49,492 research outputs found
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
Glucose, Insulin and Renin activity after sodium loading and depletion in Vipera aspis.
No full textSodium, potassium, chloride, glucose, insulin and renin activity were investigated in fasted Vipera aspis subjected for 3 days to administration of 3% NaCl 5 ml, or injection of a diuretic and water loading to produce sodium depletion. After sodium loading, plasma sodium and glucose were significantly elevated if compared with those of controls, while plasma renin-like activity and plasma insulin were depressed. The insulin and somatostatin producing cells (B- and D-cells) showed only a weak immunoreactivity, while in the glucagon producing cells (A-cells) the immunoreactivity was stronger if compared with the handled controls. After sodium depletion, plasma sodium and glucose were significantly depressed and plasma renin-like activity and plasma insulin were significantly elevated. A strong immunoreactivity was present in B- and D-cells and only a weak immunoreactivity was detectable in the A-cells. These data suggest that the secretory activity of the endocrine pancreas and kidney may be affected, in vipers, by sodium and/or volume status
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
Late Pliocene and Pleistocene small mammal chronology in the Italian peninsula.
No full textThe abundant documentation of small mammals in the Italian peninsula, collected over recent years, furnishes a detailed biochronological sequence mainly from the Late Pliocene onwards. An updated stratigraphic framework is here presented, based on the European small mammal biozonation. The Early Villanyian is characterized by Mimomys hassiacus, M. stehlini, and, later, poorly documented M. polonicus. The Late Villanyian localities are well characterized with M. pliocaenicus, M. pitymyoides and M. tigliensis.
The older part of the Early Biharian is documented by assemblages containing Microtus (Allophaiomys) ex gr. pliocaenicus, M. pusillus,
M. cf. ostramosensis and M. tornensis, while the later part of the Early Biharian, is characterized by advanced Microtus (Allophaiomys)
species occurring together with M. pusillus or M. blanci. In the Late Biharian M. savini, Microtus hintoni-gregaloides, Microtus (Iberomys)
ex gr. huescarensis-brecciensis and Terricola arvalidens occur. The Early Toringian with A. mosbachensis, Allocricetus bursae, Pliomys
episcopalis and small-sized Microtus brecciensis, and the Late Toringian with A. terrestris in diversified associations are quoted. The most important faunal events are calibrated by independent chronological controls, thanks to the record of small mammals from lacustrine deposits. Several figures illustrate the most significant rodent species occurring in the succession of selected Italian localities
A distributed virtual traffic light algorithm exploiting short range V2V communications
No full textThe correct and prompt definition of priorities at intersections is one of the key issues for vehicular safety and efficient traffic management. Traffic lights currently control only a limited number of intersections and increasing their number is clearly infeasible due to the high costs of deployment and maintenance. A new solution will be possible in a near future, when vehicles will be equipped with wireless technologies. Their capability of communicating and coordinating to each other will create the conditions for the implementation of a virtual traffic light (VTL) architecture, where priorities are autonomously defined by the involved vehicles. With this scenario in mind, we describe a novel VTL algorithm aiming at defining the priorities of the intersections in a distributed and controlled way. Besides the algorithm description, the main related issues are thoroughly discussed. In addition, a real implementation is detailed and the validation of the algorithm is provided. The testbed, based on the IEEE 802.11p short range wireless technology, has been reproduced in a controlled laboratory environment and in a field trial with equipped vehicles
An OFDMA-Based MAC Protocol for Next-Generation VANETs
No full textVehicular ad hoc networks (VANETs) enable higher safety, enhanced mobility management, and new infotainment services. Currently, the foreseen standard at the medium access control (MAC) layer for VANETs is IEEE 802.11p, which is based on carrier sense multiple access with collision avoidance (CSMA/CA). However, under heavy traffic conditions, CSMA/CA suffers from a high collision probability, particularly in the presence of hidden terminals. Furthermore, the adoption of the request-to-send/clear-to-send (RTS/CTS) mechanism is not effective when a high data rate is required. If high-throughput services are addressed, a new MAC protocol should, thus, be designed. To this aim, in this paper, we propose a new protocol, which is denoted as the orthogonal frequency-division multiple-access (OFDMA)-based MAC protocol for VANETs (OBV), and we compare it with other MAC protocols taken as benchmarks. To verify the feasibility and the performance of the proposed algorithm, we first propose an analytical model in a simplified scenario. Then, we develop exhaustive simulations in realistic scenarios, considering both urban and highway environments. Results show that OBV outperforms all reference protocols, even doubling their throughput under heavy-load network conditions
Optimizing the Resource Allocation of Periodic Messages with Different Sizes in LTE-V2V
No full textRecently, 3GPP has added new features to long term evolution (LTE) that allow vehicles to communicate directly with each other and with surrounding objects. These short-range communications will play a key role in the so-called cellular vehicle-to-anything (C-V2X). As a particular service, which will be the basis of most applications for automated and connected cars, each vehicle will periodically broadcast information on its identity, status, and movements through short-range vehicle-to-vehicle (V2V) communications. Given the importance of this service, great attention has been given to the associated resource allocation procedures and the number of vehicles that can be simultaneously communicating in the network. However, little attention has been paid to handling messages of different sizes, which is actually foreseen in practice in order to transmit static information with a reduced periodicity. With this in mind, we evaluate the number of vehicles that can be allocated when parameters are optimized for messages of different sizes. This objective is pursued taking into account the numerous constraints imposed by the standard, through the formalization and solution of a combinatorial optimization problem. Example results, based on 3GPP indications, show that, with respect to the optimization of the allocation based on the larger packets, it is possible to obtain an increase that varies between 10% and 30%, depending on the conditions, with peaks above 150% in specific cases
Performance Improvement through Diversity Reception for Bluetooth on the Presence of Interference
No full textIn this work, we propose an analytical framework to derive the performance of Bluetooth (BT) in the presence of an IEEE802.11g interferer. In particular, aiming at improving the performance of BT in the presence of interference still maintaining low the complexity, we propose a selection diversity scheme at the receiver side of the BT system and we exploit the spatial diversity to improve the coexistence between different systems sharing resources. We firstly analytically derive the BT performance in terms of mean block error probability and mean packet error probability averaged over Rayleigh fading, then we extend the analysis to the evaluation of the packet error outage, an important figure of merit when real time scenarios are considered. We show that a not negligible improvement for the coexistence issue of the involved systems can be achieved
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