Showing papers on "Keying published in 1994"

Adaptive trellis-coded multiple-phase-shift keying for Rayleigh fading channels

Abstract: An adaptive scheme for trellis-coded modulation of MPSK signals, called adaptive trellis-coded multiple-phaseshift keying (ATCMPSK), is proposed for slowly Rayleigh fading channels. The adaptive scheme employs a slightly modified rate 1/2 convolutional encoder and the corresponding Viterbi decoder to realize a family of codes of different rates which are employed according to channel conditions. During poor channel conditions, trellis-coded QPSK (TCQPSK) together with repetition schemes are employed. As channel conditions improve, higher rate schemes such as trellis-coded 16 PSK are used. An interleaving/ deinterleaving method suitable for the adaptive scheme is proposed. Theoretical bounds for the error performance and an exact expression for the throughput of the proposed adaptive scheme are derived, and are compared against simulation results. Simulations have been performed to measure the performance of the scheme for different parameters and some nonideal conditions. It is shown that ATCMPSK results in considerable improvement in bit-error-rate (BER) performance of MPSK signals. Under ideal conditions, gains in the range of 3-20 dB are achieved over conventional fixed rate pragmatic trellis-coded schemes.

System and method for trusted path communications

Abstract: A system and method for identifying and authenticating users and for controlling the access of those users to privileged instructions within a data enclave The data enclave includes a plurality of controllers, such as workstations, connected over a network to a security server; each data enclave is assigned a cryptographic key A personal keying device having an encrypted user unique identifier is assigned to each user; provisions are made for temporarily connecting the personal keying device to one of the controllers and for transmitting an encrypted message, including the user unique identifier and the last countersign, to the security server to authenticate the user and establish his/her access rights A mechanism for updating the countersign is provided so that trusted path communications can be established between the user and the security server

Multi-path resistant frequency-hopped spread spectrum mobile location system

Abstract: A multi-path resistant frequency-hopped spread spectrum mobile vehicle or personal location system is described which provides low cost manufacture and low power operation while still enabling the accurate location of the mobile unit over long distances and in moderate to severe multi-path conditions. The frequency-hopped spread spectrum mobile vehicle or personal location system consists of a central station, a plurality of base stations and a plurality of mobile transmitters which transmit using a frequency-hopped spread-spectrum differential bi-phase shift keying communication signal. Frequency Shift Keying modulation may also be used. Each of the plurality of base stations include an array of receiving dipole antennas and employs special algorithms for retrieving very low power frequency-hopped spread spectrum signals in a noisy and multi-path environment. The base stations use computational algorithms for determining the phase difference between each of receiving dipole antennas to determine the direction of the transmitter relative to the location of the respective base station. The multiple direction of arrival angles of the received signal at each base station are corrected based on an n-dimensional ambiguity space to locate most probable angles of arrival. The ambiguity space plot is used to eliminate erroneous comparisons of dissimilar phases of the incoming signal. The most probable values are then tracked over multiple frequency hops and a histogram analysis of the strongest surviving angles of arrival is performed. The two peaks of the histogram are used as the two most probable directions of arrival. Each base station then communicates the two relative directions of the transmitter to a central station where the location of the transmitter is determined by triangulation. The direction of arrival angles from the multiple base stations are summed in a least mean square approach to find a single direction of arrival which is then plotted on a gnomonic projection to correct for the curvature of the earth.

