Set of Radio Interface Technologies

Description

A Set of Radio Interface Technologies (SRIT) is a formalized concept within 3GPP that specifies a particular collection of radio access technologies. It is not a single protocol or interface but a defined set used for specifying requirements, capabilities, and testing scenarios, particularly for User Equipment (UE) and network nodes that support multiple RATs. An SRIT explicitly lists which RATs are included, such as LTE (E-UTRA), NR (New Radio), UTRA (WCDMA/TD-SCDMA), or even GSM/EDGE (GERAN). The definition allows for precise statements about which combinations of technologies a device or network feature must support. For example, an SRIT for a UE might be {LTE, NR} to denote it is an LTE-NR dual-connectivity capable device.

In practical application, SRITs are used in several key areas. First, in RF (Radio Frequency) conformance testing specifications (e.g., 3GPP TS 37.910), an SRIT defines the combination of RATs for which a UE's transmitter and receiver performance is tested. Tests cover scenarios like simultaneous transmission/reception on multiple RATs, ensuring no harmful interference and that performance requirements are met for each RAT in the set. Second, in feature specifications like carrier aggregation (CA) or dual connectivity (DC), an SRIT can define the permissible or required RAT combinations for a given feature deployment. This provides a clear framework for interoperability.

Architecturally, the SRIT concept acknowledges the heterogeneous nature of modern radio access networks (HetNets). It moves beyond single-RAT specifications to model the real-world environment where a UE may be connected to an LTE anchor cell and an NR secondary cell, or be capable of handover between them. The SRIT is a tool for system designers and test engineers to create unambiguous requirements. It is closely tied to the UE's declared capabilities via RRC (Radio Resource Control) signaling or UE capability transfer procedures, where the UE informs the network of the RATs and band combinations it supports, which can be interpreted as one or more SRITs.

Purpose & Motivation

The SRIT concept was introduced to address the growing complexity of multi-RAT devices and networks. Prior to its formalization, specifications often dealt with each RAT in isolation. However, with the advent of features like LTE-WLAN aggregation (LWA), LTE-NR dual connectivity (EN-DC), and later NR-NR DC, there was a need for a standardized way to refer to and specify requirements for specific combinations of technologies. This was driven by the industry's move towards seamless multi-RAT operation, where devices can leverage multiple radio links for enhanced data rates, reliability, and mobility.

Its creation, notably in Release 9 alongside early work on LTE-Advanced, provided a foundational model for defining UE and network behavior in a multi-RAT context. It solved the problem of ambiguous references to "multi-mode" devices by providing a precise, enumerable set. This precision is crucial for conformance testing, ensuring that a device claiming to support LTE and NR together is tested under all the relevant combined operational scenarios, not just each RAT independently. It also aids in network planning and feature development by clearly scoping which technology combinations are in scope for a particular specification or network deployment option.

Key Features

• Formally defines a specific combination of radio access technologies (e.g., {E-UTRA, NR})
• Used as a basis for defining RF conformance test requirements for multi-RAT UEs
• Provides a clear scope for features like carrier aggregation and dual connectivity
• Enables precise specification of UE capabilities and network requirements
• Supports testing of simultaneous transmission and reception across different RATs
• Facilitates unambiguous communication in standards and network planning

Evolution Across Releases

Defining Specifications