Showing papers on "Phase-shift keying published in 2000"

A comparison of SNR estimation techniques for the AWGN channel

Abstract: The performances of several signal-to noise ratio (SNR) estimation techniques reported in the literature are compared to identify the "best" estimator. The SNR estimators are investigated by the computer simulation of baseband binary phase-shift keying (PSK) signals in real additive white Gaussian noise (AWGN) and baseband 8-PSK signals in complex AWGN. The mean square error is used as a measure of performance. In addition to comparing the relative performances, the absolute levels of performance are also established; the simulated performances are compared to a published Cramer-Rao bound (CRB) for real AWGN and a CRB for complex AWGN that is derived here. Some known estimator structures are modified to perform better on the channel of interest. Estimator structures for both real and complex channels are examined.

Maximum-likelihood classification for digital amplitude-phase modulations

Abstract: We apply the maximum-likelihood (ML) method to the classification of digital quadrature modulations. We show that under an ideal situation, the I-Q domain data are sufficient statistics for modulation classification and obtain a generic formula for the error probability of a ML classifier. Our study of asymptotic performance shows that the ML classifier is capable of classifying any finite set of distinctive constellations with zero error rate when the number of available data symbols goes to infinity.

Digital Modulation Techniques

Abstract: Baseband modulation frequency shift keying phase shift keying minimum shift keying continuous phase modulation multi-H phase shift keying quadrature amplitude modulation other nonconstant envelope modulations multicarrier modulation spread spectrum modulation coded modulation applications in baseband data communications applications in wired telephony applications in wireless mobile communications applications in fixed terrestrial microwave links applications in satellite links.

Improved codes for space-time trellis-coded modulation

Abstract: Space-time coded modulation has been shown to efficiently use transmit diversity to increase spectral efficiency. We propose new trellis codes found through systematic code search. These codes achieve the theoretically maximal diversity gain and improved coding gain compared to known codes.

On the computation and reduction of the peak-to-average power ratio in multicarrier communications

Abstract: For any code C defined over an equal energy constellation, it is first shown that at any time instance, the problem of determining codewords of C with high peak-to-average power ratios (PAPR) in a multicarrier communication system is intimately related to the problem of minimum-distance decoding of C. Subsequently, a method is proposed for computing the PAPR by minimum-distance decoding of C at many points of time. Moreover an upper bound on the error between this computed value and the true one is derived. Analogous results are established for codes defined over arbitrary signal constellations. As an application of this computational method, an approach for reducing the PAPR of C proposed by Jones and Wilkinson (1996) is revisited. This approach is based on introducing a specific phase shift to each coordinate of all the codewords where phase shifts are independent of the codewords and known both to the transmitter and the receiver. We optimize the phase shifts offline by applying our method for computing the PAPR for the coding scenario proposed by the ETSI BRAN Standardization Committee. Reductions of order 4.5 dB can be freely obtained using the computed phase shifts. Examples are provided showing that most of the gain is preserved when the computed optimal phase shifts are rounded to quantenary phase-shift keying (PSK), 8-PSK, and 16-PSK type phase shifts.

Performance analysis of maximal ratio combining and comparison with optimum combining for mobile radio communications with cochannel interference

Abstract: The performance of maximal ratio combining for space diversity reception in digital cellular mobile radio systems is studied for communications in the presence of multiple cochannel interference (CCI) sources and is compared to optimum combining. The main contribution of the paper is that the analysis accounts for fading of the signal of interest (SOI) as well as the cochannel interference (CCI). The paper considers BPSK signalling in flat, quasi-static channels. Rayleigh or Rice fading is assumed for the SOI, while CCI is assumed subject to Rayleigh fading. Channels associated with interference sources are assumed independent and identically distributed. Using a multivariate statistical analysis approach and assuming equal-power interference sources, analytical expressions are derived for the density function of the array output signal-to-interference ratio (SIR), the outage probability, and the average probability of bit error with maximal ratio combining. Earlier results obtained for optimum combining and Rayleigh fading are extended to the case when the SOI is subject to Rice fading. A limited analysis of the equal gain combiner is also presented.

