Showing papers on "Pulse-position modulation published in 1997"

Channel reuse strategies for indoor infrared wireless communications

Abstract: We examine systems of fixed-channel reuse for base stations in an indoor infrared wireless communication system. The following techniques are compared: time-division multiple access (TDMA) using on-off keying (OOK) or pulse-position modulation (PPM); frequency-division multiple access (FDMA) using binary phase-shift keying (BPSK) or quadrature phase-shift keying (QPSK); code-division multiple access (CDMA) using OOK with direct-sequence spreading by m-sequences or optical orthogonal codes (OOCs). We define a parameter /spl gamma/, which equals the signal-to-noise ratio (SNR) for unit optical path gain and is proportional to the square of the transmitted average optical power. Using measured pathloss data, it is found that in a system using hexagonal cells and a reuse factor of three, for cell radii above 3 m, TDMA with OOK or 2-PPM, and CDMA using OOCs all require approximately the same /spl gamma/ to achieve a worst-case bit-error rate (BER) of 10/sup -9/ within a cell. Using TDMA with 4-PPM results in a 6-dB decrease in the required value of /spl gamma/. CDMA using m-sequences requires an increase in /spl gamma/ of 5 dB over TDMA using OOK, and FDMA with BPSK requires an increase of 12 dB. For a given reuse factor N in the noise-limited regime, the required value of /spl gamma/ decreases in inverse proportion to N/sup 2/ for TDMA schemes and inversely with N for FDMA and CDMA schemes. For cell radii below 3 m, cochannel interference dominates the systems using TDMA, FDMA, and CDMA with an OOC, resulting in an irreducible BER above 10/sup -9/ at cell radii below 1.5 m. Only CDMA with m-sequences does not develop an irreducible BER, making it the only choice for cell radii below 1.5 m.

Trellis-coded pulse-position modulation for indoor wireless infrared communications

Abstract: We analyze the performance of trellis-coded pulse-position modulation (PPM) on indoor, wireless infrared channels. We show that maximum-likelihood sequence detection (MLSD) of trellis-coded PPM is very effective in mitigating the multipath dispersion on such channels. We present code search results for high constraint-length, rate-2/3, 8-PPM and rate-3/4, 16-PPM codes. We provide bit-error rate curves and intersymbol interference power-penalties for MLSD of PPM with these codes, evaluated on ceiling-bounce channel models with delay spread per bit duration ratios of 0.01-0.3. Finally, we present Monte Carlo simulation results to verify our analysis.

Method and apparatus for emulating a frequency modulation device

Abstract: A system and method are disclosed for emulating a frequency modulation sound chip with minimal hardware and utilizing the excess capacity of current computer systems. In one embodiment, the frequency modulation emulation apparatus includes a frequency modulation emulator suitable to communicate with a computer system. The frequency modulation emulator provides an addressable memory space, substantially similar to an emulated addressable memory space of the emulated frequency modulation sound chip, such that a frequency modulation application implemented on the computer system can communicate with the frequency modulation emulator. The emulator chip receives audio data through the addressable memory space from the frequency modulation application and, the frequency modulation application is unaware that the frequency modulation emulator is receiving the audio data rather than the emulated frequency modulation sound chip. A frequency modulation generator is implemented on the computer system. The frequency modulation generator receives the audio data from the frequency modulation generator. The frequency modulation generator processes the audio data to produce an audio signal in a manner that is substantially similar to the operation of the emulated frequency modulation sound chip. Thus, minimal hardware is used to emulate a frequency modulation sound chip, and utilizing the excess capacity of current computer systems.

Signal selection for the indoor wireless impulse radio channel

Abstract: In this paper we investigate communications using quaternary pulse position data modulation over the indoor impulse radio multiple access channel disturbed with multipath. The performance of four quaternary signal sets with different correlation properties is assessed.

