Showing papers on "Keying published in 1997"

Analysis of M-ary phase-shift keying with diversity reception for land-mobile satellite channels

Abstract: An analytical technique well suited to numerical analysis is presented for computing the average bit-error rate (BER) and outage probability of M-ary phase-shift keying (PSK) in the land-mobile satellite channel (LMSC) with microdiversity reception. Closed-form expressions are found for L-branch microdiversity using both selection diversity combining (SDC) and maximal ratio combining (MRC). These expressions are extended to include both M-ary coherent PSK (M-PSK) and differential PSK [M-differential PSK (DPSK)]. Following previous empirical studies, the LMSC is modeled as a weighted sum of Rice and Suzuki distributions. Numerical results are provided illustrating the achievable performance of both M-PSK and M-DPSK with diversity reception. Using measured channel parameters, the performance in various mobile environments for various satellite elevation angles is also found.

Designing Touch Screen Numeric Keypads: Effects of Finger Size, Key Size, and Key Spacing:

Abstract: Designing numeric keypads for point-of-sale devices to optimize keying speed and accuracy while efficiently utilizing touch screen real estate is a challenge. Existing design guidelines for touch s...

Fading-resistant modulation using several transmitter antennas

Abstract: This paper proposes a bandwidth-efficient fading-resistant transmission scheme which implements transmitter diversity using L antennas at the base station. When the antennas are spaced sufficiently far apart, the transmission from each antenna undergoes a different degree of fading. These transmissions are coordinated to mitigate the effects of Rayleigh fading, and the mobile receiver can recover the entire L-dimensional transmitted vector signal as long as the signal energy of at least one coordinate is large enough. L-dimensional fading-resistant signal constellations are generated by maximizing a figure of merit for the Rayleigh fading channel. This scheme offers a significant performance improvement over a conventional single-antenna binary phase-shift keying (BPSK) scheme when coding is ineffective due to slow fading.

Computer system for protecting software and a method for protecting software

Abstract: A method for protecting an item of software, wherein at least one first challenge means is associated with said protected item of software, and at least one first response means accesses one private keying material. At least a third means (either challenge or response also exists). The first challenge means has no access to the said private keying material. The first response means proves to the first challenge means that the first response means has access to the private keying material. The first challenge means validates this proof using the public keying material that corresponds to the first response means' private keying material.

Performance of direct-sequence spread-spectrum RAKE receivers with random spreading sequences

Abstract: In this paper, we derive error probability expressions for binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) spread direct-sequence spread-spectrum (DSSS) systems employing random spreading sequences with RAKE receivers. The derived expressions accurately take into account the effect of interpath interference which usually has been neglected in previous analyses. Selection, equal gain, and maximal ratio techniques are considered for diversity combining. Two possible finger assignment strategies, one based on the instantaneous amplitudes and another based on the average powers of the multipath components, are considered for the assignment of multipath components to the available demodulating fingers in the RAKE receiver. Also, various simple, and in many cases, closed-form approximations for the error probabilities are derived and their accuracies are assessed.

Synchronization of chaotic lasers by optical feedback for cryptographic applications

Abstract: We propose a new scheme for synchronization of the optical chaos generated by a semiconductor laser subjected to external reflection. The scheme is based on optical feedback and will be analyzed from the viewpoint of static and dynamic properties and of robustness to external perturbations and noise. An application to cryptographic communications (chaotic shift keying) is finally proposed.

Feedforward ML-based timing estimation with PSK signals

Abstract: We propose a new nondata-aided clock recovery scheme for phase-shift keying (PSK) modulated signals. Its derivation is based on maximum-likelihood (ML) methods and leads to a feedforward structure that can be easily implemented in digital form. The algorithm exhibits improvements with respect to other existing circuits, especially with small excess bandwidth factors. Its performance is assessed by simulation for quaternary PSK (QPSK) and 8PSK formats.

Electronic copy protection mechanism using challenge and response to prevent unauthorized execution of software

Abstract: A copy protection mechanism for protecting software against copying, consists of a challenge mechanism embedded in each protected item of software. The challenge mechanism has no access to the customer's private keying material. In operation, the challenge mechanism sends a random challenge to the customer's signature server. The signature server signs the challenge, using the customer's private keying material and then returns the signed challenge to the challenge mechanism. The challenge mechanism then verifies the signed challenge, using the customer's public keying material, and prohibits the customer from using some or all of the protected item of software unless the verification is successful. The mechanism permits every customer to receive an identical copy of the copy protected program with the embedded challenge mechanism.

