Selectivity threshold between mono-carrier and multi-carrier solutions

This paper compares the capacity obtained either with a mono-carrier waveform or with a multi-carrier waveform with respect to the channel selectivity. Analysis is given considering the Peak- to Average-Power Ratio of the retained solutions. A new mixed approach is proposed. It is based on a selectivity threshold definition showing where we should use a mono-carrier approach and where the multi-carriers approach gives a higher capacity.Cet article présente une comparaison des capacités obtenues avec une forme d’onde mono-porteuse et une forme d’onde multi-porteuses en fonction de la sélectivité du canal de transmission. L’analyse est menée en considérant avec attention le facteur de crête de la forme d’onde choisie. Une approche mixte avec un seuil de basculement d’une forme d’onde à l’autre est proposée

OFDM and CDMA, unified approach and channel-matched spreading codes generation algorithm

In this paper TDMA, CDMA, MC-CDMA and OFDM are presented through an unified formalism. The cyclic prefix insertion is extended to all approaches presented and not only restricted to OFDM. Many fundamental results are highlighted. It is for example shown that if we are looking for a family of orthogonal spreading sequences being yet orthogonal after a one chip delay then we have not another choice than OFDM. Different kind of receivers, involving a same « channel » matrix, are presented : OFDM receiver, Rake receiver and MMSE receiver. All these receivers involve a same channel matrix representing the effect of the propagation channel, the cyclic prefix insertion and its suppression. Finally an algorithm for generating spreading sequences matched to a given propagation channel is introduced. Spreading sequences generated having unequal transmission properties, a power and modulation allocation algorithm is introduced for them. Performances obtained are then very close to those obtained through the OFDM approach.Cet article s'appuie sur un formalisme matriciel qui permet de présenter les approches TDMA, CDMA, MC-CDMA et OFDM de manière unifiée. La formalisation généralise l'emploi du préfixe cyclique, initialement réservé à l'OFDM, à toutes ces approches. Elle permet de mettre en lumière plusieurs résultats fondamentaux de manière très rapide. On montre ainsi que si l'on cherche des séquences d'étalement CDMA qui sont orthogonales et dont l'orthogonalité résiste à une imprécision temporelle d'un élément de la séquence alors, obligatoirement, ces séquences sont les sinusoïdes complexes utilisées en OFDM. On développe ensuite les différentes formes possibles des récepteurs. Le récepteur MMSE, le récepteur RAKE et le récepteur classiquement utilisé dans le cas de l'OFDM sont exprimés en faisant intervenir une même matrice « canal » qui intègre à elle seule l'insertion du préfixe cyclique, la convolution par la réponse impulsionnelle du canal et la suppression du préfixe cyclique. Enfin, dans le cas d'un canal connu, on introduit une méthode de conception de séquences d'étalement adaptées au canal. Les séquences de cette famille affichant des performances de transmission inégales, on propose alors de leur appliquer, comme on le fait pour l'OFDM, un algorithme d'allocation de puissances d'émission et de schémas de modulation. On montre alors que les performances de transmission obtenues sont comparables à celles de l'OFDM

Teores de água no solo e eficácia do herbicida glyphosate no controle de euphorbia heterophylla.

