Link Quality Degradation Research Articles

Deep gateway switching

This paper deals with the problem of data-enhanced gateway switching technique in high throughput satellite systems. Feeder links deployed in high frequency bands (i.e. Ka band or higher) suffer from substantial link quality degradation due to atmospheric events, specially rain. In order to solve this problem, operators deploy redundant gateways in different locations with the aim of configuring the best set of gateways in case of strong fading event occur in any of the teleport locations. In an operational environment, this switch is neither seamless nor instantaneous and non-negligible time-to-switch and switching times appear. As a result, the switching process requires to be pre-emptive and anticipate those fading events. With external prediction meteorological data, we build a data-based model able to predict a gateway outage and, therefore, when the switch shall be implemented. The mathematical model boils down to be a non-linear online regression problem. Numerical results show the performance of the system with real operational data.

Heterogeneous Architecture for DSRC/LTE Vehicular Communication Networks Based on the ITS Reference Architecture with Fuzzy Logic for Decision-Making

Methods to integrate different access technologies such as heterogeneous communication architecture remains a challenge. Among a variety of V2X-supporting access technologies, Dedicated Short Range Communication (DSRC) and cellular communications, e.g., Long Term Evolution (LTE) is promising reliable and efficient vehicular communications. DSRC has been designed to allow for direct low-latency communications among different vehicles (i.e., V2V) and between vehicles and roadside units (RSU). On the other hand, DSRC suffers from link quality degradation with the presence of buildings and vehicles, especially in urban areas, where channel collisions become serious when vehicle density is high. LTE networks can provide wide area coverage and are favorable to bandwidth-greedy applications, which require high data rates and reliability. Considering the relatively high end-to-end delay for message transmission due to the long transmission time interval (TTI) current LTE networks have drawbacks regarding latency to support highfrequency safety-related information exchange among vehicles in local areas. Combining LTE and DSRC approaches as a heterogeneous solution is essential to fast introduce V2X services for future automated driving. By this intelligent Vertical Handover (VHO) algorithms are needed to ensure seamless connectivity of vehicles to the best network at a particular point in time. For this paper, we propose a 3- input fuzzy-logic-based VHO scheme for Heterogeneous DSRC/LTE Vehicular Communication Networks. The simulation results in this paper show that the proposed 3- input fuzzy-logic model can be able to make decisions and select the best network to connect to base on the network with the highest HF value. The 3-input fuzzy-logic model was also tested in a vehicular highway scenario simulation. The proposed model shows optimized communication results in terms of the mean end-to-end delay against that of the literature.

저전력 IoT 네트워크에서 불안정한 노드를 회피하는 적응적인 ADP-RPL

A recent challenge is that IoT devices tend to be configured in an LLN environment. LLN has thousands of nodes with limited processing power, memory, and energy, and these nodes are typically connected by lossy links. The RPL for LLN is designed for use in resource-constrained devices in industry, homes, and cities. The primary purpose of the RPL is to provide IPv6 connectivity for many battery-powered embedded devices using low-power radios. The RPL is expected to be very active in smart factories in Industry 4.0. However, smart factories are an environment with high interference and mobility. Although RPL is designed for LLN, energy consumption may increase due to frequent parent changes in unstable networks. Adaptive RPL (ADP-RPL) calculates the degradation of link quality as the rank value increases and the parent"s change time and then reflects it in the rank value sent to neighboring nodes. In order to prevent frequent parent changes, we used a threshold that is proportional to the rank of neighboring nodes. In this paper, we evaluated the performance of ADP-RPL using a Cooja simulator. As a result, ADP-RPL shows better performance with more nodes. In order to evaluate performance in the actual environment, a test was performed in an environment in which GET and POST messages were transmitted using the CoAP protocol. RE-Mote device was used to evaluate the indoor space where interference occurred. In the real environment, the rate of ADP-RPL transmission failure and the number of parent changes were reduced compared to RPL.

