Showing papers on "Pulse-position modulation published in 1987"

Trellis-coded modulation with redundant signal sets Part I: Introduction

Abstract: rellis-Coded Modulation (TCM) has evolved over the past decade as a combined coding and modulation technique for digital transmission over band-limited channels. Its main attraction comes from the fact that it allows the achievement of significant coding gains over conventional uncoded multilevel modulation without compromising bandwidth efficiency. T h e first TCM schemes were proposed in 1976 [I]. Following a more detailed publication [2] in 1982, an explosion of research and actual implementations of TCM took place, to the point where today there is a good understanding of the theory and capabilities of TCM methods. In Part 1 of this two-part article, an introduction into TCM is given. T h e reasons for the development of TCM are reviewed, and examples of simple TCM schemes are discussed. Part I1 [I51 provides further insight into code design and performance, and addresses. recent advances in TCM. TCM schemes employ redundant nonbinary modulation in combination with a finite-state encoder which governs the selection of modulation signals to generate coded signal sequences. In the receiver, the noisy signals are decoded by a soft-decision maximum-likelihood sequence decoder. Simple four-state TCM schemes can improve. the robustness of digital transmission against additive noise by 3 dB, compared to conventional , uncoded modulation. With more complex TCM schemes, the coding gain can reach 6 dB or more. These gains are obtained without bandwidth expansion or reduction of the effective information rate as required by traditional error-correction schemes. Shannon's information theory predicted the existence of coded modulation schemes with these characteristics more than three decades ago. T h e development of effective TCM techniques and today's signal-processing technology now allow these ,gains to be obtained in practice. Signal waveforms representing information sequences ~ are most impervious to noise-induced detection errors if they are very different from each other. Mathematically, this translates into therequirement that signal sequences should have large distance in Euclidean signal space. ~ T h e essential new concept of TCM that led to the afore-1 mentioned gains was to use signal-set expansion to I provide redundancy for coding, and to design coding and ' signal-mapping functions jointly so as to maximize ~ directly the \" free distance \" (minimum Euclidean distance) between coded signal sequences. This allowed the construction of modulation codes whose free distance significantly exceeded the minimum distance between uncoded modulation signals, at the same information rate, bandwidth, and signal power. The term \" …

Highly Efficient Digital Mobile Communications with a Linear Modulation Method

Abstract: Although linear modulation methods can achieve high spectrum efficiency, very little attention has been directed to their use in mobile radio systems. This is mainly due to the fact that the nonlinearity of the transmitter power amplifier tends to spread the spectrum and thus eliminate any spectrum efficiency advantage gained through the use of linear modulation methods. In this paper, a linear modulation system is proposed, which solves the above difficulty and which gives higher spectrum efficiency than conventional digital FM. The modulation/demodulation method is \pi /4 shift QPSK and phase-shift detection with a limiter-discriminator and an integrate-and-dump filter. By introducing a cartesian coordinate negative feedback control, 35 percent power efficiency at 10 W output power and - 60 dB relative out-of-band radiation are simultaneously achieved with a class "AB" amplifier, owing to the 29 dB feedback gain. The receiver configuration is easy to realize and gives immunity against fast fading through the use of noncoherent detection with limiter-discriminator. By using a novel decision method, bit error rate performances under both nonfading and fading condition are comparable to those obtained by digital FM. These results make it possible for linear modulation methods to achieve higher spectrum efficiency than is possible with conventional digital FM methods in mobile radio communications.

Acquisition sequences in PPM communications (Corresp.)

Abstract: In pulse position modulation (PPM) communications an acquisition sequence is needed to establish frame synchronization for subsequent data transmission. This sequence must have PPM structure (one pulse per frame) and desirable autocorrelation properties for its detection. The problem of finding aperiodic PPM acquisition sequences having the minimum possible autocorrelation for all off-shifted positions is investigated. Sequences with the maximum possible number of frames have been found up to frame size 15 . Examples are given for every frame length up to 88 , and powers of two up to 1024 . An interesting relation between the PPM sequence problem, Costas and sonar arrays, and Golomb's ruler is explored.

