Showing papers on "Pulse-position modulation published in 1994"

Wireless Infrared Communications

Abstract: The use of infrared radiation as a medium for high-speed short-range wireless digital communication is discussed. Available infrared links and local-area networks are described. Advantages and drawbacks of the infrared medium are compared to those of radio and microwave media. The physical characteristics of infrared channels using intensity modulation with direct detection (IM/DD) are presented including path losses and multipath responses. Natural and artificial ambient infrared noise sources are characterized. Strategies for designs of transmitter and receivers that maximize link signal-to-noise ratio (SNR) are described. Several modification formats are discussed in detail, including on-off keying (OOK) pulse-position modulation (PPM), and subcarrier modulation. The performance of these techniques in the presence of multipath distortion is quantified. Techniques for multiplexing the transmissions of different users are reviewed. The performance of an experimental 50-Mb/s on-off-keyed diffuse infrared link is described.

Ultrafast time hopping CDMA-RF communications: code-as-carrier, multichannel operation, high data rate operation and data rate on demand

Abstract: An ultrashort pulse time hopping code-division-multiple-access (CDMA) RF communications system in the time-frequency domain comprises a transmitter including a short duration pulse generator for generating a short duration pulse in the picosecond to nanosecond range and a controller for controlling the generator, code means connected to the controller for varying the time position of each short pulse in frames of pulses in orthogonal superframes of ultrafast time hopping code division multiple access format, precise oscillator-clock for controlling such timing, encoding modems for transforming intelligence into pulse position modulation form, antenna/amplifier system A homodyne receiver is provided for receiving and decoding the coded broadcast signal, and one or more utilization devices are connected to the homodyne receiver Preferably, the codes are orthogonal codes with the temporal coding of the sequence of ultrafast, ultrawideband pulses constituting the carrier for transmission by the antenna system The homodyne receiver includes a bank of decoder/modems, an acquisition system/matched filter for synchronizing to a superframe transmission, identifying coded sequencers in the superframe and assigning the transmissions to a selected decoder/modem on the basis of code recognition The system is adapted for multichannel operation and provides a high overall data rate in the 500 mbs range for maximum multichannel operation

Modulation and coding for throughput-efficient optical systems

Abstract: Optical direct-detection systems are currently being considered for some high-speed intersatellite links, where data rates of a few hundred megabits per second are envisioned under power and pulsewidth constraints. The authors investigate the capacity, cutoff rate, and error-probability performance of uncoded and trellis-coded systems for various modulation schemes and under throughput and power constraints. Modulation schemes considered are on-off keying, pulse-position modulation (PPM), overlapping PPM, and multipulse (combinatorial) PPM. >

Short range inductively coupled communication system employing time variant modulation

Abstract: A short range magnetically coupled wireless communication system (fig. 1) employs time variant modulation of a high repetition rate pulse stream and magnetic coupling between a transmission magnetic element and a receiving magnetic element (16). The pulse stream is modulated by an input audio frequency signal in the time domain, for example through pulse position modulation (2A), pulse width modulation or pulse symmetry modulation (2B). The receiving magnetic element is coupled to a demodulator circuit which detects the transmitted pulses induced in the receiving magnetic element and reproduces the audio frequency signal (fig. 6). Transmission over short range is thus efficiently accomplished through magnetic coupling in a simple low cost low power consumption communication system.

New PPM-CDMA hybrid for indoor diffuse infrared channels

Abstract: An original hybrid pulse position modulation code division multiple access (PPM-CDMA) communication technique that uses optical orthogonal codes (OOCs) is proposed and studied in the context of the indoor infrared channel. At the optimum PPM order and over the range of parameters considered, the hybrid is shown to achieve more than five times the bit rate achievable using conventional on off keying (OOK) CDMA under bandwidth constraints. Original results are presented for the false alarm errors due to the OOC crosscorrelations, and the optimum system operating parameters that minimise these errors are specified.