Objetivo-se avaliar a eficácia do herbicida glyphosate no controle de Euphorbia heterophylla se desenvolvendo em solo com diferentes teores de água e determinar qual o menor teor de água do solo que não prejudica a ação desse herbicida no controle desta planta daninha. O delineamento utilizado foi o de blocos casualizados em esquema fatorial 6 x 5, sendo, seis intervalos entre a última irrigação e a aplicação do herbicida (0, 6, 12, 24, 48 e 72 horas) e de cinco doses de glyphosate (0, 180, 360, 720, e 1.080 g ha-1 de equivalente ácido). Quando as plantas atingiram estádio de três pares de folhas foi aplicado 10 mm de chuva simulada, conforme tratamento previsto. Ao término do período de simulação de chuva, aplicou-se o herbicida. Aos 7, 20, 34 e 41 dias após a aplicação (DAA) foi avaliado o controle e, aos 41 DAA foi avaliada a massa seca de raízes e da parte aérea. Após a análise dos dados, verificou-se que a partir da dose de 720 g ha-1 de glyphosate obteve-se controle satisfatório de E. heterophylla, independente do intervalo entre a última irrigação e a aplicação do herbicida. Pulverizações de 360 g ha-1 de glyphosate a intervalos menores que 48 horas entre a última irrigação e sua aplicação e em solo com teor de água maior que 0,09 cm3 cm-3 não prejudicaram a eficácia do herbicida. Teores de água no solo acima de 0,14 cm3 cm-3 não prejudicaram a eficácia do glyphosate, aplicado em dose superior a 180 g ha-1, no controle de E. heterophylla

Effects of peeling methods on the quality of cubiu fruits

Cubiu (Solanum sessiliflorum Dunal) is an Amazonian Basin native fruit. Its importance comes from its high contents of pectin. Currently, processing technologies are necessary for the substitution of the traditional system (small crops and small-scale processing) for a larger scale system and thus increase the use of biodiversity and promote the implementation of Local Productive Arrangements of agribusiness in the Amazon. This research aims to evaluate the methods of peeling cubiu. Ripe fruits were divided into lots (150 each) and subjected to the following treatments: immersion in 2.5% NaOH boiling solution for 5 minutes, exposure to water vapor, and immersion in water at 96 ºC for 5, 10, 15 and 20 minutes. The peel released during heat treatment and immediately removed under running tap water. In the control treatment, the fruits were manually peeled (unheated) with a stainless steel knife. The treatments were evaluated for completeness and ease of peeling, tissue integrity, texture, and peroxidase activity. The immersion in 2.5% NaOH boiling solution (5 minutes) stood out as the best treatment since it inhibited the enzymatic browning and intensified the natural yellow color of the cubiu fruit and easily and fully peeled the whole fruit more rapidly without damaging its tissues. This treatment was chosen as the most advantageous because it can promote simultaneous peeling and bleaching. Therefore, it is recommended for cubiu industrial processing

Joint Transmit Diversity And Downlink Beamforming By Using A Minimum Ber Criterion

In this work, we propose a novel criterion to find the optimum precoder for joint transmit diversity and downlink beamforming. This precoder is an extension of the purely spatial downlink beamforming and can be seen as a transformation that transforms K real antennas into L virtual antennas, with L ≤ K. The proposed criterion is based on the minimization of the received BER and extends the previous technique [1] (Eigen-Beamforming) to any type of channel distribution, not only Rayleigh. Simulation results show that the proposed technique is equivalent to Eigen-Beamforming for Rayleigh channel, but outperforms the latter for Rician channels, providing substantial improvement. This makes the proposed technique an attractive solution for the general application, where the channel type is not known a priori. © 2006 IEEE.231236Zhou, S., Giannakis, G.B., Optimal Transmitter Eigen-Beamforming and Space-Time Block Coding Based on Channel Correlations (2003) IEEE Transactions on Information Theory, 49 (7), pp. 1673-1690. , JulyAlamouti, S.M., A simple transmit diversity technique for wireless communications (1998) IEEE Journal on Select Areas in Communications, 16 (8), pp. 1451-1458. , OctoberTarokh, V., Seshadri, N., Calderbank, A.R., Space-time codes for high data rate wireless communications: Performance criterion and code construction (1998) IEEE Transactions on Information Theory, 44 (2), pp. 744-765. , MarchTarokh, V., Jafarkhani, H., Calderbank, A.R., Space-Time Block Codes from Orthogonal Designs (1999) IEEE Transactions on Information Theory, 45 (5), pp. 1456-1467. , JulySeshadri, N., Winters, J.H., Two signaling schemes for improving the error performance of frequency-division-duplex (FDD) transmissions systems using transmitter antenna diversity (1993) Proc. IEEE Vehicular Technology Conference, pp. 508-511. , Secausus, USA, MayLiberti, J., Rappaport, T.S., (1999) Smart Antennas for Wireless Communications, , 1st ed. Prentice HallNarula, A., Lopez, M.J., Trott, M.D., Wornell, G.W., Efficient Use of Side Information in Multiple-Antenna Data Transmission over Fading Channels (1998) IEEE Journal On Selected Areas In Communications, 16 (8), pp. 1423-1436. , OctoberCavers, J.K., Optimized use of diversity modes in transmitter diversity systems (1999) Proc. IEEE 49th Vehicular Technology Conference (VTC'99), 3, pp. 1768-1773. , Houston, USA, 05-16 MayYacoub, M.D., (1993) Foundations of mobile radio engineering, , Boca Raton: CRC PressProakis, J.G., (1989) Digital Communications, , 2nd ed. McGraw-HillHaykin, S., (1996) Adaptive Filter Theory, , 3rd ed. Prentice HallShiu, D.-S., Foschini, G.J., Gans, M.J., Kahn, J.M., Fading correlation and its effects on the capacity of multi-element antenna systems (2000) IEEE Transactions on Communications, 48 (3), pp. 502-513. , Marc

