Showing papers on "Keying published in 2002"

Bit-error rate for free-space adaptive optics laser communications.

Abstract: An analysis of adaptive optics compensation for atmospheric-turbulence-induced scintillation is presented with the figure of merit being the laser communications bit-error rate. The formulation covers weak, moderate, and strong turbulence; on-off keying; and amplitude-shift keying, over horizontal propagation paths or on a ground-to-space uplink or downlink. The theory shows that under some circumstances the bit-error rate can be improved by a few orders of magnitude with the addition of adaptive optics to compensate for the scintillation. Low-order compensation (less than 40 Zernike modes) appears to be feasible as well as beneficial for reducing the bit-error rate and increasing the throughput of the communication link.

Spectrally efficient noncoherent communication

Abstract: This paper considers noncoherent communication over a frequency-nonselective channel in which the time-varying channel gain is unknown a priori, but is approximately constant over a coherence interval. Unless the coherence interval is large, coherent communication, which requires explicit channel estimation and tracking prior to detection, incurs training overhead which may be excessive, especially for multiple-antenna communication. In contrast, noncoherent detection may be viewed as a generalized likelihood ratio test (GLRT) which jointly estimates the channel and the data, and hence does not require separate training. The main results in this paper are as follows. (1) We develop a "signal space" criterion for signal and code design for noncoherent communication, in terms of the distances of signal points from the decision boundaries. (2) The noncoherent metric thus obtained is used to guide the design of signals for noncoherent communication that are based on amplitude/phase constellations. These are significantly more efficient than conventional differential phase-shift keying (PSK), especially at high signal-to-noise ratio (SNR). Also, known results on the high-SNR performance of multiple-symbol demodulation of differential PSK are easily inferred from the noncoherent metric. (3) The GLRT interpretation is used to obtain near-optimal low-complexity implementations of noncoherent block demodulation. In particular, this gives an implementation of multiple symbol demodulation of differential PSK, which is of linear complexity (in the block length) and whose degradation from the exact, exponential complexity, implementation can be made as small as desired.

Postnonlinearity compensation with data-driven phase modulators in phase-shift keying transmission.

Abstract: A novel scheme for postnonlinearity compensation is proposed to reduce the phase jitter in phase-shift keying transmission. A phase modulator is used to modulate the phase of the data pulses in front of the receiver. The magnitude of the phase modulation is proportional to the detected pulse intensity, and the sign is opposite to that of the nonlinear phase shift caused by self-phase modulation. Thus, the nonlinear phase noise induced by amplitude fluctuation and self-phase modulation is partially compensated for. We show by numerical simulations that a differential phase-shift keying dispersion-managed soliton system at 10 Gbits/s with such postnonlinearity compensation can provide greater than 3 dB of improvement in ultralong-haul dense wavelength-division multiplexing transmissions.

Performance analysis of equalized OFDM systems in Rayleigh fading

Abstract: Channel estimation is usually needed to compensate for the amplitude and phase distortions associated with a received orthogonal frequency-division multiplexing (OFDM) waveform. This paper presents a systematic approach for analyzing the bit-error probability (BEP) of equalized OFDM signals in Rayleigh fading. Closed-form expressions for BEP performance of various signal constellations [phase-shift keying (PSK), differential phase-shift keying (DPSK), quaternary phase-shift keying (QPSK)] are provided for receivers that use a linear pilot-assisted channel estimate. We also derive the optimal linear channel estimates that yield the minimum BEP and show that some previous known results are special cases of our general formulae. The results obtained here can be applied to evaluate the performance of equalized single-carrier narrowband systems as well.

CF-RZ-DPSK for suppression of XPM on dispersion-managed long-haul optical WDM transmission on standard single-mode fiber

Abstract: We present a new optical modulation format chirp-free return-to-zero differential phase shift keying (CF-RZ-DPSK), which enables wavelength-division-multiplexing (WDM) transmission at 10 Gb/s/ch at a channel spacing of 100 GHz over 3000 km without significant impairments due to cross-phase modulation (XPM). A transmitter setup is presented, which allows a simple implementation of CF-RZ-DPSK with two Mach-Zehnder modulators in push-pull operation. The robustness toward XPM is shown theoretically with the help of a simple analytical model for the XPM-induced phase modulation. The superior performance of CF-RZ-DPSK over other modulation formats [RZ-ampfitude shift keying (ASK), nonreturn-to-zero (NRZ)-DPSK, and NRZ-ASK, respectively] is clarified. Finally, simulation results for CF-RZ-DPSK in comparison to RZ-ASK show the superior performance of the newly proposed modulation format in a dense WDM setup.

