Showing papers on "Pulse-position modulation published in 1996"

Adaptive modulation system with variable coding rate concatenated code for high quality multi-media communication systems

Abstract: This paper proposes an adaptive modulation system with a concatenated code (AMS-CC) for land mobile communications to achieve high quality, high bit rate transmission in Rayleigh fading environments. The proposed system adaptively controls the coding rate of the inner convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. The performances in Rayleigh fading environments are evaluated theoretically and by computer simulation. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

Performance of pulse-position modulation on measured non-directed indoor infrared channels

Abstract: We examine the performance of pulse-position modulation (PPM) on measured channels with intersymbol interference (ISI). We summarize the bit-error-rate performance of unequalized systems and review the performance of maximum-likelihood sequence detection (MLSD) for PPM over ISI channels with additive white Gaussian noise. We evaluate the performance of PPM links over 46 experimentally measured indoor infrared channels. Detailed results are presented for 2, 4, 8, and 16-PPM at bit rates of 10 Mb/s and 30 Mb/s, and these techniques are compared to on-off keying. Our results show that when MLSD is employed, 16-PPM provides the best average-power efficiency among the modulation techniques considered in this study.

Performance of infrared transmission systems under ambient light interference

Abstract: Optical transmission systems are mainly impaired by the shot noise induced by ambient light, the transmitted optical power limitations (high path losses), the channel bandwidth limitations owing to multipath dispersion and the interference produced by artificial light sources. Several modulation and encoding schemes have been proposed for this channel and their performance has been studied and presented by several authors while neglecting the effects of the artificial light interference. The work reported extends the previous analysis by taking into account the optical power penalty induced by artificial light interference. An analytical approach is used to estimate this. In practical systems, the effect of the interference is usually mitigated using electrical highpass filters. In the paper the combined effect of interference and highpass filter is evaluated. The presented results show that the interference produced by fluorescent lamps driven by electronic ballasts induce high power penalties in OOK and L-PPM systems, even when electrical highpass filtering is used, for data rates up to 10 Mbit/s. For the interference produced by incandescent lamps and fluorescent lamps driven by conventional ballasts, the power penalty induced in OOK systems can be effectively reduced using highpass filtering, while PPM is very tolerant to that interference even without any highpass filtering. The major conclusion is that artificial light interference have to he considered both in system design and performance evaluation.

Effect of electronic-ballast fluorescent lighting on wireless infrared links

Abstract: Fluorescent lamps driven by electronic ballasts emit an infrared (IR) signal that is periodically modulated at rates of tens of kilohertz, and which can severely impair the performance of IR wireless links. The impact of fluorescent interference can potentially be reduced by highpass electrical filtering, but such filtering induces intersymbol interference (ISI). The authors present expressions for the bit error rate (BER) of systems using on-off keying (OOK) and pulse-position modulation (PPM) in the presence of both a deterministic interfering signal and ISI. They have measured the interference waveforms from lamps driven by 22 and 45 kHz ballasts, and have used the measured waveforms to evaluate the performance of IR links using OOK and 2, 4, 8 and 16 PPM at bit rates of 1, 10, and 100 Mbit/s. When the fluorescent interference is normalised to the signal power required in the absence of this interference, the penalties incurred by OOK are found to be essentially independent of bit rate. At 1 Mbit/s, PPM suffers approximately the same penalties as OOK, but as the bit rate is increased, the degradation of PPM becomes progressively much smaller. In the absence of measures to prevent ISI, first-order highpass filtering is not effective in improving the performance of OOK, but can substantially improve PPM link performance at bit rates of 10 and 100 Mbit/s.

Sensitivity evaluation of optical wireless PPM systems utilising PIN-BJT receivers

Abstract: A new hybrid optical wireless system based on pulse position modulation (PPM) and PIN-BJT receivers is proposed and its performance is evaluated. The system is operated at a bit rate of 10 Mbit/s and h=0.85 /spl mu/m. The receiver achieves a low noise current of /spl sim/2.7 pA//spl radic/Hz. Original results are presented demonstrating that the system can achieve a sensitivity of -50.5 dBm at an error rate of 10/sup -9/. This represents a sensitivity improvement of 9.8 dB over a comparable on-off keying (OOK) PIN-BJT system. The sensitivity enhancement has a significant impact on the optical wireless network, where the maximum allowed transmitted power is limited by safety issues. Moreover, the use of PPM offers other advantages, such as the low average power which is suited for battery operation and a high peak power that aids detection.

