COMM-2.1

Method of Optimal Directions for Frame Design
Kjersti Engan, Sven O Aase, John H Husøy (Høgskolen i Stavanger)

A frame design technique for use with vector selection algorithms, for example Matching Pursuits (MP), is presented. The design algorithm is iterative and requires a training set of signal vectors. The algorithm, called Method of Optimal Directions (MOD), is an improvement of the algorithm presented in [1]. The MOD is applied to speech and electrocardiogram (ECG) signals, and the designed frames are tested on signals outside the training sets. Experiments demonstrate that the approximation capabilities, in terms of mean squared error (MSE), of the optimized frames are significantly better than those obtained using frames designed by the algorithm in [1]. Experiments show typical reduction in MSE by 20-50%.

COMM-2.2

Performance of Ordered Statistics Decoding for Robust Video Transmission on the WSSUS Channel
Wu-hsiang J Chen, Jenq-Neng Hwang (University of Washington)

This paper investigates the performance of ordered statistics decoding of linear block codes with binary differential phase-shift-keying (2DPSK) transmission on the wide-sense-stationary uncorrelated-scattering (WSSUS) Rayleigh fading channel. For typical mobile speed 60 mph, tropospheric scatter radio communication at carrier frequency 900 MHz and very low bit rate video communication at transmission speed 32 kbit/s, the channel is modeled as a frequency non-selective, slow fading environment without inter-symbol interference (ISI). At bit error rate (BER) 10^(-5), 34.5 dB and 38 dB gains compared to uncoded 2DPSK are obtained for the decoding of the (24, 12, 8) extended Golay code and the (128, 64, 22) extended BCH code with sufficient degree of interleaving.

COMM-2.3

Joint Source-Channel Decoding for Variable-Length Encoded Data by Exact and Approximate MAP Sequence Estimation
MoonSeo Park, David J Miller (The Pennsylvania State University)

Joint source-channel decoding based on residual source redundancy is an effective paradigm for error-resilient data compression. While previous work only considered fixed rate systems, the extension of these techniques for variable-length encoded data was recently independently proposed by the authors [6],[7] and by Demir and Sayood [1]. In this paper, we describe and compare the performance of a computationally complex exact maximum a posteriori (MAP) decoder [6], [7], its efficient approximation [6], [7], an alternative approximate MAP decoder [1], and an improved version of this decoder suggested here. Moreover, we evaluate several source and channel coding configurations. Our results show that the approximate MAP technique from [6], [7] outperforms other approximate methods and provides substantial error protection to variable-length encoded data.

COMM-2.4

Gaussian modeling for channel errors diagnosis in image transmission
Fabrice Labeau, Luc Vandendorpe, Benoit Macq (UCL Communications and Remote Sensing Laboratory)

In this paper we propose an original study of the reconstruction of subband compressed images impaired by channel transmission errors. The method proceeds in two steps : first a detection scheme is applied to determine which coefficients of the subband decomposition have been affected by transmission, and then an estimation step tries to evaluate the erroneous coefficients. In our model, subband coefficients are considered to be drawn from jointly gaussian random processes. Based on this assumption, conditional statistics can be computed which enable to test the likelihood of a given set of received coefficients with respect to the rest of the image. The detection and estimation processes are derived from these statistics. The method is validated through simulation and visual results are provided. The drawbacks of the method are outlined and explained through the discrepancies between the gaussian assumption and real world images, namely around image edges.

COMM-2.5

The application of Walsh Tranform for forward error correction
Farokh Marvasti, Man Hung Ng, Mohammad Reza Nakhai (King's College London)

In this paper, we present a novel class of forward error correcting codes constructed using the discrete Walsh transform. They are a class of double-error correcting codes defined on the field of real numbers. An iterative decoding algorithm for Walsh transform codes is developed and implemented. The error correcting performance of Walsh transform codes over an AWGN channel is evaluated. Selected Walsh transform code parameters are compared to those of the well-known BCH codes.

COMM-2.6

Modulating Waveforms for OFDM
Zoran D Cvetkovic (AT&T Labs - Research)

Orthogonal frequency division multiplexing (OFDM) is a popular transmission technique that is employed in applications such as Digital Audio Broadcasting, Asymmetric Digital Subscriber Line and wireless LAN. In this work we consider design of modulating waveforms for OFDM in the presence of delay spread and system impairments such as frequency offset and jitter. We give a complete parameterization of OFDM modulating waveforms. Increasing robustness of OFDM to frequency offsets requires using long modulating waveforms. To make implementation of OFDM systems with long modulating waveforms feasible we propose fast implementation algorithms. Some preliminary modulating waveform design examples are presented. The presented waveforms demonstrate that robustness of OFDM systems to impairments can be improved by allowing certain degradation of unnecessarily good performance of the state of the art OFDM systems in ideal operating conditions.

COMM-2.7

Efficient Method for Carrier Offset Correction in OFDM System
Hongya Ge (New Jersey Institute of Technology, Newark, NJ 07102, USA.), Kun Wang (New Jersey Institute of Technology, Newark, NJ 07102)

In this work, we present a simple approach to estimate and correct the carrier offset in an orthogonal frequency division multiplexing(OFDM) system. The approach leads to a computationally and statistically efficient estimator for the carrier offset. Computer simulations verify that the estimation accuracy is comparable to the Cramer-Rao bound(CRB). We demonstrated that by incorporating the estimated carrier offset(obtained using reasonable frames of OFDM data) in the demodulation process, the bit-error-rate(BER) can approach that of the ideal OFDM system with no carrier offset.

COMM-2.8

Classification of Modulation Modes Using Time-Frequency Methods
Helmut Ketterer, Friedrich Jondral (Universitat Karlsruhe, Institut fur Nachrichtentechnik), Antonio H Costa (University of Massachusetts Dartmouth, Department of Electrical and Computer Engineering)

This paper proposes a new technique for feature extraction of modulated signals which is based on a pattern recognition approach. The new algorithm uses the cross Margenau-Hill distribution, autoregressive modeling, and amplitude variations to detect phase shifts, frequency shifts, and amplitude shifts, respectively. Our method is capable of classifying PSK2, PSK4, PSK8, PSK16, FSK2, FSK4, QAM8 and OOK signals. Unlike most of the existing decision- theoretic approaches, no explicit a priori information is required by our algorithm. Consequently, the method is suitable for application in a general non- cooperative environment. Furthermore, our approach is computationally inexpensive. Simulation results on both synthetic and "real world" short-wave signals show that our approach is robust against noise up to a signal-to- noise ratio (SNR) of approximately 10 dB. A success rate greater than 94 percent is obtained.

COMM-2.9

Pulse Train Deinterleaving: Algorithms and Cost Criteria
Keith S.M. Lee, Michael J. Rowe, Vikram Krishnamurthy (University of Melbourne)

Consider the problem where pulse trains transmitted from a known number of sources are received on a single communications channel. These pulses are corrupted with noise. The deinterleaving problem is to determine which source contributed which pulse and the periods and phases of each source. This paper explores the performance of a number of deinterleaving algorithms. We propose an alternative to the existing forward dynamic programming (FDP) technique: simulated annealing (SA). It can use either the same cost function as for FDP, or an L1 or L2 norm output error cost function. We also investigate modelling the noise by heavy-tailed distributions, in addition to white Gaussian noise (WGN).

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Last Update: February 4, 1999 Ingo Höntsch