Showing papers on "Pulse-position modulation published in 2004"

Accurate evaluation of multiple-access performance in TH-PPM and TH-BPSK UWB systems

Abstract: A characteristic function method is proposed for precisely calculating the bit-error probability of time-hopping (TH) ultra-wideband (UWB) systems with multiple-access interference in an additive white Gaussian noise environment. The analytical expressions are validated by simulation and used to assess the accuracy of the Gaussian approximation. The Gaussian approximation is shown to be inaccurate for predicting bit-error rates (BERs) for medium and large signal-to-noise ratio (SNR) values. The performances of TH pulse position modulation (PPM) and binary phase-shift keying (BPSK) modulation schemes are accurately compared in terms of the BER. It is shown that the BPSK system outperforms the binary PPM system for all values of SNR. The sensitivity of the performance of the modulation schemes to the system parameters is also addressed through numerical examples.

Analog space-time coding for multiantenna ultra-wideband transmissions

Abstract: Ultra-wideband (UWB) transmissions have well-documented advantages for low-power, peer-to-peer, and multiple-access communications. Space-time coding (STC), on the other hand, has gained popularity as an effective means of boosting rates and performance. Existing UWB transmitters rely on a single antenna, while ST coders have mostly focused on digital linearly modulated transmissions. In this paper, we develop ST codes for analog (and possibly nonlinearly) modulated multiantenna UWB systems. We show that the resulting analog system is able to collect not only the spatial diversity, but also the multipath diversity inherited by the dense multipath channel, with either coherent or noncoherent reception. Simulations confirm a considerable increase in both bit-error rate performance and immunity against timing jitter, when wedding STC with UWB transmissions.

The effect of NBI on UWB time-hopping systems

Abstract: This letter presents an analysis of the effect of narrowband interference (NBI) on ultrawideband (UWB) time-hopping (TH) systems in the presence of multipath fading using both analytical derivations and simulations. Our analysis demonstrates that NBI may be an issue in some instances. In addition, we suggest three NBI suppression schemes for combating NBI in UWB TH systems. Single-link performance of these schemes in conjunction with a Rake-type receiver structure is estimated for both the ideal all-Rake receiver and the simpler partial-Rake receiver in an indoor environment. Two UWB pulse shapes that meet the Federal Communications Commission rules for UWB communications are considered in the investigation.

Power-efficient multispot-diffuse multiple-input-multiple-output approach to broad-band optical wireless communications

Abstract: In multispot-diffuse multiple-input-multiple-output (MSD-MIMO) system configuration, a communications channel can be considered virtually ideal at data rates of hundreds of megabits per second. Thus, the main concern is power efficiency. We propose a transceiver optical design that creates a reconfigurable transmitter output and independent communications channels. The transmitter employs multiple light sources that can be turned on and off, independently. In this way, an optical signal is provided only where it is needed. The receiver utilizes an imaging optical system and a segmented photodetector, thus performing direction diversity reception. We show that when maximum ratio combining is employed on the received electric signals and power-efficient modulation schemes such as L-level pulse-position modulation are used, significant power savings can be achieved. We also investigate the vulnerability of MSD-MIMO links to shadowing and blockage and their effects on communications cell size and required transmit power in a cellular configuration.

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

Abstract: We present new trellis codes based on multiple-pulse-position modulation (MPPM) for wireless infrared communication. We assume that the receiver uses maximum-likelihood sequence detection to mitigate the effects of channel dispersion, which we model using a first-order lowpass filter. Compared to trellis codes based on PPM, the new codes are less sensitive to multipath dispersion and offer better power efficiency when the desired bit rate is large, compared with the channel bandwidth. For example, when the bit rate equals the bandwidth, trellis-coded (17 2)-MPPM requires 1.4 dB less optical power than trellis-coded 16-PPM having the same constraint length.

