Showing papers on "Phase-shift keying published in 1987"

The Effects of Time Delay Spread on Portable Radio Communications Channels with Digital Modulation

Abstract: Frequency-selective fading caused by multipath time delay spread degrades digital communication channels by causing intersymbol interference, thus resulting in an irreducible BER and imposing a upper limit on the data symbol rate. In this paper, a frequencyselective, slowly fading channel is studied by computer simulation. The unfiltered BPSK, QPSK, OQPSK, and MSK modulations are considered first to illustrate the physical insights and the error mechanisms. Two classes of modulation with spectral-shaping filtering are studied next to assess the tradeoff between spectral occupancy and the performance under the influence of time delay spread. The simulation is very flexible so that different channel parameters can be studied and optimized either individually or collectively. The irreducible BER averaged over fading samples with a given delay profile is used to compare different modulation/detection methods, while the cumulative distribution of short-term BER is employed to show allowable data symbol rates for given values of delay spread. It is found that both GMSK and QPSK with a raised-cosine Nyquist pulse are suitable for a TDM/TDMA digital portable communications channel.

Spectral Correlation of Modulated Signals: Part II--Digital Modulation

Abstract: As a continuation of Part I, the spectral correlation function is presented for a variety of types of digitally modulated signals. These include digital pulse-amplitude, pulse-width, and pulse-position modulation, and various types of phase-shift keying and frequency-shift keying. The magnitudes of the spectral correlation functions are graphed as the heights of surfaces above a bifrequency plane, and these graphs are used as visual aids for comparison and contrast of the spectral correlation properties of different modulation types.

Direct-Sequence Spread Spectrum with DPSK Modulation and Diversity for Indoor Wireless Communications

Abstract: Direct-sequence spread spectrum with differential phase shift-keying (DPSK) modulation and code-division multiple-access is a promising approach for wireless communications in an indoor environment, which is characterized in this paper by a Rayleigh-fading multipath channel. In this study, we consider two specific channel models having different path-delay distributions and average path power profiles. A star configuration, in which each user exercises average power control in transmitting to a central station, is the basic communication unit, which could be one cell in a cellular hierarchy. We obtain the performance of a single link between a user and its receiver in the central station, and consider two types of diversity, selection diversity and predetection combining to exploit the multipath. A similar system with coherent PSK (CPSK) modulation has been studied previously for one of the channel models considered here. For the same channel model, we show that the irreducible error probability with selection diversity is about half an order of magnitude higher when DPSK is used instead of CPSK. With predetection combining, the performance improves significantly in comparison with selection diversity as the diversity order increases. DPSK modulation with predetection combining is akin to coherent PSK with optimal maximal-ratio combining, but is simpler to implement. The performance with selection diversity for a second channel model, which is based on measurements in an office building, is not significantly different. This indicates that the spreadspectrum approach is rather robust to the path-delay distribution and average path-power profile.

Polarization independent coherent optical receiver

Abstract: This paper describes an optical heterodyne receiver for DPSK signals which can receive an optical signal having an arbitrary polarization state. This is achieved by splitting the received signal between two orthogonal polarization axes and processing the resulting two signals as in a conventional DPSK heterodyne receiver. The sum of the two demodulated signals provides a baseband signal independent of the polarization state of the received optical signal. When the receiver noise is dominated by the shot noise of the photodetectors, the receiver provides a BER of 10-9for an average number of 22 photon/bit. In comparison, a conventional optical heterodyne receiver requires under the same noise condition 20 photon/bit to achieve the same BER for a received optical signal polarized along the polarization axis of the local optical signal.

