High-speed Communication Systems Research Articles

OFDM for payload communications of UAS: channel estimation and ICI mitigation

For real-time transmission of high-bandwidth sensor data from an unmanned aircraft vehicle (UAV) to the ground station (GS) in an unmanned aircraft system, a high-speed payload communication system is essential. While orthogonal frequency-division multiplexing (OFDM) is very effective for terrestrial wideband systems, possible higher speed of UAVs or higher carrier frequencies can increase the Doppler shift, and therefore increase the inter-carrier interference (ICI) in OFDM systems. In these scenarios, the complete frequency-domain channel matrix should be estimated and used for ICI mitigation and data recovery. In this study, a time-domain pilot-based channel estimation scheme is described to estimate the entire frequency-domain channel matrix for moderate-to-high Doppler OFDM systems. Simulation results indicate that the new scheme provides better performance compared with channel estimation schemes designed for low Doppler scenarios that partially estimate the frequency-domain channel matrix. The comparison is also presented with the other full channel estimation scheme, named autoregressive scheme, showing a comparable performance with much lower complexity for the new scheme.

Channel measurements and models for high-speed train wireless communication systems in tunnel scenarios: a survey

The rapid developments of high-speed trains (HSTs) introduce new challenges to HST wireless communication systems. Realistic HST channel models play a critical role in designing and evaluating HST communication systems. Due to the length limitation, bounding of tunnel itself, and waveguide effect, channel characteristics in tunnel scenarios are very different from those in other HST scenarios. Therefore, accurate tunnel channel models considering both large-scale and small-scale fading characteristics are essential for HST communication systems. Moreover, certain characteristics of tunnel channels have not been investigated sufficiently. This article provides a comprehensive review of the measurement campaigns in tunnels and presents some tunnel channel models using various modeling methods. Finally, future directions in HST tunnel channel measurements and modeling are discussed.

Position-Aided Large-Scale MIMO Channel Estimation for High-Speed Railway Communication Systems

We consider channel estimation for high-speed railway communication systems, where both the transmitter and the receiver are equipped with large-scale antenna arrays. It is known that the throughput of conventional training schemes monotonically decreases with the mobility. Assuming that the moving terminal employs a large linear antenna array, this paper proposes a position-aided channel estimation scheme whereby only a portion of the transmit antennas send pilot symbols and the full channel matrix can be well estimated by using these pilots together with the antenna position information based on the joint spatial-temporal correlation. The relationship between mobility and throughput/DoF is established. Furthermore, the optimal selections of transmit power and time interval partition between the training and data phases as well as the antenna size are presented accordingly. Both analytical and simulation results show that the system throughput with the position-aided channel estimator does not deteriorate appreciably as the mobility increases, which is sharply in contrast with the conventional one.

Performance Improvement of LeastSquares Adaptive Filter for High-Speed Train Communication Systems

The downlink communication channel from high-altitude platform (HAP) to high-speed train (HST) in the Ka-band is a slowly time-varying Rician distributed flat fading channel with 10-25 dB Rician K factor. In this respect, the received signal is mainly affected by the Doppler shift of the line-of-sight (LOS) link. In order to increase receiver performance, we propose to firstly compensate the Doppler shift of the received signal before least-squares (LS) adaptive filtering is pursued. Implementing the proposed method requires a priori knowledge of the time-varying phase of the LOS component. This is justified since signalling between the train and the controller exists such that the train velocity and location are predictable. Implementing the proposed method to the recursive LS (RLS) received beamforming algorithm shows reduction of mean square error (MSE) and bit error rate (BER).