Channel reuse strategies for indoor infrared wireless communications

Abstract: We examine systems of fixed channel reuse for base stations in an indoor infrared wireless communication system. The following techniques are compared: time-division multiple access (TDMA) using on-off keying (OOK) or pulse-position modulation (PPM), frequency-division multiple access (FDMA) using binary phase-shift keying (BPSK), and code-division multiple access (CDMA) using OOK with direct-sequence spreading by m-sequences or optical orthogonal codes (OOCs). TDMA using PPM is found to offer superior performance in terms of complexity and average optical power required to cover a room.

Digital underwater acoustic voice communications

Abstract: 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.

Effect of electronic-ballast fluorescent lighting on wireless infrared links

Abstract: Fluorescent lamps driven by electronic ballasts emit an infrared (IR) signal that is periodically modulated at rates of tens of kilohertz, and which can severely impair the performance of IR wireless links. The impact of fluorescent interference can potentially be reduced by high-pass electrical filtering, but such filtering induces intersymbol interference (ISI). We present expressions for the bit-error rate (BER) of systems using on-off keying (OOK) and pulse-position modulation (PPM) in the presence of both a deterministic interfering signal and ISI. We evaluate the performance of IR links using OOK and 2-, 4-, 8-, and 16-PPM at bit rates of 1, 10, and 100 Mb/s. The penalties incurred by OOK are found to be essentially independent of bit rate. At 1 Mb/s, PPM suffers approximately the same penalties as OOK, but as the bit rate is increased, the degradation of PPM becomes progressively much smaller In the absence of measures to prevent ISI, first-order highpass filtering is not effective in improving the performance of OOK, but can substantially improve PPM link performance at bit rates of 10 and 100 Mb/s.

Hearing assist system employing time variant modulation transmission to hearing aid

Abstract: A short range magnetically coupled wireless communication system employs time variant modulation of a high repetition rate pulse stream and magnetic coupling between a transmission magnetic element and a receiving magnetic element. The pulse stream is modulated by an input audio frequency signal in the time domain, for example, through pulse position modulation, pulse width modulation or pulse symmetry modulation. The receiving magnetic element is coupled to a demodulator circuit which detects the transmitted pulses induced in the receiving magnetic element and reproduces the audio frequency signal. Transmission over short range is thus efficiently accomplished through magnetic coupling in a simple, low cost, low power consumption communication system.

Performance of multiple pulse position modulation on multipath channels

Abstract: The effect of multipath dispersion on multiple pulse position modulation (MPPM) and its variants PPM and overlapping PPM are examined. Upper bounds for the error probability of each modulation scheme in the presence of intersymbol interference are presented, considering both an unequalised receiver and the optimal maximum-likelihood sequence detection receiver. Numerical results show that all the PPM-based schemes are approximately equally sensitive to multipath dispersion, and significantly more sensitive to multipath dispersion than on-off keying when maximum-likelihood sequence detection is used.

Hybrid pulse width modulation/sigma-delta modulation power digital-to-analogue converter

Abstract: A new digital signal processing technique is presented for power digital-to-analogue converters which offers high linearity and a substantial reduction in clock frequency compared to conventional pulse width modulation converters. The basis of the technique is to group together pulses from the output of a single bit sigma-delta modulator. A model is derived which shows that the system output is essentially a pulse width modulated sequence. Noise and distortion are introduced by the pulse grouping but are considerably reduced using noise shaped feedback around the pulse grouper. Simulation results are presented which validate the model and indicate the performance of the technique with ideal and nonideal output stages.

On the capacity of the asynchronous T-user M-frequency noiseless multiple-access channel without intensity information

Abstract: We discuss an achievable rate region for the asynchronous T-user M-frequency multiple-access channel without intensity information. The problem is formulated in terms of frequencies, but the results are also applicable to pulse position modulation (PPM) schemes. It is shown that the achievable sum rate for T users reduces from (M-1) bits per channel use in the synchronous multiple-access situation to at least (M-1)/spl middot/ln (2) bits per channel use in the asynchronous situation. In particular, the result shows that for instance, for multitone M-ary frequency shift keying multiple access, in asynchronous operation, multiple user interference reduces the capacity maximally by a factor ln(2)=0.693 relative to the ideal TDMA system.

A universal space vector modulation strategy based on regular-sampled pulse-width modulation [invertors]

Abstract: A universal space vector modulation (USVM) strategy based on regular-sampled PWM technique is presented which minimizes the switching losses. It is shown that the reduction of the switching losses results from the selected null switching states inverter control. Moreover, it is shown that the simple universal space vector modulation strategy can be implemented in software using a digital signal processor in real-time. Simulation and experimental results are presented to confirm the theoretical analysis.

