Showing papers on "Keying published in 1990"

The performance of rate-compatible punctured convolutional codes for digital mobile radio

Abstract: The unequal error protection capabilities of convolutional codes belonging to the family of rate-compatible punctured convolutional codes (RCPC codes) are studied. The performance of these codes is analyzed and simulated for the first fading Rice and Rayleigh channels with differentially coherent four-phase modulation (4-DPSK). To mitigate the effect of fading, interleavers are designed for these unequal error protection codes, with the interleaving performed over one or two blocks of 256 channel bits. These codes are decoded by means of the Viterbi algorithm using both soft symbol decisions and channel state information. For reference, the performance of these codes on a Gaussian channel with coherent binary phase-shift keying (2-CPSK) is presented. A number of examples are provided to show that it is possible to accommodate widely different error protection levels within short information blocks. Unequal error protection codes for a subband speech coder are studied in detail. A detailed study of the effect of the code and channel parameters such as the encoder memory, the code rate, interleaver depth, fading bandwidth, and the contrasting performance of hard and soft decisions on the received symbols is provided. >

Microcellular direct-sequence spread-spectrum radio system using N-path RAKE receiver

Abstract: A microcellular local area network (LAN) for indoor communications is proposed using code-division multiple access (CDMA) and differential phase-shift keying (DPSK) for data modulation. The pseudonoise (PN) codes in the transmitters of the base station are mutually synchronized. For this purpose, sets of Gold code sequences having low cross correlation have been found by an exhaustive computer search. Together with wideband measurements of the indoor radio channel at 900 MHz, a five-path RAKE receiver was designed to combat fading effects and to process the time diversity by using multipath signal reception. Each receiver path is demodulated independently. Several methods of diversity combining of these paths have been investigated. Acquisition and tracking of the spreading code in the receiver are controlled by a digital signal processor (DSP). Experimental results of the CDMA system are presented, showing the behavior in a multipath environment. >

Means for keeping keying elements with a connector assembly

Abstract: Means 1 in the form of a cover for a connector assembly 86, a skirt 2' of the cover encircling a front end 4 of the connector assembly 86, connecting means 7 for connecting the cover to the connector assembly 86 when the skirt 2' is removed from the front end 4, internal webs 9, 9 of the cover lodged in a gap 29 in the front end 4 to retaini the cover on the front end 4, and pockets 11, 11, 11 external to the skirt 2' frictionally receiving the keying elements 94, 94', 94" in the absence of any one of the keying elements 94, 94', 94" in the connector assembly 86.

Digital transmission through a land mobile satellite channel

Abstract: An analytical derivation of the probability of bit error noncoherent frequency-shift keying (FSK) and coherent phase-shift keying (PSK) signals transmitted through a land-mobile satellite channel is described. The channel characteristics used in the analysis are based on a recently developed model which includes the combined effects of fading and shadowing. Analytical expressions for the probability of bit error of FSK and coherent phase-shift keying (CPSK) signals are obtained. The results show that large amounts of signal-to-noise ratio (SNR) are required to compensate for the combined effect of fading and shadowing. An analytical expression for the irreducible probability of bit error of a CPSK signal due to phase variations caused by fading and shadowing is derived. The results described should be useful in the design of land mobile satellite communication systems. >

A concatenated coded modulation scheme for error control

Abstract: A concatenated coded modulation scheme is presented for error control in data communications. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary phase-shift keying (PSK) modulation. Error performance of the scheme is analyzed for an additive white Gaussian noise (AWGN) channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner-code and a relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The scheme is particularly effective for high-speed satellite communications for large file transfer where high reliability is required. A simple method is also presented for constructing block codes for M-ary PSK modulation. Soome short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft-decision Viterbi decoding algorithm. Furthermore, some of these codes are phase invariant under multiples of 45 degrees rotation. >

Spread spectrum communication system

Abstract: A spread spectrum communication system includes a transmitter and a receiver, and an on-off keying signal is inputted to the transmitter. A carrier signal is modulated by the on-off keying signal, and a spread spectrum signal is produced by multiplying a modulated signal by a first PN code (16) which is repetition of 3-bit data. The spread spectrum signal is transmitted through a transmission antenna (19). In the receiver, a second PN code which is repetition of 4-bit data larger than the first PN code by 1 bit is generated. Therefore, a phase of the second PN code becomes coincident with a phase of the first PN code every 12 bits. Then, a spread spectrum demodulation is performed by multiplying (24) a received spread spectrum signal by the second PN code to reproduce the carrier signal being modulated by the on-off keying signal. The on-off keying signal is restored by envelope -detecting a reproduced carrier signal.