Nano-structured metal-semiconductor-metal photodetector for sensor network systems

The advanced and smart ways to produce complex nano-structures have incorporated new capabilities in various aspects of science and technology where structures on nano-meter scales are desirable including high-speed communication and sensor networks, and future biomedical sensors and detectors. In recent years, there has been a growing interest towards the miniaturization of optical and electrical components with faster and more efficient performance. The development of nano-materials and nano-structures design provides great opportunity for building multifunctional sensing elements which are smaller and more efficiently incorporated. Furthermore they have other useful characteristics like reduced production cost and minimized power consumption. Wireless sensor network systems have been identified as one of the most important technologies for the 21st century (Chong et. al., 2003). It can be deduced from its name that sensor network systems are composed of several sensor nodes, where each component is responsible for a function in the whole system, where it can consist of different kinds of sensors such as, thermal, visual, biomedical, infrared, acoustics, etc. Recent wireless communication system development requires a concurrent speedy advancement of sensors characteristics as well as the system performance. Therefore, it is very important to make the progress in sensors design with tiny dimensions, suitable for communication over a sensor network system with specified purposes such as, monitoring different parameters, namely humidity, temperature, light in household, cities, and different environments (Ian-Akyildiz et al., 2002). The main focus of this review is to design and model an optimized plasmonics-based metal-semiconductor-metal photodetectors (MSM-PDs) with sub-wavelength architectures that is useful for high-speed optical communication systems and sensor network systems. Nano-structures designed on top of the electrodes trigger surface plasmon polaritons (SPPs) excitation and enable routing and manipulation of the light to be eventually trapped into the device active region.

QAM Quantum Noise Stream Cipher Transmission Over 100 km With Continuous Variable Quantum Key Distribution

We report the first on-line high-speed and large-capacity secure optical communication system. This was realized by combining a quadrature amplitude modulation/quantum noise stream cipher technology where a coherent multi-level optical signal is hidden in quantum noise and a quantum key distribution technology where secure key delivery is realized with an extremely weak laser light comparable to a single photon. In our security analysis, we adopt a realistic assumption, namely, that an adversary does not have a lossless fiber. To show the advantage of this scheme, we performed a 128 QAM, 70-Gbit/s single-channel transmission over 100 km with a spectral efficiency of as high as 10.3 bits/s/Hz. This is the fastest data rate and highest spectral efficiency yet achieved in quantum cryptography with a realistic assumption.

A Generic Reconfigurable Mixed Time and Frequency Domain QAM Transmitter with Forward Error Correction

In the past three decades, Field Programmable Gate Arrays (FPGAs) have emerged to be the backbone of digital signal processing, especially in high-speed communication systems. However, today, these devices are clocked below 1GHz and improvement in performance stays a big challenge on all abstraction layers, right from system architecture down to physical technology. Far and wide, myriad number of researches are done on methodologies and techniques which can deliver higher throughput with lower operating frequencies. Towards this projected objective, in this paper an efficient modulation technique like Quadrature Amplitude Modulation (QAM) along with mixed time and frequency domain approach and Forward Error Correction (FEC) technique have been utilized to employ a generic scalable FPGA based QAM transmitter with filter parallelization being executed in mixed domain. The system developed in this paper achieves an effective throughput of 12.8Gb/s for 256-QAM with 16 parallel inputs having an operating frequency of 201.25MHz, while a 18.7Gb/s effective throughput is realized with 32 parallel inputs at 146MHz. Thereby, it paves down a promising methodology for applications where having higher clock frequencies is a hard limit.

Viterbi equalization for long-distance, high-speed underwater laser communication

In long-distance, high-speed underwater laser communication, because of the strong absorption and scattering processes, the laser pulse is stretched with the increase in communication distance and the decrease in water clarity. The maximum communication bandwidth is limited by laser-pulse stretching. Improving the communication rate increases the intersymbol interference (ISI). To reduce the effect of ISI, the Viterbi equalization (VE) algorithm is used to estimate the maximum-likelihood receiving sequence. The Monte Carlo method is used to simulate the stretching of the received laser pulse and the maximum communication rate at a wavelength of 532 nm in Jerlov IB and Jerlov II water channels with communication distances of 80, 100, and 130 m, respectively. The high-data rate communication performance for the VE and hard-decision algorithms is compared. The simulation results show that the VE algorithm can be used to reduce the ISI by selecting the minimum error path. The trade-off between the high-data rate communication performance and minor bit-error rate performance loss makes VE a promising option for applications in long-distance, high-speed underwater laser communication systems.

