Digital Pulse Position Modulation Research Articles

Performance of burst-mode receivers for optical digital pulse position modulation in passive optical network application

A DC coupled burst-mode receiver for digital pulse position modulation (DPPM) is proposed for the first time. An analysis of the potential performance benefits of using such a receiver configuration in the upstream of a passive optical network is given. An optical pre-amplifier is assumed. Bit error rate expressions are derived and the performance is evaluated in terms of sensitivity and threshold acquisition penalty. Results are compared with a DC-coupled on–off keyed non-return-to-zero burst-mode receiver, and it is seen that DPPM's continuous mode sensitivity advantage (about 8 dB for the optimal case) is only reduced to 7.7 dB when overhead preamble is restricted to 12 bits and 6 dB when restricted to 6 bits. Thus, if necessary, DPPM can almost recover its sensitivity advantage by a trade off with preamble length. As such DPPM can potentially offer an increase in optical network unit numbers by a factor of 4 or, alternatively, an increase in range of around 20 km.

Comparison of pulse position modulation and pulse width modulation for application in optical communications

Different modulation methods for optical wireless have different power and bandwidth efficiencies. Each approach has a direct bearing on the quality and effectiveness of wireless optical communications. As two prime examples, pulse position modulation (PPM) and pulse width modulation (PWM) are compared. The comparison includes the power and bandwidth efficiencies, the power spectrum distribution, and the ability to resist intersymbol interference. Compact system models of multilevel digital PPM (L-PPM), and multilevel digital PWM (L-PWM) are also introduced. The results show that L-PPM has advantages in power efficiency and an approximately uniform spectral distribution, whereas L-PWM has a greater ability to resist intersymbol interference.

Minimising intersymbol interference in optical-fibre dicode PPM systems

Dicode pulse-position modulation (PPM) has been proposed as an alternative modulation format to conventional digital PPM, since it offers comparable receiver sensitivities while operating at significantly lower slot-clock rates. A recent numeric analysis considered the performance of dicode PPM, using slope detection, in a dispersive environment. In this paper, consideration is given to an alternative detection strategy, and new results are presented that show that intersymbol interference (ISI) can be eliminated through the use of central decision detection combined with raised cosine filtering. This leads to a more simplified receiver design and results in equivalent sensitivity performance at high fibre bandwidths and significantly improved performance at lower fibre bandwidths. Practical approximations to this approach are considered and design rules presented for determining the bandwidth of both the preamplifier and a simple 3rd order Butterworth equalisation filter. It is shown that setting the bandwidth of both the preamplifier and equaliser to 0.6 times the dicode slot rate gives sensitivities within 0.2 dB of ideal dicode PPM raised cosine filtering, and that such a receiver can operate over a wide range of fibre bandwidths, with minimal degradation in sensitivity.

Indoor optical wireless systems employing dual header pulse interval modulation (DH‐PIM)

AbstractThis paper assesses the performance of dual header pulse interval modulation (DH‐PIM) over indoor optical wireless systems. DH‐PIM being anisochronous scheme offers a built‐in symbol synchronization capability. Theoretical and simulation results demonstrate that DH‐PIM offers shorter symbol length, improved transmission rate and bandwidth requirement and a comparable power spectral density profile compared with digital pulse interval modulation (DPIM) and pulse position modulation (PPM) schemes.It is shown that DH‐PIM2, with wider pulse duration is the preferred option when the available channel bandwidth is limited and higher optical power is tolerable. Whereas DH‐PIM1, with narrower pulse width, exhibits comparable power requirements but a marginally higher bandwidth compared with DPIM, and is also more bandwidth efficient than PPM at the cost of increased power requirement. However, at higher bit resolutions, i.e. M⩾7, DH‐PIM1 is both bandwidth and power efficient compared with PPM. Error rate analysis show that DH‐PIM offers improved packet error rate compared with on‐off‐keying (OOK) and DPIM, but marginally inferior as compared with PPM. The power requirement and penalty due to intersymbol interference for non‐dispersive and dispersive channels is analysed and the results show that for given parameters, DH‐PIM requires marginally higher optical power compared with PPM and DPIM, but it supports the same bit rate at much less bandwidth requirement. Copyright © 2005 John Wiley & Sons, Ltd.

Spectral characterisation of dicode PPM Format

Dicode pulse position modulation (PPM) is a new modulation format that offers improved sensitivity over digital PPM but at a reduced line-rate. For the first time, the spectral characterisation of the dicode PPM modulation format is considered and original expressions for predicting both the continuous and discrete spectrum are presented.

Pulse Position Modulation for Spectrum-Sliced Transmission

An original analysis is presented for spectrum-sliced (SS) transmission employing digital pulse position modulation (PPM) and maximum likelihood detection. The treatment is placed within the context of low-cost access networks, where system parameters allow employment of the Gaussian approximation. SS-PPM is compared to on-off keying (SS-OOK) in the presence of dispersion and found to be typically some 2-4 dB more sensitive. In addition, comparison is made with laser-based OOK where the optimum SS-PPM configuration reduces or eliminates the SS power penalty.