Sequence detection and equalization for pulse-position modulation

Abstract: We propose several strategies for detecting digital pulse-position modulation (PPM) in the presence of intersymbol interference and additive white Gaussian noise. We develop an equivalent vector channel by viewing PPM as a binary block code, and use this vector channel to derive the maximum likelihood (ML) sequence detector. We also propose three sub-optimal block-by-block detectors, all of which use block decision-feedback equalization (DFE) to mitigate inter-block interference, but differ in how they mitigate intra-block interference: the ML-BDFE accounts for it in an optimal way, the comparator-BDFE uses linear equalization, and the correcting-scalar-DFE uses DFE. We illustrate low-complexity implementations of these equalizers, and compare their performance to the ML detector using Monte-Carlo simulations. >

Transmission of electronic information by pulse position modulation utilizing low average power

Abstract: A method and apparatus are shown for generating and transmitting very short and widely separated high frequency sine-wave pulses of electromagnetic energy into space. A transistor, a charging capacitor, and an inductor are coupled into a first series loop path to form a discharge circuit. A bias voltage source, the same charging capacitor, and a charging resistor are coupled into a second series loop path to form a recharging circuit. The bias voltage source is selected to be capable of biasing the forward conduction path of the transistor near its breakdown condition. An original information signal is sampled upon each occurrence of a periodic reference signal, and the transistor is then triggered into its breakdown or avalanche mode. The starting times of successive transmitted pulses are modified in accordance with a pulse position modulation protocol.

Coded multipulse modulation in optical communication systems

Abstract: An optical communication system using coded multipulse position modulation is described. The position of the pulses in each signalling interval are derived from general binary constant weight codes. The combined coding and modulation of multiple pulses provides a minimum distance between any two signaling frames. Photon counting is used at the receiving end for noiseless optical channel in which only quantum noise exists. For noisy optical channel with avalanche photodetector, threshold demodulation is used in which an optical pulse is considered present in a slot where the photoelectron count exceeds a given threshold. It is shown that this multipulse system gives better performance than the conventional single pulse system. The performance analysis can be applied to and binary constant weight code since only the general parameters of length, minimum distance, and weight of the code are needed. >

Performance evaluation of L-pulse-position modulation on non-directed indoor infrared channels

Abstract: We examine the performance of high-speed non-directed infrared links using L-pulse-position modulation (L-PPM). When used with intensity modulation and direct detection, L-PPM leads to high average-power efficiency, because of its high peak-to-average power ratio. We derive an expression for the BER of an L-PPM link on an ISI channel. Using the measured characteristics of multipath indoor infrared channels, we calculate BER curves and ISI power penalties for 2-, 4-, 8- and 16-PPM links operating at 10 and 30 Mb/s. Our results indicate that L-PPM is a very promising modulation technique for high-speed non-directed infrared communication. >

Maximum-Likelihood Symbol Synchronization and Detection of OPPM Sequences

Abstract: For an optical Poisson channel, we consider the problem of symbol synchronization and detection of chip- synchronized, random overlapping pulse-position modulation (OPPM) sequences. Maximum-likelihood algorithms are derived for both synchronization and detection and for soft and hard data, and their performances are evaluated through simulations and an upper bound on the symbol detection and symbol synchronization probabilities. As for the case of pulse-position modulation previously studied, it is seen that a performance ceiling exists when only chip synchronization is present, which can be removed through the periodic insertion of synchronizuble symbols in the random data stream.

Slot and frame synchronisation in optical fiber PPM systems with dispersed pulse shapes

Abstract: The problem of determining the precise slot boundaries and achieving frame synchronisation is a highly demanding one in optical fiber PPM due to temporal nature of the format. Here we present an original spectral characterisation of the PPM process. We establish the requirements to realise discrete spectral slot and frame rate components. In particular we reveal the dependency of the frame rate component on the modulation index and data probability distribution, while establishing that slot components are independant of both effects. The dependence of the slot component on pulse shapes is investigated and examined for the important class of dispersed pulse shapes associated with optical fibers