Reducing the peak-to-average power ratio of orthogonal frequency division multiplexing signal through bit or symbol interleaving

Abstract: An interleaver-based technique for improving the peak-to-average power ratio (PAP) of an orthogonal frequency division multiplexing signal is presented. For this technique, K-1 random interleavers are used to produce (K-1) permuted sequences from the same information sequence. The PAPs of the permuted sequences and the original information sequence are then computed using K oversampled fast Fourier transforms (OFFTs). The sequence with the lowest PAP is chosen for transmission. Results show that for 256 subcarriers and quadrature phase shift keying data symbols, even with K=2, the 0.1% PAP is reduced by 1.3 dB and with K=4 it is reduced by 2 dB. The 0.1% PAP can be reduced by 3 dB and the 0.01% PAP by 4 dB at a cost of 16 OFFTs and a data rate loss of <0.8% with K=16.

Monolithically integrated resonator microoptic gyro on silica planar lightwave circuit

Abstract: We report a novel configuration of resonator microoptic gyro (MOG), which is monolithically integrated on silica planar lightwave circuit (PLC) with countermeasures for noise factors. Optical ring-resonator gyros suffer mainly from polarization fluctuation induced noise and backscattering induced noise. We discuss eigenstate of polarization in the waveguide to clarify behavior of the former and propose a countermeasure with control of the waveguide birefringence. As for the latter, binary phase shift keying (B-PSK) with a special signal processing is proposed. Thermooptic (TO) phase modulation is the only one scheme to apply B-PSK in the silica waveguide, whose bandwidth is limited to /spl sim/1 KHz. To utilize the narrow bandwidth of the TO modulator effectively, we propose an electrical signal processing scheme and a modulation waveform to compensate the frequency response. By constructing an experimental setup, suppression of the backscattering induced noise is demonstrated, and the gyro output is observed with applying an equivalent rotation.

Iterative decoding for coded noncoherent MPSK communications over phase-noisy AWGN channel

Abstract: A family of interleaved systems for communicating over the additive white Gaussian noise (AWGN) channel with noisy or unknown phase is investigated Each system comprises convolutional code or turbo code, interleaver, binary phase shift keying or quaternary phase shift keying modulation and differential or similar encoding The receiver performs jointly and iteratively the decoding and the channel demodulation in the presence of unknown phase utilising an observation interval exceeding two symbols All systems exhibit good performance with various levels of phase noise The convolutional code, achieving bit error rate (BER) below 10/sup -3/ at bit energy over noise spectral density ratio (E/sub b//N/sub 0/) of 24 dB with no phase noise, outperforms the turbo code slightly over AWGN channels due to limited capability of the iterative algorithm in this setting The turbo code is superior in bursty channels, modelling for example a block erasures fading environment When the carrier phase is unknown but constant over an interval of ten symbols, the turbo coded system achieves BER lower than 10/sup -3/ at E/sub b//N/sub 0/ of 26 dB, that is 13 dB away from the capacity limit of this channel

Serial concatenated trellis coded modulation with rate-1 inner code

Abstract: We develop new, low complexity turbo codes suitable for bandwidth and power limited systems, for very low bit and word error rate requirements. Motivated by the structure of previously discovered low complexity codes such as repeat-accumulate (RA) codes with low density parity check matrix, we extend the structure to high-level modulation such as 8PSK, and 16QAM. The structure consists of a simple 4-state convolutional or short block code as an outer code, and a rate-1, 2 or 4-state inner code. Two design criteria are proposed: the maximum likelihood design criterion, for short to moderate block sizes, and an iterative decoding design criterion for very long block sizes.

