Chapter 9: Regulatory Aspects of 802.11

An objection often raised about 802.11 applications is that because the spectrum used by 802.11 (2.4 GHz for 802.11b and 5.8 GHz for 802.11a) is unlicensed, it will inevitably become overused (called tragedy of the commons) to a point of being unusable at which time the government (U.S. or other) will step in to control the spectrum, making it no longer free, thus costing the service provider his or her profit margin and relegating the market to deep-pocketed monopolists.

This chapter explores the considerations wireless service providers should take into account when deploying service on unlicensed 802.11 bands. Next, it explores a new initiative from the Federal Communications Commission (FCC), which heralds a change to spectrum management that may actually serve to liberalize the FCC's approach to what spectrum is unlicensed. Finally, the chapter covers an initiative in the U.S. Congress to free more spectrum for the use of broadband wireless Internet applications. If anything, it appears that the U.S. government is developing a policy to encourage the use of unlicensed spectrum.

The Current Regulatory Environment

Even though 802.11 operates in unlicensed spectrum, a service provider must know a number of things in order to stay out of trouble with state and federal authorities. The following paragraphs outline the most prominent problem areas.

Spectrum is managed by a number of different organizations. The most visible to the general public is the FCC. The FCC manages civilian, state, and local government usage of the radio spectrum. The FCC regulations are contained in the "Code of Federal Regulations, Title 47."

At the time of this writing, the FCC has very limited resources for enforcement, as the trend for the last couple of decades has been deregulation and the reduction of staffing in the enforcement bureaus. The National Telecommunications and Information Administration (NTIA), which works with the Interdepartmental Radio Advisory Committee (IRAC), also manages federal use of the spectrum.

The following sections are a brief overview of what a service provider needs to be concerned about when operating in unlicensed spectrum. This synopsis was provided by Tim Pozar of the Bay Area Wireless Users Group based on many years experience advising friends and clients on what they can and cannot do with unlicensed spectrum.

Power Limits

Ideally, a well-engineered path has just the amount of power required to get from point A to point B with good reliability. Good engineering limits the signal to only the area being served. This has the effect of reducing interference and enabling more efficient use of the spectrum. Using too much power covers more area than is needed and could potentially interfere with other users of the band. Because 802.11 is designed for short-range use, such as offices and homes, it is limited to very low power.

802.11b—Its Relationship to FCC Part 15, Section 247 Regulatory aspects of 802.11 per Part 15 are oriented around the applications of the wireless technologies. The distinction is point-to-multi-point and point-to-point.

Point to Multipoint 802.11 service providers are allowed up to 30 dBm or 1 watt of Transmitter Power Output (TPO) with a 6 dBi antenna or 36 dBm or 4 watts effective isotropic radiated power (EIRP). The TPO needs to be reduced 1 dB for every decibel of antenna gain over 6 dBi.

Point to Point The FCC encourages the use of directional antennas to minimize interference to other users. In fact, the FCC is more lenient with point-to-point links by requiring only the TPO to be reduced by one-third of a decibel instead of a full decibel for point to multipoint. More specifically, for every 3 dB of antenna gain over a 6 dBi antenna, a wireless Internet service provider (WISP) needs to reduce the TPO 1 dB below 1 watt. For example, say a 24 dBi antenna is 18 dB over a 6 dBi antenna. This requires lowering a 1 watt (30 dBm) transmitter 18/3 or 6 dB to 24 dBm or 1/4 watt.

802.11a—FCC Part 15, Section 407 Regulatory aspects of 802.11 per Part 15 are oriented around the applications of the wireless technologies. The distinction is point-to-multi-point and point-to-point.

Point to Multipoint As described before, the Unlicensed National Information Infrastructure (U-NII) band is chopped into three sections. The low band runs from 5.15 to 5.25 GHz, with a maximum power of 50 mW (TPO). This band is meant to be in-building only as defined by the FCC's Rules and Regulations Part 15.407(d) and (e):

• (d) Any U-NII device that operates in the 5.15–5.25 GHz band shall use a transmitting antenna that is an integral part of the device.

• (e) Within the 5.15–5.25 GHz band, U-NII devices will be restricted to indoor operations to reduce any potential for harmful interference to co-channel MSS operations.

The middle band runs from 5.25 to 5.35 GHz, with a maximum power limit of 250 mW. Finally, the high band runs from 5.725 to 5.825 GHz, with a maximum transmitter power of 1 watt and antenna gain of 6 dBi or 36 dBm or 4 watts EIRP.

