Showing papers on "Pulse-position modulation published in 1999"

Differential pulse-position modulation for power-efficient optical communication

Abstract: We examine the use of differential pulse-position modulation (DPPM) for optical communication systems using intensity modulation with direct detection in the presence of additive white Gaussian noise. We present expressions for the error probability and power spectral density of DPPM. We show that for a given bandwidth, DPPM requires significantly less average power than pulse position modulation (PPM). We also examine the performance of DPPM in the presence of multipath intersymbol interference (ISI). We find that the ISI penalties incurred by PPM and DPPM exhibit very similar dependencies upon the channel RMS delay spread. We discuss the use of chip-rate and multichip-rate equalization to combat ISI. Finally, we describe potential problems caused by the nonuniform bit-rate characteristic of DPPM, and we propose several solutions.

Communication techniques using monopulse waveforms

Abstract: This paper studies wireless communication systems using technology that does not require a carrier signal. The vehicle used for transmission is a monopulse waveform. Such waveforms possess a bandpass nature, having no DC content. The short time duration of these waveforms, typically nanoseconds, provides has an ultrawide bandpass characteristic, with a spectrum in the range of hundreds of megahertz, making them ideally suited for a spread spectrum communication system. The temporal representations of several monopulse signals are illustrated, and the power spectral densities of the Gaussian and Rayleigh monopulse waveshapes are presented. The relationship between effective time duration, peak-to-RMS value, and bandwidth is detailed. The spectral effect of pulse amplitude modulated data and pulse position modulated data is compared. A methodology for efficient data transmission and a technique for rate doubling at no cost in bandwidth is described. Diversity methods to mitigate a harsh environment, such as those encountered in fading channels, jamming, and multipath situations, are introduced.

An active tagging system using circular-polarization modulation

Abstract: An active read/write microwave tagging system using circular-polarization modulation as a novel modulation scheme for radio-frequency identification systems is presented. The proposed modulation scheme reduces demodulation complexity and power consumption on the battery-powered tag. Additional coding of the circular-polarization modulated data reduces transmission errors due to polarization inversion at multipath propagation. In multiple-reader environments, the main jamming threat occurs from power carriers of different interrogators. A combination of circular-polarization modulation and frequency hopping is presented that shows an increased immunity against multipath phenomena for multiple-tag and multiple-reader environments.

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

Abstract: We examine the performance of two decision-feedback equalizers (DFEs) for pulse-position modulation (PPM) on measured nondirected indoor infrared channels with intersymbol interference. 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. Our results show that a symbol-rate DFE provides performance that closely approaches that of the optimal MLSD.

A performance analysis of optical overlapping PPM-CDMA communication systems

Abstract: Direct-detection optical code-division multiple-access (CDMA) systems employing overlapping pulse-position modulation (OPPM) schemes are proposed. Both upper and lower hounds on the bit error rate (BER) are derived taking into account the effect of both multiple-user interference and receiver shot noise. The photodiodes' dark currents are neglected since their effect is minor. The throughput limitation of this system is evaluated as well. Performance characteristics are then compared to optical CDMA systems employing traditional ON-OFF keying (OOK) and pulse-position modulation (PPM) schemes. It is shown that under fixed data rate and chip time, OPPM-CDMA system superperforms both traditional systems. Moreover, it is shown that the throughput limitation of OPPM-CDMA is almost 6.7 times greater than that of OOK-CDMA.

Apparatus and methods for providing high-penetration messaging in wireless communications systems

Abstract: A message, e.g., a control message, a short message, a voice message or a data message, is transmitted on at least one of a first communications channel having a first redundancy level or a second communications channel having a second, higher redundancy level. A radio communications signal is received on one of the first communications channel and the second communications channel. The received radio communications signal is demodulated to recover the message using a first demodulation scheme if the radio communications signal is received on the first communications channel and using a second demodulation scheme if the radio communications signal is received on the second communications channel. According to an aspect of the invention, the received radio communications signal is coherently demodulated if the radio communications signal is received over the first communications channel and non-coherently demodulated if the radio communications signal is received over the second communications channel. According to another aspect, the message is transmitted on the first communications channel using a first modulation constellation, and transmitted on the second communications channel using a second modulation constellation representing a subset of the first modulation constellation. In other embodiments of the present invention, a first radio communications signal is transmitted representing the message encoded according to one of a first code or a second code that represents a concatenation of the first code and an additional code, such as an orthogonal code or a quasi orthogonal code. Related systems and apparatus are also described.

