Spatial exclusion zone

Description

The spatial exclusion zone is a concept defined in 3GPP specifications for radiated immunity testing of base station equipment, specifically for Integrated Access and Backhaul (IAB) nodes of type 1-O and type 2-O. It refers to a range of angles around the equipment under test (EUT) where no radiated immunity tests are conducted. This zone is typically a half-sphere around the EUT's radiating direction, meaning that the tests are only performed in the forward direction of the antenna, and the backward directions are excluded. The purpose of this exclusion is to simplify the test setup and reduce the complexity of evaluating the equipment's immunity to external electromagnetic fields, as the backside of the antenna is not intended to receive or transmit signals in normal operation.

The spatial exclusion zone is defined in several 3GPP specifications, including TS 37.114 (for IAB type 1-O and type 2-O), TS 38.113 (for BS type 1-O), TS 38.114 (for BS type 2-O), and TS 38.175 (for IAB). These specifications detail the test procedures for radiated immunity, which is a type of electromagnetic compatibility (EMC) test that verifies the equipment's ability to function correctly in the presence of external electromagnetic fields. The spatial exclusion zone is a key parameter in these tests, as it defines the angular region where the test signals are not applied. The zone is typically specified in terms of azimuth and elevation angles relative to the EUT's antenna boresight. For example, the exclusion zone might cover all angles behind the antenna, i.e., a half-sphere, while the tests are performed in the front half-sphere.

The rationale for the spatial exclusion zone is based on the physical characteristics of the base station antenna. In a typical deployment, the antenna is mounted such that its main beam points outward to cover a cell sector. The backside of the antenna is usually mounted against a wall or pole, and the radiation in that direction is minimal. Therefore, external electromagnetic fields are unlikely to impinge on the equipment from the backside. By excluding the backside from immunity testing, the test effort is reduced, and the test setup is simplified. Additionally, the exclusion zone helps to avoid testing in directions where the equipment's response is not representative of real-world conditions.

The spatial exclusion zone was introduced in Rel-15, initially for BS type 1-O and BS type 2-O. In Rel-16, the definition was updated to include IAB type 1-O and IAB type 2-O, reflecting the introduction of IAB in 5G NR. IAB is a feature that allows base stations to wirelessly backhaul traffic, and the testing requirements for IAB nodes are similar to those for regular base stations. The definition has remained essentially the same in subsequent releases, with minor editorial changes. The spatial exclusion zone is an important concept for equipment manufacturers and test laboratories, as it defines the scope of radiated immunity testing and ensures that tests are conducted in a consistent and repeatable manner.

In summary, the spatial exclusion zone is a defined angular region where radiated immunity tests are not performed for IAB type 1-O and type 2-O base stations. It simplifies testing by excluding the backside of the antenna, which is not used for normal operation. The concept is specified in 3GPP TS 37.114, 38.113, 38.114, and 38.175, and has been part of the specifications since Rel-15. It reflects the practical considerations of testing large antenna systems and ensures that EMC tests are focused on the relevant directions.

Purpose & Motivation

The spatial exclusion zone exists to simplify and streamline radiated immunity testing for base station equipment, particularly for IAB nodes. Radiated immunity tests are part of electromagnetic compatibility (EMC) requirements, ensuring that equipment can operate correctly in the presence of external electromagnetic fields. However, testing the entire spherical space around a base station is impractical and unnecessary, as the equipment is designed to operate with its antenna pointing in a specific direction. The backside of the antenna is typically shielded or not used for reception, so external fields from that direction are unlikely to affect performance. By defining a spatial exclusion zone, the specifications allow manufacturers and test labs to focus testing on the relevant directions, reducing test time and cost.

Before the introduction of the spatial exclusion zone, radiated immunity tests might have required testing in all directions, which was cumbersome and time-consuming. The exclusion zone provides a standardised way to define the angular region where tests are not required, ensuring consistency across different test setups. This is particularly important for massive MIMO and AAS (Active Antenna System) base stations, where the antenna array is integrated into the equipment and the radiating direction is well-defined. The exclusion zone also helps to avoid testing in directions where the equipment's response might be dominated by the mounting structure or other non-representative factors.

The spatial exclusion zone was introduced in Rel-15 as part of the 5G NR specifications, reflecting the need for efficient testing of advanced antenna systems. It has been maintained in subsequent releases, with the definition extended to cover IAB nodes in Rel-16. The concept is now an established part of 3GPP EMC test specifications and is used by test labs worldwide. It represents a pragmatic approach to testing, balancing the need for thorough verification with the practical constraints of testing large antenna systems.