Optimal power control in Cognitive MIMO systems with limited feedback

In this paper, the problem of optimal power allocation in Cognitive Radio (CR) Multiple Input Multiple Output (MIMO) systems is treated. The focus is on providing limited feedback solutions aiming at maximizing the secondary system rate subject to a constraint on the average interference caused to primary communication. The limited feedback solutions are obtained by reducing the information available at secondary transmitter (STx) for the link between STx and the secondary receiver (SRx) as well as by limiting the level of available information at STx that corresponds to the link between the STx and the primary receiver PRx. Monte Carlo simulation results are given that allow to quanitfy the performance achieved by the proposed algorithms

On Fixed Beamforming in Sectored mmWave Ultra Dense Networks at 73GHz

We investigate the use of fixed analogue transmit beamforming for downlink communication in millimetre-wave (mmWave) band ultra-dense networks (UDNs) at 73GHz. Our simulation study is based on 3D radiation patterns using a real design of large planar antenna arrays with different horizontal beamwidths and full characterisation of interference. The effects of network densification are captured through different ratios of the number of access points (APs) to the number of users. We quantify the system\u27s performance by evaluating outage and achievable rate. The results show that users with rates around the mean benefit more from the densification than from narrowing the beamwidth, but for users with low rates, narrow beams also provide a significant increase in throughput

Optimal Power Allocation for Energy Recycling Assisted Cooperative Communications

We investigate the problem of optimal power allocation for energy recycling cooperative communications systems, employing full duplex relays, based on the criterion of maximizing the rate, or equivalently the Signal to Noise Ratio (SNR), of the system. A system model is investigated where each time slot is split into an information transmission phase, during which the Source (S) transmits information to the destination (D) and a full-duplex Relay (R), and an energy harvesting phase. During the energy harvesting phase, R relays information to D, while concurrently it performs energy harvesting, exploiting a signal transmitted by S and energy recycling, exploiting its own transmission. For this system model, we formulate a rate/SNR maximization problem, in order to compute the optimal source power levels for both information transfer and energy transfer phases. The cost function of this optimization problem is then substituted by a sharp approximation, which allows for obtaining an analytically tractable power allocation. The performance of the resulting power allocation is then assessed by means of Monte Carlo simulations, and it is found that it outperforms existing solutions. It is therefore shown that our proposed solution can contribute towards increasing the range of IoT networks

Coordinated Shared Spectrum Precoding with Distributed CSIT

In this paper, the operation of a Licensed Shared Access (LSA) system is investigated, considering downlink communication. The system comprises of a Multiple-Input-Single-Output (MISO) incumbent transmitter (TX) - receiver (RX) pair, which offers a spectrum sharing opportunity to a MISO licensee TX-RX pair. Our main contribution is the design of a coordinated transmission scheme, inspired by the underlay Cognitive Radio (CR) approach, with the aim of maximizing the average rate of the licensee, subject to an average rate constraint for the incumbent. In contrast to most prior works on underlay CR, the coordination of the two TXs takes place under a realistic Channel State Information (CSI) scenario, where each TX has sole access to the instantaneous direct channel of its served terminal. Such a CSI knowledge setting brings about a formulation based on the theory of Team Decisions, whereby the TXs aim at optimizing a common objective given the same constraint set, on the basis of individual channel information. Consequently, a novel set of applicable precoding schemes is proposed. Relying on statistical coordination criteria, the two TXs cooperate in the lack of any instantaneous CSI exchange. We verify by simulations that our novel coordinated precoding scheme outperforms the standard underlay CR approach

Joint Sensing and Reception Design of SIMO Hybrid Cognitive Radio Systems

In this paper, the problem of joint design of Spectrum Sensing (SS) and receive beamforming (BF), with reference to a Cognitive Radio (CR) system, is considered. The aim of the proposed design is the maximization of the achievable average uplink rate of a Secondary User (SU), subject to an outage-based Quality-of-Service (QoS) constraint for primary communication. A hybrid CR system approach is studied, according to which, the system either operates as an interweave (i.e., opportunistic) or as an underlay (i.e., spectrum sharing) CR system, based on SS results. A realistic Channel State Information (CSI) framework is assumed, according to which, the direct channel links are known by the multiple antenna receivers (RXs), while, merely statistical (covariance) information is available for the interference links. A new, closed form approximation is derived for the outage probability of primary communication, and the problem of rate-optimal selection of SS parameters and receive beamformers is addressed for hybrid, interweave and underlay CR systems. It is proven that our proposed system design outperforms both underlay and interweave CR systems for a range of system scenarios

Exploring the Simultaneous Effect of Total Ion Concentration and K:Ca:Mg Ratio of the Nutrient Solution on the Growth and Nutritional Value of Hydroponically Grown Cichorium spinosum L.