On Joint Symbol and Frame Synchronization for Direct-Detection Optical Communication Systems

Abstract: An approximate maximum-likelihood rule (ML) is derived for joint symbol and frame synchronization with pulse-position modulation, Simulation results show that this approximate rule performs virtually as well as the optimum ML rule over a wide range of practical signal-to-noise ratios. Yet it is substantially simpler to implement.

Carrier Phase and Clock Recovery for Continuous Phase Modulated Signals

Abstract: This paper presents an analysis of a synchronization circuit to be used for carrier-phase and symbol-timing recovery in continuous phase modulation systems. M -ary modulation formats with arbitrary pulse shaping and rational modulation indexes are assumed. Circuit performance is expressed in terms of variances of phase and timing errors. Numerical results are provided for some important cases, including minimum shift keying and tamed frequency modulation. Theoretical results are found in good agreement with computer simulations.

A power-efficient linear digital modulator and its application to an anti-multipath modulation PSK-RZ scheme

Abstract: This paper describes a new concept in modulation methods for high speed digital mobile communications. Linear modulation is introduced to allow amplitude variation in the modulated signal. This primarily brings the advantage that sharp cut-off band restriction can be performed to enhance the transmission efficiency. Also, we can adopt as a multipath strategy an amplitude-shift anti-multipath modulation technique, which is found to be more effective than its phase-shift counterpart. A linear modulation method is presented to meet the mobile radio requirement on power efficiency. We finally derive a narrow-band anti-multipath modulation scheme, with required bandwidth compatible with other narrow-band modulation techniques and with superior anti-multipath effect.

Optical disk and optical disk apparatus with error correction

Abstract: This invention relates to an optical disk, in which part of the sectors are reproduction-only sectors and remaining sectors are recording-reproduction sectors. Data and first error correcting codes for the data are recorded in advance in the reproduction-only sectors, and second error correcting codes for data over a plurality of reproduction-only sectors are recorded in advance in other reproduction-only sectors. At data reproduction, only sectors which are unrecoverable by the first error correction codes undergo error correction by the second error correcting codes, and the corrected data with the first error correcting codes being appended are recorded in the recording-reproduction sectors. Later on, when data in sectors unrecoverable by the first error correcting codes are needed, the above-mentioned recorded sectors are read out. Data storage about twice the capacity of the data recording areas is made possible by adopting the PWM (pulse width modulation) recording for the data reproduction-only area and the PPM (pulse position modulation) recording for the recording-reproduction area.

Multilevel QAM Modulation Techniques for Digital Microwave Radios

Abstract: A pilot carrier injection method is described together with feedback balance coding which reduces spectral power near the carrier. Robustness of carrier recovery using the pilot carrier injection method is theoretically estimated. The estimation suggests that recovered carrier SNR higher than 40 dB can be expected even under muitipath fading with notch depth of 45 dB located just at the carrier frequency. Signatures for multipath fading are estimated for a 64-QAM system with transversal equalizers as a countermeasure. Measured signatures agree reasonably well with the calculated ones. Dependences of signatures on modulation level, transversal equalizer tap number, and rolloff rate are also shown.

Optical Communications Link Design For The Tracking And Data Acquisition System

Abstract: The communications performances of laser intersatellite links for a future NASA data-relay system are analyzed, and block diagrams of necessary optical terminals are generated based on technology projected to be available by 1992. Direct-detection optical communications subsystems are selected to interconnect two geosynchronous (GEO) satellites separated by 160 deg along the GEO arc and to interconnect a low-earth-orbit (LEO) satellite and either of the GEO satellites. The terminal designs are based on power budget calculations performed for the various links with and without an optical background in either the receiver or transmitter fields of view (FOVs). Optical antennas with 18-cm and 30-cm primary mirror diameters on the LEO and GEO satellites can achieve a 0.000001 average bit error rate during normal operations in each of the forward and return optical links with beginning-of-life (BOL) power margins of approximately 7 dB. With an optical background in the receiver FOV, communications in the GEO-GEO return link are interrupted, the LEO-GEO return link is undegraded, and the GEO-GEO and LEO-GEO forward links remain functional with reduced BOL power margins. With an optical background in the transmitter FOV, the GEO-GEO forward and return links are noticeably degraded, the LEO-GEO return link is only slightly degraded, and the LEO-GEO forward link remains undegraded.

