Snjezana Rimac-Drlje

Comparison of Propagation Models Accuracy for WiMAX on 3.5 GHz

Fixed Wireless Access (FWA) networks based on WiMAX technology provide efficient packet radio interface enabling high data transmission rates. The accurate prediction of path losses is a crucial element in the first step of network planning. This paper presents few empirical models suitable for path loss prediction in mobile as well as fixed wireless systems like WiMAX. Experimental measurements of received power for the 3.5 GHz WiMAX system are made in urban and suburban areas of Osijek, Croatia. Measured data are compared with those obtained by four prediction models: SUI model, COST 231 Hata, Macro Model and Model 9999. Analysis is made separately for location with NLOS and LOS propagation conditions. Standard deviation of the prediction error for NLOS condition is the lowest for the SUI model. The Macro Model achieved the lowest error standard deviation for LOS propagation conditions.

Influence of temporal pooling method on the objective video quality evaluation

Objective video quality evaluation incorporates spatial and temporal degradation effects to calculate quality grade for each video frame alone, as well as the overall quality grade for the whole sequence. Distortion visibility depends not only on the level of degradation but also on video content and viewers preferences. Temporal pooling is a method that collapses series of frame quality scores to one quality score for whole video sequence and it should be aware of an influence of the video quality variation to the human overall judgments of quality. In this paper six pooling methods applied to five objective video quality metrics are compared. The best prediction capability has been obtained by those pooling methods that reflect two phenomena: a recency effect and the worst quality section influence. Moreover, the statistics of individual frames scores tends to be of high importance and strongly influences pooling method capabilities.

Receiving Power Level Prediction for WiMAX Systems on 3.5 GHz

Worldwide Interoperability for Microwave Access (WiMAX) is a new wireless broadband technology based on IEEE 802.16 standard. Its radio interface enables high data transmission rates in the frequency range of 2-11 GHz and 10-66 GHz. The existing empirical models, most often used for path loss prediction, are mostly developed for frequencies below 2 GHz. This paper analyses empirical models suitability for the receiving power prediction in complex urban environments for a WiMAX system working at 3.5 GHz. Predicted values have been compared with values measured in urban and suburban areas as well as in rural surrounding of city Osijek in Croatia. Received power prediction is obtained by four empirical propagation models: SUI C, COST 231-Hata, Macro model and Ericsson model. Analysis is made separately for locations with urban, suburban and rural propagation conditions.

Spatial Masking and Perceived Video Quality in Multimedia Applications

In modern communication systems with video transmission as their important part, objective video quality evaluation is necessary in the QoS (quality of service) assessment. This article analyzes spatial masking effects on the visibility of compression artifacts, and consequently its importance in the digital video quality evaluation process. Luminance masking and texture masking are mechanisms referred to as having a great influence on the objective quality metrics fidelity. Eleven maskers (6 for luminance and 5 for texture) are constructed, and their effectiveness is analyzed first for each masker alone, and then for combinations of luminance and texture maskers. By nonlinear addition of luminance and texture maskers used in a simple pixel-based quality metric a high correlation with subjective mean opinion scores (MOS) is obtained (Pearson correlation coefficient higher than 0.95).

Business models and cost optimization of wireless rural broadband access implementation

Aiming at the reduction of the existing digital gap between many rural and urban european areas as well as at the optimization of the rural broadband access deployment costs, several rural broadband deployment cases in the Republic of Croatia are compared in this paper. The comparison is conducted from the business and the regulatory point of view, and the possibilities of the cost-effective solutions for rural broadband access implementation are evaluated. The advantages of wireless over wired access are taken into account. Hence, wireless WiMAX broadband access implementation is analyzed in the paper. In order to foster further broadband implementation in rural areas and to point on the possible cost-effectiveness of wireless broadband access deployments in Croatian rural areas, the given results help in choosing the optimized wireless access solutions for the given rural scenarios.

Overview of OFDM channel estimation techniques for DVB-T2 systems

Systems that are modeled according to DVB-T and DVB-T2 standards use Orthogonal Frequency Division Multiplexing (OFDM) as a modulation scheme. OFDM uses N parallel streams to ensure high-rate data transmission. Distinct carriers are used to transmit data streams. In OFDM subcarriers are orthogonal in order to ensure that receiver can distinguish separate signals carried by different subcarriers. Generally there are three approaches in estimating channel transfer function in systems that use OFDM, pilot symbols, scattered pilot tones and eigenvalue-decomposition-based methods. Pilot symbols are mainly used for initial channel estimation. Scattered pilot tones are used to help track changes in channels over time. The complexity of the first two methods can be reduced with the eigenvalue-decomposition-based methods. In recent studies multiple channel estimation techniques, mostly based on pilot patterns stemmed from initial estimation techniques. This paper gives an overview of the standard channel estimation methods used in OFDM and recently developed improved channel estimation methods.

Influence of spatial and temporal activity of upscaled video on its perceived quality

High network resources costs led to the increasingly usage of scalable video coding in video transmission over the network. Prior to displaying on user device, the transmitted video should be spatial and/or temporal upscaled in order to ensure the acceptable perceived quality level. In this work the relationship between the spatio-temporal activity of upscaled sequence and its perceived quality is examined. The experiments are performed for videos presented on PC and on smartphone, while three different activity measures are analyzed. It is shown that the newly-introduced spatio-temporal activity measure, called SITImean, achieves a high level of correlation with subjective quality scores. Therefore it could be used as an indicator of upscaled video quality, replacing the expensive subjective quality evaluation tests.