Interference from mobile satellite systems through terrain scattering

Abstract

The emerging generation of personal communications satellites, built to communicate with handheld telephone units, will generate power flux on earth that is orders of magnitude higher than that of the present satellite service, and its potential interference with terrestrial-based systems is of concern. It is proposed here that the flux scattered from the ground surface into the antenna main beam and near sidelobes may cause higher interference than direct coupling into the antenna. This mechanism, previously observed in terrestrial systems, may not be mitigated by adaptive hulling techniques, and is less angle-dependent. A simple model is developed, to be used as a computational tool for assessing the interference and its functional dependence on governing parameters. In the absence of proper terrain scattering models, examples are evaluated by borrowing results from interference observed in terrestrial microwave links, which indicate the possible severity of the effect.

Prediction of multipath delay profiles in mountainous terrain

“…Models of the propagation loss of a delayed path scattered from mountainous terrain have been presented in [4], [5], [10]- [12], [17], and [23] based on the bistatic radar equation (1) where wavelength; scattering cross section of the target; transmitted and received powers; transmitter/scatterer, scatterer/receiver, and transmitter/receiver path lengths. Furthermore, with is the relative delay between direct and delayed paths and is a time reference.…”

“…Thus the integral becomes the sum (4) where is the normalized scattering cross section of the patch of area with area , and the patches are chosen such that . By performing the integral over different range cells, the squared magnitude of the channel impulse response is obtained as (5) where the are local mean or spatial average values.…”

“…With this approach, the range cells are of size such that each term in (5) corresponds to a major mountain slope (or significant portion thereof) visible from both transmitter and receiver. The impulse response is approximated by (5), where in each term is the sum of all components within these large range cells centered at , and the delta functions are replaced by broad pulses or clusters with unit area and nominal width . Thus (3) for a particular mountain slope is simplified to (6) where is the area of the mountain slope (width × height) estimated from a topographical map.…”