Showing papers on "Keying published in 2001"

Binary Offset Carrier Modulations for Radionavigation

Abstract: Current signaling for GPS employs phase shift keying (PSK) modulation using conventional rectangular (non-return to zero) spreading symbols. Attention has been focused primarily on the design of the spreading code and selection of the keying rates. But better modulation designs are available for next-generation radionavigation systems, offering improved performance and the opportunity for spectrum sharing while retaining implementation simplicity. This paper describes a class of particularly attractive modulations called binary offset carrier (BOC). It presents important characteristics of modulations for radionavigation, introduces several specific BOC designs that satisfy different applications in evolving radionavigation systems, describes receiver processing for these modulations, and provides analytical and numerical results that describe the modulations' performance and demonstrate advantages over comparable conventional PSK modulations with rectangular spreading symbols.

Iterative channel estimation and decoding of pilot symbol assisted turbo codes over flat-fading channels

Abstract: A method for coherently detecting and decoding turbo-coded binary phase shift keying (BPSK) signals transmitted over frequency-flat fading channels is discussed. Estimates of the complex channel gain and variance of the additive noise are derived first from known pilot symbols and an estimation filter. After each iteration of turbo decoding, the channel estimates are refined using information fed back from the decoder. Both hard-decision and soft-decision feedback are considered and compared with three baseline turbo-coded systems: (1) a BPSK system that has perfect channel estimates; (2) a system that uses differential phase shift keying and hence needs no estimates; and (3) a system that performs channel estimation using pilot symbols but has no feedback path from decoder to estimator. Performance can be further improved by borrowing channel estimates from the previously decoded frame. Simulation results show the influence of pilot symbol spacing, estimation filter size and type, and fade rate. Performance within 0.49 and 1.16 dB of turbo-coded BPSK with perfect coherent detection is observed at a bit-error rate of 10/sup -4/ for normalized fade rates of f/sub d/T/sub s/=0.005 and f/sub d/T/sub s/=0.02, respectively.

Performance analysis of combined transmit-SC/receive-MRC

Abstract: The average bit-error rate of transmit antenna selection combined with receive maximum-ratio combining is computed as a function of the transmit antenna update rate when using binary phase-shift keying in flat Rayleigh fading channels. This scheme achieves an order of diversity equal to the product of the number of transmit and receive antennas. Therefore, it can gain significant diversity benefits over traditional receive diversity schemes by distributing the antennas over the transmit and receive side.

Analysis of channel effects on direct-sequence and frequency-hopped spread-spectrum acoustic communication

Abstract: Multiuser underwater acoustic communication is one of the enabling technologies for the autonomous ocean-sampling network (AOSN). Multiuser communication allows vehicles, moorings, and bottom instruments to interact without human intervention to perform adaptive sampling tasks. In addition, multiuser communication may be used to send data from many autonomous users to one buoy with RF communications capability, which will then forward the information to shore. The two major signaling techniques for multiuser acoustic communication are phase-shift keying (PSK) direct-sequence spread-spectrum (DSSS) and frequency-shift keying (FSK) frequency-hopped spread-spectrum (FHSS). Selecting between these two techniques requires not only a study of their performance under multiuser conditions, but also an analysis of the impact of the underwater acoustic channel. In the case of DSSS, limitations in temporal coherence of the channel affect the maximum spreading factor, leading to situations that may be better suited to FHSS signals. Conversely, the multipath resolving properties of DSSS minimize the effects of frequency-selective fading that degrade the performance of FSK modulation. Two direct-sequence receivers potentially suitable for the underwater channel are presented. The first utilizes standard despreading followed by decision-directed gain and phase tracking. The second uses chip-rate adaptive filtering and phase tracking prior to despreading. Results from shallow water testing in two different scenarios are presented to illustrate the techniques and their performance.