26 m/5.5 Gbps air-water optical wireless communication based on an OFDM-modulated 520-nm laser diode.

We experimentally demonstrate a high-speed air-water optical wireless communication system with both downlink and uplink transmission employing 32-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) and a single-mode pigtailed green-light laser diode (LD). This work is an important step towards the future study on optical wireless communications between underwater platforms and airborne terminals. Over a 5-m air channel and a 21-m water channel, we achieve a 5.3-Gbps transmission without power loading (PL) and a 5.5-Gbps transmission with PL in the downlink. The corresponding bit error rates (BERs) are 2.64×10-3 and 2.47×10-3, respectively, which are below the forward error correction (FEC) criterion. A data rate of 5.5 Gbps with PL at a BER of 2.92×10-3 is also achieved in the uplink.

A Novel Signal Regeneration Technique for High Speed DPSK Communication Systems

In long haul communication systems, the signal regeneration is frequently used technique that provides the long reach for high-speed transmission and reception systems. During high speed and distance transmission signal fades below a definite level due to transmission impairments; Bit error rate (BER) increases rapidly that degrades the system performance. In this work, a novel signal regeneration technique is proposed for 60 Gb/s differential phase shift keying transceiver system that transmits and receives the high-speed signal over single mode fiber at transmission distance of 300 km. The designed system is modeled mathematically and its real time simulation are demonstrated. It is examined that novel proposed technique is significantly regenerating the signal for 300 km fiber length. The proposed technique has achieved the BER of 10−19 with eye open diagram in the presence of high amplitude noise, phase noise and dispersion per kilometer in optical fiber transmission. At the receiver, the proposed system has adequately mitigated the amplitude noise up to 88% and phase noise up to 89% from the transmitted signal. The proposed system will be helpful for system design engineer to design high-speed communication with required BER before its physical realization to provide quality performance for future generation high-speed communication system.

Integrated multi-port circulators for unidirectional optical information transport

On-chip photonic networks hold great promise for enabling next-generation high speed computation and communication systems. It is currently envisioned that future integrated photonic networks will be capable of processing dense digital information on a single monolithic platform by involving a multitude of optical components ranging from lasers to modulators, to routers, interconnects and detectors. Among the possible functionalities to be incorporated in such arrangements is the ability to route information in a unidirectional way among N-ports - a capability typically afforded through the use of optical circulators. Yet, in many settings, what is basically needed is re-routing information in a unidirectional fashion without necessarily invoking optical isolation. Of interest would be to devise strategies through which miniaturized optical devices can be monolithically fabricated on light-emitting semiconductors by solely relying on physical properties that are indigenous to the material itself. By exploiting the interplay between non-Hermiticity and nonlinearity, here we demonstrate a new class of chip-scale information transport devices on spatially modified III-V quantum well systems. These unidirectional structures are broadband (over 2.5 THz) at 1550 nm, effectively loss-free, color-preserving, and in proof-of-principle demonstrations have provided 23 dB isolation when used under pulsed-mode conditions at milliwatt (mW) power levels.

A high-speed phosphorescent LED-based visible light communication system utilizing SQGNRC precoding technique

Peak-over-average power ratio (PAPR) control utilizing precoding technique based on square root-generalized raised cosine function is proposed and verified experimentally through a visible light communication system employing phosphor-based white light-emitting diodes for the first time. The simulation results show that the improved precoding matrix can further reduce PAPR by nearly 1 dB compared with existing precoding matrix based on square root raised cosine function and significantly achieve 3.5 dB improvement in contrast to original signals without precoding. The experimental result also proves that the bit error rate performance can be effectively improved by 1.62 dB at the same bandwidth and 0.76 dB at the same raw data rate in terms of quality factor when proposed precoding technique is applied, which clearly demonstrates its benefit and feasibility.

