Statistics of Measured Body Loss for Mobile Phones



It is well known that the transmitted or received power by a mobile handset is reduced due to the presence of the user, where the ratio of power with and without user is denoted the body loss. The body loss may vary significantly depending on the antenna/handset design. Therefore, minimizing the body loss is an obvious way of improving the performance of future handsets. It is, however, important to note that the body loss may vary considerably from one user to another, even for the same handset and mobile environment, and thus this needs to be taken into account when measuring the body loss. In the work presented in [Nielsen et al, 2001] the uncertainty of body loss measurements is investigated via statistics of the body loss measured for 200 test users of a GSM handset in a realistic propagation environment. The body loss variation among users may be considered random and cumulative distribution functions have been estimated for three different handset antennas. The measurements show that the distributions can be approximated reasonably as Gaussian. Assuming Gaussian distributions, about 8 test persons are required for mean body loss estimation for the whip antenna with a 90 % confidence interval of ± 1dB, whereas about 13 test persons are necessary for the helix antenna, and about 9 for the patch. The helix antenna thus results in a larger spread in body loss than both the whip and the patch antenna. CPK Annual Report - Figure 4.5.10 (Two-sided 90 % confidence interval size for the sample mean body loss as function of the number of body loss measurements for the whip (dashed) and the helix (solid)) shows the confidence interval size versus the number of measurements. (Jesper Ø. Nielsen, Gert F. Pedersen, Kim Olesen, Istvan Z. Kovacs)
Effektiv start/slut dato31/12/200131/12/2001