Adaptive nonuniform phase-shift-key modulation for multimedia traffic in wireless networks

Abstract: The characteristics of mobile wireless communication channels fluctuate for many reasons, including movement of the radios, changes in path attenuation, and variations in interference. Several adaptive signaling techniques have been proposed for use in wideband code-division multiple-access (CDMA) systems including adaptive data rates, adaptive spreading code rates, discontinuous transmission, and multicode CDMA. We introduce adaptive signaling techniques that use nonuniform phase-shift-key (PSK) modulation. These techniques have several advantages for use in CDMA communications, and they support multimedia transmission by simultaneously delivering different types of traffic, each with its own required quality of service. The signaling methods that we propose deliver a basic message at a specified error rate and simultaneously deliver an additional message by exploiting any extra capability that is available. We show that by adapting the location of the points in a PSK constellation, the throughput can be maximized for the additional message while maintaining an acceptable error rate for the basic message. Responses to larger changes in channel quality are accomplished by adapting the PSK constellation size, signaling rate, and error-correcting code. Examples of adaptive signaling schemes that employ nonuniform PSK constellations are presented, including an application to a cellular CDMA system.

LMMSE detection for DS-CDMA systems in fading channels

Abstract: The linear minimum mean-squared-error (LMMSE) criterion can be used to obtain near-far resistant receivers in direct-sequence code-division multiple-access systems. The standard version of the LMMSE receiver (postcombining LMMSE) minimizes the mean-squared error between the filter output and the true transmitted data sequence. Since the detector depends on the channel coefficients of all users, it cannot be implemented adaptively in fading channels due to severe tracking problems. A modified criterion for deriving LMMSE receivers (precombining LMMSE) in fading channels is presented. The precombining LMMSE receiver is independent of the users' complex channel coefficients, and it effectively converts the time-varying Rayleigh fading channel to an equivalent fixed additive white Gaussian noise channel from the point of view of updating the detector. The performance of the LMMSE receivers in fading channels is studied via computer simulations and numerical analysis. The results show that the postcombining LMMSE receiver has potentially larger capacity, but it cannot be used in fast fading channels. The precombining LMMSE receiver has slightly worse capacity than the postcombining LMMSE receiver, but remarkably larger capacity than the conventional RAKE receiver at the signal-to-noise ratios of practical interest.

Multilevel coded modulation for unequal error protection and multistage decoding. II. Asymmetric constellations

Abstract: In this paper, theoretical upper bounds and computer simulation results on the error performance of multilevel block coded modulations for unequal error protection (UEP) and multistage decoding are presented. It is shown that nonstandard signal set partitionings and multistage decoding provide excellent UEP capabilities beyond those achievable with conventional coded modulation. The coding scheme is designed in such a way that the most important information bits have a lower error rate than other information bits. The large effective error coefficients, normally associated with standard mapping by set partitioning, are reduced by considering nonstandard partitionings of the underlying signal set. The bits-to-signal mappings induced by these partitionings allow the use of soft-decision decoding of binary block codes. Moreover, parallel operation of some of the staged decoders is possible, to achieve high data rate transmission, so that there is no error propagation between these decoders. Hybrid partitionings are also considered that trade off increased intraset distances in the last partition levels with larger effective error coefficients in the middle partition levels. The error performance of specific examples of multilevel codes over 8-PSK and 64-QAM signal sets are simulated and compared with theoretical upper bounds on the error performance.

Space-time coding and channel estimation scheme, arrangement and method

Abstract: The evolution of high rate data services within future wireless networks will call for new RF access technologies to enable substantial increases in overall system spectral efficiency at an acceptably low cost to the user. Space-Time Coding (STC) is an antenna array processing technology currently simulating considerable Interest across the wireless industry. The invention provides a space-time coding apparatus having an input, a trellis encoder, a modulator, a demultiplexer, and a set of signal outputs wherein the input is operable to receive a stream of data. This allows de-multiplexing to take place after coding and modulation has been performed. The trellis encoder comprises a convolutional encoder operable to sequentially group data to provide coded bits to provide QPSK symbols. By the selection of convolutional encoder rates and/or modulation alphabets STCs of any desired dimensionality may be produced including multi-dimensional codes.

