Mobile Handset Performance Evaluation Using Spherical Measurements

Description

Antennas and Propagation One important aspect of a mobile handset is its ability to receive and transmit signal power. The performance in this respect is important for both the user and the network operator, since the battery lifetime of a handset will be influenced, as will the network coverage and capacity. When evaluating the communication performance of a mobile handset it is necessary to include the antenna, as the antenna has a large influence on the communication. This can be seen from the fact that all mobile handsets fulfill the system criterion within the small tolerances allowed, but still some handsets have coverage where others do not. This can be explained only by the antenna, which is not included in the type approval but of course will be included in actual use. In the evaluation of the communication performance of a mobile handset, the single most important parameter is the signal power received by either the mobile handset or the base station. The received signal power depends directly on the transmitted power level in addition to the orientation and polarization properties at the transmitter and the receiver, as described by the antenna radiation patterns. All this comes directly from Friis' transmission law. The amount of transmitted and received power depends for any given antenna on the antenna efficiency including the matching between the antenna and the transmitter or receiver. This part can be obtained in an anechoic room by measuring the transmitted or received power in all directions followed by an integration over the sphere. Inclusion of the direction and polarization properties of the transmitted or received power is difficult in the case of a mobile handset, since the handsets typically are used in a multipath environment, where the signal may be received from many directions and with different polarizations. In order to find the resulting received power, knowledge of the distribution of the incoming power is needed. The mean effective gain (MEG) is defined as the mean received power in the case of a scattered environment with respect to a reference antenna. In the current project two ways of investigation have been considered, * Direct measurements of the MEG in the environment/network. * Measurements of the spherical radiation pattern of the handset followed by computation of the MEG using models of the received power in the mobile environment. The latter way of evaluating the performance has a number of advantages over the first, most importantly that the evaluation does not require propagation measurements which may be difficult and also requires access to a network. Furthermore, measurements in the network can only be done with fully operational handsets. With the purpose of verifying the feasibility of using spherical radiation pattern measurements and models of the mobile channel for the performance evaluation, the following have been investigated. * Sampling density and frequency of operation In this work the MEG is computed from measured spherical radiation patterns of five different mobile handsets, both in free space and including a human head & shoulder phantom. Different models of the environment allow a comparison of the MEG obtained for realistic models based on measurements with the total radiated power (TRP) and the total isotropic sensitivity (TIS). All the comparisons are based on the MEG values obtained for different orientations of the handsets in the environments. For practical measurements it is important to minimize the measurement time. Hence, the work includes a study of the variation in MEG when the number of samples in the spherical radiation pattern is reduced. Furthermore, the frequency dependence of the MEG was investigated, and a method is proposed for reducing the required number of measurements on different frequencies. * Uncertainty due to handset mounting on phantom In order to simulate the influence of a real user the measurements the spherical radiation patterns are made with the handsets mounted on a phantom user. The measurements are only expected to be repeatable if the same setup is used, i.e., the same phantom and the same mounting of the handset on the phantom. In this work the influence of mounting errors on the TRP, TIS, and MEG is investigated. Knowledge about the error due to incorrect mounting is necessary in determining requirements for both the mounting accuracy as well as for other parts of the measurement system that may introduce errors in standardized performance measurements. Radiation patterns of six handsets have been measured while they were mounted at various offsets from the reference position defined by the CTIA certification. The change in the performance measures are investigated for both the GSM-900 and the GSM-1800 band. * Comparison of anechoic room and in-network measurements In this work the results obtained via the spherical radiation patterns are compared with the equivalent performance obtained in a live GSM network using data from the Abis network interface. This method does not require altering of the handsets and the testing uses normal calls in the network. The investigation is based on measurements with four different commercially available handsets carried out in two different indoor environments and involving 22 test users. In addition a series of measurements were also made with a phantom simulating the handset user, allowing a test of how well the phantom represents the average user. (Jesper Ødum Nielsen, Gert Frølund Pedersen)
StatusFinished
Effective start/end date01/01/200131/12/2002