Coding of subregions for content-based scalable video

Abstract: We propose a scheme for coding subregions in video scenes to provide content-based scalable video. For each region, a special color is used to represent the nonobject area, and the resulting frames are coded using conventional video coding algorithms. At the decoder, the region shape is recovered based on chroma keying, and hence, content-based manipulations are made possible. A number of techniques that eliminate boundary artifacts common to region-based coding are presented. In this scheme, no explicit shape coding is needed, and advantages of existing coding algorithms are retained. This scheme was submitted to ISO MPEG-4 and performed very well in the subjective tests.

Method and apparatus for coding segmented regions which may be transparent in video sequences for content-based scalability

Abstract: A method and apparatus for generating region frames from video frames are disclosed which employs an industry standard encoder to lessen the negative impact on the quality of the transmitted video sequence while consuming fewer bits. The invention utilizes image segmentation and color replacement techniques to create the region frames. Each region frame includes a subject region, zero or more previously segmented regions and zero or more non-subject regions. The subject region is defined by the pixels of the original video frame. The previously segmented regions and non-subject regions are assigned replacement pixels P n ,y and C n , respectively. The replacement pixel C n is chosen to indicate a color that is not likely to be confused with any color in the subject region R n . The replacement pixels P n ,y are chosen such that the compression ratio of the region frame data is maximized. Using the region frames, content based scalability can be provided without the need for special encoders and/or channels having a wider bandwidth. The decoder may comprise color or chroma keying apparatus or circuitry keying on the replacement color C n . Instead of keying on a single value, two thresholds may be assigned to define a boundary condition or a subject semi-transparent region. The decoder is forwarded data of the two thresholds and a flag is sent to indicate the dial boundary or semi-transparent region coding. A blending process blends the foreground and background of the semi-transparent object.

A suboptimal algorithm for modulation classification

Abstract: In this paper we present a suboptimal algorithm for modulation classification to classify the general M-ary phase-shifted keying (MPSK) signal buried in additive white Gaussian noise (AWGN). We first derive the phase density functions of MPSK signals, then develop the required statistics for modulation classification and demonstrate a classifier for CW, binary phase-shifted keying (BPSK), quadrature phase-shifted keying (QPSK), and 8PSK. The structure of the proposed classifier is flexible and is easy to expand. The performance of classifier is evaluated in terms of the probability of successful classification. An example (BPSK/QPSK case) is provided to demonstrate the capabilities of the proposed classifier. The performance is evaluated through the theoretical approach and the Monte Carlo computer simulations and is compared with that previously published in 1992. It is shown that the performance of the proposed classifier is better. Further improvement in performance can be obtained by increasing the length of observation interval.

Polarization recovery in optical polarization shift-keying systems

Abstract: For the first time, a solution to the problem of recovering and tracking the signal constellation at the receiver side for binary and octonary digital optical transmission systems employing the modulation of polarization (POLSK) is proposed and analyzed. The effect of two recovery algorithms on the system performance is evaluated in terms of power penalty induced at P(e)=10/sup -9/, acquisition and tracking speed, and hardware complexity. The results show that very small penalties are obtainable in practical situations by properly designing the recovery algorithms.

Code-phase-shift keying: a power and bandwidth efficient spread spectrum signaling technique for wireless local area network applications

Abstract: Code-phase-shift keying (CPSK) is a novel direct-sequence spread-spectrum (DS-SS) signaling system employing M different code phase shifts of a single pseudonoise (PN) code sequence for M-ary signaling. CPSK offers increasing thermal noise immunity as M increases, and totally mitigates the effect of carrier frequency tone interference. It maintains good performance in a Rician fading channel, and a RAKE receiver could be used to improve the performance in a Rayleigh fading channel. The improved power and bandwidth efficiency of CPSK makes it suitable for wireless local area network applications.

System for simultaneous game data and arena display control

Abstract: A game data and arena display control apparatus includes a game control keyboard which includes a plurality of keys for generating respective keying signals in accordance with progress of play of a game. A processor is responsive to the keying signals for controlling the starting and stopping of a game clock, and for determining and storing a plurality of game data. The processor is further responsive to the keying signals to generate a first output signal indicative of game data, and a second output signal indicative of user selected data. A monitor is responsive to the processor for displaying information concerning operation of the apparatus during play of the game. A first output port is connected to the processor for outputting the first output signal to an arena scoreboard. Finally, a second output port is connected to the processor for outputting the second output signal to an arena display board. A database of team and player information and statistics is stored in a storage device which can be accessed by the processor during operation of the apparatus. By means of the game data and arena display control apparatus, team results and player statistics can be collected and updated simultaneously with control of a scoreboard and/or display board, by a single operator, during play of a game.