Performance Measurements Of A Diode Laser Optical Communications Link With Q=4 PPm Signaling

Abstract: The theoretical and measured performance characteristics of a direct detection optical communication system are reported. The system consisted of a semiconductor diode laser, silicon avalanche photodiode detector, and used Q = 4 optical pulse position modulation signaling to transmit binary source data at a rate of 25 megabits/sec. Operation at a receiver bit error probability of 10 to the -6th was demonstrated at received signal energies corresponding to an average of 160 detected photons per PPM symbol, or 80 photons per source bit.

Static driving device for liquid crystal indicator

Abstract: PURPOSE:To easily display a half tone by applying the pulse train of the pule width of a half period portion to a common electrode, bringing plural pulses and the first pulse of a pulse signal train having the pulse width of two times of said pulse, to a pulse position modulation in accordance with a variable density detecting signal, and applying them to a segment electrode. CONSTITUTION:The pulse train of the pulse width of a half period portion from a pulse signal generator 1 is applied to the common electrode of a liquid crystal indicator 5. Also, the variable density gradation of an inputted image signal is detected by a gradation detector 2, and applied to a pulse position modulator 3. By this modulator 3, the pulse of the pulse width of a half period portion from the generator 1, and one pulse in a pulse train consisting of one pulse having the pulse width of two times of said pulse are brought to a pulse position modulation in accordance with the variable density gradation from the detector 2. Also, a pulse position modulating signal is applied to each segment electrode of the indicator 5 from an LCD driver 4, and the image of an intermediate gradation is displayed easily.

Theoretical performance of direct detection optical communication with AlGaAs laser transmitters, avalanche photodiode detectors, and color-coded PPM signaling

Abstract: Theoretical performance characteristics are presented for a direct detection optical communication system that has peak power limited laser diode transmitters and avalanche photodiode photodetectors. The singal format consists of the transmission of a group of L binary source digits as a single light pulse at one of N nonoverlapping optical center frequencies (colors) in one of M possible time slots. The system achieves a given received symbol error probability at lower peak signal intensities with a less complicated receiver structure than can be obtained with an ordinary pulse position modulation system of the same alphabet size and source data rate.

Laser Diodes Communications For The European Data Relay System

Abstract: The use of optical communications for the high data-rate links of the future European Data Relay Satellite System has been receiving growing attention for the past few years. This paper presents a system design based upon GaALAs laser diodes transmitters and direct-detection receivers. A Wavelength Division Multiplexing technique is used to accomodate data-rates up to 500 Mb/s on the return link with moderate antenna diameters. Si CCD matrices are used as acquisition and tracking sensors, and angular error informations are extracted directly from the communication signal, thus avoiding the need for a dedicated tracking beacon. Expected performances are given ; The system is shown to be capable of supporting variable user requirements. The architecture of the terminals, including adequate redundancies, is described. Mass estimates are given.

Optical disk and optical disk apparatus

Abstract: This invention relates to an optical disk, in which part of the sectors are reproduction-only sectors (11A, 11B; 14A, 14B) and remaining sectors are recording-reproduction sectors (12, 15). Data and first error correcting codes for the data are recorded in advance in the reproduction-only sectors, and second error correcting codes for data over a plurality of reproduction-only sectors are recorded in advance in other reproduction-only sectors. At data reproduction, only sectors which are unrecoverable by the first error correction codes undergo error correction by the second error correcting codes, and the corrected data with the first error correcting codes being appended are recorded in the recording-reproduction sectors. Later on, when data in sectors unrecoverable by the first error correct­ing codes are needed, the above-mentioned recorded sectors are read out. Data storage about twice the capacity of the data recording areas is made possible by adopting the PWM (pulse width modulation) recording for the data reproduction-only area and the PPM (pulse position modulation) recording for the recording-­reproduction area.

