Optimal Demodulation Research Articles

Bit-Interleaved Coded Modulation With Iterative Decoding in Impulsive Noise

Power-line communications (PLC) suffers performance degradation due mainly to impulsive noise interference generated by electrical appliances. This paper considers the application of bit-interleaved coded modulation with iterative decoding (BICM-ID) in Class-A impulsive noise environment to improve the spectral efficiency and error performance of PLC. In particular, the optimal soft-output demodulator and its suboptimal version are presented for an additive Class-A noise channel so that iterative demodulation and decoding can be performed at the receiver. The effect of signal mapping on the error performance of BICM-ID systems in impulsive noise is investigated, with both computer simulation and a tight error bound on the asymptotic performance. Extrinsic information transfer chart analysis is carried out to illustrate the convergence properties of different mappings. The superior performance of BICM-ID compared to the orthogonal frequency-division multiplex technique is also clearly demonstrated

Iterative demodulation/decoding methods based on Gaussian approximations for lattice based space-time coded systems

In this letter, we study iterative demodulation and decoding methods for lattice based space-time coded systems concatenated with convolutional codes. We first apply the optimal MAP demodulation and the suboptimal linear MMSE methods to lattice based space-time demodulation and decoding. We then propose two other methods based on the idea of soft interference cancellation and in one method vector Gaussian approximation is used and in the other method scalar Gaussian approximation is used. We also present the EXIT chart analyses for the performance analyses for these iterative methods. Both theoretical and simulation results show that the performance of the vector Gaussian approximation method is the same as that of the linear MMSE method but in some cases the vector Gaussian approximation method has lower complexity. The complexity of the scalar Gaussian approximation method is the lowest among these different methods and grows linearly with the transmission rate while it still has an acceptable performance. Full diversity and full rate lattice based space-time coding is compared with the BLAST scheme and simulations show that the former has a better performance than the later even with the proposed suboptimal iterative demodulation and decoding methods.

디지털 가전채널 변동특성을 반영한 최적 변복조 시스템에 관한 연구

전디지털 가전을 위한 전력선통신에서의 전력선은 통신기능과는 별도로 부하와 연계된 전력전송이라는 본래의 이용 목적이 존재하므로 일반 전화선이나 케이블선과 같은 전용 통신선로에 비하여 전력 부하의 변동특성에 따른 전송로상의 통신에 대한 잡음 및 간섭특성이 수시로 발생하는 특성을 나타내고 있다.BR 따라서, 본 논문에서는 이러한 디지털 가전용 전력선통신 기반의 부하변동특성을 실측데이터를 기반으로 모델링 하여 각각의 부하변동특성에 따른 복수개의 변ㆍ복조 방식 성능을 평가하여, 부하변동별 최적의 변ㆍ복조 방식을 도출하였다.BR 본 논문에서 제시한 부하변동 특성에 따른 복수개의 변ㆍ복조 방식 성능을 비교 분석하기 위하여, 부하변동특성에 따른 다양한 잡음 환경 하에서의 컴퓨터 시뮬레이션을 통해 정량적으로 분석하고, 하드웨어 구현 등을 통해 제안하는 최적의 변ㆍ복조 방식에 대한 전력선통신 시스템의 유용성을 확인하였다.

BER sensitivity to mistiming in ultra-wideband impulse radios - part II: fading channels

We investigate timing tolerances of ultra-wideband (UWB) impulse radios. We quantify the bit-error rate (BER) sensitivity to epoch timing offset under different operating conditions, including frequency-flat fading channels, dense multipath fading channels, multiple access with time hopping, and various receiver types including sliding correlators and RAKE combiners. For a general correlation-based detector, we derived in Part I unifying expressions for the decision statistics as well as BER formulas under mistiming, given fixed channel realizations. In Part II, we provide a systematic approach to BER analysis under mistiming for fading channels. The BER is expressed in terms of the receiver's energy capture capability, which we quantify under various radio operating conditions. We also develop the optimal demodulator in the presence of timing offset and show a proper design of the correlation-template that is robust to mistiming. Through analyses and simulations, we illustrate that the reception quality of a UWB impulse radio is highly sensitive to both timing acquisition and tracking errors.

