Giuliano Benelli

An ARQ Scheme with Memory and Soft Error Detectors

This paper describes a technique for increasing the efficiency of an ARQ communication system utilizing error detection codes. In this technique the blocks containing errors are not discarded at the receiver, as in the conventional ARQ systems. Such blocks are retained in order to make use of the information contained in them. A reliability value is associated to each demodulated symbol; this reliability value is updated every time a new retransmission is made, even if the vector received is in error. The process of updating the symbols often eliminates automatically the errors introduced by the channel. The results obtained by means of a simulation show that this method offers a considerable reduction in the average number of retransmissions, in comparison with conventional ARQ systems.

HIPS: hyper-interaction within physical space

HIPS is a project recently funded by the European Commission within the I-Cube initiative whose main aim is to study new technologies and interaction modalities that allow people to navigate both a physical space and a related information space at the same time, with a minimal gap between the two. The project envisages a portable electronic tour guide (to exhibitions, museums, archaeological sites, expositions distributed over a city, and to cities themselves) which empowers visitors to determine themselves the structure of a tour, according to their own criteria, interests and needs and which allow different information delivery modalities.

Multiple-symbol differential detection of GMSK for mobile communications

A new multiple differential detection (MDD) sequence estimator is described which uses a decision feedback for the demodulation of a GMSK signal. This technique is based upon a maximum-likelihood sequence estimation of the transmitted phases rather than on a symbol-by-symbol detection. An upper and a lower bound on the bit error probability of the described detector in the case of an AWGN channel and a two-ray Rayleigh fading channel are derived. The performance of the detection algorithm in a mobile radio communication system is obtained through computer simulation. Comparisons with the coherent detection algorithm show that the proposed detection algorithm is quite attractive both in an AWGN and in a multipath channel. >

Simplified Viterbi processors for the GSM Pan-European cellular communication system

The GSM cellular system provides the European countries with a common digital mobile radio structure for overland communications. This paper illustrates an implementation of a GSM receiver in which two reduced complexity Viterbi processors are used: the first one for the demodulation of the GMSK signal and the second one for the decoding operations. The performance of the receiver is evaluated through a channel simulator for mobile communications. The results show that in many cases the proposed receiver allows the significant reduction of the computation complexity with respect to the classical Viterbi processor. In particular, for mean and high signal-to-noise ratios, a reduction of four times in the computational burden is obtained. >

An ARQ Scheme with Memory and Integrated Modulation

In this paper, the integration of the modulation operation in an automatic-repeat-request scheme, using error-detecting codes, is analyzed. A new protocol is described, in which the modulation operation facilitates the recovery of the transmitted code word. The results show a net improvement in the throughput of the automatic-repeat-request scheme, particularly for mean and high error-rate conditions. Continuous-phase-frequency shift keying modulations, which present a low bandwidth occupancy, are particularly considered.

A new method for the integration of modulation and channel coding in an ARQ protocol

A method for the integration of the modulation operation in an automatic-repeat-request (ARQ) scheme is described. This method uses a memory for the successive transmissions of a codeword and, through a suitable encoding operation, the Euclidean distances among the codewords are significantly increased with the number of transmissions. The application of the described method to some different modulation schemes, such as M-ary PSK with M>2 and continuous-phase frequency shift keying modulation, is described. The optimum combination of the modulation and channel coding operations for some short block codes is also presented. The results of the theoretical analysis show that the method described permits improving both the error probability and the throughput of an ARQ protocol with respect to similar schemes. >

Two new coding techniques for diversity communication systems

In classical diversity techniques used in combating fading and in spread-spectrum systems, the same information is transmitted over m>or=2 channels, and the overall error probability is reduced by a suitable combination of the m received signals. Two techniques are proposed whereby the signals transmitted over the m channels corresponding to a given message can be encoded through a suitable error-correcting coding operation, thereby enhancing reductions in the receiver-side bit error probability with respect to classical diversity techniques. Gains have also been achieved by introducing a soft decoding operation at the receiver side and, in spread-spectrum systems, by adding side information. Applications to fading-affected communication systems and spread-spectrum systems are discussed. >

Performance analysis of a PRMA protocol suitable for voice and data transmissions in low Earth orbit mobile satellite systems

Mobile satellite systems (MSSs) are expected to play a significant role in providing users with communication services worldwide. In such a context, low Earth orbit (LEO) satellite constellations seem to be a good solution to attain a global coverage and to allow the use of low-power lightweight mobile terminals. This paper analyzes the performance of a novel medium access control (MAC) scheme suitable for applications in LEO-MSSs, named packet reservation multiple access with hindering states (PRMA-HS), that has been derived by proper modifications of the well-known PRMA protocol. We envisage a mixed traffic with voice sources and data sources with different quality of service (QoS) requirements. The good behavior of the proposed PRMA-HS scheme is validated by extensive comparisons with the classical PRMA protocol. Finally, it is shown that PRMA-HS efficiently supports integrated voice and data traffic in LEO-MSSs.

Improving wavelet-based merging of panchromatic and multispectral images by contextual information

Low-level, or pixel-based, fusion tends to use efficiently the information data acquired by sensors having different spatial and radiometric resolutions. Several methods have been proposed for merging panchromatic and multispectral data. Recently, multiresolution analysis has become one of the most promising methods for the analysis of remote sensing images. The use of the wavelet “a trous” algorithm allows to apply a dyadic wavelet to merge nondyadic data, by using a stationary or redundant transform, for which decimation is not carried out. The high-resolution coefficients of the image having high spatial resolution, may be added to the luminance component of the multispectral data. This procedure, namely AWL, which starts from a redundant bandpass representation of the image data, is very appealing, because the spectral quality is obviously highly preserved. However, it may suffer from a non-uniform spatial enhancement of the multispectral bands. In this paper, a method is proposed which uses spatial local information on the wavelet planes obtained from the “a trous” wavelet decomposition. The paper aims to improve the additive method by incorporating contextual spatial information to reduce possible overenhancement of the multispectral data in the image regions having higher spectral content, e.g., in highly textured regions.

Design of a digital MLSE receiver for mobile radio communications

A digital receiver suitable for use in the future GSM pan-European cellular system is described. The receiver uses a maximum-likelihood sequence estimation (MLSE) implemented by means of the Viterbi algorithm to compensate for the heavy selective distortions caused by multipath propagation. The performance of the receiver is evaluated through a channel simulator suitable for mobile communications. The results obtained show the good behavior characteristics for the receiver in different modes of operation. Easy implementation of the device using VLSI technology is expected.<<ETX>>