Object-based assessment of satellite precipitation products

An object-based verification approach is employed to assess the performance of the commonly used high-resolution satellite precipitation products: Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), Climate Prediction center MORPHing technique (CMORPH), and Tropical Rainfall Measurement Mission (TRMM) Multi-Satellite Precipitation Analysis (TMPA) 3B42RT. The evaluation of the satellite precipitation products focuses on the skill of depicting the geometric features of the localized precipitation areas. Seasonal variability of the performances of these products against the ground observations is investigated through the examples of warm and cold seasons. It is found that PERSIANN is capable of depicting the orientation of the localized precipitation areas in both seasons. CMORPH has the ability to capture the sizes of the localized precipitation areas and performs the best in the overall assessment for both seasons. 3B42RT is capable of depicting the location of the precipitation areas for both seasons. In addition, all of the products perform better on capturing the sizes and centroids of precipitation areas in the warm season than in the cold season, while they perform better on depicting the intersection area and orientation in the cold season than in the warm season. These products are more skillful on correctly detecting the localized precipitation areas against the observations in the warm season than in the cold season

Influence of irrigation schemes used in regional climate models on evapotranspiration estimation: Results and comparative studies from California's Central Valley agricultural regions

The agricultural sector is the largest consumer of water in California. The impacts of irrigation on local and/or regional weather and climate have been studied and reported in recent literature. However, because of the lack of observations and realistic irrigation schemes employed in the numerical models, most previous studies fall in the category of sensitivity tests, focusing on temperature variations. The results being reported in this paper are obtained by incorporating into the MM5/Noah land surface model an irrigation method practiced in California's farming sector. The proposed irrigation scheme is based on the principle that irrigation occurs when available soil-water content is less than the maximum allowable water depletion (SWm), which depends on both soil type and crop type. The study's focus was to evaluate the impact of a more realistic irrigation scheme on surface fluxes, especially evapotranspiration (ET). It is demonstrated that more accurate amounts and patterns of ET in the Central Valley are realized, as compared to ET estimates (in terms of amounts and spatial distribution) obtained from remotely sensed observation as well as in situ ground data. It is demonstrated that significant discrepancies of ET estimates between different irrigation schemes used in regional hydroclimate modeling exist, which may result in erroneous conclusions about the impact of irrigation on regional water balance, especially over and near agricultural areas. © 2012 by the American Geophysical Union

How significant is the impact of irrigation on the local hydroclimate in Californias Central Valley? Comparison of model results with ground and remote-sensing data

The effect of irrigation on regional climate has been studied over the years. However, in most studies, the model was usually set at coarse resolution, and the soil moisture was set to field capacity at each time step. We reinvestigated this issue over the Central Valley of California's agricultural area by: (1) using the regional climate model at different resolutions down to the finest resolution of 4 km for the most inner domain, covering California's Central Valley, the central coast, the Sierra Nevada Mountains, and water; (2) using a more realistic irrigation scheme in the model through the use of different allowable soil water depletion configurations; and (3) evaluating the simulated results against satellite and in situ observations available through the California Irrigation Management Information System (CIMIS). The simulation results with fine model resolution and with the more realistic irrigation scheme indicate that the surface meteorological fields are noticeably improved when compared with observations from the CIMIS network and Moderate Resolution Imaging Spectroradiometer data. Our results also indicate that irrigation has significant impacts on local meteorological fields by decreasing temperature by 3°-7°C and increasing relative humidity by 9-20%, depending on model resolutions and allowable soil water depletion configurations. More significantly, our results using the improved model show that the effects of irrigation on weather and climate do not extend very far into nonirrigated regions. Copyright 2011 by the American Geophysical Union

Symbol-by-symbol APP decoding of the Golay code and iterative decoding of concatenated Golay codes

An efficient coset based symbol-by-symbol soft-in/soft-out a posteriori probability (APP) decoding algorithm is presented for the Golay code. Its application in the iterative decoding of concatenated Golay codes is analyzed.published_or_final_versio