Trellis Coded Modulation for 4800-9600 bits/s Transmission Over a Fading Mobile Satellite Channel

Abstract: The combination of trellis coding and MPSK signaling with the addition of asymmetry to the signal set is discussed with regard to its suitabllity as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in this paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, our results will only reflect the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

Highly Efficient Digital Mobile Communications with a Linear Modulation Method

Abstract: Although linear modulation methods can achieve high spectrum efficiency, very little attention has been directed to their use in mobile radio systems. This is mainly due to the fact that the nonlinearity of the transmitter power amplifier tends to spread the spectrum and thus eliminate any spectrum efficiency advantage gained through the use of linear modulation methods. In this paper, a linear modulation system is proposed, which solves the above difficulty and which gives higher spectrum efficiency than conventional digital FM. The modulation/demodulation method is \pi /4 shift QPSK and phase-shift detection with a limiter-discriminator and an integrate-and-dump filter. By introducing a cartesian coordinate negative feedback control, 35 percent power efficiency at 10 W output power and - 60 dB relative out-of-band radiation are simultaneously achieved with a class "AB" amplifier, owing to the 29 dB feedback gain. The receiver configuration is easy to realize and gives immunity against fast fading through the use of noncoherent detection with limiter-discriminator. By using a novel decision method, bit error rate performances under both nonfading and fading condition are comparable to those obtained by digital FM. These results make it possible for linear modulation methods to achieve higher spectrum efficiency than is possible with conventional digital FM methods in mobile radio communications.

Frame Synchronization for Gaussian Channels

Abstract: The problem of locating a periodically inserted frame synchronization pattern in random data for a M -ary digital communication system operating over the additive white Gaussian noise channel is considered. The optimum maximum-likelihood decision rule, high signal-to-noise approximate maximum likelihood decision rule, and ordinary correlation decision rule for frame synchronization are derived for both coherent and noncoherent phase demodulation. A general lower bound on synchronization probability is derived for the coherent correlation rule. Monte Carlo computer simulations of all three decision rules, along with evaluations of the lower bound for the coherent correlation rule, were performed for the coherent MPSK, coherent, and noncoherent M ary orthogonal, and 16 QAM signaling schemes. These results show that in each case the high signal-to-noise maximum-likelihood rules have a performance nearly equal to that of the maximum-likelihood rules over a wide range of practically interesting signal-to-noise ratios (SNR's). These high SNR decision rules also provide significant performance improvement over the simple correlation rules. Moreover, they are much simpler to implement than the maximum-likelihood decision rules and, in fact, are no more complex than the correlation rules.

Forward Error Correction Coding for Fading Compensation in Mobile Satellite Channels

Abstract: Fading in mobile satellite communications severely degrades the performance of data transmission. The channel is modeled with nonfrequency selective Rice and Rayleigh fading. Also, stored channel simulation is used for hardware data transmission. FEC coding with Viterbi decoding of convolutional codes, and Berlekamp-Massey decoding of Reed-Solomon codes, are used to compensate for the fading. In addition to interleaving, channel state and erasure information improve the performance of the decoder. The BER after decoding is calculated for specific codes on several channels and for different transmission schemes. Using very simple channel state and erasure information gives 2-7 dB additional coding gain. These gains have been verified by hardware data transmission on synthetic fading channels and stored mobile satellite channels.

Mobile digital communications via tone calibration

Abstract: A new digital signaling technique that is particularly suited for channels impaired by multipath fading is presented. The proposed modulation scheme employs a continuous-wave (CW) tone to calibrate the mobile channel against the multipath-induced phase uncertainties. This technique is applicable to quaternary phase shift keying as well as to more complicated signal constellations such as M-ary phase shift keyed schemes. The advantages of tone calibration are: 1) robustness of the receiver and 2) elimination of the link dependent error floor. Furthermore, since the CW tone can also be used for coherent signal demodulation, carrier phase acquisition can be achieved within a bit time. This property is particularly attractive when a burst of data with a short burst length has to be detected. This radio technique is useful for both the terrestrial mobile and the newer satellite-aided mobile communication (SAMC) services.

