Base transceiver station

Résumé

La base transceiver station (en français : station de transmission de base ou station émettrice-réceptrice de base) (BTS) est un des éléments de base du système cellulaire de téléphonie mobile GSM. Elle est appelée plus communément « antenne-relais GSM » (à différencier de l'antenne-relais UMTS, de type Node B). Schématiquement, cette cellule (base du maillage d'un réseau de téléphonie mobile) est composée essentiellement d'un élément d'interface avec la station la contrôlant (la BSC), d'un ou plusieurs émetteurs et récepteurs (transceiver, TRX) et d'une à trois antennes. Fonction Elle est chargée de la liaison radio avec les stations mobiles. Les rôles principaux d'une BTS sont :

l'activation et la désactivation d'un canal radio ;
le multiplexage temporel (accès multiple à répartition dans le temps ou TDMA) et la gestion des sauts de fréquences (ėtalement de spectre par saut de fréquence ou frequency hopping) ;
le chiffrement du contenu à transmettre (pour prése

Source officielle

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Schemes and architectures for wireless ad hoc networks and cooperative communication

Tarik Tabet

The focus of this thesis is on the study of decentralized wireless multi-hop networks. We are particularly interested in establishing bounds on the traffic-carrying capabilities of wireless ad hoc networks and conditions on the scalability of such networks with node mobility. This theoretical investigation brings forward challenges on the design of such networks. This leads to a second part of this thesis that considers the feasibility and the design of physical layer architectures and schemes for decentralized wireless multi-hop networks. In the first part of this thesis, bounds on the capacity of wireless ad hoc networks with two types of non-uniform traffic patterns are established. We focus on the impact of traffic patterns where local communications predominate and show the improvement in terms of per user-capacity over ad hoc networks with unbounded average communication distances. We then study the capacity of hybrid wireless networks, where long-distance relaying is performed by a fixed overlay network of base-stations. We investigate the scaling of capacity versus the number of nodes and the density of base-stations in the area of the network. It is shown that the gain in performance is mainly due to the reduction in the mean number of hops from source to destination. Then, we investigate the impact of mobility on the ad hoc network capacity. We propose a set of necessary and sufficient conditions under which the long-term averaged throughput in an ad hoc network can remain constant as the number of nodes increases. The main idea is to use a connectivity graph that does not represent the actual physical network, but rather the available communication resources. This graph also allows to translate the problem of maximizing the throughput in ad hoc networks to the multi-commodity flow problem and directly apply related results. In contrast to these macroscopic studies, in the second part we focus on a microscopic analysis of ad hoc wireless networks. We are interested in characterizing the performance of decentralized multiple-access and retransmission schemes for multi-hop wireless networks with the goal of drawing conclusions on cross-layer design. We investigate different transmission strategies in order to assess the tradeoff between spatial density of communications and the range of each transmission. We present tools for characterizing the spatial throughput as a function of topological parameters (e.g node population density) and system parameters (propagation, bandwith etc). The results of this work also show that coding and retransmissions provide means of reliable communication coupled with a completely decentralized multiple-access strategy. Finally, an efficient protocol for the delay-limited fading Automatic Retransmission reQuest (ARQ) single relay channel is considered for cooperative communications. The proposed protocol exploits two kinds of diversity: (i) space diversity available through the cooperative (relay) terminal, which retransmits the source's signals, (ii) ARQ diversity obtained by leveraging the retransmission delay to enhance the reliability. The performance characterization is in terms of the achievable diversity, multiplexing gain and delay tradeoff for a high signal-to-noise ratio (SNR) regime. Then, by letting the source's power level vary over the retransmission rounds, we show the benefits of power control on the diversity.

EPFL2007

Chargement

In this work, a complete passive UHF RFID system for capacitive sensing applications is developed to be used in food quality monitoring and supply chain management. All the components of the RFID system including the base station, the base station antenna, the tag chip, and the tag antenna is designed, implemented, and tested. The operation of all the components are shown by measurements and their performance is characterized. The remote powering subsystem consists of the tag antenna and the rectifier. Measurement results showed a maximum power conversion efficiency of 65% for the antenna-rectifier pair operated at 866 MHz. The rectifier is a three-stage, differential rectifier with threshold compensation, that offers high power conversion efficiency. The tag antenna is an inductively-coupled, meandered dipole that is impedance matched to the tag chip. The dimensions of the tag antenna are 83 x 20mm, and the measured far-field gain of the tag antenna is 1.2 dB. A supply generation subsystem is implemented in order to generate a stable, regulated supply voltage for high-precision sensor interfaces. The supply generation subsystem consists of the low drop-out (LDO) voltage regulator, a bandgap voltage reference, and a supply insensitive current source. The power supply rejection ratio (PSRR) of the LDO is greater than 55 dB. Data communication is realized by backscatter modulation because it offers lower circuit complexity and low power consumption on the tag side. The scattering properties of the tag antenna and the backscatter modulation is theoretically analyzed and an optimum antenna impedance for backscatter communication is calculated. The scattering properties of the tag antenna are characterized by measurements in an anechoic chamber. One of the innovations of this work is the novel pulse-width modulation based backscatter communication, in which the information is encoded in the duty-cycle of the signal. This method decreases the circuit complexity and power consumption on the tag side when used with phase-locked loop (PLL) based sensor interfaces. A monostatic base station with a homodyne receiver is implemented for the passive RFID system. A microstrip patch antenna is custom designed and fabricated for the base station. The input return loss of the base station antenna is measured to be -20 dB, whereas its measured far-field gain is 3.6 dB. An isolator that is based on a directional coupler with an intentional mismatch at the unused port is designed and fabricated for the base station. The measured directivity of the isolator is 50.5 dB. A PLL-based capacitive sensor interface is implemented for differential sensors. The integration of such a low-power circuit in an RFID tag is the main innovation of this work. The differential nature of this sensor interface makes it immune to supply voltage variations. The sensor interface can work with supply voltages as low as 0.3 V. The power consumption of the interface is 300 nW, for 0.3 V supply voltage. The resolution of the sensor interface is determined to be 6.4 bit by post-layout simulations. Two tag architectures for two different approaches for sensor interfaces are proposed: the generic passive UHF RFID platform for sensing applications and the SimpleTag - a novel, low-power UHF RFID tag for differential printed capacitive sensors. The circuits are implemented in UMC 0.18 um CMOS technology.

EPFL2015

Chargement

In this paper, we address the resource allocation problem of device-to-device (D2D) communications underlaying orthogonal frequency division multiple access (OFDMA) based cellular systems by exploiting the efficiency that comes from an ensemble of graph theory and Knapsack problem. It is possible to construct the conflict graph of the D2D pairs by finding the maximal independent sets. Then, we use those independent sets as inputs to Knapsack problem iteratively in order to find D2D groups which allocate the subchannels. In Knapsack problem, we consider a maximum interference level that the base station is exposed at each subchannel. We illustrate that the proposed resource allocation method significantly outperforms graph coloring in terms of average data rate for the high number of underlaying D2D pairs in cellular systems.

IEEE2018

Chargement