Fabrizio Frescura

DSP based OFDM demodulator and equalizer for professional DVB-T receivers

This work treats the design of base-band processing subsystems for professional DVB-T receivers using 1600 MIPS, fixed point DSPs. We show the results about the implementation of OFDM demodulation, channel estimation and equalization functional blocks, for the 2k/8k modes. The adoption of general purpose DSPs provides a great flexibility in the development of different configurations of the receiver. Furthermore it enables the feasibility of adaptive equalization schemes, where the quality of the channel estimation varies according to both channel characteristics and speed of the channel variations. The 16/32 bit fixed point architecture leads to a very low implementation loss, and a careful optimization of the pipeline architecture of the processor allows the receiver to obtain short processing delays. The flexibility of the software approach along with the obtained performance make the proposed implementation very interesting in professional and high-end receivers for interactive, multimedia applications of DVB-T.

JPEG2000 and MJPEG2000 transmission in 802.11 wireless local area networks

In this paper the transmission of JPEG2000 and motion JPEG2000 codestream in 802.11 WLAN environment is analyzed. The issues related to the transmission of JPEG2000, using non-reliable protocols as UDP-RTP, are investigated and a proper protection scheme for dealing with such an environment is presented, along with the obtained performance with different systems parameters. The proposed technique addresses a wide range of multimedia applications such as wireless PC to digital projector multimedia presentations, point to multipoint digital slide projection, wireless video-surveillance systems.

Error Protection and Interleaving for Wireless Transmission of JPEG 2000 Images and Video

The transmission of JPEG 2000 images or video over wireless channels has to cope with the high probability and burstyness of errors introduced by Gaussian noise, linear distortions, and fading. At the receiver side, there is distortion due to the compression performed at the sender side, and to the errors introduced in the data stream by the channel. Progressive source coding can also be successfully exploited to protect different portions of the data stream with different channel code rates, based upon the relative importance that each portion has on the reconstructed image. Unequal error protection (UEP) schemes are generally adopted, which offer a close to the optimal solution. In this paper, we present a dichotomic technique for searching the optimal UEP strategy, which lends ideas from existing algorithms, for the transmission of JPEG 2000 images and video over a wireless channel. Moreover, we also adopt a method of virtual interleaving to be used for the transmission of high bit rate streams over packet loss channels, guaranteeing a large PSNR advantage over a plain transmission scheme. These two protection strategies can also be combined to maximize the error correction capabilities.

JPWL - an extension of JPEG 2000 for wireless imaging

In this paper, we present an overview of the JPWL standardization activity. JPWL is an extension of JPEG 2000 for the efficient transmission of JPEG 2000 images over an error-prone wireless network. More specifically, JPWL supports a set of tools for error protection and correction, including forward error correcting codes (FEC), unequal error protection (UEP), data partitioning and interleaving

Performance comparison of multicarrier DS-SS radio access schemes for WLAN using measured channel delay profiles

In this paper we propose two different MCM (multicarrier modulation)-DS-SS radio access schemes for WLANs and we evaluate their performance in terms of bit error rate and frame error rate by using measured channel delay profiles, in different indoor environments. By comparing the obtained performance with the results of the DS-SS physical layer of the IEEE 802.11 standard, we point out some important architectural aspects and the potential limiting factors of the performance.

Combined OFDM-CDMA configuration for multimedia wireless applications

This paper analyses the applicability of OFDM modulation when combined with CDMA for multimedia wireless systems operating in an indoor environment. We demonstrate the motivations and benefits deriving from this combination. Particular emphasis is given to channel equalisation techniques, designed to face different problems arising in the up-link and in the down-link. In particular, an equalisation technique based on channel inversion, combined with carrier interleaving and adaptive suppression of noisy carriers, is proposed in the down-link, while a pre-equalisation approach is used in the up-link. The analysis provides both BER performance and computational cost of the most important procedures that are to be implemented within multimedia terminals. The computational cost analysis is carried out using commercial DSP platforms.

Objective and subjective quality assessment between JPEG XR with overlap and JPEG 2000

JPEG XR (eXtended Range) is a recently standardized format for still images compression. It adopts a Lapped Biorthogonal Transform (LBT) that helps in reducing visual artifacts, in particular those due to blocking effects. In this paper, we compare JPEG XR with JPEG 2000, in terms of both objective and subjective visual quality. The adopted objective parameters are the computational complexity and the PSNR. In order to improve the analysis, and to evaluate if JPEG XR can be a feasible alternative to JPEG 2000, subjective tests in a projector-based environment have been set up, from which the benefits of the overlap operator of JPEG XR have been assessed, especially at high compression ratios.

Digital Cinema package transmission over wireless IP networks

In this paper we present a method for the quasi-reliable transfer of Digital Cinema (DC) content over packet-lossy IP networks, such as wireless networks. By employing the MXF (Material eXchange Format) encapsulation, reliable transmission of MXF keys backup, and compressed frames Forward Error Correction (FEC), we show that visual artifacts due to packet losses are virtually cancelled, and decoder crashes can be avoided. DC video content adopts JPEG 2000 for image coding; in this standard, an extension, called JPEG 2000 for Wireless (JPWL), is provided to combat codestream (i.e., compressed image) errors. For the PCM audio, a combination of FEC and error concealment provides no or minimum degradation.

Error Correction and Concealment for JPEG 2000 Video Transmitted over Wireless Networks

The transmission of compressed video sequences over wireless networks represents a particularly challenging problem, since the obtained visual quality strongly depends on the characteristics of the error-prone channel and on the tools used to compress the original sequence. In this paper, we present some methods for error concealment and error correction, which can be used when JPEG 2000 is adopted as compression tool. A judicious use of the scalability properties, error correction tools supplied by this standard, and an appropriate data interleaving algorithm can provide a good performance when compared with other error recovery methods.

Increased Capacity of DS-CDMA Mobile Systems on Frequency-Selective Slow Fading Channels

In this paper we will examine the performances of Direct-Sequence Code Division Multiple Access (DS-CDMA) systems, designed for digital mobile radio communications, using a RAKE receiver. In order to study system performances in terms of the users number per cell (or per channel), we assume the Offset-Quadrature Phase-Shift Keyed (OQPSK) signalling and 4-phase sequences with near-optimum correlation properties as signature sequences. We found that the adoption of the above sequences allows an increase of about 50% of users number with respect to the case in which quadriphase sequences, derived from binary Gold sequences, are adopted.