Limits to long-haul coherent transmission set by the Kerr nonlinearity and noise of the in-line amplifiers

Abstract: The effect of Kerr nonlinearity and noise of the erbium amplifiers is investigated in a link in which dispersion is zero to all orders. The analytical expressions for the error probability at the receiver are found for a differential phase shift keying modulation format. The role of the total bandwidth of the amplified spontaneous emission noise is discussed. >

Modulation and coding for throughput-efficient optical systems

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

Trellis-coded continuous-phase frequency-shift keying with ring convolutional codes

Abstract: Trellis-coding techniques are applied to continuous-phase frequency-shift keying (CPFSK). A new coding scheme based on convolutional codes on the ring of integers modulo-P is shown to be a natural way to apply trellis coding to CPFSK. Previous work has decomposed CPFSK into two parts: a linear encoder, with memory called the continuous phase encoder (CPE), and a memoryless modulator (MM), where the CPE often has a code structure defined over the ring of integers modulo-P. The combination of a modulo-P convolutional channel encoder (CE) and the CPE is a linear modulo-P encoder. Design examples are given for rate-1/2 coded quaternary CPFSK with modulation indexes 1/2 and 1/4, and rate-2/3 coded octal CPFSK with modulation index 1/8. Combinations are optimized in the normalized minimum Euclidean distance sense for a given total number of states in the overall MLSE receiver. Numerical results show that this new coding scheme consistently obtains better performance than previous schemes. >

Digital quadriphase-shift keying modulator

Abstract: A digital quadriphase-shift keying modulator is described which generates a modulated intermediate carrier frequency (IF) based on a desired number of samples for each input information bit. The design includes a ROM (or RAM) look-up table which stores digitized waveforms. The inphase and quadrature components of a complex baseband signal are translated to an IF at a multiple of the sampling rate simply by alternating the inphase and quadrature samples and alternating signs. The real IF output is produced by summing the inphase and quadrature signals.

An adaptive maximum likelihood receiver for correlated Rayleigh-fading channels

Abstract: The paper develops a receiver structure for random Gaussian signals in additive noise based on the classic maximum likelihood (M-L), estimator-correlator derivation of Kailath [1960], and applies it to differential phase shift keying (DPSK) on the correlated Rayleigh-fading channel. It is shown to lower the error floor found in the performance of conventional DPSK receivers by orders of magnitude. In addition, the maximum-likelihood procedure is shown to make uncorrelated symbol decisions. The performance of both conventional and optimal receivers, which require knowledge of the channel statistics, is examined analytically. A recursive, channel-adaptive version of the optimal receiver, utilizing decision feedback to estimate the channel statistics, is developed. Its simulated performance shows no penalty compared to theoretical calculations which require explicit knowledge of the channel statistics. >

Higher-order differential phase shift keyed modulation

Abstract: Advanced modulation/demodulation techniques which are robust in the presence of phase and frequency uncertainties continue to be of interest to communication engineers. The authors are particularly interested in techniques which accommodate slow channel phase and frequency variations with minimal performance degradation and which alleviate the need for phase and frequency tracking loops in the receiver. They investigate the performance sensitivity to frequency offsets of a modulation technique known as binary double differential phase shift keying (DDPSK) and compare it to that of classical binary differential phase shift keying (DPSK). They also generalize their analytical results to include n/sup -th/ order, M-ary DPSK. The DDPSK (n=2) technique was first introduced in the Russian literature circa 1972 and was studied more thoroughly in the late 1970s by Pent and Okunev. They present an expression for the symbol error probability that is easy to derive and to evaluate numerically. They also present graphical results that establish when, as a function of the signal energy-to-noise ratio and normalized frequency offset, binary DDPSK is preferable to binary DPSK with respect to performance in additive white Gaussian noise. Finally, they provide insight into the optimum receiver from a detection theory viewpoint. >

