comparison of measured and predicted path loss

1. Comparison of Measured and Predicted Path-Loss for
UMTS and GSM 900 Systems in Istanbul Macro-Cell
Model
Refet Ram˙ız
Yıldız Technical University, GSM System Test and Measurement Lab. (YildizCell), Turkey
Ekrem Ozorbeyi, Akın ¨Oz¨ozl¨u
Turkcell ˙Ileti¸sim Hizmetleri A.S¸. Turkcell Maltepe Plaza, Turkey
Due to the diversity of the environments where mobile communications occur, each propagation
model is devised for a specific type of environment; macro-cell, micro-cell, pico-cell. In general there is
a relationship between these models and types of environments for which they are suitable. Here the
macro-cell models are considered. The empirical and semi-empirical models are suitable for macro-
cells with homogeneous characteristics. The macro-cells are large areas with transmitter antenna well
above the surrounding buildings and usually there is no direct visibility between the transmitter and
the receiver (NLOS). The models of Okumura-Hata, COST 231-Hata, Lee, Ibrahim and Parsons,
McGeehan and Griffiths, Atefi and Parsons, Sakagami-Kuboi are empirical based. These models
consider wholly or partly; heights of the Tx antenna, Rx antenna, the building close to Rx, and
frequency, distance between Tx and Rx, gain of the Tx and Rx antennas, the percentage of the area
covered by buildings and area occupied by buildings, plane-earth equation, angle formed by the street
axes and the direction of the incident wave and of course the diffraction loss. Also older cities with
narrow, twisting streets, modern cities with long, straight, wide streets are taken into consideration.
However, the semi-deterministic models of Ikegami, Walfisch and Bertoni, Xia and Bertoni, COST 231-
Walfisch-Ikegami are suitable for homogenous urban environments. There, GTD and GO techniques
are applied to the ideal city with flat terrain and with buildings of uniform height. A NLOS situation
is assumed and diffracted rays as well as the reflection coefficients of the building faces are evaluated.
Beside the parameters given in the empirical models, the curvature of the earth due to the distance
and Tx antenna height is used and some empirical corrections are included to adopt the models to the
features of European cities.
Since the current GSM 900 system of Turkcell is working on the TDMA base, there is only one case
to be considered between a BTS and an MS. All other sub-parameters are for making optimisation of
the selected model. However, there are two different bases defined within the UMTS system; FDD base,
TDD base. Due to the 3GPP RF Systems scenarios, there are FDD/FDD, TDD/TDD, FDD/TDD
methodologies for co-existencies, and different macro-cell propagation models are defined for each
MS to MS, BS to MS, BS to BS, MS to BS communications case where the buildings are assumed
nearly uniform height. The number of the cells for each operator in the macro-cellular environment
is assumed equal or higher than 19 too. Here, the outdoor model based on the formula of H. Xia
is given by J. E. Berg and the log-normal fading and the distance loss is calculated by an extended
Okumura-Hata model.
The BTSs of the Turkcell are located on the bases of the Okumura-Hata path-loss model. Con-
sidering the new UMTS system characteristics, the new cell planing configuration, power control,
interference modelling, etc. it is required to obtain the optimum path-loss model for the UMTS
system that will be established around Istanbul area.
In this paper, the field in the case of multiple knife-edge is considered and the reflective properties
of ground and surface building materials (Limestone, Brick, Concrete, etc.) are evaluated to enhance
the accuracy of the predictions. The environmental data of raster and vectorial forms are examined
and the environment is divided into cells that contains the corresponding information. The number of
the buildings, facets of each building and the facets from walls, roofs, floors/ceilings, and ground are
considered together with the first, second order effects.