Showing papers on "Pulse-position modulation published in 1983"

Prime sequences: quasi-optimal sequences for OR channel code division multiplexing

Abstract: A new family of multiplexing sequences suitable for low duty cycle pulse position modulation schemes and for frequency hopped stread spectrum systems is introduced. The sequences have maxima in their crosscorrelation functions of two or one.

Pulse-Position Modulation for Transmission Over Optical Fibers with Direct or Heterodyne Detection

Abstract: The best monomode optical fiber links have bandwidths orders of magnitude greater than that of the information currently transmitted over them. This excess bandwidth can be exploited using digital PPM to improve receiver sensitivity. This paper analyzes the receiver sensitivity of an optical PPM system over a slightly dispersive channel, i.e., where both "wrong slot" and "false alarm" errors are important. It is shown that receiver sensitivity of better than 100 photons per binary bit-time is theoretically possible using direct detection and uncoded PPM. Ideal heterodyne detection should reduce this to below 5 photons per binary bit-time. Timing extraction and a digital modulation method are discussed.

Optical communication system using pulse position modulation

Abstract: An optical communication system using digital pulse position modulation employs a mode locked laser with a mode locking frequency equal to the time slot frequency of the modulation and means dependent on groups of consecutive digits of the data to be transmitted to select pulses from the laser for transmission. In one example, 4-bit groups from the data for transmission select one out of 20 pulses from the laser thus leaving a guard interval of 4 time slot periods between position modulated pulses. An encoder and a decoder for converting between digitally encoded data and position modulated pulses are described. These use a counter driven by clock pulses at the time slot frequency to supply inputs alternately to two encoding logic circuits or two multiplexers.

Q-switched semiconductor diode lasers

Abstract: Diode lasers with an intracavity electroabsorption modulator have been operated with full on/off modulation at rates of 3 GHz. In addition, modulation of the lasers has been shown up to a detector-limited frequency of 6 GHz. A new model of these devices, which includes amplified spontaneous emission and high gain is developed in this paper. A quasi-static gain approximation is introduced and the dynamics of the electron and photon population are modeled by three coupled nonlinear difference equations which can be numerically solved with very little computation time. The model predicts the possibility of a new mode of Q -switched operation with the capacity for repetition rates of tens of gigahertz and binary pulse position modulation at rates of the order of 10 Gbits/s.

Design of Coding and Modulation for Power-Efficient Use of a Band-Limited Optical Channel

Abstract: We show that Q -ary pulse-position modulation with raised cosine pulses minimizes the average power (photons/s) required to communicate at a specified throughput rate (nats/s) over a band-limited, noisy optical channel. The best choice of Q is identified, as are other encoder parameters.

Pulse code modulation rate converter

Abstract: A pulse code modulation rate converter is described for interfacing into aommunication system, apparatus designed for operation at two different, and specific, transmission rates.

Towards the fundamental limits of optical-fiber communications

Abstract: We review the theoretical limits which restrict transmission over optical fibers. The fundamental limit on channel capacity is 1 nat/photon with a coherent detection receiver or with a thermal-noise-limited receiver. With an ideal photon-counting receiver, the theoretical capacity is infinite. A practical limit of a few nats per photon for direct detection requires a bandwidth expansion consistent with monomode fibers and fast digital circuits and is 35-40 dB better than current direct detection receivers. This limit may be approached by receiver improvements (10 dB with direct detection, 17 dB with optimum coherent detection), by using digital pulse-position modulation (PPM) (10-13 dB) and by using error-correcting codes where constraints on system complexity allow.

Optimization of low-frequency properties of eight-to-fourteen modulation

Abstract: A description is given of the eight to fourteen modulation system (EFM) designed for the Compact Disc Digital Audio System with optical read-out. EFM combines high information density and immunity to tolerances in the light path with low power at the low-frequency end of the modulation bit stream spectrum. In this modulation scheme, blocks of eight data input bits are transformed into fourteen channel bits, which follow certain minimum and maximum run-length constraints by using a code book. To prevent violation of the minimum and maximum run-length constraints a certain number of merging bits are needed to concatenate the blocks. There are cases where the merging bits are not uniquely determined by the concatenation rules. This freedom of choice thus created is used for minimizing the power of the modulated bit sequence at low frequencies. The paper presents the results of algorithms that were used to minimize this low frequency content.

