Showing papers on "Phase-shift keying published in 1990"

Very low rate convolution codes for maximum theoretical performance of spread-spectrum multiple-access channels

Abstract: A spread-spectrum multiple-access (SSMA) communication system is treated for which both spreading and error control is provided by binary PSK modulation with orthogonal convolution codes. Performance of spread-spectrum multiple access by a large number of users employing this type of coded modulation is determined in the presence of background Gaussian noise. With this approach and coordinated processing at a common receiver, it is shown that the aggregate data rate of all simultaneous users can approach the Shannon capacity of the Gaussian noise channel. >

Trellis-coded multidimensional phase modulation

Abstract: A 2L-dimensional multiple phase-shift keyed (L*MPSK) signal set is obtained by forming the Cartesian product of L two-dimensional MPSK signal sets. A systematic approach to partitioning L*MPSK signal sets that is based on block coding is used. An encoder system approach is developed. It incorporates the design of a differential precoder, a systematic convolutional encoder, and a signal set mapper. Trellis-coded L*4PSK, L*8PSK, and L*16PSK modulation schemes are found for 1 >

Maximum likelihood sequence estimation of CPM signals transmitted over Rayleigh flat-fading channels

Abstract: A method for the sequential updating of log-likelihood functions for maximum-likelihood sequence estimation is presented. It is shown that, in a general case, this method can be implemented using Kalman filtering techniques. For the special case of Rayleigh flat fading and continuous phase modulation (CPM) signaling, this approach is shown to lead to an attractive receiver structure. This type of receiver, called the linear predictive receiver, can be implemented in the form of the Viterbi algorithm with the trellis updates being computed using a bank of finite pulse response (FIR) filter and square operations. Simulation results are presented that demonstrate the superiority of the linear predictive receiver over receivers employing differential detection, in the presence of fast fading. It is shown that the optimal linear predictive receiver does not possess an irreducible error rate for a class of Rayleigh fading channels used to model terrestrial mobile channels. >

On the detection and classification of quadrature digital modulations in broad-band noise

Abstract: Optimal and suboptimal decision rules for the detection of constant-envelope quadrature digital modulations in broadband noise are derived and analyzed. The effect of various stochastic models for the carrier phase is examined in detail, while no epoch or frequency uncertainty is assumed. The delay-and-multiply type of detector is considered. A new binary/quadrature phase shift keying (BPSK/QPSK) classifier is compared to the more traditional ad hoc techniques of a square-law classifier and a phase-based classifier (weighting on the phase histogram). The new classifier is derived by approximating the likelihood-ratio functionals of phase-modulated digital signals in white Gaussian noise, hence is named the quasi-log-likelihood ratio (qLLR) rule. It is shown analytically that its performance is significantly better than that of intuitively designed phase-based rules or the conventional square-law classifier. >

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. >

Automatic modulation classification using zero crossing

Abstract: A modulation recogniser that automatically reports modulation types of constant-envelope modulated signals is developed using zero-crossing techniques The zero-crossing sampler, as a signal conditioner, has the advantage of providing accurate phase transition information over a wide dynamic frequency range Signal parameters such as zero-crossing variance, carrier-to-noise ratio (CNR) and carrier frequency are estimated Phase difference and zero-crossing interval histograms play the role of features for modulation recognition The classifier performance is given in the form of a confusion matrix The simulation results obtained demonstrate that a reasonable average probability of correct classification is achievable for CNR ≥ 15 dB

Optimum utilization of the channel capacity of a satellite link in the presence of amplitude scintillations and rain attenuation

Abstract: By considering the global fading process on the link caused by rain attenuation and amplitude scintillations, particularly at K/sub a/ band, it is possible to derive a long-term statistical model of the satellite channel capacity. The four-parameter distribution, which combines amplitude scintillations and rain fade within an up/down link system, is presented. Also presented are the degradation (and improvement) of bit error rate (BER) in the presence of amplitude scintillations, thus complementing the flat fade effect due to rain only. By implementation of adaptive communication systems, a more efficient channel capacity utilization is possible. The concepts and the use of novel analytical expressions combining a log-normal model of rain fade with a Moulsley-Vilar distribution for scintillations are illustrated. These are then applied to a very-small-aperture terminal (VSAT) example of a 29/19-GHz digital communications link through the Olympus satellite using M-ary phase shift keying (PSK) modulation schemes. >

Performance of directly modulated DFB lasers in 10-Gb/s ASK, FSK, and DPSK lightwave systems

