over Fiber Technology and Networks, Springer Publication (Under Review).

Patent:

S.R. Abdollahi, S. E. Abdollahi , “Multi Channel Programmable DCO ”, Reg. No.: 32273, I. R. of Iran, Jun. 2005.