Adaptive Demodulation in Differentially Coherent Phase Systems: Design and Performance Analysis

Adaptive Demodulation (ADM) is a newly proposed rate-adaptive system which operates without requiring Channel State Information (CSI) at the transmitter (unlike adaptive modulation) by using adaptive decision region boundaries at the receiver and encoding the data with a rateless code. This paper addresses the design and performance of an ADM scheme for two common differentially coherent schemes: M-DPSK (M-ary Differential Phase Shift Keying) and M-DAPSK (M-ary Differential Amplitude and Phase Shift Keying) operating over AWGN and Rayleigh fading channels. The optimal method for determining the most reliable bits for a given differential detection scheme is presented. In addition, simple (near-optimal) implementations are provided for recovering the most reliable bits from a received pair of differentially encoded symbols for systems using 16-DPSK and 16- DAPSK. The new receivers offer the advantages of a rate-adaptive system, without requiring CSI at the transmitter and a coherent phase reference at the receiver. Bit error analysis for the ADM system in both cases is presented along with numerical results of the spectral efficiency for the rate-adaptive systems operating over a Rayleigh fading channel.Comment: 25 pages, 11 Figures, submitted to IEEE Transactions on Communications, June 1, 201

Error mitigation using RaptorQ codes in an experimental indoor free space optical link under the influence of turbulence

This paper is a postprint of a paper submitted to and accepted for publication in [journal] and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital LibraryIn free space optical (FSO) communications, several factors can strongly affect the link quality. Among them, one of the most important impairments that can degrade the FSO link quality and its reliability even under the clear sky conditions consists of optical turbulence. In this work, the authors investigate the generation of both weak and moderate turbulence regimes in an indoor environment to assess the FSO link quality. In particular, they show that, due to the presence of the turbulence, the link experiences both erasure errors and packet losses during transmission, and also compare the experimental statistical distribution of samples with the predicted Gamma Gamma model. Furthermore, the authors demonstrate that the application of the RaptorQ codes noticeably improves the link quality decreasing the packet error rate (PER) by about an order of magnitude, also offering in certain cases an error-free transmission with a PER of ∼10−2 at Rytov variance value of 0.5. The results show that the recovery rate increases with the redundancy, the packet length and the number of source packets, and it decreases with increasing data rates.This work was supported by the European Space Agency under grant no. 5401001020. We are very grateful to Dr. E. Armandillo for enlightening discussions. This research project also falls within the frame of COST ICT Action IC1101 - Optical Wireless Communications - An Emerging Technology (OPTICWISE). J. Perez's work is supported by Spanish MINECO Juan de la Cierva JCI-2012-14805.Pernice, R.; Parisi, A.; Ando, A.; Mangione, S.; Garbo, G.; Busacca, AC.; Perez, J.... (2015). Error mitigation using RaptorQ codes in an experimental indoor free space optical link under the influence of turbulence. IET Communications. 9(14):1800-1806. https://doi.org/10.1049/iet-com.2015.0235S18001806914Tsukamoto, K., Hashimoto, A., Aburakawa, Y., & Matsumoto, M. (2009). The case for free space. IEEE Microwave Magazine, 10(5), 84-92. doi:10.1109/mmm.2009.933086Paraskevopoulos, A., Vučić, J., Voss, S.-H., Swoboda, R., & Langer, K.-D. (2010). Optical Wireless Communication Systems in the Mb/s to Gb/s Range, Suitable for Industrial Applications. IEEE/ASME Transactions on Mechatronics, 15(4), 541-547. doi:10.1109/tmech.2010.2051814Ghassemlooy, Z., Le Minh, H., Rajbhandari, S., Perez, J., & Ijaz, M. (2012). Performance Analysis of Ethernet/Fast-Ethernet Free Space Optical Communications in a Controlled Weak Turbulence Condition. Journal of Lightwave Technology, 30(13), 2188-2194. doi:10.1109/jlt.2012.2194271Ciaramella, E., Arimoto, Y., Contestabile, G., Presi, M., D’Errico, A., Guarino, V., & Matsumoto, M. (2009). 1.28-Tb/s (32 $\times$ 40 Gb/s) Free-Space Optical WDM Transmission System. IEEE Photonics Technology Letters, 21(16), 1121-1123. doi:10.1109/lpt.2009.2021149Parca, G. (2013). Optical wireless transmission at 1.6-Tbit/s (16×100  Gbit/s) for next-generation convergent urban infrastructures. Optical Engineering, 52(11), 116102. doi:10.1117/1.oe.52.11.116102Hulea, M., Ghassemlooy, Z., Rajbhandari, S., & Tang, X. (2014). Compensating for Optical Beam Scattering and Wandering in FSO Communications. Journal of Lightwave Technology, 32(7), 1323-1328. doi:10.1109/jlt.2014.2304182Ghassemlooy, Z., Popoola, W. O., Ahmadi, V., & Leitgeb, E. (2009). MIMO Free-Space Optical Communication Employing Subcarrier Intensity Modulation in Atmospheric Turbulence Channels. Communications Infrastructure. Systems and Applications in Europe, 61-73. doi:10.1007/978-3-642-11284-3_7Garcia-Zambrana, A. (2007). Error rate performance for STBC in free-space optical communications through strong atmospheric turbulence. IEEE Communications Letters, 11(5), 390-392. doi:10.1109/lcomm.2007.061980Abou-Rjeily, C. (2011). On the Optimality of the Selection Transmit Diversity for MIMO-FSO Links with Feedback. IEEE Communications Letters, 15(6), 641-643. doi:10.1109/lcomm.2011.041411.110312García-Zambrana, A., Castillo-Vázquez, C., & Castillo-Vázquez, B. (2010). Rate-adaptive FSO links over atmospheric turbulence channels by jointly using repetition coding and silence periods. Optics Express, 18(24), 25422. doi:10.1364/oe.18.025422Andò, A., Mangione, S., Curcio, L., Stivala, S., Garbo, G., Pernice, R., & Busacca, A. C. (2013). Recovery Capabilities of Rateless Codes on Simulated Turbulent Terrestrial Free Space Optics Channel Model. International Journal of Antennas and Propagation, 2013, 1-8. doi:10.1155/2013/692915MacKay, D. J. C. (2005). Fountain codes. IEE Proceedings - Communications, 152(6), 1062. doi:10.1049/ip-com:20050237Shokrollahi, A. (2006). Raptor codes. IEEE Transactions on Information Theory, 52(6), 2551-2567. doi:10.1109/tit.2006.874390Anguita, J. A., Neifeld, M. A., Hildner, B., & Vasic, B. (2010). Rateless Coding on Experimental Temporally Correlated FSO Channels. Journal of Lightwave Technology, 28(7), 990-1002. doi:10.1109/jlt.2010.2040136Wang, N., & Cheng, J. (2010). Moment-based estimation for the shape parameters of the Gamma-Gamma atmospheric turbulence model. Optics Express, 18(12), 12824. doi:10.1364/oe.18.012824Zvanovec, S., Perez, J., Ghassemlooy, Z., Rajbhandari, S., & Libich, J. (2013). Route diversity analyses for free-space optical wireless links within turbulent scenarios. Optics Express, 21(6), 7641. doi:10.1364/oe.21.007641Pernice, R., Perez, J., Ghassemlooy, Z., Stivala, S., Cardinale, M., Curcio, L., … Parisi, A. (2015). Indoor free space optics link under the weak turbulence regime: measurements and model validation. IET Communications, 9(1), 62-70. doi:10.1049/iet-com.2014.043

