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R. David Koilpillai

Bio: R. David Koilpillai is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Phase noise & Orthogonal frequency-division multiplexing. The author has an hindex of 6, co-authored 30 publications receiving 126 citations. Previous affiliations of R. David Koilpillai include Dublin City University & Indian Institutes of Technology.

Papers
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Journal ArticleDOI
TL;DR: For the first time, to the best of the knowledge, the fronthaul network for providing simultaneous 4G and 5G services by propagating LTE signals in coexistence with UF-OFDM is demonstrated.
Abstract: Fifth generation (5G) mobile communications will require a dense deployment of small cell antenna sites and higher channel bandwidth, in conjunction with a cloud radio access network (C-RAN) architecture This necessitates low latency and high-capacity architecture in addition to energy- and cost-efficient fronthaul links An efficient way of achieving such connectivity is to make use of an opticalfiber- based infrastructure where multiple wireless services may be distributed over the same fiber to remote radio head (RRH) sites In this work, we demonstrate the spectral containment of fourth generation (4G) Long-Term Evolution (LTE) signals and 5G candidate waveforms—generalized frequency division multiplexing and universally filtered orthogonal frequency division multiplexing (UF-OFDM) through a directly modulated link Seventy-five bands of LTEand 10 bands of 5Gwaveforms are successfully transmitted over a 25 km analog intermediate frequency signal over fiber (AIFoF) link through our setup, limited only by the bandwidth of the laser For the first time, to the best of our knowledge, we demonstrate the fronthaul network for providing simultaneous 4G and 5G services by propagating LTE signals in coexistence with UF-OFDM

43 citations

Journal ArticleDOI
TL;DR: In this article, three different techniques for the compensation of the laser frequency offset (FO) and phase noise (PN) in an optical heterodyne analog radio-over-fiber (A-RoF) system are presented.
Abstract: Optical heterodyne analog radio-over-fiber (A-RoF) links provide an efficient solution for future millimeter wave (mm-wave) wireless systems. The phase noise of the photo-generated mm-wave carrier limits the performance of such links, especially, for the transmission of low subcarrier baud rate multi-carrier signals. In this work, we present three different techniques for the compensation of the laser frequency offset (FO) and phase noise (PN) in an optical heterodyne A-RoF system. The first approach advocates the use of an analog mm-wave receiver; the second approach uses standard digital signal processing (DSP) algorithms, while in the third approach, the use of a photonic integrated mode locked laser (MLL) with reduced DSP is advocated. The compensation of the FO and PN with these three approaches is demonstrated by successfully transmitting a 1.95 MHz subcarrier spaced orthogonal frequency division multiplexing (OFDM) signal over a 25 km 61 GHz mm-wave optical heterodyne A-RoF link. The advantages and limitations of these approaches are discussed in detail and with regard to recent 5G recommendations, highlighting their potential for deployment in next generation wireless systems.

29 citations

Proceedings ArticleDOI
01 Nov 2011
TL;DR: Voice services over Adaptive Multiuser channel in One Slot (VAMOS) performance in the presence of GMSK interferer is presented and WL metric is proposed which incorporates error covariance between I/Q components in the metric computation.
Abstract: Voice services over Adaptive Multiuser channel in One Slot (VAMOS) performance in the presence of GMSK interferer is presented. Widely-Linear (WL) MMSE filtering is used to cancel the co-channel GMSK interferer while performing α-QPSK detection. In this paper, two ways of estimating the Sub Channel Power Imbalance Ratio (SCPIR) are discussed. Due to the colouration of the resultant impairment after filtering, WL metric is proposed which incorporates error covariance between I/Q components in the metric computation. WL RSSE is used as the equalizer. Simulation results using the proposed receiver architecture show significant performance important over conventional VAMOS receivers.

17 citations

Proceedings ArticleDOI
01 Oct 2019
TL;DR: In this article, the effect of subcarrier baud rate and frequency offset variations on the performance of a 60 GHz OFDM signal generated using unlocked fiber lasers was analyzed in a 25 km mm-wave A-RoF heterodyne system.
Abstract: The phase noise (PN) of a photo-generated mmwave carrier, resulting from frequency and phase fluctuations of uncorrelated laser sources, limits the performance of heterodyne/millimeter-wave analog radio-over-fibre links. This work analyzes the effect of subcarrier baud rate and frequency offset (FO) variations on the performance of a 60 GHz OFDM signal generated using unlocked fiber lasers. Conventional digital techniques for FO and PN compensation, in a 25 km mm-wave A-RoF heterodyne system, are shown to overcome relatively large FOs and to enable the successful transmission of kHz range sub-carrier baud rates – in line with recent 5G recommendations.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate phase conjugate generation of 10 GBd PM-QPSK signal, simultaneously in both input and output ports of the SOA, with a penalty of < 1.5 dB.
Abstract: We experimentally demonstrate polarization-insensitive phase conjugate generation in a semiconductor optical amplifier (SOA) using a counter-propagating and cross-polarized degenerate pump. The polarization-insensitive operation is achieved in both the ports of the SOA through Bragg scattering four-wave mixing. The nature of polarization transformation of the process necessitates the selection of frequency of the signal to be larger than that of the pump for the penalty-free performance of the polarization-insensitive conjugate generation. We demonstrate the phase conjugate generation of 10 GBd PM-QPSK signal, simultaneously in both input and output ports of the SOA, with a penalty of <1.5 dB.

