Description
The Transceiver Array Boundary (TAB) is a fundamental architectural concept within 3GPP specifications that defines the functional and physical separation point between the baseband processing unit (BBU) and the radio transceiver array (often part of the Remote Radio Head or Active Antenna Unit) in a base station. It establishes a standardized interface that delineates where digital baseband signal processing ends and analog radio frequency (RF) transmission/reception begins. This boundary is critical for disaggregating the traditional monolithic base station, enabling more flexible and scalable network deployments.
Architecturally, the TAB sits within the gNB in 5G NR or the eNB in LTE. On one side of the boundary, the baseband unit handles digital signal processing tasks such as channel coding, modulation/demodulation, and layer mapping for MIMO. On the other side, the transceiver array encompasses the RF components, including digital-to-analog converters (DACs), analog-to-digital converters (ADCs), power amplifiers, low-noise amplifiers, filters, and the physical antenna elements. The interface at the TAB typically involves the exchange of digitized time-domain IQ (In-phase and Quadrature) samples or frequency-domain resource element data, along with necessary control and synchronization signals.
The TAB's role is pivotal for implementing advanced antenna systems (AAS) and massive MIMO. By standardizing this boundary, 3GPP ensures interoperability between baseband and RF units from different vendors, fostering a competitive ecosystem. It underpins key technologies like beamforming, where precise control over the phase and amplitude of signals at each antenna element is required. The TAB defines the point up to which beamforming weights can be applied digitally and where the analog RF chain takes over. This separation is essential for network architectures such as Centralized RAN (C-RAN), where the baseband processing is pooled in a central location, connected via fronthaul to remote radio units, with the TAB defining the functional split options for this fronthaul interface.
Purpose & Motivation
The Transceiver Array Boundary was introduced to address the growing complexity and performance demands of multi-antenna systems in LTE-Advanced and 5G NR. Prior to its formal definition, base station implementations were largely integrated, vendor-specific solutions, making it difficult to mix and match baseband and radio units. This lack of standardization hindered innovation, increased costs, and limited deployment flexibility for operators. The TAB was created to decouple these components, enabling a modular approach to base station design.
The primary motivation was to support the evolution towards Advanced Antenna Systems (AAS) and massive MIMO, which require a high degree of coordination between numerous transceiver paths. A standardized boundary allows for specialized development of baseband processors (focusing on computational power and algorithms) and radio units (focusing on RF performance and energy efficiency) independently. This is particularly important for new deployment models like Cloud RAN (C-RAN), where the baseband processing is virtualized and centralized, necessitating a well-defined, low-latency, high-bandwidth interface to the remote radio heads. The TAB provides the architectural foundation for these split architectures, specifying functional splits (like Option 7-2x) that determine which processing happens before and after the boundary, directly impacting fronthaul requirements and overall system performance.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (7 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-13, normative work from Rel-15.
In Release 15, the TAB (Transceiver Array Boundary) function was newly introduced as a defined conducted interface for Satellite Access Node (SAN) Type 1-H, specifying it as the point between the transceiver unit array and the composite antenna where conducted requirements like output power and receiver sensitivity are applied. This release formally distinguished the TAB connector, where individual conducted measurements are taken, from the Radiated Interface Boundary (RIB) used for over-the-air requirements. Consequently, specific parameters such as maximum carrier output power per TAB connector (P_max,c,TABC) and reference sensitivity (P_REFSENS) were defined at this boundary for the first time.
- CR to TS 37.145-2: Correction of Radiated Interface Boundary (RIB) definition TS 37.145CR0125
In Release 16, the key update for the Transceiver Array Boundary (TAB) function was the correction of the mapping of TAB connectors to the TAB connector TX minimum cell group, ensuring proper power aggregation and requirement application for Satellite Access Nodes (SANs) type 1-H. This refinement clarified how conducted transmitter and receiver characteristics, such as output power and reference sensitivity, are defined and measured at the individual TAB connector interface between the transceiver unit array and the composite antenna. The changes provided more precise definitions for applying power-related requirements, including out-of-band and spurious emissions, at this conducted boundary.