Subcarrier communication system

Abstract: A communication system (100) is provided for transmitting data to mobile receivers utilizing a subcarrier within a commercial FM channel of a radio station (55). The data transmitted is first encoded in encoder (112), utilizing a forward error correction code. The sequence of the encoded data is altered in interleaver (116), subdivided into a plurality of subframes, in framing and synchronization circuit (120), which also adds channel state bits to each subframe. The framed data is modulated onto the subcarrier in the differential quadrature phased shift keying modulator (130), the output of which is coupled to the FM modulator (52) of radio station transmitter (50). The transmitted radio frequency signals may be received by a vehicle antenna (12) for coupling to the vehicle's FM receiver (80). The modulated subcarrier is recovered from the FM demodulator (84) of the receiver (80), the modulated subcarrier being demodulated to recover the encoded digital data therefrom. The channel state bits included with the data are extracted from the digital data and utilized to form a data reliability factor for each bit of the encoded data. The data reliability factors thus obtained are associated with each bit of the data in a deinterleaver (360). Deinterleaver (360) provides each data bit in proper sequence, with its associated data reliability factor to a decoder (370). The decoded digital data is provided to a vehicle traffic computer (90) for processing and presentation of traffic information to a user on a display (92).

Novel monolithic multifunctional balanced switching low-noise amplifiers

Abstract: A novel multifunctional balanced switching low-noise amplifier (BSLNA) which can be used as a low-noise amplifier, a low-noise switch, or a broad-band 180/spl deg/ phase shifter is proposed. Two monolithic BSLNA's at Ka- and W-band frequencies are demonstrated using the 0.1 /spl mu/m pseudomorphic (PM) InP- and GaAs-based HEMT technologies, respectively. Potential applications of the novel BSLNA are in on-off keying (OFK) or binary phase-shift keying (BPSK) in communication systems and input switch for Dicke-switched radiometer systems. The extensions of this BSLNA structure to be a single-pole double-throw switch and a crossbar switch to interchange two signal paths are also addressed. >

Frequency shift keying (FSK) demodulator for use in low signal-to-noise ratio environments

Abstract: A frequency-shift keying (FSK) demodulator demodulates a binary signal encoded in an FSK signal. The present invention employs a bandpass filter to filter out noise and pass the frequencies used in the modulation. A comparitor converts the received signal into a square wave. A divider reduces the frequency of the square wave signal by a dividing factor. A counter counts the number of square wave transitions in a predetermined time period. A decision device receives the dividing factor from the divider, and uses this factor to adjust the count measured. The adjusted count is compared to counts pertaining to modulated frequencies to select a frequency. A bit value associated with the selected frequency is output for the time period being demodulated.

Multicarrier modulation for narrowband PCS

Abstract: Investigation of multicarrier modulation has demonstrated the feasibility of using this modulation format to deliver relatively high channel bit rates (24 kbps) to a low cost, pager-like personal communications service (PCS) terminal that enjoys long battery life (e.g., one month on a few pen-light cells). This is to be compared to the 1200 bps carried by typical current paging systems or the 6250 bps attained by the new ERMES paging system. While more complex modulation formats, such as PSK and QAM, might achieve higher bit rates in less (power, size, cost) constrained environments, amplitude keying of the component subcarriers allows simple noncoherent energy detection that is found to be robust in this short message delivery application. >

Multidimensional 16-PSK Trellis Codes for Fading Channels

Abstract: Multidimension modulation has been observed to have advantages over 2-dimensional schemes and therefore has become an important research topic. This paper investigates the code search problem for trellis-coded multidimensional phase modulation for fading channels. New set partitionings for 16 Phase-Shift Keying (16-PSK) are proposed using the effective code length (ECL) and the minimum product distance (PD) as the code design criteria. The proposed codes compare favourably with the existing multidimensional trellis codes for fading channels in terms of error rate performance. The error rate performance is evaluated using Monte Carlo simulation.

