Optimizing UAV positioning and source nodes to improve FSO system performance in dual-hop networks

The work described in this paper proposes two Smart Hybrid-Automatic Repeat Request (SHARQ) schemes with incremental redundancy, that are developed for a dual-hop network of two relays implementing cooperative communication. In a dual-hop network consisting of multiple relays, one of the most challenging tasks is to determine an appropriate trade-off point between the end-to-end block-error rate (BLER) and an additional delay caused due to HARQ retransmissions in two hops. The retransmissions can either be initiated at the relay nodes or at the source node. HARQ protocol for such a network, should therefore be capable of dynamically deciding the node-of-retransmission. The SHARQ schemes proposed here are designed intelligent in a way that they take into account the presence of two relays and the benefit of using cooperative schemes. Basically the system developed here, intends to provide the combined benefits of diversity gain from cooperative schemes and the throughput improvement from SHARQ in a best possible way. This paper explicitly compares the most basic case of single relay system without HARQ and cooperation with the most advanced scenarios of cooperative communication with SHARQ schemes. It is observed that the latter of the two above scenarios results in throughput improvement of almost 4dB in terms of SNR.

In this paper, we investigate the theoretical performance analysis of opportunistic scheduling for dual-hop cognitive relay network with multiuser in the secondary system. Different from the existing work, we take the consideration of primary user's interference with opportunistic scheduling technique and theoretically derive the influence of the interference from primary transmitter for the scenario. The cumulative distribution function (CDF) of signal-to-noise ratio (SNR) is formulated and the exact close-form expression of the cognitive relay network outage probability is derived. After calculating the asymptotic outage probability in high SNR regime and asymptotic error probability, we provide an adaptive power allocation scheme in the secondary system to optimize the capacity of system. It is confirmed that the opportunistic scheduling technique for multiuser has a positive influence on the performance of cognitive networks. Moreover, the adaptive power allocation can also promote system performance. Finally, numerical simulations are provided to support and directly reflect the correctness of our analytic results.

Cooperative communication has been widely investigated to improve performance of wireless networks. In cooperative wireless system, various MIMO scheme such as OSTBC, CDD and V-BLAST can be easily applied and obtain diversity or multiplexing gain. These schemes cannot obtain diversity and multiplexing gain simultaneously. To guarantee both high throughput and reliable transmission, hybrid STBC can be applied. However, this typical hybrid scheme requires complex structure at the destination and generates a rate loss according to increasing the number of transmit antennas. Moreover, in cooperative wireless system, hybrid STBC is inflexible to choose relays because relays require specific STBC encoder. Therefore, in this paper, we propose the cooperative hybrid CDD scheme which can be easily applied with arbitrary number of relays without any rate loss. Furthermore, a modification is not necessary at the destination although the number of relays is changed.

In this paper, we investigate the secrecy performance of multiuser dual-hop relay networks where a base station (BS) communicates with multiple legitimate users via the assistance of a trustful regenerative relay in the presence of multiple eavesdroppers. In particular, the maximal ratio transmission (MRT) scheme is exploited at the BS and a threshold-based multiuser scheduling scheme is employed over the legitimate users, while concerning the imperfect decoding at the regenerative relay. Furthermore, we consider the passive eavesdropper scenario and non-colluding eavesdropping mode. In order to quantify the secrecy performance of the considered system, the new exact closed-form expression for the secrecy outage probability is derived. In addition, conducive and simple high SNR approximation for the secrecy outage probability is also presented, which capacitates further insights into the impact of key system parameters on secrecy performance. Numerical results are provided to verify our theoretical analyses and illustrate the impact of key system parameters on the secrecy outage performance.

Many wireless local area network (WLAN) performance estimations are done with the assumption of uniformly distributed stations (STAs). In practice, on the contrary STAs are distributed unevenly among access points (APs), causing hot-spots and under utilized APs in a wireless network. Considering a WLAN is made up of multiple APs, having some APs carrying excessive loads (i.e. hot-spots) degrades both the considered APs as well as the overall network performance. The system performance can be improved by associating incoming STAs effectively throughout the network, in a sense to balance the network load evenly between APs and relieve the hot-spot congestion. Currently employed user association method in IEEE 802.11 WLANs considers only the received signal strength of APs at STAs, and associates STAs to the closest (in signal strength sense) AP, ignoring its load and interference value.Novel user association algorithms are required for congestion relief and network performance improvement. In this work, a new distributed association algorithm taking into consideration not only the received signal strength of the APs at STAs but also AP loadings and interference is proposed. A new AP load calculation method acknowledging the interference between STAs and APs is presented. Our simulations demonstrate that the proposed algorithm can improve the overall system throughput performance more than 50% and offers a better load distribution across the network compared to conventional association algorithm.

In this paper, we investigate the impact of hardware impairments on the outage performance and the instantaneous capacity of dual-hop decode-and-forward (DF) satellite relay networks in the presence of co-channel interference. Specifically, the exact closed-form expression for the outage probability and the analytical expression for the instantaneous capacity of the system are derived over a shadowed-Rician fading channel, which provides a fast means to evaluate the impact of hardware impairments on the system performance. Our results demonstrate that the outage floor occurs and the capacity upper bound appears when the hardware impairments exist. In addition, simulation results were provided to verify the correctness of the analytical results.

In this paper, performance of FSO system with DAPPM (A L = 16) scheme has been analysed. We find that, at relatively low turbulence, increasing the×number of amplitude levels improves the performance of the DAPPM scheme. At relatively high turbulence, performance is improved initially and then it starts degrading.