Space-time turbo codes with full antenna diversity

Abstract: In attempting to find a spectrally and power efficient channel code which is able to exploit maximum diversity from a wireless channel whenever available, we investigate the possibility of constructing a full antenna diversity space-time turbo code. As a result, both three-antenna and two-antenna (punctured) constructions are shown to be possible and very easy to find. To check the decodability and performance of the proposed codes, we derive non-binary soft-decoding algorithms. The performance of these codes are then simulated and compared with two existing space-time convolutional codes (one has minimum worst-case symbol-error probability; the other has maximal minimum free distance) having similar decoding complexity. As the simulation results show, the proposed space-time turbo codes give similar or slightly better performance than the convolutional codes under extremely slow fading. When fading is fast, the better distance spectra of the turbo codes help seize the temporal diversity. Thus, the performance advantage of the turbo codes becomes evident. In particular, 10/sup -5/ bit-error rate and 10/sup -3/ frame-error rate can be achieved at less than 6-dB E/sub b//N/sub 0/ with 1 b/s/Hz and binary phase-shift keying modulation. The practical issue of obtaining the critical channel state information (CSI) is also considered by applying an iteratively filtered pilot symbol-assisted modulation technique. The penalty when the CSI is not given a priori is about 2-3 dB.

A new family of MMSE multiuser receivers for interference suppression in DS/CDMA systems employing BPSK modulation

Abstract: We deal with interference suppression in asynchronous direct-sequence code-division multiple-access (CDMA) systems employing binary phase-shift keying modulation. Such an interference may arise from other users of the network, from external low-rate systems, as well as from a CDMA network coexisting with the primary network to form a dual-rate network. We derive, for all of these cases, a new family of minimum mean-square-error detectors, which differ from their conventional counterparts in that they minimize a modified cost function. Since the resulting structure is not implementable with acceptable complexity, we also propose some suboptimum systems. The statistical analysis reveals that both the optimum and the suboptimum receivers are near-far resistant, not only with respect to the other users, but also with respect to the external interference. We also present a blind and a recursive least squares-based, decision-directed implementation of the receivers wherein only the signature and the timing of the user to be decoded and the signaling time and the frequency offset of the external interferer are assumed known. Finally, computer simulations show that the proposed adaptive algorithm outperforms the classical decision-directed RLS algorithm.

Method and apparatus for keying ink supply containers

Abstract: Embodiments of the present invention comprise containers for consumable substances, such as ink, and the corresponding receiving stations, such as inkjet printers. The containers and receiving stations have mating keying features indicative of a characteristic of the consumable substance, such as the ink family. Embodiments of the mating features include protuberances with a T-shaped cross section, and corresponding T-shaped slots. Preferred embodiments of containers and receiving stations are disclosed having two keying features with four unique orientations per feature, for a total 16 key permutations.

Key distribution for secure multimedia multicasts via data embedding

Abstract: The problem of controlling access to multimedia multicasts requires the distribution and maintenance of keying information. The conventional approach to distributing keys is to use a channel independent of the multimedia content. We propose a second approach that involves the use of a data-dependent channel, and can be achieved for multimedia by using data embedding techniques. Using data embedding to convey rekeying messages can provide an additional layer of security when compared with the traditional approach. We then introduce multicast key distribution, and employ a recent tree-based key distribution scheme to exhibit the factors involved in transmitting keys using data embedding.

Optical differential phase shift keying (DPSK) direct detection considered as a duobinary signal

Abstract: Optical differential phase shift keying (DPSK) may be considered as a duobinary signal. Considering duobinary coding properties, we show theoretically and experimentally that the complicated Mach-Zehnder modulator used at the receiver side can be replaced by a standard narrow optical filter.

80-Mb/s QPSK and 72-Mb/s 64-QAM flexible and scalable digital OFDM transceiver ASICs for wireless local area networks in the 5-GHz band

Abstract: With the advent of mobile communications, voice telecommunications became wireless. Future applications, however, target multimedia, messaging, and high-speed Internet access, all expressing the need for a broadband high-speed wireless access technique. Both the domestic multimedia and the wireless local area network (WLANs) business markets are addressed. Established systems deliver 2-11 Mb/s based on spectrally inefficient spread-spectrum techniques, where scalability has reached a limit. The next generation of modems requires spectrally more efficient low-power and highly integrated solutions. We describe here the design of two digital baseband orthogonal frequency division multiplex (OFDM) signal processing ASICs, implementing respectively a quaternary phase-shift keying (QPSK)-based 80-Mb/s and a 64 quadrature amplitude modulation (QAM)-based 72-Mb/s digital inner transceiver. The latter partially matches the Hiperlan/2 and IEEE 802.11a standards. Joint development of signal processing algorithms and architectures along with on-chip data transfer, control, and partitioning leads to a low-power, yet flexible and scalable implementation. Both ASICs were designed in a unique object-oriented C++ design flow starting from algorithm level. The ASICs were successfully tested in a 5-GHz testbed both for file data transfer and web-cam multimedia transmission.