A Simplified Method for Prediction of Multipath Fading Outage of Digital Radio

Abstract: We propose a simplified method based on the correlated Rayleigh probability distribution of in-band radio signals. It can be efficiently applied to the calculation of the outage for various radio path length, propagation terrain, radio frequency, bandwidth, and digital modulation techniques. Predicted results are compared to various propagation data.

Decoding with Stretched Pulses in Laser PPM Communications

Abstract: The design and performance of optical PPM communication systems with ideal (rectangular) pulses have been well documented. However, many optical channels (fibers, atmosphere, clouds) are extremely dispersive to narrow pulses, producing receiver pulses that are spread (stretched) in time. This stretching produces interslot interference within a PPM frame, and if severe enough, can stretch over several frames (intersymbol interference). In this paper, laser pulse stretching in optical PPM formats is investigated in terms of performance degradation and decoder design alternatives. Several methods are considered for combating the pulse stretching, including pulse equalization, extended pulse integration, and pulse shape matching. Performance of these methods is compared for the case of exponential stretching and Gaussian statistics.

On continuous phase modulation in cellular digital mobile radio systems

Abstract: This paper considers the application of constant-amplitude, partial-response, continuous-phase modulation with simple near-optimum receivers to cellular digital mobile radio systems. These smoothed modulation schemes have low spectral sidelobes and narrow main lobes. A combiner for time-division retransmission systems with space diversity is given for continuous-phase modulation. Cochannel interference and adjacent-channel interference are calculated for continuous-phase modulation in cellular systems with frequency reuse. The efficiency of 3RC and 4RC modulations with space diversity is evaluated for conventional cellular systems.

Error exponents for a direct detection optical channel

Abstract: Error exponent bounds for a noise free optical channel using a direct detection receiver are computed for the cases of Pulse Position Modulation (PPM) and for the basic channel with binary output and average intensity constraint. Some consequences are derived regarding the behavior of the interleaving scheme suggested by Massey, the optimality of the PPM format and the significance of the Ro parameter.

Modulation circuit of a digital-to-analog converter

Abstract: A modulation circuit of a D/A converter comprises a pulse number modulation circuit for modulating some bits of digital data and for dispersing a pulse or pulses in one or more resultant pulses, a pulse width modulation circuit for modulating the remain bits of the digital data and for dividing pulses in a resultant pulse train and a combination circuit for combining and positioning at least one pulse in the pulse train adjacent the pulse or pulses in the one or more resultant pulses formed by the pulse number modulation circuit.

An Integrated Voice-Data Communication System for VHF Links

Abstract: In this work, a combined amplitude-phase modulation communication system is considered. Amplitude modulation is used to transmit a voice signal, and phase modulation is used for data transmission. Such a scheme was studied as a possible realization of a data channel between aircraft and ground station, which can be introduced without great modifications of the actual on-board equipment. The performance of the combined modulation system is evaluated through a computer simulation.

Signal-to-noise performance of the pulse-interval and width-modulation system

Abstract: A simple formula for the signal-to-noise ratio at the output of the pulse-interval and width-modulation (PIWM) system is derived. The predicted performance is compared with measured data obtained from a hardware model of the system. Simulation results are in good agreement with predictions.

On the tandem connection of differential encoding systems: The case of cascaded quantizers

Abstract: A tandem differential pulse code modulation (DPCM) system structure is developed and the design problem formulated. In the simplified case of cascaded quantizers, the low-to-high and high-to-low bit rate tandems are examined and the performance limitations discussed, Finally the performance of tandem DPCM systems operating at various bit rates is evaluated by simulation.