Differential phase shift keying direct sequence spread spectrum single SAW based correlator receiver

Abstract: This paper presents a SAW based correlator receiver for a Differential Phase Shift Keying Direct Sequence Spread Spectrum (DPSK/DSSS) receiver. The DPSK modulation format allows the noncoherent data demodulation while the SAW device correlator acts as the despreading operator. In a conventional DPSK receiver, the received signal is normally split into a lower and upper path. One of the paths contains a correlator, while the other path contains a one data bit delay element and another correlator. The outputs of both paths are then fed to a noncoherent data demodulator. This paper combines both the delay element and the two correlators in a single SAW device, and therefore a better temperature tracking mechanism, simplicity, as well as the elimination of the broadband SAW delay line are achieved. The SAW structure contains a broadband SAW transducer, and two serially coded Pseudo Noise (PN) DPSK filters. The SAW based correlator was built on lithium tantalate. The center frequency was set to 150 MHz, with a 63 chip PN spreading code and a data rate of 300 kbps. Experimental measurements in both the time and frequency domains were performed and were compared to computer simulation predictions

Error probability bounds for M-PSK and M-DPSK and selective fading diversity channels

Abstract: A method is described for obtaining tight closed-form bounds on the probability of error for M-ary phase-shift keying (M-PSK) and M-ary differential phase-shift keying (M-DPSK) on fading diversity channels. The channels exhibit doubly selective fading and have specular components. In addition, the random impulse responses of the diversity channels may be correlated; and the probability distributions for the fading on different diversity channels need not be the same. Error probability expressions are given for binary DPSK, 8-DPSK, and 16-DPSK modulation as examples of the application of the general method described. >

An iterative near-far resistant algorithm for joint parameter estimation in asynchronous CDMA systems

Abstract: An asynchronous multiuser communication system is considered where K users share an additive white Gaussian channel. Binary phase-shift keying and direct sequence spread spectrum signaling is employed for data modulation. In this work, we propose an algorithm for near-far resistant joint parameter estimation and data detection for multiuser systems: the successive interference cancellation scheme employs a stochastic approximation (SA) method for estimating delays, the expectation-maximization (EM) algorithm for obtaining carrier phase and amplitude estimates, and a multistage algorithm for data detection. Using an SA-scheme, the complexity of the receiver structure can be considerably reduced. Monte Carlo simulations illustrate the capability of the system to obtain parameter estimates even in the presence of strong interferers such that the near-far effect can be overcame.

Adaptive touch recognition

Abstract: PURPOSE: To provide an adaptive contact recognition method for reducing the frequency of the keying errors of active control keys without reducing the number of active control functions that can execute simultaneous display and for efficiently selecting/displaying the active control functions. CONSTITUTION: In a contact sensing-type user interface panel, control key display areas 16 and 18 are provided for the adjacent active control keys 17 and 19, and extension contact bands 20 and 22 larger than the control key display areas 16 and 18 are regulated for the active control keys 17 and 19. When the other active control key is installed near the contact sensing-type user interface panel, the sizes of the extension contact bands 20 and 22 automatically change and they avoid being overlapped with the other extension contact band. When a user touches the extension contact band 20 of the contact sending-type user interface panel, the active control function by the active control key, which corresponds to the touched extension contact band 20, is displayed.

Hands-free two-way radio communication system

Abstract: The hands-free, two-way communication radio includes a multiple channel transmitter/receiver having one of the channels designated a primary communication channel. The transmitter/receiver is also operable in a scan mode to scan multiple channels for communication signals. The radio also includes an interface operatively connected to the multiple channel transmitter/receiver and a hands-free microphone operatively connected to the transmitter/receiver through the interface. A foot pedal actuator is provided for keying the hands-free microphone to allow transmission of a message over the multiple channel transmitter/receiver. Further, the radio includes a switching mechanism operative in response to actuation of the foot pedal for providing a control signal to the multiple channel transmitter/receiver. This control signal results in the multiple channel transmitter/receiver switching to the primary communication channel for transmission of the message. The invention also includes the combination of the interface, hands-free microphone and foot pedal actuator and switching system for retrofit conversion of a standard radio to hands-free operation.