A PPM Gaussian monocycle transmitter for ultra-wideband communications

Abstract: A Gaussian pulse generator incorporating a pulse position modulator for use in an impulse radio ultrawideband system is described. The pulse generator is preceded by a programmable pulse position modulator and comprises a cascade of complex first-order systems, which, in turn, are made up of differential pairs employing partial positive feedback. The resulting PPM Gaussian pulse generator is designed in IBM 0.18 /spl mu/m Bi-CMOS IC technology. Simulations predict the correct operation of the circuit for supply voltages of 1.8 V and a power consumption of 30 mW. The output monocycle indeed approximates a Gaussian monocycle, having a pulse duration of about 250 ps. Proper modulation of the pulse in time is confirmed.

A MAC protocol for UWB Very Low Power Mobile Ad-hoc Networks based on Dynamic Channel Coding with Interference Mitigation

Abstract: We propose a MAC protocol for very low radiated power (1 microwatt) ultra-wide band (UWB) mobile ad-hoc networks. Unlike traditional approaches, our protocol fully utilizes the specific nature of the physical layer of UWB. This makes it possible to reach a reasonably high bit rate per source in spite of the low power, while being fully distributed. We use dynamic channel coding as an efficient way to adapt to varying channel conditions due to mobility and interference. Our design is based on existing theoretical findings that state that it is optimal to allow interfering sources to transmit simultaneously, as long as they are outside a well-defined exclusion region around a destination, and to adapt the channel code to this interference; in contrast, interference from inside the exclusion region should be combatted. We use pulse position modulation, as is commonly done with UWB. The very low power assumption implies that pulses are infrequent. This property, together with a demodulation scheme that cancels much of the interfering energy, allows us to mitigate interference from nodes in the exclusion region. This scheme is entirely local to a destination and involves no protocol action. In addition, sources constantly adjust their channel codes (thus their bit rates) and send incremental redundancy as required. Contention between sources sending to the same destination is solved by a private MAC protocol, i.e., a set of interactions that involve only the nodes that want to talk to the same destination. Carrier sensing is not used, as it is practically impossible with UWB. We show by simulation that we achieve a significant increase in network throughput, compared to traditional MAC protocols that are separated from the physical layer.

Performance analysis of DS-UWB multiple access under imperfect power control

Abstract: Ultra-wideband (UWB) technology is characterized by transmitting extremely short duration radio impulses. To improve its multiple-access (MA) capability, UWB technology can be combined with traditional spread-spectrum techniques. So far, much of the research has focused on perfect power-control conditions and on employing time-hopping spread-spectrum with impulse radio using pulse-position modulated signals. In this letter, we outline the attractive features of direct-sequence (DS) UWB MA systems employing antipodal signaling and compare it with time hopping. Performance of DS-UWB communication systems, in terms of MA capability and bit-error rate performance, are evaluated under both perfect and imperfect power-control conditions. An upper bound on the total combined bit-transmission rate is derived.

Electronic equalization for advanced Modulation formats in dispersion-limited systems

Abstract: We investigate in this letter the use of electronic equalization on dispersion-limited systems for different modulation formats. Besides analyzing equalization on standard nonreturn-to-zero (NRZ) intensity modulation as a reference, we focus on two advanced modulation formats, duobinary (DB) and differential phase-shift keying (DPSK) which are recently gaining a lot of attention. We demonstrate that the introduction of an electronic equalizer strongly improves standard NRZ performance, whereas, it has a limited effect on DB and DPSK formats. Moreover, we give rules for the optimal choice of the equalizer transversal filter parameters, i.e., the number of taps and the delay between taps.

PSSS - parallel sequence spread spectrum a physical layer for RF communication

Abstract: Parallel sequence spread spectrrim PSSS pro1ides a physical layer for RF data communication. It is based on an overlap of cyclically shified binary spreading sequences modulated with Mary PAM. QAM and PSK. Coding, modulation and channel equa1ization can be integrated and allow a flexiable tradeoff hetween data rate, energy efficiency and multipath fading resistonce at a low electronic complexity. This paper describes the principles of the transmission procedure including the spreading, overlap and modulation. Some results are shown from AWGN-channels with different modulation procedurers.

