. Commercial microwave radio links forming cellular communication networks are known to be a valuable instrument for measuring near-surface rainfall. However, operational communication links are more uncertain relatively to the dedicated installations since their geometry and frequencies are optimized for high communication performance rather than observing rainfall. Quantification of the uncertainties for measurements that are non-optimal in the first place is essential to assure usability of the data. In this work we address modeling of instrumental impairments, i.e. signal variability due to antenna wetting, baseline attenuation uncertainty and digital quantization, as well as environmental ones, i.e. variability of drop size distribution along a link affecting accuracy of path-averaged rainfall measurement and spatial variability of rainfall in the link's neighborhood affecting the accuracy of rainfall estimation out of the link path. Expressions for root mean squared error (RMSE) for estimates of path-averaged and point rainfall have been derived. To verify the RMSE expressions quantitatively, path-averaged measurements from 21 operational communication links in 12 different locations have been compared to records of five nearby rain gauges over three rainstorm events. The experiments show that the prediction accuracy is above 90% for temporal accumulation less than 30 min and lowers for longer accumulation intervals. Spatial variability in the vicinity of the link, baseline attenuation uncertainty and, possibly, suboptimality of wet antenna attenuation model are the major sources of link-gauge discrepancies. In addition, the dependence of the optimal coefficients of a conventional wet antenna attenuation model on spatial rainfall variability and, accordingly, link length has been shown. The expressions for RMSE of the path-averaged rainfall estimates can be useful for integration of measurements from multiple heterogeneous links into data assimilation algorithms.

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Prediction of rainfall intensity measurement errors using commercial microwave communication links

The discrepancy between real-world radio channel behavior and its standard modeling in simulations (unit disk graph) is a major reason for protocols to perform differently - often worse - than predicted when deployed in a real-world setup. As researchers having to deal with real ad hoc networks are aware of, assuming a fixed border for a node's communication range might not only lead to inaccurate results but also to a wrong judgment on the comparison between different protocols. We have set up a simulation study to investigate the effects of realistic channel characteristics on packet forwarding strategies for vehicular ad hoc networks. The contributions of this paper are threefold: i) we provide a performance evaluation of various routing/forwarding strategies under the realistic non-deterministic Nakagami radio propagation model and compare the results with the ones obtained using the standard two-ray-ground model. Validated German highway movement patterns are used to model node mobility. ii) We demonstrate that realistic channel conditions present an opportunity and not only a drawback for some forwarding strategies. More specifically, we show that for contention-based forwarding (CBF) techniques, realistic channel characteristics provide a positive impact in terms of an increased average hop distance. iii) We provide an analytical derivation of the expected hop distance for CBF that provides a basis to optimally adjust CBF parameters

Effects of a realistic channel model on packet forwarding in vehicular ad hoc networks

Spectrum slicing WDM for FSO communication systems under the heavy rain weather

Proposed parameters of specific rain attenuation prediction for Free Space Optics link operating in tropical region

Inter-vehicle communications (IVC) has the potential to play an important role in many future vehicle and traffic applications. Much of this will occur in the automated vehicle control and safety systems (AVCSS) arena, and to a lesser extent in the advanced transportation management and information systems (ATMIS) arena. One such ATMIS application where IVC can be used is in decentralized traffic information systems. These systems do not require extensive infrastructure and management centers to collect and disseminate traffic information. Instead, information can be shared among vehicles through periodic broadcast messages. An adaptive dissemination mechanism for this is described in this paper. In the proposed design, each participating vehicle can adapt their transmission interval according to the current traffic speed and also disseminate the traffic information of different segments at different rates according to the distance to its current position. This dissemination scheme ensures the efficient distribution of information within the vehicle network. We have designed, developed, and tested this methodology using a unique traffic simulation environment that has been effectively augmented with wireless communication capability. Both analysis and simulation results show that the bandwidth that the system requires is far below the bandwidth of current 802.11 wireless links and the system can reach the accuracy requirement even at a low penetration rate

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An adaptive dissemination mechanism for inter-vehicle communication-based decentralized traffic information systems

A fundamental quantity in the calculation of rain attenuation statistics is the specific attenuation (attenuation per unit distance). The power-law form of rain specific attenuation is very convenient and is commonly used. It is expressed as α R k ⋅ , where k and α are the power-law parameters, and R is the rain rate in mm/h. Limited number of power-law parameters were available in the technical literature for certain raindrop size distributions. Some of these parameters had reservations for rain-rate ranges. New power-law parameters for four different (gamma, lognormal, Laws and Parsons, and Marshall and Palmer) raindrop size distributions are made. For a rain temperature of 0 C, k and α with polarization dependence are presented here for rain rates from 0 to 150 mm/h over the frequency range of 100 5 − GHz.

