Transmitter exclusion band

Description

The transmitter exclusion band is a concept in 3GPP specifications related to electromagnetic compatibility (EMC) testing of radio equipment. It defines a band of frequencies over which no tests of radiated immunity of a transmitter are made. Radiated immunity tests assess a device's ability to withstand external electromagnetic fields without performance degradation. The exclusion band is expressed relative to the carrier frequencies used by the base station's activated transmitters. This means that the exclusion band is centered around the operating frequencies of the transmitter, and within this band, the transmitter is not subjected to immunity testing because it would be impractical or unnecessary.

The exclusion band is specified in TS 21.905, TS 25.113, TS 36.113, TS 37.113, and TS 38.113. These specifications cover EMC requirements for base stations, repeaters, and user equipment. The exclusion band is typically defined as a percentage of the carrier frequency or as a fixed bandwidth around the carrier. For example, in some specifications, the exclusion band might be ±5% of the carrier frequency. The exact definition depends on the radio access technology and frequency band.

The purpose of the exclusion band is to avoid testing the transmitter's immunity at frequencies where it is transmitting, as the transmitter's own signal would interfere with the test. Immunity tests involve applying an external electromagnetic field to the equipment and monitoring its performance. If the equipment is transmitting at the same frequency, the test would be invalid. Therefore, the exclusion band ensures that the test is performed only at frequencies outside the transmitter's operating band.

The exclusion band is important for ensuring that EMC testing is both meaningful and efficient. It allows manufacturers to focus on frequencies where the device is susceptible to interference, while avoiding unnecessary testing at frequencies where the device is inherently immune due to its own transmission. This reduces test time and cost. The exclusion band is also used in conjunction with other EMC parameters, such as the immunity test level and the performance criteria.

The definition of the transmitter exclusion band has remained largely unchanged since its introduction in Release 6. There was a minor wording change in Release 15, where the closing parenthesis was moved, but the technical meaning is identical. In Release 17, the wording was slightly rephrased but the substance remained the same. This consistency reflects the stable nature of EMC requirements. As new frequency bands and technologies are introduced, the exclusion band concept continues to be applied, ensuring that EMC testing remains relevant and effective.

Purpose & Motivation

The transmitter exclusion band exists to make radiated immunity testing practical and meaningful for radio transmitters. Radiated immunity tests are designed to ensure that a device can operate correctly in the presence of external electromagnetic fields, such as those from other transmitters or electrical equipment. However, testing a transmitter's immunity at its own operating frequency is not feasible because the transmitter's own signal would dominate the test environment, making it impossible to distinguish the effects of the external field. The exclusion band solves this by defining a frequency range around the carrier where no immunity tests are performed.

Historically, as cellular technologies proliferated, the need for standardized EMC testing became critical to ensure coexistence and reliable operation. The exclusion band was introduced in 3GPP Release 6 as part of the EMC specifications for base stations and user equipment. It provided a clear rule for test laboratories and manufacturers, eliminating ambiguity about which frequencies to test. This helped harmonize EMC requirements across different regions and technologies.

The exclusion band also reflects the physical reality that a transmitter is inherently immune to external signals at its own frequency because it is transmitting at that frequency. The receiver, however, may be susceptible, but immunity tests for receivers are separate. Thus, the exclusion band is a pragmatic solution that balances the need for thorough testing with the constraints of the test environment. It continues to be relevant as new radio technologies and frequency bands are introduced, ensuring that EMC testing remains efficient and effective.