On space-frequency coding using cyclic delay diversity for OFDM-based transmission systems

We present a space-frequency coding scheme using cyclic delay diversity (CDD) for an orthogonal frequency division multiplexing (OFDM)-based transmission system. CDD is a simple multiple transmit antenna approach for increasing the frequency selectivity of the channel seen at a single antenna receiver. This is due to the insertion of virtual echoes caused by antenna specific cyclic delays in the time domain at the transmitter. On each antenna a shifted version of the signal is sent, with these shifts being performed in the frequency domain. This allows the receiver to apply optimum demodulation, and thus exploit the diversity introduced by CDD. We optimize the selection of the time domain cyclic delays in the CDD so as to get full spatial diversity with the proposed space-frequency codes with CDD (SFC-CDDs) scheme. Moreover, we show simulation results for SFC-CDD, which confirm theoretical results with respect to the achieved spatial diversity, and present a comparison with the well-known Alamouti scheme implemented as SFC.

Using topography statistics to help phase unwrapping

Conventional techniques approach phase unwrapping (PU) as an optimisation problem, where figures of merit like the total branch-cut length, the number of cuts, etc. are to be minimised. They disregard the properties of the field to be unwrapped: the topography, i.e. the DEM, projected in the SAR reference. The purpose of the paper is to fill this gap by providing statistics of the ‘fringe maps’. The Woodward theorem is exploited to link the interferogram power spectrum density (PSD) with the probability density function (PDF) of the phase gradient that would result in a likely topography. A parametric model of the expected, unwrapped PG PDF is then derived by exploiting the fractal properties of topography. Its parameters can be accurately estimated given the wrapped PG. This model provides useful statistical information for phase unwrapping. It is then possible, for example, to estimate the number of residuals, to find the best azimuth presumming factor and to find the optimal interferogram range demodulation. Finally, the author exploits the second-order statistics of the PG field (as a fractal) to derive a suitable approximation for the expected length of the branch cuts.

Error performance of mismatched receivers for linear-coded modulation

Optimum demodulation of intersymbol interference may be performed using maximum-likelihood sequence estimation receivers. Standard performance analysis of these receivers assume that the receiver has perfect knowledge of the channel. We assume instead a mismatched receiver that uses an imperfect estimate of the channel to decode the information sequence. A free-distance expression for a mismatched ML receiver is derived and applied to the case of linear-coded modulation. A truncated union bound approximation accurately predicts the error probability.

Optimum Semicodeless Carrier-Phase Tracking of L2

ABSTRACT: This paper discusses the performance of various codeless and semicodeless techniques used to obtain the carrier phase of the GPS L2 signal without knowledge of the encrypted Anti-Spoofing (AS) Y-code. Four known techniques have been published in the past: squaring, cross-correlation, P-code aided L2 squaring, and Z-tracking. All these techniques perform significantly worse than an ideal phase lock loop. Five new techniques are presented in this paper: (1) code-aided L2 Costas loop with W-bit integrate and dump arm filtering, (2) P-code aided L1, L2 cross-correlation, (3) soft decision Z-tracking, (4) optimum L2 demodulation motivated by maximum a posteriori (MAP) estimation theory, and (5) linear approximation of the MAP approach. The first three are modifications of existing techniques, with improved performance. Techniques 4 and 5 are optimum and near-optimum techniques based on statistical estimation theory, and provide the best performance in squaring loss and mean time to cycle slip.

Optimum modulation and demodulation matrices for solar polarimetry

Both temporal and/or spatial modulation are mandatory in current solar polarimetry [Appl. Opt. 24, 3893 (1985); 26, 3838 (1987)]. The modulating and demodulating processes are mathematically described by matrices O and D, respectively, on whose structure the accuracy of Stokes parameter measurements depend. We demonstrate, based on the definition of polarimetric efficiency [Instituto de Astrofísica de Canarias Internal Report (1994); ASP Conf. Ser. 184, 3 (1999)], that the maximum efficiencies of an ideal polarimeter are unity for Stokes I and for (Q(2) + U(2) + V(2))(1/2) and that this occurs if and only if O(T)O is diagonal; given a general (possibly nonideal) modulation matrix O, the optimum demodulation matrix turns out to be D = (O(T)O)(-1)O(T); and the maximum efficiencies in the nonideal case are given by the rms value of the column elements of matrix O and are reached by modulation matrices such that O(T)O is diagonal. From these analytical results we distill two recipes useful in the practical design of polarimeters. Their usefulness is illustrated by discussing cases of currently available solar polarimeters. Although specifically devoted to solar polarimetry, the results here may be applied in practically all other branches of science for which polarimetric measurements are needed.