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Project IEEE 802.16 Broadband Wireless Access Working Group Title Power-Law Parameters of Rain Specific Attenuation

Re: 802.16 Physical Layer Task Group Call for Contributions: Modeling Issues, Session #5 Abstract The antenna height and directivity are used in the classification of statistical channel models for local multipoint distribution service (LMDS). When directional a ntennas are used and the antennas are sufficiently high providing a line -of-sight (LOS) propagation path between the transmitter and receiver, the statistics of the radio channel can be described by the lognormal or Nakagami -m distribution. The channel sta tistics fits the Rician distribution, if omni -directional antennas are used. The directivity of antennas sets the direction of arrival signals and limits the number of propagation paths. When omni-directional antennas are used and at least one of the anten nas is lower than the surrounding obstacles, and hence an LOS propagation path is absent, the radio channel is described by the statistics of the Rayleigh distribution. The above -mentioned channel models can be used to evaluate the performance of LMDS systems.

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Project IEEE 802.16 Broadband Wireless Access Working Group Title Classification of Statistical Channel Models for Local Multipoint Distribution Service Using Antenna Height and Directivity

We recommend the usage of an expanded set of power-law parameters in calculating the rain specific attenuation. We believe that this expansion is needed to accommodate an expanded set of raindrop size distributions, because the raindrop size distribution changes with geographical location and can strongly influence rain attenuation. Generally, the power-law parameters for Laws and Parsons (L-P) and Marshall and Palmer (M-P) distributions are used for estimating rain specific attenuation. We suggest, however, that it is more reasonable to use a gamma raindrop size distribution for high latitude locations and a lognormal raindrop size distribution for tropical regions. We further show that the specific attenuation for L-P raindrop size distribution is nearly the same as the specific attenuation obtained from power-law parameters of the ITU-R model. Purpose To provide an input to the specific area ''Propagation Model''. Notice This document has been prepared to assist the IEEE 802.16. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release The contributor acknowledges and accepts that this contribution may be made public by 802.16.

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Project IEEE 802.16 Broadband Wireless Access Working Group Title Recommendation: Use of Various Raindrop Size Distributions for Different Geographical Locations in Calculating the Rain Specific Attenuation

Re: 802.16.1 Physical Layer Task Group Call for Contributions, Session #6 Abstract We recommend a flexible channel propagation model, which includes no more than three taps and has flexible tap gains and tap delays. The tap gains have a progressive decrease relationship, while the tap delays have a progressive increase one. The model is valid under the following assumptions: (1) there is line-of-sight propagation, (2) highly directional antennas are used at least at the receive; (3) heavy-rain attenuation effects are not taken into account, and (4) a -20 dB threshold is applied, which excludes multi-path components with amplitudes below the threshold. The available radio channel measurements support the model.

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Title Recommendation on Channel Propagation Model for Local Multipoint Distribution Service Date Submitted

Two explicit-form formulations are presented for radio propagation predictions for local multipoint distribution service. The first formulation accounts for multiple forward diffraction by rows of buildings only. The second formulation is an extension of the first one, and it accounts for multiple diffraction by rows of tree canopies and buildings, including the effects of propagation through the trees between rows of buildings. When the base transceiver station antennas are sufficiently high, the attenuation of the buildings varies around the value of free space and the building effect is negligible, because a line-of-sight (LOS) propagation path between the base transceiver station antenna and building-rooftop subscriber transceiver station antenna exists and plays a major role. The tree canopies which extend above the building rooftop heights block the LOS propagation path and cause additional signal attenuation. The attenuation effect of the buildings is significant if the base transceiver station antennas are not sufficiently high.

Project IEEE 802.16 Broadband Wireless Access Working Group Title Formulations of Multiple Diffraction by Buildings and Trees for Propagation Prediction

Nader Moayeri

Papers

Project IEEE 802.16 Broadband Wireless Access Working Group Title Power-Law Parameters of Rain Specific Attenuation

Project IEEE 802.16 Broadband Wireless Access Working Group Title Classification of Statistical Channel Models for Local Multipoint Distribution Service Using Antenna Height and Directivity

Project IEEE 802.16 Broadband Wireless Access Working Group Title Recommendation: Use of Various Raindrop Size Distributions for Different Geographical Locations in Calculating the Rain Specific Attenuation

Title Recommendation on Channel Propagation Model for Local Multipoint Distribution Service Date Submitted

Project IEEE 802.16 Broadband Wireless Access Working Group Title Formulations of Multiple Diffraction by Buildings and Trees for Propagation Prediction