High-speed Communication Links Research Articles

A Framed-Pulsewidth Modulation Transceiver for High-Speed Broadband Communication Links

A 20 Gb/s serial link transceiver employing a framed-pulsewidth modulation (FPWM) scheme that overcomes the signal-to-noise (SNR) degradation without a linearity requirement is presented. The FPWM scheme encodes data at the location and the width of the pulses in a frame spanning multiple unit intervals (UI) while maintaining a minimum pulsewidth equal to 1 UI. The test chip achieves a coding gain of 33 %, which allows a total throughput of 20 Gb/s while keeping the baud rate of 15 Gb/s. The equalization core incorporating programmable 3-tap pre-emphasis at the transmitter and a continuous-time linear equalizer (CTLE) at the receiver compensates for the channel insertion loss up to 12 dB at the baud frequency, and achieves $2.2\times0.48$ mm 2 and consumes 90.6 mW from a 0.9 V supply which renders the power efficiency of 4.53 mW/Gb/s.

A high-speed radio-over-free-space optics link using wavelength division multiplexing-mode division multiplexing-multibeam technique

Radio-over-Free-Space Optics (RoFSO) is a key technology for providing high-speed communication links in rural areas. In this work, an orthogonal frequency division multiplexing based RoFSO transmission link has been designed by adopting hybrid wavelength division multiplexing (WDM), mode division multiplexing (MDM) and multibeam technique. The proposed link is investigated under heavy fog weather conditions and its performance is compared for 1-beam and 4-beams transmission using numerical simulations. The numerical results show faithful transportation of high-speed data at 2000 m with acceptable performance of the link. Furthermore, the link performance is compared with previously reported works and the proposed RoFSO link with hybrid WDM-MDM-multibeam technique demonstrates an enhanced link range and transmission capacity performance.

Comprehensive power management scheme for the intelligent operation of photovoltaic‐battery based hybrid microgrid system

This study proposes a comprehensive power management scheme (CPMS) for the economical and smart operation of a photovoltaic (PV) battery based Hybrid Microgrid (HMG) system. The solar-PV, DC-loads and battery storage are interfaced to DC-bus of the HMG. The battery is integrated into the DC-bus using a bidirectional energy storage converter (BESC). The voltage and frequency of AC-bus are regulated by utility grid and bidirectional interlinking converter (BIC) during grid-connected and islanded modes of operation, respectively. The proposed CPMS obviates high-speed communication link between converters for maintaining the system stability during power disturbances. Therefore, the vulnerability to collapse due to communication link failure is eliminated, thereby enhancing system reliability. The operational performance of HMG is improved with the proposed CPMS by providing additional features (minimisation of operating cost of the HMG, enhancement in voltage regulation of the DC-bus etc.) using low-speed communication network. The proposed CPMS can also be extended to a larger HMG system by utilising the full bandwidth of the communication network. Further, the proposed CPMS enables HMG to seamlessly switch from grid-connected to islanded mode and vice-versa. Experimental results validating the efficacy of the proposed CPMS are presented.

Control analysis of parallel DC-DC converters in a DC microgrid with constant power loads

This paper proposes a general methodology for designing hierarchical control schemes for DC microgrids loaded by constant power loads. This paper addresses issues when interfacing sources with a wide voltage range allowing for any general choice for a power source. The control strategy consists of two levels. The lower level consists of droop-based primary controllers. This controller enables current-sharing among paralleled sources and also damps limit cycle oscillations due to constant power loads. The higher level is a secondary controller which compensates for voltage deviations due to primary controller and performs voltage control of the microgrid. It also maintains the current sharing obtained in the primary stage. In the proposed secondary control, high-speed communication links to the primary controllers is implemented. The stability conditions are explained using the equivalent circuit of converters. Using this approach, stability conditions can be derived for microgrids of an arbitrary size and converter topology. The proposed control scheme is shown to be scalable and robust. The results obtained for the three basic DC-DC converter configurations are compared based on a microgrid with a parallel configuration of buck-boost converters. Simulations and experimental results are presented to verify the validity of the proposed control schemes.