A theoretical analysis of the performance of code division multiple access communications over multimode optical fiber channels-part I: transmission and detection

Abstract: This paper presents results of a theoretical investigation to evaluate the performance of code division multiple access communications over multimode optical fiber channels in an asynchronous, multiuser communication network environment. The system is evaluated using Gold sequences for spectral spreading of the baseband signal from each user employing direct-sequence biphase shift keying and intensity modulation techniques. The transmission channel model employed is a lossless linear system approximation of the field transfer function for the /spl alpha/-profile multimode optical fiber. Due to channel model complexity, a correlation receiver model employing a suboptimal receive filter was used in calculating the peak output signal at the ith receiver. The performance measures for the system, i.e., signal-to-noise ratio and bit error probability for the ith receiver, are derived as functions of channel characteristics, spectral spreading, number of active users, and the hit energy to noise (white) spectral density ratio. >

Direct differential detection of phase-shift-keyed signals: a local-oscillatorless DPSK receiver

Abstract: The phase-diversity mixing concept, originally applied in communication receivers to local-oscillator-aided reception, is here applied to the direct (i.e. local-oscillatorless) differential detection (D3) of phase-shift-keyed (PSK) transmissions. The received signal and its delay replica are first compared by means of a quadrature mixer, directly at the receiver front end, at the optical or microwave signal stage. The baseband phase-diversity signals thus obtained are linearly transformed in a baseband phase equaliser, and thus cancel out undesired, detrimental phase shifts which invariably occur in the wave-generating and wave-conveying components. The resulting D3PSK receiver is robust under variations in carrier frequency and in differential delay. Its development establishes coherent modulation methods, such as PSK and narrowband FSK, as viable alternatives to on/off keying, which at present is exclusively used in direct detection systems.

On-off keying assisted acquisition scheme for burst mode DS/SS packet radio

Abstract: Code Division Multiple Access (CDMA) is a promising technology for future digital cellular and personal communications. To despread the pseudo noise (PN) code and thus understanding the message sent, synchronization (acquisition fluid tracking) is necessary in priori. As a matter of fact, the throughput of a packet mode CDMA system is directly related to the performance of its frame synchronization algorithm. In this paper, we propose a new acquisition technique for packet mode CDMA operating in the Rayleigh fading channel. The technique is based on on-off keying (during the preamble section) followed by a Markov chain search. The length of the preamble is a design parameter and the performance measure is the throughput of packets. We have tested our new scheme on a flat fading and a selective fading channel, based on a fixed blocking probability criterion. Specifically for the latter case, we adopt a RAKE receiver to combat the multipath effect, and introduce a windowing technique which we found effective in overcoming the temporary increase in noise level caused by partial correlation of the PN sequence used. Results in both cases show that the proposed on-off keying technique is more efficient than many others in the literature such as the coincidence detector or simple Markov search. >

Fixed reference shift keying modulation for mobile radio telecommunications

Abstract: A method and apparatus for improved mobile radio telecommunications employs the transmission of a pilot reference signal within the coherence band of the modulated carrier wave. The receiver in this system uses instantaneous phase estimation techniques of the pilot and carrier received waveforms to provide immunity from phase distortion introduced by the channel.

Motion-compensated matteing

Abstract: Matteing and chroma-key are well-known techniques in frequent use in television production. When they are used, it is generally necessary to ensure that the camera remains stationary in order for the inserted picture material to remain in the correct position with respect to the foreground picture material. This places significant constraints on the use of these techniques. To allow matteing and keying to be used in the presence of camera motion in situations where mechanical sensors are inappropriate, a motion estimation algorithm is needed that can measure global image motion to a high degree of accuracy. The paper describes the development of such an algorithm, tailored to this application. If the algorithm is used in conjunction with a keying unit and a blue background, the background cannot be a uniform shade of blue, but must contain enough information to allow reliable motion estimation to be carried out. In such circumstances, the key signal can be used to indicate the areas of the image which correspond to background, so that the estimation process can ignore foreground areas. In applications where a blue background is not used, it is necessary to use other means to disregard areas having motion different from that to be tracked. Although the motion parameters can be used to drive a conventional DVE, this may be unsuitable for the generation of a full-screen background image, or when the image is being enlarged. Therefore, a specialised kind of image manipulator is being developed for this application.