Error Probability Evaluation for Systems Employing Differential Detection in a Rician Fast Fading Environment and Gaussian Noise

Abstract: A method is presented for determining the error probability of a receiver using differential detection in the presence of Gaussian noise and fast Rician fading. Equations for the covariances of the fading component are derived, which include the effect of IF filter distortion. It is shown that these equations may be readily evaluated numerically. A simple formula for the error probability is derived for systems using BPSK and a matched filter receiver. An example of the error probability is given using this receiver. Also given is an example of a system using MSK with a practical IF filter. Different spectral shapes and bandwidths for the fading process are investigated for this example and their effect on the error probability is determined.

Trellis Coding with Asymmetric Modulations

Abstract: Traditionally symmetric signal constellations, i.e., those with uniformly spaced signal points, have been used for both uncoded and coded systems. Although symmetric signal constellations are optimum with no coding, the same is not necessarily true for coded systems. This paper shows that by designing the signal constellations to be asymmetric, one can, in many instances, obtain a performance gain over the traditional symmetric constellations combined With trellis coding. In particular, we consider the joint design of n/(n + 1) trellis codes and asymmetric 2^{n+1} -point signal constellations, which has no bandwidth expansion relative to an uncoded 2n-point symmetric signal set. The asymptotic performance gains due to coding and asymmetry are evaluated in terms of the minimum free Euclidean distance d free of the trellis. A comparison of the maximum value of this performance measure to the minimum distance d min , of the uncoded system is an indication of the maxiamm reduction in required E_{b}/N_{0} that can be achieved for arbitrarily small system bit error rates. Bit error probability analysis is carried out for general cases. A few examples are given to show the performance gain due to the asymmetry of the signal set. It is to be emphasized that the introduction of asymmetry into the signal set does not affect the bandwidth or power requirements of the system; hence, the abovementioned improvements in performance come at little or no cost. Asymmetric signal sets in coded systems first appear in the work of Divsalar and Yuen [1], [2]. Here we expand upon these results by considering various types of asymmetric signal sets combined with the optimum (in the sense of maximum d free ) trellis code having 2, 4, 8, and 16 states. The numerical results obtained will clearly demonstrate the tradeoff between the additional savings in required E_{b}/N_{0} and the additional complexity (more trellis states) needed to achieve it.

Performance of DS/SSMA Communications in Impulsive Channels--Part I: Linear Correlation Receivers

Abstract: The performance of digital linear correlation receivers is studied in a multiuser environment. There are assumed to be two types of sources interfering with data transmission: multiple-access interference, and additive channel noise which is attributed to impulsive noise sources in the environment. The contribution of multiple-access interference is examined by considering K asynchronous users transmitting simultaneously over a linear channel using the binary PSK direct-sequence spreadspectrum multiple-access (DS/SSMA) technique. Alternatively, the effects of the non-Gaussian impulsive channel in such a system are studied by modeling the samples of noise after front-end filtering. Errorprobability performance under these conditions is compared to that for additive white Gaussian noise (AWGN) channels. Due to computational complexity, exact analysis is limited here to systems utilizing short spreading sequences. Computationally simple methods are proposed for approximating the average error probability when the length of the signature sequences is large. Furthermore, some asymptotic results are obtained for the case of infinitely long sequences. In all cases, performance variation is examined as the shape of the noise density varies with SNR held constant. The results of this analysis indicate that the presence of impulsive noise can cause significant performance degradation over that predicted from an AWGN model, even when the total noise power does not increase.

Error Probablity for Optimal and Suboptimal Quadratic Receivers in Rapid Rayleigh Fading Channels

Abstract: The exact performance of optimal and suboptimal quadratic receivers in a binary hypothesis test between jointly distributed zero mean complex Gaussian variates is derived. The probability of error is given as a function of the characteristic values of a generalized eigenvalue problem set up in terms of the covariance matrix of the received signal-plus-noise and in the matrix of the quadratic form of the receiver. The results include the exact performance of various types of suboptimal receivers including those previously derived for the envelope matched filter for MFSK and the noncoherent DBPSK receiver in rapid Rayleigh fading, nonfrequency-selective channels. Also, the performance of near-optimal stationary process-long observation time [SPLOT] receivers, "energy detectors," and other approximately optimal receivers may be calculated for noncoherent signaling in the same channel.

