Showing papers on "Keying published in 1996"

Keying system and composite image producing method

Abstract: In a keying system, an image of an object is gained and a plurality of the background images each of which is obtained correspondingly to a view angle of a view point in a three-dimensional space to be imaged and a view position of the view point therein are stored on a memory device. The background image from the plurality of background images stored in the memory device is selectively read according to the view angle and the view position preliminarily defined in accordance with the image of the object. A chroma-keying composition is performed between the background image and the image of the object thereby producing a composite image.

System for preventing global positioning satellite signal reception to unauthorized personnel

Abstract: A selective or tailored system for denying global positioning satellite (GPS) signal reception to unauthorized GPS receivers yet enabling authorized receivers to maintain access to the GPS system. The invention includes two basic units, the first being a tailored jamming unit which radiates an encoded denial or jamming waveform and the second being one or more receiver units including an interference or jamming signal suppression system which allows GPS user equipments to decode and suppress the jamming signal and receive the GPS satellite signal in the denial environment. The receiver unit decodes the encoded jamming signals. The jamming or denial signals, in its simplest form, employs a bi-polarization keying (BPK) defined as synchronously switching and radiating between two (or more) polarization states (or radiators) at a near 100-percent denial duty-cycle. The radiated signal's polarization, effective radiated power (ERP) level, noise bandwidth and density, and keying modulation (or switching rate) of the radiators are selected to provide sufficient diversity of the interference signal in victim GPS system to prevent normal C/A and/or P(Y) code receiver operation. The encoded switching modulation waveform to control switching between the denial polarization states uses a pseudo-noise encryption technique which allows asynchronous reception, decoding and synchronization for authorized users possessing essential codes, time information, and secure matched synchronization techniques implemented in an adaptive polarization feed network prior to inputting to the GPS receiver. The transmit system or network can deny GPS equipment operation over an area controlled by the effective radiated power radiation pattern of the transmit unit. The receive system or network can achieve synchronized polarization mismatch against the denial or jamming sources and also achieve suppression against other forms of interference sources.

Channel reuse strategies for indoor infrared wireless communications

Abstract: We examine systems of fixed channel reuse for base stations in an indoor infrared wireless communication system. The following techniques are compared: time-division multiple access (TDMA) using on-off keying (OOK) or pulse-position modulation (PPM), frequency-division multiple access (FDMA) using binary phase-shift keying (BPSK), and code-division multiple access (CDMA) using OOK with direct-sequence spreading by m-sequences or optical orthogonal codes (OOCs). TDMA using PPM is found to offer superior performance in terms of complexity and average optical power required to cover a room.

"BASS 300 PARACOM": a "model" underwater parametric communication system

Abstract: Parametric transduction offers valuable advantages for underwater acoustic communications. Perhaps the most significant benefit is the fact that high directivity is achieved by means of a physically small transmit transducer. This feature may, ultimately, be employed to permit long-range, low-frequency communication using a compact source. The high directivity is desirable to combat multipath propagation and to achieve data communications in water which is shallow by comparison with range. A real-time, high data-rate "model" differential phase shift keying (DPSK) communication system has been constructed and demonstrated. This system uses parametric transduction, with a 300-kHz primary frequency and a 50-kHz secondary frequency. Experimental results show that the system can be employed to combat multipath propagation in shallow water and can achieve high data-rate text and color image transmission at 10 and 20 kb s/sup -1/ for 2-DPSK and 4-DPSK, respectively, through a transmission bandwidth of 10 kHz. The "model" system was developed to confirm performance predictions for a future, operational long-range link employing a 50-kHz primary frequency and a 5-kHz secondary frequency.