Nutrient-efficient plants and agricultural systems could tackle issues resulting from conventional agriculture. Spiny chicory (Cichorium spinosum L.), a very adaptive, wild edible vegetable, is gaining commercial interest as a functional food. Floating-raft hydroponics is a method commonly used for the commercial cultivation of leafy vegetables due to numerous advantages compared to soil cultivation. In this paper, the simultaneous effects of different potassium, calcium and magnesium ratios and different electrical conductivity (EC) levels on the growth and mineral composition of hydroponically grown C. spinosum were investigated. Four nutrient solutions (NS) were compared, two NS with low EC (L, 2.4 dS/m) and two with high EC (H, 3.6 dS/m) with K:Ca:Mg ratios of either 50:40:10 or 40:50:10. The results showed no interactions between the two factors. No significant effects were observed on the fresh and dry weight, leaf number and leaf area. High EC levels increased the K content and decreased the Mn and Zn content in the leaf tissues. The 40:50:10 ratio led to increased Ca content in plant tissues. The Nitrate-N was only affected by the EC level and was increased under H conditions, whereas the total-N was not affected

Energy efficient power allocation for carrier aggregation enabled communications systems

The Energy Efficiency (EE) of Carrier Aggregation (CA) enabled communications systems is studied. In more detail, the problem of the optimal power allocation for CA enabled systems exploiting multiple Parallel Frequency Bands (PFBs) is addressed based on an EE maximization criterion. Both the case of full Channel State Information at the Transmitter (CSIT) as well as the case of quantized CSIT are studied and novel EE-optimal power allocation algorithms are derived. The derived algorithms are used in order to investigate the relation between the system's EE and the system design parameters, e.g. The number of PFBs, the number of feedback bits and the fading conditions. Focusing on the problem of optimal feedback allocation, it is shown by means of simulations that the optimal allocation of feedback to the PFBs is related to the fading conditions. Moreover, focusing on the problem of the selection of the number of PFBs, it becomes evident that the optimal selection of the number of PFBs is strongly related to the number of available feedback bits. Thereby, the interplay between EE-optimal feedback and power allocation design and system parameters is explored. 2016 IEEE.Scopu

Current situation of greenhouse vegetable production in Greece

The total greenhouse area in Greece amounts to about 5,600 ha, which corresponds to approximately 0.12% of the total cultivated area of the country. Of this area, 92% (5,200 ha) is used for vegetable production and only 8% (400 ha) is occupied by ornamental crops. Nearly 93% of the total greenhouse area of Greece is plastic-covered but nearly 96% of the greenhouses used for vegetables in Greece are plastic-covered. Glasshouses are used mainly in floriculture. The main vegetable crops in the Greek greenhouses are tomato and cucumber followed by pepper. Crete is the leading region of Greece in greenhouse production, followed by Peloponnese, Macedonia, Thessaly, Central Greece, Epirus and Aegean Islands. A significant proportion of the greenhouse area used for vegetables is occupied by high tunnels. Low tunnels are used to a large extent too, particularly for early melon, watermelon and strawberry production. Only a minor percentage (about 17%) of the greenhouse area used for vegetable production is heated in Greece. The level of automation in the greenhouses used for vegetable production in Greece is unsatisfactory. Computer controlled automation systems are only exceptionally used in greenhouse vegetable production. The fuel cost for greenhouse heating is relatively high in Greece and, therefore, most vegetable greenhouses are not heated. However, heating in the winter is necessary to attain proper temperature levels for high yield and good quality products. Currently, soilless culture in Greece occupies approximately 180 ha, which is nearly 3.3% of the total greenhouse area. Soil solarization and soilless culture in combination with grafting seem currently the safest and most effective practices to overcome the problem of soil-borne pathogens in intensively cultivated greenhouses in Greece