Enhanced resolution pulse width modulation control

Abstract: A pulse width modulation system provides for enhanced output resolution through software control. The pulse width modulation control system normally has a control period during which the pulse width modulation state assumes a predetermined one of a plurality of output states. The method herein toggles between two adjacent output states during any single control period to effectuate a resultant system response characteristic of a system having a greater number of available output states. Furthermore, certain preferred implementations may also suppress undesirable harmonic excitation of the system through quasi-random toggling.

Performance analysis and channel capacity for multiple-pulse position modulation on multipath channels

Abstract: Although multiple pulse-position modulation performs well on ideal channels, its performance on multipath channels is degraded significantly. In an attempt to quantify the inherent penalty due to multipath dispersion, we evaluate upper bounds for the error probability of each modulation scheme in the presence of intersymbol interference, considering both an unequalized receiver and the optimal maximum-likelihood sequence detection receiver. We also present upper and lower bounds of the channel capacity for multiple pulse-position modulation and its variants, PPM and overlapping PPM. Numerical results show that the PPM-based schemes are significantly more sensitive to multipath dispersion than is on-off keying.

Selection of an optimal modulation scheme for digital communications over low voltage power lines

Abstract: There is an ever increasing demand for environmental management of buildings, office automation, security monitoring or remote control of customer appliances and remote meter reading. The AC low voltage power line would be an ideal communications medium for digital data. Several systems for power line communications (PLC) were presented. The reliability of PLC is strongly influenced by time-variant and frequency-selective attenuation and interference on the power line channel. Various experiments were made to evaluate different PLC systems and set up a channel model. This paper gives a short summary of typical transfer characteristics and interference to be observed at power line networks. It is shown that at transmission over a single phase of the power supply system the maximum phase jitter of the time-variant transfer function is in most cases below 90/spl deg/. In the second part important modulation schemes are evaluated for applicability to power line communications. This evaluation considers chirp modulation, direct sequencing phase shift keying modulation (PN/PSK) and hopping techniques with spectral redundancy given by carriers with M different frequencies. The selection of the optimal modulation technique considers the European standard EN 50065, which restricts both the frequency range and the maximum signal amplitude. This paper deals with modulation schemes, using M frequencies, namely classic frequency hopping modulation (MFH) and the multifrequency,phase modulation (MFH/PSK and MF/PSK). Significant advantages of M frequency phase modulation in comparison with classic frequency hopping are pointed out.

Performance of modulation‐level‐controlled adaptive modulation systems

Abstract: The multivalued quadrature amplitude modulation (QAM), such as 16 QAM, is a very useful technique in land mobile communication since a high-speed transmission can be realized without enlarging the transmission band. The technique has a problem, however, in that it is not robust against the decrease of the received signal level due to fading or the effect of the delayed waves, which easily deteriorates the transmission quality. To solve such a problem, this paper proposes an adaptive modulation system where the number of modulation levels is adjusted according to the condition of the channel. In the proposed system, the instantaneous C/N0 and the delay spread are estimated as the condition of the channel, using a method based on time division multiple access/time division duplex (TDMA/TDD). When the channel is in a good situation, a highspeed transmission is executed using a larger number of modulation levels such as 256 QAM. When the channel is in a bad condition, a modulation method with a small number of modulation levels, such as quadraphase-shift keying (QPSK), is used, which is robust against the noise or the delayed waves. By this scheme, it is possible to realize a high-speed transmission without deteriorating the transmission quality, compared to the conventional system with the fixed number of modulation levels. The transmission performance is evaluated by a computer simulation, and it is shown that a high-speed transmission can be realized without deteriorating the transmission quality, compared to the QPSK system, in the uniform Rayleigh fading condition as well as in the situation containing delayed waves.

Trellis-coded pulse-position modulation for indoor wireless infrared communications

Abstract: We analyze the performance of trellis-coded pulse-position modulation (PPM) on indoor, wireless infrared channels. We show that maximum-likelihood sequence detection (MLSD) of trellis-coded PPM is very effective in mitigating the multipath dispersion on such channels. We present code search results for high constraint-length, rate-2/3, 8-PPM and rate-3/4, 16-PPM codes. We provide bit-error-rate curves and intersymbol interference power penalties for MLSD of PPM with these codes, evaluated on ceiling-bounce channel models with delay spread per bit duration ratios of 0.02 to 0.3. Finally, we present Monte Carlo simulation results to verify our analysis.