A two-step approach to restorable dynamic QoS routing

Aiming at minimizing the combined bandwidth cost of a pair of disjoint active and backup paths, a popular approach to designing Restorable Dynamic QoS Routing schemes is based on Integer Linear Programming (ILP) formulation. Owing to the very different natures of active and backup paths, we found this approach problematic. In this paper, we propose a simple alternative approach, called two-step routing. In the first step, active path is found using the widest-shortest path (WSP) routing. In the second step, the corresponding backup path is determined using one of the three variants of shortest-widest path (SWP) routing, Basic-SWP, Approximate-SWP and Composite-SWP. Combining both steps, three novel restorable routing algorithms, SBW, SAW and SCW, are obtained. Comparing with the existing best-known algorithms, we show that our two-step routing approach yields noticeably lower call blocking probability, shorter active path length, and adjustable backup path length (depending on the SWP variant adopted). Besides, our two-step routing approach gives a much shorter running time than the ILP approach, which makes it more attractive for dynamic routing.published_or_final_versio

Efficient path protection using Bi-directional WDM transmission technology

Bi-directional WDM transmission is a technique that allows wavelengths to be transmitted simultaneously in both directions in a single fiber. Compared with unidirectional WDM systems, it not only saves the cost of deploying extra fibers, but also allows more flexible bandwidth provisioning. To exploit the advantages brought by this flexibility, we investigate path protection based on bi-directional WDM transmission system in this paper. With path protection, a call is accepted if and only if an active data path together with a disjointed backup path can be found in the network. With bi-directional WDM, backup resources sharing in both directions of a fiber is possible. To encourage resources sharing, new cost functions are judiciously designed. Based on them, two original path protection schemes are proposed in this paper, BiPro and BiProLP, where BiProLP aims at further economizing the hardware cost incurred by BiPro. In contrast to the traditional unidirectional schemes, we show that both BiPro and BiProLP can yield noticeably lower call blocking probability, higher system capacity and snorter active/backup path length. © 2005 IEEE.published_or_final_versio

Performance of turbo codes with fading compensation in multipath channels

This paper studies the performance of turbo-coded system in the frequency non-selective correlated Rayleigh fading channels. The turbo-coded system employs a pilot-symbol-aided (PSA) technique for fading compensation and interleaving for spreading the error bursts to reduce the error rate. The PSA technique is also used to provide the decoder with channel side information (CSI) for better performance in fading channel. Two PSA techniques, three normalized Doppler spreads and different interleaving sizes have been investigated. Results of computer simulations have shown that, an improved first-order fading prediction technique can improve the BER performance by a factor of about 62, relative to those obtained using the pilot symbols only. Results have also shown that an interleaving depth equal to one-quarter the reciprocal of normalized Doppler spread can achieve a good BER performance.published_or_final_versionThe IEEE 49th Vehicular Technology Conference (IEEE-VTS 1999), Houston, TX., 16-20 May 1999. In IEEE-VTS Vehicular Technology Conference Proceedings, 1999, v. 3, p. 2413-241

A Novel MAC Scheduling Algorithm for Bluetooth System

Data exchange within a Bluetooth piconet is masterdriven. The channel/slot utilization thus depends on the efficiency of the scheduling algorithm adopted by the master. In this paper, a novel MAC layer scheduling algorithm, called Floating Threshold (FT), is proposed. Unlike existing approaches, FT allows the master to estimate the backlog queue status at each slave accurately based only on a single feedback bit and a floating threshold. The master can then derive an optimized packet transmission schedule. Using simulations, we show that FT outperforms existing algorithms in terms of channel utilization, packet delay and packet dropping probability.published_or_final_versio

On bursty packet loss model for TCP performance analysis

In this paper, we study the timeout probability of TCP Reno under the bursty packet loss model, which is widely used to represent the loss characteristics of TCP under drop-tail FIFO queues. With a detailed analysis on the three timeout reasons for TCP Reno, we show that the impact of timeout has been underestimated in the existing literature. Surprisingly, we find that this more precise representation of timeout probability does not match the actual performance of TCP under drop-tail FIFO queues. Therefore we conclude that the bursty loss model is incapable of capturing the behavior of drop-tail FIFO queues, and using bursty loss model to analyze TCP performance is flawed. © 2005 IEEE.published_or_final_versio