Ultra wide band transmitter

Abstract: The present invention is a transmitter system comprising a data modulation unit, a transmitter unit and an antenna. The data modulation unit is configured to generate a digital stream of pulse data which is synchronized with a master clock. The data modulation unit is configured to support pulse streams having different modulation techniques. The different modulation techniques include on-off keying and pulse amplitude modulation. The data modulation unit may be configured to include both a pulse amplitude modulation module and a pulse repetition frequency module.

Transmitter having a sigma-delta modulator with a non-uniform polar quantizer and methods thereof

Abstract: The invention relates to a sigma-delta N-phase keying modulator having non-uniform polar quantisation. According to one embodiment of the invention, a quantiser produces a quantised output so that it represents a symbol, selected from a set of N symbols, depending on to which of the N non-symmetric cells, covering the complex plane in a non-overlapping manner, the phase of said symbol belongs. This may reduce the occurrence of larger phase transitions, which may lead to increased efficiency. The selection of non- symmetric cell boundaries may also affect the noise shaping spectrum of a sigma-delta N-PSK modulator. The invention also relates to an N-phase keying modulation method and a mobile telephone or transmitter including the modulator described above.

Selection diversity for wireless communications in Nakagami-fading with arbitrary parameters

Abstract: By means of analytical and numerical methods, the probability of error and the outage probability of a selection diversity RAKE receiver system employing direct sequence/code division multiple access (DS/CDMA) is derived. A noise-limited propagation environment is modeled as a Nakagami (1960)-fading channel with arbitrary fading parameters and unequal mean power at the receiver. New analytical expressions are derived for the average probability of error and outage probability. Binary detection schemes are considered including binary phase-shift keying (PSK) and frequency-shift keying (FSK). Both coherent and noncoherent detection is considered as well as identical and arbitrary fading. It is shown that the effect of arbitrary fading on system performance is significant and may not be ignored.

A low-power all-digital FSK receiver for space applications

Abstract: A frequency-shift keying (FSK) receiver has been designed for deep space applications which exhibits potential for ultra low power performance. The receiver is based on a novel, almost all-digital architecture. It supports a wide range of data rates and is very robust against large and fast frequency offsets due to Doppler. The architecture utilizes subsampling and 1-bit data processing together with a discrete Fourier transform-based detection scheme to enable power consumption dramatically lower than implementations reported in the literature. Novel and power-efficient algorithms are derived for frequency and timing tracking. Most of the power saving techniques are applicable to a variety of applications, but some are achieved by taking advantage of the asymmetric power constraints for the receiver and the transmitter as well as the absence of adjacent channel interferers. The worst-case bit-error rate (BER) performance of the receiver is just 2.5 dB below that of the optimal uncoded noncoherent FSK receiver at a BER of 10/sup -6/ and better for lower BERs.

Chaotic on–off keying for secure communications

Abstract: We experimentally demonstrate a chaotic on–off keying method for secure communications by using chaos synchronization in two microchip lasers. The output of the microchip laser in the transmitter is externally modulated with an acousto-optic modulator at ∼4 MHz. One encodes a digital message in the chaotic carrier by turning the modulation on and off at 100 kHz. Because the accuracy of synchronization for the slave laser in the receiver tends to be degraded in the presence of external modulation in the injection laser signal, one can distinguish two binary states. The digital message can be recovered as an envelope of the chaotic oscillation when the difference between the two laser outputs of the transmitter and the receiver is calculated.

Low-rate super-orthogonal channel coding for fiber-optic CDMA communication systems

Abstract: In this paper, we consider using practical low-rate error correcting codes in fiber-optic code division multiple-access (CDMA) communication systems. To this end, a different method of low-rate channel coding is proposed. As opposed to the conventional coding schemes, this method does not require any further bandwidth expansion for error correction in fiber-optic CDMA communication systems. The low-rate channel codes that are used for demonstrating the capabilities of the proposed method are super-orthogonal codes. These codes are near optimal and have a relatively low complexity. We evaluate the upper bounds on the bit-error probability of the proposed coded fiber-optic CDMA system assuming both on-off keying and binary pulse position modulation schemes. It is shown that the proposed method significantly outperforms the uncoded systems for various receiver structures such as a correlator with and without hard-limiter and chip-level detector. Furthermore, the performance of the proposed coded fiber-optic CDMA system is also evaluated in the presence of different values of dark current.