System and method producing improved frame synchronization in a digital communication system

Abstract: In a digital audio broadcasting (DAB) system having a radio-frequency (RF) transmitter and a corresponding RF receiver, a system and method for providing improved frame synchronization is provided. In accordance with the preferred embodiment, the RF transmitter formats a DAB signal into a sequence of frames, each frame having a header with a predefined grouping of psuedo-random number sequences comprising 100 symbols. Of these 100 symbols, 86 symbols of the header preferable are used for frame synchronization and characterization of a communications channel, while the remaining 14 symbols are used for interleaver and data synchronization in an interleaved fashion. The formatted DAB signal, including the frame sequences, is transmitted to the receiver preferably using quadrature phase-shift keying modulation. At the receiver, a correlator, utilizing a synchronization detection algorithm, is generally designed to match a predetermined symbol pattern within the received signal. Once the frame synchronization is established, the channel is characterized and the data symbols are recovered.

Performance analysis and channel capacity for multiple-pulse position modulation on multipath channels

Abstract: Although multiple pulse-position modulation performs well on ideal channels, its performance on multipath channels is degraded significantly. In an attempt to quantify the inherent penalty due to multipath dispersion, we evaluate upper bounds for the error probability of each modulation scheme in the presence of intersymbol interference, considering both an unequalized receiver and the optimal maximum-likelihood sequence detection receiver. We also present upper and lower bounds of the channel capacity for multiple pulse-position modulation and its variants, PPM and overlapping PPM. Numerical results show that the PPM-based schemes are significantly more sensitive to multipath dispersion than is on-off keying.

Diversity with distributed decisions combining for direct-sequence CDMA in a shadowed Rician-fading land-mobile satellite channel

Abstract: The performance of two diversity schemes with distributed decisions combining is analyzed and compared with that of the selection and maximal ratio-combining schemes for binary-phase shift keying (BPSK) direct-sequence code-division multiple access (DS-CDMA) in a shadowed Rician-fading land-mobile satellite channel. In the first scheme of distributed decisions combining, the combiner collects only the binary branch decisions to make the data decision. In the second scheme, the combiner makes the data decision using the branch decisions and the channel states. Both symmetrical and asymmetrical diversity branches are considered. Based on optimal likelihood ratio testing, a new data decision rule is devised for the detection of the spread-spectrum signals in the DS-CDMA system. Upper bounds are employed for the performance evaluation of the diversity combining schemes when the bit error probability is difficult to compute. Numerical results are presented for the satellite channel under light, average, and heavy shadowing.

Synchronization techniques for a frequency-hopped wireless transceiver

Abstract: The implementation of robust synchronization algorithms and architectures for master-slave configured frequency-hopped radios with frequency-shifted keying (FSK) modulation is described. The synchronization scheme, both acquisition and tracking, is based on a simple time division duplexing (TDD) frame structure, which consists of a pilot tone, a frame ID (Word Sync), and actual data. The acquisition process is accomplished by means of frame synchronization, based on coarse energy detection of the received signal and the pattern matching of a 2l-digit Barker code. The proposed scheme for synchronous-access frequency-hopped transceivers is much simpler than a parallel search method based on parallel matched filters, and relatively faster compared to a PN acquisition scheme based on serial search. Although FSK signals are detected noncoherently, a frequency tracking loop is required to compensate for the carrier frequency offset between the transmitter and receiver. The receiver also needs a time tracking loop to recover the clock from the received data. Both loops use a digital phase-locked loop architecture with programmable loop bandwidths.

FSK demodulation using an adaptive recursive digital filter

Abstract: A second-order adaptive recursive digital filter is used for frequency-shift keying (FSK) demodulation. Explicit formulas are derived for the noise variance in the frequency detector, and optimum transmitter carrier frequencies and detector threshold frequencies are calculated. A formula for the adaptation time is derived and the error probability is found. Computer simulations verify the derived results.

