Realistic Propagation Model Research Articles

Cooperative vehicle positioning with multi-sensor data fusion and vehicular communications

Vehicular positioning with multi-sensor fusion has achieved promising results in recent years. Having potential benefit from the emerging vehicular communications based on IEEE 802.11p dedicated short-range communication (DSRC), cooperative positioning opens new opportunities to support several vehicular applications. In addition, radar based active safety functions and GPS are being integrated into modern vehicles. With the availability of information from multiple sources, exchange of sensor information and multi-sensor fusion can be applied to obtain the precise positioning of vehicle without substantial additional cost. However, the main challenge in data fusion is the inherent data association problem due to dissimilar measurement update rate of DSRC and automotive radar. To overcome these challenges, this paper proposes a robust positioning approach considering track-to-track matching and fusion of position information obtained from multiple on-board sources such as GPS receiver, Vehicle-to-vehicle communication and automotive radar. Realistic 3D road traffic and wave propagation model is developed using a ray-tracing tool and the effectiveness of the proposed concept was evaluated. The system concept is validated by conducting extensive simulation considering realistic car following model. Results show that the proposed cooperative positioning method exhibits significant improvement in terms of positioning accuracy.

Analyzing 5G RF System Performance and Relation to Link Budget for Directive MIMO

Wideband fifth generation systems utilizing high carrier frequency and multiple-input multiple-output (MIMO) raise major challenges for the system design. Wave propagation and practical hardware tradeoffs at higher frequency ranges provide new boundary conditions for the implementation. This paper addresses system performance boundaries and the analysis method toward multibeam communications at millimeter wave. We combine analysis from antennas and propagation to the radio frequency (RF) transceiver specifications and beamforming requirements. Realistic propagation model and antenna implementation are used to generate beam-specific path gains and provide a wide variety of user scenarios. Using this approach, system level interdependencies and RF performance boundaries can be verified with different antenna configurations in various propagation environments. As an example, we present MIMO link budget analysis targeting 10 Gbits/s for multiple devices in the office scenario at 27 GHz.

Interference aware bandwidth estimation for load balancing in EMHR-energy based with mobility concerns hybrid routing protocol for VANET-WSN communication

The main goal of Vehicular Ad Hoc Networks (VANETs) is to improve driving safety. However, VANETs may not guarantee timely detection of dangerous road conditions or maintain communication connectivity when the network density is low, which may pose a risk to driving safety. Towards addressing this problem, the VANET is integrated with the inexpensive Wireless Sensor Network (WSN). Sensor nodes are deployed along the roadside to sense road conditions, and to buffer and deliver information about dangerous conditions to vehicles regardless of the density or connectivity of the VANET. The most challenging features in VANETs are their dynamic topology and mobility, where vehicles are moving at variable and high speeds and in different trajectories. In contrast, the challenge in the WSN is in managing the limited energy resources of the nodes, since the performance of WSNs strongly depends on their lifetime. Thus, the fundamental design challenge in designing routing protocols for a hybrid network of VANET-WSN is to maximize network lifetime and connectivity, and to minimize delay and energy consumption. To overcome these challenges, this research investigates the effects of different Quality of Service (QoS) parameters on forwarding decisions in an efficient distributed position based routing protocol, and focuses on bandwidth estimation. Bandwidth estimation is of great importance to network Quality of Service assurance, network load balancing, and routing. In this research, a bandwidth estimation strategy based on normalized throughput of a link, taking into account the interference and packet loss ratio in discrete time for every successfully delivered packet is proposed for a hybrid network of VANET-WSN. The simulation results show that the strategy is effective, and can accurately estimate the bandwidth of VANET-WSN. A comprehensive performance analysis in representative urban scenarios is performed that takes into account realistic propagation models and real city scenario traffic.

Relay Placement for Coverage Extension in Cellular Wireless Networks Under Composite Fading Model

In relay-assisted cellular networks, mobile stations are connected to base station through two or more single-hop communication links, where the intermediate nodes act as relay stations (RSs). The focus of this paper is on two-hop relay assisted cellular networks, where optimal relay placement is a crucial issue for achieving maximum extension of the cell coverage. However, the location of RS has significant impact on signal-to-interference plus noise ratio (i.e., SINR) and outage probability experienced on the access and backhaul links. Moreover, the frequency re-use factor also has significant influence on the SINR. In this paper, we develop analytical models for computing the SINR and outage probability performance of a two-hop relay assisted cellular network for both downlink (DL) as well as uplink (UL) transmission scenarios, considering the impact of path loss, shadowing, Nakagami fading and co-channel interference. We then investigate optimal placement of RS while satisfying the required criterion on probability of correct decoding, initially by considering the DL scenario alone and then by considering both DL and UL scenarios jointly. Through extensive evaluations, we report the impact of realistic propagation models on outage probability, optimal relay position and the cell coverage radius. Further, the model can be used to find the impact of co-channel re-use factor on optimal relay positioning in two-hop cellular networks.

