Correlation properties for radio channels from multiple base stations to two antennas on a small handheld terminal

It is generally understood that in Rayleigh fading radio channels, sufficient decorrelation for antenna diversity purposes is found at the mobile at antenna separations larger than about λ/2. However, it has been indicated that with dissimilar antennas with less separation on a small handset, still good diversity gain can be achieved(Pedersen et al. 1999). We present measurements of correlation properties with two similar antennas on our new small measurement handset (Kotterman et al. 2001) (connected by optic fibre, not by conducting cable) of indoor channels at 2140 MHz, including the user. The set-up is with three base stations (BS) simultaneously in order to simulate interference and macro diversity situations. We measured with two types of antennas, monopoles and patches (separation 0.29λ and 0.16λ resp.) in two buildings (old and modern construction) in two different BS configurations, each with up to twelve test users. At the smallest separation of 0.16λ the power correlation between branches remained below 0.83 for the fast fading (median values around 0.5). On the other hand, the slow fading can be strongly correlated between BSs (median value 0.8).