Spectrum sharing communications system for monitoring available spectrum

Claim 1

A mobile communuications network in which signals are transmitted and received between at least one base station and at least one user terminal over a common block of frequency spectrum that is shared with an incumbent radio system having a plurality of incumbent radio stations, said mobile communications network comprising: means for periodically measuring signal levels of signals falling within a plurality of frequency segments of said common block of frequency spectrum, said measuring means comprising: monitoring antennas, said monitoring antennas collectively having plural polarizations and being arranged to have spatial diversity; a spectrum analyzer coupled to said monitoring antennas for producing data representative of a signal level contained within at least one frequency band received by each of said antennas; means for controlling said spectrum analyzer; and means for processing information, including data produced by said spectrum analyzer, to produce data representative of a frequency of an incumbent receiver and a degree of RF isolation between at least one of said monitoring antennas and said incumbent receiver; means for identifying which of said plurality of incumbent radio stations are nearby incumbent radio stations based on the signal levels measured by said measuring means; means for calculating whether interference is likely to occur between said mobile communications network and at least one of the nearby incumbent radio stations identified by said identifying means; means for periodically creating parameters, representative of the range of frequencies on which said user terminal transmits and receives said signals, based on a likelihood of interference calculated by said calculating means; and means for periodically assigning frequencies on which said user terminal transmits and receives said signals based on the parameters created by said creating means.