Vehicle mounting apparatus of an automatic vehicle location system

Abstract: A vehicle mounting apparatus for an automatic vehicle location system having a omni-directional antenna, a transmitting and receiving switch, an oscillator frequency converters, a frequency-shift keying demodulator, post office committe standard associate group decoder, a pseudorandom noise signal generator, a phase-shift keying modulator, a transmitting signal generator, a power amplifier, and a power supplier. The vehicle mounting apparatus receives a referencing signal from a control center and transmits an answer signal relating to location of a vehicle to be located.

Audio-augmented data keying

Abstract: Present-day limitations of the conventional touch-tone keypad are overcome permitting alphabetic information to be entered into a distant computer. The caller speaks a speech portion into a telephone handset, and then types out the speech portion on the touch-tone keypad. The computer receiving the call converts the spoken voice information into a form suitable for additional digital processing, as by extracting speech-recognition features from the spoken information (32). The computer processes the typed numeric string into a list of all the possible combinations of characters it could represent (31). The extent of correlation between the features of the spoken speech portion and each of the combinations is determined (33), and the combination having the highest correlation is taken to be the speech portion entered by the user (34).

Error probabilities of fast frequency-hopped MFSK with noise-normalization combining in a fading channel with partial-band interference

Abstract: An error probability analysis performed for an M-ary orthogonal frequency-shift keying (MFSK) communication system employing fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a frequency-nonselective, slowly Rician fading channel with partial band interference is discussed. Diversity is obtained using multiple hops per data bit. Noise-normalization combining is employed by the system receiver to minimize partial-band interference effects. The partial-band interference is modeled as a Gaussian process. Thermal noise is also included in the analysis. Forward error correction coding is applied using convolutional codes and Reed-Solomon codes. Diversity is found to dramatically reduce the degradation of the noise-normalization receiver caused by partial-band interference regardless of the strength of the direct signal component. Diversity offers significant performance improvement when channel fading is strong, and performance improvement is obtained for high modulation orders (M>2). Receiver performance is improved when diversity, higher modulation orders, and coding are combined. >

Automatic picture taking machine

Abstract: An automatic picture taking system has a housing which may be in the form of a booth. The housing contains a video camera (20) and is arranged to produce a video picture of a subject in a picture taking zone (3). The video picture can be converted to a print e.g. using a digital thermal colour printer (24, 25). The video picture is stored in memory and can be processed to give a desired composition prior to printing. The picture may consist of the image of the subject which is separated from the background using chroma keying and which is then combined with a selected electronically pre-stored background or foreground.

Adaptive modulation as a fade countermeasure. An olympus experiment

Abstract: With the launch of the European Space Agency's Olympus-1 satellite, a whole new era of communication experiments in the 20/30 GHz bands will start. Of particular interest will be those experiments concerned with fade countermeasures for the very small aperture terminals (VSATs). Portsmouth Polytechnic's experiment will focus on adaptive modulation as a type of fade countermeasure, and this paper introduces and describes the whole concept. Based on the assumption that the performance of a VSAT operating at 20/30 GHz band will be affected to a major extent by amplitude scintillations and rain fading, the performance of a range of combinations of earth-station power amplifier and antenna characteristics is presented. An adaptive multi-phase shift keying technique is then compared with conventional systems in terms of availability and data throughput. It is shown that such a fade countermeasure contributes to increasing both the overall system availability and the total data throughput of a digital communication system, while the inevitable reductions in data rate occur smoothly.

Performance evaluation of multilevel polarisation shift keying modulation schemes

Abstract: The performance of coherent optical transmission systems using multilevel polarisation modulation is derived in terms of the symbol error probability. Four new multilevel modulation schemes based on equipower signal constellations at the vertices of regular polyhedra inscribed into the Poincare sphere are proposed. For an increasing number of signals in the constellation, the shot noise performance of these systems show a remarkably less rapid degradation with respect to standard multilevel schemes with an equal number of signals.