Design and Experimental Evaluation of a Time-Interleaved ADC Calibration Algorithm for Application in High-Speed Communication Systems

In this work we investigate a new background calibration technique to compensate sampling phase errors in time-interleaved analog-to-digital-converters (TI-ADCs). Timing mismatches in TI-ADC degrade significantly the performance of ultra-high-speed digital transceivers. Unlike previous proposals, the calibration technique used here optimizes a metric directly related to the performance of the communication system. Estimation of gradient of the mean-squared-error (MSE) at the slicer with respect to the sampling phases of each interleave, are computed to minimize the time errors of the TI-ADC by controlling programmable analog time delay-cells. Since (i) dedicated digital signal processing (DSP) such as cross-correlations or digital filtering of the received samples are not required, and (ii) metrics such as MSE are available in most commercial transceivers, the implementation is reduced to a low speed state-machine. The technique is verified experimentally by using a programmable logic-based platform with a 2 GS/s 6-bit TI-ADC. The latter has been fabricated in $0.13μm CMOS process, and it provides flexible sampling phase control capabilities. Experimental results show that the signal-to-noise ratio penalty of a digital BPSK receiver caused by sampling time errors in TI-ADC, can be reduced from 1 dB to less than 0.1 dB at a bit-error-rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> .

CubeSat quantum communications mission

Quantum communication is a prime space technology application and offers near-term possibilities for long-distance quantum key distribution (QKD) and experimental tests of quantum entanglement. However, there exists considerable developmental risks and subsequent costs and time required to raise the technological readiness level of terrestrial quantum technologies and to adapt them for space operations. The small-space revolution is a promising route by which synergistic advances in miniaturization of both satellite systems and quantum technologies can be combined to leap-frog conventional space systems development. Here, we outline a recent proposal to perform orbit-to-ground transmission of entanglement and QKD using a CubeSat platform deployed from the International Space Station (ISS). This ambitious mission exploits advances in nanosatellite attitude determination and control systems (ADCS), miniaturised target acquisition and tracking sensors, compact and robust sources of single and entangled photons, and high-speed classical communications systems, all to be incorporated within a 10 kg 6 litre mass-volume envelope. The CubeSat Quantum Communications Mission (CQuCoM) would be a pathfinder for advanced nanosatellite payloads and operations, and would establish the basis for a constellation of low-Earth orbit trusted-nodes for QKD service provision.

Accuracy of Ranging Based on DMT Visible Light Communication for Indoor Positioning

In this letter, we propose a ranging estimation scheme for indoor positioning based on high-speed visible light communication (VLC) system. The proposed scheme could provide high accuracy position of the receiver, without affecting the transmission efficiency of VLC. Discrete multi-tone (DMT) VLC signals emitted from light-emitting diodes (LEDs) are employed for both of high-speed communication and ranging estimation. The ranging estimation is implemented by measuring the received signal strength (RSS) of each sub-carrier of DMT training sequence based on the power attenuation model. The Cramer-Rao bound as the theoretical accuracy limit of the estimation is derived. Calculations for a typical indoor scenario show that the proposed RSS-based ranging estimation could achieve high accuracy of centimeter level.

