Satellite Access Node Radio Frequency Bandwidth Edge

Description

The SAN RF Bandwidth edge is a fundamental parameter in the 3GPP specifications for Satellite Access Nodes (SANs), particularly in the context of Non-Terrestrial Networks (NTN). It represents the frequency of one of the edges—either the lower or upper boundary—of the SAN RF Bandwidth, which is the total range of radio frequencies over which the SAN can transmit or receive signals. This parameter is essential for defining the operational spectrum of a satellite node and ensuring compatibility with user equipment (UE) and ground-based networks.

In the architecture of an NTN, the SAN acts as the space-borne or airborne equivalent of a terrestrial base station (gNB or eNB). The SAN RF Bandwidth edge is used in radio frequency (RF) requirement specifications such as 3GPP TS 36.108 (for LTE NTN) and TS 38.108 (for NR NTN). These specifications define conducted and over-the-air (OTA) requirements for SANs, including frequency stability, unwanted emissions, and adjacent channel leakage ratio (ACLR). The edges of the RF bandwidth are critical reference points for these measurements, as they determine the boundaries within which the SAN must operate and outside of which emissions must be suppressed.

From an operational perspective, the SAN RF Bandwidth edge helps in coordinating spectrum usage between different satellite beams, between satellite and terrestrial networks, and across multiple operators. It is also used in link budget calculations and interference analysis. For example, when a SAN employs frequency reuse across multiple beams, the edges of each beam's RF bandwidth must be carefully managed to avoid inter-beam interference. Similarly, when the SAN shares spectrum with terrestrial networks (e.g., in FR1 bands), the edges define the guard bands required to protect adjacent services.

The parameter is defined in 3GPP specifications as the frequency of one of the edges of the SAN RF Bandwidth. It is typically expressed in MHz or GHz and is referenced in test procedures for SAN conformance. The exact value depends on the allocated spectrum and the SAN's configuration, such as the number of beams, carrier aggregation, and modulation schemes. In Rel-17 and later, with the introduction of NTN in 5G NR, the SAN RF Bandwidth edge has become even more important due to the need to support higher frequency bands (e.g., Ka-band, Ku-band) and wider bandwidths to meet throughput demands.

Overall, the SAN RF Bandwidth edge is a key concept for engineers designing, deploying, and testing satellite access networks. It ensures that SANs operate within their allocated spectrum, minimize interference, and meet regulatory requirements, thereby enabling reliable and efficient NTN communications.

Purpose & Motivation

The SAN RF Bandwidth edge exists to provide a precise, standardized reference for the frequency boundaries of a Satellite Access Node's operating bandwidth. This is necessary for several reasons: first, to ensure that SAN transmissions remain within the allocated spectrum and do not cause harmful interference to adjacent channels or services; second, to enable consistent testing and measurement of RF requirements across different SAN implementations; and third, to facilitate spectrum sharing and coordination between satellite and terrestrial networks.

Before the introduction of NTN in 3GPP, terrestrial base stations had well-defined RF bandwidth edges, but satellite systems often used proprietary or region-specific definitions. The integration of satellite access into 5G NR (Rel-17) required a unified framework. The SAN RF Bandwidth edge addresses the limitations of previous approaches by providing a common definition that can be used in both conducted and OTA testing, as specified in 36.108 and 38.108. It also supports the unique challenges of satellite communications, such as large propagation delays, Doppler shift, and wide coverage areas, by allowing flexible bandwidth configurations while maintaining strict emission limits.

In summary, the SAN RF Bandwidth edge solves the problem of spectrum boundary definition in NTN, enabling regulatory compliance, interference mitigation, and interoperability. It is a foundational parameter for the design and validation of satellite access nodes in 5G and beyond.