Showing papers on "Pulse-position modulation published in 1982"
TL;DR: In this article, the performance of a coded PPM optical communication system that suffers log-normal fading during transmission was analyzed and the coding gain in link margin was shown to be substantial.
Abstract: In the presence of atmospheric or aircraft boundary layer turbulence, an optical channel may need large amounts of link margin to combat fading and beam spreading. Channel coding can reduce the average transmitter power required for reliable communication. This paper analyzes the performance of a coded PPM optical communication system that suffers log-normal fading during transmission. For moderate turbulence strengths, the coding gain in link margin is shown to be substantial.
49 citations
TL;DR: The comparisons show clearly the superiority of high-level modulation and the inferiority of offset modulation, and demonstrate significant improvements for each of two adaptive equalizers postulated here.
Abstract: A major source of impairment in microwave digital radio is multipath fading, a phenomenon sufficiently prevalent on many paths to frustrate, the attainment of reliability objectives. Performance during multipath fading depends on such system parameters as channel bandwidth and type of modulation, and on details of the receiver processing (e.g., adaptive schemes, synchronization schemes). This paper compares the performance of different digital radio techniques in the presence of multipath fading. The measure used is the expected fraction of time, conditioned on the occurrence of a fading event, that the eye pattern at the receiver detector is closed. This measure is plotted against spectral efficiency (bit rate/channel bandwidth) for various types of modulation (QPSK, offset QPSK, 8-PSK, 16-PSK, 16-QAM, and offset 16-QAM) and for various forms of carrier recovery, timing recovery, transmit/receive filtering, and adaptive equalization. The computations assume a multipath fading frequency response described by a first-order complex polynomial, where the coefficients obey an empirically derived probability law reported previously. The comparisons show clearly the superiority of high-level modulation and the inferiority of offset modulation. The comparisons also demonstrate significant improvements for each of two adaptive equalizers postulated here.
40 citations
TL;DR: Error probability bounds are presented, showing the relative improvement in detectability that appears possible by resorting to block encoding over multiple frames in PPM encoding.
Abstract: Pulse position modulation (PPM) is a popular signaling format in pulsed optical communication links. PPM encoding is extended to include block pulse encoding over multiple PPM frames. Maximum likelihood decoding operations associated with this encoding are developed for both shot-noise limited and thermal-noise limited optical receiver models. Both ideal (Poisson) and avalanche photodetectors are considered, and it is shown that optimal block decoders involve combinations of linear and quadratic operations. Error probability bounds are presented, showing the relative improvement in detectability that appears possible by resorting to block encoding over multiple frames.
25 citations
TL;DR: The performance of four digital modulation techniques are compared to one another when each is received in the presence of adjacent channel interference.
Abstract: The performance of four digital modulation techniques are compared to one another when each is received in the presence of adjacent channel interference. The interfering waveforms that each modulation format sees are identical to the modulation format under consideration. The four types of modulation are QPSK, 8-PSK, 16QASK, and QPR. Upper bounds to the probability of error are derived and used to evaluate the relative merits of the different schemes.
22 citations
TL;DR: In heterodyne systems, a local laser beam is coherently combined with the received optical field and the resulting field detected, and the signal energy per transmitted bit is divided by the quantum noise.
Abstract: The transmission of information by optical signals over a space channel with a power efficiency of 2.5 bits/detected photon markedly increases the amount of information that can be transmitted to satellites. An account is given of the research program at the Jet Propulsion Laboratory that is attempting to demonstrate that optical signals can be used to transmit information over a space channel with this power efficiency. It is noted, however, that the ability to attain 2.5 bits/detected photon (or higher) depends heavily on the validity of the mathematical models used in the performance analysis. Therefore, verification of the channel dark current noise models is a crucial first step. Another prerequisite is a high-brightness, single-spatial mode laser emitter. It is believed that single spatial model devices with power outputs of about 1W can be achieved by coherently combining a number of GaAs lasers in what effectively amounts to a phased array.