Connector keying system

Abstract: The connector keying system has a first connector housing (4) with a mating surface and a second connector housing (2) with a mating surface. The second housing (2) is movable relative to the first housing (4). In this system a programming of the keying shall occur automatically as the connector housings (2, 4) are mated together. This achieved as follows: A keying means receiving recess (23) is provided on the mating surface of the first connector housing (4) proximate an end thereof. A keying means is provided in the recess (23). The keying means has a first (22) and a second keying member (24). The first keying member (22) is secured to the first connector housing (4) by first securing means (50, 52). The second keying member (24) is frictionally maintained in corporation with the first keying member (22). The second keying member (24) has second securing means which are provided to cooperate with the second connector housing when the connector housings (2, 4) are mated together.

Performance of Optimum and Adaptive Frequency-Shift Filters for Cochannel Interference and Fading

Abstract: Analog and digital carrier modulated signals, such as AM, digital QAM, PSK, and FSK, exhibit correlanon among spectral components separated by multiples of the keying rate and separated by the doubled carrier frequency plus multiples of the keying rate. This spectral redundancy can be exploited to facilitate rejection of cochannel interference, while maintaining minimal signal distortion. It also can be exploited to mitigate the effects of frequency-selective fading with minimal noise amplification. The spectral redundancy is exploited by filtering and adding frequency-shifted versions of the corrupted data. This paper presents the results of a study to evaluate the performance capabilities of optimum and adaptive frequencyshift filters for severely corrupted carrier-modulated signals including AM, BPSK, and QPSK.

Performance evaluation of polarisation shift keying modulation schemes

Abstract: This letter is concerned with coherent optical transmission systems using polarisation modulation. Exact results are derived for the error probability of all binary schemes so far proposed, including a differential demodulation scheme which allows either electro-optic or electronic polarisation tracking.

A model for local/mobile radio communications with correct packet capture

Abstract: The performance of a local/mobile radio communications system utilizing the slotted ALOHA multiple random access protocol is analyzed. The probability of correct packet capture is evaluated for a local/mobile packet radio system using ideal coherent binary phase-shift keying (BPSK) modulation. Both the near/far effect and the effect of Rayleigh fading on the probability of correct packet capture are taken into account, but the effect of thermal noise is neglected since the interference due to competing packets is dominant in practical systems. The probability of correct packet reception is evaluated for a system using spatial diversity. In addition, the effect on system performance of either convolutional coding with hard decision Viterbi decoding or binary linear block coding with hard decision decoding is evaluated. The pseudo-Bayesian algorithm that has been developed to stabilize a packet system based on the slotted ALOHA protocol at maximum channel throughput is found to be adaptable to the local mobile operating environment. For the system considered here, channel throughputs as high as 0.66 can be obtained. >

Phase-noise-canceled differential phase-shift-keying (PNC-DPSK) for coherent optical communication systems

Abstract: A modulation scheme using a nonlinear demodulation process, phase-noise-canceled differential phase-shift keying (PNC-DPSK), is used to circumvent the effects of phase noise in a phase-shift keying (PSK) system. A theoretical description of the system is given, and results of an experimental test system are shown to be in good agreement with the predictions. In particular, it is shown that the phase-noise-induced bit error rate (BER) floor can be eliminated despite using lasers with linewidths comparable to the data rate. Furthermore, for an optimized PNC-DPSK system, the degradation at high signal-to-noise compared to heterodyne PSK with ideal sources (i.e. no phase noise) should only be approximately=3 dB. >

Soft-limiter receivers for coded DS/DPSK systems

Abstract: The performance of a soft-limiter metric and a quantized soft-limiter metric is evaluated for coded DS/DPSK (direct sequence/differential phase shift keying) in the presence of worst case pulse jamming and background noise. The metrics are easy to implement and do not require jammer state information. Instead they rely on the use of receiver thresholds, which must be adjusted according to the code rate and the received bit-energy-to-background-noise ratio. The performance of the metrics is evaluated by using the cutoff rate criterion and a number of specific convolutional and block codes. It is shown that the metrics can offer a significant soft-decision decoding gain and can perform to within 0.5-1.5 dB of the maximum-likelihood soft-decision metric with perfect jammer state information. >

