Gigabit Class Research Articles

Design of a 10 GHz optical wireless communication link using low power C-band laser diode

This article deals with the proposed design of a 10 GHz optical wireless communication (OWC) link using 1550 nm Laser source for long range communication channel. Optical communication is the backbone of next generation gigabit class communication system and optical fiber communication plays an important role to fulfill the requirement of gigabit communication. But OWC is very useful where optical fibers cannot be laid off. A 10 GHz communication channel bandwidth has been designed in this article using very low power (2 mW) 1550 nm laser diode. A long range communication channel of 3 km has been considered with maximum bit-error-rate (BER) of 10−9. This system has been designed to withstand high atmospheric attenuation up to 11.67 dB/km, without affecting the BER and link range. An auto alignment method and automatic laser power control method have also been described with all necessary design parameters of the system.

Modeling and analysis of multi-channel gigabit class CWDM-VLC system

Wavelength Division Multiplexing (WDM) is one possible solution to increase the data rate for Visible Light Communication (VLC). Coarse WDM (CWDM) was used to increase data rate in traditional optical fiber systems. In this work, we propose CWDM for a VLC system using multiple LEDs with different monochromatic colors in the full visible spectrum. Besides, optical filters are used to separate different wavelengths from received signals and to maximize their performance, while minimizing crosstalk. Spacing between the channels is 20 nm, and the combination of channels produce white light for indoor illumination. The simulation results show very good performance in terms of bit error rate (BER) and improve data rate for an indoor VLC link. This VLC-CWDM system can achieve a data rate of 3.2 Gb/s and 7.2 Gb/s for 10 and 20 channels, respectively. Comparatively, the current WDM-VLC system can achieve 1.97 Gb/s data rate with the same simulation parameters.

Laser-Diode-Based Visible Light Communication: Toward Gigabit Class Communication

VLC is an emerging optical wireless communication technology that can be added as a complementary feature into existing lighting infrastructures for alleviating pressure on the rapidly dwindling radio frequency spectrum. Although LEDs have been traditionally used as transmitters in VLC, the growing urgency for higher data rates in the gigabit class range has deviated focus toward the consideration of LDs as potential sources for VLC due to their unique features of high modulation bandwidth, efficiency, and beam convergence. This article focuses on the principles of LD-based VLC systems, highlighting the operational characteristics and link configurations. The unique features of LDs compared to LEDs are discussed alongside the communication and illumination aspects of different classifications of LD-VLC. The challenges in terms of practical implementation and the potential applications that might arise from this communication technology are also discussed.

Innovative Tools and Processes for Mobile Communications Research and Education

Coming generations of engineering graduates and researchers will be expected to develop an integral set of skills to adapt themselves to the mobile communications industry and market expectations. To meet these demands universities will need to collaborate and innovate in their education styles, research tools and processes. The evolution of remote experimentation and the availability of state-of-the-art mobile communications test systems bring new opportunities to this field, such as experimentation with Gigabit class LTE-A. In this paper we discuss how this equipment could be adopted for educational purposes and how it can be included in federated research environments.

Symmetric 10 Gb/s wavelength reused bidirectional RSOA based WDM-PON with DPSK modulated downstream and OFDM modulated upstream signals

A 10Gb/s bidirectional wavelength division multiplexing passive optical network (WDM-PON) with reflective semiconductor optical amplifier (RSOA) based colorless optical network unit (ONU) is proposed and analyzed for next generation gigabit class optical access network. Differential phase shift keying (DPSK) modulated signal is used in downstream and further reused as a seeding wavelength for upstream data modulation. By exploiting the constant envelope property of DPSK seed signal, the re-modulation noise in upstream receiver is effectively minimized without employing any constraint on extinction ratio of downstream signal. Orthogonal frequency division multiplexing (OFDM) signal is used in upstream transmission to overcome the limited bandwidth (∼1GHz) response of RSOA remodulation. The results show that the proposed 10Gb/s symmetric WDM-PON can achieve good performance over 25km fiber transmission with error free operation in downstream and bit error rate (BER) lower than forward error correction (FEC) limit in upstream.