Ghost-pulse reduction in 40-Gb/s systems using line coding

Abstract: At high bit rates, four-wave mixing and nonlinearities in the optical channel give rise to ghost pulses. In this letter, we propose the application of modulation codes to tackle this effect.

On the performance evaluation of TH and DS UWB MIMO systems

Abstract: In this paper, we analyze the performance of ultra-wideband (UWB) multiple-input multiple-output (MIMO) systems employing various modulation and multiple access schemes, including time hopping (TH) M-ary pulse position modulation (MPPM), TH binary phase shift keying (BPSK), and direct sequence (DS) BPSK. We quantify the performance merits of UWB space-time (ST) systems regardless of the specific coding scheme. For each modulation scheme, we introduce a framework that enables us to compare UWB MIMO systems with conventional UWB single-antenna systems in terms of diversity and coding gain. Moreover, we adopt the real orthogonal design (ROD) as the engine code for UWB ST codes. We find the closed form expressions of the average pairwise error probability (PEP) bound for all of the schemes under the hypothesis of Nakagami flat fading channels. The extension to frequency-selective fading case is also briefly addressed. Finally, simulation results are presented to support the theoretical analysis.

Infrared transmission for intervehicle ranging and vehicle-to-roadside communication systems using spread-spectrum technique

Abstract: In this paper, an infrared intervehicle ranging and vehicle-to-roadside communication systems are studied. A direct-sequence spread-spectrum (DS-SS) technology is employed to obtain the robustness against multiuser interference and ambient light noise. We compare the correlation properties for various optical spreading codes such as an optical orthogonal code (OOC), a prime code, an extended prime code, and a modified m-sequence. The performance of the infrared DS-SS ranging and communication system is evaluated by computer simulation over a channel in consideration of multipath dispersion, multiuser interference, and a background light noise. The infrared DS-SS intervehicle ranging system using an OOC has lower ranging error rate (RER) than ranging systems using a prime code, an extended prime code, and modified m-sequences even if there is the interference from other users and lightwave dispersion. In the infrared DS-SS vehicle-to-roadside communication system, L-ary pulse position modulation (L-PPM) is used as a modulation scheme due to high average power efficiency. It is shown that the proposed system achieves smaller BER performance as the modulation order L increases and the proposed system with a (361,6,1,1) OOC has a smaller BER than that with a (181,6,1,1) OOC.

Ultra wide-band communications with blind channel estimation based on first-order statistics

Abstract: Ultra wideband (UWB) communication holds great potential for significantly improved data rate in future wireless systems. Accurate channel estimation and synchronization are critical for successful operation of a UWB system. We propose in this paper a completely blind channel estimation and synchronization algorithm for UWB systems that employ pulse-position modulation. The algorithm exploits the first-order cyclostationarity in the received signal and performs certain circular deconvolution. The complexity is extremely low - only some "overlap-add" operations and FFT operations are needed. The algorithm is capable of simultaneously estimating multiple (say, more than 60) channel taps and there is no ambiguity in either the amplitude or the phase of the estimated channel. It is shown that using the estimated channel from 500 information symbols, the performance can approach that with the known channel within 2 dB in signal to noise ratio for bit error rate less than 0.01.

