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					                            WORKPACKAGE 4 – PHYSICAL LAYER OF WIRELESS SYSTEMS

Introduction
WP 4 covers all aspects related to the design of the physical layer of wireless systems. It is organized into two main research lines,
dealing with i)modulation, source and channel coding schemes, and ii) multiuser detection and time-space coding for multiple
antenna systems. A unified approach is pursued, aiming to the global optimization of the transmission system. Joint activities have
been carried out with Workpackages 3 and 6, for aspects related to implementation issues (computational complexity of algorithms,
definition of proper HW/SW architectures) and integration of the selected algorithms in common demonstrators.
RESEARCH LINE N. 1: CHANNEL CODING AND EFFICIENT MULTIDIMENSIONAL MODULATION SCHEMES
FOR NEXT GENERATION CELLULAR PHONES
In this section, the main achievements in the fields of channel coding, efficient multidimensional modulation schemes, joint source-
channel coding for wireless multimedia are briefly described.
Resilient MQ coder and SISO decoder for arithmetic codes - It is well known that arithmetic codes (AC) exhibit excellent
performance in terms of entropy coding, but are extremely sensitive to transmission errors due to heavy error propagation. The AC
can be modified so as to keep a given amount of coding redundancy, to be employed by the decoder in order to perform error
detection. We have modified in this sense the AC embedded in JPEG2000 (MQ coder); the resilient MQ is being considered for
inclusion in the JPEG 2000 Part 11 (JPWL). We have designed efficient MAP estimators, able to achieve error correction as well;
both hard and soft decoding have been taken into account and the performance has been tested in the case of image and video
transmission. The proposed strategy can be recognized as a joint source channel coding approach and presents a number of benefits,
when compared to more traditional separated source and channel coding, e.g. the fine grain coding rate scalability. The development
of a SISO module for AC decoding is part of the ongoing work on this topic, aiming at the design of serially concatenated schemes.
For details see [1,5,10,11,13,16].
Multiple description coding (MDC) - MDC is recognized as an effective method to protect multimedia information transmitted
over networks subject to erasures. The basic principle is to create multiple correlated descriptions of the same data, which can be
independently decoded, yielding mutually definable information. Most methods proposed in literature (MD quantization, correlating
transforms) are not compatible with standard image/video co-decoding tools;. We have devised methods aiming at generating MDC
of images by means of pre-post processing to standards [8,9]. A method has also been proposed, which preserves a given ROI
defined in accordance with the JPEG 2000 syntax [17].
Rate allocation algorithms optimized for error-prone environment. - Proper models for the correlated packet loss patterns
typical of the wireless environment, such as the Gilbert-Elliot model, have been incorporated in the rate allocation procedure to
drive the selection of coding parameters. Unequal and hybrid loss protection methods have been proposed [2,6,7,12,14,15].
Demontrator – A hardware-software demonstrator of H.263 video streaming with turbo-codes has been developed, in cooperation
with WP3. Analysis of the complexity of various algorithms for the wavelet transform computation has been performed [3,4].
Design and analysis of concatenated coding schemes – During the second year of activity, research efforts have been devoted to
the design of interleavers connecting the two constituent codes. Design methods that yield improved performance in the “error
floor” region have been addressed. To this end, techniques aiming at improving the code minimum distance have been devised.
Moreover, the problem of designing optimum encoders for non binary modulation schemes has been addressed. The implementation
of a parallel Turbo decoder architecture with conflict-free access to the memory was also solved by the use of a suitable mapping
between input variables and memory banks. Design and analysis of concatenated coding schemes: Moreover, the problem of
designing ad-hoc turbo-encoders for non binary modulation schemes has been addressed [18,19].
RESEARCH LINE N. 2: MULTIUSER DETECTION AND TIME-SPACE CODING FOR MULTIPLE ANTENNA
SYSTEMS
Study of a low-complexity iterative multiuser receiver - A new suboptimal Turbo receiver for coded CDMA is being studied.
The user-separating front-end of this receiver has been thought of as the extension of linear multiuser detectors to an iterative
structure. In the first few iterations, it behaves like a standard MMSE filter, while from a given iteration on it becomes si mply a
matched filter bank. The switching iteration is chosen according to an SNR-maximizing criterion. The complexity of this receiver is
shown to be very low, linear in the number of users. Simulations show that, for sufficiently high signal-to-noise ratios, the linear-US
receiver tends to single-user performance. At present, extensions of the proposed receiver to the case of multiple transmit antennas
is being sought [20-23].
Space-time coding - The activities carried out in this second year are related to the performance comparison of suboptimal linear
and non linear interfaces for the decoding of space-time codes transmitted on radio channels affected by fading when multiple
antennas are used both at the transmitted and at the receiver. First of all, the performance of receivers for multiple antenna systems
have been evaluated for some space-time coding schemes proposed in literature (e.g. the BLAST method). As terms of comparison,
the BER and FER, as well as the computational complexity, have been considered. Maximum likelihood (ML) receivers, non linear
BLAST-like interfaces and common linear interfaces (e.g. ZF and MMSE) have been simulated, when applied to convolutional
coding schemes. Quasi static Rayleigh fading has been assumed. Subsequently, a novel MMSE receiver based on iterative
decoding has been proposed, which approaches the ML receiver performance with lower computational complexity. At present, this
receiver is being evaluated on systems employing turbo-codes. The goal is to devise low complexity, high spectral efficiency, high
performance systems with a large number of tx and rx antennas (e.g. 8x8 or 16x16). For details, please refer to [24-27]. Another
research activity is concerned with the design of signal constellations for wireless channels, based in the application of algebraic
number theory. The problem of designing space-time codes for CDMA systems, that does not require channel estimation and
exploits the turbo principle in the decoder, has also been addressed. For details, see [28-33].
Published or submitted papers (June 2002- June 2003)