20 citations
01 Sep 1982
TL;DR: In this article, a class of receivers called conditionally nulling receivers is defined for quantum noise limited optical communications, which can decide at each moment in time whether or not to coherently combine a predetermined local oscillator field with the received optical field, prior to performing an energy measurement (photodetection) on the combined field.
Abstract: A class of receivers called conditionally nulling receivers is defined for quantum noise limited optical communications. These receivers have the ability to decide at each moment in time whether or not to coherently combine a predetermined local oscillator field with the received optical field, prior to performing an energy measurement (photodetection) on the combined field. Conditionally nulling receivers are applicable to pulse position modulation and related modulation schemes, which have the property that, at each moment in time, the transmitted signal is in one of only two states, on or off. The local oscillator field which may or may not be added by the receiver is an exact replica of the negative of the received on field; hence, the receiver can exactly null the on signal if the on signal is present and the receiver chooses to use the local field. An ideal conditionally nulling receiver achieves very nearly the same error probability (within a multiplicative factor varying froom 1 to 2.15) as the optimum quantum measurement for quantum noise limited detection of M-ary PPM signals. In contrast, other known receiving methods, such as direct, heterodyne, and homodyne detection, are exponentially suboptimum.
18 citations
01 Sep 1982
TL;DR: A class of receivers called conditionally nulling receivers is defined for quantum noise limited optical communications that have the ability to decide at each moment in time whether or not to coherently combine a predetermined local oscillator field with the received optical field, prior to performing an energy measurement (photodetection) on the combined field.
Abstract: A class of receivers called conditionally nulling receivers is defined for quantum noise limited optical communications. These receivers have the ability to decide at each moment in time whether or not to coherently combine a predetermined local oscillator field with the received optical field, prior to performing an energy measurement (photodetection) on the combined field. Conditionally nulling receivers are applicable to pulse position modulation and related modulation schemes, which have the property that, at each moment in time, the transmitted signal is in one of only two states, on or off. The local oscillator field which may or may not be added by the receiver is an exact replica of the negative of the received on field; hence, the receiver can exactly null the on signal if the on signal is present and the receiver chooses to use the local field. An ideal conditionally nulling receiver achieves very nearly the same error probability (within a multiplicative factor varying froom 1 to 2.15) as the optimum quantum measurement for quantum noise limited detection of M-ary PPM signals. In contrast, other known receiving methods, such as direct, heterodyne, and homodyne detection, are exponentially suboptimum.
16 citations
DOI•
01 Aug 1982TL;DR: The results show that both detection schemes are worthy of further consideration for use in the field of digital data communication, especially in HF communication applications, where carrier interference is a common impairment.
Abstract: The paper examines the application of pulse-compression techniques used in radar systems to FSK and PSK detection. Noncoherent FSK and differentially coherent PSK detection schemes using a mixer followed by a pulse-compressor matched filter are investigated. The mixer-PCMF combination, which acts as a predetector processor, converts the FSK modulation into pulse-position modulation and the PSK modulation into pulse-polarity modulation. A microprocessor-supervised experimental system for the FSK and DPSK detection schemes has been constructed and used to perform error-rate measurements for both schemes in the presence of additive white Gaussian noise and carrier interference. Some practical imperfections were also examined to determine their effect on system performance. The results show that both detection schemes are worthy of further consideration for use in the field of digital data communication, especially in HF communication applications, where carrier interference is a common impairment.
7 citations
TL;DR: In this article, an inverter drive employing the pulse position modulation technique is analyzed in the context of adjustable frequency induction motor drives, where the firing angles depend on the chopping ratio and are independent of the actual values of the carrier and modulating frequency.