Semi-hidden markov models for visible light communication channels

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering, Johannesburg 2018Visible Light Communication (VLC) is an emerging field in optical wireless communication that uses light emitting diodes (LEDs) for data transmission. LEDs are being widely adopted both indoors and outdoors due to their low cost, long lifespan and high efficiency. Furthermore, LEDs can be modulated to provide both illumination and wireless communication. There is also potential for VLC to be incorporated into future smart lighting systems. One of the current challenges in VLC is being able to deal with noise and interference; including interference from other dimmed, Pulse-Width Modulated (PWM) LEDs. Other noise includes natural light from the sun and artificial light from other non-modulating light sources. Modelling these types of channels is one of the first steps in understanding the channel and eventually designing techniques for mitigating the effects of noise and interference. This dissertation presents a semi-hidden Markov model, known as the Fritchman model, that discretely models the effects of as well as errors introduced from noise and interference in on-off keying modulated VLC channels. Models have been developed for both the indoor and outdoor environments and can be used for VLC simulations and designing error mitigation techniques. Results show that certain channels are able to be better modelled than others. Experimental error distributions shows insights into the impact that PWM interference has on VLC channels. This can be used for assisting in the development of error control codes and interference avoidance techniques in standalone VLC systems, as well as systems where VLC and smart lighting coexist. The models developed can also be used for simulations of VLC channels under different channel conditionsXL201

High Dimensional Modulation and MIMO Techniques for Access Networks

Exploration of advanced modulation formats and multiplexing techniques for next generation optical access networks are of interest as promising solutions for delivering multiple services to end-users. This thesis addresses this from two different angles: high dimensionality carrierless amplitudephase (CAP) and multiple-input multiple-output (MIMO) radio-over-fiber (RoF) systems. High dimensionality CAP modulation has been investigated in optical fiber systems. In this project we conducted the first experimental demonstration of 3 and 4 dimensional CAP with bit rates up to 10 Gb/s. These results indicate the potentiality of supporting multiple users with converged services. At the same time, orthogonal division multiple access (ODMA) systems for multiple possible dimensions of CAP modulation has been demonstrated for user and service allocation in wavelength division multiplexing (WDM) optical access network. 2 x 2 MIMO RoF employing orthogonal frequency division multiplexing (OFDM) with 5.6 GHz RoF signaling over all-vertical cavity surface emitting lasers (VCSEL) WDM passive optical networks (PONs). We have employed polarization division multiplexing (PDM) to further increase the capacity per wavelength of the femto-cell network. Bit rate up to 1.59 Gbps with fiber-wireless transmission over 1 m air distance is demonstrated. The results presented in this thesis demonstrate the feasibility of high dimensionality CAP in increasing the number of dimensions and their potentially to be utilized for multiple service allocation to different users. MIMO multiplexing techniques with OFDM provides the scalability in increasing spectral effciency and bit rates for RoF systems. High dimensional CAP and MIMO multiplexing techniques are two promising solutions for supporting wired and hybrid wired-wireless access networks

Performance analysis of a MIMO Optical wireless link with space Time Block Code (STBC)

This thesis report is submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Computer Science and Engineering, 2010.Cataloged from PDF version of thesis report.Includes bibliographical references (page 22).Performance analysis will be carried out for space time block coded multiple input multiple output (MIMO) optical wireless link considering nakagami-m fading model. The diversity reception in the receiving will be carried out by multiple receiving antenna with maximal ratio combining (MRC) technique. The expression of the receiver output will be derived for several sets of space time block codes considering the above fading model. The probability density function (PDF) of the output of the MRC combiner will be developed and will be used to find the unconditional average bit error rate (BER). The performance results will be evaluated numerically in terms of BER for several scode and system parameters. The optimum system design parameters wll be determined at a given BER.Md. Zahirul IslamB. Computer Science and Engineerin