Experimental modal decomposition of acoustic field in cavitation tunnel with square duct test section

The operational requirements for naval and research vessels have seen an increasing demand for quieter ships either to comply the ship operational requirements or to minimize the influence of shipping noise on marine life. To estimate the future radiated noise of a ship, scale measurements are realized in cavitation tunnel. DGA Hydrodynamics operates its cavitation tunnel with low background noise which allows such measurements. Understanding acoustic propagation in cavitation tunnel remains a challenge. The success of an accurate acoustic measurement depends both on a realistic propagation model and also on an efficient control of acoustic sensor characteristics. This short communication presents the results of experiments performed in GTH (Large Cavitation Tunnel) at DGA Hydrodynamics. An acoustic source radiates pure sine wave at the entrance of the test section and generates an acoustic field measured with flush mounted hydrophones. A modal decomposition is then performed to fit measurements. Complex amplitudes of all propagative modes could be estimated both for upstream and downstream propagation. Results show that for a given frequency range, modal decomposition could be an accurate model for acoustic propagation. Furthermore, different configurations of the test section and source locations have been investigated and show acoustic properties of the tunnel.

Line of Sight(LoS) Probability Prediction for Satellite and HAPs Communication in Trabzon, Turkey

The knowledge of Line of Sight (LoS) probability is curicial to estimate signal attenuation correctly in mobile wireless communication. Especially in built-up areas, more accurate LoS probability determination helps to obtain more realistic propagation models or path loss models. Geographic Information Systems (GIS) and City Information Systems (CIS) are used to provide a necessary data to calculate the LoS probability. In this study, LoS analyzes are made via Arcgis software for the most well-known streets in Trabzon, Turkey. For these analyzes, the Earth''s surface is accepted as flat and a simple geometrical approach is used for calculations in this paper. A Matlab algorithm was created to calculate LoS probability depending on the elevation angle which is an important parameter for satellite services. LoS probability vs. elevation angle is presented for interested streets. As a result, LoS probability for Trabzon dependent elevation angle is estimated and presented.

Measurement-Based Wideband Analysis of Dynamic Multipath Propagation in Vehicular Communication Scenarios

Realistic propagation modeling requires a detailed understanding and characterization of the radio channel properties. This paper is based on channel sounder measurements with 1 GHz bandwidth at a carrier frequency of 5.7 GHz and particular tracking methods. We present statistical models for the number of, birth rate, lifetime, excess delay and relative Doppler frequency of individual multipath components (MPCs). Our findings are concluded from 72 measurement runs in eight relevant vehicular communication scenarios and reveal wide insights into the dynamic propagation process in vehicular communication scenarios.

A cost-effective, environmentally-aware undersea infrastructure to enhance community resilience to tsunamis

The focus of this paper is on mitigating the impact of near-field tsunami detection on humans and the environment. We propose a hybrid network infrastructure that combines an undersea sensor network with fiber optic cable for cost effective, timely, and reliable near-field tsunami detection. We first formulate a cost minimization problem for near-field tsunami detection. To capture important characteristics of the environment, the optimization model incorporates into its formalization important sea environment factors and a realistic acoustic propagation model. A heuristic approach is developed to derive a near-optimal solution to the original cost minimization problem. To demonstrate the viability of the proposed model, a case study, focused on Padang City is used, and a comparative analysis of different network configurations, using different design parameters and cost scenarios is performed. Three different cost functions, namely linear, power-law, and logarithmic, are used in the analysis. The results show that the heuristic computes efficient network configurations when a solution exists, for the linear, logarithmic, and power-law cost functions. However, further assessment should be made on the results to anticipate a local maximum that may exist in the cost function.