Long haul optical communication system

Abstract: A high bit rate, long haul optical communication system encodes a polarization interleaved stream of RZ optical pulses using phase shift keying (PSK) or differential phase shift keying (DPSK), in contrast to conventional on-off keying (OOK). The polarization interleaved stream of RZ optical pulses can be used for PSK or DPSK encoding of either one data stream having a bit rate that is the same as the optical stream pulse rate, or two (or more) independent data streams which individually each have lower bit rates, but which, when combined, have the same rate as the optical stream pulse rate. The latter arrangement essentially accomplishes polarization multiplexing (P-MUX). Individual wavelengths can be combined in a WDM or DWDM system, wherein, at the transmitter, multiple streams of polarization interleaved pulses, each stream having a different wavelength, are combined. At the receiver, the received combined signal is wavelength division demultiplexed, and the encoded data in each wavelength channel is recovered by a PSK or DPSK receiver, which, in the DPSK example, usually consists of a delay demodulator and a balanced detector. The transmission medium and laser power may be managed, for example so that the pulse transmission comprises solitons.

Mixed-signal map-configurable integrated chaos generator for chaotic communications

Abstract: This paper proposes a mixed-signal map-configurable chaos generator suitable for silicon integration, and makes an exhaustive analysis of its error sources and tolerance to the onset of saturation. The developed methodology has been applied in the design, embedded in a complete frequency-modulated differential-chaos shift keying (FM-DCSK) modem, of a chaos generator which achieves 10 bit resolution at a maximum clock frequency of 20 MHz, from a 3.3-V power supply.

Validating keying material by using a validation area of read-only media to prevent playback of unauthorized copies of content stored on the media

Abstract: In one aspect of the invention is a method for preventing unauthorized copies of a medium, such as a DVD, from being played by a compliant device by using the validation area (VA) region of a medium to validate keying material. A compliant device is a device that will validate keying material. In one embodiment of the invention, a compliant device validates keying material by using the value in the VA region of the medium. In alternative embodiments, a compliant device will validate keying material by checking correspondence between keying material written to a non-VA region of a medium and validation data written to a VA region of a medium. In the alternative embodiments, if the keying material does not correspond to the validation data, then a compliant device will prevent the contents of the medium from being played.

Keying system for electrical connector assemblies

Abstract: A keying system for an electrical connector assembly includes a male connector having a body portion, a mating end formed by a plurality of terminal-receiving silos extending from the body portion, and a plurality of support walls integrally joining the silos and combining therewith to define a pattern of interior keying channels. A female connector has a mating end formed by a receptacle, with a plurality of terminals including contact portions extending into the receptacle for insertion into the silos of the male connector. A plurality of locating walls within the receptacle define a pattern of keying members for insertion into the keying channels of the male connector to thereby polarize the connectors.

Long haul transmission in a dispersion managed optical communication system

Abstract: Phase shift keying (PSK) or differential phase shift keying (DPSK) used as the coding scheme in a high bit rate, long haul dispersion-managed optical transmission system, in which the signaling format is RZ. The system can combine multiple individual channels with different wavelengths in a WDM or dense wavelength division multiplexed (DWDM) arrangement. Dispersion management can be provided using several techniques, such as by using dispersion managed solitons, quasi-linear transmission or conventional RZ transmission with pre-compensation and post-compensation.

System for improving the visibility in vehicles

Abstract: A system for improving the visibility in vehicles, including the following: an illumination optical system (2) for continuous radiation of infrared pulsed light; an associated receiver optical system (3) for receiving reflected components of the radiated light; a display (4) for representing information obtained by the receiver optical system (3), and a device (5, 6) for determining the presence of glare in the receiver optical system (3) from a foreign vehicle illumination optical system and for changing the keying interval or duty cycle of the infrared pulsed light of the illumination optical system (2) driven with fixed keying interval in dependence upon the vehicle direction of travel in such a manner that the glare is eliminated. Therein the illumination optical system is driven is driven with a fixed keying interval depending upon the vehicle direction of travel or, in certain cases, the direction of illumination. In an alternative embodiment, the illumination optical system (2) is operated at a wavelength which depends upon the vehicle direction of travel or, in certain cases, the direction of illumination.

