Natasa Neskovic

Modern approaches in modeling of mobile radio systems propagation environment

In this article a review of popular propagation models for wireless communication channels is given. Macrocell, microcell, and indoor prediction methods are considered separately. Advantages and disadvantages of these models are discussed. Also, some practical improvements of the existing models as well as some new models are given.

Indoor electric field level prediction model based on the artificial neural networks

A new field strength prediction model for the mobile phone environment is presented. The model is based on the principles of popular feedforward neural networks. Utilizing a new artificial neural network model some important disadvantages of both deterministic and empirical models can be overcome. In order to build the model, extensive field strength measurements were carried out inside two different buildings. The analysis of the model has shown that the proposed model is fast, accurate (on the order of the focal mean measurements uncertainty) and reliable.

Macrocell electric field strength prediction model based upon artificial neural networks

A new macrocell prediction model for mobile radio environment is presented. The use of feedforward artificial neural networks makes it possible to overcome some important disadvantages of previous prediction models, including both deterministic and statistical types. Our sample implementation is based upon extensive electric field strength measurements (in the 900-MHz frequency band) that were carried out in the city of Belgrade using six different test transmitter locations. Comparison between the data obtained by the proposed electric field strength prediction model and independent measurement sets show that the proposed model is sufficiently accurate for use in planning mobile radio systems.

Vehicle Positioning Using GSM and Cascade-Connected ANN Structures

Procuring location information for intelligent transportation systems is a popular topic among researchers. This paper investigates the vehicle location algorithm based on the received signal strength (RSS) from available Global System for Mobile Communications (GSM) networks. The performances of positioning models, which consisted of cascade-connected (C-C) artificial neural network (ANN) multilayer feedforward structures employing the space-partitioning principle, are compared with the single-ANN multilayer feedforward model in terms of accuracy, the number of subspaces, and other positioning relevant parameters. C-C ANN structures make use of the fact that a vehicle can be found only in a subspace of the entire environment (roads) to improve the positioning accuracy. The best-performing C-C ANN structure achieved an average error of 26 m and a median error of less than 5 m, which is accurate enough for most of the vehicle location services. Using the same RSS database obtained by measurements, it was shown that the proposed model outperforms kNN and extended Kalman filter (EKF)-trained ANN positioning algorithms. Moreover, the presented ANN structures replace not only the positioning algorithms but the overloaded map-matching process as well.

A Generalized 2-D Linearity Enhancement Architecture for Concurrent Dual-Band Wireless Transmitters

A novel generalized two dimensional (2-D) digital predistortion (DPD) architecture for concurrent dual-band transmitters is presented. The proposed architecture is based on simultaneous injection of in-band intermodulation (IM) and cross-modulation (CM) distortion products. A general fundamental-frequency model for concurrent dual-band transmitter is developed theoretically and proofed experimentally. An individual impact of each IM and CM distortion component is theoretically derived and analyzed. It is clearly proven by theoretical analysis and experiments that the proposed predistorter improves the in-band and out-of-band performances of both signals. The simulation and experimental studies are performed using various signal sets. The proposed predistorter does not depend on frequency separation between bands and has low computational complexity in comparison with concurrent dual-band DPDs state-of-the-art. In addition, it is clearly shown in experiments that when using iterative simultaneous injections, a phenomenon known as distortion compensation limit can be reduced. A presence of memory effects and their mitigation in frequency domain for each band of concurrent dual-band transmitter are also demonstrated in experiments.

STATISTICAL ANALYSIS OF ELECTROMAGNETIC RADIATION MEASUREMENTS IN THE VICINITY OF GSM/UMTS BASE STATION ANTENNA MASTS

As a result of dense installations of public mobile base station, additional electromagnetic radiation occurs in the living environment. In order to determine the level of radio-frequency radiation generated by base stations, extensive electromagnetic field strength measurements were carried out for 664 base station locations. Base station locations were classified into three categories: indoor, masts and locations with installations on buildings. Having in mind the large percentage (47 %) of sites with antenna masts, a detailed analysis of this location category was performed, and the measurement results were presented. It was concluded that the total electric field strength in the vicinity of base station antenna masts in no case exceeded 10 V m(-1), which is quite below the International Commission on Non-Ionizing Radiation Protection reference levels. At horizontal distances >50 m from the mast bottom, the median and maximum values were <1 and 2 V m(-1), respectively.

