Signal level Enhanced Network Selection

Description

Signal level Enhanced Network Selection (SENSE) is a feature defined in 3GPP specifications 24.368 and 31.102, introduced in Release 19. It enhances the traditional network selection procedures used by user equipment (UE) when choosing a public land mobile network (PLMN). In legacy network selection, the UE prioritizes PLMNs based on a predefined order: the home PLMN (HPLMN), equivalent home PLMNs (EHPLMN), user-controlled PLMNs, operator-controlled PLMNs, and others. Signal level is typically considered only as a secondary criterion, and often only to determine whether a cell is suitable for camping. SENSE changes this by incorporating signal level measurements more prominently into the network selection decision, particularly when multiple PLMNs are available with similar priority.

The core mechanism of SENSE involves the UE performing signal level measurements on cells belonging to different PLMNs during the network selection process. Instead of simply selecting the highest-priority PLMN that provides acceptable service, the UE evaluates the signal quality of each candidate PLMN and selects the one that offers the best trade-off between priority and signal level. This is particularly useful in border areas where multiple networks overlap, or in shared network deployments where several operators share the same radio access network. By selecting the PLMN with the strongest signal, the UE can achieve better throughput, lower latency, and improved battery life due to reduced transmit power requirements.

SENSE is implemented through enhancements to the UE's network selection algorithms and is controlled by parameters stored in the USIM (Universal Subscriber Identity Module) and the UE's non-volatile memory. Specification 31.102 defines the USIM file structure and parameters that support SENSE, such as the list of PLMNs and their associated signal level thresholds. Specification 24.368 defines the non-access stratum (NAS) configuration and procedures for network selection, including how the UE evaluates signal levels and applies them to the selection decision. The UE may also receive SENSE-related parameters from the network via over-the-air (OTA) updates or NAS signalling.

The SENSE procedure begins when the UE is powered on or loses coverage and needs to select a PLMN. The UE scans for available PLMNs and measures the signal level of each cell it detects. It then ranks the PLMNs based on a combination of priority and signal level. The exact ranking algorithm may be operator-configurable, allowing the operator to define the weight given to signal level versus priority. For example, an operator might specify that a lower-priority PLMN with a significantly stronger signal can be selected over a higher-priority PLMN with a weak signal. Once a PLMN is selected, the UE proceeds with cell selection and registration.

SENSE also interacts with other network selection features, such as Equivalent PLMN (EPLMN) handling and Manual Network Selection. In manual mode, the UE presents a list of available PLMNs to the user, and SENSE can enhance this list by indicating signal levels or sorting by signal strength. In automatic mode, SENSE operates transparently to the user. The feature is particularly beneficial for international roaming, where a user may have access to multiple visited PLMNs. By selecting the network with the best signal, the user experiences better service quality without manual intervention.

From a standards perspective, SENSE represents a shift towards more intelligent and user-centric network selection. It leverages the increasing capabilities of modern UEs to perform frequent and accurate signal measurements without excessive battery drain. The feature is expected to be widely adopted in 5G and future networks, where network densification and spectrum sharing create complex radio environments with multiple overlapping PLMNs.

Purpose & Motivation

SENSE was developed to improve the user experience during network selection by prioritizing signal quality alongside traditional PLMN priority. In legacy systems, a UE would often select a high-priority PLMN even if its signal was weak, leading to poor call quality, dropped connections, and increased power consumption. This was particularly problematic in border areas, at airports, or in shared network environments where multiple PLMNs are available. SENSE addresses this by allowing the UE to consider signal level as a primary factor when selecting among PLMNs of similar priority.

The motivation for SENSE also comes from the growing complexity of mobile networks. With the advent of 5G, network slicing, and shared infrastructure, users may have access to multiple PLMNs that offer different levels of service. Traditional network selection, based solely on priority lists, cannot adapt to dynamic radio conditions. SENSE introduces a more dynamic and context-aware selection process, ensuring that the UE connects to the network that can provide the best performance at the moment of selection.

Furthermore, SENSE helps operators manage their networks more efficiently. By encouraging UEs to select the PLMN with the best signal, it reduces the load on weaker cells and improves overall spectral efficiency. It also supports national roaming and MVNO scenarios, where multiple operators share the same radio access network. In such cases, SENSE ensures that UEs are distributed across the available PLMNs in a way that optimizes both user experience and network resource utilization. The inclusion of SENSE in Release 19 specifications reflects the ongoing evolution of network selection mechanisms to meet the demands of increasingly heterogeneous and dense radio environments.