Showing papers on "Pulse-position modulation published in 1992"

Variable modulation communication method and system

Abstract: In a variable modulation communication method, the transmission quality of a transmission path is monitored. If the transmission quality is good, communication is performed while the transmission time is shortened by using a multilevel modulation scheme. If the transmission quality is bad, communication is performed while the transmission time is prolonged by using a modulation scheme having a smaller number of levels than the multilevel modulation scheme. A variable modulation communication apparatus is also disclosed.

Synchronous telemetry receiver and receiving method for an implantable medical device

Abstract: A synchronous telemetry receiver and receiving method for reception from an implantable medical device of a PPM signal including a plurality of bits each having a sync pulse and at least one data pulse of equal amplitude. Capability is provided for restoring correct phase in the event that a sync pulse is missing or incorrectly received for any reason. A high-frequency clock and counter are provided for counting clock pulses during the time interval between each data pulse and its respective sync pulse in order to obtain a measurement of the time interval.

Pulsed pen for use with a digitizer tablet

Abstract: An inductive pen (16) repetitively transmits pulses of an oscillatory signal having a characteristic frequency. Pen state information, such as pen tip contact switch information, are encoded by a number of techniques. These techniques include pulse width modulation or pulse position modulation, so as to convey pen state information to a digitizing tablet (10) in a manner that does not adversely affect pen position determinations. The pen state information may also be encoded on the oscillating signal by Frequency Shift Keying (FSK), Phase Shift Keying (PSK), or Amplitude Modulation (AM). A digitizer tablet (10) includes circuitry for detecting the transmitted pen state information, the circuitry accommodating the selected modulation scheme. The tablet (10) is responsive to the transmitted pulses for placing tablet circuitry in a low-power consumption state between pulses so as to conserve tablet power.

Spectral characterisation and frame synchronisation of optical fibre digital PPM

Abstract: The discrete time decoding of data in pulse position modulation calls for accurate timing synchronisation, particularly at the frame rate. In the Letter, for the first time the spectral properties of optical fibre digital PPM are considered. An original expression is presented for predicting the spectrum and it is shown that, unlike satellite PPM, a component exists at the frame rate which may be used for timing extraction purposes. Further, it is illustrated that the modulation index can be used to enhance this component by up to 19dB. This has been verified practically, with the results agreeing to within 1 dB of those predicted from the original expression presented.

Spread spectrum pulse position modulation-a simple approach for Shannon's limit-

Abstract: A spread spectrum pulse position modulation (SS-PPM) system is proposed and its basic performances are described. In many direct sequence spread spectrum (DS-SS) systems, each demodulator is desired to use an only pseudonoise (PN) matched filter for simple structure and low cost. Such systems as on-off keying (SS-OOK) or differential phase-shift keying (SS-DPSK) systems have been conventionally used. The present authors propose the spread spectrum pulse position modulation (SS-PPM) system as one of such systems, and show that the SS-PPM system has the following advantages: (1) higher data rate (about 4 times higher than the other conventional SS systems under the same bandwidth and the same code length), (2) superior performance of bit error rate (BER) to the other systems (BER characteristics of the SS-PPM system improves with increasing the number of chip slot of the SS-PPM system, and it approaches Shannon's limit). Furthermore they evaluate asynchronous CDMA performance of the SS-PPM system by theory and computer simulation. >

A comparison of coherent digital PPM with PCM

Abstract: Digital pulse position modulation (PPM) is a preferred modulation format for the ideal photon counting channel and optical intersateilite links. Here we examine its potential for the coherent optical fibre communications channel. We present a thorough performance and optimisation analysis. Comparisons, at a wavelength of 1.5 m, are made with shot-noise limited coherent PCM (homodyne and heterodyne ASK, FSK and PSK) over a range of fibre band-widths and varying PPM word size. We conclude that for moderate to high fibre bandwidths homodyne digital PPM should achieve an improvement in sensitivity of typically 5 dB over homo-dyne PSK PCM

Differentially coded and guard pulse position modulation for communication networks

Abstract: In a wireless infrared communications system, a technique for encoding data for serial transmission and the correlative technique for decoding the transmitted data. A data transmission period is divided into a plurality of slots. In a given pair of slots, the first slot comprises a gray code sequence of bits and a check bit, and the second slot comprises the same gray code sequence of bits and the complement of the check bit in the first slot. The last slot in a transmission time period comprises a guard slot to separate transmission time periods. A decoder receives the encoded data, and for a given slot derives calculated data for the slot from the gray code sequence of bits and the check bit. The check bit for the given slot is compared with a calculated check bit of the previous slot to determine if a predetermined relationship exists. If the predetermined relationship exists, the received encoded data is selected as the output of the decoder, and if the predetermined relationship does not exist, the calculated data is selected as the output of the decoder. The calculated check bit is derived from the output of the decoder for a slot, and is compared with the check bit of the encoded data for the following slot.