Point to Point As with 802.11b, the FCC does give some latitude to point-to-point links in Part 15.407(a)(3). For the 5.725–5.825 GHz band, the FCC allows a TPO of 1 watt and up to a 23 dBi gain antenna without reducing the TPO 1 dB for every 1 dB of gain over 23 dBi.

Part 15.247(b)(3)(ii) does allow the use of any gain antenna for point-to-point operations without having to reduce the TPO for the 5.725–5.825 GHz band.

Interference

Of course, interference is typically the state of the signal you are interested in while it is being destructively overpowered by a signal you are not interested in. The FCC provides a specific definition of harmful interference in Part 15.3(m):

• (m) Any emission, radiation, or induction that endangers the functioning of a radio navigation service or of other safety services or seriously degrades, obstructs, or repeatedly interrupts a radiocommunications service operating in accordance with this chapter.

Because this band has other users, interference will be a factor in 802.11 deployments. The 2.4 GHz band is a bit more congested than the 5.8 GHz band, but both have their co-users. Table 9-1 describes the other users of this spectrum and what interference mitigation may be possible for each.

Table 9-1: Spectrum allocation for 802.11 and co-users

Part/User	Start GHz	End GHz
Part 87	0.4700	10.5000
Part 97	2.3900	2.4500
Part 15	2.4000	2.4830
Fusion lighting	2.4000	2.4835
Part 18	2.4000	2.5000
Part 80	2.4000	9.6000
Industrial, Scientific, and Medical (ISM)—802.11b	2.4010	2.4730
Part 74	2.4500	2.4835
Part 101	2.4500	2.5000
Part 90	2.4500	2.8350
Part 25	5.0910	5.2500
U-NII low	5.1500	5.2500
U-NII middle	5.2500	5.3500
Part 97	5.6500	5.9250
U-NII high	5.7250	5.8250
ISM	5.7250	5.8500
Part 18	5.7250	5.8750
Source: Tim Pozar, Bay Area Wireless Users Group from FCC sources

Devices that Fall into Part 15 This band includes unlicensed telecommunications devices like cordless phones, home spy cameras, and frequency-hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS) local area network (LAN) transceivers. Operators have no priority over or parity with any of these users, and any device that falls into Part 15 must not cause harmful interference to all licensed and legally operating Part 15 users and must accept interference from all licensed and legally operating Part 15 users. This is stated in Part 15.5(b) and (c):

• (b) Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by ISM equipment, or by an incidental radiator.

• (c) The operator of a radio frequency device shall be required to cease operating the device upon notification by a Commission representative that the device is causing harmful interference. Operation shall not resume until the condition causing the harmful interference has been corrected.

Operators of other licensed and nonlicensed devices can inform you of interference and require that you terminate operation. It doesn't have to be a Commission representative.

Using 802.11b, you can interfere even if you are on different channels, as the channels are 22 MHz wide and only spaced 5 MHz apart. Channels 1, 6, and 11 are the only channels that do not interfere with each other. (See Table 9-2.)

Table 9-2: Spectrum bands of 802.11b

Channel	Bottom (GHz)	Center (GHz)	Top (GHz)
1	2.401	2.412	2.423
2	2.406	2.417	2.428
3	2.411	2.422	2.433
4	2.416	2.427	2.438
5	2.421	2.432	2.443
6	2.426	2.437	2.448
7	2.431	2.442	2.453
8	2.436	2.447	2.458
9	2.441	2.452	2.463
10	2.446	2.457	2.468
11	2.451	2.462	2.473
Source: Tim Pozar, Bay Area Wireless Users Group from FCC sources

Devices that Fall into the U-NII Band Unlike the 2.4 GHz band, this band does not have overlapping channels. The lower U-NII band has eight 20 MHz wide channels. You can use any of the channels without interfering with other radios on other channels that are within earshot. Ideally, it would be good to know what other Part 15 users are out there. Looking into groups under the banner of Freenetworks is a good place to start.

