A Random Access Protocol for Pilot Allocation in Crowded Massive MIMO Systems

The Massive MIMO (multiple-input multiple-output) technology has great potential to manage the rapid growth of wireless data traffic. Massive MIMO achieves tremendous spectral efficiency by spatial multiplexing of many tens of user equipments (UEs). These gains are only achieved in practice if many more UEs can connect efficiently to the network than today. As the number of UEs increases, while each UE intermittently accesses the network, the random access functionality becomes essential to share the limited number of pilots among the UEs. In this paper, we revisit the random access problem in the Massive MIMO context and develop a reengineered protocol, termed strongest-user collision resolution (SUCRe). An accessing UE asks for a dedicated pilot by sending an uncoordinated random access pilot, with a risk that other UEs send the same pilot. The favorable propagation of Massive MIMO channels is utilized to enable distributed collision detection at each UE, thereby determining the strength of the contenders' signals and deciding to repeat the pilot if the UE judges that its signal at the receiver is the strongest. The SUCRe protocol resolves the vast majority of all pilot collisions in crowded urban scenarios and continues to admit UEs efficiently in overloaded networks.Comment: To appear in IEEE Transactions on Wireless Communications, 16 pages, 10 figures. This is reproducible research with simulation code available at https://github.com/emilbjornson/sucre-protoco

Random Access Protocols for Massive MIMO

5G wireless networks are expected to support new services with stringent requirements on data rates, latency and reliability. One novel feature is the ability to serve a dense crowd of devices, calling for radically new ways of accessing the network. This is the case in machine-type communications, but also in urban environments and hotspots. In those use cases, the high number of devices and the relatively short channel coherence interval do not allow per-device allocation of orthogonal pilot sequences. This article motivates the need for random access by the devices to pilot sequences used for channel estimation, and shows that Massive MIMO is a main enabler to achieve fast access with high data rates, and delay-tolerant access with different data rate levels. Three pilot access protocols along with data transmission protocols are described, fulfilling different requirements of 5G services

Random Pilot and Data Access in Massive MIMO for Machine-type Communications

A massive MIMO system, represented by a base station with hundreds of antennas, is capable of spatially multiplexing many devices and thus naturally suited to serve dense crowds of wireless devices in emerging applications, such as machine-type communications. Crowd scenarios pose new challenges in the pilot-based acquisition of channel state information and call for pilot access protocols that match the intermittent pattern of device activity. A joint pilot assignment and data transmission protocol based on random access is proposed in this paper for the uplink of a massive MIMO system. The protocol relies on the averaging across multiple transmission slots of the pilot collision events that result from the random access process. We derive new uplink sum rate expressions that take pilot collisions, intermittent device activity, and interference into account. Simplified bounds are obtained and used to optimize the device activation probability and pilot length. A performance analysis indicates how performance scales as a function of the number of antennas and the transmission slot duration

Desempenho de cultivares de girassol (Helianthus annuus. L.) no Estado do Rio Grande do Norte.

Este trabalho teve como objetivo avaliar o comportamento produtivo de diversas cultivares de girassol. O ensaio foi instalado no Município de Canguaretama/RN no ano agrícola de 2007( 6º22 ? S, 35º 07? W, altitude de 5m, temperatura média anual de 25 ºC O solo é classificado como latossolo amarelo de textura arenosa. A precipitação ocorrida durante a condução do ensaio foi de 904,6 mm. O delineamento experimental foi blocos ao acaso, com quatro repetições. Fez-se uma adubação utilizando-se a fórmula: 60-80-60 kg/ha mais 2 kg/ha de boro.Os materiais avaliados mostraram-se precoces, com uma média de 39 dias para atingir o florescimento inicial. Os rendimentos médios de grãos das cultivares ficaram entre 1.356 kg/ha e 2.581 kg/ha, com média geral de 1.829 kg/ha.Três cultivares apresentaram rendimentos médios de grãos acima de 2.200 kg/ha, sobressaindo-se os materiais M 734, HLA 863 e GIRA 19 e com o teor de óleo superior a 42 %

Desempenho produtivo de cultivares de girassol (Helianthus annuus L.) sob condições irrigadas no Rio Grande do Norte.

Este trabalho teve como objetivo avaliar o desempenho produtivo de cultivares de girassol em regime de irrigação. O ensaio foi conduzido na Estação Experimental da EMPARN, (Ipanguaçu,RN, 05º37? S 36º50? W , 70 m). O solo foi é um Neossolo de alta fertilidade, com adubação de 50-20-20 kg/ha + 2kg de Boro.. Utilizou-se irrigaçãoi por sulco e durante o ciclo da cultura foram aplicados 510 mm de água.. Foram avaliadas 26 cultivares, sendo 24 híbridos e 02 variedades em foi blocos ao acaso, com 04 repetições. As médias de rendimentos de grãos (aquênios) variaram de 2.110 kg/ha a 4.120 kg/ha, com média de 3.218 kg/ha. Sobressaíram-se os híbridos GRIZZLY, T 700, MG 52, NEON, HLS 03 e o HÉLIO 358, com respectivamente, 4.120 kg/ha, 4.097kg/ha, 3.705kg/ha, 3.638 kg/ha, 3.633 kg/ha e 3.610 kg/ha. Os maiores rendimentos de óleo foram obtidos com os genótipos MG 52, HÉLIO 358, HLS 03 e BRS-Gira 11, acima de 1.500kg/ha

Propagação rápida de mandioca no nordeste brasileiro.

bitstream/CPATC/19574/1/ct-45.pdfISSN 1678-1945

Improved semiclassical density matrix: taming caustics

We present a simple method to deal with caustics in the semiclassical approximation to the thermal density matrix of a particle moving on the line. For simplicity, only its diagonal elements are considered. The only ingredient we require is the knowledge of the extrema of the Euclidean action. The procedure makes use of complex trajectories, and is applied to the quartic double-well potential.Comment: 20 pages, 7 figures. Revised version, accepted for publication in Phys. Rev.