Time Division Multiplexing Technique Research Articles

OTDM transmitter using WDM-TDM conversion with an electroabsorption wavelength converter

An all-optical multiplexing technique using wavelength division multiplexing (WDM)-time division multiplexing (TDM) conversion with an electroabsorption wavelength converter has been proposed and demonstrated. The effectiveness of this WDM-TDM conversion technique for various pulsewidth settings was experimentally investigated. The fluctuation of the signal performance, which was inevitably caused by the coherent crosstalk between adjacent pulses in the conventional optical time division multiplexing (OTDM) technique, were successfully suppressed, even in the case of wide pulse duration. High Q-factor performance has been maintained for a wide range of duty ration from 36% to 74%. By introducing this technique to the optical time division multiplexer, a highly stable and high-quality 40-Gb/s optical signal can be effectively produced without generating the short pulse or setting two tributaries at orthogonal polarization states, and without introducing high-speed electronics for signal multiplexing. The WDM-TDM conversion with an electroabsorption wavelength converter was extended to 60-Gb/s operation by using three 20-Gb/s tributaries. A clear eye opening was confirmed for a waveform after the WDM-TDM conversion of the 60-Gb/s signal.

Optical sampled subcarrier multiplexing scheme for nonlinear distortion reduction in lightwave CATV networks

A nonlinear distortion reduction scheme is proposed and demonstrated for subcarrier multiplexed optical CATV networks based on optical sampling and optical time division multiplexing techniques. Intermodulation distortion is reduced by about 10 dB for a 40-channel system.

160 Gbit/s field transmission over 116 km standard single mode fibre using 160 Gbit/s OTDM and 40 Gbit/s ETDM demultiplexer

T. Systems Nova, Technologiezentrum, the first 160 Gbit/s RZ transmission experiment over field-installed standard fibre G.652 is reported. The transmitter rests upon the optical time division multiplexing (OTDM) technique. At the receiver, a 160 Gbit/s to 40 Gbit/s OTDM demultiplexer followed by 40 Gbit/s electrical signal processing (ETDM) is used. The results are compared with 160 Gbit/s to 10 Gbit/s OTDM demultiplexing experiments. The OTDM demultiplexer is based on cross phase modulation in a semiconductor optical amplifier.

A multi-frequency TDMA/TDM system for a VSAT terminal network operating in Ka band

FH-JFDA (Frequency Hopping-Jitter Free Demand Assignment) is a satellite access scheme suitable for VSAT systems and designed for the Ka band (20–30 GHz). It uses the FH-TDMA (Frequency Hopping-Time Division Multiple Access) technique on the in-bound link towards the hub station, and the TDM (Time Division Multiplexing) technique on the out-bound link, from the hub towards the traffic stations. Each traffic station is allowed to transmit to the hub in temporal slots assigned by the hub itself, generally hopping among different TDMA carriers at each data burst transmission. The hub station retransmits the data received by using two TDM carriers modulated at different bit rates. It tries to maintain the same temporal position of the real time data packets when it switches between the two carriers in order not to introduce any further jitter on data. The fade countermeasure system adopted is based on the up-link power control and on data bit rate changing. This paper describes the FH-JFDA MAC protocol, the algorithm for assigning the transmission temporal slots, the algorithm adopted by the hub station for mapping the TDMA transmissions onto the TDM links, and the fade countermeasure technique used. The results of the investigation on one particular parameter of the system, which influences the choice of the TDMA assignment procedure, are also presented. A possible realization of the system using two transponders of the Italsat National coverage payload is also included in the paper, and the performance of the fade countermeasure system is evaluated.

Adaptive time and frequency resource assignment with COFDM for LMDS systems

In this letter, a wireless local multipoint distribution system (LMDS) at millimeter waves for the last-mile broad-band distribution to users of interactive services is investigated. The system analyzed employs a coded orthogonal frequency-division multiplexing transmission scheme with frequency-division multiplexing (FDM) and/or time-division multiplexing techniques and adaptive carrier allocation to counteract the effects of the wireless communication channel. The idea of deploying the reverse channel (exploited by the user for interactivity purposes) to provide channel information to the broadcasting transmitter is introduced. System performance is evaluated for an urban microcellular radio system in an actual propagation environment and the choices of the optimum multiplexing technique and carrier allocation algorithm are discussed in the case of ideal feedback. It is found that a pure FDM technique combined with an adaptive carrier allocation algorithm giving priority to users having the largest path loss leads to the best performance.

