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Abstract - COMM8 |
 |
COMM8.1 |
Pilot Symbol Assisted Diversity Reception for a Fading Channel S. Bulumulla, S. Kassam, S. Venkatesh (University of Pennsylvania, USA) Pilot symbol assisted modulation is a promising scheme to mitigate the effect of fading in a wireless channel. Analytical results for the performance of this scheme are available. Although the use of diversity is known to improve the performance of receivers used in fading channels, pilot symbol assisted diversity reception has not been studied. In this paper, we derive an exact probability of error expression for such a receiver as a function of the channel estimation error variance and the number of diversity channels. An upper bound for the probability of error, which illustrates the advantage of using diversity, is also obtained. A numerical example is provided. |
| COMM8.2 |
Estimation of FM Modulation of Multi-Component Signals from the Fourier Phase D. Nelson (US Department of Defense, USA) Spectral phase is a quantity which is normally discarded in analyzing signals. In this paper, the concept of a complex time-frequency representation is presented. In this representation, the rows are narrow bandpass filtered representations of the original signal, and the columns are broadband Fourier spectra. Methods are developed which exploit the spectral phase of the surface to recover the FM modulating functions of an FM modulated tone and an FM modulated multi-component harmonic signal. |
| COMM8.3 |
Conditional Maximum Likelihood Frequency Estimation for Offset Modulations J. Riba, G. Vázquez, S. Calvo (UPC, Spain) The use of spectrally efficient continuous phase modulations for mobile communications may lead to a serious performance degradation of the classical frequency error detectors (FEDs) due to the presence of self-noise. This contribution presents a new statistically efficient frequency estimation algorithm for staggered modulations. The cancellation of the self-noise is accomplished by the use of the Conditional ML principle, well known in the context of array processing, as an alternative to the Unconditional ML, typically applied in the communications field. The paper also provides a new Cramer Rao Bound (CRB) which is more accurate than the so-called Modified CRB (MCRB) extensively applied to synchronization problems. |
| COMM8.4 |
A Signal Processing Approach for Effective Reduction of Timing Jitter due to the Acoustic Effect T. Adali, B. Wang, A. Pilipetski, C. Menyuk (University of Maryland, Baltimore, USA) We introduce a signal processing approach to compensate for the timing jitter produced by the acoustic effect in soliton communications. The other main sources of timing jitter, the Gordon-Haus effect and the polarization effect, are inherently stochastic. By contrast, the acoustic effect is deterministic and becomes the dominant source of bit error rates in standard soliton systems when the bit rates are more than 10 Gbits.s and the transmission distance is more than several thousand kilometers. We exploit the deterministic nature of the acoustic effect to introduce a scheme that predicts the amount of timing jitter as a function of the previous transmitted bits and uses the information to adjust the sampling period of the received soliton pulses. We demonstrate successful application of the scheme by simulations and discuss implementation issues. |
| COMM8.5 |
Cost-Efficient Approximation of Linear Systems with Repeated and Multi-channel Filtering Configurations A. Kutay (Bilkent University, Turkey); F. Erden (Tampere University of Technology, Finland); H. Ozaktas, O. Arikan, C. Candan, O. Guleryuz (Bilkent University, Turkey) It is possible to obtain either exact realizations or useful approximations of linear systems or matrix-vector products arising in many different applications, by synthesizing them in the form of repeated or multi-channel filtering operations in fractional Fourier domains, resulting in much more efficient implementations with acceptable decreases in accuracy. By varying the number and configuration of filter blocks, which may take the form of arbitrary flow graphs, it is possible to trade off between accuracy and efficiency in the desired manner. The proposed scheme constitutes a systematic way of exploiting the information inherent in the regularity or structure of a given linear system or matrix, even when that structure is not readily apparent. |
| COMM8.6 |
QoS Considerations for DMT-based ADSL and VDSL Systems M. Colin (IEMN/OAE, France); C. Modlin (Amati Communications Corporation, USA); M. Gharbi, M. Gazalet (IEMN/OAE, France) Thanks to their high bandwidth ability, Asymmetric Digital Subscriber Lines (ADSL) and Very high speed DSL (VDSL) are access technologies that permit the transmission of several applications simultaneously on telephonic subscriber lines. Considering that these applications may require a different Quality of Service (QoS), and particularly different Bit Error Rates (BER), for transmission, this paper addresses the problem of providing simultaneously two BERs for transmission over a DMT-based ADSL or VDSL link. Both coded and uncoded systems are considered. |
| COMM8.7 |
Computational Reduction During Idle Transmission in DSL Modems A. Chellali, M. Polley, A. Gatherer (Texas Instruments, USA) This document decribes two methods for reducing computational requirements during idle transmission in remote access systems incorporating digital suscriber line (DSL) modems, including asymmertical DSL (ADSL) systems. These methods save processing power during idle transmission by generating an idle signal using low complexity techniques. The generated idle signal is made spectrally compatible with xDSL systems and a non-disruptive signaling scheme is used to indicate to the far end receiver the transition between idle to active or active to idle status. A technique is presented that modulates the phase of the pilot tone to signal status transitions to the remote receiver. The computational complexity at the receiver is reduced because full demodulation and decoding is not required to determine tha an idle signal is being transmitted. |
| COMM8.8 |
On the Implementation of Adaptive Equalizers for Wireless ATM with an Extended QR-Decomposition-Based RLS-Algorithm C. Drewes, R. Hasholzner, J. Hammerschmidt (Technische Universitaet Muenchen, Germany) An extended QR-decomposition (QRD)-based RLS-algorithm is introduced, applicable for equalization, allowing an estimate of the transmitted symbol, when it is a-priori unknown. To achieve low-cost implementations strength reduction and square-root free Givens-rotations are applied. Several QRD-based RLS-algorithms are compared in terms of the number of mathematical operations. The QR-RLS-algorithm indicates lowest complexity and is always a good candidate,when a huge trainig overhead has to be avoided, resulting in an equalizer of less than 15 taps. Finally, the hardware complexity of a 13 MBaud-DFE for wireless ATM is estimated. |
| COMM8.9 |
A New Test of Stationarity and its Application to Teletraffic Data S. Vaton (ENST Paris, France) In this contribution we generalize the test of sphericity as a test of stationarity for time-series. The sphericity statistics is in our case a measure of distance between the empirical correlations calculated on two contiguous segments of the same process. We prove that under the hypothesis of stationarity the logarithm of the sphericity converges in distribution to a quadratic form in a multidimensional gaussian random variable with a convergence rate that is equal to the length of the observation window. We then derive a test of proportionality of the correlations of the process on the two segments. This new test is applied to test if the traffic measured on today's broadband networks is stationary. The results that we obtain are connected to many previous works according to which the traffic generated by modern high-speed networks is a stationary and long-range dependent process. |
| COMM8.10 |
Probability of Detection of Residual Echo Based on Magnitude-Squared Coherence Estimate C. Sui (Lucent Technologies, USA) Residual echo is a distorted, partially-canceled, and transient echo of the near-end speech signal returned from the remote network. Previous work has shown that residual echo can be detected and reduced by using a nonlinear processing technique based on frequency coherence. In this paper a mathematical approach to evaluate this nonlinear processor and the algorithm for computing the probability of detection using the magnitude-squared coherence estimate are presented. |
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