A space-time model for frequency nonselective Rayleigh fading channels with applications to space-time modems

Abstract: This paper extends the traditional Clarke/Jakes (1968, 1974) model for a frequency flat fading process in a land mobile radio system to facilitate the examination of coherent space-time demodulation systems. The work develops a space-time correlation function using a ring of scatterers model around the mobile unit. The resulting correlation function permits the investigation of a variety of issues concerning base station configurations in space-time systems. The interrelationship of the fading process between the space and the time domain is explored. A detailed example regarding the effects of antenna separation in a receiver diversity system is considered. A set of design rules for interleaving depth and antenna separation in a space-time modem is presented and quantified.

Iterative source/channel-decoding using reversible variable length codes

Abstract: In this paper we describe a trellis representation of variable length coded data which is capable of being used for bit-level or symbol-level maximum a posteriori (MAP) decoding of variable length codes (VLC) A bit-level soft-input/soft-output module is derived and is applied in an iterative decoding structure consisting of an outer variable length code and an inner convolutional code Due to their inherent redundancy reversible variable length codes (RVLC) yield good results with this system We present simulation results in terms of symbol error rate performance when the data is transmitted over a fully interleaved Rayleigh fading channel using BPSK modulation As measure for the symbol error rate the Levenshtein distance is used which regards the self-synchronizing properties of variable length codes better than a simple symbol-by-symbol comparison

Bit error probability of M-ary quadrature amplitude modulation

Abstract: So far the general expression of bit error rate (BER) has not been derived for M-ary square quadrature amplitude modulation (QAM). In this paper, a generalized closed-form BER expression of M-ary square QAM with Gray code bit mapping is derived and analyzed in the presence of additive white Gaussian noise (AWGN) channel.

BER performance of OFDM-MDPSK system in frequency-selective Rician fading with diversity reception

Abstract: A closed form formula is derived for the bit error rate (BER) of orthogonal-frequency-division-multiplexing (OFDM) with M-ary differential-phase-shift-keying (MDPSK) systems in frequency-selective Rayleigh and Rician fading channels with diversity reception. New BER curves are obtained as a function of the rms delay spread of the diffused component for three different types of delay profiles: (1) one-sided exponential, (2) uniform and (3) double spike profiles. Both slow and fast fading conditions are considered. It is shown that the existence of a strong line-of-sight (LOS) component and the use of reception diversity can effectively improve transmission performance.

Comparison of DPSK and MSK bit error rates for K and Rayleigh-lognormal fading distributions

Abstract: The composite Rayleigh-lognormal distribution is mathematically intractable for the analytical evaluation of such a communication system performance metric as bit error rate. The composite K distribution closely approximates the Rayleigh-lognormal and is potentially useful for analytical manipulations. In this contribution we derive the bit error rates of differential phase-shift keying (DPSK) and minimum shift keying (MSK), in manageable closed forms, for the K distribution model of multipath fading and shadow fading, and show, numerically, the close agreement between these results and those based on the Rayleigh-lognormal distribution.

A frequency and symbol synchronization system for OFDM signals: architecture and simulation results

Abstract: A data-aided frequency and symbol synchronization scheme for M-QAM OFDM signals is suggested. At first, the phase discriminator (PD) and frequency discriminator (FD) for, respectively, the symbol and frequency synchronization loop are described. Second, the transfer function and design parameters of the loop filters are provided. The acquisition and tracking performance of the synchronization system are evaluated using simulation for a 4-PSK signal constellation. The cases of additive white Gaussian noise (AWGN) and frequency and time selective multipath Rayleigh channels are separately tested.