Suboptimal filtering in a zero-guard, dicode PPM system operating over dispersive optical channels

Optimal filters for use in digital pulse position modulation (PPM) systems consist of a noise-whitened matched filter followed by a proportional-derivative-delay (PDD) network. Although the PDD network can be removed, with a small loss in sensitivity, the practical implementation of the remaining matched filter is complex. An alternative is to use suboptimal filtering and the use of a third-order Butterworth filter in a zero-guard interval dicode PPM system operating over a dispersive optical channel is examined. Gaussian-shape received pulses are assumed, and a bandwidth-limited PIN–bipolar receiver with both frequency invariant and variant noise is considered. This original analysis shows that the bandwidth of the Butterworth filter is relatively independent of the channel. It is also shown that the performance of such a filter is superior to that of a noise-whitened matched filter. It is concluded that a dicode PPM system can use a simple third-order Butterworth filter. The best predicted sensitivities when coding 1 Gbit/s PCM data are −37.48 dBm in a high-bandwidth link and −32.24 dBm with a link bandwidth equal to 1.2 times the data rate.

Analysis of dicode pulse position modulation using a PINFET receiver and a slightly/highly dispersive optical channel

PINFET receivers have been considered for use in digital pulse position modulation (PPM) links, where they can give sensitivities far greater than that achievable with pulse code modulation (PCM). However, digital PPM suffers from a very large bandwidth expansion factor, resulting in line rates that can be prohibitively high. An alternative is dicode PPM and the paper is concerned with the use of a PINFET receiver and a noise-whitened matched filter in such a scheme. With this particular implementation, the line rate is four times that of the PCM, making it a viable alternative to digital PPM. The original analysis presented predicts that such a system can give a sensitivity of -59.51 dBm when operating with high fibre bandwidth and 155.52 Mbit/s PCM data. The impact of intersymbol interference is also studied and it is shown that the system can offer a sensitivity of -53.33 dBm at a bandwidth of 1.5 times the PCM bit-rate. These sensitivities should be compared with a predicted PCM sensitivity of -51.95 dBm when operating in a high-bandwidth link.

Dicode pulse-position modulation: a novel coding scheme for optical-fibre communications

Pulse position modulation (PPM) schemes have been proposed as a method of utilising the bandwidth available in optical fibres, with a 5-11 dB improvement in sensitivity being achieved compared to an equivalent pulse code modulation (PCM) system. However, this improvement comes at a cost. If digital PPM is used, the final data rate can be almost 23 times that of the original PCM, and this makes implementation difficult. The author describes a novel coding technique that combines dicode, a tertiary code sometimes used in magnetic recording, and digital PPM to form dicode PPM. It is shown that dicode PPM gives a receiver sensitivity greater than digital PPM while operating at only four times the original data rate. Original results presented predict that a high fibre bandwidth dicode PPM system can give sensitivities of -50.44 dBm and -44.27 dBm when operating with 155.52 Mbit/s and 1 Gbit/s PCM data, respectively. This should be compared to typical PCM sensitivities of -38 dBm and -28 dBm. It is also shown that dicode PPM outperforms digital PPM at low fibre bandwidths by 3.02 dB.

Fast word synchronisation for digital pulse-position modulation

A new word synchronisation method for digital pulse-position modulation is proposed which allows faster frame acquisition. Application is intended in high-speed wireless optical communications.

Slot synchronization by reducing the PPM pulsewidth in wireless optical systems

Digital pulse position modulation is an attractive modulation scheme in indoor wireless optical transmission systems because of its power efficiency. In this brief, slot synchronization by means of a reduced pulsewidth is discussed, the scheme is compared to on-off keying, and design rules for slot synchronizers are presented. The sensitivity deterioration of the prototype due to slot clock jitter is only 0.2 dB (optical power level).

Wireless optical PPM telemetry and the influence of lighting flicker

Digital pulse-position modulation (PPM) is attractive to apply in wireless optical-telemetry systems because of its power efficiency. Usually, the bit-error rate is assumed to depend solely on the noise level. The detrimental influence of optical interference is overlooked. In this paper, interference measurements are reported, models that describe interference are presented, and it is shown that the influence of interference can be significant. Further, new rules for system design in the presence of interference are reported. It appears that, compared with the influeuce of noise, the flicker of incandescent lamps is usually negligible, but the flicker of fluorescent lamps is not negligible.

Digital underwater acoustic voice communications

This paper describes the design of an underwater acoustic diver communication system controlled by a digital signal processor. The speech signal transmission rate is compressed by using linear predictive coding (LPC) and the extracted parameters are transmitted through the water to a synchronized receiver by employing digital pulse position modulation (DPPM). The pulse position in each time frame is estimated by an energy detection and decision algorithm which enables the received LPC parameters to be recovered and used to synthesize the speech signal.

