Wireless Microphones over TV white spaces: how to deal with?

Certainly, dealing with wireless microphones (WM) in spectrum sharing contexts is one of the major bottlenecks that shape the performance of TV bands-based cognitive radio since it is very hard to keep tracking the on-off evolution of WMs activity allowed to operate over the core TV spectrum. However, regulatory bodies like FCC are aware of this issue and have planned some preventive actions to be undertaken:

1) Wireless microphones are either licensed (under FCC Part 74) or unlicensed (under FCC Part 15). Licensed WMs do not cause any problems since they are fully managed and controlled, they are allowed to operate at power levels up to 250 mW. Yet, most wireless microphones are not licensed and thus compromise the cognitive use of TV bands, this class of WMs is restricted to 50 mW transmissions to avoid perturbing the spectrum incumbents.

2) Licensed and unlicensed WMs can function on reserved channels, available channels and white space channels [1]. The latter type of channels needs requesting registration from the FCC to be used by WMs. It is indispensable to understand the difference between the three channel types for a complete understanding of how WMs will be monitored in a TV white spaces (TVWS) context:

  a) Reserved channel: In every location, the FCC has reserved two channels for the exclusive use of wireless microphones, centered around channel 37. No other devices are allowed to operate in these two channels. 

  b) Available channel: Unlike TV band devices (TVBD), an available channel is a channel that can be occupied by a wireless microphone. Available channels take place in locations where TV band devices are prohibited due to regulation limitations. For instance, fixed TVBDs are not allowed in a channel adjacent to a broadcast TV station and operation on TV channels below TV21 is not permitted for personal/portable TVBDs. 

  c) White space channel: A channel which both wireless microphones and TV band devices can use and thus mutual interference can occur on that channel.

These channel categories can be easily identified using TVWS database solutions like: http://whitespaces.spectrumbridge.com/whitespaces/home.aspx.

3) For a WM to use a white space channel, FCC has envisaged the possibility of requesting temporary additional channels in cases where users may need more frequencies than what they can obtain in reserved and available channels (large venues, major events,...). The FCC-approved channels must be submitted to a database administrator to appear in the central spectrum database so that they will be unavailable for use by other TVBDs.

It is obviously seen that FCC rule-markings have tackled the complexity of managing the dynamics of WMs [2] by proposing well defined regulations and best practices. The proposed rules make it possible to track and forecast the activity of WMs via the TVWS database solution without the need for spectrum sensing. Moreover, it is the timing constraints of WMs that impact more the frequency of the database check (once a day for FCC, every two hours for OFCOM).

BIBLIOGRAPHY

[1] http://www.fcc.gov/help/faqs-unlicensed-wireless-microphone-registrations#what_if_equipment.

[2] http://www.fohonline.com/home/20-features/6676-wireless-microphone-update-for-unlicensed-users.html.