Networks for Maintaining System-Level Availability for an Exploring Robot

In this paper, we provide an analysis of fixed-position communication nodes in a network for maintaining availability during robot exploration of unknown environments. Based on realistic wireless propagation models in different environments, the communication path loss as the robot moves is characterized. The nodes are then described, and we discuss a simple scalable policy for their deployment. The resulting network of multiple nodes reduces path loss to an acceptable threshold and has a tree structure. Considering the effect of shadowing, another policy is developed for node deployment that influences the system-level availability metric. We also demonstrate how this metric is influenced by exploration strategies and communication routing policies.

A comparison of Mamdani and Sugeno fuzzy based packet scheduler for MANET with a realistic wireless propagation model

The mobile nature of the nodes in a wireless mobile ad-hoc network (MANET) and the error prone link connectivity between nodes pose many challenges. These include frequent route changes, high packet loss, etc. Such problems increase the end-to-end delay and decrease the throughput. This paper proposes two adaptive priority packet scheduling algorithms for MANET based on Mamdani and Sugeno fuzzy inference system. The fuzzy systems consist of three input variables: data rate, signal-to-noise ratio (SNR) and queue size. The fuzzy decision system has been optimised to improve its efficiency. Both fuzzy systems were verified using the Matlab fuzzy toolbox and the performance of both algorithms were evaluated using the riverbed modeler (formally known as OPNET modeler). The results were compared to an existing fuzzy scheduler under various network loads, for constant-bit-rate (CBR) and variable-bit-rate (VBR) traffic. The measuring metrics which form the basis for performance evaluation are end-to-end delay, throughput and packet delivery ratio. The proposed Mamdani and Sugeno scheduler perform better than the existing scheduler for CBR traffic. The end-to-end delay for Mamdani and Sugeno scheduler was reduced by an average of 52% and 54%, respectively. The performance of the throughput and packet delivery ratio for CBR traffic are very similar to the existing scheduler because of the characteristic of the traffic. The network was also at full capacity. The proposed schedulers also showed a better performance for VBR traffic. The end-to-end delay was reduced by an average of 38% and 52%, respectively. Both the throughput and packet delivery ratio (PDR) increased by an average of 53% and 47%, respectively. The Mamdani scheduler is more computationally complex than the Sugeno scheduler, even though they both showed similar network performance. Thus, the Sugeno scheduler is more suitable for real-time applications.

Nanocavitation around a crack tip in a soft nanocomposite: A scanning microbeam small angle X-ray scattering study

We explore nanocavitation around the crack tip region in a styrene-butadiene random copolymer filled with typical carbon black (CB) particles used in the rubber industry for toughening the rubber. Using quasistatic loading conditions and a highly collimated X-ray microbeam scanned around the crack tip, we demonstrate the existence of a damage zone consisting of nanovoids in a filled elastomer matrix. The existence of voids near the crack tip is demonstrated by a significant increase of the scattering invariant Q/Q0 in front of both fatigued and fresh cracks. The size of the zone where cavities are present critically depends on the macroscopic strain em, the loading history, and the maximum energy release rate G applied to accommodate the crack. Our findings show that nanovoiding occurs before fracture in typical CB-filled elastomers and that realistic crack propagation models for such elastomers should take into account a certain level of compressibility near the crack tip. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 422–429

Two-Stage Channel Quantization for Scheduling and Beamforming in Network MIMO Systems: Feedback Design and Scaling Laws

This paper proposes an efficient two-stage channel quantization and feedback scheme for the downlink limited-feedback network multiple-input multiple-output (MIMO) system. In the first stage, the users report their best set of base-station antenna and physical resource block combinations, and the base-stations schedule the best user for each antenna in each resource block. The scheduled users are then polled in the second stage to feedback their quantized channel vectors. This paper proposes an analytical framework to show that, under a total feedback budget of B bits, the number of bits assigned to the second feedback stage should scale as log B, and in quantizing channel vectors from different base-stations, each user should allocate feedback bits in proportion to the channel magnitudes in dB scale. Under these optimized bit allocations, the overall sum rate of the system is shown to scale double-logarithmically with B, linearly with the total number of antennas, and logarithmically with transmit power, thus achieving both multiuser diversity and spatial multiplexing gains under limited feedback. Finally, realistic wireless propagation model of an urban small-cell deployment is used to show that the proposed scheme can approach the performance of a network MIMO system with full channel state information with only modest amount of channel feedback.