In this paper, the performance of cognitive radio networks under Resume (RR) and Restart (RS) retransmission strategies for interrupted secondary calls is investigated. System performance is analyzed and evaluated in terms of secondary users' blocking probability and mean transmission delay. For the RR strategy, a trellis-based mathematical analysis is proposed and developed for the calculation of the secondary users' mean total transmission delay. Considering that service time for secondary users is Coxian distributed, numerical results are shown to quantitatively compare the performance of the RR and RS retransmission strategies. It is found that the value of the coefficient of variation (CoV) of service time of SUs plays a major role in the system performance of cognitive radio networks under RR or RS strategies. For scenarios where the CoV of service time for SUs has values around 1, the RS strategy is preferred over the more complex RR strategy. On the contrary, as the CoV of the service time of SUs increases, the system performance improvement becomes significantly greater for the RR strategy relative to the RS strategy.

This paper studies the problem of secure dual-hop AF network in the presence of eavesdropper. We study the secrecy performance of partial relay selection with outdated channel state information (CSI). We propose a system secrecy where two sources and destination simultaneously transmit the legitimate and the jamming signal respectively. The selected relay forwards the combined signal to the legitimate receiver and the eavesdropper. We derive a closed-form expression for lower bound on the ergodic secrecy capacity (ESC) under different assumptions of the eavesdropper channel gains. We verify that the system performance is degraded as the correlation coefficient decreases. Simulation results are considered to verify the exactness of the proposed mathematical analysis.

In this paper the number of paths in a multipath routing protocol and distribution of neighbour nodes in the discovered routes are studied for networks with frequent topology changes. Specifically, we consider how the placement of neighbour nodes, which are used by the source node to reach a destination in a multipath routing protocol, affects total network power consumption. We develop an analytical model, verified by simulation, which shows that, while the network performance is affected by source node speed and route length, it also depends on the geometric arrangement of neighbour nodes around the source node. The results reveal that total network power consumption is minimized when the moving source node has six well distributed neighbour nodes, and one path to the destination via each neighbour node.

Dynamic network models are widely employed for system analysis and performance evaluation of computer and communication systems. In dynamic networks each arc is weighted with a capacity and a transit time. The former is the maximum amount of flow that can travel through the arc per unit time, the later is the time period needed for flow to travel through the arc. In this article, an additional weight operation probability, is assigned to each arc to note the capability of the arc's successful transition. The performance of dynamic networks is defined by the probability that the maximum dynamic flow from source to sink within required time horizon is no less than specified threshold. To the best of our knowledge, no existing article had considered dynamic flow and network reliability simultaneously. Based on facts that there is always a maximum dynamic flow among the temporally repeated flows and the maximum temporally repeated flow can be obtained via an equivalent minimum cost maximum flow problem, we present a pioneering algorithm to compute performance of dynamic networks by solving minimum cost maximum flow and two-terminal capacity reliability at the same time.

Physical topology is a major determinant of the system performance of optical backbone networks, and it is important to understand the relationships between physical topology features and system performance for better system design. For application in elastic optical backbone network systems, we propose a framework of correlation analysis to examine these relationships comprehensively, and we use the framework to investigate the relationships between various physical topology features and system performance. The results of numerical experiments suggest that four important physical topology features are strongly correlated with the system performance. Specifically, the average number of hops and the algebraic connectivity are strongly correlated with only the communication capacity, whereas the average path length and the geodesic distance Laplacian spectral radius are strongly correlated with both the capacity and the cost. The geodesic distance Laplacian spectral radius is a newly defined quantity that is expected to expand the possibilities of physical topology design in the future. Through combinations of these features, we classify physical topology designs and examine the relationships between the classification, real networks, and graph generation algorithms.

The hydraulic analysis of potable water is essential for acquiring an accurate understanding of the network’s operation and its associated issues, as well as for employing a scientific approach to its potential expansion, given the continuous rise in population density and urban development. The aim of the present study is to evaluate the operational performance of the water distribution network in the Muhandisin Al-Nidal neighborhood in Karbala City. The study utilized CAD Earth, Google Earth Pro, and WaterGEMS CONNECT Edition version 2 to construct a hydraulic model for simulating the behavior of the pipe network. The measurements of water flow at the source nodes were conducted using a wall-mounted ultrasonic flow meter (Eurosonic 2000). The model was calibrated at 17 connection points, encompassing pressures and flow. Pressure readings were acquired at designated points utilizing Bourdon gauges. study was examined as a steady-state analysis and during the peak period of daily consumption to assess the outcomes. The results indicated a significant reduction in pressure within the network pipes with a correlation coefficient of 0.95 and pressures ranging from 1.63 psi (1.15 m H₂O) to 9.36 psi (6.58 m H₂O). The flow velocities in the internal distribution system and major pipes ranged from 0.0001 to 0.546 m/s, indicating suboptimal hydraulic performance of the network.

Impact analysis of transport network disruptions using multimodal data: A case study for tunnel closures in Stockholm

The Ethernet-based network protocol is widely using in industrial environments. Its advantages include high speed, high performance, operation over long distances, and better interoperability. A number of techniques are used to implement the Ethernet protocol for the needs of industrial processes that must provide real time processes. This paper analyses network performance of an Embedded system based master using EtherCAT. The network performance characteristics of the Embedded systems are compared by considering into the factors affecting their performance in a network system. This may determine reasons why network performance differs between factors.