Dr Sujan Rajbhandari

Senior Research Assistant

Research Project: Application of Wavelets and Artificial Neural Network for Indoor Optical Wireless Communication Systems

Funding Source: Northumbria University

Research Group: Optical Communications Research Group (OCRG), Intelligent Modelling Lab (IML)

Membership of Professional Bodies: MIEEE, MIET

 

Research Project

The bandwidth congestion in radio wave and microwave frequencies has forced the communication scientist to look for fresh alternatives. There is still ongoing research on improving performance by utilising the available bandwidth in the best possible way, the other looked for the most obvious choice, the optical communication. The concept of light as a means of communication goes back to pre-historic time where human being used fire, sun, star and sign language to communicate. In the modern world of communication, utilization of infrared light initiated in the form of optical fibre. A single optical fibre can carry such a huge amount of data that it is unimaginable that the bandwidth per end user is limited to 1-10 Mbps. It is mainly due to the fact that the last mile access is all based on the radio and microwave frequencies. Though concept of the fibre to the home promises a bandwidth of gigahertz per user, it is very costly and environmentally unfriendly because of necessity to digging to deploy the fibre. Optical wireless system (OWS) is the best and affordable solution. The combination of optical fibre and OWS (both indoor and outdoor) could not only solve the problem of bandwidth congestion for a foreseeable future, but also avoid necessity of converting optical signal to electrical signal and back as new technologies are developing to process signal in optical domain itself.  This could be a great advantage as the data rates in optical communications are limited only by electronics. Beside the bandwidth of millions times that of microwave and radio wave frequencies, OWS has other advantages which includes the unregulated bandwidth, free from electromagnetic interference, secure links, and small cell size.

The present day researches focus on reducing the effect of the noise due to ambient light, transmitted power limitation due to eye and skin safety, intersymbol interference due to multipath propagation, blocking probability in line-of-sight links, and improving mobility. My research is focused on applying artificial intelligent and modern signal processing tools like discrete wavelet transform (DWT) to improve the performance of a receiver for indoor OWS.

The power penalty due to artificial light interference (ALI) can be very high in indoor optical channel making the optical link practically infeasible. A denoising method based on a DWT to remove the ALI from the received signal is investigated. The concept here is to separate the spectrum of modulating signal and interfering signal using wavelet decomposing. The received signal is first decomposed into different DWT levels; the ALI is then removed from the signal before reconstructing the signal. A significant reduction in the power penalty is observed using DWT. Comparative study of DWT based denoising scheme with that of the high pass filter (HPF) show that DWT not only can match the best performance obtain using a HPF, but also offers a reduced complexity and design simplicity.

The high power penalty due to multipath induced intersymbol interference makes a diffuse optical link practically infeasible at higher data rates. An artificial neural network based techniques are investigated to reduce the effect of interference and study shows a much improved performance. The research also focuses on developing prototype of the optical wireless communication in FPGA and DSP and characterise the channel effect for indoor and outdoor optical wireless communication.

Research Interests
1) Indoor optical wireless communication (Visible and Infrared)
2) Free space optics for outdoor application.
3) Modulation techniques
4) Error control codes
5) Signal processing (wavelet transforms)
6) Artificial neural network
7) Adaptive equalization
8) Channel characterization

Refereed Journal Papers

1. S. Rajbhandari and Z. Ghassemlooy, “Optimizing the performance of digital pulse interval modulation with guard slots for diffuse indoor optical wireless links”, accepted for publication in IET Microwaves, Antennas & Propagation.
2. X. Tang, Z. Ghassemlooy, S. Rajbhandari, W. O. Popoola and C. G. Lee, “Coherent optical binary polarization shift keying heterodyne system in the free space optical turbulence channel”, accepted for publication in IET Microwaves, Antennas & Propagation.
3. S. Rajbhandari; Z. Ghassemlooy; and M. Angelova, "Effective denoising and adaptive equalization of indoor optical wireless channel with artificial light using the discrete wavelet transform and artificial neural network", IEEE Journal of Lightwave Technology, vol.27, No.20, pp.  4493-4500, Oct. 2009.
4. S. Rajbhandari, Z. Ghassemlooy and M. Angelova,” Bit error performance of diffuse indoor optical wireless channel pulse position modulation system employing artificial neural networks for channel equalisation,” IET -Optoelectronics, vol.3, no.4, pp. 169-179, August 2009.
5. Z. Ghassemlooy, S. Rajbhandari, and N. M. Aldibbiat, “Convolutional coded dual header pulse interval modulation for photonic wireless links” IET -Optoelectronics, vol.3, no.3, pp.142-148, June 2009.
6. S. Rajbhandari; Z. Ghassemlooy; and M. Angelova, "Performance of the wavelet transform-neural network based receiver for DPIM in diffuse indoor optical wireless links in presence of artificial light interference," IJEEE, Vol. 5, no. 2, pp.102-111. 2009.
7. S. Rajbhandari, N. M. Aldibbiat, and Z. Ghassemlooy, “Analysis and evaluation of symbol retransmission in optical wireless links employing DH-PIM”, European Transaction on Telecommunications, vol. 20. 2009, pp. 217-225.
8. Z. Ghassemlooy, R. Dickenson, and S. Rajbhandari, "Wavelet transform - artificial neural network receiver with adaptive equalization for a diffuse indoor optical wireless OOK link", Mediterranean Journal of Computers and Networks, vol.  5, no. 1, pp. 1-9, 2009.