Comparison of coherent and differential detection of BPSK and QPSK in a quasistatic fading channel

Abstract: The advantage of coherent detection over differential detection for quadrature phase-shift keying (QPSK) and binary phase-shift keying (BPSK) in a flat-fading channel is evaluated based on receiver-sensitivity analysis using three performance criteria. QPSK is concentrated upon to perform simulations for a frequency-selective fading channel. Spectral efficiency improvement due to better frequency reuse for the more sensitive coherent detection is evaluated with a combination of analysis and simulation. It is found that coherent detection with perfect carrier recovery is superior to differential detection by at least 2.4 dB, which converts to about a 30% improvement in spectral efficiency in a two-dimensional, frequency reuse system with a fourth-power propagation exponent. This advantage is preserved even if diversity selection is used to mitigate fading. >

Spread-spectrum multi-h modulation

Abstract: Applying a direct random spreading sequence to a digital information sequence prior to multi-h modulation creates a new class of signals called spread-spectrum multi-h (SSMH) signaling. By spreading a known bandwidth efficient modulation scheme, the power spectral density is controlled so that the transmitted spectrum will have a wide, flat mainlobe and rapid sidelobe rolloff. Coincidentally, the power efficient modulation allows transmission at lower signal-to-noise ratios when the receiver knows a priori the spreading sequence and modulation index sequence. Optimal receiver structures are derived and numerically evaluated in an additive white Gaussian noise environment. It is shown that performance is dependent on the spreading sequence, the modulation indexes, and the possible phase states and can exceed direct sequence binary phase-shift keying by 1-2 dB at bit error rates of 10/sup -5/. Composite likelihood ratio analysis reveals a reduction of 50-70% in detectability of completely known SSMH signals vis-a-vis direct-sequence binary phase shift keying (DS/BPSK) at error rates of 10/sup -4/. >

Coding of optical on-off keying signals impaired by phase noise

Abstract: The benefits of coding for an optical communication system that employs binary on-off keying and heterodyne detection are quantified. The system is impaired by laser phase noise as well as by additive white Gaussian noise (AWGN). A receiver structure especially designed to mitigate the effects of phase noise in the presence of AWGN is assumed. This special receiver structure requires a wider-band front-end IF filter than would be required for a phase-noise-free signal. The results, computed for several different coding schemes, indicate that the benefits of coding are large and the costs are small. For a linewidth-to-bit-rate ratio ( beta T) of 0.64 (for example, 45 Mb/s and 29 MHz linewidth), a half-rate binary code that can correct 3 bit errors provides a 50% reduction in the required IF filter bandwidth (and, therefore, the required IF) and about 5 dB of reduction in required laser power. The benefits of coding are greatest under high- beta T conditions, corresponding to low bit rates where coders and decoders are most practical to implement. >

Combined amplitude and polarisation shift keying optical coherent modulation

Abstract: The letter proposes and analyses two coherent transmission schemes using combined amplitude and polarisation shift keying (CAPSK). The bit-error-rate results (with respect to shot and Gaussian receiver noise) show a performance very close to that of the best performing schemes known so far.

Video keying circuitry incorporating time division multiplexing

Abstract: Multi-keying circuitry for inserting a plurality of keys into a background television signal where at least the keying signal processing circuitry is time shared by control circuitry to effect the key insertions. The control circuitry includes dual port rams and RAM-DAC's to facilitate the time share operation. Circuitry for effecting transitions between the keys either individually or in groups is disclosed as is circuitry for previewing the keys or the transitions thereto either individually or in groups.