Realization of Omnidirectional CubeSat Crosslink by Wavelength-Selective Optical Transceiver

Advanced space missions, e.g., interplanetary exploration and Earth observation embrace constellation or swarm-like CubeSat configuration to achieve unprecedented spatial and temporal resolutions at a significantly lower investment. The realization of high-speed inter-CubeSat data communication link is mandatory to ensure the success of such missions. In this article, we present a scalable high-speed CubeSat crosslink implementation based on the wavelength-selective optical transceiver (WSOT) design. System performance based on the state-of-the-art components that satisfy the stringent size, weight, power, and cost requirements has been investigated. We estimate that with a 15 mm transceiver aperture size and 1 W peak bit power, the system attains communication distance up to 125 and 80 km for 400 Mb/s and 800 Mb/s data rates, respectively. Additionally, we present the optical and mechanical design of five transceiver units that can fit inside a 3U CubeSat to achieve a full field of regard (360°) to enable omnidirectional high-speed optical communication. Further performance improvements are possible through incorporating advanced amplifiers, error correction coding, and large aperture optics.

Monolitic Hybrid Transmitter-Receiver Lens for Rotary On-Axis Communications

High-speed rotary communication links exhibit high complexity and require challenging assembly tolerances. This article investigates the use of optical wireless communications (OWC) for on-axis rotary communication scenarios. First, OWC is compared with other state-of-the-art technologies. Different realization approaches for bidirectional, full-duplex links are discussed. For the most promising approach, a monolithic hybrid transmitter-receiver lens is designed by ray mapping methodology. Ray tracing simulations are used to study the alignment-depended receiver power level and to determine the effect of optical crosstalk. Over a distance of 12.5 m m , the lens achieves an optical power level at the receiver of − 16.2 dBm to − 8.7 dBm even for misalignments up to 3 m m .

A Novel CDR-Based Low-Cost Time-Interleaved-ADC Timing Calibration

Digital signal processing (DSP)-based system is a common architecture for high-speed communication links. One of the most important components for DSP-based architectures is the analog-to-digital convertor (ADC). Most of the high-speed ADCs are implemented as time interleaved ADC (TI-ADC). One of the major challenges in TI-ADC is the timing mismatch between the parallel sub-ADCs. The calibration of this mismatch increases system cost and complexity. In this article we propose a new background calibration method based on existing clock and data recovery (CDR) circuits. The timing mismatch can be calibrated using a simple and unique CDR per sub-ADC. Using the existing phase error detector and pulse gain estimator of the regular CDR, the calibration circuit becomes very low-cost, requiring only a first order loop, and a slow numerically controlled oscillator (NCO). VCSEL-based lab experiments are performed, which demonstrate the proposed method efficiency, performance and robustness.

Performance of grey‐coded IQM‐based optical modulation formats on high‐speed long‐haul optical communication link

In this article the performance of grey-coded advanced optical modulation formats is evaluated on a single-channel high-speed long-haul optical communication link and are compared to the respective differential-coded modulation formats. Polarisation division multiplexed optical in-phase quadrature modulator (IQM) structure and homodyne detection scheme are used to realise 100 Gbps quadrature phase-shift keying (QPSK), 120 Gbps 16-ary quadrature amplitude modulation (16-QAM), 360 Gbps 32-QAM and 480 Gbps 64-QAM modulation formats. Advanced digital signal processing unit with various pre-processing and recovery stages such as direct current blocking, normalisation, low-pass Bessel filter, resampling, quadrature imbalance compensation, chromatic dispersion compensation, non-linear compensation, timing recovery, adaptive equalisation, down-sampling, frequency offset estimation, and carrier phase estimation is used at the receiving end to compensate for signal impairments during propagation. Maximum transmission distances of 7200, 1050, 560, and 360 km have been achieved at an acceptable bit error rate for QPSK, 16-QAM, 32-QAM, and 64-QAM, respectively. The grey-coded systems outperformed the differential-coded systems regarding optical signal-to-noise ratio requirement, receiver sensitivity, and transmission distance.