Wireless audible indication system with battery status indicator

Abstract: A wireless audible indication system comprising a transmitter and a receiver. An embodiment of the transmitter includes a modulator formed by a microprocessor and a radio frequency oscillator. The modulation format employed is selectable by the user using severable jumper wires. A battery status circuit is included which verifies the status of a battery within the transmitter. The modulator transmits a low battery bit to the receiver in order to alert the user of a weak transmitter battery. An embodiment of the receiver includes a superregenerative detector which produces an intermediate signal upon receiving a radio frequency signal. A signal processing circuit, which includes an active peak detector stage and a discrete comparator stage, is used to process the intermediate signal. A microprocessor controls a sound generator circuit in response to the processed intermediate signal. The microprocessor, which normally operates in an inactive mode, is awaken using a wake-up circuit upon reception of the radio frequency signal. A battery status circuit is included to verify the status of a battery within the receiver. Embodiments of the transmitter and receiver employ a pulse position modulation scheme.

RF data communication link for wireless audible indication system

Abstract: A wireless audible indication system comprising a transmitter and a receiver. An embodiment of the transmitter includes a modulator formed by a microprocessor and a radio frequency oscillator. The modulation format employed is selectable by the user using severable jumper wires. A battery status circuit is included which verifies the status of a battery within the transmitter. The modulator transmits a low battery bit to the receiver in order to alert the user of a weak transmitter battery. An embodiment of the receiver includes a superregenerative detector which produces an intermediate signal upon receiving a radio frequency signal. A signal processing circuit, which includes an active peak detector stage and a discrete comparator stage, is used to process the intermediate signal. A microprocessor controls a sound generator circuit in response to the processed intermediate signal. The microprocessor, which normally operates in an inactive mode, is awaken using a wake-up circuit upon reception of the radio frequency signal. A battery status circuit is included to verify the status of a battery within the receiver. Embodiments of the transmitter and receiver employ a pulse position modulation scheme.

Performance of PLL-based optical OPPM communication systems

Abstract: The power spectral density (PSD) of a direct-detected optical signal with overlapping pulse-position modulation (OPPM) scheme is derived. It is demonstrated that this spectrum contains a strong periodic component at the signal symbol frequency, thereby enabling a simple PLL device to provide joint symbol and slot synchronization. The variance of the timing error for a linearized PLL synchronizer is shown to be mainly dominated by, and is inversely proportional to, the product of the PLL closed-loop bandwidth and symbol duration of the OPPM signal. The performance of a shot-noise limited PLL-based optical OPPM communication system is then assessed in terms of the overall system symbol error rate. >

Wireless audible indication system with low power signal processing

Abstract: A wireless audible indication system comprising a transmitter and a receiver. An embodiment of the transmitter includes a modulator formed by a microprocessor and a radio frequency oscillator. The modulation format employed is selectable by the user using severable jumper wires. A battery status circuit is included which verifies the status of a battery within the transmitter. The modulator transmits a low battery bit to the receiver in order to alert the user of a weak transmitter battery. An embodiment of the receiver includes a superregenerative detector which produces an intermediate signal upon receiving a radio frequency signal. A signal processing circuit, which includes an active peak detector stage and a discrete comparator stage, is used to process the intermediate signal. A microprocessor controls a sound generator circuit in response to the processed intermediate signal. The microprocessor, which normally operates in an inactive mode, is awaken using a wake-up circuit upon reception of the radio frequency signal. A battery status circuit is included to verify the status of a battery within the receiver. Embodiments of the transmitter and receiver employ a pulse position modulation scheme.

Performance of coded multi-pulse PPM with imperfect slot synchronization in optical direct-detection channel

Abstract: The performance of coded multi-pulse pulse position modulation (MPPM) consisting of m slots and 2 pulses, denoted as (m, 2) MPPM, with imperfect slot synchronization is analyzed. Convolutional codes and Reed-Solomon (RS) codes are employed for (m, 2) MPPM, and the bit error probability of coded (m, 2) MPPM in the presence of the timing offset is derived. In each coded (m, 2) MPPM, we compare the performance of some different code rate systems. Moreover, we compare the performance of both systems at the same information bit rate. It is shown that in both coded systems, the performance of code rate-1/2 coded MPPM is the best when the timing offset is small. Further, convolutional coded (m, 2) MPPM on the constraint length k/spl ges/7 performs better than Reed-Solomon coded (m, 2) MPPM for the same code rate. >

