3 - Interference and Coexistence

Abstract

This chapter describes some of the issues related to interference and coexistence. The wireless industry, governments, and regulatory bodies have amassed a depth of research into the level to which ultra wideband (UWB) will interfere with other systems operating in the same frequency bands. Although the interpretations vary slightly and the type of UWB access technology plays some role in the level of interference, most agree that any UWB transmission must be limited to avoid the risk of harmful interference. The technique showing the greatest promise to eliminate harmful interference in the presence of very sensitive services is Detection and Avoidance (DAA). In this approach, the UWB transmitter detects the presence of other active services (detection), and then reduces its power in that specific band (avoidance). This technique shows great promise but has not been included in commercial products yet. To ensure its market and technical success, UWB cannot cause harmful interference with other services operating in the same frequency range. Industry experts and standards bodies agree that, to be successful, UWB transmitters must detect other services that are active in the vicinity and avoid interfering with them. Some proposed approaches include controlling transmit power, switching off UWB devices that are close to primary PCs in office environments, limiting the duty cycle of UWB devices, and moving UWB devices to higher frequencies. In addition to spectrum masks, regulations in Japan, Europe, and other countries will also likely require DAA.