11 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a review of underwater routing protocols for UWSNs is presented, which classify the existing protocols into three categories: energy-based, data-based and geographic information-based protocols.
Abstract: Underwater wireless sensor network (UWSN) is currently a hot research field in academia and industry with many underwater applications, such as ocean monitoring, seismic monitoring, environment monitoring, and seabed exploration. However, UWSNs suffer from various limitations and challenges: high ocean interference and noise, high propagation delay, narrow bandwidth, dynamic network topology, and limited battery energy of sensor nodes. The design of routing protocols is one of the solutions to address these issues. A routing protocol can efficiently transfer the data from the source node to the destination node in the network. This article presents a review of underwater routing protocols for UWSNs. We classify the existing underwater routing protocols into three categories: energy-based, data-based, and geographic information-based protocols. In this article, we summarize the underwater routing protocols proposed in recent years. The proposed protocols are described in detail and give advantages and disadvantages. Meanwhile, the performance of different underwater routing protocols is analyzed in detail. Besides, we also present the research challenges and future directions of underwater routing protocols, which can help the researcher better explore in the future.

70 citations

Journal ArticleDOI
TL;DR: It is shown that by replacing the stand-alone optical modulator with an InP-based externally modulated laser chip for the implementation of the IFoF transmitter, a 16-Gb/s aggregate capacity was showcased on a 7-km fiber link and 5-m wireless channel with a 4-band 16-QAM encoded at 1 Gbaud.
Abstract: We experimentally demonstrate a multiband intermediate frequency-over-fiber/mmWave (IFoF/mmWave) fiber/wireless mobile fronthaul link for gigabit capacity over the unlicensed V-band (57–64 GHz). Digital synthesis of the multiband radio waveforms is performed at the baseband unit using digital subcarrier multiplexing technique, whereas digital predistortion is exploited to cope with the analog IFoF channel impairments without any further baseband processing at the digital-free remote radio head. Commercial optoelectronic components and analog V-band radio and antenna equipment for 7-km fiber and 5-m wireless transmission are employed to successfully demonstrate both uplink and downlink connectivity. An aggregate capacity up to 24 Gb/s was demonstrated with a 6-band 1 Gbaud 16-QAM on a 7.2-GHz analog bandwidth over the combined fiber/wireless channel showing error vector magnitude (EVM) values below the 3GPP requirements (<12.5%) for 5G systems. Multiformat assignment on each subcarrier was also realized by using M-PSK and 16-QAM schemes to achieve 18-Gb/s connectivity for both uplink and downlink, while demonstrating flexible resource allocation capabilities. By replacing the stand-alone optical modulator with an InP-based externally modulated laser chip for the implementation of the IFoF transmitter, a 16-Gb/s aggregate capacity was showcased on a 7-km fiber link and 5-m wireless channel with a 4-band 16-QAM encoded at 1 Gbaud. Successful operation with robust EVM performance was demonstrated using also the 6-band scheme of 1 Gbaud QPSK bands.