        1.    M. Grangetto, E. Magli, G. Olmo, ``Robust video transmission over error-prone channels via error correcting
              arithmetic codes”, accepted for publication on IEEE Communications Letters, May 2003
        2.    S. Gnavi, M. Grangetto, E. Magli, G. Olmo ``Rate allocation for video transmission over lossy correlated networks”,
              IEE Electronics Letters, Vol. 38, No. 20, pp. 1171-1172, Sept. 2002
        3.    S. Gnavi, B. Penna, M. Grangetto, E. Magli, G. Olmo ``Wavelet kernels on a DSP: a comparison between lifting and
              filter banks for image coding”, Applied Signal Processing "Special Issue on Implementation of DSP and
              Communication Systems", Vol. 2002, No. 9, pp. 981-989, Sept. 2002
        4.    M. Grangetto, E. Magli, M. Martina, G. Olmo ``Optimization and implementation of the integer wavelet transform for
              image coding”, IEEE Transactions on Image Processing, Vol. 11, No. 6, pp. 596-604, June 2002
        5.    M. Grangetto, G. Olmo, P. Cosman ``Error correction by means of arithmetic codes: an application to resilient image
              transmission”, ICASSP 2003 - IEEE Int. Conf. on Acoustics, Speech, and Signal Processing, Hong Kong, Apr. 2003
        6.    C. Cucco, M. Grangetto, E. Magli, G. Olmo ``Few decoders in the encoder: a low complexity encoding strategy for
              H.26L”, ICASSP 2003 - IEEE Int. Conf. on Acoustics, Speech, and Signal Processing Hong Kong, Apr. 2003
        7.    S. Gnavi, M. Grangetto, E. Magli, G. Olmo, ``Comparison of rate allocation strategies for H.264 video transmission
              over wireless lossy correlated networks”, ICME 2003 - IEEE Int. Conf. on Multimedia and Expo, Baltimore, USA,
              July 2003
        8.    G. Olmo, T. Tillo ``Trade off between robustness and R-D performance in zero padding multiple description”, Seventh
              International Symposium on Signal Processing and its Applications Paris (France), July 1-4, 2003
        9.    G. Olmo, T. Tillo “ROI-preserving multiple description coding based on pre- and post-processing to standard
              encoders, “ Sixth Baiona Workshop on Signal Processing in Communications, 2003
        10.   M. Grangetto, E. Magli, G. Olmo, ``Error correcting arithmetic coding for robust video compression,” Sixth Baiona
              Workshop on Signal Processing in Communications, 2003
        11.   M. Grangetto, P. Cosman, ``MAP decoding of arithmetic codes with a forbidden symbol”, ACIVS 2002 – Advanced
              Concepts for Intelligent Vision Systems, Ghent, Belgium , September 2002.
        12.   M. Grangetto, E. Magli, M. Marzo, G. Olmo ``Guaranteeing Quality of Service for image transmission by means of
              Hybrid Loss Protection,” ICME 2002-IEEE International Conference on Multimedia and Expo, Lausanne,
              Switzerland, Aug. 2002
        13.   M. Grangetto, P. Cosman, G. Olmo, ``Joint source/channel coding and MAP decoding of arithmetic codes”, submitted
              to IEEE Trans. on communications, March 2003
        14.   M. Grangetto, E. Magli, G. Olmo, ``Ensuring quality of service for image transmission: hybrid loss protection”,
              submitted to IEEE Trans. on Image Processing, 2003
        15.   M. Grangetto, E. Magli, G. Olmo, ``Fast code-rate optimization for robust image transmission over lossy packet
              networks”, submitted to IEEE Trans. on Communications, June 2002
        16.   M. Grangetto, E. Magli, G. Olmo, “Error sensitivity data structures and retransmission algorithms for robust JPEG
              2000 wireless imaging”, submitted to IEEE Trans. on Consumer Electronics, May 2003.
        17.   G. Olmo, T. Tillo, “Directional Multiple Description Scheme for still images,” submitted to 10 th IEEE International
              Conference on Electronics, Circuits and Systems, April 2003
        18.   B. Scanavino, G.M. Maggio, Z. Tasev and L. Kocarev :"Ultra-Fast Convergence Iterative Decoding Based on
              Transient Dynamics Suppression,” submitted to Softcomm 2003
        19.   B. Scanavino, G.M. Maggio, Z. Tasev and L. Kocarev: "A Novel Stopping Criterion for Turbo Codes Based on the
              Average a Posteriori Entropy", submitted to Globecom 2003.
        20.   Tarable, G. Montorsi and S. Benedetto, "A Linear Front End for Iterative Soft Interference Cancellation and Decoding
              in Coded CDMA", submitted to IEEE Transactions on Communications, Dec. 2002.
        21.   Tarable, G. Montorsi and S. Benedetto, "Analysis and Design of Interleavers for Iterative Multiuser Receivers in
              Coded CDMA Systems", submitted to IEEE Transactions on Information Theory, Jan. 2003.
        22.   A.Tarable and F. Alesiani, "Differential Space-Time CDMA", submitted to IEEE Global Conference on
              Communications, (Globecom 2003), Feb. 2003.
        23.   A.Tarable, G. Montorsi and S. Benedetto, "Mapping interleaving laws to parallel Turbo decoder architectures",
              accepted at the 3rd International Symposium on Turbo Codes, May 2003.
        24.   E. Biglieri, A. Nordio, and G. Taricco, ``Space-Time coding with iterative receiver interfaces'', proceedings of
              DIMACS 2002.
        25.   E. Biglieri, A. Nordio, and G. Taricco, ``Suboptimum receiver interfaces for coded multiple antenna systems'',
              proceeedings of ICC, Anchorage, Alaska, May 2003.
        26.   E. Biglieri, A. Nordio, and G. Taricco, ``Performance of certain receiver interfaces for space time coded MIMO fading
              channels'', proceedings ISIT 2003, Yokohama, Japan.
        27.   E. Biglieri, A. Nordio, and G. Taricco, ``Suboptimum Receiver Interfaces and Space-Time Codes'', to be appeared on
              IEEE Transactions on Signal Processing, 2003.
         28. F. Oggier, E. Bayer-Fluckiger, E. Viterbo: "New algebraic constructions of rotated cubic lattice constellations
             for the Rayleigh fading channel", ITW 2003, Paris , France, March 31 - April 4, 2003, pp. 263-266.
         29. A.Nordio and E. Viterbo: "Permutation Modulation for Fading Channels", ICT 2003, Tahiti , French Polynesia,
             February 23 - March 1, 2003
         30. J. Boutros, G. Caire, and E. Viterbo, H. Sawaya, and S. Vialle: "Turbo code at 0.03 dB from capacity limit", ISIT
             2002, Lausanne, Switzerland, June 2002, p. 56.
         31. E. Viterbo: "Trellis Decoding of Permutation Modulation", accepted to ISIT 2003, Yokohama, Japan, June 30 - July
             4, 2003.
         32. F. Oggier, E. Bayer-Fluckiger, and E. Viterbo: "New algebraic constructions of rotated cubic lattice constellations for
             the Rayleigh fading channel", submitted to IEEE Trans. on Information Theory, December 2002.
         33. E. Viterbo: "Recent results on signal constellation designs for transmission over Rayleigh fading channels", invited
             paper GRETSI 2003, Paris, France, September 8 - 11, 2003