Blind channel and carrier frequency offset estimation using periodic modulation precoders

Abstract: Previous results have shown that blind channel estimators, which are resilient to the location of channel zeros, color of additive stationary noise, and channel order overestimation errors, can be developed for communication systems equipped with transmitter-induced cyclostationarity precoders. The present paper extends these blind estimation approaches to the more general problem of estimating the unknown intersymbol interference (ISI) and carrier frequency offset/Doppler effects using such precoders. An all-digital open-loop carrier frequency offset estimator is developed, and its asymptotic (large sample) performance is analyzed and compared to the Cramer-Rao bound (CRB). A subspace-based channel identification approach is proposed for estimating, in closed-form, the unknown channel, regardless of the channel spectral nulls. It is shown that compensating for the carrier frequency offset introduces no penalty in the asymptotic performance of the subspace channel estimator. Simulations are presented to corroborate the performance of the proposed algorithms.

Tight error bounds for nonuniform signaling over AWGN channels

Abstract: We consider a Bonferroni-type lower bound due to Kounias (1968) on the probability of a finite union. The bound is expressed in terms of only the individual and pairwise event probabilities; however, it suffers from requiring an exponentially complex search for its direct implementation. We address this problem by presenting a practical algorithm for its evaluation. This bound is applied together with two other bounds, a recent lower bound (the KAT bound) and a greedy algorithm implementation of an upper bound due to Hunter (1976), to examine the symbol error (P/sub a/) and bit error (P/sub b/) probabilities of an uncoded communication system used in conjunction with M-ary phase-shift keying (PSK)/quadrature amplitude (QAM) (PSK/QAM) modulations and maximum a posteriori (MAP) decoding over additive white Gaussian noise (AWGN) channels. It is shown that the bounds-which can be efficiently computed-provide an excellent estimate of the error probabilities over the entire range of the signal-to-noise ratio (SNR) E/sub b//N/sub 0/. The new algorithmic bound and the greedy bound are particularly impressive as they agree with the simulation results even during very severe channel conditions.

Performance of antenna array systems with optimum combining in a Rayleigh fading environment

Abstract: The effect of cochannel interference on the performance of digital mobile radio systems in a Rayleigh fading environment is studied. The average bit error rate (BER) of an antenna array system with an optimum combining scheme that maximizes the output signal-to-interference-plus-noise ratio (SINR) is analyzed. BER expressions which are easy to evaluate numerically are derived for coherent binary phase shift keying (BPSK) schemes in an environment with cochannel interference and noise.

On the performance of iterative noncoherent detection of coded M-PSK signals

Abstract: Differential encoding is often used in conjunction with noncoherent demodulation to overcome carrier phase synchronization problems in communication systems employing M-ary phase-shift keying (M-PSK) It is generally acknowledged that differential encoding leads to a degradation in performance over absolutely encoded M-PSK systems with perfect carrier synchronization In this paper, we show that when differential encoding is combined with convolutional encoding and interleaving, this degradation does not necessarily occur We propose a novel noncoherent receiver for differentially encoded M-PSK signals that is capable of significantly outperforming optimal coherent receivers for absolutely encoded M-PSK using the same convolutional code This receiver uses an iterative decoding technique and is based on a multiple differential detector structure to overcome the effect of the carrier phase error In addition, to better illustrate the benefits of the powerful combination of convolutional encoding, interleaving, and differential encoding, we also present an iterative coherent receiver for differentially encoded M-PSK

A comparison of detection algorithms including BLAST for wireless communication using multiple antennas

Abstract: Detection algorithms for single user wireless communication using multiple antennas at both the transmitter and receiver in a Rayleigh (flat) fading environment are compared. The system includes N transmitting antennas, M receiving antennas (N/spl les/M) and repetition coding at the transmitter (delay diversity). The linear decorrelating (LD) and minimum mean squared error (MMSE) detectors are compared with their D-BLAST and V-BLAST versions using bit error ratio versus signal-to-noise ratio simulation. For BPSK, the MMSE detector and its BLAST versions perform best and yield almost indistinguishable BER curves. The LD detector performs worst. For fixed N, as M increases, all the BER curves converge. The effect of error propagation in the BLAST schemes is shown to be non-negligible.

