Early Spread-Spectrum Regulations
Prior to 1985, the use of spread-spectrum modulation was not permitted in the United States (and most countries) for commercial communication. Its use was limited mainly to experimental and military use. In 1985, the FCC changed Part 15 of the Code of Federal Regulations to permit the use of spread-spectrum modulation in certain ISM bands. The FCC rules tend to discourage use of amplifiers, high-gain antennas, and other means of increasing RF radiation significantly. The rules are further intended to discourage systems that are installed by inexperienced users and that either intentionally or unintentionally do not comply with FCC regulations for use in the ISM band. The rationale behind the strict regulations is to enable multiple RF networks to coexist with minimum impact on one another by exploiting the properties of spread-spectrum technology.Basically, these rules seek to limit RF communications in the ISM band to a well-defined region (that is, wireless local-area network), while ensuring multiple systems can operate with minimum impact on one another. These two needs are addressed by limiting the transmitter power and the type and gain of antennas used with a given system, and by requiring a greater degree of RF energy efficiency or spreading.The IC followed the FCC rules very closely, and in many cases adopted the FCC regulations on a word-for-word basis. The rest of the world soon followed suit, enacting regulations to govern the growing number of WLAN products. You will read more about these regulations throughout this chapter.
Intentional Versus Unintentional Radiators
In the discussion of the regulations throughout this chapter, a distinction is made between intentional and unintentional radiators. A spread-spectrum transmitter is designed to send out (or emit) an RF signal. This (or any radio transmitter for that matter) is known as an intentional radiator. Intentional radiators emit signals that are wanted (or intended for emission).Although this chapter focuses on the intentional emissions of 802.11 transmitting devicesin other words, the radio energy produced to transmit informationcertain regulations refer to unintentional radiators. Practically any electronic device also emits unintentional RF emissions of some level of energy that can impact the operation of other devices. Unintentional radiators are devices that emit radio signals typically not designed for transmission. (These are, in most cases, unwanted signals.)These unintentional radiations are also subject to regulation. In the FCC regulatory domain, the level of unintentional emissions falls into two general categories: Class A or Class B. The FCC Class A device allows for a higher emission amount, and regulations of this class apply to devices designed for operation in industrial, office, and similar commercial environments. The FCC Class B device must meet a more stringent standard that applies to operation in residential environments and commercial environments representing a superset of the two.A similar set of dual standards exists in the European Telecommunication Standards Institute (ETSI) domain, which falls under the Conférence Européene des Administrations des Postes et des Télécommunications Administrations (translated to European Conference of Postal and Telecommunications [CEPT]). The document #EN-55022 describes these standards. ETSI follows similar naming conventions in that it has a Class A for commercial use and a Class B for residential operation, although the classes do not identically match the FCC Class A and Class B in terms of emission allowances.emissions standard (Class A) than their lower-cost counterparts designed for installation in the home. It is typical for enterprise-destined APs to be FCC Class B certified, even though it is not an absolute requirementit just shows a generally higher level of quality.Almost all electronic devices, including 802.11 devices as well as your computers, televisions, video game machines, radios receivers, and so on, have a Class A or Class B rating. |
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