Zero-outage Strategy For Multi-antenna Broadcast Channels With Limited Feedback

Transmission techniques for the wireless multi-antenna broadcast channel often require that the receivers feed back their channel state information (CSI) to the transmitter. In this paper, we propose a limited feedback method to approximate zero-forcing beamforming. Each user feeds back quantized information about channel direction and a deterministic lower bound on its signal-to-interference-plus-noise ratio (SINR), which require no more than an integer and a real number. With this information, the Base Station performs user scheduling, beamforming and rate adaptation. In this method, the information from both receiver and transmitter sides are taken into account to arrive at a tight lower bound on the supported rate of each user. Since a lower bound on the SINR is fed back, the proposed method avoids outage. We discuss the feedback load of the method, and show numerical results of the relationship between sum-rate and feedback load, SNR and number of users, as well as a comparison with similar methods. ©2008 IEEE.8185Tse, D., Viswanath, P., (2005) Fundamentals of Wireless Communications, , Cambridge University Press, first editionCosta, M., Writing on dirty paper (corresp.) (1983) Information Theory, IEEE Transactions on, 29 (3), pp. 439-441. , MayViswanath, P., Tse, D.N.C., Laroia, R., Opportunistic beamforming using dumb antennas (2002) Information Theory, IEEE Transactions on, 48 (6), pp. 1277-1294. , JunSharif, M., Hassibi, B., On the capacity of MIMO broadcast channels with partial side information (2005) Information Theory, IEEE Transactions on, 51 (2), pp. 506-522. , FebKountouris, M., Gesbert, D., Pittman, L., Transmit correlation-aided opportunistic beamforming and scheduling using reciprocal channel information in multiuser mimo scheduling (2006) Proc. EUSIPCO Conference, Florence, ItalyYoo, T., Jindal, N., Goldsmith, A., Multi-antenna broadcast channels with limited feedback and user selection (2007) IEEE Journal on Selected Areas in Communications, 25, pp. 1478-1491. , SeptemberKountouris, M., De Francisco, R., Gesbert, D., Slock, D.T.M., Salzer, T., Efficient metrics for scheduling in MIMO broadcast channels with limited feedback (2007) ICASSP 2007, 3, pp. III109-III112. , AprilLove, D.J., Heath Jr., R.W., Strohmer, T., Grassmannian beamforming for multiple-input multiple-output wireless systems (2003) Information Theory, IEEE Transactions, 49 (10), pp. 2735-2747. , on, OctYoo, T., Goldsmith, A., "On the optimality of multiantenna broadcast scheduling using zero-forcing beamforming (2006) Selected Areas in Communications, IEEE Journal on, 24 (3), pp. 528-541. , Marc