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

Implementation Of A Raptorq-Based Protocol For Peer To Peer Network

The object of this thesis is to develop and test a Ruby based implementation of the RaptorQP2P protocol. The RaptorQP2P protocol is a novel peer-to-peer protocol based on RaptorQ forward error correction. This protocol facilitates delivery of a single file to a large number of peers. It applies two levels of RaptorQ encoding to the source file before packet transmission. Download completion time using RaptorQP2P was found to be significantly improved comparing to BitTorrent. We developed a Ruby interface to the Qualcomm proprietary RaptorQ software development kit library. Then we achieved the two levels of RaptorQ encoding and decoding with the Ruby interface. Our implementation uses 5 threads to implement RaptorQP2P features. Thread 1 runs as a server to accept the connection requests from new peers. Thread 2 works as a client to connect to other peers. Thread 3 is used for sending data (pieces) and thread 4 is to receive data from neighboring peers. Thread 5 manages the piece map status, the peer list, and choking of a peer. We first tested communication modules of the implementation. Then we set up scheduled transmission tests to validate the intelligent symbol transmission scheduling design. Finally, we set up a multi-peer network for close to practical tests. We use 5 RaspberryvPi single-board computers to act as 1 seeder and 4 leechers. The seeder has the whole file and delivers the file to the 4 leechers simultaneously. The 4 leechers will also exchange part of the file with each other based on what they have received. Test results show that our implementation attains all the features of RaptorQP2P: the implementation uses two levels RaptorQ encoding; a peer is able to download a piece from multiple neighbors simultaneously; and a peer can send the received encoded symbols of a piece to other peers even if the peer does not have the full piece yet

THE INFLUENCE OF THE PACKET SIZE ON END TO END DELAY OF VIDEO DATA CODED WITH RAPTORQ CODES AND NETWORK CODES IN VEHICULAR ADHOC NETWORKS

The transmission of video files in Vehicular Adhoc Networks (VANETs) has become very prevalent as commuters prefer video data during travel. The delay with which the data is received becomes very significant as video packets received after their scheduled deadlines become useless. The performance of the network may significantly be reduced on such packet drops especially with mobile networks. This work aims at the reduction of end to end delay of video packets by applying the two techniques- Network Coding (NC) and RaptorQ (RQ) codes. The techniques are implemented in four VANET scenarios and an extensive analysis is done by varying the packet sizes during the transmission of three files of various sizes. The End to End Delay (EED) and Packet Delivery Ratio (PDR) are measured and plotted for all scenarios. The results show the influence of packet size on these parameters considered and the suitability of the techniques applied. The observations also show that RQ proves better for smaller files and NC suits better when the file size increases

S-RLNC based MAC Optimization for Multimedia Data Transmission over LTE/LTE-A Network

The high pace emergence in communication systems and associated demands has triggered academia-industries to achieve more efficient solution for Quality of Service (QoS) delivery for which recently introduced Long Term Evolution (LTE) or LTE-Advanced has been found as a promising solution. However, enabling QoS and Quality of Experience (QoE) delivery for multimedia data over LTE has always been a challenging task. QoS demands require reliable data transmission with minimum signalling overheads, computational complexity, minimum latency etc, for which classical Hybrid Automatic Repeat Request (HREQ) based LTE-MAC is not sufficient. To alleviate these issues, in this paper a novel and robust Multiple Generation Mixing (MGM) assisted Systematic Random Linear Network Coding (S-RLNC) model is developed to be used at the top of LTE MAC protocol stack for multimedia data transmission over LTE/LTE-A system. Our proposed model incorporated interleaving and coding approach along with MGM to ensure secure, resource efficient and reliable multiple data delivery over LTE systems. The simulation results reveal that our proposed S-RLNC-MGM based MAC can ensure QoS/QoE delivery over LTE systems for multimedia data communication

FREE SPACE OPTICS LINKS AFFECTED BY OPTICAL TURBULENCE: CHANNEL MODELING, MEASUREMENTS AND CODING TECHNIQUES FOR ERROR MITIGATION