Abstract: A comparison is presented of the performance of amplitude-shift-keying (ASK), frequency-shift keying (FSK), and differential-phase-shift-keying (DPSK) lightwave systems which operate at 10 Gb/s with directly modulated 1550-nm distributed feedback (DFB) laser transmitters and conventional 1310-nm dispersion-optimized fiber. Computer modeling techniques were used to accurately simulate the amplitude modulation response and the frequency modulation response of DBF lasers. The system performance is evaluated from simulated eye patterns for both direct and heterodyne detection. With the narrow-optical spectral widths of these signal formats, fiber chromatic dispersion limits up to 70 km were obtained for transmission at 1550-nm using conventional 1310-nm optimized fiber. >

Method and apparatus for digitally processing a high definition television augmentation signal

Abstract: A method and apparatus for digital encoding are described for compressing the augmentation channel signals (chrominance and luminance signals for panel information and high frequency luminance and line difference signal) so that this information can be transmitted in a 3 MHz wide RF channel using a digital transmission scheme such as QPSK. Analog signal components are sampled and converted to digital signals. Each of the signals is fed into a separate coder which reduces the number of bits/pixel required to reconstruct the original signal. Compression is achieved by quantization and removal of redundancy. The compression scheme is based on the use of DCT together with VLC. Each augmentation signal has its own coder, which is adapted to the unique statistics of this signal.

Modulation and demodulation techniques in optical heterodyne PSK transmission systems

Abstract: Modulation and demodulation techniques are described for an optical PSK heterodyne transmission system operating at 560 Mb/s and 1.2 Gb/s. Performance limitations affecting the receiver sensitivity in a 1.2-Gb/s DPSK system, such as laser phase noise, phase modulation depth, IF center frequency deviation, and local laser power, are studied. High receiver sensitivities for PSK systems were achieved. The applicability of the Mach-Zehnder modulator as a phase modulator for 1.2-Gb/s DPSK is also demonstrated. A 1.2-Gb/s DPSK transmission of over 100 km, using polarization diversity with novel polarization-insensitive automatic frequency control in an attempt to overcome signal fading caused by polarization fluctuation in the transmitting fiber, is also described. A receiver sensitivity of less than -42.8 dBm and varying within 1.4 dB for all states of polarization was achieved. A multichannel high-definition TV (HDTV) transmission experiment using a DPSK polarization-diversity tunable receiver is described. >

The performance of trellis-coded MDPSK with multiple symbol detection

Abstract: The idea of using a multiple (more than two) symbol observation interval to improve error probability performance is applied to differential detection of trellis-coded multiple phase-shift keying (MPSK) over an additive white Gaussian noise (AWGN) channels. An equivalent Euclidean distance measure per trellis branch is determined for this detection scheme. This is used to define an augmented (larger multiplicity) trellis code whose distance measure is the conventional squared Euclidean distance typical of conventional trellis-coded modulation on the AWGN. Such an augmented multiple trellis code is a convenient mathematical tool for simplifying the analysis. Results are obtained by a combination of analysis and computer simulation. It is shown that only a slight increase (e.g. one symbol) in the length of the observation interval will provide a significant improvement in bit error probability performance. >

TCM on frequency-selective fading channels: a comparison of soft-output probabilistic equalizers

Abstract: Suboptimal, low-complexity nonlinear equalizer structures derived from the probabilistic symbol-by-symbol maximum a posteriori probability (MAP) algorithm and the M-ary soft-output Viterbi algorithm (SOVA) are investigated. Both algorithms deliver reliability information for each symbol. The complexity of both algorithms in their simplest form is of the order of the conventional reduced-state Viterbi equalizer with hard outputs. Simulation results for a terrestrial time-varying frequency-selective fading channel are given. Realistic channel estimation at high Doppler speeds is included. The coding gain of the investigated 8-state trellis-coded 8-PSK scheme is about 6 dB at a BER (bit error rate) of 10/sup -3/. The gain by making use of soft-decisions is about 4-5 dB at a BER of 10/sup -3/. >

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. >

Optimal noncoherent detection of PSK signals

Abstract: The optimal noncoherent sequential receiver for PSK signals, and some reduced complexity near-optimal decoder structures are derived. The performance of the optimal noncoherent receiver asymptotically approaches that of the coherent detector. The proposed suboptimal structures have performance close to the optimal receiver, but their complexity remains low. Evaluation of the new schemes for the pi /4-QPSK (the new North American standard for cellular mobile radio) and 8-PSK indicate improvements of up to 1.9 dB (at BER=10-4).