Comparative evaluation of the performance of anti-multipath modulation techniques for digital mobile radio systems

Abstract: A comparative evaluation of the performance of Manchester coded PSK (MC-PSK), phase shift keying return to zero (PSK-RZ) and phase shift keying varied phase (PSK-VP) anti-multipath modulation techniques is presented. A two-ray propagation channel model using various delay spread values has been employed. The effect of spectral shaping of the transmitted signal on the BER performance of each of these modulation schemes, using Butterworth lowpass and square-root raised cosine premodulation filters, is investigated. The BER performance results obtained using these modulation techniques are compared with that of differential phase-shift keying (DPSK) modulation. It is shown that for a frequency non-selective fading channel, the performance of the anti-multipath modulation schemes is comparable to that of simple DPSK. However as the channel becomes frequency selective, the performance of the anti-multipath modulation systems improves beyond that provided by the DPSK system. >

Differential overlapping pulse position modulation in optical direct-detection channel

Abstract: We propose differential overlapping pulse position modulation (DOPPM) in optical direct-detection channel to achieve higher capacity and cutoff rate than pulse position modulation (PPM), differential PPM (DPPM) or overlapping PPM (OPPM) when the bandwidth and the average power of the channel are constrained. In order to achieve higher throughput, the proposed modulation scheme allows more than one pulse-positions per pulsewidth over DPPM. In DOPPM the slots after the optical pulse in the block are deleted by using the differential technique and the next symbol starts just after the optical pulse of the previous symbol. To avoid frame synchronization problems, we analyze the performance of DOPPM under the window scheme that causes the degradation on the performance of DOPPM but is easy to analyze. We analyze both the capacity and the cutoff rate of DOPPM under this scheme. It is shown that DOPPM has higher capacity and cutoff rate than PPM, DPPM and OPPM when the average received number of photons per slot is somewhat large. >

A nondirective infrared transceiver for indoor high speed wireless data communication

Abstract: A prototype of the 1 Mbps nondirective infrared wireless transmission system was designed, and tested. The system design considerations such as the channel property, optoelectronics devices characteristics, and modulation schemes are discussed, and the circuit design and implementation are described. In this system, pulse position modulation (PPM) with short pulse duration and an analog-multiplier type demodulator were used. The feasibility of nondirective transmission is fully demonstrated, showing that it can support successful data communication in a typical room. The system architecture can be upgraded to data rates such as 2 Mbps or higher by only changing the circuit parameters. >

Trellis coded overlapping multi-pulse pulse position modulation in optical direct detection channel

Abstract: We analyze the error performance of overlapping multipulse pulse position modulation (OMPPM) in optical direct-detection channel with existing noise. Moreover we analyze the error performance of trellis-coded OMPPM with the small overlap index N=2 in optical direct-detection channel to achieve significant coding gains over uncoded MPPM with the same pulsewidth. First we analyze the block error probability of OMPPM in the background noise case by using the distance defined as the number of nonoverlapping pulsed chips between symbols. Second by using this distance, we partition the OMPPM signals and apply the four-state and the eight-state codes described by Ungerboeck (1982,1987) to OMPPM. It is shown that TCM is effective for OMPPM in optical direct-detection channel. The four-state and the eight-state trellis coded OMPPM can achieve gains of 1.56 dB and 3.37 dB over uncoded MPPM at the error probability of 10/sup -6/ in background noise case, respectively. >

Direct detect modulations of high speed indoor diffused infrared wireless transmission

Abstract: High speed indoor diffused infrared wireless transmission is greatly needed for data and multimedia applications. We investigated the error rate performance of OOK (on off keying), NRBI (non-return-to zero with bit insertion), M-ary PPM (pulse position modulation), and two novel coded direct detect modulations, DCGPPM (differentially coded and guarded PPM) and MRLC (modified run length code), by adopting representative channel modeling from measurements and simulations. Practical implementation issues have been further considered. From our results, we suggest DCGPPM at 10 M bps, 4-ary PPM or DCGPPM at 20 M bps, OOK or NRBI at 40 M bps; and MRLC at 100 M bps, for the baseband direct detect transmission of indoor wireless optical transmission.

