Limited Coverage Area Research Articles

Two-Dimensional Line of Sight Interference Analysis of LMDS Networks for the Downlink and Uplink

Local multipoint distribution systems (LMDS), which are operating worldwide in the frequency range of 26 to 43 GHz, have large bandwidths of 0.1 up to 2 GHz, but a very limited area coverage due to line of sight constraints and large propagation losses. As suggested in the Cellular Radio Access for Broadband Services (CRABS) Report , a high spectral efficiency can be obtained for a regular network of squared cells with a dual frequency and polarization reuse scheme. However, this frequency and polarization reuse leads to cochannel and adjacent channel interference. In this paper, we report a systematic two-dimensional study of interference in such a regular LMDS network for the downlink and uplink in order to assess the impact of different geometric and propagation parameters. The paper reports simple formulas to estimate the areas of high interference levels within an LMDS cell as a function of the half-power beamwidth of the customer-site antennas for the downlink. The effect on the carrier-to-interference distribution over a LMDS cell is evaluated by varying the half-power beamwidth of the customer-site antennas, the time percentage of short term enhancement due to atmospheric multipath and focusing effects and the cell dimensions. We also introduce a simple technique by reorientation of the customer-site antennas for interference reduction. The results presented in this paper can be used to carry out system-level design for interference-limited LMDS cells.

AM/FM: An Open or Closed Case?

In this article I attempt to highlight the main issues and arguments which surround the question of establishing commercial FM broadcasting services in regional areas. I mope to provide a guide to the complex and delicate questions concerning the future of commercial radio, particularly AM/FM conversion in regional areas. It is necessary to consider regional and metropolitan areas separately because of the very different characteristics of the (markets involved. It seems unquestionable that there will not be any wholesale conversion to FM in the metropolitan areas because of a) technical considerations, including frequency availability, and b) successfully established programming which would not benefit from FM broadcast; for example, mainly current affairs/news formats. In regional areas wholesale conversion would not occur primarily because of FM's limited coverage area and also because of the lower penetration rate of FM receivers.