A neural approach to automatic pulse repetition interval modulation recognition

Abstract: The intervals between the pulse time of arrival (TOA) values of a radar pulse train nearly always follow a specific modulation type. We pursue a fully automated neural approach for deducing this modulation type. The approach is shown via simulation to be extremely reliable and robust to the problems of missing and spurious pulses, as well as requiring only relatively few pulse TOA values.

Chaotic carrier pulse position modulation communication system and method

Abstract: A chaotic carrier pulse position modulation communication system and method is disclosed. The system includes a transmitter and receiver having matched chaotic pulse regenerators. The chaotic pulse regenerator in the receiver produces a synchronized replica of a chaotic pulse train generated by the regenerator in the transmitter. The pulse train from the transmitter can therefore act as a carrier signal. Data is encoded by the transmitter through selectively altering the interpulse timing between pulses in the chaotic pulse train. The altered pulse train is transmitted as a pulse signal. The receiver can detect whether a particular interpulse interval in the pulse signal has been altered by reference to the synchronized replica it generates, and can therefore detect the data transmitted by the receiver. Preferably, the receiver predicts the earliest moment in time it can expect a next pulse after observation of at least two consecutive pulses. It then decodes the pulse signal beginning at a short time before expected arrival of a pulse.

A wireless telecommunications system that mitigates the effect of multipath fading

Abstract: A wireless telecommunications system is disclosed that mitigates multipath fading through an improvement in transmit diversity. Furthermore, embodiments of the present invention are well-suited for use with all forward channel multiplexing schemes (e.g., frequency-division multiplexing, time-division multiplexing, code-division multiplexing, etc.) and all modulation techniques (e.g., amplitude modulation, frequency modulation, phase modulation, etc.). An illustrative embodiment of the present invention comprises: a signal inverter (613) for inverting and alternately not-inverting a first signal in accordance with a schedule (615) to create a second signal; a first antenna for transmitting the first signal; and a second antenna for transmitting the second signal.

Methods and apparatuses for synchronization and modulation type detection

Abstract: In a communication system including a transmitter and a receiver, the receiver is synchronized with the transmitter, and a modulation type in a signal transmitted by the transmitter and received by the receiver is detected. A first portion of the received signal is correlated with one or more signals representing modulation types used by the communication system to detect the type of modulation being used in the received signal. Synchronization is established between the transmitter and the receiver. The first portion may be correlated with each of one or more different signals representing various modulation types used in the communication system to detect the type of modulation used. Alternately, the first portion of the received signal may be derotated by different amounts to produce a plurality of derotated signals that are correlated with the signal representing modulation used by the communication system in order to detect the type of modulation used. If the correlation does not result in a determination of the modulation type, either a predetermined modulation type is selected as the modulation type, or the decision of the modulation type is made at a later stage based, e.g., on a comparison of signal qualities or equalization results.

Performance of Binary Turbo-Coded 256-ary Pulse-Position Modulation

Abstract: This article compares the performance of binary turbo codes and Reed{Solomon (RS) codes in an optical communications system employing high-order pulseposition modulation (PPM) and an avalanche photodiode (APD) detector. Despite restriction of the turbo codes to binary alphabets and very simple 4- or 8-state encoders, they have coding gains 0.5-dB to 0.7-dB higher than equivalent-rate RS codes when using 256-PPM, employing a typical APD detector, and operating at an end-to-end bit-error rate (BER) of 10 i5 . BER curves are given for code rates of 1/3 and 1/2, using a variety of turbo and RS coding methods. The simulations use an accurate modeling of APD output statistics instead of typical but less accurate Poisson or Gaussian approximations.

Direct detection optical overlapping PPM-CDMA communication systems with double optical hardlimiters

Abstract: Direct detection optical code-division multiple-access (CDMA) communication systems involving overlapping pulse-position modulation (OPPM) is considered. Double optical hardlimiters placed before and after the correlator at the receiver side is proposed for this system. The performance (in terms of the bit error probability) of this system is evaluated taking into account the effect of both the multiple-user interference and the photodetector shot noise. Both the receiver dark current and thermal noise are ignored in our analysis since their effect is very minor. The performance of the above receiver is compared to that of the OPPM-CDMA correlator receiver without hardlimiters, OPPM-CDMA optimum receiver, and OOK-CDMA optimum receiver. Our results reveal that, for given pulsewidth and throughput constraints, significant improvement in the performance is acquired when adding double optical hardlimiters to the correlator of the OPPM-CDMA receiver. Moreover the performance of this system is asymptotically close to the optimum OPPM-CDMA system and is considerably superior to the optimum OOK-CDMA system. It is also reported that the capacity of the proposed system is about 5.3 times greater than that of the optimum OOK-CDMA system.