A new modulation technique based on digital pulse interval modulation (DPIM) for optical‐fiber communication

AbstractA novel digital pulse time modulation (PTM) technique called digital pulse interval modulation (DPIM) is presented, in which the input signal information is transmitted by the time intervals between two succeeding pulses. DPIM has simplicity of circuit configuration combined with other attractive features of digital pulse position modulation (DPPM) for optical‐fiber communications. This article derives theoretical expressions for transmission capacity, code characteristics, and power spectral density (PSD), and the analytical results are compared with experimental data. © 1995 John Wiley & Sons, Inc.

On the spectral estimation and synchronization of the cyclostationary optical fibre PPM process

Digital pulse position modulation (PPM) has been shown to be attractive for implementation over the optical fibre channel when the laser transmitters are average power limited and the channel bandwidth is abundant. The synchronization requirements for optical fibre PPM however have not yet been addressed. We present an original mathematical formulation for the problem of spectral prediction and synchronization in PPM based on the cyclostationary properties of the format. Further we predict the conditions required to achieve and optimize both slot and frame synchronization. The major system parameters including the modulation index, data probability distribution and pulse shape are catered for and used in the analysis. A novel technique, capable of coping with the different PPM word sizes, is presented and used to achieve frame phase extraction directly from the PPM stream. Appropriate mathematical models are developed and used to predict the spectral properties at the output of the frame phase synchronizer. Original practical results measured on a PPM system are presented and shown to agree with the theoretical models and predictions to within 1 dB. >

Underwater voice communications using digital techniques

A digital signal processor (DSP) based voice communication system for divers with a 2400 bit/s transmission rate is described. Each speech signal frame is analysed using linear predictive coding (LPC) and the essential parameters such as amplitude, pitch period and digital filter coefficients are extracted. These parameters are transmitted through a water channel at a rate of 2400 bit/s by employing digital pulse position modulation (DPPM)

Optical‐fiber digital PPM systems employing PIN‐FET receivers

AbstractAn analysis is presented for the optimum detection of digital pulse position modulation employing PIN‐FET receivers. The results demonstrate a sensitivity improvement of 7.2 dB over an equivalent PCM system when operating at a bit rate of 50 Mbits/s. Calculations have also been performed for a causal approximation to the optimum receiver and it is shown that this leads to only a 0.5‐dB reduction in sensitivity. Finally, receiver design implications are examined for higher bit‐rate operation and the results obtained for a 565‐Mbit/s system demonstrate an improvement of 6 dB over PCM.

Timing Considerations for Optical Fibre PPM

AbstractDigital pulse position modulation (PPM) has been shown to be an effective modulation format for the optical fibre channel. It is paricularly attractive as it can exploit the abundant mono‐mode optical fibre bandwidth to offer improved performance. The format is a discrete time modulation format wherein synchronisation at both the slot and the frame levels is vital. In this paper we derive an original analytic expression that predicts the spectral properties of optical fibre digital PPM on the basis of its cyclostationary random properties. We establish the conditions required to achieve both slot and frame synchronisation and further, we show that the system synchronisability can be optimised in terms of its parameters. In particular, we consider die effect of the pulse shape, modulation index and the data probability distribution on the spectral properties. Finally, we present original practical results measured on a 128‐ary PPM system and show that they are within 1 dB of those predicted by our analytic model. We conclude that optical fibre digital PPM synchronisation can be achieved and further, optimised, in terms of the major system parameters.

Analogue optical fibre communications

* Chapter 1: Subcarrier multiplexing in optical communication network * Chapter 2: Coherent techniques in analogue signal transmission * Chapter 3: Analogue intensity modulation for optical-fibre video transmission * Chapter 4: Pulse time modulation techniques for optical fibre communications * Chapter 5: Soliton pulse position modulation * Chapter 6: Optical fibre digital pulse position modulation * Chapter 7: Performance assessment of subcarrier-multiplexed optical systems * Chapter 8: Optoelectronics for millimetre-wave radio over fibre systems * Chapter 9: Optical generation and delivery of modulated mm-waves for mobile communications * Chapter 10: Optical receiver design for optical-fibre SCM systems * Chapter 11: Optical fibre amplifiers and WDM

Frame synchronization of optical fiber dppm with dispersed pulse shapes

AbstractOptical digital pulse position modulation (DPPM) is an effective modulation format for both free space and fiber communications. However, for the latter, system synchronization has not been considered. Here, we address this issue and present an original expression, supported by practical results, for evaluating the frame spectral properties of optical fiber DPPM. We use the established properties to optimize frame synchronization while using a dispersed DPPM pulse shape which is representative of optical fiber systems © 1992 John Wiley & Sons, Inc.