Conference Papers

9. H. Le-Minh, Z. Ghassemlooy, M. Ijaz, S. Rajbhandari, O. Adebanjo, S. Ansari and E. Leitgeb, “Experimental study of bit error rate of free space optics communications in laboratory controlled turbulence”, accepted for IEEE Globecom 2010.
10. D. Chuckravanen, S. Rajbhandari, and  M. Angelova, “Continuous wavelet analysis of physiological data for various pacing strategies”, presented in 28th International Colloquium on Group - Theoretical Methods in Physics.
11. S. Rajbhandari, Z. Ghassemlooy, and M. Angelova, “A study of discrete wavelet transform based denoising to reduce the effect of artificial light interferences for indoor optical wireless communication”, Proceeding of the 7th Symposium on Communication Systems, Networks and Digital Signal Processing 2010 (CSNDSP 2010), ISBN: 978-1-86135-370-2, pp. 658-662, Newcastle upon Tyne, UK, July 2010.
12. J. Faith and S. Rajbhandari, “The use of linear projections in the visual analysis of signals in an indoor optical wireless link”, Proceeding of the 7th Symposium on Communication Systems, Networks and Digital Signal Processing 2010 (CSNDSP 2010), ISBN: 978-1-86135-370-2, pp. 680-685, Newcastle upon Tyne, UK, July 2010.
13. X. Tang, Z. Ghassemlooy, S. Rajbhandari, W. O. Popoola, C. G. Lee, E. Leitgeb , V. Ahmadi, “Free-space optical communication employing polarization shift keying coherent modulation in atmospheric turbulence channel”, Proceeding of the 7th Symposium on Communication Systems, Networks and Digital Signal Processing 2010 (CSNDSP 2010), ISBN: 978-1-86135-370-2, pp. 663-668, Newcastle upon Tyne, UK, July 2010.
14. M., Ijaz, O. Adebanjo, S. Ansari, Z. Ghassemlooy, S. Rajbhandari, H. Le Minh, A. Gholami, E. Leitgeb, “Experimental investigation of the performance of OOK-NRZ and RZ modulation techniques under controlled turbulence channel in FSO systems.”11th Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking and Broadcasting, 21-22 June, Liverpool, UK, pp. 296-300, 2010
15. R. Paudel, H. Le-Minh, Z. Ghassemlooy, and S. Rajbhandari, “High speed short range optical wireless ground-to-train communications”, The 11th annual Postgraduate Symposium on the convergence of Telecommunications , Networking & Broadcasting (PGNET 2010),21-22 June, ISBN: 978-1-902560-24-3, Liverpool, UK, pp 367-371, 2010.
16. A. Bahrami, T. Kanesan, W.P. Ng, Z. Ghassemlooy, A. Abd El Aziz and S. Rajbhandari,” Performance evaluation of radio-over-fibre (RoF) system using Mach-Zehnder Modulator (MZM) and on-off keying (OOK) modulation schemes” The 11th annual Postgraduate Symposium on the convergence of Telecommunications, Networking & Broadcasting (PGNET 2010),21-22 June, ISBN: 978-1-902560-24-3, Liverpool, UK, pp 66-69, 2010.
17. S. Rajbhandari and Z. Ghassemlooy, “Optimizing the performance of digital pulse interval modulation with guard slots for diffuse indoor optical wireless links”, Mosharaka International Conference on Communications, Propagation, and Electronics (MIC-CPE 2010), 5-7 March 2010, Amman, Jordan, pp.18-23.
18. X. Tang, Z. Ghassemlooy, S. Rajbhandari, W. O. Popoola and C. G. Lee, “Performance of coherent optical binary polarization-shift-keying heterodyne system in free space optical communications using a lognormal atmospheric turbulence model”, Mosharaka International Conference on Communications, Propagation, and Electronics (MIC-CPE 2010), 5-7 March 2010, Amman, Jordan, pp.30-35.
19. X. Tang, S. Rajbhandari, W. O. Popoola, Z. Ghassemlooy, E. Leitgeb, S. S. Muhammad and G. Kandus, “Performance of BPSK subcarrier intensity modulation free-space optical communications using a log-normal atmospheric turbulence model” accepted for publication in SOPO2010, Chengdu, China.
20. S. Rajbhandari, Z. Ghassemlooy, and M. Angelova, “The efficient denoising artificial light interference using discrete wavelet transform with application to indoor optical wireless system”, Tenth international symposium on Communication Theory and Application (ISCTA'09), pp. 155-160, Ambleside, UK, July 2009.
