Open Topics

Vol. 63, n° 7-8, July-August 2008
Content available on Springerlink

A classification of methods for efficient power amplification of signals

Yves Louët and Jacques Palicot

SUPELEC, Avenue de la Boulaie, CS 47601, 35576 Cesson-Sévigné Cedex, France

Abstract This paper presents a classification of methods that have been proposed to address nonlinear power amplification of highly fluctuating signals in telecommunications. The classification proposed uses a tree-like representation wherein each branch refers to a group of methods that all have a common characteristic. By virtue of this representation, each node corresponds to a test used to discriminate between different methods. From top to bottom, these tests are “What is the target of the method?,” Is the method downward-compatible?,” “Is the bit error rate degraded?,” “Is there a useful data rate loss?,” and “Does the method require changes in the amplification function?” By collating all these requirements, an original classification is proposed that is open enough to allow new methods to be added. It only concerns methods located either only at the transmitter or at both transmitter and receiver. The context of this study generally concerns multicarrier signals (especially orthogonal frequency division modulation) but can be applied to any multiplex of modulated signals.

Keywords PAPR mitigation . Linearization . Classification . Methods

Speech signals protection via logo watermarking based on the time-frequency analysis

Irena Orović, Predrag Zogović, Nikola Zarić and Srdjan Stanković

Faculty of Electrical Engineering, University of Montenegro, Podgorica, Montenegro

Abstract A procedure for logo watermarking of speech signals is proposed. In order to take full advantage of both time and frequency domains, we have used joint time- frequency representation of speech signal, which provides a more comprehensive information compared to each domain individually. Time-frequency-based selection of the discrete Fourier transform coefficients is used for logo embedding. The proposed coefficients selection provides both the imperceptibility and robustness requirements. The binary logo is embedded by using the concept of bit-plane modification. The logo extraction procedure is provided as well. The robustness of the proposed procedure is tested under various attacks such as compression, noise addition, filtering, re-sampling, re-quantization, time stretch, pitch scaling, etc.

Keywords Logo watermarking . Speech signals . Time-frequency analysis

A comparison analysis of prefiltering methods in space-time trellis-based reduced-state turbo-detection

Sami Chtourou1, Raphaël Visoz and Antoine O. Berthet3

1 ISECS, route Menzel Chaker, km 0.5, Sfax, Tunisia
2 France Télécom R&D, 38-40, rue du Général Leclerc, 92794 Issy les Moulineaux, France
3 Department of Telecommunications, SUPELEC, Plateau de Moulon, 91192 Gif-sur-Yvette, France

Abstract In this paper, we investigate two different prefiltering strategies, i.e., multiple input multiple output (MIMO) channel shortening and MIMO whitened matched filtering, to decode iteratively a space time bit interleaved coded modulation transmitted over MIMO block fading intersymbol interference channels using a trellis-based post-detector. Indeed, resorting to such front-ends allows significant complexity gain when compared to the optimal maximum a posteriori-based turbo-receiver. While those two approaches have been exhaustively visited in the past, their fair comparison in terms of trade-off between complexity and performance has – to our knowledge – never been tackled before. This paper aims at giving some valuable insights about the respective benefits of these two prefiltering methods with respect to the channel characteristics and overall receiver complexity.

Keywords MIMO ISI channels · Turbo-receivers · Trellis-based detectors · Channel shortening · Whitened matched filtering

Performance comparison between Gaussian interleaver, Rayleigh interleaver, and dithered golden interleaver

Lahcène Hadj Abderrahmane and Safouane Chellali

Centre National des techniques Spatiales, No. 1 Avenue de la Palestine, BP 13, Arzew-Oran, Algeria

Abstract This paper is a proposal for a new form of random interleaver for a turbo code based on the probability distribution of channel statistic model of transmission, instead of a uniform probability distribution. In our work, we use the normal (Gaussian) and Rayleigh probability distribution in accordance with the channel type and compare them with classic random interleaver (uniform distribution) and with dithered golden interleaver [invention of the Communications Research Centre (CRC)]. The results show that this new form of random interleaver gives identical results compared to the simulated case of dithered golden interleaver.