Interferometric ultrafast SOA-based optical switches: From devices to applications

All-optical switches are fundamental building blocks for future, high-speed optical networks that utilize optical time division multiplexing (OTDM) techniques to achieve single channel data rates exceeding 100 Gb/s. Interferometric optical switches using semiconductor optical amplifier (SOA) non-linearities perform efficient optical switching with < 500 fJ of control energy and are approaching optical sampling bandwidths of nearly 1 THz. In this paper, we review work underway at Princeton University to characterize and demonstrate these optical switches as processing elements in practical networks and systems. Three interferometric optical switch geometries are presented and characterized. We discuss limitations on the minimum temporal width of the switching window and prospects for integrating the devices. Using these optical switches as demultiplexers, we demonstrate two 100-Gb/s testbeds for photonic packet switching. In addition to the optical networking applications, we have explored simultaneous wavelength conversion and pulse width management. We have also designed high bandwidth sampling systems using SOA-based optical switches as analog optical sampling gates capable of analyzing optical waveforms with bandwidths exceeding 100 GHz. We believe these devices represent a versatile approach to all-optical processing as a variety of applications can be performed without significantly changing the device architecture.

Time-division multiplex technique for producing concentration profiles in flow analysis

A technique is described which uses computer controlled solenoid valves for creating concentration profiles for various flow-based methods of analysis. These profiles can be quickly selected through software and, similarly, parameters such as the volume of the sample, carrier and reagents can be set and altered when required with minimal changes to the hardware. The technique has been demonstrated for flow titration and flow injection but is equally applicable to other methods. In all these methods, only a single channel pump is required to draw the mixed solutions through the detector and individual solutions are introduced into the flowing stream by selection through solenoid operated valves. Results are presented for the determination in water samples of calcium using potentiometric titration and orthophosphate by flow injection using the molybdenum blue method. The technique uses only small volumes of solutions and is fully automated and so is ideal for use in portable instrumentation.

Exploitation of the Fiber Capacity in Optically Amplified Transmission Systems

As is well known, single-mode optical fibers have a huge optical bandwidth but the exploitation of this optical ether for optical transmission systems is limited by several degrading effects that are present both in the fiber and in other devices composing the link. However, in recent years several techniques have been proposed and tested to show how the system capacity can approach total exploitation of the fiber bandwidth.In this work we survey the main optically amplified communication systems that have been proposed to achieve very-high-capacity transmission and analyze their performances by means of numerical simulations. Numerical simulation is a fundamental tool for the study of optical communication because analytical theories are not able to take into consideration all the effects that are simultaneously present in a real link.The study reports a comparison among the performance of digital intensity modulation systems with direct detection considering both the non-return-to-zero and the return-to-zero (soliton) format, as well as the time and wavelength division multiplexing techniques. The results show how exploitation of the Kerr nonlinearity, use of the in-line filtering process, and introduction of dispersion management are the best means to limit the degrading effects of chromatic dispersion and ASE noise.

Ultrahigh-bit-rate optical transmission research in Japan

Recent progress toward ultrahigh-bit-rate optical fibre transmission systems employing optical time-division multiplexing (TDM) techniques is reviewed. Focus is placed on 100 Gbit s$^{-1}$ optical TDM transmission systems and the related technologies studied in Japan. Successful 100 Gbit s$^{-1}$ TDM transmission experiments over 200-500 km and the key technologies are described, including ultrashort optical pulse generation, all-optical multiplexing-demultiplexing and optical timing extraction techniques, together with state-of-the-art performances and future prospects.

Entwicklungstendenzen photonischer Nachrichtennetze

Photonic networks are the base of a future broadband Internet that permits an easy access to the variety of multimedia services. Optical frequency- and time-division multiplexing techniques enable an optimum matching of the photonic network's capacity to the increasing communications demand thereby reacting to the requirements of new services in a flexible way. Flexibility and reliability with high profitability are the crucial characteristics of future photonic networks.

ATM shared-memory switching architectures

ATM will provide flexibility in bandwidth allocation and will allow a network to carry heterogeneous services ranging from narrowband to wideband services. The challenge is to build fast packet switches able to match the high speeds of the input links and the high performance requirements imposed. The CCITT has standardized the asynchronous transfer mode (ATM) as the multiplexing and switching principle for the broadband integrated services digital network (B-ISDN). ATM is a packet and connection-oriented transfer mode based on statistical time division multiplexing techniques. The information flow is organized in fixed-size packets called cells, consisting of a user information field (48 octets) and a header (5 octets). The primary use of the header tag is to identify cells belonging to the same virtual channel and to make routing possible. Cell sequence on a virtual channel is preserved, a very low cell loss probability must be guaranteed (< 10/sup -/12), and intensive error and flow control protocols are provided at the edges of the network.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An optical fiber sensor system for fire detection in hazardous environments

Optical fiber sensors can overcome many of the shortcomings of conventional electronic sensors. This work describes an optical-fiber fire-detection system comprising temperature and smoke sensors interrogated by a time division multiplexing technique. The proposed fire-detection system not only monitors temperature variations in numerous points, but also provides an approximate evaluation of the density of any smoke present. The system is configured as a network that can be easily expanded, as shown by the results of experimental testing on a system composed of four temperature sensors and one smoke sensor.