SNR enhancement of intensity noise-limited FOGs

The signal-to-noise ratio (SNR) of fiber-optic gyroscopes (FOGs) is directly impacted by the optical power coupled to the interferometric circuit. The optical intensity noise produced by the optical broadband source becomes the major component of the total noise at the output when the optical power reaching the detector is more than a few tens of microwatts. This work shows the implementation of a signal processing scheme capable of promoting reduction of the source intensity noise around the proper frequency of birefringent FOG, where the optimum signal demodulation takes place, yielding a better SNR. The total SNR has been enhanced 6.6 dB by means of a 20.4 dB reduction in the noise component associated only with the source intensity noise.

Block demodulation of MDPSK with low complexity

A new block demodulation (NBD) of MDPSK with low complexity is proposed. The error patterns of conventional differential detection (CDD) are analysed, and the decisions of CDD and the knowledge of error patterns are employed to reduce the complexity of optimum block demodulation (OBD). The complexity of NBD increases in a roughly linear fashion with block length N, while OBD increases exponentially with N. Simulations show almost the same performance.

Optimum demodulation of PN spread spectrum signalsin the presence of narrowband interference

The optimum demodulation code for pseudo-noise (PN) binary phase shift keying systems in the presence of a strong sinusoidal interference is shown to be the sum of the PN code and a sinusoidal sequence. The new demodulation method has greatly improved performance compared to PN code demodulation.

Optimized three-dimensional recovery from two-dimensional images by means of sine wave structured light illumination

A common problem in manufacturing design is the accurate rendering of a 3-D object into a digitized 3-D representation. Such a rendering can be used to duplicate or modify existing objects as well as perform quality control and object recognition in automated manufacturing operations. A structured light technique that uses a sinusoidal illumination pattern to retrieve 3-D information is presented. This technique requires only one image of a surface area to process the topology and can be accomplished with incoherent light. The sine section technique projects a sinusoidal pattern onto an object and recovers the local slopes (first order), which are then combined to reconstruct the surface topology. Surface variations act to create a wideband frequency modulation (zero to infinite frequency), so an optimum frequency demodulation technique is developed to yield average slopes in local regions of the illuminated area. A reconstruction algorithm is introduced that uses these slopes with minimum mean square error. The performance of this technique appears to be very robust and insensitive to intensity variations. Results are presented for recovery of synthesized surfaces corrupted in altitude by additive colored Gaussian spatial noise. The colored noise is generated with a fractal filter to best emulate real surface topologies.

Sequential amplitude estimation in multiuser communications

Considers the problem of multiuser amplitude estimation, i.e., the problem of estimating the amplitudes of several digital communications signals superimposed in the same channel. This problem is of importance in communications environments such as spread-spectrum radio networks, in which nonorthogonal multiplexing is used. Multiuser amplitude estimation is a critical prerequisite to the optimum demodulation of such signals using, for example, Verdu's algorithm. In the present paper, a sequential detection-estimation approach is applied to this problem, and several estimation paradigms, including the method of moments and likelihood-based estimators, are considered. The consistency, asymptotic variance, and complexity of these estimators are examined. A new method of constructing a recursive consistent and asymptotically efficient estimation algorithm out of a consistent estimator sequence is also suggested and is applied to the current setup. It is seen that detector-estimators that use these estimators in Verdu's algorithm result, asymptotically, in (known-amplitude) optimum error probabilities with little relative increase in complexity per demodulated bit. >

Dual-signal receiver structures for simultaneous reception of two BPSK modulated co-channel signals using signal cancellation

In this paper a dual-signal receiver concept is proposed for simultaneous reception of two narrowband Binary Phase Shift Keying (BPSK) modulated co-channel signals, e.g. two desired signals of different strength. The principle of the proposed receiver concept is based on signal separation and cancellation, by decorrelation of the large signal using the estimated data, followed by demodulation of the small signal. A possible implementation of the receiver concept is presented in detail. The Bit Error Rate (BER) for both signals is derived and numerical and simulation results are presented for two receiver structures with different second demodulator: (1) the coherent BPSK demodulator; (ii) the differentially coherent (DPSK) demodulator. The channel is assumed to be an Additive White Gaussian Noise (AWGN) channel without fading. Comparison of the BER performance of the small signal to the optimum result when only AWGN is present, shows that nearly optimum demodulation of the small signal is possible when the signal strength difference is not too small.