FSO is an optical wireless line-of-sight communication system able to offer good broadband performance, electromagnetic interference immunity, high security, license-free operation, low power consumption, ease of relocation, and straightforward installation. It represents a modern technology, significantly functional when it is impossible, expensive or complex to use physical connections or radio links. Unfortunately, since the transmission medium in a terrestrial FSO link is the air, these communications are strongly dependent on various atmospheric phenomena (e.g., rain, snow, optical turbulence and, especially, fog) that can cause losses and fading. Therefore, in worst-case conditions, it could be necessary to increase the optical transmission power, although, at the same time, it is needed to comply to safety regulations. The effects of the already mentioned impairments are: scattering (i.e., Rayleigh and Mie) losses, absorption and scintillation. The first two can be described by proper attenuation coefficients and increase if the atmospheric conditions get worst. As regards scintillation, it is a random phenomenon, appreciable even under clear sky. Because of scintillation, in FSO links, the irradiance fluctuates and could drop below a threshold under which the receiver is not able to detect the useful signal. In this case, communications suffer from erasure errors, which cause link outages. This phenomenon becomes relevant at high distance, but it can also be observed in 500m-long FSO links. Moreover, the optical turbulence intensity can change of an order of magnitude during the day: it reaches its maximum around midday (when the temperature is the highest) and, conversely, it is lower during the night. In order to reduce or eliminate these impairments, different methods (both hardware and software) were studied and reported in literature. Hardware solutions focus on aperture averaging effects to reduce irradiance fluctuations, in particular by using a bigger detector or multi-detector systems. On the other hand, software techniques mostly focus on transmission codes. Rateless codes are an innovative solution, suitable for channels affected by erasure or burst errors. They add a redundant coding (also settable on the fly) to the source data, allowing the receiver to successfully recover the whole payload that, otherwise, would be corrupted or partially lost. To test rateless codes, recovery capabilities in FSO channels, detailed information about the occurring signal fading are needed: in particular, its depth, temporal duration and statistics. For this reason, I have implemented a time-correlated channel model able to generate an irradiance time-series at the receiver side, at wide range of turbulence conditions (from weak to strong). The time-series represents a prediction of temporal irradiance fluctuations caused by scintillation. In this way, I was able to test the recovery capabilities of several types of rateless codes. I have performed measurement campaigns in order to characterize Free Space Optics links affected by the optical turbulence. In particular, I have used three different setups placed in the Laboratory of Optics of the University of Palermo and in the Optical Communication Laboratory of the Northumbria University. Thanks to an in-depth post-processing of the collected data, I was able to extract useful information about the FSO link quality and the turbulence strength, thus proving the effectiveness of the Gamma-Gamma model under several turbulence conditions. In Chapter 1, I will introduce the theory of optical wireless communications and, in particular, of Free Space Optics communications. In detail, I will describe the advantages and the impairments that characterize this kind of communication and discuss about its applications. In Chapter 2, the adopted channel models are presented. In particular, these models are able to predict irradiance fluctuations at the detector in Free Space Optics links and were designed for terrestrial and space-to-ground communications at different link specifications, turbulence conditions and temporal covariance. Firstly, a brief description of the employed irradiance distribution and of the irradiance covariance functions is presented. The details of the above mentioned channel model implementation and the performance are then described. Finally, in order to detail the channel model features, several examples of irradiance fluctuation predictions are depicted. In Chapter 3, the details of a measurement campaign, focused on the analysis of optical turbulence effects in a FSO link, will be treated. Three different measurement setups composed of different typologies of laser sources, detectors and turbulent channels will be described. Data post-processing will be discussed. Moreover, a performance evaluation of the terrestrial channel model described in Chapter 2 will be discussed. In Chapter 4, rateless codes will be presented. These codes introduce a redundancy by means of repair symbols, associated to the source data, and, in case of losses, they are able to recover the source data without any need for retransmission. They can also manage large amounts of data and offer very interesting features for erasure channels and multicast/broadcast applications. Three different classes of rateless codes will be described and, in particular: Luby Transform, Raptor and RaptorQ codes. Moreover, the performance of the rateless codes in Free Space Optics links will be investigated. The implemented simulators are based on the channel models presented in Chapter 2 and focus on the study of rateless codes recovery capabilities when erasure errors due to fadings occur. The results on the performance of three rateless codes typologies, in two different FSO links, will be illustrated. All the research work was supported by the European Space Agency (grant no. 5401001020). Experimental activities were performed in collaboration with the Optical Communications Research Group of the Northumbria University and within the COST IC1101 European Action