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In this paper, an encryption, compression and transmission scheme is proposed. The scheme is based on fractional-order chaotic systems combined with Discrete Wavelet Transform (DWT) and Quadrature Phase Shift Keying (QPSK) modulation. The cipher performs rounds of digital operations between the vector states of the fractional-order system and the image to be encrypted. The implementation of the transmission process is made between a pair of software defined radio modules through a QPSK modulation scheme. The experimental results and security analysis show adequate performances for several applications in the presence of multiple attacks and environmental noise.

The transmission of images over wireless channels is increasing with advances in wireless communication technologies. However, ensuring secure and efficient transmission is a major challenge because intrusive receivers may be present, wireless channels have high bit error rates and limited bandwidth. This paper proposes a wireless transmission scheme for encrypted images to establish reliable and robust communications. The proposed scheme comprises on the transmitter side, encryption, compression, channel coding and modulation, and their inverse processes at the receiver. The Discrete Wavelet Transformed and the Huffman coding are employed for image compression, whereas convolutional coding is used as a technique for error correction. The system is implemented with the USRP NI-2920 modules and LabVIEW Communications 2.0 software, allowing the transmission of encrypted images both in real and simulated environments. The results show that the proposed system is robust and efficient against channel degradation.

Radio frequency identification (RFID) is a technology with numerous benefits in applications where objects have to be identified automatically. However, cost, fragile tags, collision and reading errors are some of issues to be concerned with in an RFID implementation. Mainly, this paper proposes a method for tag identification and a method for the selection of the binary codes to program on the tags in order to facilitate the identification process. For the identification method a heuristic based on Hamming distance is developed where the basic idea is to utilize the information obtained in consecutive read attempts to help identify a tag. For the selection method three models based on Hamming distance are also developed which strive to find the set with the greatest dissimilarity among the codes. Computer simulations are performed to verify the validity of the proposed methods.

Adequate quality of Internet Protocol (IP) services demand low transmission delays. However, packets traveling in a network are subject to a variety of delays that degrade severely the quality of service in real-time applications. This paper presents a general packet jitter-assessment methodology for a multi-node path in the presence of heavy-tailed traffic. Using the extreme-value theory, it is shown that delay performance is governed by a proposed networking-processing factor |T|lambda dependent on the traffic characteristics, the processing time along the path segments and the number of nodes in a route. |T|lambda allows the establishment of design constraints and the definition of a feasibility space for a routing algorithm in order to guarantee a quality of service (QoS). Copyright © 2003 AEI.

A Position Location (PL) scheme for mobile users on the outskirts of coverage areas is presented. The proposed methodology makes it possible to obtain location information with only two land-fixed references. We introduce a¨general formulation and show that maximum-likelihood estimation can provide adequate PL information in this scenario. The Root Mean Square (RMS) error and error-distribution characterization are obtained for different propagation scenarios. In addition, simulation results and comparisons to another method are provided showing the accuracy and the robustness of the method proposed. We study accuracy limits of the proposed methodology for different propagation environments and show that even in the case of mismatch in the error variances, good PL estimation is feasible.

This chapter addresses the relevance of location information as an important resource that supports other applications. This information is important for better network planning, development of new location-based services, fast deployment of assistance services, and support of surveillance and safety regulations, among others. Accuracy of location acquisition processes is an important factor because the potential for multiple new location-based services depends on it. However, noise is always present at least in two forms. Measurements taken with electronic instruments are inherently noisy and estimation algorithms introduce noise of their own in the assumption process. For this reason, this chapter explores several methods and techniques. A well- balanced solution should take into account the compromise between accuracy and delay and/or complexity. Many solutions have been proposed for new needs and new applications which demand more timely and accurate position locations of users or objects.

Smart antennas are a suitable technology to increase the capacity of cellular systems. However, under severe channel conditions, the capacity gain may be small. This work presents a general methodology for the analysis of the effect of the angular power dispersion on the capacity gain for a CDMA system when using smart antennas. System capacity is expressed in terms of a supportable mean number of subscribers per angular sector and it is shown that maximum and mean number of subscribers criteria can be considered equivalent. Formulations for a single cell as well as for multi-tier scenarios are presented. Omni-directional case and non-spread scenarios are shown to be particular cases of the methodology introduced. Capacity is determined for a smart antenna system, both for general antenna beam patterns and general spread characteristics. Copyright © 2004 AEI