Description
Cumulative Adjacent Channel Leakage Ratio (CACLR) is a stringent radio frequency (RF) conformance test parameter defined in 3GPP specifications for base stations (Node B, eNB, gNB) and user equipment. It quantifies the transmitter's ability to confine its emitted power within its allocated channel bandwidth, specifically by measuring the aggregate leakage power that spills over into a defined set of adjacent frequency channels. Unlike the simpler Adjacent Channel Leakage Ratio (ACLR), which typically considers only the first adjacent channel, CACLR sums the leakage power across several adjacent channels (e.g., the first, second, and sometimes third adjacent channels) and compares this cumulative unwanted power to the power in the main transmitted channel. This provides a more comprehensive assessment of a transmitter's spectral purity and its potential to cause wideband interference.
The measurement methodology for CACLR is detailed in 3GPP TS 25.104, 36.104, and 38.104 for UTRA, E-UTRA, and NR respectively. The test setup involves a calibrated signal analyzer or a specialized test receiver. The device under test transmits a standardized test signal at a specified output power. The receiver then measures the power within the bandwidth of the assigned channel (P_assigned) and the integrated power within the bandwidths of the specified adjacent channels (P_adj1, P_adj2, ...). The CACLR is then calculated as the ratio of the sum of the powers in the adjacent channels to the power in the assigned channel, usually expressed in decibels (dB). A lower CACLR value indicates better performance, meaning less power is leaking into neighboring bands. The exact number of adjacent channels considered and the required limit values are specified per radio access technology (RAT), frequency band, and channel bandwidth.
CACLR's role is fundamental in the network's physical layer performance. It directly impacts the capacity and quality of service in multi-operator and multi-carrier environments. High CACLR can cause significant interference to receivers in adjacent channels, degrading their signal-to-interference-plus-noise ratio (SINR) and leading to dropped calls, reduced data throughput, and inefficient spectrum utilization. By enforcing strict CACLR requirements, 3GPP ensures that base stations and devices can coexist in the same geographical area without causing unacceptable degradation to each other's services. This is particularly vital for Time Division Duplex (TDD) deployments, where base stations may transmit simultaneously on adjacent channels, and for Carrier Aggregation (CA) scenarios where a device or base station aggregates multiple component carriers that are closely spaced in frequency.
Purpose & Motivation
CACLR was introduced to address the limitations of single-channel ACLR measurements in modern, spectrum-congested cellular networks. As networks evolved from single-carrier deployments to more complex architectures like Carrier Aggregation, network sharing, and dense small cell deployments, the potential for aggregated interference from a single transmitter into multiple nearby channels became a critical concern. A transmitter might pass individual ACLR tests for each adjacent channel but still generate a significant total amount of out-of-band emission when its leakage across several channels is combined. This cumulative effect could desensitize receivers operating on non-immediate adjacent channels, a scenario not adequately captured by traditional metrics.
The creation of CACLR was motivated by the need for a more holistic and realistic interference assessment tool. It solves the problem of ensuring predictable and manageable interference levels in real-world scenarios where multiple channels from the same or different operators are deployed in close spectral proximity. By setting a limit on the total unwanted power a transmitter can emit into a block of spectrum adjacent to its allocation, CACLR protects the overall integrity of the radio environment. This allows regulators and operators to pack channels more tightly, improving overall spectral efficiency and enabling higher network capacity, which is essential for meeting the growing demand for mobile broadband services. It represents an evolution in RF conformance testing from component-level analysis to system-level interference management.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (118 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-10, normative work from Rel-15.
In Release 15, the specifications introduced new test procedures and corrections for the Cumulative Adjacent Channel Leakage Ratio (CACLR). Specifically, this included the addition of Multi-User (MU) evaluation for testing output power, ACLR, and Operating Band Unwanted Emissions (OBUE) in the Radiated Configuration (RC) test method. The release also delivered corrections to text and tables for OTA ACLR and OBUE, as well as a correction for the channel spacing applicable to certain intraband Carrier Aggregation combinations.
- CR to TS 37.145-2: OTA Adjacent Channel Leakage Ratio (6.7.3) and OTA Operating band unwanted emissions (6.7.5) - corrections to text and tables TS 37.145CR0055
- CR to TR 37.843: Addition of MU evaluation for testing output power, ACLR and OBUE in RC test method in subclause 10.4 TS 37.843CR0020
- Correction of channel spacing for band 46 intraband CA band combinations with 10 MHz bandwidth TS 36.104CR4737
- CR to TS 37.105: absolute ACLR limit TS 37.105CR0077
In Release 16, the CACLR function was updated to correct the ACLR (Adjacent Channel Leakage Ratio) limit for operation in non-contiguous spectrum, as specified in a Change Request to TS 37.104. This correction addressed specific deployment scenarios to ensure proper coexistence and spectral efficiency.