Multiplexed subcarrier control in wavelength division multiplexed broadband networks

Abstract: In a wavelength division multiplexed network having a plurality of nodes and having optical channels at wavelengths λi, where i=1 . . . N, for transmission of optical signals over optical interconnection means, control for informing the network of which nodes are transmitting at which frequencies and for token holding. Control is provided without the need for a second transmitter at each node and another control channel. Data signals are provided at baseband by keying the optical signal at a data repetition rate. Control signals are imposed on a wavelength λt of a transmitting node as a subcarrier. Receiver means at each node respond to a λt from another channel to receive information. The node also includes means for all wavelengths λi and demodulating the subcarrier therefrom to derive control information. Means are provided for producing controls signals each corresponding to a channel and formatting the serial control sequence so that the data rate for control information does not increase as a function of network traffic.

Spread spectrum multiple-access with DPSK modulation and diversity for image transmission over indoor radio multipath fading channels

Abstract: As demand for networked multimedia applications is increasing rapidly, it is important to provide the ubiquitous accessibility for these services in wireless communication environment. Such access allows users to share novel multimedia applications without any geographical restrictions. We investigate the application of the well-known antimultipath spread spectrum code-division multiple access (SS-CDMA) techniques to image transmission related to the development of next-generation multimedia wireless local area networks within a building. SS-CDMA is particularly well suited to a subband coding scheme that divides the image information into multiple parallel data streams using an analysis filter bank, each of which is multiplied by its unique spreading code. All the product signals are then transmitted at the same time in the same radio channel, even though the total bandwidth of all the signals may exceed the channel bandwidth. Each received signal is independently recovered at the decoder by multiplying its spreading code and all the recovered subbands are then reassembled by a synthesis filter bank into a close reproduction to the original image. A forward error correction (FEC) scheme based on convolutional codes with interleaving is proposed to minimize the effect of bursty channel errors on the picture quality degradation. Better image quality can be achieved by using the predetection diversity combining in order to combat the indoor multipath distortion. In this paper, the image quality of subband image transmission via SS-CDMA indoor fading channels with differential phase shift keying (DPSK) modulation is evaluated and examined. Simulation results show that the image peak signal-to-noise (PSNR) ratio is inversely related to a logarithmic function of bit error rate when each subband employs equal protection channel coding.

An algorithm for joint detection in fast frequency hopping systems

Abstract: An algorithm for joint detection in fast frequency hopping/multiple frequency shift keying (FFH/MFSK) multiple access (MA) systems is presented. The new algorithm-referred to as REC algorithm-enables maximum likelihood (ML) joint detection with low computational effort. The REC algorithm drastically reduces the number of candidates to be checked when straightforward ML joint detection is applied, thus overcoming the problem of a tremendously large computational effort.

Speech versus keying in command and control: effect of concurrent tasking

Abstract: As a result of Poock's influential work in the early 1980s, command and control is generally believed to be one specific application where speech input holds great advantages over keyed data entry. However, a recent paper (Damper & Wood, 1995 “Speech versus keying in command and control applications ”, International Journal of Human-Computer Studies, 4 2 , 289-305) has questioned this interpretation of Poock’s data because the experimental conditions seemed to bias the results against keyed entry. While Damper and Wood modelled their experiments on Poock's, however, there were important differences which mean that their conclusions are uncertain. The objective of the work reported here was to determine if the major difference-the omission of concurrent, secondary tasking from their study-could explain Damper and Wood's observed superiority of keying over speech. Simulated command and control experiments are described in which speech input, abbreviated command keying and full command keying are compared under dual-task conditions. We find that speech input is no faster (a nonsignificant 1.23% difference) and enormously more error-prone (1038%, highly significant) than abbreviated keying for the primary data entry task, but allows somewhat more (11.32%, not significant) of a secondary information-transcription task to be completed. Full keying has no advantages whatsoever: we believe that this confirms the methodological flaw in Poock's work. If recognizer errors (as opposed to speaker errors) are discounted, however, speech shows a clear superiority over keying. This indicates that speech input has potential for the future-especially for high workload situations involving concurrent tasks-if the technology can be developed to the point where most errors are attributable to the speaker rather than to the recognizer.