Binary phase shift keying modulation system

Abstract: A low cost spread spectrum modulator for BPSK, or Binary Phase Shift Keying capable of outputting the high modulation rate and suppressed carrier output needed in spread spectrum systems. The present invention provides high quality BPSK modulation without the double balance mixers as required in the prior art, thereby dispensing with the necessity of complex transistor/potonciometer or diode/transformer arrangements. The present invention provides BPSK modulation utilizing only one transformer, which can be adjusted for carrier suppression and two transistors, allowing the present system to be driven from low power CMOS logic levels, yet producing eight db of gain.

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. >

ASK and FSK coherent lightwave systems: a simplified approximate analysis

Abstract: A simplified approximate analysis of amplitude shift keying (ASK) and frequency shift keying (FSK) coherent optical communication systems is presented. The analysis accounts for the phase noise of the transmitter and the local oscillator lasers and for the additive Gaussian noise stemming from the shot noise and thermal noise. The analysis yields a closed-form estimate of the bit error rate (BER) and allows an immediate physical insight and appreciation of the impact of the IF filter bandwidth, laser linewidth, and bit rate on the system performance. The theory also yields reasonably accurate estimates of the optimum IF bandwidths and of the sensitivity penalty stemming from the phase noise. >

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. >

On the error probability of linearly modulated signals on Rayleigh frequency-flat fading channels

Abstract: Consideration is given to optimal detection of linearly modulated signals subject to multiplicative Rayleigh-distributed distortion and additive white Gaussian noise. For coherent detection, regenerated amplitude and phase references are employed at the receiver to compensate for amplitude and phase deviations from the correct values. A system model is formulated under the assumption of perfect symbol timing and in the absence of intersymbol interference, producing a final additive noise term, applied just before the detection, which contains the effects of the original additive and multiplicative distortions and of the errors in the phase and amplitude references. By determining the probability density function of this final noise term for arbitrary types of linear modulation, it is possible to perform exact calculations of error probabilities. >

Directional signal modulation by means of switched spaced antennas

Abstract: The theory of modulation by hopping or by commutation among a number of spaced antennas is presented The theory brings out the important considerations and criteria for determining the separation of discrete antennas in time and/or space that produces a desired modulation In addition, antenna hopping and commutation are proposed for generating direction-dependent spread spectrum to enhance receiving system anti-interference processing gain and/or transmitted signal camouflage and LPI, as well as to provide an effective means for channel monitoring and analytical probing >

Digital frequency estimation in burst mode QPSK transmission

Abstract: In burst digital transmission using PSK (phase shift keying) modulation with coherent detection, the recovery of the carrier reference phase and the symbol clock is a key aspect. If all users have a common clock synchronization, symbol timing needs not to be recovered in each burst. A digital processor for carrier recovery without preambles, in the presence of frequency offset, is considered. As an example, a 2 Mb/s QPSK transmission system is considered in which E/sub b//N/sub o/=10 dB, and the burst and estimation interval length L=15. Using the algorithm described and averaging eight successive estimated frequency offsets, in order to eliminate anomalous errors, the BER (bit error rate) degradation is equal to 0.14 dB when Delta f=20 kHz. >

Convolutionally interleaved PSK and DPSK trellis codes for shadowed, fast fading mobile satellite communication channels

Abstract: Using a model from the literature, the performance of convolutionally interleaved phase-shift-keying (PSK) and differential phase-shift-keying (DPSK) trellis codes for digital speech transmission over shadowed mobile satellite communication channels is determined by computer simulation. First the characteristics of fading channels are examined and analyzed in terms of the probability distributions of amplitude, phase, and burst errors. A statistical method, using a histogram approach, is utilized along with the simulations of fading channels to generate these probability distributions. A test for channel burst error behavior is presented. A periodic convolutional interleaver/deinterleaver to be used with trellis coding to combat slow fading in digital, shadowed mobile satellite channels is designed. This interleaver ha less than half the time delay for the same bit error performance than a block interleaver. The results show that the periodic convolutional interleaver provides considerable improvement in the error and time delay performance of mobile satellite communication channels for up to average shadowing conditions as compared to other techniques. >

M-ary frequency shift keying with limiter-discriminator-integrator detector in satellite mobile channel with narrowband receiver filter

Abstract: An expression is derived for the error probability of M-ary frequency shift keying with a limiter-discriminator-integrator detector and a narrowband receiver filter in the satellite mobile channel. This channel contains, as special cases, the Gaussian and Rayleigh (land mobile) channels. The error probability is computed as a function of various system parameters for M=2, 4, 8 symbols and a third-order Butterworth receiver filter. >

Hybrid modulation satellite communication system

Abstract: In a satellite communication system including a plural small earth stations (3-8), a relay earth station (2) and a satellite (1), information transmission is undertaken by primary modulation of carrier wave, and transmission of operation status of each small earth station (3-8) is carried out by secondary modulation of said carrier wave. Primary modulation may be BPSK or multiphase PSK (MPSK), and secondary modulation may be PSK, ASK or FSK. Said operation status may be receive signal quality in each small earth station, and the relay earth station (2) may adjust transmit power to said small earth station such that the receive signal quality at small earth stations satisfies desired criteria irrespective of rain attenuation.