A novel multi-antenna impulse radio UWB transceiver for broadband high-throughput 4G WLANs

Abstract: In the last years, a lot of attention has been devoted to both multi-antenna systems with space-time orthogonal block coding (STOBC) and ultra wideband (UWB) transceivers based on impulse-radio (IR) technologies. In this short contribution we anticipate the architecture of a novel transceiver merging both multi-antenna and pulse position modulation (PPM) IR-UWB techniques and then we test the performance in flat-faded application scenarios typical of emerging broadband 4G WLANs. Three main appealing features are retained by the sketched transceiver scheme. First, it allows to equip the UWB receiver with reliable estimates of the (possibly time-varying) underlying multiple-input multiple-output (MIMO) UWB without reducing the overall information throughput conveyed by the system. Second, the performance confirms that the proposed transceiver is able to achieve "full diversity" even at SNRs as low as 1.5-2 dB. As a consequence, the resulting BERs outperform those of current Single-Input Single-Output (SISO) IR-UWB transceivers over two orders of magnitude even at SNR's as low as 3-4 dB. Third, at target BER's below 10/sup -2/ and radiated powers around 250 /spl mu/W, the coverage ranges allowed by the proposed MIMO IR-UWB scheme typically outperform those of conventional SISO IR-UWB ones of about two orders of magnitude.

Performance analysis and tradeoffs for dual-pulse PPM on optical communication channels with direct detection

Abstract: The performance and tradeoffs of multipulse position modulation (MPPM) are investigated and compared with that of the traditional (single) pulse position modulation (PPM) scheme typically employed on the optical direct-detection channel. While the primary motivation for the consideration of the problem is to provide performance improvement for deep-space optical communications where narrow high-peak-power transmitted pulses offer significant advantages in terms of detection probabilities and background suppression capabilities at the receiver, the results obtained are sufficiently generic as to apply to other applications.

Circuit and method for pulse width modulation

Abstract: A circuit and a method for performing pulse width modulation are provided. A pulse density modulator (PDM) is applied to receive the least N bits of the input data and to generate a pulse density modulation signal. The number of pulse of the pulse density modulation signal in 2{circumflex over ( )}N frames correspond to a value of the least N bits of the input data. An adder is applied to generate a PWM data by adding a value of the most M bits of the input data to a value of the pulse density modulation signal generated by the PDM. A pulse width modulator is applied to generate a PWM signal dithering in 2{circumflex over ( )}N frames according to the PWM data generated by the adder, so as to improve the audio quality of pulse width modulation and the Electro-Magnetic Interference (EMI) phenomenon.

Pulse width modulation fan control

Abstract: In one embodiment, a fan control system includes a temperature-sensing device that is adapted to sense a temperature of a component and output a temperature feedback signal, and a pulse width modulation control circuit that is configured to receive the temperature feedback signal output from the temperature-sensing device and a separate fan command signal and, relative to those signals, generate a pulse width modulation signal that is sent to a pulse width modulation controlled fan.

System and method for transitioning between modulation formats in adjacent bursts triggering on data flow

Abstract: A system and method are provided for transitioning between modulation formats in adjacent transmit bursts. The system includes a modulation system having a data interface, first modulation circuitry operating according to a first modulation format, and second modulation circuitry operating according to a second modulation format. During a transition between a first transmit burst in the first modulation format and a second transmit burst in the second modulation format, the data interface receives a timing signal signifying a start of data for the second transmit burst. In response to the timing signal, the second modulation circuitry resets, and the data interface delays the data for the second transmit burst by a modulator delay time. By delaying the data for the second transmit burst, a glitch caused by resetting the second modulation circuitry arrives at the output of the second modulation circuitry prior to the data for the second transmit burst.

Pulse position amplitude modulation for time-hopping multiple access UWB communications

Abstract: In this paper, we propose a new modulation scheme called pulse amplitude position modulation (PPAM) for ultra-wideband (UWB) communication systems. PPAM combines pulse position modulation (PPM) and pulse amplitude modulation (PAM) to provide good system performance and low computational complexity. A set of MN-ary, M=2/sup k/, N=2/sup N/. PPAM signals are constructed from N-ary orthogonal PPM signals by including M-ary PAM signals in each dimension. It is shown that MN-ary PPAM has better performance than MN-ary PAM and less complexity than MN-ary PPM for MN>2. The channel capacity of PPAM is determined for a time-hopping multiple access UWB communication system. The error probability and performance bounds are derived for a multiuser environment. In particular, it is shown that for M=2. 2N-ary PPAM signals have better performance than 2N-ary PPM with the same throughput and half the computational complexity.