Method and apparatus for robust communication based upon angular modulation

Abstract: A robust encoding and decoding system of the present invention for communicating binary information using angular modulation system is disclosed. Binary information to be transmitted is data words consisting of 8 data bits, a parity bit, and two additional coding bits at the end of the data word. A transmitter transmits the data words using a binary phase-shift keying (BPSK) modulated signal. The receiver compares the phase of incoming BPSK modulated signal against a local reference signal and records the phase characteristics of the BPSK signal. The receiver also records the amplitude of the recovered data signal. The receiver demodulates and decodes the BPSK signal using a rotating frame of reference that tracks the current phase of the recovered data signal. The receiver tests the parity bit of each word to detect errors. If an error is detected, the receiver attempts to correct the error using the record phase and amplitude information.

Keying system for electrical connector

Abstract: A keying system for an electrical connector (10, 16) is disclosed. Keying members (160, 234) are provided in mating pairs so that one is assembled to the cable connector (10) and the other is assembled to the mating panel connector (16). Each of the keying members (160, 234) is assembled by inserting it into the open end of the connector so that lugs (186, 236) in the dielectric insert (44, 218) within the connector enter camming slots (178) in the keying member (160, 234) which is then twisted to lock it in place. The keying members can be easily and conveniently assembled and disassembled in the field by the end user.

Continuous-Phase Modulations for CDMA Radio Communications: Modem Architecture and Performance

Abstract: In this paper we analyze the structure and the performance of a digital modem for band-limited spread-spectrum signals to be employed in a radio communication network with asynchronous code-division multiple access and constant-envelope continuous-phase modulation. After a description of the modem structure and the evaluation of its bit error rate in the presence of co-channel interference, we tackle the key point of code synchronization. In particular, we present a detailed analysis of the code acquisition strategy, assessing its performance in terms of false alarm probability, missed detection probability and mean acquisition time. Furthermore, we address the problem of code chip timing recovery, describing the performance of three different code tracking loops in terms of the steady-state RMS chip timing error jitter. The analytical approach we present can be applied to any Continuous Phase Modulation (CPM) format that can be approximated by an Offset-QAM signal, such as Gaussian-filtered Minimum-Shift Keying (GMSK).

Two-stage multiuser detection for asynchronous CDMA using DPSK signalling

Abstract: In this paper, a two-stage multiuser detector for asynchronous code division multiple access (CDMA) using differential phase shift keying (DPSK) is proposed and analyzed. The detector operates using tentative bit decisions of the bilinear decorrelating detector to estimate the multiple access interference corrupting the desired signal. The two-stage detector subsequently subtracts the reconstructed interference from the received signal, and then forms final bit estimates using a bank of conventional differential phase shift keying (DPSK) detectors. Numerical examples indicate that the two-stage detector may offer a significant performance advantage over the bilinear decorrelator with little added complexity.

Performance of code division multiple access in non-directed diffuse optical wireless channel

Abstract: The optical wireless channel has abundant available bandwidth and is suitable for high data rate, indoor communications. In this paper, the performance of CDMA as a multiple access technique for optical wireless communication is examined. As the signature sequence, a (43,3,1,1) and a (63,3,1,1) optical orthogonal code (OOC) are used. Information data is modulated through a simple on-off keying (OOK) modulation scheme. A data rate of 2 Mbps is used and the bit error rate (BER) performance is simulated with respect to signal-to-noise ratio (SNR), number of users, and threshold values. It is possible to find the optimum number of users and the optimum threshold value from the results. It is seen that interference from other users actually helps to improve the BER performance, up to a certain number of users.