Realistic and Efficient Radio Propagation Model for V2X Communications

Multiple wireless devices are being widely deployed in Intelligent Transportation System (ITS) services on the road to establish end-to-end connection between vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) networks. Vehicular ad hoc networks (VANETs) play an important role in supporting V2V and V2I communications (also called V2X communications) in a variety of urban environments with distinct topological characteristics. In fact, obstacles such as big buildings, moving vehicles, trees, advertisement boards, traffic lights, etc. may block the radio signals in V2X communications. Their impact has been neglected in VANET research. In this paper, we present a realistic and efficient radio propagation model to handle different sizes of static and moving obstacles for V2X communications. In the proposed model, buildings and large moving vehicles are modeled as static and moving obstacles, and taken into account their impact on the packet reception rate, Line-of-sight (LOS) obstruction, and received signal power. We use unsymmetrical city map which has many dead-end roads and open faces. Each dead-end road and open faces are joined to the nearest edge making a polygon to model realistic obstacles. The simulation results of proposed model demonstrates better performance compared to some existing models, that shows proposed model can reflect more realistic simulation environments.

Tsunami Modeling to Validate Slip Models of the 2007 M w 8.0 Pisco Earthquake, Central Peru

Following the 2007, August 15th, Mw 8.0, Pisco earthquake in central Peru, Sladenet al. (J Geophys Res 115: B02405, 2010) have derived several slip models of this event. They inverted teleseismic data together with geodetic (InSAR) measurements to look for the co-seismic slip distribution on the fault plane, considering those data sets separately or jointly. But how close to the real slip distribution are those inverted slip models? To answer this crucial question, the authors generated some tsunami records based on their slip models and compared them to DART buoys, tsunami records, and available runup data. Such an approach requires a robust and accurate tsunami model (non-linear, dispersive, accurate bathymetry and topography, etc.) otherwise the differences between the data and the model may be attributed to the slip models themselves, though they arise from an incomplete tsunami simulation. The accuracy of a numerical tsunami simulation strongly depends, among others, on two important constraints: (i) A fine computational grid (and thus the bathymetry and topography data sets used) which is not always available, unfortunately, and (ii) a realistic tsunami propagation model including dispersion. Here, we extend Sladen’s work using newly available data, namely a tide gauge record at Callao (Lima harbor) and the Chilean DART buoy record, while considering a complete set of runup data along with a more realistic tsunami numerical that accounts for dispersion, and also considering a fine-resolution computational grid, which is essential. Through these accurate numerical simulations we infer that the InSAR-based model is in better agreement with the tsunami data, studying the case of the Pisco earthquake indicating that geodetic data seems essential to recover the final co-seismic slip distribution on the rupture plane. Slip models based on teleseismic data are unable to describe the observed tsunami, suggesting that a significant amount of co-seismic slip may have been aseismic. Finally, we compute the runup distribution along the central part of the Peruvian coast to better understand the wave amplification/attenuation processes of the tsunami generated by the Pisco earthquake.

Design of MIMO Antennas for Indoor Base Station and Mobile Terminal

Two design parameters, SNR and correlation, are key factors for enhancing channel capacity in MIMO systems. Achieving high SNR and low correlation is desirable in antenna design. This paper discusses the relation between channel capacity and these two parameters, and presents simple formulas of this relation for propagation channels and antenna coupling of mobile terminals. According to these guidelines, indoor base station antennas are designed and examined using propagation measurements. We also present a suitable antenna design for mobile terminal antennas and based on a realistic propagation model, predicted the channel capacity of the antenna.

Multihop relaying and multiple antenna techniques: performance trade-offs in cellular systems

Two very important and active areas of wireless research are multihop relaying and multiple antenna techniques. Wireless multihop relaying can increase the aggregate network data capacity and improve coverage of cellular systems by reducing path loss, mitigating shadowing, and enabling spatial reuse. In particular, multihop relaying can improve the throughput for mobiles suffering from poor signal to interference and noise ratio at the edge of a cell and reduce cell size to increase spectral efficiency. On the other hand, multiple antenna techniques can take advantage of scattering in the wireless channel to achieve higher capacity on individual links. Multiple antennas can provide impressive capacity gains, but the greatest gains occur in high scattering environments with high signal to interference and noise ratio, which are not typical characteristics of cellular systems. Emerging standards for fourth generation cellular systems include both multihop relaying and multiple antenna techniques, so it is necessary to study how these two work jointly in a realistic cellular system. In this paper, we look at the joint application of these two techniques in a cellular system and analyze the fundamental tradeoff between them. In order to obtain meaningful results, system performance is evaluated using realistic propagation models.