Performance of equicorrelated ultra-wideband pulse-position-modulated signals in the indoor wireless impulse radio channel

Abstract: Impulse radio (IR) is a spread spectrum (SS) wireless technique in which ultra-wideband (UWB) communication waveforms that consist of trains of time-shifted subnanosecond pulses are modulated to convey information exclusively in the relative time position of the pulses. In this paper we describe the construction of equally correlated (EC) pulse position modulation (PPM) signals, using trains of binary time-shift-keyed UWB subnanosecond pulses. The performance of the EC UWB PPM signals in the indoor IR channel with detection using a Rake receiver is analyzed.

Efficient encoding and detection method and device for binary intensity modulated optical data signals

Abstract: A waveform encoding method and device provide for generating/receiving a power efficient binary intensity modulated optical data signal from a binary source signal which minimizes a time between adjacent pulse transitions and maximizes a pulse peak amplitude for transmission over a low-power wireless infrared link. In generating the signal, the method includes: generating a Q-ary pulse position modulation, Q-PPM, encoded data signal from binary data where Q represents 2 L time slots and L is a predetermined integer representing a predetermined number of binary source bits of the power efficient binary intensity modulated optical data signal; generating an efficient binary intensity modulated signal by increasing the pulse peak amplitude of the Q-PPM encoded data signal by a factor of k, k a predetermined value, and decreasing a pulse width of the Q-PPM encoded data signal by k; and transmitting the efficient binary intensity modulated signal over the low-power wireless infrared link.

Performance limitations of free-space optical communication satellite networks due to vibrations: direct detection digital mode

Abstract: Free-space optical communication between satellites net- worked together can permit high data rates between different places on Earth. The use of optical radiation as a carrier between the satellites permits very narrow beam divergence. Due to the narrow divergence and the large distance between the satellites, pointing from one satellite to another is difficult. The pointing task is further complicated by vibration of the pointing system caused by tracking noise and mechanical impacts. In this work we derive mathematical performance models for digital direct detection communication satellite networks as a function of the system parameters, the number of satellites, and the vibration amplitude. The optical intersatellite network model considered includes a transmitter sat- ellite, regenerative satellites, and a receiver satellite all networked to- gether. A comparison between three communication system modulation schemes—on-off keying (OOK), pulse position modulation (PPM), and pulse polarization binary modulation (PPBM)—is presented. These mod- els are the basis for optical communication tracking- and pointing-system design of appropriate complexity and performance to make the network as simple and inexpensive as possible. From the analysis it is clear that even low vibration amplitude of one satellite pointing system decreases the network performance dramatically. © 1997 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(97)01111-2)

Methods and systems for communicating information using separable modulation constellations

Abstract: A source set of bits is modulated according to a modulation constellation to produce a modulated communications signal, wherein the modulation constellation preferably is Gray-coded and is selected to provide a communications signal from the source set of bits such that real and imaginary components of the communications signal map to mutually exclusive first and second subsets of the source set of bits. The modulated communications signal is communicated over a communications channel. Soft information for the first subset of bits of the source set of bits is determined from a real component of a product of a channel transfer characteristic and the communicated modulated signal, the channel transfer characteristic characterizing communications over the communications channel. Soft information for the second subset of bits of the source set of bits is determined from an imaginary component of the product of the channel transfer characteristic and the communicated modulated signal. Iterative aspects for higher-order modulation and demodulation are also provided. Related systems and apparatus are also described.

Multilevel differential polarization shift keying

Abstract: We analyze the performance of coherent optical communication systems which employ polarization shift keying (PolSK) modulation, introducing for the first time the requirements for multilevel, differential PolSK. For M-ary signal constellations with M>2, the three-dimensional (3-D) nature of the signal constellations within Stokes space requires the use of double-differential modulation and detection (M-DDPolSK). Coding constraints on the signals place an additional restriction on such systems. We present detailed analysis and simulations for a 6-DDPolSK modulation scheme in which the signal points are located at the vertices of an octahedron in Stokes space.