Scheduling Strategy for Multimedia Heterogeneous High-Speed Train Networks

Recently, the high-speed train has been recognized as a fast and popular public transportation system that brings significant convenience to passengers. How to efficiently provide passengers broadband mobile services, such as voice over IP (VoIP) and multimedia services, is receiving increasing attention. To fulfill passengers' diverse demands, we consider a heterogeneous network (HetNet) structure consisting of trackside access points (TAPs) and base stations (BSs) in a high-speed rail communication system (HRCS). First, we formulate a service-scheduling problem aiming at minimizing the end-to-end delay of VoIP and multimedia services as an infinite-horizon time-average expected delay constraint Markov decision process (CMDP) model. In particular, to provide a suitable scheduling selection scheme, this paper proposes a hybrid scheduling strategy to satisfy various delay requirements. Second, we utilize the martingale theory to obtain the theoretic value of the end-to-end delay bounds under two kinds of scheduling mechanisms: first in first out (FIFO) and earliest deadline first (EDF). In the simulation, we use three kinds of real wireless data traces, namely, VoIP, gaming, and User Datagram Protocol (UDP), to evaluate our algorithms by using the Nakagami- $m$ fading channel. From the results, we verify the optimality of the proposed scheduling algorithm in average end-to-end delay performance over FIFO and EDF and the working principle of the hybrid scheduling strategy. In addition, the martingale end-to-end delay bounds are remarkably tight to the real data trace simulation results.

Channel measurements and models for high-speed train wireless communication systems in tunnel scenarios: a survey

The rapid developments of high-speed trains (HSTs) introduce new challenges to HST wireless communication systems. Realistic HST channel models play a critical role in designing and evaluating HST communication systems. Due to the length limitation, bounding of tunnel itself, and waveguide effect, channel characteristics in tunnel scenarios are very different from those in other HST scenarios. Therefore, accurate tunnel channel models considering both large-scale and small-scale fading characteristics are essential for HST communication systems. Moreover, certain characteristics of tunnel channels have not been investigated sufficiently. This article provides a comprehensive review of the measurement campaigns in tunnels and presents some tunnel channel models using various modeling methods. Finally, future directions in HST tunnel channel measurements and modeling are discussed.

3D non-stationary wideband circular tunnel channel models for high-speed train wireless communication systems

This paper proposes three-dimensional (3D) non-stationary wideband circular geometry-based stochastic models (GBSMs) for high-speed train (HST) tunnel scenarios. Considering single-bounced (SB) and multiple-bounced (MB) components from the tunnel's internal surfaces, a theoretical channel model is first established. Then, the corresponding simulation model is developed using the method of equal volume (MEV) to calculate discrete angular parameters. Based on the proposed 3D GBSMs, important time-variant statistical properties are investigated, such as the temporal autocorrelation function (ACF), spatial cross-correlation function (CCF), and space-Doppler (SD) power spectrum density (PSD). Results indicate that all statistical properties of the simulation model, verified by simulation results, can match well those of the theoretical model. The statistical properties of the proposed 3D GBSMs are further validated by relevant measurement data, demonstrating the flexibility and utility of our proposed tunnel GBSMs.

A Planar Broadband Antenna for the E-Band Gigabyte Wireless Communication

A planar broadband antenna with a center frequency of 81.75 GHz is proposed in this communication, which is composed by an open-ended pentagonal slot etched on the broad surface of a substrate-integrated waveguide (SIW) and a short circuited metallic via inserted inside the ring slot. The broadband SIW 180° phase-shifter and the SIW power-divider are deployed in the design to implement the beam-forming network. As a demonstration, a $2 \times 8$ array is designed on a 0.5 mm thick Rogers5880 substrate, and fabricated by using the low-cost printed circuit board process. Experiments are carried out to verify the design, which show that the measured antenna has a 10 dB return loss bandwidth from 77 to 86. 5 GHz, that is, the fractional bandwidth of 11.6%. The proposed antenna is a promising candidate for the E -band high-speed wireless communication system.

Systematic design of highly birefringent photonic crystal fibers

This article systematically designs and theoretically investigates a highly birefringent photonic crystal fiber (HB-PCF) for reducing the effect of polarization mode dispersion in high-speed optical communication system. To achieve a high modal birefringence in the proposed HB-PCF, four types of HB-PCF were designed by adding some birefringence-enhancing factors step by step in sequence. Ultimately, as per the simulation results, in the condition of single-mode operation, the numeric values of modal birefringence and confinement loss of the proposed HB-PCF is about 21.85 × 10− 3 and 0.47 dB/km at the habitual wavelength λ = 1.55 µm of optical-fiber communications.