"Lemat" is an acronym for Libro Electronico de Matematicas, which means Electronic Book of Mathematics. It is a project developed by a group of teachers at secondary school and university levels, with two main objectives: the design, testing and implementation of new models of teaching strategies based on new technologies and focused on student learning, creating digital contents of mathematics of general interest for students in the two last years of secondary school and university students in first year of technology and sciences- To create a work-group for collaboration between different education levels, opening up ways of communication, thinking and cooperation, and making it possible to translate its aims to the real world.Access to Lemat Project is free with an anonymous password (User: ucex0201, password: LEMAT) through the ldquovirtual classroomrdquo of Cantabria University at www.aulavirtual.unican.es.

The advent of mobile wireless Internet technology coupled with media streaming has raised the expectation of having quality consumer experience in using voice over IP (VoIP) over wireless LAN (WiFi) environment. In order to provide VoIP call quality comparable to regular telephony, one must correlate the performance impact of various parameters on VoIP over WiFi networks. Past work of Linden, J. (2004) has stressed the importance of adaptive jitter buffering (AJB) and latency management in wireless VoIP endpoints. Recent studies have focused on studying individual impact of components, namely, code- aware aspects, audio-quality awareness and wireless-specific optimizations, on jitter buffer technology. This paper studies the combined impact of the various components affecting adaptive jitter buffer (AJB) design. Our proposed AJB algorithm is codec-aware, E-model audio-quality aware, and co-exists with wireless optimizations such as frame packing and repeating. Moreover, our AJB design is based on actual network delay characteristics, obtained via a signaling protocol, as opposed to on packet inter-arrival times, thereby making our work novel in this domain.

This paper evaluates the performance of Volterra equalizers and maximum-likelihood sequence detection (MLSD) receivers for compensation of signal distortion in nonlinear band-limited satellite systems. In addition, the performance of a receiver with a fractionally-spaced equalizer followed by a Volterra equalizer is studied (FSE-Volterra equalizer). For the equalizers, adaptation of the equalizer weights is considered including a multiple-step LMS algorithm which improves the convergence characteristics. Two MLSD receiver structures are considered: the optimum receiver consisting of a matched-filter bank followed by a Viterbi (1967) detector and a suboptimum receiver consisting of a single receiver filter followed by a Viterbi detector. The performance of the MLSD receivers is then compared to that of the equalizers.

Requirements for CDMA high-speed data (HSD) services make one of the distinguish marks between second generation and third generation (3G) wireless systems. cdma2000 provides 3G capacity, high data rates of up to 2 Mb/s and services. This paper describes a generalized frame structure for the support of sub-frames within cdma2000. This structure is parameterized such that it can be configured for efficient operation, depending on the radio environment and mobile station complexity, in order to provide several degrees of freedom. Impact on both convolutional code and turbo-code physical layer implementation is investigated. The results show the benefits of using the sub-frames technique.

Of the feedforward transmitter diversity methods considered for 3rd generation PCS/cellular systems one such method is known as phase sweeping transmitter diversity (PSTD). Since PSTD does not require a modification of the mobile station receiver, an important feature of this method is compatibility with 2nd generation as well as 3rd generation mobile stations. Furthermore, this method of transmitter diversity does not require specification in a standard. This paper provides an introduction to PSTD as it applies to IS-95 and cdma2000; the form of the received PSTD signal at the mobile station; compatibility issues between 2G and 3G; and link performance for AWGN, Rayleigh, and Ricean channel models.

Turbo codes have enjoyed a great attention. Among different soft-output decoding algorithms of turbo codes only maximum a posteriori (MAP) decoding as an iterative soft-output decoder (BCJR) allows for achieving an acceptable BER performance at Eb/No levels within only 1 dB of the value corresponding to the Shannon capacity. The drawback of the MAP algorithm is the excessive memory required. Here, we investigate the so-called symbol-based turbo codes. These codes allow for a reduced required memory by 30% for the BCJR method.

This paper compares the forward link performance of a direct spread CDMA system with a spreading bandwidth of 3.6864 MHz and a multicarrier system consisting of 3 carriers each with spreading bandwidth of 1.2288 MHz. These systems are under consideration for the forward link of the next generation CDMA cellular/PCS systems. This paper summarizes performance comparison results of the two systems for a data rate of 9.6 kbps with the IMT-2000 vehicular and pedestrian channel models. Performance results are given for speeds of 3 and 30 km/h. The results indicate that the two systems have comparable performance for the above data rate and the IMT-2000 channel models.