Microcontroller-based underwater acoustic ECG telemetry system

Abstract: The paper presents a microcontroller based underwater acoustic telemetry system for digital transmission of the electrocardiogram (ECG). The system is designed for the real time, throughwater transmission of data representing any parameter, and it was used initially for transmitting in multiplexed format the heart rate, breathing rate and depth of a diver using self contained underwater breathing apparatus (SCUBA). Here, it is used to monitor cardiovascular reflexes during diving and swimming. The programmable capability of the system provides an effective solution to the problem of transmitting data in the presence of multipath interference. An important feature of the paper is a comparative performance analysis of two encoding methods: pulse code modulation (PCM) and pulse position modulation (PPM).

Spread spectrum pulse position modulation communication system

Abstract: A first spread spectrum pulse position modulated signal with a pseudonoise code is generated. A second spread spectrum pulse position modulated signal with an inverted pseudonoise code is generated. A third spread spectrum pulse position modulated signal with a pseudonoise code is generated. A fourth spread spectrum pulse position modulated signal with an inverted pseudonoise code is generated. The first and second spread spectrum pulse position modulated signals are added together and thus a fifth spread spectrum pulse position modulated signal is formed. The third and fourth spread spectrum pulse position modulated signals are added together and thus a sixth spread spectrum pulse position modulated signal is formed. Quadrature modulation is performed on the fifth and sixth spread spectrum pulse position modulated signals.

Programmable PPM/PWM writing system for optical disk

Abstract: A programmable writing system for an optical disk drive which is adaptable for pulse position modulation (PPM) and pulse width modulation (PWM) pulse generation. The writing circuit is responsive to a PPM/PWM mode command for generating programmed laser pulse signals. Specifically, a pattern detector is responsive to the PPM/PWM mode command for detecting input data. The detected data is provided to a pulse selector for selecting programmed pulse power and/or duration values, which operate a pulse generator to set pulse power levels and/or to set the duration of the generated laser pulse signals. In PWM mode, the pattern detector provides a toggle signal with each detected signal and the pulse selector responds to the toggle signal to alternate between providing mark pulse power and/or duration values and providing space duration values to thereby provide alternating mark and space signals.

Laboratory experimental results of an adaptive modulation/TDMA/TDD for wireless multimedia communication systems

Abstract: This paper reports laboratory experimental results of a time division multiple access/time division duplex (TDMA/TDD) based adaptive modulation system to verify feasibility and its usefulness for future wireless multimedia communication systems. The developed system employs a symbol rate and modulation level controlled adaptive modulation in which the modulation scheme is selected from full-rate 64-ary quadrature amplitude modulation (64 QAM), full-rate 16 QAM, full-rate quaternary phase shift keying (QPSK), 1/2-rate QPSK, 1/4-rate QPSK, 1/8-rate QPSK and no transmission according to the expected channel condition for the transmitted signal. The experimental results confirm that the developed system is very effective in achieving high quality and high bit rate transmission of around 1 Mbit/s without any special anti-frequency selective fading techniques even under frequency selective fading conditions with its d delay spread of less than 250 ns and f/sub d/ of less than 10 Hz.

Underwater acoustic voice communications using digital pulse position modulation

Abstract: The paper presents a novel technique for underwater acoustic voice communications. The speech signal is compressed prior to transmission by using linear predictive coding and transmission of appropriate speech parameters is achieved by digital pulse position modulation. The main emphasis is on the reception of the multipath-dominant signal and on the demodulation process.

Pulse position modulation communications protocol

Abstract: A method for modulating a radio signal has the steps of: predetermining a first time interval so as to define a data word; generating a synchronization pulse, the synchronization pulse initiating a single data word having a length of the predetermined first time interval; and generating a single data pulse within the data word after a second time interval with respect to the synchronization pulse, the length of the second time interval defining at least one character. Defining at least one character by a single data pulse after a second time interval with respect to the synchronization pulse enhances an energy efficiency of the transmitted radio signal while mitigating a duty cycle thereof.

