1,721,776 research outputs found
MC-CDMA Bit Error Probability and Outage Minimization through Partial Combining
No full textThis work addresses the performance evaluation, in terms of bit error probability (BEP) and bit error outage (BEO), for the down-link of multi-carrier code division multiple access systems. A partial combining technique depending on a parameter adapted to the system load and the mean signal-to-noise ratio is proposed to counteract both interference and thermal noise and optimized to minimize both BEP and BEO. The performance is improved with respect to previously known techniques such as maximal ratio combining, orthogonal restoring combining and equal gain combining
Wireless multimedia through heterogeneous satellite networks
No full textThe transmission of multimedia services through heterogeneous satellite networks is analyzed by means of measures over a real test-bed inside the Telecommunication Laboratory at CSITE-CNR, University of Bologna, Italy. An IEEE 802.11 wireless local area network (WLAN) is integrated with a wired LAN and connected to a video on demand (VoD) server through the ITALSAT II Ka-band satellite link made available by CNIT (Consorzio Nazionale Interuniversitario per le Telecomunicazioni). At first, the WLAN radio link is characterized in terms of mean received power for different terminal locations. After that, MPEG-1 video streams with different data-rate are transmitted from the VoD server to many wireless stations. A traffic characterization, for both the single source and the aggregated traffic, is carried out, and quality of service is measured, in terms of average dropped ratio, as a function of channel conditions, data-rate, and the number of wireless terminals requiring the service
Inhomogeneous Poisson Sampling of Finite-Energy Signals with Uncertainties in Rd
Full text linkSpatiotemporal signal reconstruction from samples randomly gathered in a multidimensional space with uncertainty is a crucial problem for a variety of applications. Such a problem generalizes the reconstruction of a deterministic signal and that of a stationary random process in one dimension, which was first addressed by Whittaker, Kotelnikov, and Shannon. In this work we analyze multidimensional random sampling with uncertainties jointly accounting for signal properties (signal spectrum and spatial correlation) and for sampling properties (inhomogeneous sample spatial distribution, sample availability, and non-ideal knowledge of sample positions). The reconstructed signal spectrum and the signal reconstruction accuracy are derived as a function of signal and sampling properties. It is shown that some of these properties expand the signal spectrum while others modify the spectrum without expansion. The signal reconstruction accuracy is first determined in a general case and then specialized for cases of practical interests. The optimal interpolator function is derived and asymptotic results are obtained to show the impact of sampling non-idealities. The analysis is corroborated by verifying that previously known results can be obtained as special cases of the general one and by means of a case study accounting for various settings of signal and sample properties
A Utility-Based Approach for Adaptive QAM with Diversity and Ambiguous CSI
No full textAdaptive M -ary quadrature amplitude modulation
(M -QAM) with subset diversity (SSD) is a way to cope with
quality of service variations in small and large-scale fading chan-
nels. We consider a slow adaptive modulation (SAM) technique
that adapts the constellation size to the slow variation of the
channel due, for example, to shadowing. SAM technique is more
practical than fast adaptive modulation (FAM) techniques, that
require adaptation to fast fading variations, even if it has been
has been shown to provide substantial increase in throughput
with respect to fixed schemes while maintaining an acceptable
low bit error outage (BEO). In addition SAM is less complex
than FAM and requires a lower feedback rate to the transmitter.
Performance of adaptive modulation and SSD techniques are
affected by non-ideal channel estimation. Here, we propose an
analytical framework to evaluate spectral efficiency and BEO for
slow adaptive QAM with SSD and imperfect channel knowledge.
We propose a utility-based approach to SAM, which accounts
for the abovementioned CSI imperfections. Our utility-based
approach is relevant to the game-theoretic approach, in which a
particular strategy (the transmitted power and the modulation
constellation option) is chosen by the decision-making control-
unit of the transceiver as a response to the set of possible (however uncertain) channel conditions
DSP-based satellite CDMA modem: a low complexity implementation
No full textThis paper presents a reliable and low complexity scheme for acquisition, tracking and frequency offset recovery for a DSP-based satellite CDMA modem. An analysis of the performance, in terms of false alarm probability, detection probability and mean acquisition time, is carried out as a function of the complexity and the level of interference. The proposed scheme, based on a dedicated frame format, appears able to cope with the DSP complexity constraint also for high levels of interference. A DSP implementation and numerical results, obtained by means of analytical evaluations and measurements on a real test-bed, are given
Vocabolario multilingue dell'Aids
No full textThis dictionary contains more than 400 terms related with the infection by HIV and AIDS that are commonly used in the healthcare field (terms related to biological characteristics of HIV, clinical and epidemiological aspects of HIV / AIDS or disease treatment). Every term is given in Italian, in six Romance languages (Catalan, Spanish –variants of Spain and Mexico--, French, Galician, Portuguese – variants of Portugal and Brazil-- and Romanian), and in English
Optimal Threshold Evaluation for TORC Detector of MC-CDMA Systems in Fading Channel
No full textIn this paper we investigate the performance of a
multi carrier-code division multiple access (MC-CDMA) system,
adopting an adaptive threshold orthogonality restoring combining
(TORC) detection technique. The analytical framework
we developed allows to derive the value of the threshold that
optimizes the performance in terms of bit error probability
as a function of the number of subcarriers, the number of
active users and the signal-to-noise ratio. This opens the way to
an adaptive variation of the threshold following slow processes
variations. A not negligible performance improvement, very close
to the optimum, but more complex, minimum mean square error
(MMSE) technique is shown
Combined partial equalization for MC-CDMA wireless systems
No full textWe analyze a combined equalization technique for multi carrier-code division multiple access (MC-CDMA) systems which consists in performing both pre-equalization at the trans- mitter and post-equalization at the receiver. In particular, a parametric partial equalization (PE) technique is considered at both sides, and we derive a generalized analytical framework to evaluate the bit error probability (BEP) and choose the optimal PE parameters which minimizes the BEP depending on system parameters
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
Utility-Based QAM Adaptation with Diversity and Ambiguous CSI under Energy Constraints
No full textAdaptive M -ary quadrature amplitude modulation (M-QAM) with subset diversity is a way to cope with the quality of service variations in small and large-scale fading channels. We consider a pilot-assisted slow adaptive modulation (SAM) technique that adapts the constellation size and the pilots energy to slow variations of the channel due to shadowing. The SAM technique is less complex and requires a lower feedback rate with respect to fast adaptive modulation techniques. We present an analytical framework to evaluate the bit-error probability for pilot-asisted slow adaptive QAM with subset diversity and imperfect channel state information (CSI) together with a utility-based approach to SAM. It accounts for the imperfect CSI, and is related to the game-theoretic approach, in which a particular strategy (the pilots energy and the constellation signaling) is chosen as a response to the set of possible channel conditions
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