Digital pulse interval modulation for optical free space communication links

Abstract: This paper introduces digital pulse interval modulation (DPIM), a new form of pulse time modulation format well-suited to use in free-space optical-links by virtue of its simplicity, increased transmission capacity and the absence of receiver synchronisation problems. Theoretical expressions are presented for transmission capacity, code characteristics and power spectral density, along with measurement from an experimental free-space prototype, showing the advantages of this new modulation scheme.

Integrators in Pulse Width Modulation

Abstract: Many control methods for switching circuits employ an integrator to realize Pulse-Width-Modulation. Depending how the integrator is used, the dynamic performance differs greatly. This paper presents a systematic evaluation of the function of integrators in some representative integrator related PWM methods, such as ASDTIC control, Delta/Delta-Sigma Modulation, Modulated Integral Control, and One-Cycle Con- trol. In general, zero steady-state error is granted for all meth- ods. Further, the variable frequency controU methods are able to achieve onecycle dynamic response. In the constant frequency category, however, only the OneCycle Control method achieves one-cycle dynamic response, ie, it realizes zero dynamic track- ing error in the cycle average sense. In this paper, performance enhancement rules were explored for variblle frequency control method in order to reduce the frequency variation. all methods. For the One-Cycle Control method, a pulse position modulation effect is identified which deteriorates the perturbation rejection ability of the single-side modulated One-Cycle Control method in the high frequency range. As a result, a double-side modula- tion is propold that effectively reduces this effect. In addition, a fast reset mechanism is suggested that improves the switching error correction. This paper also provides a general approach to use integr&)tors in PWM to realize arbitrary function.

Circuit and system challenges in IR wireless communication

Abstract: IR wireless transceivers pose interesting challenges for circuit design. There are two basic types of IR wireless transmission: 1) directed, where the transmitting device must be pointed at the receiver, and 2) diffuse, where the IR signal is emitted into a large solid angle and receiving devices collect the signal reflected off walls and ceiling, thus requiring little or no pointing. Unlike RF, IR schemes employ baseband modulation. At data rates up to 60 kb/s, amplitude shift keying has been used. At higher data rates, RZI or pulse position modulation data encoding schemes (L-PPM where L is the number of slots) are used for more efficient modulation.

M-ary FSK signalling for incoherent all-optical CDMA networks

Abstract: We present a novel approach for the combination of M-ary FSK data signalling with incoherent all-optical code division multiple access (CDMA) systems In contrast to well-known pulse position modulation (PPM) schemes no critical frame synchronisation is necessary and less frequencies than in wavelength division multiplexing (WDM) are needed, resulting in an improved performance The M-ary source coding leads to a lower repetition rate of the used tunable mode locked laser or to a higher data rate than in OOK/CDMA systems The filter bank of the maximum likelihood detector can be easily realized by arrayed waveguides The theoretical performance for optical orthogonal codes (OOC) is analysed and a comparison to OOK and PPM is given

Pulse position modulation protocol

Abstract: Methods and apparatus for use in communication between a remote control and a receiving unit provide power saving modes of operation and enable remote control use of high data generating devices, such as a trackball. A pulse position modulation protocol is provided in which the position of a single pulse, such as an infrared pulse is located in time in one of three or more locations. In the preferred embodiment, the pulse is provided at least in one of eight states, and more preferably in one of sixteen states. In the latter arrangement, a single bit provides for a hex data output by a single pulse. In this way, a single pulse may substitute for what otherwise would have been multiple pulses in a binary protocol. Power savings may be achieved through this method. A time base compensation method is provided in which the remote control provides two detectable events separated by a predetermined time as measured by the remote control time base or clock. The receiving unit measures the time difference between the two events as determined by the receiver's time base or clock. A correction factor is then applied to subsequent detections of time differences between events as sent by the remote control. In the preferred embodiment, a multiplicative factor is applied. Dual protocol remote control devices may be provided wherein a first protocol is utilized in conjunction with a second protocol comprising the pulse position modulated system, such as the hex based system. In this manner, a binary protocol may be utilized for lower channel or lower data transfer arrangements and the pulse position modulation protocol may be utilized for relatively high data generating devices, such as a trackball. The protocol is advantageously utilized with high key identification numbers, such as those above 255.

Random discrete PWM method for DC-DC power converters

Abstract: A random discrete pulse-width modulation (RDPWM) scheme is examined and compared with the randomised pulse-position modulation (RPPM) method for DC-DC power conversion. The RDPWM method has no switching harmonics while the RPPM method has significant switching harmonics. Power spectral characteristics of the two methods are presented and discussed.