Frame synchronization for optical overlapping pulse-position modulation systems

Abstract: The maximum-likelihood rules for locating data frames in direct-detection optical communication systems utilizing overlapping pulse-position modulation (OPPM) are derived under two distinct assumptions of symbol and chip synchronization, respectively. Various approximations to the optimal rules are identified, as well as upper and lower bounds on the probability of correct synchronization. Further, the problem of sequence design based on a maximum peak-to-sidelobe distance criterion is studied, and upper bounds on peak-to-sidelobe distance for sequences of OPPM symbols are derived. Some good sequences are obtained through a computer search. >

A preliminary performance evaluation of a linear frequency hopped modem

Abstract: The benefits of using linear modulation methods for a frequency hopping (FH) transmission system in narrowband, i.e., voice cellular networks, are considered. In particular, the use of a 16-level modulation scheme derived from 16 QAM combined with FH is evaluated operating in a channel subject to noise and multipath fading, characteristic of the mobile environment. >

Reed-Solomon coded homodyne digital pulse position modulation

Abstract: A performance and optimisation analysis for both uncoded homodyne digital PPM and digital PPM employing Reed-Solomon error-correction codes is presented. System performance for a range of fibre bandwidths and PPM symbol sizes is analysed, and it is shown how the predetection filter may be configured in order to minimise the three error sources and achieve maximum transmission efficiency (nats/photon). Results are presented at a bit rate of 565 Mbit/s and a wavelength of 1.5 mu m. It is shown that there are optimum PPM symbol sizes, fibre bandwidths and Reed-Solomon code rates at which to operate. The conclusion is that uncoded digital PPM offers an improvement of 5 dB over homodyne PSK PCM, and that the Reed-Solomon error-correction coded system offers a 4 dB improvement over uncoded PPM, when operating at the optimum 3/4 code rate.

Frame synchronization of optical fiber dppm with dispersed pulse shapes

Abstract: Optical 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.

Optical space communications employing pulse position modulation

Abstract: The authors review optical technologies for space communications. Initially the advantages of this technology are described and the tradeoffs between direct detection and coherent detection explained. As a model for deep space communications, the ideal photon counting channel is used and it is illustrated that the most efficient modulation format is pulse position modulation (PPM). They go on to consider optical sources and photodetectors and explain the reasoning that has led to the selection of GaAlAs semiconductor lasers and avalanche Si photodiode detectors. The channel configurations that are currently being pursued by NASA and ESA are described.

Demodulation processing circuit with time interval counting feature

Abstract: In a demodulation circuit for demodulating a pulse position modulation (PPM) signal, and a camera having the demodulation circuit, a change in PPM signal is counted by an up/down counter which is switched between count-up and count-down modes every time the PPM signal changes. When a carry signal is output from the counter, the carry signal is latched, and the PPM signal is demodulated into binary data on the basis of the presence/absence of the carry signal in the count-up mode and the carry signal in the count-down mode.

Optical digital pulse-position modulation: experimental results for heterodyne detection using suboptimal filtering

Abstract: Original practical and theoretical results are presented for heterodyne detection of optical digital pulse-position modulation (λ = 1.523 μm) employing suboptimal filtering. The measured sensitivity was –62.7 dBm when operating with a 20 ns slot width and 16 data-pulse positions. This represents an improvement of 16.8 dB over an equivalent suboptimal direct detection digital pulse-position modulation system. With –18 dBm of local oscillator power, the sensitivity was within 8.6 dB of the shot-noise limit.