21. R. Kharel, S. Rajbhandari, K. Busawon, and Z. Ghassemlooy, “Digitization of chaotic signal for reliable communication in non-ideal channels”, proceeding of International Conference on Transparent Optical Networks ’’Mediterranean Winter’’ 2008 (ICTON-MW'08), ISBN: 978-1-4244-3485-5, pp. Sa1.2 (1-6), Marrakech, Morocco, 11-13 Dec., 2008.  Invited Plenary Paper.
22. Z. Ghassemlooy, R. Dickenson, and S. Rajbhandari, “Signal detection and adaptive equalization using wavelet transform - artificial neural network in diffuse indoor optical wireless links”, XIII Congreso Internacional de Telecomunicaciones SENACITEL 2008, Valdivia, Chile, November 2008.
23. S. Rajbhandari, Z. Ghassemlooy, and M. Angelova, “Performance of DWT-ANN based signal detector/equalizer for DPIM in practical indoor optical wireless links”, proceeding of the 6th Symposium on Communication Systems, Networks and Digital Signal Processing 2008 (CSNDSP 2008), ISBN: 978-1-4244-1876-3, pp. 106-109, Graz, Austria, July 2008.
24. S. Rajbhandari, Z. Ghassemlooy, and M. Angelova, "Signal detection and adaptive equalization using a discrete wavelet transform – artificial neural network for OOK indoor optical wireless links", ICEE 2008, Tehran, Iran, 13-15 May 2008, Paper No. 2808.
25. Z. Ghassemlooy, and S. Rajbhandari, “Performance of diffused indoor optical wireless links employing neural and adaptive linear equalizers,” Invited paper, 6th ICICS, 10-13 Dec. 2007, Singapore, Paper No. P0455, 1-4244-0983-7/07/.
26. Z. Ghassemlooy, W.O. Popoola, S. Rajbhandari, M. Amiri, and S. Hashemi, "A synopsis of modulation techniques for wireless infrared communication," Invited paper, Intern. Conf. on Transparent Optical Networks - Mediterranean Winter (ICTON-MW'07), Sousse, Tunisia, 6-8 Dec. 2007.
27. S. Rajbhandari, Z. Ghassemlooy and M. Angelova, "The Performance of PPM using Neural Network and Symbol Decoding for Diffused Indoor Optical Wireless Links", 9th International conference on Transparent Optical Networks (ICTON2007), pp.161-164, Rome, Italy.
28. S. Rajbhandari, Z. Ghassemlooy, and M. Angelova, "Performance of OOK with ANN Equalization in Indoor Optical Wireless Communication system," The 8th  annual Postgraduate Symposium on the convergence of Telecommunications , Networking & Broadcasting (PGNET 2007), ISBN 1-9025-6016-7,  Liverpool , UK,   pp 86-90, June 2007.
29. S. Rajbhandari, Z. Ghassemlooy, N. Aldibbiat, M. Amiri, and W.O. Popoola, “Convolutional coded DPIM for indoor non-diffuse optical wireless link”, The 7th IASTED International Conferences on Wireless and Optical Communications (WOC 2007), ISBN 978-0-88986-659-1, Montreal, Canada, pp. 286-290, May-Jun. 2007.
30. N. Aldibbiat, S. Rajbhandari and F. Ghassemlooy, “Convolutional Coded DPIM for Indoor Optical Wireless Links”, LCS2006, UCL, London, 2006.
31. S. Rajbhandari, Z. Ghassemlooy, and N.M. Aldibbiat, “Performance of convolutional coded dual header pulse interval modulation in infrared links “, Proceeding of the 6th annual postgraduate symposium on the convergence of telecommunications, networking and broadcasting (PGNET) ,ISBN 1-9025-6013-9, pp 227-231 Liverpool , UK, June 2006.
Technical Report, Presentations and Posters

32. Z. Ghassemlooy, S. Rajbhandari, M. Ijaz, O. Adebanjo and S. Ansari, “Experimental comparison of different modulation schemes for free-space optics communication in the presence of turbulence in a controlled environment”, Propagation tools and data  for integrated Telecommunication, Navigation and Earth Observation systems, 26-28 April 2010, Athens, Greece.
33. S. Rajbhandari, Z. Ghassemlooy and M. Angelova: “Wavelet transform and artificial neural network for digital signal detection and equalization in optical wireless communication”, UK GRAD Program Yorkshire & North East Hub, Poster Competition & Network Event, York, UK, 7 March 2008, Poster No. 48.
34. S. Rajbhandari, Z. Ghassemlooy and M. Angelova :"Application of Neural Network and Wavelets for Digital Signal Detection and Equalization in Indoor Optical Wireless System" presented at Northumbria CEIS research seminar, 9 May 2007.

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