Coding to relax laser linewidth requirements and improve receiver sensitivity for coherent optical BPSK communications

Abstract: BPSK (binary phase-shift keying) modulation with heterodyne demodulation is used in conjunction with convolutional codes to illustrate the feasibility of using coding to relax the laser linewidth requirements and improve the receiver sensitivity. The Viterbi algorithm is used, and the performance of the phase-locked loop in the carrier recovery circuit is studied. The results show that the relaxing factor of the laser linewidth can be larger than 12 at 10/sup -9/ bit error rate when a (2, 1) convolutional code with constraint length 11 is used. When the linewidth is fixed, this code can improve the receiver sensitivity by more than 9 dB. >

Highly bandwidth efficient transmission through continuous polarisation modulation

Abstract: A binary coherent optical transmission scheme using continuous polarisation shift keying (CPOLSK) is proposed and analysed. Its bandwidth efficiency turns out to be better than that of MSK.

M‐ary FSK with limiter discriminator integrator detection and DPSK with differential phase detection in a Rician Fading channel

Abstract: We derive an expression for the error probability of M-ary differential phase shift keying with differential phase detection and of M-ary frequency shift keying with limiter discriminator integrator detection which is valid for Rician. Rayleigh and Gaussian channels.

Two-stage Doppler phasor corrected TCM/DMPSK for shadowed mobile satellite channels

Abstract: A two-stage Doppler-phasor correction algorithm for mobile satellite, DSP-based modems is presented. The modulation considered is trellis-coded, differential phase-shift keying (DPSK) involving eight signal points. The Doppler phasor rather than the Doppler frequency is corrected as it leads to easy realization in DSP-based software. The Doppler phasor correction algorithm that is presented has a setup mode where the data are known and a data mode where the data are unknown. As such, it is intended for stream data or digital speech transmission. Both computer simulation and analytical techniques are used in the performance analysis. >

Polarisation independent detection by synchronous intra-bit polarization switching in optical coherent systems

Abstract: A novel approach to polarization diversity transmission is discussed in connection with achieving polarization-independent coherent detection with minimum IF bandwidth, as required in high-bit-rate optical systems. This is obtained by stepping the polarization of the field between two orthogonal states at the same frequency as the bit rate. This approach is promising, avoiding complicated receivers, and particularly suitable for a distribution network where switching at the transmitter can be shared among several receivers, reducing system complexity. Computer simulations have been performed for both amplitude- and frequency-shift keying. Critical system parameters are examined and excess penalty is evaluated. In addition to square-wave modulation, sinusoidal modulation has been considered. An optimum value of the modulation depth exists for which the penalty is reduced with respect to the square-wave. >

Coded and uncoded M-PSK and CPM signals on nonlinear bandpass channels: an approach to a fair comparison

Abstract: The performances of several coded and uncoded M-ary phase-shift keying (M-PSK) schemes and two representative continuous-phase modulation (CPM) schemes are compared on a given nonlinear bandpass channel with adjacent channel interference (ACI). It is shown that, due to their constant envelope, the CPM schemes are not degraded by the nonlinearity and allow saturated operation of the high-power amplifier (HPA). In this case the only degradation is produced by ACI. The PSK schemes are assumed to be filtered with conventional square-root Nyquist filters and are very bandwidth efficient. The results of simulations are presented for 4-PSK, offset 4-PSK, coded and uncoded 8-PSK, minimum-shift keying (MSK), and a four-stage CPM scheme with smoothed frequency impulse (M=4, h=1/2, 3RC). It is shown that coded 8-PSK maintains or improves its gain over 4-PSK in the nonlinear channel, when the operating point of HPA is carefully optimized. MSK suffers mainly from ACI, and for narrow channels it is outperformed even by 4-PSK. The 3RC-CPM scheme shows nearly the same performance as coded 8-PSK. >

Digital intermediate frequency demodulation technique for cellular communication systems

Abstract: A novel modulation scheme suitable for digital cellular communication systems is proposed. This scheme first converts the IF (intermediate frequency) signal to a logic level; phase detection is then performed entirely by digital operations. Since analog components such as an I/Q detector and A/D (analog/digital) converters are eliminated with this scheme, a low power consuming and adjustment free receiver can be realized. An application to pi /4-shifted QPSK (quadrature phase-shift keying) demodulation is considered. An experimental receiver for pi /4-shifted QPSK has been built to evaluate its performance. The results show a bit error rate of 1*10/sup -2/ at 12-dB Eb/N/sub 0/ with postdetection diversity under fast fading environments. The results are quite satisfactory, showing good potential for future digital cellular communication applications. >