ISI-reduced modulation over a fading multipath channel

Abstract: The idea of using the channel eigenvectors as the basis for a block based signaling scheme over a fading multipath channel is introduced. This basis minimizes the product of the average fading attenuations along different dimensions. The ISI from the preceding blocks (intra-block ISI) is modeled by an additive Gaussian noise. To reduce the effect of the intra-block ISI, a number of zeros are transmitted between successive blocks. The number of zeros is optimized to minimize the average probability of error. As the transmission of zeros reduces the bandwidth efficiency, this optimization procedure is more useful for lower bit rates. By applying quadrature amplitude modulation (QAM) to each dimension, a set of two-dimensional subchannels with unequal fadings is obtained. A coherent M-PSK constellation is employed over each QAM subchannel. The authors propose two methods to distribute the rate and energy between the subchannels. >

PPM versus PCM for optical local-area networks

Abstract: Pulse-position modulation (PPM) is presented within the context of a local-area network (LAN) application. A simplified analysis is used to calculate the advantage of converting from pulse-code modulation (PCM) to PPM signalling in a LAN, assuming in each case the same fibre network and the same optical transmitting device. Although PPM exploits its wide bandwidth to give greater sensitivity in noise, the true system advantage is obtainable only by using a large peak-to-mean-power ratio in the transmitter. It is shown that this performance is possible for both a laser diode and for an edge-emitting LED. An experimental system is reported, operating at a data rate of 4 Mbit/s, and good correspondence with theory is obtained. Design procedures are given for broad classes of situation.

Optical fiber n-ary PPM: the question of slot synchronization

Abstract: An original model is established and used to predict the spectral properties of optical fiber pulse position modulation (PPM). A suitable random variable is built into the model to represent the stochastic data sequence encoded. The spectral prediction is then used to examine the problem of slot synchronization under two conditions, first when the channel dispersion is negligible, then when Gaussian type pulses are received. The model is shown to be capable of catering for the different PPM parameters and is used to optimize slot synchronization using these parameters under each of the two conditions. Practical results measured on a PPM system are given and shown to agree with the theoretical predictions, concluding with those conditions that optimize slot synchronization.

Spread spectrum pulse position modulation communication system

Abstract: PURPOSE:To realize the reception system offering higher performance than that of the on/off keying system with only one matched filter by sending a specific filter. CONSTITUTION:A pseudo noise series whose period is L is used and a data symbol to be sent is an M value, and one frame consists of M+L-1+j slot (j>=0). Moreover, a transmitter consists of a module M+L-1+j counter 2, an M detector 3, a comparator 4, a serial parallel converter 5, a module M adder 6, a register 8, a pseudo noise(PN) signal generator 9, and a modulator 10. Then the pseudo noise of an L slot length starting from one slot in an M value from the start of the frame is inserted and the inserted slot position of the pseudo noise is made correspondent to the data symbol and the data symbol is subject to differential coding and a consecutive frame is sent. Thus, the higher performance than that of the on/off keying system is attained and the performance close to the code shift keying is realized with only one matched filter.

Experimental error correction results for optical digital pulse-position modulation

Abstract: Original practical and theorical results are presented for the detection and correction of errors in a direct detection optical (λ = 1.523 μm) digital pulse-position modulation (digital PPM) system. These results show the degradation in system performance due to interframe interference and an original method of correcting this type of error is presented. This error correcting method was then used to enhance the performance of a Reed-Solomon (RS) coded, digital PPM system.

Numerical simulation of a 325 Mbit/s QPPM optical communication system

Abstract: Optical digital receivers are being considered for intersatellite laser communication links. A demonstration system is being designed to operate at 325 MBit/s, using quaternary pulse position modulation (QPPM). Laboratory experiments have been conducted using a 50 MBit/s prototype system. A numerical model has been developed to simulate a QPPM optical receiver. The 50 MBit/s system was simulated to verify the validity of the model. The model was then used to simulate the projected behavior of the 325 MBit/s system. The model predicts a bit error rate of 10.6 at 38 incident photons per bit for 820 nm light.

10.6-μm laser heterodyne system with acousto-optic frequency modulation

Abstract: A 10.6-micron laser heterodyne receiving system with acoustooptic frequency modulation is described. In this system, the first-order diffraction beams are used as the optical signal modulation beam in the transmitting optical terminal, a 77 K-PV-HgCdTe detector is used as heterodyne reception device in the receiving optical teminal, and the Stark cells are used in the transmission and reception terminals in order to stabilize the frequencies of local and signal laser. With the application of frequency shift key digital modulation, the terminal bit error rate is better than 10 exp -8.

