1,720,978 research outputs found
A comparison between outage probability evaluations in microcellular systems
No full textThe effects of cochannel interference in a UHF microcellular system operating in a Ricean/Rayleigh fading environment are investigated: the aim is to prove in the microcell domain the validity of a simplified analytical methodology, already successfully applied in traditional cellular structures, which allows to evaluate almost effortlessly the outage probability, i.e., the probability of failing to achieve a satisfying signalto-interference ratio. The results obtained confirm the validity of this new approach also in the microcell environment, for a wide range of the parameters involved in the system, fading and propagation model description
Performance of a 3rd Generation Radio Link Control Protocol on a Multicarrier DS-CDMA System
No full textThis work investigates the behavior of a 3 rd Generation Radio Link Control Protocol on the forward link of a Multicarrier DS-CDMA architecture that employs Walsh and Quasi-Orthogonal channelization codes. Protocol performance is analytically assessed, determining the average delay suffered by a data unit transferred over the radio channel. For alternative allocation policies of Walsh and Quasi-Orthogonal codes, the effects on throughput of different transmission qualities and size of protocol data units are evaluated. system design
Voice and data services in multicode and variable spreading factor DS-CDMA systems
No full textThis paper analyzes the uplink capacity of multicode and variable spreading factor DS-CDMA cellular systems which accommodate users with different transmission rate requirements. It takes into account imperfect power control on slow signal fluctuations due to shadowing, the presence of Rayleigh fading and a random location of the users. The circumstance where the portable transmits to the nearest base station is examined; when shadowing only is present, the possibility that the user chooses the least interfered among Nc nearest base stations is also considered. System capacity is determined analytically, employing two distinct approximations featuring low computational costs, as well as by simulation. The latter approach allows to compare the accuracy of the analytical approximations for a wide range of system parameters
Multicarrier DS-CDMA performance with different assignment strategies of quasi-orthogonal codes
No full textAlternative code assignment policies for the forward link of a multicarrier DS-CDMA system employing the recently proposed quasi-orthogonal sequences are put forth in this paper. It is demonstrated how different allocation strategies of quasi-orthogonal codes alter the interference level suffered by active units; it is also shown how to shape the rate of interference growth as a function of the number of active users within the reference cell, by implementing some specific code allocation patterns. The performance, in terms of average bit error probability, achieved by various schemes is assessed in a frequency selective fading environment, and the advantages of different solutions highlighted. ©2002 IEEE
On the assignment of Walsh and quasi-orthogonal codes in a multicarrier DS-CDMA system with multiple classes of users
No full textSeveral code allocation policies, suitable for the forward link of a Multicarrier DS-CDMA mobile radio system that employs Walsh and quasi-orthogonal sequences, were presented. Their effect on system performance was evaluated in the presence of a single class of users. The performance achieved by two classes of subscribers was assessed in a frequency selective fading environment
A Statistical Characterization of the Actual Cooperative Perception Messages and a Generative Model to Reproduce Them
No full textThis paper provides two novel contributions to
vehicular cooperative perception. Firstly, it puts forth an approach to generate the actual perception messages broadcasted
by connected autonomous vehicles. Relying on data gathered
by autonomous vehicles and originally collected for computer
vision purposes, it produces perception messages in accordance
with the standard ETSI rules. The statistical properties of the
messages are determined, showing that their size is remarkably
affected by the driving scenario and the policy adopted to
discern when an object is seen by the vehicle, and to a lesser
extent by the selection of the message generation frequency.
Secondly, the paper proposes a generative model to synthetically
replicate the sequences of perception messages. The ability of
the model to successfully capture the characteristics and the
temporal correlation of the real data is demonstrated in a
reference scenario. The model adoption is promising in largescale numerical simulations, where the perception messages of
many vehicles have to be faithfully reproduced
Impact of assembly algorithms on end-to-end performance in Optical Burst Switched networks with different QoS classes
No full textThis paper investigates the performance of a complete OBS (Optical Burst Switched) network that implements the JET (Just Enough Time) reservation mechanism. The network under examination adopts a core node architecture with no fiber delay lines and a limited set of wavelength converters, while featuring an edge node architecture with a mix of input, output and shared buffers. We investigate the overall network performance and design, specifically focusing on burst delay and end-to-end TCP throughput. In order to study the OBS network behavior, we develop a modular and flexible simulation tool, that we call MOBSSIM (Modular OBS Simulator). MOBSSIM is the means to accurately build an arbitrary topology OBS network via its main functional blocks, edge and core routers: its sound degree of development enables us to accurately evaluate several figures of merit, e.g., burst blocking probability and delay, and also allows for a critical comparison of alternative design solutions in terms of assembly algorithms, reservation strategies and QoS oriented routing
Performance evaluation of an interference based admission control scheme in T/CDMA systems with voice and data users
No full textThis paper analyzes the behavior of two time-code division architectures serving voice and data applications on the uplink of a cellular system. Both solutions attribute speech users one code over a time slot, whereas data users are granted several codes over the same time slot or a single code over several time slots. Call admission control is performed by a channel assignment algorithm which dynamically attributes resources if specified levels of transmission quality are met. The blocking probability of the two classes of users is determined, and it is demonstrated that the multicode T/CDMA approach performs better than the multislot solution and than a pure CDMA system
Efficient algorithms for the assignment of OVSF codes in wideband CDMA
No full textThis paper proposes some novel techniques to accommodate users with different transmission rate requirements in a CDMA system which employs orthogonal variable spreading factor codes. Several static and dynamic code assignment strategies are put forth and their behavior investigated, in terms of call blocking probability and number of required call reassignments. Their efficiency in dealing with various traffic loads is demonstrated, quantitatively showing the superior performance of our dynamic scheme with respect to a so-called "optimal" code assignment strategy recently presented in the literature.This paper proposes some novel techniques to accommodate users with different transmission rate requirements in a CDMA system which employs orthogonal variable spreading factor codes. Several static and dynamic code assignment strategies are put forth and their behavior investigated, in terms of call blocking probability and number of required call reassignments. Their efficiency in dealing with various traffic loads is demonstrated, quantitatively showing the superior performance of our dynamic scheme with respect to a so-called "optimal" code assignment strategy recently presented in literature
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