Much interest has been generated in portable telephones and data terminals inside buildings. In a radio environment plagued by the severe fading effects of multipath and the dynamics of a changing channel, diversity is required. While considerable theory has been developed on diversity techniques, there have been few published results of indoor diversity measurements, particularly in the 1.7-2.0 GHz band. This paper evaluates three diversity techniques at 1.75 GHz based on simultaneous measurements of envelope fading due to both moving people and motion of a four-branch receiver. The experiment was conducted in various rooms on one floor of a university building having a common construction type of double plasterboard walls, cement floors, and acoustic tile ceilings. Path-loss characteristics of this environment had a distance power law exponent of N= 2.85 or equivalently, an estimated wall loss of 3.0 dB. Results presented here provide a direct comparison of two-branch space, two-branch frequency, and four-branch space/frequency (hybrid) diversity. Envelope cross correlations had averages less than 0.1 for space diversity with AS (antenna separation) > λ/4 and values less than 0.2 for ΔF (frequency diversity spacing) >10 MHz. Two-branch average diversity gain using selection combining was at least 10 dB at 99% signal availability for all AS including λ/4 (4.3 cm), allowing such a technique to be used on a hand-held terminal, and for frequency diversity with ΔF>5 MHz. With these parameters four-branch hybrid diversity had gains >15 dB. The distribution of diversity gains varied within ±2.5 dB between transmission paths which should be considered for a worst-case link design. The reported gains allow reasonable estimations of system fade margins based on required availabilities when using diversity in similar buildings.
IEEE Transactions on Vehicular Technology
Department of Systems and Computer Engineering

Todd, S.R. (Stephen R.), El-Tanany, M, & Mahmoud, S.A. (1992). Space and Frequency Diversity Measurements of the 1.7 GHz Indoor Radio Channel Using a Four-Branch Receiver. IEEE Transactions on Vehicular Technology, 41(3), 312–320. doi:10.1109/25.155978