Ultraviolet-to-blue color-converting scintillating-fibers photoreceiver for 375-nm laser-based underwater wireless optical communication

Underwater wireless optical communication (UWOC) can offer reliable and secure connectivity for enabling future internet-of-underwater-things (IoUT), owing to its unlicensed spectrum and high transmission speed. However, a critical bottleneck lies in the strict requirement of pointing, acquisition, and tracking (PAT), for effective recovery of modulated optical signals at the receiver end. A large-area, high bandwidth, and wide-angle-of-view photoreceiver is therefore crucial for establishing a high-speed yet reliable communication link under non-directional pointing in a turbulent underwater environment. In this work, we demonstrated a large-area, of up to a few tens of cm2, photoreceiver design based on ultraviolet(UV)-to-blue color-converting plastic scintillating fibers, and yet offering high 3-dB bandwidth of up to 86.13 MHz. Tapping on the large modulation bandwidth, we demonstrated a high data rate of 250 Mbps at bit-error ratio (BER) of 2.2 × 10-3 using non-return-to-zero on-off keying (NRZ-OOK) pseudorandom binary sequence (PRBS) 210-1 data stream, a 375-nm laser-based communication link over the 1.15-m water channel. This proof-of-concept demonstration opens the pathway for revolutionizing the photodetection scheme in UWOC, and for non-line-of-sight (NLOS) free-space optical communication.

A Novel Equalizer for 112 Gb/s CAP-Based Data Transmission Over 150 m MMF Links

In this paper a novel feedforward and decision feedback equalizer is proposed for the first time for use in short-reach high-speed communication links based on carrierless amplitude and phase (CAP) modulation. The proposed new equalizer mitigates crosstalk between the in-phase (I-) and quadrature (Q-) channels resulting from the non-linear phase response of the link enabling significant improvement in the link performance when operating at high data rates. The structure of this novel equalizer is introduced, its operation is described, and simulation and experimental studies on short-reach high-speed MMF links using 850 nm multimode VCSELs are presented. Data transmission tests are carried out over 150 m of OM4 MMF at 112 Gb/s using CAP modulation and the proposed CAP equalizer, and a bit-error-rate (BER) within the hard-decision forward error-correction (HD-FEC) threshold of 3.8 × 10−3 is achieved. The link is also tested when a conventional equalizer is used instead of the CAP equalizer and when adaptive discrete multitone (DMT) modulation is applied. The performance of the link is compared for these different transmission schemes and it is shown that the use of the novel equalizer and CAP modulation outperforms the other two schemes. The proposed equalizer can be implemented with low additional complexity, providing a potential cost-effective solution enabling >100 Gb/s single-lane data transmission in short-reach MMF-based links.

A Sallen Key All Pass Filter for Noise Reduction in Visible Light Communication Systems

Visible-light communication (VLC) uses a solid-state illumination device for generating high speed communication links. VLC is used throughout world for eliminating the shortage of wireless spectrum resources. The VLC is generally an Optical Wireless Communication (OWC) method and this uses the Light Emitting Diode (LED) for data transmission through the optical wireless channel. The data transmission though the VLC is affected by ambient light interference due to the environment. In this paper, an efficient filter is designed to eliminate the ambient light noises from the received signal. The filter used in the VLC system is Sallen key All Pass Filter (APF) and the red LED and Photo detector (PD) is used in the transmitter and receiver respectively. The Sallen key APF contains three different filter structures such as low pass, band pass and high pass filter. The Sallen APF uses the filter process with respect to the noise. This proposed system is implemented in two different tools namely MATLAB and Electric VLSI. The performance of the proposed system is analyzed in terms of Bit Error Rate (BER), area, power consumption and data rate.

THz-to-optical conversion in wireless communications using an ultra-broadband plasmonic modulator

Future wireless communication networks will need to handle data rates of tens or even hundreds of Gbit s−1 per link, requiring carrier frequencies in the unallocated THz spectrum1,2. In this context, seamless integration of THz links into existing fibre-optic infrastructures3 is of great importance to complement the inherent portability and flexibility advantages of wireless networks and the reliable and virtually unlimited capacity of optical transmission systems. On the technological level, this requires novel device and signal processing concepts for direct conversion of data streams between the THz and optical domains. Here, we demonstrate a THz link that is seamlessly integrated into a fibre-optic network using direct THz-to-optical (T/O) conversion at the wireless receiver. We exploit an ultra-broadband silicon-plasmonic modulator having a 3 dB bandwidth in excess of 0.36 THz for T/O conversion of a 50 Gbit s−1 data stream that is transmitted on a 0.2885 THz carrier over a 16-m-long wireless link. Optical-to-THz (O/T) conversion at the wireless transmitter relies on photomixing in a uni-travelling-carrier photodiode. A high-speed wireless THz communication link is seamlessly integrated into a fibre-optic network. The demonstration relies on an ultra-broadband modulator exploiting two-dimensionally localized gap plasmons for direct conversion of the THz signals to the optical domain.