Multipath Diversity Reception of Spread-Spectrum Multiple-Access Communications

Abstract: The analysis of a multipath-combining receiver for directsequence spread-spectrum communications through a specular multipath channel is developed. The analysis applies to systems that use quadriphase-shift-keyed, offset quadriphase-shift-keyed, minimum-shiftkeyed, or binary phase-shift-keyed modulation. The measures of performance are the signal-to-noise ratio and approximations to the error probability involving the signal-to-noise ratio. The performance of a multipath-combining receiver is determined not only for the case of a single transmitter, but also for the case of multiple interfering transmit, ters. Furthermore, the performance of the system is determined in terms of parameters of the signature sequences. These parameters can be used as guides in selecting signature sequences for the system. Results are also given for the case of randomly generated signature sequences.

Theory for optical heterodyne DPSK receivers with post-detection filtering

Abstract: We present a general theoretical model for optical heterodyne DPSK receivers for optical communications systems where transmitter and local oscillator lasers have significant linewidths. Quantum phase noise in the lasers is treated as such, but in contrast with previous models for DPSK, receiver noise and local oscillator shot noise are treated as additive noise on the receiver output voltage, as this allows a straightforward description of the effects of post-detection filtering. As a consequence of the detection scheme, a key issue is to account for the non-Gaussian statistics of the output voltage, and this is done using a Chernov bound formulation. Detailed numerical results for a typical 140 Mbit/s p-i-n-FET front end are presented. It is found that heterodyne DPSK gives improved receiver sensitivity compared to other heterodyne detection schemes for IF linewidths below 0.7 percent of the data rate.

Correction to "Design and Experimental Results for a Direct-Sequence Spread-Spectrum Radio Using Differential Phase-Shift Keying Modulation for Indoor, Wireless Communications"

Abstract: We report on our design and measurements that have been made for a direct-sequence spread-spectrum radio using differential phase-shift keying modulation for a wireless PBX. We describe the design and implementation of a transmitter and a receiver using a surface acoustic wave (SAW) filter matching the spread-spectrum code of a user. The receiver performance is within 1 dB of the theoretical performance of a differential phase-shift keying (DPSK) receiver in the presence of additive white Gaussian noise. We also show receiver performance in a multipath fading indoor environment with multipath fade notches of up to 50 dB depth. The indoor channel multipath fading can be overcome by using an equal gain diversity combiner which is suitable when DPSK modulation is used. We confirm that the indoor mean power level attenuation follows the inverse fourth power of the distance. Also, we investigate the multiple-access capability of the system by introducing an interfering transmitter with a different spread-spectrum code sequence.

Multiple trellis coded modulation

Abstract: A technique for designing trellis codes to minimize bit error performance for a fading channel. The invention provides a criteria which may be used in the design of such codes which is significantly different from that used for average white Gaussian noise channels. The method of multiple trellis coded modulation of the present invention comprises the steps of: (a) coding b bits of input data into s intermediate outputs; (b) grouping said s intermediate outputs into k groups of si intermediate outputs each where the summation of all si,s is equal to s and k is equal to at least 2; (c) mapping each of said k groups of intermediate outputs into one of a plurality of symbols in accordance with a plurality of modulation schemes, one for each group such that the first group is mapped in accordance with a first modulation scheme and the second group is mapped in accordance with a second modulation scheme; and (d) outputting each of said symbols to provide k output symbols for each b bits of input data.

A Novel Anti-Multipath Modulation Technique DSK

Abstract: This paper describes a new modulation technique called DSK (double phase-shift keying) which shows an interesting antimultipath feature over mobile frequency-selective fading environments. The effect of this technique is shown for various multipath channels by detection waveform and theoretical bit error rate (BER) analyses. A result obtained from a laboratory test is also presented. In the latter part of the paper, a generalized form of DSK is described and extensive investigations are made so as to clarify the anti-multipath effect of DSK in view of the diversity concept and to further explore the possibility of a narrowband scheme. A major result shows that this technique can give a kind of diversity effect which is implicit in the arrival of signals via multiple paths with different delays.