Invitation to seminars

E. Viterbo, Joint Workshop on Communications and Coding, November 3-6th, 2002, Barolo, Italy
E. Viterbo, Séminaire de Théorie des Nombres, Algorithmique et Cryptographie, November 21-22, 2002, Université Toulouse II
Mirail, France. (http://www.univ-tlse2.fr/grimm/algo/seminaire/exposes2002-2003.html)
E. Viterbo Workshop on Algebra and Communications, 16-17 Janvier 2003, EPFL, Lausanne Switzerland. (http://alg-geo.epfl.ch/)

Research proposals

    1.   JPEG.IT: “systems and applications based on JPEG2000”, MIUR PRN (“Programmi di ricerca scientifica di rilevante
         interesse nazionale”), submitted April 2003; responsible for CERCOM: Gabriella Olmo

    2.   NEWCOM: proposal for a Network of Excellence in Wireless Communications, submitted to IST – VI FP, April 2003;
         responsible for CERCOM: Gabriella Olmo

    3.   UMEDIA: proposal for a Network of Excellence “Universal Media Lab”, submitted to IST- VI FP, April 2003; responsible
         for CERCOM: Gabriella Olmo

National/International Cooperations

    1.   Cooperative research on topics related to H.264 co-decoding with the University of Padova (I) and with ST
         Microelectronics (responsible: G. Olmo)
    2.   Scientific cooperation with the Center of Wireless Communications, San Diego, USA (Prof. P. Cosman), and with INRIA,
         Rennes research Unit, F, (Dr. C. Guillemot) on resilient arithmetic coding (responsible: G. Olmo)
    3.   Scientific cooperation with Texas A&M University, USA (Prof. Z. Xiong) on distributed source coding (responsible E.
         Magli)
    4.   Participation in the Working Group JPWL (JPEG 2000 for wireless applications) (responsible: E. Magli)

				
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