Q-Switched Semiconductor Diode Lasers With Integrated Modulators

Abstract: Q-switched semiconductor diode lasers with an integrated modulator have been operated with full on/off modulation at rates of 3 GHz. In addition, modulation of the lasers has been shown up to a detector-limited frequency of 6 GHz. A new model of these devices, which includes amplified spontaneous emission and high gain, predicts the possibility of a new mode of Q-switched operation with the capacity for repetition rates of tens of gigahertz and binary pulse position modulation at rates of the order of 10 Gbit/sec.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Error performance of single pulse ppk system with maximum value type decision model

Abstract: The error performance of single pulse PPK system with maximum value type decision model is discussed in this paper. The word error probability in the case when noises exist is analysed and the energy necessary for transmitting each information bit is calculated. The detection characteristics of this system are made clear by comparing it with a threshold type decision model and ordinary systems. It is shown that the maximum value type of decision scheme is always superior to the threshold type. It can reduce the word error probability of PPK system further or make the energy efficiency of PPK system higher under the condition of given tolerable error probability. INTRODUCTION In 1980, a digitized 2-ary pulse communication system(being called PCM-PPK telemetry system) was presented by Li You-Ping(1). A feasible decision device model based on using “time checked” synchronization was introduced. It was shown that the energy efficiency of single pulse PPK system is higher than that of ordinary binary systems. The decision model adopted in that paper was threshold type scheme. However its optimum decision threshold depends on signal-to-noise ratio (see appendix), and any deviation of decision threshold from the optimum value will have some effects on the performance of system(2). A decision scheme without threshold – the maximum value type decision model is discussed in this paper. There is no problem of selecting optimum threshold in this scheme. The analyses of word error probability and energy efficiency for this scheme show that using maximum value decision can make the word error probability of PPK system lower for a certain signal-to-noise ratio, or the energy efficiency will be higher for a given error probability. The value $ of the maximum value type scheme is 2 dB smaller than that of the threshold type, and 4 dB smaller than that of the binary PSK system roughly. MAXIMUM VALUE DECISION SCHEME The decision scheme presented in (1) can be simplified as Fig.1, where synchronous timing circuits are omitted. When a certain sample Uk exceeds the threshold level Uo the PPK/PCM converter (a counter in fact) will send a PCM data according to its sampling order number. This scheme can be called a threshold type decision scheme, or be abbreviated to PPK(TT). The selection of threshold value Uo depends on the length M of PCM data word, and the signal-to-noise ratio r. The optimum values \"opt of relative threshold \" = Uo /A(i.e. the ratio of the dicision threshold value Uo to the peak voltage A of IF signal) and the word error probability Pew under \"opt are listed in table A-1 and A-2 in appendix. The block diagram of maximum value type decision scheme, abbreviated to PPK (MV), is shown in Fig.2a. In this scheme the samples Uj are not directly compared with threshold level Uo. The N samples are compared each other in proper order,the largest one of them is considered as the sample of signal pulse, and the sampling order number of this sample is converted to corresponding PCM data by PPK/PCM conveter. The engineering realization of maximum value selector is not very complex, it may be constructed by ingeniously combining sample-hold circuits, comparator and digital circuits (Fig.2b). As long as the velocity permitting, it may consist of digital circuits only. WORD ERROR PROBABILITY AND ENERGY EFFICIENCY From the principle of PPK(MV), we know that, so long as the N-1 noise samples in space positions do not exceed the sample of signal with noise in signal position, the PPK signal can be decided correctly. Otherwise the word error will appear. It is well known that the output voltage Un of a envelope detector is subject to Reyleigh distribution when the signal is absent

Cutoff Rates for a Noisy Multiple Access Channel

Abstract: The cutoff rates for a discrete memoryless multiple access channel are important not only as measures of the maximum achievable data rates in practice but also as parameters in performance calculations. These parameters are evaluated for the case of hard decision signal detection on an L user channel with an M-ary signal set. Examples of applications are given from tone interference or partial band noise interference on the frequency shift keying (FSK) channel and photon counting on the photon pulse position modulation channel.