Method for decoding and error correcting data of tactical air navigation and distance measuring equipment signals

Abstract: A method and apparatus for encoding and decoding data on navigation signal pulse pairs utilizes pulse position modulation (PPM). The pulse interval between a first pulse and a second pulse of the pulse pair is varied depending on whether the logic value of the data to be encoded is a logic "0" or a logic "1". A tri-graph encoding process converts the raw input data into encoded input data. Each input data bit is encoded into three bits with each bit having the same logical value as the input data bit. The encoded input data is then encoded on the navigation signal using a pulse position modulation (PPM) technique. A decoder recovers the encoded data and provides an error correction process for high data integrity that corrects certain bit errors that may occur during the transmission and reception of the data on the navigation signal. The error correction process detects and corrects errors such as a missing bit, an extra bit or a bit error.

Implementation and performance of QAM-level-controlled adaptive modulation for land mobile communications

Abstract: The hardware implementation and performance of an adaptive modulation system in which a suitable level of quadrature amplitude modulation (QAM) is selected for each time slot are reported for land mobile communications. The authors confirm that the system provides a twofold improvement in spectral efficiency compared to a non-adaptive modulation system.

Transform modulations for mobile communications

Abstract: A new modulation scheme called transform modulations is proposed which improves the system performance in frequency-flat fading mobile channels. They ameliorate the effect of the fadings over the transmitted signal by spreading the information in time, using a linear transform operator. The design of this scheme is discussed and its advantages are shown by means of simulations. The relationship of this scheme with OFDM modulation is also analyzed.

Performance limitations of free-space optical communication satellite networks due to vibrations: direct-detection digital mode

Abstract: Free space optical communication between satellites networked together can permit high data rates between different places on earth. The use of optical radiation as a carrier between the satellites permits very narrow beam divergence angles. Due to the narrow beam divergence angle and the large distance between the satellites the pointing from one satellite to another is complicated. The pointing task is further complicated due to vibration of the pointing system caused by tracking noise and mechanical impacts. In this work we derive mathematical performance models for digital direct detection communication satellite networks as a function of the system parameters, the number of satellites, and the vibration amplitude. The optical inter- satellite network model considered includes a transmitter satellite, regenerative satellites, and a receiver satellite all networked together. A comparison between three communication system modulation schemes on-off keying, pulse position modulation, and pulse polarization binary modulation is presented. These models are the basis for optical communication tracking and pointing system design of appropriate complexity and performance in order to make the network as simple and inexpensive as possible. From the analysis it is clear that even low vibration amplitude of one satellite pointing system decreases dramatically the network performance.

Hybrid permutation frequency phase modulation

Abstract: In mobile radio and satellite communications, power and bandwidth efficient modulation schemes are highly desirable, For this purpose, we propose a new modulation technique called hybrid permutation frequency phase modulation (HPM). The performance of HPM has been studied in AWGN and frequency selective Rayleigh fading channels. Coded HPM is proposed for achieving diversity transmission over fading channels.

High-speed free-space laser communication

Abstract: The laser communication system proposed here for short-distance horizontal ground links and for the link between a ground station and a geostationary satellite will provide eye-safe and power-efficient communication by using a wavelength between 1.5 and 2.2 µm. This proposal is based on the results of a space laser communication system study, and the proposed system will use high-speed optical devices and adaptive optics that actively compensate wavefront distortions. A link budget study shows that a system with a 10-Gbps bit-rate between a geostationary satellite and a ground station can be constructed using technology already available. The power efficiency of the system is expected to be improved by using a multilevel pulse position modulation scheme, short-pulse lasers, and fiber amplifiers.

Multi-channel equalization for PWM channels in magneto-optical recording

Abstract: We show by modeling and simulations that multitrack readback and equalization can lead to significant increases in the track density in magneto-optical recording without performance degradation due to two dimensional interference. We assume an architecture in which an isolated set of closely spaced tracks is read simultaneously. In an earlier paper, we described a multi-channel zero-forcing equalizer and a two-dimensional decision-feedback equalizer for this architecture, and presented their performance for PPM (pulse position modulation) optical recording channels. Since PWM (pulse width modulation) recording is more popular in magneto-optic (MO) disks, we model the PWM channel in this paper and show simulation results for the performance improvement obtained by using multi-channel equalization for data recorded in PWM format.