Method and apparatus for signal detection in ultra wide-band communications

Abstract: Methods and apparatus for detecting ultra wide-band signals using circuitry having nonlinear dynamics characteristics are disclosed. The receiver circuit can be implemented using a simple tunnel diode or using an op-amp to provide dynamic characteristics. The detector can be used in a variety of modulation schemes, including but not limited to an ON-OFF keying scheme, an M-ary pulse position modulation scheme, and a pulse width modulation scheme. The approach requires only a single frame to detect the signal.

A low bias algorithm to estimate negative SNRs in an AWGN channel

Abstract: Signal-to-noise ratio (SNR) is an important parameter in many receivers. In this letter, we derive a maximum-likelihood estimate of the amplitude of a binary phase-shift keying modulated signal and develop an iterative SNR search algorithm. Low bias is achieved for low SNR.

Baseband Transceiver Design of a 128-Kb/S Power-Line Modem for Household Applications

Abstract: Communication using power line as a medium provides a convenient and inexpensive way for data transmission and control signaling in the households. In this paper, we introduce a power-line channel model as well as architecture of a spread-spectrum baseband transceiver integrated circuit (IC) for a power-line modem. The modulation and spreading scheme used in the proposed transceiver is M-ary bi-orthogonal keying (MBOK). This transceiver runs at a chipping rate of 256 kHz and provides 128-kbps data rate. Simulation results as well as FPGA emulation verify the effectiveness of the proposed architecture for household data communication.

Multilevel pulse position modulation for efficient fiber optic communication

Abstract: Decreasing the average transmitted power in an optical fiber communication channel using multilevel amplitude modulation in conjunction with Pulse Position Modulation (PPM). This multilevel PPM method does not entail any tradeoff between decreased power per channel and channel bandwidth, enabling a lower average transmitted power compared to On/Off Keying (OOK) with no reduction in aggregate data rate. Therefore, multilevel PPM can be used in high-speed Dense Wavelength Division Multiplexed (DWDM) systems where the maximum number of channels is traditionally limited by nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), stimulated Brillouin scattering (SBS), and stimulated Raman scattering (SRS). This modulation technique can enable an increased number of channels in DWDM systems, thereby increasing aggregate data rates within those systems.

Classification of multiple M-ary frequency-shift keying signals over a Rayleigh fading channel

Abstract: We develop and analyze classifiers for multiple M-ary frequency-shift keying (MFSK) signals traveled over a static frequency nonselective Rayleigh fading channel. The classifier is based on approximating the likelihood function (LF) of the frequency modulated digital signals and is derived for both synchronous and asynchronous waveforms. Two cases are considered; the first one is concerned with the signals that have identical modulation type [for example, binary FSK (BFSK) or quaternary FSK (QFSK)]. The second case deals with the signals with different modulation type. We use complex envelope representation of the signals and noise to derive the LF. Simulation experiments are illustrated to validate the theoretical developments.

Method and apparatus for granting access by a portable phone to multimedia services

Abstract: An enhanced IMS AKA ( 21 ) that allows a UE to register with IMS for all multimedia applications to which it is subscribed. Some of the message content of some of the IMS AKA messages ( 22 ) per TS 3GPP 33.203 v 1.0.0 is augmented, and in particular, the message content of CM2 is augmented to include a list of all services to which the UE is subscribed along with either information that allows establishing SAs for each service or information that could be used as keying material or other input for other security mechanisms specific to each service.