65 citations

Journal ArticleDOI
TL;DR: The use of analog radio-over-fiber (ARoF) is proposed and demonstrated as a viable alternative which, combined with space division multiplexing in the optical distribution network as well as photonic integration of the required transceivers, shows a path to a scaleable fronthaul solution for 5G.
Abstract: The introduction of millimeter wave (mm-wave) frequency bands for cellular communications with significantly larger bandwidths compared to their sub-6 GHz counterparts, the resulting densification of network deployments and the introduction of antenna arrays with beamforming result in major increases in fronthaul capacity required for 5G networks As a result, a radical re-design of the radio access network is required since traditional fronthaul technologies are not scaleable In this article the use of analog radio-over-fiber (ARoF) is proposed and demonstrated as a viable alternative which, combined with space division multiplexing in the optical distribution network as well as photonic integration of the required transceivers, shows a path to a scaleable fronthaul solution for 5G The trade-off between digitized and analog fronthaul is discussed and the ARoF architecture proposed by blueSPACE is introduced Two options for the generation of ARoF two-tone signals for mm-wave generation via optical heterodyning are discussed in detail, including designs for the implementation in photonic integrated circuits as well as measurements of their phase noise performance The proposed photonic integrated circuit designs include the use of both InP and SiN platforms for ARoF signal generation and optical beamforming respectively, proposing a joint design that allows for true multi-beam transmission from a single antenna array Phase noise measurements based on laboratory implementations of ARoF generation based on a Mach–Zehnder modulator with suppressed carrier and with an optical phase-locked loop are presented and the suitability of these transmitters is evaluated though phase noise simulations Finally, the viability of the proposed ARoF fronthaul architecture for the transport of high-bandwidth mm-wave 5G signals is proven with the successful implementation of a real-time transmission link based on an ARoF baseband unit with full real-time processing of extended 5G new radio signals with 800 MHz bandwidth, achieving transmission over 10 km of 7-core single-mode multi-core fiber and 9 m mm-wave wireless at 255 GHz with bit error rates below the limit for a 7% overhead hard decision forward error correction

48 citations

Journal ArticleDOI
TL;DR: In this article, the authors experimentally evaluate two distinct hybrid architectures applied to 5G New Radio (NR) FiWi-Fi systems based on different optical fronthaul approaches, which operate in non-standalone (NSA) mode, defined by the 3rd generation partnership project (3GPP), for simultaneously transmitting 4G and 5G technologies through an unique FiWi system.
Abstract: The fifth-generation of mobile networks (5G) claims for a radio access network (RAN) update in order to support the enormous incoming wireless data traffic. In this context, we experimentally evaluate two distinct hybrid architectures applied to 5G New Radio (NR) FiWi systems based on different optical fronthaul approaches. The first architecture operates in non-standalone (NSA) mode, defined by the 3rd generation partnership project (3GPP), for simultaneously transmitting 4G and 5G technologies through an unique FiWi system. The three considered waveforms are as follows: a filtered orthogonal frequency division multiplexing (F-OFDM) signal at 778 MHz with 10 MHz bandwidth from our 5G flexible-waveform transceiver; a long-term evolution-advanced (LTE-A) signal with five 20 MHz sub-bands centralized at 2.24 GHz; a 5G NR signal at 2.35 GHz with 100 MHz bandwidth. On the other side, the second architecture employs radio over fiber (RoF), free space optics (FSO), and wireless technologies converged into a heterogeneous network (HetNet). The additional multi-standard and multiband optical-wireless network is based on a 10-MHz bandwidth F-OFDM signal at 788 MHz, a 100-MHz bandwidth 5G NR signal at 3.5 GHz, and a 400-MHz bandwidth M -QAM signal at 26 GHz. Throughput up to 3 and 1.4 Gbps are demonstrated for RoF/FSO and RoF/FSO/Wireless transmission, respectively.

35 citations

Journal ArticleDOI
TL;DR: A high capacity multiple-input-multiple-output (MIMO) enabled all-optical analog-millimeter-wave-over fiber (A-MMWoF) fronthaul architecture is proposed for 5G and beyond of wireless networks and a comprehensive state-of-the-art literature review on the recent research works in high capacity A-RoF fr onthaul systems and related transport technologies is presented.
Abstract: The ever-increasing proliferation of mobile users and new technologies, and the demands for ubiquitous connectivity, high data capacity, faster data speed, low latency, and reliable services have been driven the quest for the next generation, fifth generation (5G), of the wireless networks. Cloud radio access network (C-RAN) has been identified as a promising architecture for addressing 5G requirements. However, C-RAN enforces stringent requirements on the fronthaul capacity and latency. To this end, several fronthaul solutions have been proposed in the literature, ranging from transporting digitized radio signals over fiber and functional splits to an entirely analog-radio-over fiber (A-RoF) based fronthual. A-RoF is a highly appealing transport solution for fronthual of 5G and beyond owing to its high bandwidth and energy efficiency, low system complexity, small footprint, cost-effectiveness, and low latency. In this paper, a high capacity multiple-input-multiple-output (MIMO) enabled all-optical analog-millimeter-wave-over fiber (A-MMWoF) fronthaul architecture is proposed for 5G and beyond of wireless networks. The proposed architecture employs photonic MMW signals generation and mode division multiplexing (MDM) along with wavelength division multiplexing (WDM) for transporting MMW MIMO signals in the optical domain. In support of the proposed architecture design, a comprehensive state-of-the-art literature review on the recent research works in high capacity A-RoF fronthaul systems and related transport technologies is presented. In addition, the corresponding potential challenges and solutions along with potential future directions are highlighted. The proposed design is flexible and scalable for achieving high capacity, high speed, and low latency fronthaul links.

33 citations