Performance of the /spl pi//4-DQPSK, GMSK, and QAM modulation schemes in mobile radio with multipath fading and nonlinearities

Abstract: As mobile communications have become so indispensable, every possible effort should be spent to achieve the optimum operating conditions. In addition to the normal impairments associated with wireless communications, in general, the mobile channel suffers from particular limitations that confine the performance of a mobile radio system. Among those impairments are the bandwidth limitation, interference, and multipath fading. With the strong motivation toward portable radio and personal communication systems, power limitation has manifest itself in the picture, and, consequently, nonlinear operation of the amplifiers involved (hence, the channel) will have to be dealt with. Constant envelope modulation schemes have been used in digital mobile radio systems recently installed. The Gaussian minimum shift keying (GMSK) is employed in the Global System for Mobile (GSM) communications installed in Europe, while in the North American IS-54 system, the modulation scheme used is the /spl pi//4-DQPSK. As the quest for higher data rates has kept on increasing, multilevel modulation schemes have been proposed with their performance over nonlinear channels having been overlooked. The paper provides a comparative study, based on simulation, and tests the performance of various modulation schemes operating over a wide variety of mobile radio channel conditions. The effective throughput of all systems is also considered.

Optical multi-wavelength PPM for high data rate transmission on indoor channels

Abstract: In indoor optical channels, intersymbol interference (ISI) due to the multipath propagation prevents high data rate transmission. A new optical multi-wavelength PPM (pulse position modulation) has been investigated for improving the quality of transmission. In this strategy, parallel transmission is accomplished which lowers the data rate per channel and thus reduces the effect of ISI. Furthermore, this strategy also implements a parallel coding technique in the predetermined parallel branches. This parallel coding corrects errors without changing the system data rate. The simulation results show that a combination of these methods can achieve high quality transmission without reduction of the total data rate.

Adaptive suboptimum detection of optical PPM signal with detection matrix and centroid tracking

Abstract: In some applications of optical communication systems, such as satellite optical communication and atmospheric optical communication, the optical beam wanders on the detector surface due to vibration and turbulence effects, respectively. The wandering of the beam degrades the communication system performance. In this research, we derive a mathematical model of an optical communication system with a detection matrix to improve the system performance for direct detection pulse position modulation (PPM) We include a centroid tracker in the communication system model. The centroid tracker tracks the center of the beam. Using the position of beam center and an apriori model of beam spreading we estimate the optical power on each pixel (element) in the detection matrix. Based on knowledge of the amplitudes of signal and noise in each pixel, we tune adaptively and separately the gain of each individual pixel in the detection matrix for communication signals. Tuning the gain is based on the mathematical model derived in this research. This model is defined as suboptimal due to some approximations in the development and is a suboptimum solution to the optimization problem of n multiplied by m free variables, where U,mare the dimensions of the detection matrix. Comparison is made between the adaptive suboptimum model and the standard model. From the mathematical analysis and the results of the comparison it is clear that this model improves significantly communication system performance.

Multicarrier/QAM-level-controlled adaptive modulation for land mobile communication systems

Abstract: A multicarrier and an adaptive modulation combined system, where a suitable level of quadrature amplitude modulation (QAM) is selected for each carrier and time-slot using a QAM-level selection scheme, is proposed for digital land mobile communications. The advantages of the system are a mode in which information cannot be transmitted under adverse propagation conditions and a buffer memory to limit a transmission delay time. The QAM-level of each carrier is also controlled collectively according to the amount of the stored data bits in the memory. We confirmed the bit error rate (BER) performances of the system using computer simulation and we found that the system provided a noticeable BER improvement over frequency-selective fading channels and that the selection scheme was effective for a low maximum Doppler frequency and a small size of the memory.