ISM—Part 18 This band is also an unlicensed service. Typical ISM applications are the production of physical, biological, or chemical effects such as heating, the ionization of gases, mechanical vibrations, hair removal, and the acceleration of charged particles. This band carries ultrasonic devices such as jewelry cleaners and ultrasonic humidifiers, microwave ovens, medical devices such as diathermy equipment and magnetic resonance imaging (MRI) equipment, and industrial uses such as paint dryers (Part 18.107). Radio frequency (RF) should be contained within the devices, but other users must accept interference from these devices. Part 18 frequencies that could affect 802.11 devices are in the 2.400 to 2.500 GHz and 5.725 to 5.875 GHz ranges. As Part 18 devices are unlicensed and operators are likely clueless of the impact, it will be difficult to coordinate with them. Fusion lighting is also covered by Part 18.

Satellite Communications—Part 25 This part of the FCC's rules is used for the uplink or downlink of data, video, and so on to/from satellites in Earth's orbit. One band that overlaps the U-NII band is reserved for Earth-to-space communications at 5.091 to 5.25 GHz. Within this spectrum, 5.091 to 5.150 GHz is also allocated to the fixed-satellite service (Earth to space) for nongeostationary satellites on a primary basis. The FCC is trying to decommission this band for feeder use to satellites as "after 01 January 2010, the fixed-satellite service will become secondary to the aeronautical radio-navigation service." A note in Part 2.106, §5.446 also allocates 5.150 to 5.216 GHz for a similar use, except it is for space-to-Earth communications. There is a higher chance of interfering with these installations, as Earth stations deal with very low signal levels from distance satellites.

Broadcast Auxiliary—Part 74 Normally, the traffic on this band is Electronic News Gathering (ENG) video links going back to studios or television transmitters. These remote vehicles such as helicopters and trucks need to be licensed. Only Part 74 eligibles such as TV stations, networks, and so on can hold these licenses (Part 74.600). Typically, these transmitters are scattered all around an area, as TV remote trucks can go anywhere. This can cause interference to 802.11 gear such as access points (APs) deployed with omnidirectional antennas servicing an area. Also the receive points for ENG are often mountain tops and towers. Depending how 802.11 transmitters are deployed at these same locations, they could cause interference to these links. Wireless providers should consider contacting a local frequency coordinator for Part 74 frequencies that would be affected. There have been reports of FHSS devices interfering with these transmissions as the dwell time for this FHSS tends to punch holes in the video links. DHSS is less likely to cause interference to ENG users, but their links can cause problems with another person's 802.11 deployment. ENG frequencies that overlap 802.11 devices are 2.450 to 2.467 GHz (channel A08) and 2.467 to 2.4835 GHz (channel A09) (Part 74.602).

Land Mobile Radio Services—Part 90 For subpart C of this part, users can be anyone engaged in a commercial activity. They can use 2.450 to 2.835 GHz, but can only license 2.450 to 2.483 GHz. Users in subpart B would be local government. This would include organizations such as law enforcement, fire departments, and so on. Some uses may be video downlinks for flying platforms such as helicopters, also known as terrestrial surveillance. Depending on the commercial or government agency, coordination goes through different groups like the Association of Public Safety Communications Officials (APCO). Consider going to their conferences. You can also try to network with engineering companies that the government out-sources to for their frequency coordination.

Amateur Radio—Part 97 Amateur radio frequencies that overlap 802.11b are 2.390 to 2.450 GHz and 5.650 to 5.925 GHz for 802.11a. They are primary from 2.402 to 2.417 GHz and secondary from 2.400 to 2.402 GHz. There is a Notice of Proposed Rule Making (NPRM) in with the FCC to change the 2.400 to 2.402 GHz range to primary. Amateurs are very protective about their spectrum.

Fixed Microwave Services—Part 101 Users of this band are known as Local Television Transmission Service (LTTS) and Private Operational Fixed Point-to-Point Microwave Service (POFS). This band is used to transport video. The channels are allocated from 2.450 to 2.500 GHz.

Federal Usage (NTIA/IRAC) The federal government uses this band for radiolocation or radionavigation. Several warnings in the FCC's Rules and Regulations disclose this fact. In the case of 802.11b, a note in the Part 15.247(h) gives the following warning:

• (h) Spread spectrum systems are sharing these bands on a noninterference basis with systems supporting critical government requirements that have been allocated the usage of these bands, secondary only to ISM equipment operated under the provisions of Part 18 of this chapter. Many of these government systems are airborne radiolocation systems that emit a high EIRP, which can cause interference to other users.

In the case of 802.11a, the FCC has a note in Part 15.407(a)(3) stating the following:

• The Commission strongly recommends that parties employing U-NII devices to provide critical communications services should determine if there are any nearby government radar systems that could affect their operation.