摘要:

The principal factor in realising a high-performance bandwidth-efficient fibre communication system at an acceptable cost is the choice of modulation format on the optical carrier. In this context, pulse time modulation (PTM) techniques represent an attractive alternative to purely digital or analogue methods. The PTM family is reviewed, a classification system is proposed and their potential for use in high-speed fibre systems intended for the transmission of analogue data is examined.

DOI:10.1049/ip-j.1993.0055

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The dynamical behaviour of infinite periodic trains of optical fibre solitons subjected to modulation of the position of each soliton is studied by analytical methods. It is concluded that multigigahertz pulse-analogue transmission over amplified links many times longer than the linear dispersion limit at high signal-to-noise ratio is achievable. The principal limitations are the nonlinear intersoliton interaction and amplifier spontaneous emission. The analytical techniques developed are useful for the study of a wide range of modulation and noise phenomena in soliton pulse trains.

DOI:10.1049/ip-j.1993.0056

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The discrete time modulation format, known as digital PPM, has been used to exchange channel bandwidth for improved signal-to-noise ratio in optical communication systems. However, the filter that optimises signal detection is complex in that it comprises a prewhitened matched filter in cascade with a proportional-derivative-delay network. In this form, the receiver would be unrealistic for a commercial system. This paper examines the use of both optimum and suboptimum detection. Three suboptimum predetection filters are considered: a matched filter, an optimised three-pole filter and a third-order Butterworth filter. Original receiver sensitivity calculations, carried out at a bit rate of 140 Mbit/s and a wavelength of 1.3 μm, show that the optimum digital PPM system offers an 8.6 dB improvement over a typical PCM system. The suboptimum predetection filters result in sensitivity degradations of 0.4, 0.9 and 1.1 dB, respectively. This clearly illustrates that receiver complexity can be simplified without large reductions in sensitivity. In particular, the well known and simple Butterworth filter can be employed with only 1.1 dB degradation in sensitivity.

DOI:10.1049/ip-j.1993.0057

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A method for block synchronisation in optical PPM is proposed. This method is an application of the synchronisation method for PN sequences normally used in spread spectrum communication systems. In this method, the phase of the synch signal is shifted little by little, with the synch decision process carried out on the receiving side until synchronisation is attained. The decision rule is based on the fact that the number of received pulses in each frame of the synch signal must be one and that the time when the pulse is received should not be in the pre-fixed prohibited frame slot, provided that synchronisation is established. This method's synchronisation characteristics are investigated, and it is shown that block synchronisation can be established sufficiently with only 12.5% of additional prohibited slots.

DOI:10.1049/ip-j.1993.0058

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The paper describes the results to date of the RACE project R2005. The project addresses the optical generation and fibre delivery of mm-wave signals for future mobile radio and remote customer access connections. The authors identify potential application areas and appropriate performance targets for such fibre/mm-wave systems. The major issue identified is the need to achieve low-cost antenna units due to the large number of such units that would be required; this arises from the limited propagation distances achieveable at mm-wave frequencies. A brief review of current optical methods for the generation of mm-waves allows the identification of the inadequacies of these techniques and leads to a description of a new method, developed for the project, that overcomes most of the disadvantages outlined earlier.

DOI:10.1049/ip-j.1993.0059

出版商:IEE    

年代:1993

数据来源: IET

摘要:

This paper describes the application of the microwave subcarrier multiplexing technique (SCM) in an optical frequency division multiplexing (OFDM) system which employs an optical FM direct detection scheme. Direct frequency modulation of a laser diode offers the advantages of compact optical spectrum and simple driving circuit; it also permits a more effective utilisation of optical channel capacity. The carrier-to-noise ratio performance of each subcarrier channel is evaluated. The effect of laser diode phase noise and relative intensity noise as well as the intermodulation product of subcarrier channels on the overall system performance is analysed and the results presented.

DOI:10.1049/ip-j.1993.0060

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The performance of frequency-modulated (FM) subcarrier-multiplexed systems is assessed using Volterra series analysis to model laser nonlinear distortion accurately. The intermodulation-power spectral density and the carrier-to-intermodulation ratio are then determined. The performance of these systems is investigated by considering all noise contributions: intermodulation and relative intensity noise in the transmitter and receiver thermal and shot noise. Optimum performance is also identifed. A 62-channel FM video system occupying the bandwidth of 2.7–5.2 GHz provides an illustrative example.

DOI:10.1049/ip-j.1993.0061

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Optical amplifiers can be used to increase the distribution of analogue video signals over a passive optical network. The paper analyses the gains in system loss budget that can be obtained from the positioning of optical amplifiers either as transmitter power amplifiers, line amplifiers or receiver preamplifiers in a distribution network. Both AM and FM subcarrier multiplexed (SCM) video systems are considered within the constraints of operating with safe optical power levels on optical lines in the network. It is shown that under such conditions optical amplifiers can give significant advantages in the loss budget for FM SCM systems, but have limited application within AM SCM systems.

DOI:10.1049/ip-j.1993.0062

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A tuned SCM optical receiver design integrated as a GaAs MMIC is reported. The receiver is intended for use in a practical system and includes an integrated noise tuning network. A critical study of tuning networks suitable for integration is undertaken, and the details of a novel design and optimisation strategy for such networks are discussed. Simulation results predict low noise and high gain performance, and verify the validity of the design technique adopted.

DOI:10.1049/ip-j.1993.0063

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The major analogue intensity modulation schemes are assessed and compared in relation to their ability to provide high-quality transmission of high-definition television (HDTV) signals on single-mode optical fibre. The practical investigation and novel implementations for subcarrier frequency modulation (SCFM) and square wave frequency modulation (SWFM) schemes are then described prior to discussion of the relative performance attributes of these transmission systems. Both modulation techniques proved satisfactory for high-quality HDTV transmission over single-mode fibre with the balance of the measured performance and the necessary system requirements not decisively favouring either method.

DOI:10.1049/ip-j.1993.0064

出版商:IEE    

年代:1993

数据来源: IET