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In order to mitigate fading and reduce time dispersion on urban mobile radio channels, it has been proposed that future sys tems should be configured with many small cells having low powered base stations with streetlamplevel antennas. This configura~ tion contrasts with that of systems designed in the pact in which one centrally-located, high-powered base station with an elevated antenna is employed to serve a large coverage area The results of measurements made to determine propagation characteristics on urban mobile radio channels with low base station antennas and line of sight between the base and mobile units are reported in this par per. Cumulative distribution functions for envelope fading, as well as delay spread and frequency correlation Statistics are presented.In addition, comparisons are made with simlar statistics for conventional channels. There are no previously pubiished papers regarding these characteristics on microcellular-type channels.Results show that multipath propagation conditions would be significantly less Severe if small-celled systems were implemented. Root mean square delay spread averages are reduced by a factor of approximately four in comparison with thaw typical in conventional systems. In addition, microcellular-type channels have Rician, rather than Rayleigh, envelope fading characteristics, and correspondingly diaerent frequency correlation statistics. The advantage of the Rician characteristics may be twc-fold. First, on Rician channels, with narrow transmission bandwidths, a desired error rate can be achieved in a digital system with a lower received bit energy to noise power spectral density ratio than that required for equivalent performance on a Rayleigh channel. Secondly, since correlation remains high over large bandwidths it is believed that, without equalization or diversity, the bandwidth available for communication with acceptable error performance on Rician channels is significantly greater than that available on Rayleigh channels with comparable time dispersion Characteristics.

There has recently been much deliberation regarding whether indoor radio communications systems should operate in the 900 MHz band, or in the 1.7 GHz band. However, there are no propagation results available in the literature which compare indoor channel characteristics in the two bands. This paper presents the results of temporally and spatially distributed wideband (impulse response) propagation measurements on fixed indoor radio channels in these bands. Impulse response parameters, as well as envelope fading and frequency correlation statistics are presented and compared for the two bands, and for two different buildings. Results from the temporal experiments show that for a specific location in either of the two buildings, the dynamics of indoor channels are slightly less random at 910 MHz than at 1.7 GHz. It is believed, with due regard for the quasi-static nature of the fading, that this would result in marginally better performance on a given transmit/receive link in the 900 MHz band. The spatially distributed measurements showed that the structures of average impulse response envelopes differed for channels in the two buildings. In one building, rms delay spreads were slightly greater in the 1.7 GHz band for over 90 percent of transmit/receive link configurations. In the other building, rms delay spreads were marginally greater in the 900 MHz band for 70 percent of the configurations. It was also found that the standard deviation of rms delay spreads for different link configurations was greater for both frequency bands in this building. I n both buildings, the standard deviation was greater for the 1.7 GHz band results. These differences in rms delay spread standard deviations are considered to be important in the evaluation of coverage capabilities in different buildings and for different frequencies of operation.

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