Rate-adaptive modulation techniques for infrared wireless communications

Abstract: While infrared links can support transmission at high bit rates, it is difficult to maintain a signal-to-noise ratio (SNR) sufficient to support these high bit rates under all conditions using reasonable transmitter power levels. Under adverse conditions, instead of incurring abrupt link failure, it is preferable to achieve graceful degradation by lowering the bit rate until a suitably low error probability can be attained. We describe several coding and decoding schemes for rate-adaptive transmission, and we discuss their performance and implementation complexity. The codes considered are rate-compatible punctured convolutional (RCPC) codes and simple repetition codes. Each code is combined with L-ary pulse-position modulation. We present results of a search for families of good RCPC codes derived from rate-1/5 and rate-1/7 mother codes.

Optical wireless communication using digital pulse interval modulation

Abstract: This paper presents a study of digital pulse interval modulation (DPIM) as a candidate modulation scheme for optical wireless communications. DPIM code characteristics are discussed and the theoretical error probability performance of DPIM is analyzed in terms of the packet error rate. Performance comparisons are made with the more established techniques of on-off keying and pulse position modulation (PPM). We show that, for a simple threshold detector based receiver, DPIM can out perform PPM in terms of bandwidth efficiency and power efficiency, by taking advantage of its inherent variable symbol duration. Practical results are given for an experimental system in the form of eye diagrams. The use of a coding scheme with a non-uniform symbol duration does have implications for system design, which are discussed in the paper.

A novel variable-rate pulse-position modulation system with near quantum limited performance

Abstract: Pulse-position modulation (PPM), a form of orthogonal signaling, can use modulator and receiver hardware similar to that of the simple on-off-keying (OOK) modulation, but with the advantage of providing its own bit-by-bit decision threshold. This feature is of special interest when channel conditions are varying or when other non-ideal conditions, such as imperfect modulator extinction, are present. We have developed a novel PPM signaling format that takes advantage of the average power limited characteristics of erbium-doped-fiber amplifiers (EDFAs). This format permits the data rate to be varied over a wide range with near-quantum-limited performance at all rates, yet with only a single filter at the receiver. We have built a free-space optical communication system using our novel PPM signaling format demonstrating simplicity, high sensitivity, wide dynamic range, and multiple data rates.

High-sensitivity variable-rate transmit/receive architecture

Abstract: We have demonstrated unsurpassed communication performance, only 2 dB from theory, by careful matching of the transmitted waveforms and receiver filtering at all bit-rates using an average power limited (APL) transmitter anti variable duty-cycle waveforms. While we have demonstrated duty cycle enhanced (DCE) multi-rate communications from 51 Mbps through 1.244 Gbps using binary-pulse position modulation (PPM), this approach can easily be extended to higher bit-rates, other modulation formats, and is extremely well suited for M-ary PPM.

Three-level hysteresis band modulation strategy for single-phase PWM inverters

Abstract: A novel three-level adaptive hysteresis band modulation strategy for single-phase inverters is presented. It is shown that the total harmonic current distortion of the new strategy closely approximates that of the off-line precalculated harmonic minimised PWM switching angle solution sets. It is shown that the three-level adaptive hysteresis band strategy can be defined using a modulation process possessing both pulse-width and pulse-position modulation. Two strategies are presented to determine the switching angles in one quarter of the fundamental period of the PWM and the advantages of each method are discussed using a digital signal processor implementation. Both simulation and experimental results for the three-level adaptive hysteresis band PWM strategy are presented to confirm the theoretical analysis.

A comparative study of using random switching schemes for DC/DC converters

Abstract: This paper addresses a comparative investigation on the use of random modulation schemes for DC/DC power converters. The modulation schemes under investigation include randomized pulse position modulation, randomized pulse width modulation and randomized carrier frequency modulation with fixed and variable duty cycle. The study emphasizes the suitability and applicability of each scheme in DC/DC power converters, the randomness level on the effectiveness of spreading the dominating frequencies in constant frequency pulse width modulation scheme, and the low-frequency power spectral density (PSD) of each scheme. Validity of analyzes is confirmed experimentally by using a DC/DC buck converter, where the PSD of the output for each scheme is presented.

Adaptive coded modulation over slow frequency-selective fading channels

Abstract: We consider adaptive coded modulation for systems using QPSK/8PSK/16QAM constellations with a decision-feedback equalizer for slow frequency-selective fading channels. We investigate several potential channel-quality metrics that could be used to choose the correct coding and modulation scheme. We then present a threshold-adaptive algorithm that is especially useful for channels with a wide range of multipath profiles.