Performance analysis of a spread spectrum M-ary orthogonal modulation under multipath fading

Abstract: The performance of orthogonal Walsh functions spread spectrum modulation under multipath, selective Rayleigh fading channel is analyzed. This modulation scheme is used for a DS CDMA mobile communication system which is being investigated. Orthogonal modulation and noncoherent detection seems to be suitable for the up-link of a DS CDMA system in which the multi-user interference are more severe than on the down-link. For simplicity, the analysis has been carried out only for a fixed path reception. The results of analysis show that although orthogonal modulation is an effective method to combat the noise and interference in an AWGN channel, under the multipath fading channel and reception based on one path, the performance is still poor. However, a computer simulation under a more practical condition shows that this modulation scheme combined with the RAKE receiver and convolutional encoding will achieve an acceptable performance. A comparison of the simulation results for orthogonal modulation and DPSK shows that the performance of a 64-ary Walsh modulation is nearly 7 dB better than DPSK, while the bandwidth of the latter is 1.5 times more than the former. >

A class of constant envelope multi-dimensional modulation schemes for non-linearly amplified channels

Abstract: A new class of modulation schemes, called 8D-CEMS (8 dimensional constant envelope modulation scheme), with constant envelope of the modulated signal, for digital radio communications over non-linearly amplified channels is introduced. Computer simulation results show that these modulation schemes lead to significant performance improvement on non-linearly amplified channel, as required in most commercial satellite and terrestrial microwave systems. In particular, we show how to generate an 8D-CEMS that allows one to achieve a bit-error rate of P/sub be/=10/sup -4/ at E/sub b//N/sub 0/=9 dB with spectral efficiency 3 bits/s/Hz. >

Pulse Position Modulation and Extended Pulse Position Modulation with Squeezed Light

Abstract: It is shown that the performance of optical communication systems that use pulse position modulation and direct photon counting can be improved with the use of squeezed states. The effect of noise is studied. An improved version of the pulse position modulation called extended position modulation is also considered.

Effect of Imperfect Slot Synchronization on Direct-detection Optical Synchronous CDMA Communication Systems with PPM Signaling

Abstract: Effect of imperfect slot synchronization between the transmitter and the receiver on optical synchronous code-division multiple-access using pulse position modulation as data modulation (PPM/CDMA) is investigated. Optical orthogonal codes (OOC's) are employed as signature sequences, and parallel optic-fiber delay line encoders and correlators are adopted in transmitters and receivers, respectively. We derive the upper bound on the bit error probability of PPM/CDMA on condition that the receiver slot timing shifts from the transmitter timing clock. We show the bit error probability performance for some values of parameters. It is found that as the number of slots per frame increases, the timing offset should be restricted to be smaller. Further, the bit error probability performance under photocounts per second constraint is also found to be more improved than under the fixed photocounts per symbol as the number of slots in one frame increases in the small range of the timing offset.

Bandwidth-efficient correlative trellis-coded modulation schemes

Abstract: A novel digital modulation scheme is proposed that uses coding to reduce the bandwidth of a signal. The schematic diagram of the transmitter is presented, and optimisation criteria are given and applied to the transmitter. The resulting new modulation schemes are described and compared with traditional schemes. Compared to uncoded M-ary quadrature amplitude modulation, the new modulation schemes allow an increase in the data rate by up to 0.5 bit/s/Hz for a given performance, or to reduce the signal power by about 1 dB for a given data rate. >

On the performance of multicarrier modulation in a broadcast multipath environment

Abstract: Multicarrier modulation (MCM) has traditionally been used on severely distorted channels for which there is a reverse path to the transmitter. A potential area of application of multicarrier modulation is for the terrestrial broadcasting of high rate digital television, including high-definition television (HDTV). We show that certain multipath conditions can substantially degrade the performance of MCM, even when combined with coding. If certain conditions are met, however, multipath contributes positively to the performance of the MCM receiver. >