Transmission of 160-Gb/s Modified Manchester modulation over WDM system

ABSTRACTThe paper examines the performance of Modified Manchester (MM) modulation scheme over wavelength division multiplexing (WDM) in high-speed optical communication links. The MM as a new modulation technique has a narrow spectral width compared to conventional Manchester coding, which allows its implementation in WDM systems beneficial. In this study, the performance characteristics of MM and conventional Manchester modulation formats are assessed in WDM system at 10 Gb/s bitrate for each channel, for the least allowable channel spacing as well as tolerance to chromatic dispersion (CD). It is revealed from the results of simulation that MM performs meaningfully well in comparison with conventional Manchester in terms of tolerance against narrow optical filtering, spectral efficiency, which is improved by 32% and CD tolerance, which is improved by +100 ps/nm. Sixteen wavelength channels (16 × 10 Gb/s) are modulated to provide 160 Gb/s data capacity, which was transmitted successfully over 224 km standard single mode fibre (SSMF) using MM while the conventional Manchester only covered about 157 km.

NERA: A new and efficient RSU based authentication scheme for VANETs

In vehicular ad-hoc networks (VANETs), the correctness of a message requires authentication of the origin vehicle. In this paper, we introduce a novel authentication scheme for VANETs which suggests a new solution for secure vehicle communications. The proposed scheme is an road side unit (RSU) based scheme in which the master key of the Trusted Authority (TA) is embedded in a tamper-proof device provided at the RSUs. Compared with the schemes that store the master key in the on-board units, our scheme is more practical because of a secure and high speed communication link between TA and RSUs. To the best of our knowledge, this solution has not yet been devised for secure authentication in VANETs and the same objective has been fulfilled in this paper. Moreover, we introduce a formal proof to prove the security of the proposed scheme. Finally, we present a simulation and comparison indicating the performance and efficiency of our scheme.

Novel Manchester-Based Multilevel Signaling for High-Speed Optical Communication Systems

Abstract In this paper, the performance of a novel multilevel signaling based on Manchester code namely four-level Manchester Coding (4-MC) technique is investigated for next generation high-speed optical fiber communication links. The performance of 4-MC is studied and compared with conventional Manchester modulation and four-level pulse amplitude modulation (4-PAM) formats in terms of receiver sensitivity, spectral efficiency and dispersion tolerance at the bit rate of 40 Gb/s. The bit error rate (BER) calculation model for the proposed multilevel scheme has also been developed. The calculated receiver sensitivity and the chromatic dispersion tolerance at the BER of 10–9 of the proposed scheme are −22 dBm and 67.5 ps/nm, respectively. It is observed that, 4-MC scheme is superior in comparison to 4-PAM by 3.5 dB in terms of receiver sensitivity in back-to-back scenario. Therefore, the proposed scheme can be considered as an alternative to current 4-PAM system.

Multiple access technique in a high-speed free-space optical communication link: independent component analysis

Increasing usage and higher demand for wireless traffic are causing a critical need for increased bandwidth and capacity communication networks. Accordingly, multipoint free-space optical communication (FSOC) links are beginning to draw significant attention as a valuable and promising solution for satisfying new network requirements. Extensive interest has focused on investigating and developing hardware design solutions to perform multiuser FSOC. However, to meet the low size, weight, and power needs of this technology, we propose using a robust and solid signal-processing method, namely independent component analysis (ICA), to implement an optical multiple access technique. A high-speed, multipoint free space optical system composed of two independent users and two receiving sensors is introduced. FastICA and joint approximate diagonalization of eigenmatrices algorithms are exploited for multiuser detection, and extensive analysis of power ratio, data rate difference, computational complexity, achievable system capacity, turbulence generation accuracy, and turbulence severity effects on signal reconstruction is performed. Experimental results demonstrate that ICA provides suitable source separation for all tested configurations. Additionally, transmission parameters that maximize signal reconstruction performances were identified.

