DynamicFrequencySelection5ghz.pdfVIP

Dynamic Frequency Selection (DFS) and the 5GHz Unlicensed Band by Mark Briggs, Principal Engineer at Elliott Labs The advent of the 802.11a wireless market and the constant push to open up new spectrum for unlicensed use created a requirement for Dynamic Frequency Selection (DFS), a mechanism to allow unlicensed devices to share spectrum with existing radar sys- tems. The regulatory requirements for DFS, along with requirements for Transmit Power Control (TPC) and uniform channel loading have been adopted in the US, Europe and Japan and are being considered by many other regulatory domains looking at adopting the 5GHz bands for unlicensed, and possibly licensed devices. In the next few chapters, I hope to provide an overview of the current and proposed DFS require- ments for Europe and the proposed DFS requirements for the US. European Union ETSI standard EN 301 893 V1.2.3 [1],the European Union’s harmonized radio standard for unlicensed devices operating in the 5150 – 5350 MHz and 5470 – 5725 MHz frequency bands, was one of the first standards to reference DFS. It specifies the types of waveforms that systems operating in the 5250 – 5350 MHz and 5470 – 5725 MHz bands should detect and defines threshold and timing requirements as follows: Channel Availability Check Time: The time a system shall monitor a channel for presence of radar prior to initiating a communications link on that channel. Interference Detection Threshold: The minimum signal level, assuming a 0dBi antenna, that can be detected by the system to trigger the move to another channel. Channel Move Time: The time for the system to clear the channel and measured from the end of the radar burst to the end of the final transmission on the chan- nel. Channel Closing Transmission Time: The total, or ag- gregate, transmission time from the system during the channel move time. Non-Occupancy Time: A period of time after radar is detected on a channel that the channel may not b