Measurements for spectrum sharing between microwave and personal communications systems

To study the feasibility of spectrum sharing between the fixed point-to-point microwave and the proposed PCS systems, Telesis Technologies Laboratory (TTL) has undertaken comprehensive interference measurements in the San Francisco Bay area. The measurements indicate that exclusion zones for potential PCS transmission exist along the main beam of the fixed microwave link and mainly near the microwave terminals. In dense urban areas, substantially higher interference may cause as a result of specular reflections off buildings. In downtown San Francisco, it was observed a 40 to 50 dB higher interference level due to building reflections in a wide area outside the microwave main beam, which results in significantly larger exclusion zones around the microwave antennas as opposed to the case of no surrounding buildings. Because the microwave links are fixed and of known location with directional energy, the exclusion areas are usually local. It is suggested that a system with a channel bandwidth less than 5 MHz has more flexibility for spectrum sharing through deliberate frequency planning and/or dynamic channel allocation