Circuit for 2-level/4-level frequency shift key modulation

Abstract: A circuit for two-level/four-level frequency shift keying modulation, which may be used for a paging transmitter, is compatible with earlier two-level non-return to zero frequency shift keying modulation circuits and includes; a voltage leveling circuit for generating four voltage levels to selectively allow the two-level and four-level frequency shift keying modulation; a decoder for decoding the least significant bit and most significant bit data inputs to generate a decoded signal output; an analog switch for selecting the four voltage levels in accordance with the two-level or four-level frequency shift keying modulation, in response to the decoded signal; an adder for adding the selected voltage level to a reference voltage to generate a corresponding digital output voltage; an audio amplifier for amplifying an audio signal input; an input/filter selector for selecting the digital output voltage or the amplified audio signal in response to an input selection control signal and for selecting one of two filtering paths of a following stage in association with a control signal for selecting the two-level or four-level frequency shift keying modulation to generate the selected digital output voltage or the amplified audio signal via the selected filtering path; and a baseband filter for performing a first or a second filtering with a respective bandwidth for the two-level or four-level frequency shift keying modulation and for filtering the digital output voltage or the audio signal supplied through the selected one of the filtering paths.

Digital pulse-position modulation of optical fiber solitons.

Abstract: Amplitude-shift keying modulation of solitons is subject to limited capacity because of Gordon-Haus noise and soliton interaction. It is shown theoretically that the capacity can be increased beyond this limit by recoding of the modulation. The design strategy is to make the pulse train strongly interacting, which reduces the Gordon-Haus noise, and to apply subband coding to counter the effects of the information dispersion caused by the strong intersoliton interaction; the subband-coded complex is pulse-position modulated onto the soliton stream. An example shows a 2.35-times improvement in capacity at the transatlantic distance of 6000 km with this method.

Electrical connector keying system

Abstract: A keying system for an electrical connector arrangement includes a connector plug (18) having a housing (88) with a plurality of keying grooves (90) on at least one side thereof. A face plate (86) is mounted on the housing and includes at least one keying notch (92) in alignment with a respective one of the keying grooves (90). The other of the keying grooves are blocked by the face plate (86). A receptacle (26) is provided for receiving the connector plug (18). The receptacle includes a keying protrusion (48) for extending into the keying notch (92) and the respective one of the keying grooves (90). Therefore, the face plate (86) can be interchanged without changing the housing (88) to accommodate different arrays of keying protrusions (48) on the receptacle.

Comments on a widely used capture model for slotted ALOHA

Abstract: Previously (see ibid., vol.41, no.9, p.1364, 1993), the capture phenomenon in nonbit-synchronous mobile packet radio networks for binary phase shift keying (BPSK) and differential phase shift keying (DPSK) modulation was investigated. Most of the analysis is correct. Unfortunately, the mathematical expressions for state transition probabilities, adopted from previous work, have errors. Over a decade, these mathematical formulas have been used repeatedly to analyze various capture models with a finite number of users in the traditional slotted ALOHA system. In this note, we present a corrected version of the state transition probabilities.

Spread spectrum transmitter and receiver

Abstract: PROBLEM TO BE SOLVED: To conduct phase modulation capable of inverse spread spectrum processing even for quasi-synchronization detection. SOLUTION: A transmitter sends outputs of pseudo noise code generators 2a, 2b in both in-phase and quadrature components. In this case, switches 22a, 22b are used to exchange pseudo noise codes sent in in-phase and quadrature components in a form of parallel input information bits 10a, 10b and multipliers 3a, 3b are used to conduct biphase shift keying(BPSK) modulation or the components thereby conducting phase modulation of pseudo noise codes to be sent. The receiver uses the pseudo noise codes outputted from pseudo noise code generators 2a, 2b to form a 4-phase correlation device and a reception phase angle is detected from the output and information data are demodulated.

Computer peripheral module with keying elements, mold and method of manufacture

Abstract: A computer peripheral module (10) having a rectangular outline with opposing ends (11, 12) and opposing sides (13, 14). The module has keying elements (19, 31) disposed on the sides, adjacent one end, for keying with a receiving slot in a predetermined orientation. One of the keying elements (31) has upper protruding lugs (32, 33, 34) and lower protruding lugs (36, 37, 38) The upper and lower protruding lugs are offset relative to each other in a direction parallel to the side (13).