Accurate Empirical Path-Loss Model Based on Particle Swarm Optimization for Wireless Sensor Networks in Smart Agriculture

Wireless sensor networks (WSNs) have received significant attention in the last few years in the agriculture field. Among the major challenges for sensor nodes’ deployment in agriculture is the path loss in the presence of dense grass or the height of trees. This results in degradation of communication link quality due to absorption, scattering, and attenuation through the crop’s foliage or trees. In this study, two new path-loss models were formulated based on the MATLAB curve-fitting tool for ZigBee WSN in a farm field. The path loss between the router node (mounted on a drone) and the coordinator node was modeled and derived based on the received signal strength indicator (RSSI) measurements with the particle swarm optimization (PSO) algorithm in the farm field. Two path-loss models were formulated based on exponential (EXP) and polynomial (POLY) functions. Both functions were combined with PSO, namely, the hybrid EXP-PSO and POLY-PSO algorithms, to find the optimal coefficients of functions that would result in accurate path-loss models. The results show that the hybrid EXP-PSO and POLY-PSO models noticeably improved the coefficient of determination (R2) of the regression line, with the mean absolute error (MAE) found to be 1.6 and 2.7 dBm for EXP-PSO and POLY-PSO algorithms. The achieved R2 in this study outperformed the previous state-of-the-art models. An accurate path-loss model is essential for smart agriculture application to determine the behavior of the propagated signals and to deploy the nodes in the WSN in a position that ensures data communication without unnecessary packets’ loss between nodes.

An Empirical Study on the Performance of Wireless OFDM Communications in Highly Reverberant Environments

Reverberation chambers are closed reflective spaces that can emulate highly reverberant electromagnetic environments. The electromagnetic environment is primarily determined by the size of the cavity, effective conductivity, and leakage via apertures. In this effort, we investigate the performance of wireless OFDM communications in relation to the latter two by controlling the loading of a reverberation chamber and the effective aperture into a coupled cavity. A software defined radio measurement platform was used to assess the communication performance through a selection of link-level metrics including error vector magnitude, post processing signal-to-noise ratio, and throughput. The degradation of link quality is quantified for increasingly diffuse environments, as well as the improvement when leveraging a maximal ratio combining receiver diversity scheme. The link quality was found to improve in both the reverberation chamber and the coupled cavity for larger effective apertures. This result was analyzed using a time-dependent model for RF propagation in coupled cavities.

A new approach to design of weather disruption-tolerant wireless mesh networks

Wireless Mesh Networks, offering transmission rates of 1–10 Gb/s per a millimeter-wave link (utilizing the 71–86 GHz band) seem to be a promising alternative to fiber optic backbone metropolitan area networks because of significantly lower costs of deployment and maintenance. However, despite providing high transmission rates in good weather conditions, high-frequency wireless links are very susceptible to weather disruptions. In particular, heavy rain storms may lead to remarkable signal attenuation. In this paper, we introduce a new transmission technique for wireless mesh networks to mitigate the negative effects of link quality degradation due to rain storms. In particular, our method is the first one to use information on forecasted attenuation of links based on radar measurements to perform in advance the periodic updates of a network topology. Our approach is easily implementable in practice, since functionality of dynamic antenna alignment is currently offered by a number of equipment vendors. Other contributions of the paper include presentation of the ILP model of weather-resistant links formation problem followed by analysis of its computational complexity. Results of simulations, performed for three real scenarios of rain storms, show that our approach is very efficient in reducing the level of signal attenuation.

Recovery of Link Quality Degradation in Wireless Mesh Networks

Recovery of Link Quality Degradation in Wireless Mesh Networks

Recovery of Link Quality Degradation in Wireless Mesh Networks

The multiple system loops refers to a two pair of particular radios on both side of the loop. But, multiple system loops wireless mesh networks occurred often link failures because of channel clashing, obstacles, and/or based on demand of bandwidth requirement. This cause major efficiency degradation in WMNs or more expensive manual network management. This paper deals about Autonomous Link Recovery System. This makes a Multi-radio WMN automatically recall its local network channel and radio. Autonomous Link Recovery System has been implemented on ns2 based simulation and improvement of 90% efficiency.

DEMON: preemptive route recovery for AODV in multi-hop wireless networks based on performance degradation monitoring

Reactive routing protocols like ad hoc on-demand distance vector (AODV) have been widely proposed for multi-hop wireless networks (MWNs). However, these types of routing protocols only recover routes after route break detection. Considerable research efforts have been devoted to minimizing the route recovery delay or to anticipating link breaks by using preemptive mechanisms. To the best of our knowledge, state-of-the-art solutions in this space are mainly focused on mobility prediction. However, as we argue in this paper, other phenomena like interference and congestion should also be taken into account, since they can also negatively affect the performance of routes and even cause disconnections. This article presents a novel preemptive solution for AODV called performance degradation monitoring, which allows preemptive route recovery based on passive estimation of link data loss rate. Extensive simulations demonstrate that our proposal, which is sensitive to link quality degradation regardless of its nature, improves network performance in a wide range of scenarios.