Improving the efficiency of measurement procedures for assessing human exposure in the vicinity of mobile phone (GSM/DCS/UMTS) base stations

Standards stipulate 6-min time interval of averaging for measurements of radio-frequency electromagnetic fields to assess human exposure to non-ionising radiation. Having in mind the base stations of public land mobile systems, the time interval defined in such a way noticeably limits the number of measuring points in practical applications. In this paper, based on the results of measurements in the vicinity of a multisystem base station (Global System for Mobile Communications [GSM], Digital Communication System [DCS] and Universal Mobile Telecommunications System [UMTS]), it was shown that the measurement process can be significantly accelerated by using shorter time intervals of averaging--15 s, 30 s and 1 min. It was found that measurement results differed from the 6-min root-mean-square mean by 10.5 %, 15.9 and 19 %, respectively, while the uncertainty of the measurements was increased by 3.0 %, 3.8 and 4.4 %, respectively. Shorter time-averaging intervals would reduce the total duration of the exposure assessment survey, while not compromising too much on measurement quality.

Statistical analysis of electromagnetic radiation measurements in the vicinity of GSM/UMTS base station installed on buildings in Serbia

As a result of dense deployment of public mobile base stations, additional electromagnetic (EM) radiation occurs in the modern human environment. At the same time, public concern about the exposure to EM radiation emitted by such sources has increased. In order to determine the level of radio frequency radiation generated by base stations, extensive EM field strength measurements were carried out for 664 base station locations, from which 276 locations refer to the case of base stations with antenna system installed on buildings. Having in mind the large percentage (42 %) of locations with installations on buildings, as well as the inevitable presence of people in their vicinity, a detailed analysis of this location category was performed. Measurement results showed that the maximum recorded value of total electric field strength has exceeded International Commission on Non-Ionizing Radiation Protection general public exposure reference levels at 2.5 % of locations and Serbian national reference levels at 15.6 % of locations. It should be emphasised that the values exceeding the reference levels were observed only outdoor, while in indoor total electric field strength in no case exceeded the defined reference levels.

Comparison of ETX and HOP count metrics using Glomosim simulator

Routing protocols for wireless mesh networks (WMN) are traditionally focused on finding paths with the minimum hop count. In WMN the main goal is to achieve as the best possible quality and efficiency of data transmission between source and destination nodes as possible. To achieve such transmission, different parameters (power consumption, packet loss, delay, etc.) influencing data transmission need to be optimized. A routing algorithm should select better paths by taking the quality of wireless links into account. In this paper performances of two routing algorithms ETX (expected transmission count) and HOP count metric are analized and compared. Simulation results are obtained from practical implementation of ETX metric in Glomosim simulator.

Novel power-based routing metrics for multi-channel multi-interface wireless mesh networks

In this paper the problem of selecting optimal paths in a MCMI (Multi-Channel Multi-Interface) WMN (Wireless Mesh Network) is considered. The WMNs are characterized by high dynamic range of the received signal level, especially in the indoor environment. To improve the existing routing metrics and track fast changes that occur in the link state, a corresponding parameter based on the received signal level was assigned to each link. By combining this parameter and known metrics, ETX (Expected Transmission Count), WCETT (Weighted Cumulative ETT) and MIC (Metric of Interference and Channel-switching), three new metrics were formed. All metrics were incorporated in MCR (Multi Channel Routing) protocol and an appropriate propagation model was used for simulations in a real, indoor environment. Proposed metrics, original metrics, MCR protocol, and indoor propagation model were implemented in Glomosim simulator. New metrics were compared against known metrics and also among each other in terms of throughput of user data and average end-to-end delay of the network. The results have shown that proposed metrics significantly outperform original metrics. With this approach, better network performance can be achieved without any additional hardware and with minimal software changes.