Presence detection of binary-phase-shift-keyed and direct-sequence spread-spectrum signals using a prefilter-delay-and-multiply device

Abstract: The specific problem of detecting the presence of either binary-phase-shift-keyed (BPSK) signals or BPSK direct-sequence spread-spectrum (DS/SS) signals with a prefilter-delay-and-multiply (PFDM) device is considered. Using stationary process theory and Fourier analysis, the optimum PFDM structures for signal presence detection of BPSK signals with known bit rates and carrier frequencies and BPSK DS/SS signals with known chip rates and carriers in additive colored Gaussian noise are derived. The structures are optimum in the sense that they maximize the spectral signal-to-noise ratio (SNR) of an output periodic waveform which has fundamental frequency equal to the bit or chip rate of the signal. Two of the optimum structures that are derived and analyzed are the optimal prefilter-square device and the optimal PFDM with delay set to one half of the signal's bit or chip duration. >

A comparison of a limiter-discriminator, delay and coherent detection for pi /4 QPSK

Abstract: A brief description is given of limiter-discriminator, delay, and coherent detection of pi /4 quadrature phase shift keying (QPSK). Simulated bit error rate (BER) performance of these detectors in static and Rayleigh faded fields is presented. Performance in delay spread faded fields is also given. Results of the use of an equalizer with the coherent detector in delay spread faded fields is evaluated. Three methods of detecting pi /4 QPSK are evaluated. A brief description of the operation and an estimate of implementation complexity is given for each detector. Simulated results of BER performance for each detector in static, Rayleigh, and delays spread faded fields are then presented. The use of an adaptive decision feedback equalizer with a coherent detector is then evaluated for use in delay spread faded fields. >

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. >

Differential modulation and demodulation of multi-frequency digital communications signals

Abstract: Multiple-frequency modulation (MFM) is a bandwidth-efficient digital communication signaling technique that may be used effectively in mobile satellite communications links Algorithms for generating and demodulating differentially encoded multifrequency quadrature phase shift keyed (MFQPSK) signals using discrete Fourier transform (DFT) techniques are discussed The theory and a prototype system for differentially encoding and decoding MFQPSK in the frequency domain are developed By using long baud intervals and corresponding small spacing of the carrier tones, problems associated with channel fading are greatly relieved with respect to the previous method of differentially encoding the multiple carrier tones from baud to baud An MFM system has been configured to transmit MFQPSK over a 4-kHz bandpass channel Tone spacings, or baud rates, of 15, 30, 60, 120, and 240 Hz were tested Output signal-to-noise ratios were estimated by computing sample means and variances of the real and imaginary parts of X/sub a/ Experimental results are presented showing good agreement with the theory >

Performance analysis of direct-sequence spread-spectrum multiple-access communication in an indoor Rician-fading channel with DPSK modulation

Abstract: The bit error probability for direct-sequence spread-spectrum multiple-access (DS/SS-MA) in indoor radio channels is evaluated, assuming differential phase-shift-keying (DPSK) modulation, both for selection diversity and for maximal-ratio combining. The indoor radio environment is modelled as a Rician fading channel.

Linearized saturation amplifier with bidirectional control (LSA-BC) for digital mobile radio

Abstract: The design and performance of the LSA-BC, a novel power amplifier, are presented. A linear amplifier with the high efficiency of a switching-mode saturation amplifier can be realized. A high-efficiency GaAs FET is roughly linearized by dynamically varying its drain DC voltage with a high-efficiency variable-output DC-DC converter. A negative envelope feedback is utilized to compensate for the residual. The circuit construction is simple enough for use in the portable subscriber units of a digital mobile radio system. A 1.5-GHz-band 1-W LSA-BC was constructed to determine its performance with 32-kb/s roll-off QPSK (quadrature phase-shift keying). As a result, a 40% total efficiency is achieved as well as a stable third-order intermodulation distortion of -50 dB to the signal level. >