Keywords Interleaver . Golden section . AWGN. Rayleigh . BER

Modelling of state-dependent multirate systems carrying BPP traffic

Mariusz Głabowski

Communication and Computer Networks, Poznan University of Technology, Polanka 3, 60-965 Poznan, Poland

Abstract This paper presents a simple approximate calculation methodology of the occupancy distribution and the blocking probability in state-dependent systems with multirate Binomial-Poisson-Pascal traffic. The particular traffic streams are generated by an infinite, as well as by a finite, population of traffic sources. The proposed methodology is based on the generalized Kaufman-Roberts recursion. The model enables calculations to be carried out for the systems in which accepting a new call depends on an admission control algorithm (e.g., a model of a full-availability group with bandwidth reservation) as well as for those systems in which accepting a new call depends on the structure of a system (e.g., a model of a limited-availability group). The results of the analytical calculations have been compared with the simulation results of exemplary state-dependent systems.

Keywords State-dependent systems · BPP traffic · Bandwidth reservation · Multiservice traffic

Performance of joint source-channel decoding with iterative bit combining and detection

T. P Fowdur and K. M. S. Soyjaudah

Department of Electrical and Electronic Engineering, Faculty of Engineering, University of Mauritius, Reduit, Mauritius

Abstract A joint source-channel decoding scheme (JSCD) with iterative bit combining (IBC) is proposed, which exploits two types of a priori information. The first one is the a priori bit probabilities obtained from source statistics, and the second is the channel a priori probabilities obtained from saved extrinsic information of previous transmissions. The JSCD-IBC scheme also incorporates iterative detection as both a stopping criteria and mechanism for triggering retransmissions. This adds an implicit adaptivity to the system and prevents excess iterations/retransmissions from being effected. The performance of the JSCD-IBC scheme is evaluated with four different iterative detection schemes and also two different types of variable length codes, Huffman and reversible variable length codes. Simulation results show that a significant performance gain in terms of bit error rate, throughput, and number of iterations can be achieved with the JSCD-IBC scheme as compared to a separate decoding scheme.

Keywords JSCD . Iterative decoding . Iterative detection

Joint azimuth, elevation, and time of arrival estimation of diffuse sources

Hatem Boujemâa1, Insaf Jaafar1, Rim Amara2 and Mohamed Siala1

1 TECHTRA Research Unit, High School of Communications of Tunis, Route de Raoued Km 3.5, El Ghazala, 2083 Ariana, Tunisia
2 Signals and Systems Research Unit, Belvédère, 1000 Tunis, Tunisia

Abstract In this paper, we estimate the azimuth, the elevation, and the time of arrival of diffuse sources using the covariance matching estimator (COMET) algorithm. Previous works dealt with azimuth estimation of diffuse sources or azimuth and time of arrival estimation of point sources. However, in realistic situations, a tridimensional diffuse source localization is needed, which is the main objective of this paper. We show that the dimensionality of the COMET algorithm can be reduced by separating the estimation of the different source powers and the noise variance from that of the remaining parameters, namely the azimuth, the elevation, the time of arrival, and the corresponding angular and temporal spreads. As COMET still involves a multidimensional nonlinear optimization, we choose, in this purpose, the alternating projection algorithm to alleviate the corresponding complexity. The multiple signal classification (MUSIC) algorithm is processed to initialize the so-resulted algorithm. Simulations of the proposed algorithm are carried in different contexts and compared to the Cramér-Rao Bound, MUSIC algorithm, and dispersed signal parametric estimation simulation results

Keywords Diffuse source localization · COMET · MUSIC · ML · CRB · Alternating projection algorithm

An adaptive resource management for mobile terminals on vertical handoff

Faraz Idris Khan and Eui-Nam Huh

Internet Computing and Security Lab, Department of Computer Engineering, Kyung Hee University, Yongin 449-701, South Korea

Abstract Mobile communications and wireless networks are developing at a fast pace. The increasing number of mobile subscribers and terminals are the real life evidence of the fast growing development in the area of wireless communication. Wireless communication technology is now pursuing 4G (fourth generation) and seeking a scheme to provide quality of service (QoS) to the various applications continuously even moving to another network. In this paper, we proposed a dynamic resource management architecture which considers vertical handoff situation with minimal disruption of service to the users considering seamless provision of QoS. The proposed scheme efficiently manages resources and provides stable services to the mobile terminal. The simulation results show that resource management enabled mobile terminals utilize system resources, CPU and memory, efficiently improved by 40% and 65%, respectively, rather than mobile terminals without resource tuning.

Keywords Mobile communication . WLAN . Mobile terminal . TCP