Abstract: An inverter drive employing the pulse position modulation technique is analysed in this paper. It has been shown that the spectrum is very suitable for adjustable frequency induction motor drives since it contains a controllable fundamental and small higher harmonics. The firing angles depend just on the chopping ratio and they are independent, of the actual values of the carrier and modulating frequency. The time interval between two consecutive choppings is always quite sufficient for commutation. The inverter technique proposed can be employed throughout the entire frequency range of operation. Finally simulation results have shown that its performance is very satisfactory.
4 citations
TL;DR: It is shown that PWM may be an attractive alternative to pulse amplitude modulation (PAM), especially if a wide band channel is used, and that increased system bandwidth results in increased receiver sensitivity.
Abstract: The performance of a digital fiber optical system employing four-level pulse width modulation (PWM) is considered. It is shown that PWM may be an attractive alternative to pulse amplitude modulation (PAM), especially if a wide band channel is used. The probability density function (pdf) of the timing error is obtained in terms of the pdf of the noise amplitude, taking into account the thermal noise of the amplifier and the signal-dependent shot noise introduced by the photodiode detector. Near-Gaussian optical pulse edges at the receiver are assumed. Using typical system parameters, the variation of bit error rate (BER) with power level, and the effects of different bit rates, mean photodetector gain, and system bandwidths are calculated. It is observed that minimum BER's are achieved at moderate values of mean photodetector gain and that increased system bandwidth results in increased receiver sensitivity.
4 citations
TL;DR: A possible realisation of a data channel between aircraft and ground station is presented, which utilises a combined amplitude-phase modulation, which is used to transmit a voice signal and data transmission.
Abstract: A possible realisation of a data channel between aircraft and ground station is presented, which utilises a combined amplitude-phase modulation. Amplitude modulation is used to transmit a voice signal, while phase modulation is used for data transmission. Performance of this system is evaluated through a computer simulation.
Patent•
27 Nov 1982
TL;DR: In this paper, the authors propose to detect the boundary of words and to obtain economy by inserting synchronizing pulses without the provision of an exclusive use time slot, in a word synchronizing system for pulse position modulation.
Abstract: PURPOSE:To easily detect the boundary of words and to obtain economy, by inserting synchronizing pulses without the provision of an exclusive use time slot, in a word synchronizing system for pulse position modulation. CONSTITUTION:Pulses are compulsively inserted so that adjacent time slots of adjacent words (a) and (b) by modulation codes are consecutive as 1, 1. If the code of a time slot adjacent to the 1 of any of the words (a) and (b) is 1, the words (a) and (b) apart from the 1 code by >=2 time slots are taken to 1, allowing to discriminate the boundary a4, b1 of the adjacent words without any error and distinguish the inserted pulse from the code pulse, and they can be rejected at demodulation.
Journal Article•
TL;DR: This presentation will describe the progress to date on a project to design, build and demonstrate in the laboratory an optical communication system capable of conveying 2.5 bits of information per effective received photon.
Abstract: Optical communications technology promises substantial size, weight and power consumption savings for space to space high data rate communications over presently used microwave technology. These benefits are further increased by making the most efficient use of the available optical signal energy. This presentation will describe the progress to date on a project to design, build and demonstrate in the laboratory an optical communication system capable of conveying 2.5 bits of information per effective received photon. Such high power efficiencies will reduce the need for photon collection at the receiver and will greatly reduce the requirements for optical pointing accuracy, both at the transmitter as well as the receiver. A longer range program to demonstrate even higher photon efficiencies will also be described.
Proceedings Article•
01 Jan 1982TL;DR: In this article, a delta-max demodulator was proposed for Reed-Solomon coded M-ary PPM modulation over optical channels including satellite-to-satellite and DVS communications.
Abstract: The paper proposes a delta-max demodulator for Reed-Solomon coded M-ary PPM modulation over optical (laser) channels including satellite-to-satellite and deep-space-vehicle-to-relay-satellite communications. This demodulator is compared with the threshold demodulator currently in use, and the two demodulators are shown to have identical performance in the absence of background noise. The delta-max demodulator is found to outperform the threshold demodulator as the intensity of background noise increases.