High-Resolution Timer-Based Packet Pacing Mechanism on the Linux Operating System

Packet pacing is a well-known technique for reducing the short-time-scale burstiness of traffic, and software-based packet pacing has been categorized into two approaches: the timer interrupt-based approach and the gap packet-based approach. The former was originally hard to implement for Gigabit class networks because it requires the operating system to handle too frequent periodic timer interrupts, thus incurring a large overhead. On the other hand, a gap packet-based packet pacing mechanism achieves precise pacing without depending on the timer resolution. However, in order to guarantee the accuracy of rate control, the system must be able to transmit packets at the wire rate. In this paper, we propose a high-resolution timer-based packet pacing mechanism that determines the transmission timing of packets by using a sub-microsecond resolution timer. The high-resolution timer is a light-weight mechanism compared to the traditional low-resolution periodic timer. With recent progress in hardware protocol offload technologies and multicore-aware network protocol stacks, we believe high-resolution timer-based packet pacing has become practical. Our experimental results show that the proposed mechanism can work on a wider range of systems without degrading the accuracy of rate control. However, a higher CPU load is observed when the number of traffic classes increases, compared to a gap packet-based pacing mechanism.

Adaptive Power Saving Mechanism for 10 Gigabit Class PON Systems

This paper proposes a power saving mechanism with variable sleep period to reduce the power consumed by optical network units (ONUs) in passive optical network (PON) systems. In the PON systems based on time division multiplexing (TDM), sleep and periodic wake-up (SPW) control is an effective ONU power saving technique. However, the effectiveness of SPW control is fully realized only if the sleep period changes in accordance with the traffic conditions. This paper proposes an SPW control mechanism with variable sleep period. The proposed mechanism sets the sleep period according to traffic conditions, which greatly improves the power saving effect. In addition, the protocols needed between an optical line terminal (OLT) and ONUs are described on the assumption that the proposed mechanism is applied to 10 Gigabit (10G) class PON systems, i.e. IEEE 802.3av 10G-EPON and FSAN/ITU-T 10G-PON systems. The validity of the proposed mechanism is confirmed by numerical simulations.

A New Ground-to-Train Communication System Using Free-Space Optics Technology

We propose a new ground-to-train communication system using free-space optics between a train and the ground. In the proposed system, a cylindrical concave lens spreads the incoming beam from transmitter (Laser Diode: LD) horizontally to form a wide fan-shaped beam. The fan-shaped beam is projected to a train and the width of the projected beam is equal to the length of a typical bullet-train car. This transmitter with cylindrical concave lens and a receiver (Avalanche Photo Diode: APD) are installed at a train and the ground, and the horizontally spread beam is received continuously by corresponding receiver. The train can keep a communication link continuously to the ground thanks to this spread beam. We analyzed the performance of the proposed system by experiments. The experimental results show that a sufficient received Signal-to-Noise Ratio (SNR) can be obtained when a train is not moving; therefore, the signal can be received continuously even when the train is moving. Furthermore, in order to keep a continuous communication link even when the train vibrates or shifts vertically, the vertical spread angle of a laser beam is adjusted between 0.1 degrees and 0.5 degrees. These experimental results lead to the conclusion that this system is expected as a Giga-bit class high speed communication technology between the train and the ground.

小型衛星間光通信捕捉追尾装置の開発

In inter-satellite links with many Low Earth Orbit (LEO) satellites, each satellite will communicate with one or more satellites. In such cases, a satellite needs multiple, small, and light optical antennas. A communication link between satellites is not sustained at high latitudes because antenna drive angles are large due to high relative angular rates. To reduce such link lost time, a wide drive range with high speed is required for optical antennas. To meet these requirements, we propose a coude path type optical antenna. Furthermore, optical fiber application will be required to achieve optical communication of the next generation of gigabit class. Therefore, it is necessary to develop the technology which introduces the laser received with the optical antenna to an optical fiber. The optical antenna’s experimental model is equipped with optical fiber. This paper describes the mechanism, control system and experimental results of the optical antenna we have developed. The principle and performance of the coude path type optical antenna with optical fiber was verified by using an experimental model of the optical antenna.

TRIPWIRE: A SYNCHRONISATION PRIMITIVE FOR VIRTUAL MEMORY MAPPED COMMUNICATION

Existing user-level network interfaces deliver high bandwidth, low latency performance to applications, but are typically unable to support diverse styles of communication and are unsuitable for use in multiprogrammed environments. Often this is because the network abstraction is presented at too high a level, and support for synchronisation is inflexible. In this paper we present a new primitive for in-band synchronisation: the Tripwire. Tripwires provide a flexible, efficient and scalable means for synchronisation that is orthogonal to data transfer. We describe the implementation of a non-coherent distributed shared memory network interface, with Tripwires for synchronisation. This interface provides a low-level communications model with gigabit class bandwidth and very low overhead and latency. We show how it supports a variety of communication styles, including remote procedure call, message passing and streaming.