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

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

Digital video effects generator

Abstract: A digital video effects generator includes: circuit for up-sampling the digital video component signals prior to their spatial transformation and linear interpolation, thereby reducing losses due to the (sin x)/x frequency response of the sampled video signal; circuit for spatially-mapping video motion data representing the degree of video data motion between temporally adjacent video frames and for motion adaptive interpolation to selectively blend interpolated video field data in accordance therewith; circuit for pre-transform keying, thereby allowing two video signal transformations to be keyed simultaneously; circuit for selectively transforming portions of input video signals, thereby allowing selective keying of non-spatially transformed video into selected regions of the video image; circuit for selectively linking keyframes within separate effects and providing smooth parametric transitions therebetween, thereby allowing several separate effects to be combined into a single effect with smooth parametric transitions between the linked (inter-effect) keyframes; and circuit for maintaining "pinned" image corners during parametric transitions between keyframes.

Key input device

Abstract: PURPOSE: To provide the key input device with which operability can be improved and input time can be shortened as well by reducing the keying operations of key inputs at the time of 'Roman character input'. CONSTITUTION: This key input device is provided with a compound input detecting means for detecting the simultaneous keying of plural keys and a syllabic nasal key processing means for generating a character string by arranging the syllablic nasal of 'n' at the end of the character when a key for inputting this syllabic nasal of 'n' is included in the plural keys keyed at the same time. Thus, the character of two syllables including the syllabic nasal of 'n' can be inputted by one time of keying operation as well and the keying operations at the time of Roman character input are reduced so that operability can be improved and input time can be shortened as well. COPYRIGHT: (C)1996,JPO

Multiple-symbol differential detection of M-DPSK using neural network

Abstract: In this paper, the application of artificial neural network (ANN) to differential detection receiver for M-ary differential encoded phase-shift keying (MDPSK) utilizing multiple symbols is investigated. It is shown that the performance of this non-coherent receiver not only approaches its coherent receiver counterpart, but its structure is also simple and easy to implement in hardware. Some other desirable properties are obtained, such as no training process involved in this application, fast computational time and high accuracy. Simulation results are made to illustrate its superior performance. >

Nonlinear adaptive algorithms for equalisation in mobile satellite communications

Abstract: This paper considers the equalisation problem in Quadrature Phase-Shift Keying (QPSK) modulated signals which have been distorted by the passage through a transmission channel. The channel is modelled as a Rician fading channel to simulate the behaviour of the transmission channel in the mobile satellite context. The equalisation is treated as the generalisation of the channel behaviour, and some algorithms with the structure of an artificial neural network using the Multilayer Perceptron, Volterra Series and Radial Basis Function are described. Results for the BER performance of typical transversal equalisers, with Square-Root Kalman adaptation algorithm, and algorithms with artificial neural network structure are also reported and evaluated. Improved performance is exhibited by the artificial neural network approaches.

Performance of GMSK with two-bit differential detection in a land mobile radio channel

Abstract: The performance of two-bit differential detection of Gaussian minimum-shift keying (GMSK) in a cellular mobile communication channel is theoretically analyzed. The channel is modelled to reflect those encountered in a practical system; i.e., a frequency-selective fast Rayleigh-fading channel corrupted by cochannel interference and additive white Gaussian noise. A two-ray model for the channel is used and a single cochannel interferer is considered in the analysis. The Doppler effect is included as well. A closed-form expression for the probability of error is obtained. Numerical computation is used to obtain GMSK bit-error-rate performance for various combinations of channel parameters. The results are compared with those for limiter-discriminator detection with the same channel parameters. The performance of limiter-discriminator detection is found to be superior to that of two-bit differential detection. As two-bit differential detection is generally simpler to implement, the choice of detection method involves a performance versus complexity trade-off. The results presented can be used to make this trade-off.