Analogue time division multiplexing

A multiplexing method by which, in a system of N users, segments of duration T s from each user are rapidly transmitted in the channel, as analogue signals of duration T/ Ns is described. Thus, each user signal can be considered to be compressed in time by a factor of N before transmission, and the total time to transmit all N signals is Ts. At the receiving end, user signals are restored to their original duration, by an inverse mechanism of decompression. This technique allows the interlacing of N analogue signals in time and can therefore be considered as an analogue time division multiplexing (ATDM) technique. In this way, through a channel of bandwidth B, N — BjBc concurrent users of bandwidth Bc each can communicate. A four-user ATDM system was implemented and its performance was evaluated experimentally.

DESIGN AND PERFORMANCE OF A NEW MULTI-LANE AVI SYSTEM

Abstract This paper describes the complete hardware and software design of a new automatic vehicle identification (AVI) system for use on multi-lane roads and where the traffic lane disciplines are not always complied with. The system employs the randomized time division multiplexing (TDM) technique for avoiding collisions of signals transmitted from several vehicles coexisting in a wide angle detection zone of 90° × 83° × 20 m. Experiments carried out in a fully furnished teaching laboratory show an error free detection for the two-way communication between the toll-site AVI equipment and the identification tag at a IMbit/s data rate.

New automatic vehicle identification system for detection of traffic without lane discipline

Electronic road toll collection has usually been carried out on the highway using an automatic vehicle identification (AVI) system. At the toll site, physical barriers are set up between lanes so that individual vehicles can be effectively detected. Problems arise, however, in the detection of vehicles on busy city roads where barriers between lanes are not desirable and the traffic does not always maintain lane discipline. A new AVI system using a randomised time division multiplexing (TDM) technique for detecting several vehicles simultaneously entering the detection zone is described. Laboratory experiments carried out for up to eight identification tags at the same time showed that all replies were detected for 900 interrogations. Collisions between replying signals did not occur. The high-speed transmission of serial data has, however, an error rate of 3-7%. Under laboratory conditions, the detection errors were eliminated simply by allowing the tags to reply twice. >

Time division multiplexing of optical fibre sensors with sampled modulation of laser diode

A time division multiplexing technique is described in which the frequency of a laser source is modulated with a sampled ramp. The concept is demonstrated with two Mach-Zehnder interferometers in a parallel configuration, separated by a fibre delay line whose length is determined by the characteristics of the sampling waveform. Pseudo-heterodyne processing was used to recover the phase information from each interferometer. The expansion of the technique to a combined frequency and time division multiplexed fibre-optic sensing system is considered.

Traffic analysis of a local area network with a star topology

Two forms of fast circuit switching are modeled and studied through mathematical analysis and Monte Carlo simulation. The two examples described use the switching technique in an optical-fiber-based local area network with a star topology. The technique is compatible with time-division multiplexing techniques that are used for a range of traffic classes. Further, the technique trades transmission capacity for processing power, which is the critical limitation of the system. By means of a certain independence assumption, the first form of fast circuit switching is modeled as an M/G/1 queue. The results of the analysis show excellent agreement with simulation. The general result is that there is good system throughput, despite simplicity of processing. The second form, in which rather than first-come first-served the discipline is to search for a message whose destination queue is free, is studied by means of simulation alone. The results indicate an improved performance with a modest increase in processing power.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Multirate Switching Network for Broadband Channels

A broadband ISDN switching network model is presented, switching the channel types H2, H3, and H4 envisaged by the CCITT. The synchronous time division multiplex technique is applied. The switching network operates at the basic bit rate of the H2-channel; H3and H4-connections are established via multichannel connections of up to four basic channels. H2-connections which are part of one H3- or H4-connection always have to use common interconnection links. This is a favorable solution to keep digit sequence integrity for multichannel connections, but influences blocking characteristics of the switching network. The implementation of an optimal path selection method plays a fundamental role. In such a multichannel switching network, blocking probabilities for H2-, H3-, and H4-connections must be distinguished. They do not only depend on the total offered load, but also on the proportions of H2-, H3-, and H4-connections (traffic mix). The simulation results presented in this paper prove that multirate switching via multichannel connections is feasible for the broadband channel types H2, H3, and H4, and that the proposed switching network has a sufficiently high traffic capacity whatever the traffic mix may be.

Applications of wavelength-division multiplexing and time-division multiplexing to aircraft data links

Abstract A fiber optic system designed to transmit over a single optical fiber asynchronous signals previously carried by up to 48 separate metallic cables was developed as a test bed for aircraft applications of fiber optics. Advanced wavelength-division multiplexing (WDM) and time-division multiplexing (TDM) techniques were used to achieve the above-mentioned cable count reduction. Component description and system performance characteristics are presented in this paper.

Remote control of traction power over two wires

In 1979 British Rail introduced new equipment to the Edinburgh/Glasgow route, using push-pull operation to avoid lengthy turn-round delays at the terminal stations. This paper describes the design and development of the equipment ultimately provided to allow this operation, without expensive modification of the intermediate coaches on the train, by the use of TDM (time-division multiplex) techniques. The initial testing and subsequent service experience are described. A brief review of the future possibilities for this technique, and other similar equipments available, is provided.