Digital precompensation of imperfections in quadrature modulators

Abstract: Residual carrier, balance, and quadrature error imperfections that are normally present in phase/quadrature modulators limit the use of direct modulation techniques in some applications. The classical precompensation techniques are revised and an adaptive solution proposed that improves performance by some order of magnitude.

Exact bit-error probability for optimum combining with a Rayleigh fading Gaussian cochannel interferer

Abstract: We derive expressions for the exact bit-error probability (BEP) for the detection of coherent binary phase-shift keying signals of the optimum combiner employing space diversity when both the desired signal and a Gaussian cochannel interferer are subject to flat Rayleigh fading. Two different methods are employed to reach two different, but numerically identical, expressions. With the direct method, the conditional BEP is averaged over the fading of both signal and interference, With the moment generating function based method, expressions are derived from an alternative representation of the Gaussian Q-function.

BPSK and QPSK modulation classification with unknown signal level

Abstract: Modulation classification is an intermediate step between signal detection and data demodulation. It is attempted for a variety of reasons including reconnaissance, surveillance and other intelligence gathering activities. In practice, the level of a received signal is not known and not constant because of many different reasons, such as fading. In such a case, the classifier needs to estimate the signal level first and then take it into account in the classification algorithm to increase the accuracy of classification. In this paper a modulation classification algorithm with unknown signal level has been developed and tested on binary phase shift keying (BPSK) signal and quadrature phase shift keying (QPSK) signal embedded in additive white Gaussian noise (AWGN). The algorithm applies the generalized likelihood ratio test. The receiver first estimates the unknown signal level using the maximum likelihood method. The estimated signal level is then being used in the likelihood ratio test for classification. Simulations show that the proposed classifier has high accuracy and is superior to the classifier without taking into account the variations in signal level. The classification accuracy increases as the observed symbol number or the variance of the signal level increases.

Effect of mobile velocity on communications in fading channels

Abstract: In a fading channel, it is well known that the rate of channel variation is dependent on the velocity of the mobile. Consequently, depending on the channel correlation, successive symbols transmitted over the channel can suffer from very similar or possibly very different fading conditions. In this paper, we present an analytical model to evaluate the effect of mobile velocity on the performance of a communication system operating in a multipath fading channel. To incorporate the effect of velocity, a Markov process is used which captures the correlated nature of the channel. An error recursion is then developed which considers the effect of closed-loop power control, channel coding, and finite interleaving. In the numerical analysis, we use the analytical model to investigate the tradeoffs when these various schemes are used. We demonstrate how the performance of these different schemes is sensitive to mobile velocity.

Reverse link correlation filter in wireless communication systems

Abstract: A single, common correlation filter (CF) core is provided in a wireless system using CDMA. A plurality of channels with different data rates are provided in the wireless system. The channels provided in the wireless system include the access channel, the maintenance channel, and the traffic channel in which information (e.g., pilot or data symbols or both) is transmitted at the tier 1, tier 2 and tier 3 rates. The data rate for transmitting the information is programmable by digital signal processor (DSP). A user-unique code, such as a PN code, is applied to the information being transmitted in the channels of the wireless system. The information is QPSK modulated and transmitted in any one of the channels at any data rate. The transmitted information is correlated at the smallest data rate (i.e., the tier 1 rate) in the correlation filter (CF) of the wireless system by time multiplexing delayed versions of the PN code to the correlation filter core. The correlated information is then demultiplexed and pilot aided QPSK demodulated. The demodulated information is summed at the proper integer multiple of the tier 1 rate to achieve the tier 2 and tier 3 rates. The three strongest multipaths (in terms of the received power) are selected in a window or time period for optimal information recovery. Furthermore, three outputs from the demodulated information can be provided and combined for temporal diversity. Spatial diversity is achieved by providing a plurality of antennas at each receiver and a single, common correlation filter at each of the plurality of antennas of the receivers in the wireless system.