Satellite Access Node type 1-O

Description

SAN type 1-O is a specific classification of a Satellite Access Node (SAN) within the 3GPP Non-Terrestrial Network (NTN) framework. It is defined for operation in the Frequency Range 1 (FR1) NTN bands, which typically include sub-6 GHz frequencies. The '1-O' designation indicates that the requirement set for this node type consists exclusively of Over-The-Air (OTA) requirements that are defined at the Radio Interface Boundary (RIB). This means that the performance requirements are specified at the air interface, rather than at internal interfaces or reference points within the satellite or gateway. This approach simplifies the specification and testing of satellite access nodes, as it focuses on the end-to-end radio performance that directly impacts the user experience.

The SAN itself is the functional entity that provides the radio interface to User Equipment (UE) in an NTN. It may be implemented on a satellite (space-borne) or on a high-altitude platform station (HAPS). In the case of SAN type 1-O, the node operates in FR1-NTN, which is the satellite-specific variant of FR1. The OTA requirements at the RIB include parameters such as Equivalent Isotropically Radiated Power (EIRP), Error Vector Magnitude (EVM), and adjacent channel leakage ratio (ACLR), among others. These requirements ensure that the SAN transmits and receives signals with sufficient quality and within regulatory limits, enabling reliable communication with UEs and inter-operation with other network elements.

The definition of SAN type 1-O was introduced in 3GPP Release 17, which is the first release to specify NTN in detail. The relevant specifications are 36.108 (for LTE NTN) and 38.108 (for NR NTN). These documents define the requirements for satellite access nodes, including the OTA requirements at the RIB. The classification into types (e.g., type 1-O, type 2-O, etc.) helps to differentiate between different implementation options and deployment scenarios. For instance, a SAN type 1-O might be a transparent payload satellite that only amplifies and frequency-converts the signal, while other types might involve regenerative payloads with on-board processing.

In the overall NTN architecture, the SAN communicates with the satellite-gateway (earth station) and the UE. The gateway connects the satellite network to the terrestrial core network. The SAN type 1-O's OTA requirements ensure that the radio link between the SAN and the UE meets the necessary performance targets, such as data rate, latency, and reliability. This is particularly important for NTN, where the long propagation delay and Doppler effects pose unique challenges. By defining requirements at the RIB, 3GPP allows for flexibility in the internal design of the SAN, as long as the external radio performance is met.

Since its introduction in Release 17, the definition of SAN type 1-O has remained unchanged in Releases 18 and 19. This stability indicates that the initial specification was sufficient and that no updates were needed to accommodate new features or deployment scenarios. The term continues to be relevant as NTN deployments evolve, and it serves as a foundational concept for specifying and testing satellite access nodes in FR1 NTN.

Purpose & Motivation

The SAN type 1-O classification exists to provide a clear and standardized set of performance requirements for satellite access nodes operating in FR1 NTN. By focusing solely on OTA requirements at the RIB, it simplifies the specification and testing process, ensuring that different SAN implementations can interoperate and meet the quality of service expected by users. This approach also allows for innovation in internal design, as long as the external radio performance is compliant.

Prior to the introduction of NTN specifications in Release 17, there was no standardized framework for satellite access in 3GPP networks. The SAN type 1-O definition addresses the need for a common understanding of the radio performance requirements for satellite nodes, which is essential for multi-vendor interoperability and global roaming. It also helps regulators and operators to verify that satellite transmissions comply with spectrum regulations.

The motivation for defining SAN types stems from the diverse nature of satellite payloads (transparent vs. regenerative) and the different frequency bands (FR1 vs. FR2). By categorizing SANs, 3GPP can tailor requirements to specific scenarios, avoiding overly generic or stringent specifications. SAN type 1-O specifically targets FR1 NTN with transparent payloads, which are expected to be common in early NTN deployments due to their simplicity and lower cost.