Efficient microprocessor-based tandemable 32 kbit/s ADPCM/PCM transcoder

Abstract: The CCITT has adopted a Standard for a tandemable 64 kbit/s pulse code modulation (PCM) 32 kbit/s adaptive differential pulse code modulation (ADPCM) transcoder algorithm [1], [2]. This correspondence suggests slight changes in the adaptive quantizer and prediction filter which facilitate microprocessor realization while potentially improving performance. These variations are then incorporated into a real-time hardware and software system based on a single TI TMS 32010 each for the encoder and decoder. Objective and subjective results on the performance of our design are also presented.

Modulation waveform for 1200 BAUD DFSK paging transmitter

Abstract: A Continuous Phase Digital FM with premodulation shaping for Digital Paging Systems is presented. Some theoretical considerations and experimental results are included in order to validate this modulation scheme.

Effect of atmospheric turbulence on the bit error probability of a space to ground near infrared laser communications link using binary pulse position modulation and an avalanche photodiode detector

Abstract: The effect of atmospheric turbulence on the bit error rate of a space-to-ground near infrared laser communications link is investigated, for a link using binary pulse position modulation and an avalanche photodiode detector. Formulas are presented for the mean and variance of the bit error rate as a function of signal strength. Because these formulas require numerical integration, they are of limited practical use. Approximate formulas are derived which are easy to compute and sufficiently accurate for system feasibility studies, as shown by numerical comparison with the exact formulas. A very simple formula is derived for the bit error rate as a function of signal strength, which requires only the evaluation of an error function. It is shown by numerical calculations that, for realistic values of the system parameters, the increase in the bit error rate due to turbulence does not exceed about thirty percent for signal strengths of four hundred photons per bit or less. The increase in signal strength required to maintain an error rate of one in 10 million is about one or two tenths of a db.

A Comparison of Digital Modulation Techniques for Meteor Burst Communications

Abstract: This paper compares candidate modulation schemes for meteor burst communications (MBC) using average information throughput over the meteor scatter channel as the principal performance measure. Average throughput is shown to depend upon both the bandwidth efficiency and the required energy per bit to noise power spectral density ratio (i.e., E b /N o ) of a modulation scheme through the latter parameter's influence on the channel duty cycle. It is shown that among coherent modulation schemes, 8-ary biorthogonal FSK and QPSK have the best performance while among noncoherent herent modulation schemes, 8-ary orthogonal FSK has the best performance.

Binary Coding Techniques With Emphasis On Pulse Density Modulation

Abstract: Information processing systems require the data in coded form. Some generation procedures are described for pulse code, pulse width, and pulse density modulation. In case of sampling the idea of error diffusion is introduced. This concept has been developed to generate the pulse density modulation, but can also be used to advantage in other modulation techniques, e.g. pulse code modulation, to increase flexibility.

Synchronisation of line-coded digital PPM in repeatered transmission systems

Abstract: Line coding is shown to provide an effective means of controlling modulation jitter associated with digital pulse-position modulation (PPM), enabling simple phase-locked-loop (PLL) timing extraction circuits to be employed. The combination of a specific 9B2-32 code and a suitably designed third-order PLL with a maximally flat response is proposed and studied for the purpose of obtaining at dependent regenerators both frame and slot synchronisation signals. Jitter accumulation along a chain of such synchronisers is considered and shown to be acceptable, establishing that the combination of 9B2-32 line code and PLL synchroniser is well suited to repeatered digital PPM transmission.

Electronic multiplication circuit

Abstract: The arrangement according to the invention is a multiplier which works according to the time division principle, and forms the product not, as do known methods, by pulse width/pulse height modulation, but by pulse probability/pulse height modulation. This kind of modulation is achieved by comparing the signal of the multiplicand with a similarly distributed noise signal, to generate a pulse sequence with proportional time dependence. The advantage of the circuit principle according to the invention is that with it systematic error functions caused by high-frequency multiplier signals cannot occur.