Experimental results of atmospheric coherent optical communications with adaptive optics

Although there is an urgent need, it is still a significant challenge to establish high-speed laser communication links between satellites to ground stations owing to the influence of atmospheric turbulence. Adaptive optics (AO) is a considerable scheme to solve the problem. In this paper, the primary experiment of satellite-to-ground laser communication with the data rate of 5Gbps and BPSK modulation is carried out through a 500 m horizontal channel with relatively strong turbulence. A 137-element AO unit is used for correcting the phase distortion brought by the turbulence. When the AO unit is working, both the received optical power and bit error rate (BER) (All the eight experimental results of BER at different time are below 10−6.) are improved significantly. The primary results demonstrate that the ground station with AO technology has the capability to establish the satellite-to-ground laser communication links and provide a reference for the design of satellite terminals.

Novel hybrid PAPR reduction schemes for the MGFDM system

Fifth generation wireless communications are expected to serve future wireless needs such as machine-to-machine communications, tactile internet, be highly reliable, have low latency and perform satisfactorily in high speed communication links. Generalized Frequency Division Multiplexing (GFDM) is one of the promising and leading candidates proposed for the 5G physical layer waveform, to fulfill the above applications. Due to the non-orthogonal pulse shaping of individual subcarriers, GFDM suffers from self interference and also increased peak amplitude. The benefit of prolate windows can be exploited to convert a non-orthogonal GFDM system to an improved orthogonal Multi-taper GFDM (MGFDM) one. Similarly to other multicarrier (MC) techniques, MGFDM also suffers from high peak-to-average-power ratio (PAPR). In this article, we first explore some of the standard PAPR reduction approaches such as, Selective Mapping (SLM), Partial Transmit Sequence (PTS) and Zadoff–Chu Transform (ZCT) and a comparative performance is carried out in terms of the cumulative distribution function (CCDF). In addition, we propose in this article a novel hybrid Walsh–Hadamard precoding with both SLM and PTS PAPR reduction techniques to further reduce the PAPR level at the transmitter side. The Walsh–Hadamard kernel which is a square wave with values ±1 helps to reduce the PAPR without introducing distortion, compared to clipping based methods. Using these proposed schemes the results show a superior PAPR reduction improvement when compared to the conventional SLM and PTS techniques. Mathematical equations of the proposed systems were derived and the corresponding complexity analysis was carried out.

High-power blue superluminescent diode for high CRI lighting and high-speed visible light communication.

We demonstrated a high-power (474 mW) blue superluminescent diode (SLD) on c-plane GaN-substrate for speckle-free solid-state lighting (SSL), and high-speed visible light communication (VLC) link. The device, emitting at 442 nm, showed a large spectral bandwidth of 6.5 nm at an optical power of 105 mW. By integrating a YAG-phosphor-plate to the SLD, a CRI of 85.1 and CCT of 3392 K were measured, thus suitable for solid-state lighting. The SLD shows a relatively large 3-dB modulation bandwidth of >400 MHz, while a record high data rate of 1.45 Gigabit-per-second (Gbps) link has been achieved below forward-error correction (FEC) limit under non-return-to-zero on-off keying (NRZ-OOK) modulation scheme. Our results suggest that SLD is a promising alternative for simultaneous speckle-free white lighting and Gbps data communication dual functionalities.

Optimization of high speed and long haul inter-satellite communication link by incorporating differential phase shift key and orthogonal frequency division multiplexing scheme

Inter-Satellite optical wireless communication (Is-OWC) link plays significant role for transmission of data between the satellites in the space. In this work, 10 Gbps of data is transmitted over 20,000 km Is-OWC link by incorporating differential phase shift key (DPSK) modulation and orthogonal frequency division multiplexing scheme. Signal to noise ratio (SNR), total received power, constellations diagram and radio frequency spectrums are used as key metrics to evaluate the performance of proposed Is-OWC-DPSK communication system. Furthermore, the effects of receiving pointing error for proposed IS-OWC-DPSK communication system are also analysed.