Implementation and performance of an adaptive QAM modulation-level-controlled system for land mobile communications

Abstract: An adaptive modulation system for land mobile communications that can select one of the quadrature amplitude modulation levels as a suitable modulation for the propagation conditions is described. The main characteristics of the system are a mode in which information cannot be transmitted under adverse propagation conditions and a buffer memory for maintaining the data transmission rate. We confirmed the basic performance of the adaptive modulation system using the equipment we developed and we found the measured performance was consistent with computer simulation results. We also found that the adaptive modulation system provided a noticeable improvement in the spectral efficiency and transmission quality.

Performance of an indoor optical wireless PPM-CDMA system with interference cancellation schemes

Abstract: A new pulse position modulation code division multiple access (PPM-CDMA) system is proposed for an indoor optical wireless channel. As a signature sequence for CDMA an optical orthogonal code (OOC) is used. To reduce multiple access interference two interference cancellation schemes are employed: decorrelating detection and successive interference cancellation (SIC). The bit error rate of the proposed system is calculated for a conventional receiver, a decorrelating receiver, and a receiver with SIC. It is shown that PPM-CDMA systems with both decorrelating detection and SIC achieve significant SNR improvement over the system with a conventional receiver.

Investigation of the pulse time modulation techniques for transmission of wideband signals

Abstract: The choice of the modulation format is the principle factor in realising a highperformance bandwidth efficient communication system at an acceptable cost and complexity. Pulse time modulation technique represents an attractive alternative to purely digital or purely analogue modulation schemes which has received considerable attention over the years. But very little work has been reported on pulse slope modulation. In this work a pulse slope modulation introduced and full wavefonn characteristics is given. A simple novel receiver has been proposed, which is based on converting the PSM waveform into a PAM waveform by sampling the received PSM signal at the rise time interval. This design eliminates the use of a differentiator and a voltage slicer adopted in the classical demodulation technique, and it offers simplicity and improved noise performance. A new signal-t-noise formula has been presented for the first time thus enabling users to predict the system noise performance. Experimental results have shown excellent agreement to within + 1 dB with theoretical predictions using the new formula. Results obtained show the potential of PSM in tenns of simplicity and better noise perfonnance compared to its counter part pulse amplitude modulation. Although PTM has many advantages over analogue and digital schemes when employed as a single channel system, it becomes a challenge when multiplexing is involved. Isochronous PTM schemes are suitable while the anisochronous schemes are not. One solution to overcome this problem is to adopt a hybrid or compound modulation technique, where both isochronous and anisochronous schemes can be combined. Compound frequency and width modulation (CPFWM) is one such a scheme which offers bandwidth efficiency, simplicity and low cost over the more commonly used multiplexed techniques. Detailed investigation of CPFWM has been given and in an expression for its spectrum has been developed. The results obtained have been clarified practically and by means of computer simulation to within + 1 dB. In CPFWM, cross talk in the PFM and pWM channels are due to width modulation and frequency modulation, respectively. The main cause of cross talk is the carryover energy from one edge to the next edge. This effect is studied and he results obtained for the cross talk are compared with the predicted data showing an agreement to within + 1 dB. Results were also compared with time division multiplexed pulse position modulation, showing comparable performance and under certain conditions CPFWM offering better performance. Noise performance of PFM and PWM channels has been theoretically and experimentally investigated. It has been shown that PFM is superior to PWM over a wide range of modulation indices and pulse characteristics. When both channels are identical in bandwidth and modulation conditions, PFM offers a 7 dB improvement compared to PWM channel. The noise perfonnance of CPFWM system is also compared with digital and analogue modulation schemes. For 25 dB CNR CPFWM offers a 40 dB SNR which is 20 dB higher than amplitude modulation, 1 7 dB lower than PCM system. At CNR > 35 dB its performance approaches that of PCM system. Thus showing the potential of the scheme.