CELP speech coding based on an adaptive pulse position codebook

Abstract: CELP coders using pulse codebooks for excitations such as ACELP have the advantages of low complexity and high speech quality. At low bit rates, however, the decrease of pulse position candidates and the number of pulses degrades reconstructed speech quality. This paper describes a method for adaptively allocating of pulse position candidates. In the proposed method, N efficient candidates of pulse positions are selected out of all possible positions in a subframe. The amplitude envelope of an adaptive code vector is used for selecting N efficient candidates. The larger the amplitude is, the more pulse positions are assigned. Using an adaptive code vector for the adaptation, the proposed method requires no additional bits for the adaptation. Experimental results show that the proposed method increases WSNRseg by 0.3 dB and MOS by 0.15.

Performance of wireless infrared transmission systems considering both ambient light interference and intersymbol interference due to multipath dispersion

Abstract: The performance of optical wireless transmission systems is mainly impaired by the shot noise induced by ambient light, interference produced by artificial light sources, transmitted optical power limitations due to high path losses and channel bandwidth limitations due to inter-symbol interference produced by the multipath dispersion of the optical signal. The contribution of these factors to the performance evaluation of infrared links have only been addressed independently and the combined effect of these channel impairments was not presented yet. The work presented in this paper extends the previous analysis by taking into account the combined effects of both optical noise (shot noise and interference) and channel impulse response. A simulation package was used to determine the indoor optical channel impulse response due to the propagation losses and multipath dispersion under various room geometries and emitter/receiver parameters. The contribution of the interference produced by incandescent and fluorescent lamps was done through the utilization of analytical models. The penalty introduced by these channel characteristics was quantified considering the modulation schemes usually considered for optical wireless communication systems: 2-, 4- and 16-PPM (pulse position modulation) at bit rates from 1 to 10 Mbps.

Combined binary pulse position modulation/biorthogonal modulation for direct-sequence code division multiple access

Abstract: A novel modulation format is proposed for cellular direct-sequence CDMA systems where a user-specific spreading sequence is binary pulse position and biorthogonally modulated to form a set of biorthogonal spreading sequences. The modulation scheme trades the signal space used for spreading sequences with that for modulation while a global space is fixed. The interference is mainly determined by the cross correlation properties among sequences, but also affected by modulation. The effect is taken into account to evaluate the multi-user performance of the combined modulation. Compared to M-ary orthogonal modulation, the performance is shown to be almost the same while resulting in a simpler receiver structure.

Analysis of Optical PPM/CDMA System with M-Ary Convolutional Coding

Abstract: Optical Code Division Multiple Access (OCDMA) has been emerging as an attractive scheme in fiber optic communication systems as well as in space communication systems in past few years [1]–[6]. In OCDMA systems, M -ary Pulse Position Modulation (PPM), has been regarded as an efficient signalling format which has the capability to reduce the channel interference caused by the other users and also to increase the number of simultaneous users [3]–[5]. We apply error control coding to improve the system performance of pulse position modulated OCDMA (PPM/OCDMA) systems and this paper investigates the performance of M -ary PPM/OCDMA systems with M -ary convolutional coding. Dual-k code [7] is used as the M -ary convolutional code and Optical Orthogonal Codes with the maximum cross correlation value of 1 and 2 are employed as the signature sequences. We derive an expression for the bit error probability of the new system and show that combining M -ary convolutional coding and M -ary PPM results in an improved error performance. Also it is shown that the number of simultaneous users can be significantly increased with the proposed system compared to the uncoded PPM/OCDMA system with the same bit error probability and with the same information bit rate. We also analyze the system with binary convolutional coding and a comparison with the proposed system is given. key words: optical CDMA, pulse-position modulation, M-ary, convolutional coding, dual-k code

Architecture of non-synchronous open loop demodulation circuit in pulse position modulation

Abstract: A simple demodulation circuit having a reduced hardware cost and an increased using flexibility is provided. Such architecture is used in a pulse position modulation for retrieving a data from a received source signal and includes a transformation circuit operating the source signal to produce a quantized data having a plurality of data slots, a slot address detector electrically connected to the transformation circuit for reaching a peak slot address from addresses of the data slots, and a timing recovery decoder electrically connected to the slot address detector for recovering the data through decoding the peak address.