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

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

Digital communication method based on M-synchronized chaotic systems

Abstract: Chaos shift keying (CSK) is a modulation method in digital communication systems which makes use of chaos synchronization to send binary signals. This paper extends the existent method of chaotic phase-shift keying (CPSK), a form of CSK which utilizes in-phase and antiphase synchronizations. As the method is based on M-synchronization, it will be called M-CPSK. We give an example of a quaternary wireless communication system and examine the effect of noise in transmission channels on the system by computer simulation.

Cellular telephone communication protocol

Abstract: A cellular telephone communication protocol enables a communication link primarily for the transmission of voice and data. At predetermined intervals or on-demand data regarding location, an event, or a condition is sent by muting the voice audio and sending a data frame having a pre-determined sequence. Following the transmission of the location, event, or condition data transmission of voice and data is resumed. The communication link uses a half duplex, frequency shift, keying modulation technique.

The capacity of orthogonal and bi-orthogonal codes on the Gaussian channel

Abstract: This correspondence analyzes the performance of concatenated coding systems and modulation schemes operating over the additive white Gaussian noise (AWGN) channel by examining the loss of capacity resulting from each of the processing steps. The techniques described in this correspondence allow the separate evaluation of codes and decoders and thus the identification of where loss of capacity occurs. Knowledge of this capacity loss is very useful for the overall design of a communications system, e.g., for evaluating the benefits of inner decoders that produce information beyond the maximum-likelihood (ML) estimate. The first two sections of this correspondence provide a general technique for calculating the composite capacity of an orthogonal or a bi-orthogonal code and the AWGN channel in isolation. The later sections examine the composite capacities of an orthogonal or a bi-orthogonal code, the AWGN channel, and various inner decoders including the decoder estimating the bit-by-bit probability of a one, as is used in turbo codes. The calculations in these examples show that the ML decoder introduces a large loss in capacity. Much of this capacity loss can be regained by using only slightly more complex inner decoders, e.g., a detector for M-ary frequency-shift keying (MFSK) that puts out the two most likely frequencies and the probability the ML estimate is correct produces significantly less degradation than one that puts out only the most likely frequency.

An adaptive receiver for the time- and frequency-selective fading channel

Abstract: An adaptive receiver is presented in this paper for the reception of linearly modulated signals transmitted over a time- and frequency-selective fading channel. The channel is modeled as a truncated power series which represents the dispersive fading channel as a sum of three elementary flat-fading channels. The proposed receiver consists of a sequence estimator with a parallel channel estimator. The channel estimator recovers the instantaneous fading processes associated with each elementary channel and filters them to generate one-step predictions of each fading process. Some implementation difficulties and solutions are also discussed. Computer simulations using quadrature phase-shift keying (QPSK) and channels with moderate delay spreads and fade rates have been used to evaluate the performance of the receiver. The results show that our technique has potential in channels with delay spread of about 20%, signal-to-noise ratio (SNR) greater than 15 dB, and applications requiring bit-error rates (BER's) less than 10/sup -2/.

Protection of software using a challenge-response protocol embedded in the software

Abstract: A method for protecting an item of software, wherein at least one challenge is associated with the protected item of software, and at least one response accesses one private keying material. The challenge has no access to the private keying material. The challenge and the response are generating shared secret information, respectively, in accordance with an asymmetric confidentiality scheme. The response proves that it discovered the shared secret and the challenge validates the proof. The challenge proof validation procedure uses the public keying material that corresponds to the response private keying material.

Receiver integrated circuit for mobile telephone

Abstract: A receive integrated circuit for a mobile telephone comprising a variable gain amplifier for amplifying a received signal with a variable gain, a low-pass filter for attenuating harmonic components of the signal amplifier by the variable gain amplifier, and a QPSK demodulator for demodulating by quadri-phase shift keying the signal having passed through the low-pass filter, wherein signal lines interconnecting the variable gain amplifier, the low-pass filter and the quadri-phase shift keying demodulator are balanced.

Tuning in OFDM receivers

Abstract: A receiver for OFDM (orthogonal frequency-division multiplexing) signals where each subcarrier is modulated by differential phase-shift keying is described. The local oscillator of the receiver is controlled according to the following procedure: ```1. Deriving from a phase reference symbol a first frequency error signal equal to an integer multiple of the subcarrier spacing. ```2. Deriving from a phase reference symbol a second frequency error signal not exceeding the subcarrier spacing. ```3. Deriving from data symbols a third frequency error signal. and correcting the local oscillator frequency using the first and third followed by the second error signals.