Performance of a pilot symbol-aided technique in frequency-selective Rayleigh fading channels corrupted by co-channel interference and Gaussian noise

Abstract: In the current digital cellular systems, modulation with low spectral efficiency such as /spl pi//4-quaternary-phase-shift keying (/spl pi//4-QPSK) or Gaussian-minimum-shift keying (GMSK) are usually used. To cope with the ever-increasing demands for system capacity, modulation such as 16-ary modulation (16QAM) or 16-ary phase-shift keying (16PSK) are expected to be used in future. The paper studies the effects of a pilot symbol-aided (PSA) technique on the performance of 16QAM and 16PSK in frequency-selective Rayleigh fading channels corrupted by co-channel interference and Gaussian noise. The PSA technique employs both the pilot symbols and data symbols for fading estimation. Computer simulation results have shown that significant improvements on bit-error rate performance of the signals can be achieved through the use of the PSA technique.

and Its Application to Optical Cryptography

Abstract: We demonstrate that two chaotic systems, each made by two coupled semiconductor lasers, can be synchronized using direct-optical feedback. The robustness of the proposed synchronization scheme against mismatch of source parameters and difference in starting conditions is tested by numerical sim- ulations. Applications to secure data transmission are proposed, namely chaotic masking and chaotic shift keying (CSK).

Password collation system

Abstract: PURPOSE: To eliminate the need for time matching, to enhance the security without increasing number of digits and to improve the propriety of use by storing a keying state of a character and a numeral or the like in the case of storing a password. CONSTITUTION: A key matrix section 7 is used to set a destination telephone number, to set a password and to enter the password, and a registration section 8 stores the set password. In this case, the registration section 8 stores the sequence of the password and the keying state. Then an entry analysis section 9 compares the entered password with a password set in the registration section 8 to compare the entry sequence of them and compares the keying state of the key matrix section 7. When the entered password is coincident with the password set in the registration section 8 as a result of the comparison, the section 9 gives an enable signal to a control section 5 to permit the operation such as dialing. When the entry analysis section 9 discriminates dissidence, the section 9 gives an inhibit signal to the control section 5, which disables the availability of a portable telephone set.

Performance of Q/sup 2/PSK employing multiple trellis coded modulation on Rician fading channels

Abstract: In this paper the design and evaluation of 4-state multiple trellis-coded modulation (MTCM) codes for application to quadrature-quadrature phase-shift keying (Q/sup 2/PSK) are presented. Computer simulations are used to evaluate the performance of these code designs in a non-frequency selective Rician fading propagation environment. Coherent detection, and the benefits of the use of channel state information (CSI) in conjunction with MTCM are also considered. The paper has particular relevance to land mobile satellite radio.

DPSK demodulation with Doppler compensation

Abstract: This paper presents a technique for communications in the presence of rapidly varying Doppler. The modulation selected for this application is differential phase shift keying (DPSK). A number of receiver structures are proposed and their performance examined. It is shown that reliable communications can be achieved even at a data rate as low as 75 b/s and a E/sub b//N/sub 0/ of only 4-8 dB without the use of a separate beacon receiver to track the frequency variations. SHF ship-board satellite communication is considered as an example.

A multiresolution signaling scheme for frequency-hop systems

Abstract: The simultaneous transmission of correlated data streams over a single channel is of interest for communications involving multimedia applications. This paper presents a multiresolution signaling technique that employs a form of M-ary differential phase shift keying (MDPSK) within the context of a binary FSK frequency-hop system. The technique permits the addition of MDPSK modulation into existing BFSK systems without requiring replacement of existing receivers. Methods are given for incorporating Reed-Solomon error control coding, CRC error detection, and erasure generation with this scheme. Two coding/erasure configurations are analyzed and performance results are given for a frequency-hop system subject to partial-band interference.