Performance of diversity schemes for OFDM systems with frequency offset, phase noise, and channel estimation errors

Abstract: We provide expressions for the bit error rate of various transmit and receive diversity schemes for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency offset, phase noise, and channel estimation errors. The derivations are also applicable for a general multiplicative distortion of the received signal. Our results show that with perfect channel estimates, practical values of the phase noise do not significantly degrade the performance of the various diversity methods for binary phase-shift keying modulation. In contrast, the transmit diversity schemes for OFDM are much more sensitive to channel estimation errors than maximal ratio combining receive diversity.

Performance analysis of RAKE receivers for ultra-wideband communications with PPM and OOK in multipath channels

Abstract: The performance of a single-user, ultra-wideband (UWB) communication system employing binary block-coded modulation with pulse-position modulation (PPM) or on-off keying (OOK) and operating in indoor multipath channels is considered. We examine the tradeoff between receiver complexity and performance for the case of RAKE receivers with maximal-ratio combining (MRC). The derived expressions are evaluated numerically with measured UWB channel data for various cases.

Exact probability of error of BPSK communication links subjected to asynchronous interference in Rayleigh fading environment

Abstract: We derive a new expression for the exact bit-error probability for the detection of a coherent binary phase-shift keying signal experiencing a number of asynchronous interferers having unequal power levels in Rayleigh fading channels. The new expression is readily computed in terms of the coefficients of a Hermite polynomial.

Narrow band chaotic bi-phase shift keying

Abstract: A system (110) and method for signal transmission and reception by narrow band chaotic bi-phase shift keying includes a forward error correction encoder (118) for receiving input data, a data packetizer (120) in signal communication with the forward error correction encoder, a compression encoder (122) in signal communication with the data packetizer, a radio frequency link (114) in signal communication with the compression encoder, a compression decoder (124) in signal communication with the radio frequency link, a data depacketizer (126) in signal communication with the compression decoder, and a forward error correction decoder (128) in signal communication with the data depacketizer for recovering the input data by controlling the orbits of chaos; where the method includes the steps of transmitting a signal indicative of chaotic bi-phase shift keyed data, propagating the transmitted signal within a narrow frequency band, and receiving the propagated signal substantially without degradation of the indicated data by controlling the orbits of chaos.

Key transport in quantum cryptographic networks

Abstract: Methods, apparatus, and systems are provided for distributing a key between nodes. The nodes are provided separate links for carrying messages versus keying information or material. The links for carrying messages couple the nodes to a messaging network, such as the Internet. In addition, the nodes are coupled together in a key distribution network by specialized links for carrying keying information or material. The links for keying information or material are configured to ensure the security of the keying information or material. The nodes that neighbor each other in the key distribution network establish respective pairwise keys. Once the pairwise keys are established, a set of non-neighboring nodes establish a shared key by communicating a sequence of bits through the messaging network. In order to ensure the security of the sequence of bits, the sequence of bits is encrypted based on the respective pairwise keys of neighboring nodes as it is forwarded in messages through the messaging network.

Average bit-error-rate performance of band-limited DS/SSMA communications

Abstract: Direct-sequence spread-spectrum multiple-access (DS/SSMA) communications, strictly band-limited transmitter chip waveforms with excess bandwidth in the interval between zero and one, pseudo-random spreading sequences, an additive white Gaussian noise channel, and matched filter receivers are considered. First, a new expression for the average bit error rate (BER) is derived for systems with quaternary phase-shift keying (QPSK) spreading, the conventional matched filter receiver, a coherent detector for binary phase-shift keying (BPSK) data symbols, and chip waveforms that result in no interchip interference. The expression consists of a well known BER expression based on the standard Gaussian approximation to multiple-access interference and a few correction terms. It enables accurate BER evaluations without any numerical integration for various choices of system parameters of interest. The accuracy of the expression is guaranteed as long as the conditional Gaussian approximation to the cross-correlation coefficients between the desired user's spreading sequence and the interfering users' spreading sequences is valid. The expression well reflects the effect of filtering on the system performance. Extensions of the expression are discussed for systems with QPSK spreading and different detection schemes, systems with BPSK spreading, and systems with different transmit and receive filters. Monte Carlo simulation results are also provided to verify the accuracy.