Enhanced statistics-based rate adaptation for 802.11 wireless networks

Rate adaptation is a common technique to exploit channel diversity in wireless networks. Despite the many rate adaptation algorithms proposed for 802.11 networks, statistics-based schemes remain the most widely adopted approaches in commercial 802.11 products due to their simplicity and practicality. However, statistics-based schemes suffer some disadvantages. Our previous research effort revealed the rate avalanche effect that could significantly degrade the network performance of heavily loaded 802.11 networks. In this work, we propose RADAR (Rate-Alert DynAmic Rts/cts exchange), a novel enhanced rate adaptation system that can effectively alleviate the impact of the rate avalanche effect. RADAR detects rate avalanche through maintaining a dynamic range-based mapping between rates and RSSI (received signal strength indicator) measurements. It judiciously exploits dynamic RTS/CTS exchanges to effectively suppress the rate avalanche effect while at the same time minimizes the transmission overhead of RTS/CTS exchanges. Being fully compatible with current 802.11 standards, RADAR can be readily implemented in the NIC driver. Through extensive simulations using realistic channel propagation and reception models, we demonstrate that RADAR is a practical and efficient performance enhancement approach for multi-rate 802.11 networks.

Exploring an under‐ice ocean cavity with sound.

Sensible predictions of the future rise in sea level require an understanding of the melting processes underneath the floating ice sheets of Antarctica and Greenland. Acoustic transmissions into the ocean caverns underlying the ice sheets could provide time series of temperatures and currents to augment intermittent measurements by instruments lowered through the ice and carried on autonomous underwater vehicles. The wedge of diminishing height formed between the underside of the ice and the shoreward sloping seafloor will horizontally refract sound transmitted into the ocean cavern by a source seaward of the ice edge. Incoming rays come to a coastal turning point near the grounding line of the ice sheet before returning seaward. A highly idealized model of vertical mode structure and horizontal ray structure provides estimates of the transmission paths in the wedge. In the ideal case, source‐receiver separations of order 100 km for the broad Antarctic ice sheets are expected to provide good coastal returns, but separations of order 20 km for the narrow Greenland floating ice tongues are expected to result in severe reflection losses at the coastal turning points. Receivers lowered through the ice would provide valuable additional information. Further calculations using realistic propagation models are essential.

Volume-aware positioning in the context of a marine port terminal

The rapid proliferation of mobile computing devices and local wireless networks over the past few years has promoted a continuously growing interest in location-aware systems and applications. The main problem with existing positioning techniques is that they are designed to position dimensionless objects. Such an assumption may lead to practical inconsistencies, as it results in neglecting the effects of the volume of an object, its physical characteristics, and its spatial arrangement on signal propagation. In this paper, we consider the problem of positioning cargo containers in a marine port terminal, where such characteristics can be finely estimated. Based on the signal propagation map of a container yard, we propose VAPS, a volume-aware positioning system that takes advantage of the waveguide effect generated by the containers. Although VAPS is specific to the marine port scenario, its design principles can be extended and adapted to other situations. VAPS maps discrete RSSI levels into hop-counts and relies on realistic propagation models to obtain near-perfect positioning at a very low control overhead. Our extensive evaluations show how to set the parameters required in the VAPS algorithm. The results demonstrate that, in scenarios where the assumptions made by traditional approaches fail, the considerations of VAPS make the difference.

Impact of the Physical Layer Modeling on the Accuracy and Scalability of Wireless Network Simulation

Recent years have witnessed a tremendous growth of research in the field of wireless systems and networking protocols. Consequently, simulation has appeared as the most convenient approach for the performance evaluation of such systems and several wireless network simulators have been proposed in recent years. However, the complexity of the wireless physical layer (PHY) induces a clear tradeoff between the accuracy and the scalability of simulators. Thereby, the accuracy of the simulation results varies drastically from one simulator to another. In this paper, we focus on this tradeoff and we investigate the impact of the physical layer modeling accuracy on both the computational cost and the confidence in simulations. We first provide a detailed discussion on physical layer issues, including the radio range, link and interference modeling, and we investigate how they have been handled in existing popular simulators. We then introduce a flexible and modular new wireless network simulator, called WSNet. Using this simulator, we analyze the influence of the PHY modeling on the performance and the accuracy of simulations. The results show that the PHY modeling, and in particular interference modeling, can have a significant impact on the behavior of the evaluated protocols at the expense of an increased computational overhead. Moreover, we show that the use of realistic propagation models can improve the simulation accuracy without inducing a severe degradation of scalability.