1,721,138 research outputs found
Adaptive TORC Detection for MC-CDMA Wireless Systems
No full textMulti carrier code-division multiple access (MC-CDMA) is considered for beyond third generation wireless systems for its effectiveness in the presence of both multipath fading and interference. This paper analyzes MC-CDMA systems adopting an adaptive detection technique based on threshold orthogonality restoring combining (TORC). The mathematical framework here developed allows the evaluation of both the bit error probability and the bit error outage in downlink with perfect and imperfect channel state information and the derivation of the TORC threshold that optimizes the performance. The optimal threshold is analytically derived as a function of the number of subcarriers, the number of active users, and the mean signal-to-noise ratio. This also enables an adaptive variation of the threshold following slow processes fluctuations. Numerical results show very good performance of TORC with optimal threshold comparing with other combining techniques and demonstrate that the optimal threshold changes considering perfect and imperfect channel estimation. Results are shown both in uncorrelated Rayleigh fading as well as in time and frequency correlated fading channels
On the Performance of MC-CDMA Systems with Partial Combining and Multiple Antennas in Fading ChannelsVTC Spring 2008 - IEEE Vehicular Technology Conference
No full textIn this paper we analytically evaluate the downlink performance of a multi-carrier code division multiple access (MC-CDMA) system by employing partial combining when multiple antennas at the transmitter or at the receiver are considered. It is known that for single reception/transmission, the partial combining technique depends on a parameter which can be optimized as a function of the number of subcarrier, the number of active users and the SNR improving the performance with respect to other classical techniques (such as maximal ratio combining, equal gain combining, or orthogonality restoring combining). In this paper we extend the analysis considering also multiple antennas aiming at showing how the spatial diversity affects the performance as a function of the partial combining parameter
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Partial Equalization for MC–CDMA Systems in Non-Ideally Estimated Correlated Fading
No full textMulticarrier code-division multiple access (MC–CDMA) can support high data rates in next-generation multiuser wireless communication systems. Partial equalization (PE) is a low-complexity technique for combining the signals of subcarriers to improve the achievable performance of MC–CDMA systems in terms of their bit error probability (BEP) and bit error outage (BEO) in comparison with maximal ratio combining, orthogonality restoring combining, and equal-gain combining techniques. We analyze the performance of the multiuser MC–CDMA downlink and derive the optimal PE parameter expression, which minimizes the BEP. Realistic imperfect channel estimation and frequency-domain (FD) block-fading channels are considered. More explicitly, the analytical expression of the optimum PE parameter is derived as a function of the number of subcarriers, number of active users (i.e., the system load), mean signal-to-noise ratio (SNR), and variance of the channel-estimation errors for the aforementioned FD block-fading channel. We show that the choice of the optimal PE technique significantly increases the achievable system load for the given target BEP and BEO
On the Frequent Acquisition of Small Data through RACH in UMTS for ITS Applications
No full textWireless communications are currently considered the most promising solutions to provide real-time traffic information, suggest alternative routes, and help to reduce congestion. These new services are all based on the real-time acquisition of traffic information directly from vehicles, which act as sensors that travel on the roads. With the idea of having new widespread and real-time infomobility services in the short-medium term, neither installations onboard nor new roadside infrastructures that have been set up can be taken into account. Hence, in this paper, we aim at verifying the feasibility of the real-time acquisition of traffic information from vehicles in dense areas through the universal mobile telecommunication system (UMTS). In particular, we first analytically evaluate the capacity and the coverage of a UMTS cell when multiple users frequently transmit their traffic measurements to a remote control center through a shared (common) channel. Then, we extend our results to a realistic urban scenario by investigating, through simulations, the feasibility of the service and its impact on the quality of service (QoS) perceived by other users (e.g., voice)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
On the Effect of Combined Equalization for MC-CDMA Systems in Correlated Fading Channels
No full textEqualization techniques are considered in multi carrier-code division multiple access (MC-CDMA) systems to efficiently combine subcarriers contribution and improve the performance. In this paper we analytically investigate a combined equalization technique which consists in performing both pre- equalization at the transmitter and post-equalization at the receiver, by exploiting channel knowledge at both sides. To keep the framework as much general as possible, a parametric partial combining (PC) technique is considered. The analytical framework proposed allows the derivation of the bit error probability in correlated block fading channels and its dependence on the number of subcarriers, the number of active users, the mean signal-to-noise ratio (SNR) averaged over small-scale fading and, above all, the PC parameters, thus allowing the derivation of optimal equalization technique depending on fading levels
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