Normal Performance Group

Description

The Normal Performance Group is a concept introduced in 3GPP Release 19 for UEs that support Increased UE carrier monitoring for UTRA (UMTS Terrestrial Radio Access) or E-UTRA (Evolved UTRA, i.e., LTE). When a UE is configured to monitor multiple inter-frequency or inter-RAT carriers, these carriers are divided into two groups based on their expected measurement delay performance. The group that offers better delay performance—meaning the UE can measure and report on these carriers more quickly—is referred to as the normal performance group. The other group, with worse delay performance, is typically called the reduced performance group. This grouping allows the network to optimize mobility and measurement configurations by prioritizing carriers that can be measured efficiently, while still monitoring others at a slower pace.

The concept arises from the need to balance measurement accuracy and latency with UE power consumption and complexity. In multi-carrier deployments, UEs must monitor neighboring cells on different frequencies and RATs to support handover and carrier aggregation. However, not all carriers can be measured with the same speed due to factors such as UE capabilities, carrier bandwidth, and synchronization requirements. The Increased UE carrier monitoring feature allows UEs to monitor more carriers than before, but with varying performance. By categorizing carriers into normal and reduced performance groups, the network can assign measurement gaps and scheduling priorities accordingly. For example, the UE may be required to report measurements for normal performance group carriers within a shorter time, while reduced performance group carriers can be measured over a longer period.

Architecturally, this grouping is internal to the UE and is based on the UE's measurement capabilities and the network's configuration. The network (e.g., eNB or gNB) signals the list of carriers to monitor, and the UE determines which carriers fall into which group based on its implementation and the defined performance requirements in specifications like 3GPP TS 25.133 (for UTRA) and TS 36.521 (for E-UTRA). The specifications define the measurement delay requirements for each group, ensuring that the UE meets certain performance targets. The normal performance group typically includes carriers that the UE can measure with minimal interruption to its current communication, often because they are in the same frequency band or have similar characteristics. The reduced performance group may include carriers that require more complex measurement procedures, such as those in different bands or with different duplex modes.

Key components include the UE's measurement engine, the network's measurement configuration, and the performance requirements defined in 3GPP specifications. The UE must be capable of supporting Increased UE carrier monitoring, which is a UE feature that indicates it can handle more carriers than baseline. The network uses this capability to configure measurements efficiently. The grouping helps in optimizing the trade-off between measurement latency and UE power consumption. For instance, the UE can spend more time on normal performance group carriers to ensure timely handover, while spending less time on reduced performance group carriers, which might be used for less critical mobility scenarios.

In practice, the Normal Performance Group concept is used in RRC connection reconfiguration messages, where the network provides measurement objects and reporting configurations. The UE then applies its internal grouping to determine how to schedule measurements. This is particularly important in heterogeneous networks with multiple frequencies and RATs, where efficient measurement is crucial for seamless mobility. The concept is part of the broader enhancements in Release 19 for increased carrier monitoring, which aims to improve network performance and UE experience in dense deployments.

Purpose & Motivation

The Normal Performance Group was introduced to address the challenges of increased carrier monitoring in multi-frequency, multi-RAT networks. As networks evolve with more frequency layers and RATs (e.g., LTE, NR, UMTS), UEs are required to monitor an ever-growing number of carriers to support mobility and carrier aggregation. However, monitoring many carriers simultaneously can lead to increased UE power consumption, longer measurement delays, and potential degradation of service. The Increased UE carrier monitoring feature was designed to allow UEs to handle more carriers, but it became clear that not all carriers can be measured with equal efficiency. The Normal Performance Group concept provides a structured way to differentiate carriers based on their measurement delay performance, enabling the network to prioritize carriers that can be measured quickly.

Historically, before Release 19, UEs had limited capability to monitor multiple carriers, and measurement requirements were more uniform. With the introduction of Increased UE carrier monitoring, UEs can support a larger number of carriers, but the performance varies. Without grouping, the network might configure measurements in a way that either overburdens the UE or fails to meet mobility requirements. The Normal Performance Group solves this by allowing the network to know which carriers the UE can measure with better delay performance, so it can allocate measurement gaps and reporting periods appropriately. This ensures that critical carriers (e.g., those needed for handover) are measured promptly, while others are measured less frequently, optimizing the UE's measurement workload.

The motivation also includes improving the efficiency of measurement gap scheduling. Measurement gaps are periods when the UE tunes away from its serving cell to measure other frequencies. If the UE has to measure many carriers, gaps can become frequent and long, impacting throughput. By categorizing carriers into normal and reduced performance groups, the network can schedule gaps more intelligently, focusing on normal performance group carriers for critical measurements. This leads to better user experience and more efficient use of network resources. The concept is part of 3GPP's continuous efforts to enhance mobility and carrier management in increasingly complex radio environments.