How to Transmit Wi-Fi Over UHF
By J.R. Hartig
Wi-Fi over UHF has been a tantalizing theory since at least the turn of the century. Wi-Fi over UHF is known as WhiteFI. The problematic issue is the FCC's requirement that any existing signal in this spectrum not be disturbed or affected, so the technical aspects of WhiteFi must sense and redirect a signal to other available frequencies instantly. In-depth treatises rhapsodize about broader open spectrums, but in real terms as exists in late 2011, WhiteFi has no real-world application.
Step 1
Address the differences between white spaces and the ISM bands where Wi-Fi operates. UHF places greater impact on spectrum variations due to the FCC ruling mandating non-interference with wireless transmissions of primary users, also known as incumbents. An incumbent can occupy any portion of the white spaces, making more problematic the locating of available frequency space for WhiteFI.
Step 2
Compute the Hamming distance. The Hamming distance addresses the difference between locations, making an access point (AP) work harder at discerning Whitefi space. The AP must account for the possibility of multiple incumbents differing between locations.
Step 3
Conquer Temporal Variation, the factor of incumbents turning on and off at random. Wireless microphones inhabit UHF frequencies as they are used, becoming temporary incumbents. Both clients and APs must detect the presence of, and simultaneously move away from, any mic presence on a channel.
Step 4
Develop specialized hardware utilizing both a transceiver radio and a separate scanner radio. The separate scanner addresses the requirement to accurately and quickly detect the presence of incumbents.
Step 5
Use SIFT: SIFT (Signal Interpretation before Fourier Transform), is efficient, variable-bandwidth signal detection. SIFT uses a detection algorithm to determine what an AP should use as a channel width based on signal amplitudes.
Step 6
Handle disconnections. Reconnecting disconnected clients is crucial to UHF Wi-Fi success. System designs must generally disconnect and reconnect to a new UHF channel frequency within four seconds, according to the Harvard/Microsoft study, "White Space Networking with Wi-Fi-like Connectivity."
References
Writer Bio
J.R. Hartig is a Certified Physical Trainer combining an expertise in physical fitness with a passion for writing about wellness. He is in the process of developing a website on fitness counseling and has written blogs and commentaries for several health-care websites. Hartig began writing following relatives’ trials with diabetes. He devised exercises programs while pursuing his bachelor’s degree at University of California, Berkeley.