Highly reliable multilevel channel coding system using binary convolutional codes

Abstract: A multilevel channel coding system using binary convolutional codes is proposed. This system achieves high coding gain. For example, we can obtain an 8-PSK system with rate R = 2/3, which has 6.02 dB coding gain over uncoded 4-PSK and is implemented as easily as Ungerboeck's system with total encoder memory K = 4.

A comparison of data modulation techniques for land mobile satellite channels

Abstract: Several modulation schemes for transmitting data over land mobile satellite channels are compared using a Monte Carlo simulation. Schemes under consideration include differentially detected minimum shift keying (DMSK), differentially detected filtered offset quadrature phase shift keying (DOQPSK), and coherently detected binary phase shift keying with transparent tone-in-band processing (BPSK-TTIB). The transmission of data to and from a mobile radio, which is also capable of operating as an amplitude companded single sideband radio, is the application considered here. The nominal bit rate is 2400 bit/s, while the nominal channel spacing is 5 kHz. DOQPSK with nonredundant single-error correction (SEC) is shown to be a promising candidate. It is capable of outperforming DMSK with SEC by more than 1 dB. Techniques that send a reference signal along with a PSK signal and then perform coherent detection, such as BPSK-TTIB, are also shown to be inferior to DOQPSK with SEC for the class of channels considered here.

An Error Probability Formula for M-ary DPSK in Fast Rician Fading and Gaussian Noise

Abstract: A formula for the symbol error probability is derived which applies to differential detection of M -ary phase-shift keying (MDPSK) in fast Rician fading and white Gaussiau noise. This formula is an extension of a result already known for MDPSK in Gaussian noise interference.

Quadrature-quadrature phase shift keying with constant envelope

Abstract: Methods for modulating and demodulating digital data streams utilize a quadrature-quadrature phase shift keying data transmission arrangement to acheive a 100% increase in the bandwidth efficiency over known systems, such as minimum shift keying. Known arrangements utilize two dimensional data transmission. However, Q 2 PSK, in accordance with the invention, provides four dimensional transmission which doubles the rate of data transmission for a given bandwidth, at the expense of approximately 45% increase in the average energy per bit. The input data stream is demultiplexed to form four demultiplexed data streams which are formed of demultiplexed data bits, each such stream being coded to form a stream of data words formed of a predetermined number of data pulses and a parity check bit. Each such data stream is combined with a signal having carrier and data pulse-shaping components. Additionally, the data pulse-shaping components have a quadrature phase relationship with each other, thereby adding the additional two dimensions of data transmission capacity within a constant envelope.

A PSK Group Modem for Satellite Communications

Abstract: A PSK group modem which modulates and demodulates multiple PSK signals en bloc will play an important role in realizing a cost-effective satellite communications system based on the narrowband multicarrier PSK/FDMA technique. This paper briefly discusses its possible applications, and presents a developed PSK group modem including its algorithm, hardware design, and implementation. In the algorithm, filtering of respective PSK signals is effectively carried out by digital signal processing techniques applied to the digital transmultiplexer. Furthermore, in order to compensate for the difference between the operation timing of the PSK group modem and the symbol timing of each input/output data signal, digital signal processings based on a table-look-up method using ROM and a rate-conversion filter with adaptive weighting are proposed for the modulator and demodulator, respectively. An experimental 4-phase PSK group modem has been developed, and experiments have been conducted under various conditions. The measured performance of the developed hardware is also demonstrated.