Receiver for use in a code shift keying spread spectrum communications system

Abstract: A chirp spread spectrum receiver for use in a communication system that utilizes a modulation technique referred to as code shift keying (CSK). Code shift keying modulation transmits data in the form of circularly rotated chirp spreading waveforms. The data is conveyed in the amount of rotation applied to the chirp before it is transmitted. While tracking, the receiver decodes the received symbols yielding the original transmitted data. The input frequency range of the receiver is divided into one or more frequency bands whereby the receive signal is filtered, digitized and split into I and Q data streams for each frequency band. Both I and Q data streams are sampled and correlated with an adaptive template. The template in the receiver is dynamically adapted to varying conditions of the channel at each sample time using a template adaptation function.

Quasi-synchronous code-division multiple access with high-order modulation

Abstract: Code-division multiple access (CDMA) is a multiplexing technique where a number of users simultaneously access a transmission channel by modulating and spreading their signals with preassigned codewords. This paper studies the performance of CDMA signals with orthogonal (Walsh-Hadamard) codewords and synchronization errors smaller than the chip time. Two high-order modulation techniques, M-level quadrature amplitude modulation (M-QAM) and M-level phase-shift keying (M-PSK) are compared with respect to bit-error rate (BER). The results are especially important for the return channel of cable TV networks and summarized as follows: 1) Synchronization errors between transmitters lead to interference noise, whereas synchronization errors between the transmitter and the receiver lead to a decreased amplitude of the received user signal. Both effects have significant impact on the system performance. 2) Closed expressions are obtained for the BER of a CDMA signal with M-PSK and M-QAM with a given maximum synchronization error. 3) The higher the modulation order, the more sensitive the system gets for synchronization errors. 4) The BER is highly dependent on the assigned codewords out of the Walsh-Hadamard code set. 5) The BER performance of M-QAM outperforms that of M-PSK.

New ASK/FSK/PSK/QAM wave generator using multiple-output operational transconductance amplifiers

Abstract: A new circuit for generating amplitude shift keying, frequency-shift keying, phase-shift keying, and quadrature amplitude modulation (QAM) waves is proposed. The proposed circuit is built around multiple-output operational transconductance amplifiers and a number of digitally controlled switches. Simulation results which confirm the validity of the circuit are included.

Electrical distribution system with keyed channel arrangement

Abstract: An electrical distribution system includes an electrical distribution harness having a generally C-shaped channel with a keying arrangement formed therein, and an electrical connector with at least one electrical terminal array within the channel. A modular electrical component includes a mating keying arrangement complimentary to the keying arrangement in the channel, and thereby only allows the modular electrical component to be insertable into the channel and coupled with a corresponding electrical terminal array in a preselected orientation.

Tone modulation for out-of-band communication in a free-space optical communication link

Abstract: Systems and methods for the transmission of auxiliary data via a modulated carrier signal superimposed on a primary data communication signal between terminals of a free-space optical communication system are disclosed. The carrier signal is modulated with an auxiliary data signal via phase-shift keying, amplitude-shift keying, frequency-shift keying, or other suitable modulation technique, and superimposed on the primary data communication signal prior to transmission as an optical signal by a transmitting free-space optical terminal. The primary data communication signal is received by at least one photo detector coupled to a receiving free-space optical terminal that demodulates the primary data communication signal to reconstruct the auxiliary data.

Performance assessment of DPSK soliton transmission system

Abstract: An optical communication system using solitons and a coding/multiplexing scheme based on differential phase-shift keying and optical delays is proposed. The performance of such a system is analysed theoretically, based on the soliton optical phase jitter that occurs in an amplified link, and measured in a recirculating loop experiment.

High-data-rate frequency-hopping wireless communication system

Abstract: A wireless communication system including a receiver (14) adapted to receive data at 10Mbps or greater is described. The received signals are preferably binary (BFSK) and/or quaternary (QFSK) shift keying signals limited to a bandwidth of less than or equal to 5 MHz. The receiver (14) includes a demodulator capable of operating in a multipath environment. In one embodiment, a frequency-hopping wireless communication system is used and the bandwidth limitations concern the bandwidth at each hop.