UTRA ACLR

Description

UTRAACLR is a term used in 3GPP Release 19 and later to denote the Adjacent Channel Leakage Ratio (ACLR) requirements for UTRA (UMTS Terrestrial Radio Access) systems, particularly in the context of spectrum sharing and coexistence with NR (New Radio). ACLR is a measure of the amount of power leaking into adjacent channels from a transmitter, and it is critical for ensuring that transmissions in one channel do not interfere with neighboring channels. UTRAACLR specifically addresses the ACLR performance of UTRA base stations or user equipment when operating in proximity to NR carriers.

The term appears in specifications such as TS 38.101 (NR UE radio transmission and reception) and TS 38.521 (NR UE conformance testing). These specifications define the radio requirements for NR UEs, but they also include provisions for coexistence with other technologies, including UTRA. UTRAACLR is likely a parameter that specifies the maximum allowed ACLR from a UTRA transmitter into an NR channel, or vice versa, to ensure that both systems can operate without harmful interference. This is particularly important in scenarios where UTRA and NR networks share the same frequency band or are deployed in adjacent bands.

In practice, UTRAACLR requirements are used in network planning and equipment design. For example, when deploying NR in a band adjacent to a UTRA band, the NR base station must ensure that its emissions into the UTRA band are below a certain level, and the UTRA base station must do the same for the NR band. The ACLR value is typically expressed in dB, representing the ratio of the transmitted power in the assigned channel to the power measured in an adjacent channel after filtering. UTRAACLR may specify different values for different band combinations and deployment scenarios.

The introduction of UTRAACLR in Release 19 reflects the ongoing need to manage coexistence between legacy UTRA networks and new NR networks. As operators refarm spectrum from UMTS to NR, they often need to operate both technologies in the same band or adjacent bands during a transition period. UTRAACLR provides a standardized way to quantify and limit interference, enabling smoother migration. It also supports dynamic spectrum sharing (DSS) scenarios where UTRA and NR share the same carrier.

From a technical standpoint, UTRAACLR is closely related to other ACLR definitions in 3GPP, such as NR ACLR and LTE ACLR. It is measured using similar methodologies, typically with a root-raised cosine (RRC) filter and specified measurement bandwidth. The requirements are defined for both base stations (BS) and user equipment (UE), though the term UTRAACLR may apply specifically to one or the other depending on context. In TS 38.101, for example, UTRAACLR requirements are given for NR UEs to protect UTRA networks, and vice versa.

Overall, UTRAACLR is a key parameter for ensuring harmonious coexistence between UTRA and NR, facilitating spectrum refarming and multi-technology deployments. It is part of the broader set of radio requirements that enable flexible and efficient use of spectrum in 5G and beyond.

Purpose & Motivation

UTRAACLR exists to address the interference challenges that arise when UTRA (UMTS) and NR (5G) networks operate in adjacent or shared spectrum. As operators transition from UMTS to 5G, they often need to run both technologies simultaneously, either in the same band or in neighboring bands. Without proper ACLR limits, transmissions from one system could leak into the other, causing degraded performance or service disruption.

Previously, ACLR requirements were defined separately for each technology (e.g., UTRA ACLR in TS 25.104/25.101, LTE ACLR in TS 36.101). However, with the advent of NR and the need for tight coexistence, 3GPP introduced specific requirements like UTRAACLR to ensure that NR equipment does not interfere with UTRA and vice versa. This is particularly important for dynamic spectrum sharing (DSS), where UTRA and NR share the same carrier, and for scenarios where NR is deployed in bands adjacent to UTRA.

The motivation for UTRAACLR is to provide a clear, standardized metric that equipment vendors and network operators can use to design and test radios that minimize interference. It enables spectrum refarming by allowing operators to deploy NR in bands currently used by UTRA without causing harmful interference to existing UTRA services. It also supports regulatory compliance by providing a basis for coexistence studies and limits.