1,721,050 research outputs found
Coverage analysis for 2D/3D millimeter wave peer-to-peer networks
Full text linkThis paper presents a theoretical analysis for estimating the coverage probability in two-dimensional (2D) and three-dimensional (3D) peer-to-peer (P2P) millimeter-wave (mmWave) wireless networks. The analysis is carried out adopting suitable link state models and realistic propagation conditions, involving path-loss attenuation, angular dispersion, mid- and small-scale fading, which comply with recent channel measurements. The presented framework accounts in detail for the actual shape of the transmitting/receiving antenna patterns and for the spatial statistic that describes the node location, by considering the widely adopted Poisson point process, the uniform distribution, and the random waypoint mobility model. Analytical expressions for the statistic of the received power and simple integral formulas for the coverage probability in the presence of interference and noise are derived. The accuracy of the obtained estimations and of the introduced approximations is checked by independent Monte Carlo validations. As possible applications in the 3D mmWave context, the conceived mathematical theory is used to discuss the impact of the interference model on the reliability of the noise-limited approximation, and to estimate the average link capacity of an interfered P2P communication
Segmented Framed Slotted Aloha (SFSA) with Capture and Interference Cancellation
No full textThis paper investigates the throughput of a Framed Slotted Aloha (FSA) random access scheme, called Segmented FSA (SFSA), in which each packet is encoded and subdivided into segments before the transmission, and where Interference Cancellation (IC) is adopted to improve the success probability in case of collision between segments. The overall system performance is estimated by considering a decoding criterion based on the average information rate that is experienced during each communication. This criterion, which enables to properly consider the capture effect in the presence of interference, noise, and fading, is compared to the classic packet erasure channel model, with the aim of identifying the reliability of the two decoding approaches in different network scenarios. The final purpose of the presented study is to discuss the benefits of the interference diversity mechanism that is triggered by the combination of segmentation and IC in a capture channel
Low-complexity bound on irregular LDPC belief-propagation decoding thresholds using a Gaussian approximation
Full text linkSince irregular low-density parity-check (LDPC) codes are known to perform better than regular ones, and to exhibit, like them, the so-called ‘threshold phenomenon’, this Letter investigates a low-complexity upper bound on belief-propagation decoding thresholds for this class of codes on memoryless binary input additive white Gaussian noise channels, with sum-product decoding. A simplified analysis of the belief-propagation decoding algorithm is used, i.e. consider a Gaussian approximation for message densities under density evolution, and a simple algorithmic method, defined recently, to estimate the decoding thresholds for regular and irregular LDPC codes
Design of a Simple Feeding Network for 5G Multidirectional Antennas
Full text linkMultidirectional antennas are one of the enabling technologies for the widespread diffusion of intelligent vehicles, which are expected to fill smart cities in the near future characterized by the fifth generation cellular system (5G). In this context, this paper proposes a simple and versatile design procedure for a feeding network that realizes the beam steering of linear antenna arrays. The developed procedure is intended for a feedline, which must meet some requirements typical in a 5G scenario, such as, for example, easy mass production, low cost, easy integration with other system components and compactness. Precisely, a Blass matrix using the microstrip technology and identical branch line directional couplers is implemented so that the multidirectional antenna system can be entirely printed on a compact and cheap printed circuit board (PCB). However, when the coupling value is fixed in advance some pointing directions may be not realizable. So, this paper proposes an algorithm, which evaluates a desired number of beams in such a way to have a simple design procedure of a feeding network for a multidirectional linear antenna array. The effectiveness of the developed solution is validated by numerical result
Recent results on the implementation of a burst error and burst erasure channel emulator using an FPGA architecture
Full text linkThe behaviour of a transmission channel may be simulated using the performance abilities of current generation multiprocessing hardware, namely, a multicore Central Processing Unit (CPU), a general purpose Graphics Processing Unit (GPU), or a Field Programmable Gate Array (FPGA). These were investigated by Cullinan et al. in a recent paper (published in 2012) where these three devices capabilities were compared to determine which device would be best suited towards which specific task. In particular, it was shown that, for the application which is objective of our work (i.e., for a transmission channel simulation), the FPGA is 26.67 times faster than the GPU and 10.76 times faster than the CPU. Motivated by these results, in this paper we propose and present a direct hardware emulation. In particular, a Cyclone II FPGA architecture is implemented to simulate a burst error channel behaviour, in which errors are clustered together, and a burst erasure channel behaviour, in which the erasures are clustered together. The results presented in the paper are valid for any FPGA architecture that may be considered for this scope
The Use of Ceiling Fans in Reverse-Flow Mode for Comfort Cooling: Physiological Aspects and Relationship with International Standards
No full textIn a warming planet, the energy demand for space cooling is constantly increasing. Air movement can be considered an energy efficient mean to provide thermal comfort in warm season. Ceiling fans are among the most adopted sources of air movement in buildings, and they are widely used in many countries. In warm environmental conditions, ceiling fans usually blow air from the ceiling to the occupants. While the heat generated from a human body does not vary, this forced convection accelerates the heat transfer between the parts of the body skin hit by the air flow and the surrounding thermal environment. The elevated air speed increases the convective heat transfer coefficients and the rate of evaporation from those parts of the skin. In cold seasons, ceiling fans are often used in reverse-flow mode for destratification purposes. In this case, the air speed is usually much lower than the direct flow, but considerably more uniform in the room. Some manufacturing companies lately raised their interest in analyzing the reverse-flow as a means to provide thermal comfort also in summer, providing a gentler airflow that might be less likely to cause draft for the users. Hence, the aim of this study is to investigate the extent to which the reverse-flow could be used also for cooling in warm conditions. CFD simulations were used to evaluate (i) the air speed field generated using direct and reverse flow (magnitude and spatial distribution), and (ii) how the heat transfer coefficients on the different body parts vary in both cases. The former enables to provide thermo-physiological insights, while the latter a comparison with air speed values reported in standards such as ASHRAE55. The results indicate that, although more evenly distributed within the room, the generated air speed with the reverse flow is considerably low. Hence, from a physiological point of view, it would not be sufficient to provide comfort cooling. Further work with human participants will investigate whether this low speed might generate a subjective perception of comfort cooling
Design of source-matched blockwise decoded convolutional codesfor mobile communications
No full textIn this paper blockwise decoded convolutional encoding is used and evaluated for the design of an error protection coding scheme matched with the characteristics of a variable-rate speech coder's output bit-stream. The performance is evaluated for a symmetrical, interference limited, cellular system. Both microcellular and macrocellular propagation models are used. Different reuse factors are taken into consideratio
Impact of Header on Coded Slotted Aloha with Capture
No full textAmong the recently proposed non-orthogonal multiple access techniques, the Coded Slotted Aloha (CSA) scheme has been identified as one of the most efficient ones. This scheme relies on the subdivision of a packet into segments and of a slot into slices, in order to enable the transmission of different segments in different slices. With respect to SA, the CSA implementation is more sophisticated, since the header of each segment must contain proper pointers specifying the slices where the other segments of that packet lie. Purpose of this paper is to investigate the impact of these pointers on the CSA throughput by properly considering the capture effect at the receiver. To this aim, a capture analysis accounting for the modulation and the header coding rate in the presence of Rayleigh fading is developed. The numerical results, which also involve a realistic millimeter-wave channel, show that the beneficial interference diversity effect introduced by the segmentation process is not significantly reduced by the overhead due to the pointers, thus confirming the practical usefulness of the CSA scheme
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