Decision-feedback equalization of pulse-position modulation on measured non-directed indoor infrared channels

Abstract: We examine the performance of two decision-feedback equalizers (DFEs) for pulse-position modulation (PPM) on measured non-directed indoor infrared channels with intersymbol interference (ISI). PPM offers high average-power efficiency, but on ISI channels, unequalized PPM suffers severe performance penalties. We have previously examined the performance of the maximum-likelihood sequence detector (MLSD), and found that it yields significant improvements. However the MLSD often requires such large complexity and delay that it may be impractical. We investigate suboptimal, reduced-complexity equalization techniques for PPM, providing a performance analysis of zero-forcing chip-rate and symbol-rate DFEs. Detailed performance results for 2-, 4-, 8-, and 16-PPM links at bit rates of 10 Mb/s and 30 Mb/s over 46 actual measured indoor infrared channels are presented for these two DFEs. Our results show that a symbol-rate DFE provides performance that closely approaches that of the optimal MLSD.

Dual protocol remote control

Abstract: Methods and apparatus for use in communication between a remote control and a receiving unit provide power saving modes of operation and enable remote control use of high data generating devices, such as a trackball. A pulse position modulation protocol is provided in which the position of a single pulse, such as an infrared pulse is located in time in one of three or more locations. In the preferred embodiment, the pulse is provided at least in one of eight states, and more preferably in one of sixteen states. In the latter arrangement, a single bit provides for a hex data output by a single pulse. In this way, a single pulse may substitute for what otherwise would have been multiple pulses in a binary protocol. Power savings may be achieved through this method. A time base compensation method is provided in which the remote control provides two detectable events separated by a predetermined time as measured by the remote control time base or clock. The receiving unit measures the time difference between the two events as determined by the receiver's time base or clock. A correction factor is then applied to subsequent detections of time differences between events as sent by the remote control. In the preferred embodiment, a multiplicative factor is applied. Dual protocol remote control devices may be provided wherein a first protocol is utilized in conjunction with a second protocol comprising the pulse position modulated system, such as the hex based system. In this manner, a binary protocol may be utilized for lower channel or lower data transfer arrangements and the pulse position modulation protocol may be utilized for relatively high data generating devices, such as a trackball. The protocol is advantageously utilized with high key identification numbers, such as those above 255.

Security vulnerability in coherence modulation communication systems

Abstract: A simple method for detecting a signal encoded by coherence modulation without the use of any decoder interferometer is demonstrated. The technique is based on wavelength filtering of the channelled spectrum in the transmission link. To overcome this vulnerability in the scheme, more secure coherence modulation arrangements are proposed.

Digital pulse interval and width modulation

Abstract: This article investigates the implementation of a new digital pulse-time modulation (PTM) technique based on a digital pulse internal and width modulation (DPIWM) scheme. Original expressions are presented for code characterization, channel capacity, and power spectral density. These illustrate the advantages of this scheme compared with conventional pulse-code modulation (PCM). Both theoretical and simulated spectral results are given, and are shown to be in close agreement.

Performance analysis of indoor infrared wireless networks utilising PPM CDMA

Abstract: A hybrid based on pulse position modulation code division multiple access (PPM CDMA) is studied in the context of the indoor infrared LAN. The utilisation of optical orthogonal codes (OOC) as signature sequences is investigated. Original results are presented illustrating the improvement in bit rate achieved by utilising PPM CDMA rather than on-off keying (OOK) CDMA. It is demonstrated that there exists an optimum PPM order, at a given number of users. Original results are presented that evaluate the dispersion in the optical diffuse infrared channel and its effects on optical orthogonal codes (OOC). A new equalisation technique is introduced and analysed in the context of this channel. The method is shown to be effective in reducing the resultant intersymbol interference (ISI). Illustrative examples are given on an isolated pulse and a typical OOC. The results indicate that good performance can be achieved with minimum hardware overheads.

Performance analysis of multi-pulse pulse position modulation using avalanche photodiode in optical intersatellite links

Abstract: The performance of multi-pulse pulse position modulation (MPPM) using an avalanche photo diode (APD) is evaluated in optical inter satellite links (ISL's). We derive theoretical expression of bit error rate (BER) of MPPM with output statistics of APD which employ Gaussian distribution. We evaluate BER performance under the conditions that bit rate is constant (200 Mbits/s) and that bandwidth is limited (slot time period is 2.5 ns). The performance of (7,2) MPPM and (9,2) MPPM are compared with that of 4-ary PPM under both conditions. It is shown that (9,Z) MPPM using the APD has better BER performance than 4-ary PPM using the APD in optical ISL's on both conditions when average photons/nat is somewhat large.