Carrier Phase Estimation and Phase Jitter Compensation for Data Modems

This review covers some aspects of communicating digital signals from one place to another. Some basics of digital signalling and the effect of phase distortion introduced by the medium is considered. Optimum and/or suboptimum receivers for digitally modulated and phase corrupted carrier have been studied. A review of phase locked loop and carrier recovery techniques for optimal demodulation has been presented. Performance analysis of digital modulation schemes has been attempted.

Optimum soft decision demodulation for ISI channels

Two different methods of soft-decision demodulation for channels with finite intersymbol interference (ISI) in the presence of additive white Gaussian noise (AWGN) are analyzed. In both schemes, the cutoff rate R/sub 0/ of the discrete channel created by the demodulator output quantization is chosen as the design criterion. Expressions for the optimal thresholds of the quantizer associated with the demodulation of binary signals are derived. Results for the channel with memory equal to one symbol duration are presented. As a special case, the (1-D) channel with soft decision demodulation is analyzed. Closed-form solutions show that a 4-b quantizer improves performance substantially in this case. >

Influence of if narrow‐band filtering on bit error rates in coherent optical heterodyne CPFSK receiver using variable delay demodulation

AbstractIn this article we discuss a coherent optical heterodyne CPFSK receiver using optimum variable delay demodulation considering the effect of narrow‐band IF filtering or intersymbol interference (ISI) caused by it. First we investigate the error probability at the normalized bandwidth of IF filter BT = 1 for a Gaussian IF filter. Numerical results show that the impact of narrow‐band IF filtering increases with an increase in normalized IF spectral linewidth ΔvT and a decrease in modulation index h. Second, in order to decrease the impact of ISI, the optimum BT values are determined, which can minimize the error probability for given SNR. If a Gaussian IF filter is used, the optimal BT values are 1.3 for ΔvT = 0.25%, 1.4 for ΔvT = 0.5% at h = 0.5, 1.2 for ΔvT = 0.25%, 1.4 for ΔvT = 0.5% at h = 0.7, and 1.2 for all ΔvT ≤ 0.5% at h = 1. Finally, the performance of an optimal receiver employing optimum Gaussian IF filter is studied. We know that h = 1 is optimum and ΔvT ≤ 0.5% is necessary for 1‐dB EB/N0 penalty per bit at BER of 10−9. © 1992 John Wiley & Sons, Inc.

A Bayesian maximum-likelihood sequence estimation algorithm for a priori unknown channels and symbol timing

It is shown that the optimum demodulator for the case of an a priori unknown channel and symbol timing can be approximated using a modified Viterbi algorithm (VA), in which the branch metrics are obtained from the conditional innovations of a bank of extended Kalman filters (EKFs). Each EKF computes channel and timing estimates conditioned on one of the survivor sequences in the trellis. It is also shown that the minimum-variance channel and timing estimates can be approximated by a sum of conditional EKF estimates, weighted by the VA metrics. Simulated bit error rate (BER) results and averaged-squared channel/timing error trajectories are presented, with estimation errors compared to the Cramer-Rao lower bound. The BER performance of the modified VA is also shown to be superior to that obtained using a decision-directed channel/timing estimation algorithm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A parallel systems approach to universal receivers

The problem of communication over a channel with unknown characteristics is addressed. The true channel is from a known set of channels, but the transmitter and receiver do not know which of these channels is actually in effect. The goal of a universal receiver is to provide nearly optimal demodulation regardless of the channel that is actually in effect. A parallel receiver implementation is proposed for a universal scheme to cope with such uncertainty. The parallel system consists of a finite number of receivers with the property that, for each channel in the set, the performance of at least one of the receivers will be within a specified performance range. Data verification is accomplished by an appropriate coding system. Sufficient conditions for the existence of such a universal receiver for a prescribed set of channels are established, procedures are outlined for the receiver design, and an example is given to illustrate the applicability of the theory. For M-ary signaling it is shown that, from an information-theoretic viewpoint, the data verification can be achieved at no extra cost by use of the intrinsic side information that is provided by an appropriate coding scheme that also provides error correction.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>