Trellis-coded pulse-position modulation for optical communication systems impaired by pulsewidth inaccuracies

Abstract: A trellis-coded pulse-position modulation (T-PPM) scheme for direct-detection photon communications over unguided channels is described. The purpose of this signaling method is to combat performance degradation due to the spreading of received signal pulses caused by transmitting laser distortion and the finite area and bandwidth of optical detectors. The T-PPM scheme relies upon use of a set partitioning methodology to increase minimum distance using a simple convolutional encoder. The Viterbi algorithm is used at the receiver to separate the signaling set as part of the demodulation process. It is shown through both analysis and Monte Carlo simulation of an avalanche photodiode based receiver system that T-PPM can restore performance losses due to reduced peak intensity during the detection process. Furthermore, for a large range of background radiation levels, the average number of required signal photons per information bit for T-PPM is smaller than that of uncoded PPM. Specific examples show that for a symbol error rate of 0.001, when the received pulses extend over 4 PPM slot widths, the average laser energy per symbol for 256-ary T-PPM could be reduced by as much as 2 dB.

Trellis codes based on amplitude and position modulation for infrared WLANs

Abstract: In this communication we consider the use of an hybrid modulation method called amplitude and pulse-position modulation (APPM) in infrared WLAN. In this hybrid method the information is conveyed both in the position and amplitude of a pulse. The bandwidth efficiency and the capacity of this new modulation scheme are derived and compared against pulse-position modulation (PPM), which allows us to conclude that APPM can be used to improve the performance of PPM without bandwidth expansion, using trellis-coded modulation (TCM) codes. We also derive the best trellis codes for some A/spl times/2-APPM, and the results show that non-negligible coding gains can be obtained with trellis codes of moderate complexity.

Performance of an optical PPM/CDMA system with turbo coding

Abstract: In this paper, performance of an optical CDMA system with turbo coding is analyzed and simulated. It is assumed that the optical channel is an intensity-modulated (IM) channel and a direct-detection scheme is employed to detect the received optical signal. The modulation scheme used is pulse-position-modulation (PPM). From the simulation results, it is shown that turbo coding offers considerable coding gain with reasonable encoding/decoding complexity. Also, it is demonstrated that the performance of an optical CDMA system can be substantially improved by increasing the interleaver length and the number of iterations for a fixed code rate. The results in this paper can be applied, for example, to an optical wireless LAN operating in an indoor environment with multiple access applications.

Optical Wireless PPM CDMA Networks Employing OC and PC Signature Codes

Abstract: A hybrid pulse position modulation (PPM) code division multiple access (CDMA) optical communication system is proposed and its performance is analyzed using three different orthogonal coding schemes: optical orthogonal codes, prime codes and extended prime codes. The hybrid can usefully be exploited in optical wireless and optical fiber networks. Two types of PPM CDMA structures have been considered and analyzed. The implications of the structures and the coding schemes on the system bit rate and number of users are assessed. Original results are presented for the system error probability against the number of users using the three different orthogonal codes.

Optical fiber data bus modulation techniques for military avionics

Abstract: In this paper, we propose several modulation techniques for use in military avionics optical fiber data buses, namely, Extended Manchester II Bi-Phase Coding with Beginning-Stopping Flags, Partial Trilevel Manchester II Bi-Phase Coding, Four-ary Pulse Width Modulation, Two-ary Pulse Width Modulation with Amplitude-Distinguished Sync Field, Two-ary Message Pulse Width Modulation and Two-ary Sync Pulse Amplitude Modulation, respectively. Compared with an existing modulation scheme of MIL-STD-1773 avionics data buses, the proposed techniques can be effectively used to overcome the difficulty in recognizing the correct operation states of an active transmitter at the output of optical receivers. The feasibility of proposed modulation schemes are discussed, and their performance is also evaluated.

Analog pulse position modulation in harmonically mode-locked lasers

Abstract: Analog pulse position modulation of pulsed emission from a laser, which is actively and harmonically mode-locked. The laser requires: a body of an active gain medium; means for changing the gain as a function of a controllable parameter; harmonically and actively mode-locking the laser by fast periodic changes of said parameter; and superimposing slower changes on the parameter whereby the fast periodic parameter changes can be continuously shifted between the peak and the shoulder of the gain-vs-parameter curve. As proof of concept, electric control of the separation between two interleaved pulse trains from a far-infrared (1.5-4 THz) p-Ge laser, which is actively mode-locked by rf gain modulation at the second harmonic of the roundtrip frequency, is demonstrated by changing the electric bias at the rf contacts. A suggested application is telemetry using analog pulse position modulation.