Optical frequency domain differential phase shift keying in femtosecond-pulse spectral modulation systems

Abstract: We propose a novel scheme of differential phase shift keying (DPSK) in the optical frequency domain. We take advantage of the intrinsic coherence among spectral elements derived by spectrum slicing a femtosecond optical pulse, introducing differential phase modulation between adjacent spectral elements with a femtosecond-pulse shaper. Detection of the differential phase is achieved by a Mach-Zehnder (MZ) or Sagnac interferometric receiver without requirement of any external phase reference.

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

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

Software copy protection mechanism

Abstract: A copy protection mechanism for protecting software against copying, consists of a challenge mechanism embedded in each protected item of software. The challenge mechanism has no access to the customer's private keying material. In operation, the challenge mechanism sends a random challenge to the customer's signature server. The signature server signs the challenge, using the customer's private keying material and then returns the signed challenge to the challenge mechanism. The challenge mechanism then verifies the signed challenge, using the customer's public keying material, and prohibits the customer from using some or all of the protected item of software unless the verification is successful. The mechanism permits every customer to receive an identical copy of the copy protected program with the embedded challenge mechanism.

Differential PSK block demodulation over a flat correlated Rayleigh-fading channel

Abstract: A technique is proposed to design a block demodulator for differential phase shift keying (DPSK) signals over a frequency flat correlated Rayleigh-fading channel. The technique allows one to drastically reduce the error floor typically present in the bit error rate (BER) curves at high signal to noise ratios (SNRs). The main idea is to use the Karhunen-Loeve expansion to have a more precise description of the fading process at the receiver end.

Thunderbolt code computer Chinese character input method

Abstract: The thunderbolt code computer Chinese character input method is characterized by that the compound consonants and compound vowels of the Chinese phonetic alphabet are set on the keyboard of computer according to a certain regular pattern, and the "dot, horizontal, vertical, leftfalling and turning strokes" of the Chinese characters are used as basic strokes, and corresponding to digital keys respectively, and when inputting Chinese characters, firstly keying phonetic code (single phonetic or double phonetic code), then keying numeric codes of front two strokes of said Chinese character so as to implement Chinese character input. Said invention possesses the advantages of simple and popular input method, large work stock capacity, using numeric codes and the code having no need of learningby rote.

Method, system, and computer program product for spread spectrum communication using circular waveform shift-keying

Abstract: A method, system, and computer program product for spread spectrum communication is provided using circular waveform shift-keying (CWSK). Circular waveform shift-keying is a modulation technique for conveying data over a spread spectrum channel. Data symbols are encoded in a circular time shift and/or circular frequency shift of a spread spectrum waveform. In a receiver, a CWSK synchronization stage and demodulator stage can be combined on a single fast convolution ASIC chip. Using CWSK modulation and demodulation, a secure, low-cost terminal is realized that can process calls on multiple spread spectrum channels in a hubless wireless network linking large numbers of low data rate users.

Multiple symbol differentially detected multilevel codes for the Rayleigh-fading channel

Abstract: Conventional differential detection is known to perform poorly on the fast-fading Rayleigh-fading channel due to the rapid variation of the channel state. The technique of multiple symbol differential detection (MSDD) improves the error performance by detecting over a sequence of symbols and exploiting the inherent correlation of the fading process. To further reduce the error rate, we need to introduce some form of coding. Successful coding for the Rayleigh-fading channel requires interleaving to decorrelate the channel-a conflicting requirement to MSDD. We propose a solution consisting of interleaving blocks of L M-ary phase-shift keying (MPSK) symbols that are multiple symbol differentially detected. The blocks are treated as elements of an M/sup L/ symbol alphabet over which a multilevel code based on geometrically uniform partitions is defined.

Fractionally spaced linear joint detection for multitone CDMA systems

Abstract: We consider a fractionally spaced linear joint detector (FS-LIJD) for multitone code-division multiple-access (CDMA) systems. We first derive the structure of the receiver for a minimum mean-squared error (MMSE) criterion. Then, we exactly evaluate the bit-error rate (BER) achieved by this detector for binary phase-shift keying (BPSK) modulation in steady-state conditions. We consider an asynchronous scenario, where the signal of each user propagates over a two-path channel. The resistance of the detector against timing errors is studied, and the resistance against a near-far scenario is also demonstrated.