- Addition channel bandwidth of 30MHz for n50 in TS 38.104 TS 38.104CR0031
- CR for TS 38.104: adding wider channel bandwidths in Band n7 TS 38.104CR0037
- CR for TS 38.104: adding wider channel bandwidths in Band n77/n78 TS 38.104CR0105
- CR for TS 38.104: Addition channel bandwidth of 40MHz for n38 TS 38.104CR0106
- Introducing new channel bandwidth for band n28 TS 38.104CR0131
- CR for TS 38.104: adding wider channel bandwidths for n66 TS 38.104CR0139
+ 25 more changes
In Release 17, the CACLR function was updated to introduce new test requirements for the 35 MHz and 45 MHz channel bandwidths, as detailed in specifications like TS 37.104, TS 37.141, and TS 37.145-2. This expansion also involved corresponding updates to NR base station specifications in TS 38.104 to add support for these wider channel bandwidths in existing bands. Furthermore, corrections and clarifications for ACLR (Adjacent Channel Leakage Ratio) requirements, which are directly related to CACLR, were made for NR repeaters and other equipment in TS 38.106 and TS 38.115-1.
- CR to 37.104: Introduction of requirements for 35 and 45MHz channel bandwidths TS 37.104CR0949
- CR for TS 37.141: introduction of channel bandwidths 35MHz and 45MHz TS 37.141CR0990
- CR for TS 37.145-2: introduction of channel bandwidths 35MHz and 45MHz TS 37.145CR0314
- Big CR to 38.104 - Additional Channel BW TS 38.104CR0258
- Big CR to 38.104 - Additional Channel BW TS 38.104CR0291
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0319
+ 21 more changes
In Release 18, the CACLR function was updated to account for the new 3 MHz channel bandwidth introduced for NR in FR1. This included defining the specific frequency offset (FoffsetRAT) for this bandwidth for ACLR testing. Additionally, corrections and clarifications were made to the ACLR requirements for channel bandwidths less than 5 MHz to ensure accurate conformance testing.
- CR to TS 37.141 - Consideration of NR 3 MHz channel bandwidth TS 37.141CR1068
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0450
- Big CR to TS 38.104 on introduction of 3 MHz channel bandwidth TS 38.104CR0500
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0512
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0538
- CR to TS38.104: Introduction of an enhanced channel raster TS 38.104CR0536
+ 34 more changes
In Release 19, the primary update for the CACLR function was the introduction and clarification of performance requirements for a new 7 MHz channel bandwidth for NR FR1. This included specifying the necessary restrictions and corrections for base station operation with this and other channel bandwidths below 10 MHz. Furthermore, a correction was made to the unit of measurement for Over-the-Air (OTA) Adjacent Channel Leakage Ratio (ACLR).
- CR to TS37.104 Introduction of 7 MHz NR FR1 channel bandwidth TS 37.104CR1028
- CR to TS 37.105: 7MHz channel bandwidth introduction TS 37.105CR0304
- CR to TS37.141 Introduction of 7 MHz NR FR1 channel bandwidth TS 37.141CR1098
- CR to TS 37.145-2: 7MHz channel bandwidth introduction TS 37.145CR0398
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0685
- CR to 38.104 on adding new UL channel bandwidth to band n48 TS 38.104CR0698
+ 10 more changes
Explore further
Broader topics and technologies where CACLR plays a role.
Defining Specifications
3GPP specifications that define or reference CACLR, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 25.104 vj00 | UTRA FDD Base Station RF Characteristics | Rel-19 |
| TS 25.141 vj00 | UTRA FDD Base Station RF Conformance Testing | Rel-19 |
| TS 36.104 vj10 | Base Station (BS) radio transmission and reception | Rel-19 |
| TS 36.141 vj00 | E-UTRA BS Conformance Testing | Rel-19 |
| TS 37.104 vj10 | MSR Base Station RF Characteristics | Rel-19 |
| TS 37.105 vj10 | AAS Base Station Transmission & Reception Requirements | Rel-19 |
| TS 37.141 vj10 | RF Test Methods for Multi-Standard Radio Base Stations | Rel-19 |
| TS 37.145 vj10 | AAS Base Station Conducted Conformance Testing | Rel-19 |
| TS 37.802 va10 | MSR BS RF Requirements for Non-Contiguous Spectrum | Rel-10 |
| TS 37.809 vb00 | E-UTRA & MSR BS Class Requirements | Rel-11 |
| TS 37.812 vb30 | Multi-band Multi-standard Radio BS Requirements | Rel-11 |
| TR 37.843 vf70 | AAS BS Radiated RF Requirement Background | Rel-15 |
| TR 37.941 vj20 | RF Conformance Testing Background for Radiated BS Requirements | Rel-19 |
| TS 38.104 vj20 | NR Base Station RF Requirements | Rel-19 |
| TS 38.106 vj20 | NR Repeater Radio Transmission and Reception | Rel-19 |
| TS 38.115 vj20 | NR Repeater RF Conformance Testing Part 1 | Rel-19 |
| TS 38.141 vj20 | NR Base Station RF Conformance Testing Part 1 | Rel-19 |
| TS 38.174 vj10 | NR Integrated Access and Backhaul Radio Spec | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.817 | 3GPP TR 38.817 | Rel-10 |