Remote control locator

Abstract: A remote control locator including a sending unit placed at a convenient location in the home and a receiving unit attached to the remote control. The locator is based on OOK (on-off keying) modulation which is a very economical alternative to FM transmission.

Tunnel-type package identification system having a remote image keying station with an ethernet-over-fiber-optic data communication link

Abstract: A tunnel-type automatic package identification system for automatically identifying packages transported along a conveyor belt structure. The tunnel-type automatic package identification system comprises a data communications network, a package dimensioning subsystem and a package identification unit. The package identification subsystem is mounted above a conveyor belt structure in a work environment, and includes: a linear imaging subsystem having a field of view (FOV) with variable zoom and variable focus characteristics, for producing linear images of packages as said packages are transported along said conveyor belt structure and beneath said package identification subsystem; and a camera control computer operably connected to the linear imaging subsystem and the package dimensioning subsystem, and the communication medium of the data communications network. The camera control computer receives the package dimension data producing zoom and focus control signals for automatically and dynamically controlling the variable zoom and variable focus characteristics of the linear imaging subsystem as the package is transported beneath the package identification subsystem. The camera control computer receives the package dimension data, and producing zoom and focus control signals for automatically and controlling the variable zoom and variable focus characteristics of the linear imaging subsystem as the package is transported past the package identification subsystem. An image keying station, located remotely from the work environment, is connected to the communications medium by way of an Ethernet-over-fiber-optic data communication link, and enables the operator of the image keying station to visually display images of packages which can not be identified by computer-based image processing, so that the operator may read such images and manually keyed into a database, information which identifies the package associated with the operator-read image. By virtue of the present invention, images of packages can be captured with constant dpi resolution, and if necessary, manually identified at a highly remote image keying station, thereby providing increased flexibility in setting up tunnel-type automatic package identification systems in industrial environments where high noise levels and other distractions to carrying out manual image reading operations are predominant.

Differentially en/decoded orthogonal space-time block codes with APSK signals

Abstract: In this paper, we propose a differential en/decoding scheme for Alamouti's orthogonal space-time code using amplitude/phase-shift keying (STC-APSK) signals and two transmit antennas

Dispersion-tolerant transmission using a duobinary polarization-shift keying transmission scheme

Abstract: We demonstrate a novel dispersion-tolerant transmission scheme based on a three-level duobinary-encoded polarization-shift keying (PoISK) transmission format. Simulations over standard single-mode fiber demonstrate an improvement in the chromatic dispersion-limited transmission distance from /spl sim/65 km, using conventional nonreturn to zero intensity modulation to /spl sim/195 km for duobinary PoISK.

Ternary phase shift keying and its performance

Abstract: An important class of digital modulation is phase shift keying (PSK). Ternary phase shift keying (TPSK) has not been focused upon until now because it is not suitable for transmitting binary information signals. However, it has theoretically excellent features for mobile communication systems, that is, it has splendid error rate characteristics and minimum amplitude fluctuation among all of the PSK schemes. The latter feature is very appealing for usage in mobile terminals in which nonlinear amplifiers have to be used. A new class of convolutional codes is proposed in order to use the TPSK scheme in practical systems. The TPSK scheme with the new convolutional code is suitable for transmitting binary signals and it improves the error rate characteristics without bandwidth expansion.

Large-Array Signal Processing for Deep-Space Applications

Abstract: This article develops the mathematical models needed to describe the key issues in using an array of antennas for receiving spacecraft signals for DSN applications. The detrimental effects of nearby interfering sources, such as other spacecraft transmissions or natural radio sources within the array’s field of view, on signal-to noise ratio (SNR) are determined, atmospheric effects relevant to the arraying problem developed, and two classes of algorithms (multiple signal classification (MUSIC) plus beam forming, and an eigen-based solution) capable of phasing up the array with maximized SNR in the presence of realistic disturbances are evaluated. It is shown that, when convolutionally encoded binary-phase shift keying (BPSK) data modulation is employed on the spacecraft signal, previously developed data pre-processing techniques that partially reconstruct the carrier can be of great benefit to array performance, particularly when strong interfering sources are present. Since this article is concerned mainly with demonstrating the required capabilities for operation under realistic conditions, no attempt has been made to reduce algorithm complexity; the design and evaluation of less complex algorithms with similar capabilities will be addressed in a future article. The performances of the candidate algorithms discussed in this article have been evaluated in terms of the number of symbols needed to achieve a given level of combining loss for different numbers of array elements, and compared on this common basis. It is shown that even the best algorithm requires approximately 25,000 symbols to achieve a combining loss of less than 0.5 dB when 128 antenna elements are employed, but generally 50,000 or more symbols are needed. This is not a serious impediment to successful arraying with high data-rate transmission, but may be of some concern with missions exploring near the edge of our solar system or beyond, where lower data rates may be required.

