Steven J. Crowley, P.E.
Archive for the ‘Propagation’ Category
On October 13 Google filed two experimental radio applications with the FCC. The first seeks permission to test in the 3.5 GHz band in Mountain View, California and in suburban Washington D.C. The second is for testing in the 5.8, 24, 72, and 82 GHz bands in Mountain View and San Mateo County, California. The applications are redacted. Most technical detail is unavailable, but here’s what’s visible.
The interaction of radio waves in free space has never been much of a concern to this wireless engineer. Propagation models do a pretty good job of estimating received signal strength. Receivers are designed to select desired signals and reject undesired ones, within limits. “Interference takes place in the receiver,” I’ve heard more than once. Yes, there are a lot of signals in the air at once, but I’m more interested in the end result.
This summarizes a selection from 215 applications for the Experimental Radio Service received by the FCC during October, November, and December 2011. These are related to AM broadcasting, FM broadcasting, spread spectrum on HF and VHF, unmanned aerial vehicle control, electronic warfare support, small satellites, white space technology, video production, managed access, TV interference, RFID, and radar. The descriptions are listed in order of the lowest frequency found in the application.
This summarizes a selection from 173 applications for the Experimental Radio Service received by the FCC during August and September 2011. These are related to long-range low-frequency radar, amateur radio, shortwave data, wireless microphones, single-sideband, mine detection, millimeter-wave communications, signal intelligence, automotive radar, satellite feeder links, meteor-burst communications, aircraft telemetry, white space systems, border security radar, 3G and 4G applications, RFID, wind turbine testing, unmanned aerial vehicles, spacecraft telemetry and control, aircraft passenger broadband, and autonomous aircraft landing systems. The descriptions are sorted by the lowest frequency found in the application.
Recent contributions to the mobile broadband spectrum debate are reports from NAB and CTIA. I envisioned a “dueling reports” piece, but they mostly complement each other. Below I walk through the main points, adding some of my own views.
To avoid interference, wireless transceivers can switch between transmit and receive on one frequency (Time Division Duplex (TDD)). Or, they can transmit and receive at the same time on different frequencies (Frequency Division Duplex (FDD)). There’s been a flurry of press reports about a new radio system, developed by Stanford researchers, that can operate full duplex on a single channel; that is, transmitting and receiving at the same time on the same frequency, something not done before.