Performance implications of wide-band lasers for FSK modulation labeling scheme

Abstract: Optical labeling via frequency-shift keying (FSK) modulation capability of a grating-assisted codirectional coupler with sampled grating reflector laser is investigated for the first time. FSK modulation can be best implemented with only the phase section current and optical frequency deviation of 20 GHz is achieved. The measured frequency modulation response indicates the limitation of the maximum modulation rate is sufficient for Internet protocol packet optical labeling.

Adaptive modulation transmission system, transmission device, reception device, and method thereof

Abstract: An adaptive modulation transmission system is disclosed that is capable of assigning a combination of a modulation parameter and a code multiplicity according to a user requirement and a propagation path condition between a transmission device and a reception device. The transmission device includes a signal modulation unit to modulate data according to the modulation parameter, a code multiplexing unit to perform code multiplexing according to the code multiplicity, a code multiplexing controller to select the code multiplicity according to the required amount of transmission data, and an adaptive modulation controller. The adaptive modulation controller sets a threshold of the propagation path quality to define a region to which a combination of the modulation parameter and the code multiplicity is applicable, selects the combination of the modulation parameter and the code multiplicity based on a comparison result of the threshold and measured propagation path quality, and outputs the selected modulation parameter to the signal modulation unit.

Selection of modulation and codes for deep-space optical communications

Abstract: We describe several properties of deep space optical channels that lead to an appropriate selection of modulation format, pulse position modulation (PPM) order, error control code rate, and coding scheme. The selection process is motivated by capacity considerations. We compare the Shannon limit to the performance of Reed-Solomon codes and convolutional codes concatenated with PPM and show that, when iteratively decoded, concatenated convolutional codes operate approximately 0.5 dB from capacity over a wide range of signal levels, about 2.5 dB better than Reed-Solomon codes.

Transceiver Design for Ultra-Wideband Communications

Abstract: Despite the fact ultra-wideband (UWB) technology has been around for over 30 years, there is a newfound excitement about its potential for communications. With the advantageous qualities of multipath immunity and low power spectral density, researchers are examining fundamental questions about UWB communication systems. In this work, we examine UWB communication systems paying particular attention to transmitter and receiver design. This thesis is specifically focused on a software radio transceiver design for impulse-based UWB with the ability to transmit a raw data rate of 100 Mbps yet encompasses the adaptability of a reconfigurable digital receiver. A 500 ps wide Gaussian pulse is generated at the transmitter utilizing the fast-switching characteristics of a step recovery diode. Pulse modulation is accomplished via several stages of RF switches, filters, and amplifiers on a fully designed printed circuit board specifically manufactured for this project. Critical hardware components at the receiver consist of a bank of ADCs performing parallel sampling and an FPGA employed for data processing. Using a software radio design, various modulation schemes and digital receiver topologies are accommodated along with a vast number of algorithms for acquisition, synchronization, and data demodulation methods. Verification for the design is accomplished through transmitter hardware testing and receiver design simulation. The latter includes bit error rate testing for a variety of modulation schemes and wireless channels using a pilot-based matched filter estimation technique. Ultimately, the transceiver design demonstrates the advantages and challenges of UWB technology while boasting high data rate communication capability and providing the flexibility of a research testbed.

Ultra narrow band modulation

Abstract: Ultra narrow band modulation and ultra wideband modulation have common mathematical roots. The difference is in the baseband pulse width. UWB utilizes extremely short energy pulses, with long periods of no signal between pulses. UNB utilizes a continuous wave signal with individual RF cycles removed, or phase altered, to indicate a digital ONE.