BPSK demodulator and FM receiver for digital data pagers

Abstract: An FM receiver for the reception of digital data modulated on a Subsidiary Communication Authorization (SCA) subcarrier is provided with automatic tuning capability and a coherent demodulator for minimizing noise, distortion and interference. The FM receiver is tuned automatically to minimize the measured amplitude of noise and distortion at the high frequency end of the spectrum of the FM demodulator output, above the frequencies of the SCA signal. The SCA signal is tuned by a heterodyne circuit including a balanced modulator, a voltage-controlled oscillator (VCO), and a bandpass filter. The VCO is automatically tuned to maximize the measured amplitude of the SCA signal selected by the bandpass filter. For coherent detection of BPSK (Binary-Phase-Shift-Keying), the coherent demodulator is preferably and kind of data-aided Costas loop in which digital logic circuits perform phase shifting, phase detecting, a multiplying functions. The feedback of the phase error signal is preferably inhibited whenever the signal-to-noise ratio falls below the level which ensures phase-lock, for example, by inhibiting feedback whenever the amplitude of the filtered in-phase signal in the Costas loop fails to exceed a predetermined threshold level. Preferably the phase error signal is fed back through an integrating low-pass filter to control the VCO of the heterodyne circuit, and is fed back through a bandpass filter to control the oscillator of the Costas loop.

Carrier Phase and Clock Recovery for Continuous Phase Modulated Signals

Abstract: This paper presents an analysis of a synchronization circuit to be used for carrier-phase and symbol-timing recovery in continuous phase modulation systems. M -ary modulation formats with arbitrary pulse shaping and rational modulation indexes are assumed. Circuit performance is expressed in terms of variances of phase and timing errors. Numerical results are provided for some important cases, including minimum shift keying and tamed frequency modulation. Theoretical results are found in good agreement with computer simulations.

Adaptive Diversity Reception Over a Slow Nonselective Fading Channel

Abstract: We extend some previous results on adaptive receivers with memory for slow nonselective Rayleigh fading channels to the case of diversity reception. The Bayes receiver in this case is shown to be a generalized maximal ratio combiner. Error probability performance is obtained for antipodal signals such as BPSK. A simple performance upper bound is also derived. Numerical performance results are presented for the particular case of a Markov channel model.

A Practical Receiver Structure for Multi-h CPM Signals

Abstract: Multi- h schemes are bandwidth-efficient CPM signaling formats which offer means of coding without explicit redundancy. However, the required (optimal) receiver structures tend to be very complex [1], [4], [8] requiring a large number of filters of correlators. Here a reduced complexity receiver for the joint estimation of M -ary data, carrier phase, and symbol timing is realized through the use of an approximate representation of the likelihood function. Evaluation of receiver performance indicates a fraction of a decibel degradation in coding gain and almost no loss in synchronization performance.

Novel receiver structures for systems using differential detection

Abstract: Novel receiver structures are introduced which improve the bit error rate performance of differentially detected MSK and QPSK systems. These new receiver structures are based on 1) combining with feedback, 2) a simple Viterbi decoder which uses one- and two-bit detector outputs for maximum-likelihood sequence estimation, and 3) using the correlation of noise for the partial removal of its effect prior to decision. The new receiver structures presented are useful in mobile radio and mobile satellite communications where power efficiency, synchronization, and implementation complexity are of primary concern.

Trellis-Coded MPSK with Reference Phase Errors

Abstract: With trellis-coded MPSK schemes, reference phase errors have a major impact on the system performance. This paper analyzes the interrelation among the coded-modulation format, the reference phase tracker, and the carrier phase noise. A tight upper bound to the error probability of a maximum likelihood decoder is introduced. This bound reveals eight new distance-type functions which, along with the wellknown minimum Euclidean distance, characterize the coded-modulation scheme. Relationships between the new distance-type functions and the various system parameters as well as the irreducible probability of error are pointed out. Numerical results for uncoded QPSK and three Ungerboeck encoded 8-PSK schemes showy that excessive smoothing of the reference phase in presence of carder phase noise can degrade the performance of coded 8-PSK modulation considerably.