Optical communication system using correlation receiver

Abstract: The present invention provides for a system and method for an optical communication system that utilizes an optical modulator as an optical correlator in a receiver. The present invention may be used as a correlator in a receiver for an On-Off Keying (OOK) system or for a Differential Phase Shift Keying (DPSK) system. A correlation modulator is followed by a low pass filter, which together act as a correlator to determine the correlation of the received waveform with possible transmitted waveforms to produce a maximized signal-noise ratio. The result is a high data rate communication system and method that approaches the theoretical performance limit.

On the accuracy of Gaussian approximations in the error analysis of DS-CDMA with OQPSK modulation

Abstract: This paper considers the bit error probability analysis of direct-sequence code-division multiple access with offset quadrature phase-shift keying (OQPSK) modulation and random signature sequences. A statistical characterization of the decision variable at the output of the correlation receiver is obtained, and several techniques for evaluating the error performance, previously derived for binary phase-shift keying (BPSK)-modulated systems, are then extended to the case of OQPSK. This includes exact bit error evaluation, as well as various approximation methods based on Gaussian modeling of the multiple-access interference terms. These techniques, known as the standard and improved Gaussian approximations, have increasing complexity depending on the level of accuracy required. For BPSK, the standard approximation is typically found to be inaccurate, unless the number of users becomes large, and only the improved approximation yields sufficient accuracy in general. But for the case of OQPSK, the relative performance comparison developed in this paper shows that, for all practical purposes, the simple standard approximation is surprisingly very accurate even with a small number of users.

Anti-jamming performance of chaotic digital communication systems

Abstract: Among the various modulation schemes proposed for chaos-based digital communications, chaos-shift keying (CSK) and differential chaos-shift keying (DCSK) have been most thoroughly analyzed and considered for practical implementation. One important aspect of performance of any communication system is the ability to resist jamming. This area of study, however, is not available in the literature. In this paper, an analysis of antijamming performance of the coherent CSK and noncoherent DCSK systems is presented. The study includes performance analysis for the two types of systems in terms of the bit error probability under different levels of noise power, jamming power, jamming frequency and spreading factor. Computer simulations are used to verify the analytical results.

Keyed connector assembly for flat flexible circuitry

Abstract: A keying system is provided in a connector assembly for electrically interconnecting the conductors of a flat flexible circuit to the conductors of a complementary connecting device. The assembly includes a first connector having a body member for positioning the flat flexible circuit thereon. A second connector mates with the first connector and includes a pattern of keying projections isertable into a corresponding pattern of keying holes in the flat flexible circuit on the first connector.

Wavelet modulation in Rayleigh fading channels: Improved performance and channel identification

Abstract: Wavelet modulation sends multiple copies of data at multiple rates through an unknown channel. We present new methods that result in dramatic bit error rate performance improvements when multiple rates are available and utilized for demodulation. Our results indicate significantly better performance than binary phase-shift keying in fading channels. We also introduce and illustrate new algorithms that identify the channel type and mitigate the effects of intersymbol interference in frequency selective fading channels.

Direct-sequence spread-spectrum optical-frequency-shift-keying code-division-multiple-access communication system

Abstract: A direct-sequence-spread-spectrum (DSSS) optical-frequency-shift-keying (OFSK) code-division-multiple-access (CDMA) communication system is adapted with optical transmitters and receivers for preferred use fiber optical communication systems where modulated data and pseudorandom noise (PRN) codes are encoded in the optical domain and communicated over optical paths for increasing system capacity in wide area optical networks.