Detection and Localization of Link Quality Degradation in Transparent WDM Networks

Detection and Localization of Link Quality Degradation in Transparent WDM Networks

IEEE 802.11 무선랜 재밍 환경에서의 측정 기반 채널 도약 기법

In this paper, we propose a new channel hopping scheme based on IEEE 802.11h as a good countermeasure against jamming attacks in IEEE 802.11 wireless networks. 802.11h Dynamic Frequency Selection (DFS) is a mechanism which enables hopping to a best channel with full channel measurement, not a randomly chosen channel, when the current link quality degradation occurs due to interferers such as military radars. However, under jammer attacks, this needs a time for full channel measurement before a new channel hopping and due to link disconnection during the time network performance degradation is inevitable. In contrast, our proposed schemes make an immediate response right after a jammer detection since every device is aware of next hopping channel in advance. To do this, a next hopping channel is announced by Beacon frames and the channel is selected by full channel measurement within Beacon intervals. Simulation results show that proposed scheme minimizes throughput degradation and keeps the advantages of DFS.

Interference-aware fast path adaptation in wireless mesh networks

Existing multihop wireless routing protocols are incapable of reacting quickly to transient degradation of link quality rendering them unsuitable for supporting real-time applications such as streaming/interactive voice and video. This limitation in the sensitivity of the routing protocols to link quality is difficult to overcome due to the following reasons. All link quality metrics used in routing, such as ETX [1, 2] require active probing. Too frequent probing results in high overhead and can interfere with the actual traffic. Further, a time window of 5 to 10 seconds is required to gather enough probe samples to allow reasonable confidence in the statistics and avoid load sensitivity. Additional latency is also incurred in propagating routing updates.

Symbol Perforation Reduction Schemes for Orthogonal Code Hopping Multiplexing

Our previously proposed orthogonal code hopping multiplexing (OCHM) [1], [2] scheme is designed to accommodate a large number of bursty downlink users. However, it may undergo link quality degradation due to symbol perforations occurring when all code-collision symbol values are not identical. In this letter, a group-level random codeword hopping-pattem allocation (GRCHA) scheme is proposed to produce fewer symbol perforations than the previous symbol-by-symbol random codeword hopping (SRCH) of OCHM [1]. The proposed GRCHA scheme combined with the spatial filtering capability of switched-beam array antennas (SBAA) is expected to significantly reduce the symbol perforation probability in the OCHM scheme, and inter-beam softer handoff is applied to cope with high symbol perforation probability for users in overlapping beam areas of SBAA. The performance is evaluated by theoretical analysis and simulation in terms of the average symbol perforation probability. The proposed GRCHA scheme yields better performance than the SRCH scheme and the dedicated codeword allocation scheme, and the diversity gain of inter-beam softer handoff mitigates the effect of high symbol perforation probability for users in the overlapping beam areas.

A Real-Time Algorithm for Timeslot Assignment in Multirate Return Channels of Interactive Satellite Multimedia Networks

Since the digital video broadcast-return channel via satellite (DVB-RCS) standard was released in 2000, developing an interactive satellite multimedia (ISM) network has become a hot issue. In order to provide high-speed multimedia services using a DVB-RCS system, it is important to efficiently and dynamically assign the timeslots to a number of terminals according to their various demands. Also, it is imperative to improve the degradation of link quality due to rain-fade attenuation in Ka-band satellite communications. As a result, multirate superframe structures should be implemented for a relatively low data rate at the cost of stable connection to terminals in rain-fade regions and a relatively high data rate to terminals in clear-sky regions. Timeslot scheduling in this environment is studied in this paper. We mathematically formulate the timeslot assignment problem as a nonlinear integer programming problem and develop an efficient real-time solution algorithm. Extensive simulation results show that our algorithm successfully finds a feasible solution with optimality gap less than 0.05% within about 5 ms at Pentium III PC. We believe that our algorithm can be utilized as a guideline in developing real-time timeslot assignment algorithms for ISM networks.