Comprehensive performance analysis of radars using different types of sweep modulation

Abstract: A comprehensive analysis of different types of sweep modulation is presented, together with suggestions for the transmitting pulse which fulfil the basic requirements of modern radars. Linear frequency modulation is effective at lower altitudes under the condition that the time-bandwidth product is not too large. Exponential modulation is suited to medium altitudes, and linear period modulation to higher altitudes. >

Network performance of time spread PPM/CDMA systems

Abstract: A model for time spread-pulse position modulation (TS-PPM)/code division multiple access (CDMA) systems is presented. A TS signal is produced by a TS-filter, whose characteristic is a pseudonoise sequence in the frequency domain. The error probability performance is analyzed and compared with those of on-off keying (OOK) and binary phase shift keying (BPSK). It is shown that at the same transmission speed TS-PPM is superior to TS-OOK and TS-BPSK due to the dramatic decrease of multiple access interference. The throughput of the network is analyzed, and its relation to the length of pseudonoise sequence and the packet length is also discussed. >

Pulse position modulation for distribution of video signals on optical fiber

Abstract: Optical fiber distribution networks are being exploited for the provision of video and other wide band services. Digital transmission of these signals is expensive because of the requirement for a complex and costly codec. For short length subscriber links, analog transmission could be preferred for the low cost of the modulator. This thesis investigates the performance of multichannel video transmission over optical fibers using pulse position modulation (PPM). The performance of PPM is compared to amplitude modulation vestigial sideband (AM-VSB), frequency modulation (FM), and pulse code modulation (PCM), in terms of the demodulated signal-to-noise ratio (SNR) relative to the SNR at the optical receiver. It is shown that PPM SNR performance is comparable to PCM and FM modulation methods. Furthermore, PPM permits some transmission nonlinearity and allows the use of low cost optical transmitters. Integrated services using PPM video signals and multiplexed PCM voice and data signals are also possible.

Pulse forming network bank for pulse pair generation in gas lasers

Abstract: A gas laser with the ability to perform at a high repetition rate without a large increase in average output power requirement, resulting in smaller lasers, smaller power supplies, smaller pulse forming networks and lower power consumption than is required in prior art devices. There is provided a unique pulse-forming network (PFN) bank wherein two energy storage capacitors (125, 135) are charged simultaneously and discharged sequentially into the same gas laser (140) to generates a pair of high peak power laser pulses. The time interval between the two pulses is limited only by the recovery time of a high voltage switch. A gas laser provided with the network in accordance with the present invention transmits information by pulse position modulation (PPM) . The information content is limited only by the jitter of the high voltage switch (80, 90). A laser transmitting information by PPM can easily contain in two pulses what a laser transmitting pulse code modulation (PCM) can contain in twelve pulses. Without the present invention, a gas laser requires a much larger power supply to transmit information by PPM because it must recharge the PFN between lasings. Since a gas laser utilizing the PFN in accordance with the present invention does not recharge between lasings, it can also provide shorter inter-pulse timing.

Performance measurement results for a 220 Mbps QPPM optical communication receiver with an EG/G Slik APD

Abstract: The performance of a 220 Mbps quaternary pulse position modulation (QPPM) optical communication receiver with a 'Slik' silicon avalanche photodiode (APD) and a wideband transimpedance preamplifier in a small hybrid circuit module was measured. The receiver performance had been poor due to the lack of a wideband and low noise transimpedance preamplifier. With the new APB preamplifier module, the receiver achieved a bit error rate (BER) of 10 exp -6 at an average received input optical signal power of 4.2 nW, which corresponds to an average of 80 received (incident) signal photons per information bit.

The design and implementation of a 7B2-16 optical digital PPM line code

Abstract: Considers the design and implementation of a 7B2-16 line code for an optical fibre digital PPM system employing a PIN-FET receiver. A code word map is presented and the encoder state probability distribution evaluated. The 7B2-16 code has an efficiency of 87.5% and it has been designed such that the redundancy is used to minimise the timing jitter associated with large pulse position disparities. A low-speed coder has been implemented and practical results show that the jitter is reduced to 18% of that of the uncoded case. >

New formulation and plots for error probability in the pulse position modulation (PPM) photon counting satellite-to-earth channel

Abstract: In digital satellite-to-earth transmission the entry of substantial undesired solar radiation into the receiver antenna is sometimes unavoidable. When the signal transmission takes the form of incoherent optical pulse position modulation (PPM) the parameters of signal and consequent intense noise can fall outside the range of routinely available classical numerical results on symbol error probability. This paper presents an alternative system for parametrization of signal and noise in the classical PPM channel, i.e. that characterized by Poisson photon arrival statistics for signal itself, the noise itself, and the signal plus noise. The resulting formulation for error probability, the scheme for probability calculation, and the simple, compact plots of error probability versus newly conceived parameters cover the entire range of signal and noise intensities, from weakest to strongest. Of course, when properly interpreted the new results agree entirely with classically available numerical results within the parametric range of the former.