Unified modulator for continuous phase modulation and phase-shift keying

Abstract: A “unified” modulator for multiple modulation schemes (e.g., GMSK and 8PSK) is described. The waveform for each modulation scheme is generated based on a set of one or more pulse shaping functions. The waveforms for all supported modulation schemes may be generated based on a composite set of all the different pulse shaping functions. The unified modulator includes a filter for each pulse shaping function in the composite set. To generate the waveform for a selected modulation scheme, the set of one or more filters for this modulation scheme is enabled and all other filters are disabled. The outputs from all enabled filters are summed to generate a modulator output. When switching between modulation schemes, a smooth transition may be obtained by (1) providing a suitable data pattern for each filter to be enabled or disabled and (2) generating symbols for the new modulation scheme with an appropriate initial phase.

Transmission rate changing method, and base station apparatus using the same

Abstract: The modulation/demodulation unit modulates information to be transmitted, or demodulates information received. The time slot control unit assigns time slots to a terminal apparatus when the base station apparatus establishes connection with the terminal apparatus. The quality derivation unit derives the quality of the transmission links as appropriate. The modulation mode control unit determines the modulation modes suitable for the quality of the transmission links for the up link and down link, respectively. Moreover, when the remaining period of the time slots is greater than or equal to a threshold value, the modulation mode control unit determines to change the modulation modes currently in use into the modulation modes determined. When the remaining period is smaller than the threshold value, the modulation mode control unit determines to keep using the modulation modes currently in use without changing to the modulation modes determined.

An adaptive UWB modulation scheme for optimization of energy, BER, and data rate

Abstract: For many networks, different types of data require various QoS (quality of service) constraints such as bit error rate (BER), data rate, or energy dissipation. High data rate, low power dissipation, and simple RF circuitry make ultra wideband (UWB) an attractive technology to meet many QoS requirements. Typical UWB systems are built to meet QoS constraints even under the worst environmental conditions, although the worst environmental conditions occur infrequently. To prevent this waste of resources, we propose a UWB physical layer that adapts its modulation scheme to meet QoS requirements efficiently. The system employs m-ary PPM and adapts its pulse repetition interval (PRI) and/or the number of bits per symbol (log/sub 2/m). Compared to a non-adaptive system, the adaptive system can improve BER up to 50%, energy by 60%, or data rate by 260%.

Receiving/backscattering arrangement and method with two modulation modes for wireless data transmission as well as modulation arrangement therefor

Abstract: For transmitting data, a receiving/backscattering arrangement receives, modulates and reflects or backscatters electromagnetic waves emitted by a base station. The modulation corresponds to the data to be transmitted and is carried out selectively using first and/or second different modulation methods depending on the received field strength of the received electromagnetic waves. Preferably, phase shift keying is used especially or at least at low field strengths at far range, while amplitude shift keying is used additionally or alternatively for high field strengths at close range. The two modulation methods can be superimposed. A circuit arrangement includes two different modulator arrangements to perform the two modulation methods depending on the received field strength. The second modulator arrangement preferably comprises a multi-stage voltage multiplier circuit with a modulated switching device intervening in one of the stages to achieve the modulation.

Equivalent system model of ISI in a frame-differential IR-UWB receiver

Abstract: A discrete-time equivalent system model is derived for the intersymbol interference in a differential ultra wideband (UWB) impulse radio (IR) system operating in a multipath propagation environment. Data is transmitted using differential binary modulation on a frame-level (i.e., among UWB pulses), which is a variant of the well-known transmitted reference UWB schemes, proposed for higher data rates. It is shown that the UWB system is accurately modeled as a second-order discrete time Volterra system. Equations are presented to determine the coefficients of this non-linear model. The impact of noise is characterized. The proposed model can be used to develop signal processing algorithms for UWB-receivers in order to enhance the data rate or multiuser capabilities, for instance.