- CR to 37.105: correction of TAB connectors mapping to TAB connector TX min cell group, Rel-16 TS 37.105CR0170
- CR to T 38.104: Implementation of endorsed draft CRs from RAN4#92 (Rel-16) (Mirrors changes in R4-1908440 for Rel-15 TS 38.104) - R4-1907940, "Draft CR to TS 38.104: Correction on the terminology in FRC tables in A.1 and A.2" - R4-1908307, "Draft CR to TS 38.104: Clarification on application of OTA receiver requirements for BS supporting polarization" - R4-1908387, "Draft CR for TS38.104: editorial correction for reference meausrement channel" - R4-1908619, "Draft CR to TS38.104: Correction on interferer frequency offset values for ACS" - R4-1908629, "Draft CR to TS38.104: Corrections on EVM window length (Annex B.5.2, C.5.2)" - R4-1908774, "DraftCR to 38.104: Editorial Corrections to redudant units in clause 10.8.3" - R4-1908805, "Draft CR to 38.104: Limits in FCC title 47 for OTA operating band unwanted emissions (9.7)" - R4-1909270, "Draft CR to TS 38.104: Receiver spurious emissions frequency correction" - R4-1909309, "DraftCR to TS 38.104: text corrections, Rel-15" - R4-1909310, "DraftCR to 38.104: correction of TAB connectors mapping to TAB connector TX min cell group, Rel-15" - R4-1909416, "draft CR 38.104 - correct reference to annex F" - R4-1910066, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1910069, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1910072, "Draft CR on NR UCI on PUSCH performance requirements for TS 38.104" - R4-1910075, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1910078, "Draft CR to TS38.104: Updates to NR PRACH performance requirements" - R4-1910081, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1910084, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1910088, "Draft CR for 38.104: Performance requirements for NR PUCCH format 1" - R4-1910089, "Draft CR for 38.104: Performance requirements for NR multi-slot PUCCH" - R4-1910094, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1910431, "Corrections to EVM calculations in 38.141-1 annex B" - R4-1910462, "Draft CR to 38.104: Correction on regional requirements (4.5)" - R4-1910493, "Draft CR to TS 38.104 correction to Annex C.7" - R4-1910606, "Draft CR for TS 38.104: Channel spacing for adjacent NR carriers" TS 38.104CR0034
In Release 18, the TAB (Transceiver Array Boundary) function was explicitly defined for the new SAN Type 1-H, establishing it as the conducted interface between the transceiver unit array and the composite antenna for both transmitter and receiver requirements. Specific power parameters, such as P_rated,c,TABC and P_max,c,TABC, were introduced for this connector, and requirements like out-of-band emissions, spurious emissions, reference sensitivity, and dynamic range were now mandated to be measured at the individual TAB connectors. This provided a clear, standardized conducted reference point alongside the existing radiated (OTA) requirements for satellite access nodes.
- Big CR for BS demodulation requirements for Rel-18 MIMO in 38.104 TS 38.104CR0635
In Release 19, the TAB function was refined with the removal of TAB connectors as a defined interface for certain requirements, simplifying the model. This change was accompanied by improvements to the description of the base station array antenna model to enhance clarity. The updates specifically focus on the technical definitions and application of conducted requirements at the transceiver array boundary for Satellite Access Node (SAN) equipment.
Explore further
Broader topics and technologies where TAB plays a role.
Defining Specifications
3GPP specifications that define or reference TAB, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 36.108 vj10 | Satellite Access Node RF Requirements | Rel-19 |
| TS 36.181 vj30 | E-UTRA RF Test Methods for Satellite Access Node | Rel-19 |
| TS 36.214 vj00 | E-UTRA Physical Layer Measurements | Rel-19 |
| TS 37.105 vj10 | AAS Base Station Transmission & Reception Requirements | Rel-19 |
| TS 37.114 vj00 | EMC for Active Antenna System Base Stations | Rel-19 |
| TS 37.145 vj10 | AAS Base Station Conducted Conformance Testing | Rel-19 |
| TS 37.842 vd30 | BS RF Requirements for Active Antenna Systems | Rel-13 |
| TR 37.843 vf70 | AAS BS Radiated RF Requirement Background | Rel-15 |
| TS 38.104 vj20 | NR Base Station RF Requirements | Rel-19 |
| TS 38.108 vj20 | NTN NR Satellite Access Node RF Requirements | 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 38.181 vj10 | NR Satellite Access Node RF Testing | Rel-19 |
| TS 38.817 | 3GPP TR 38.817 | Rel-13 |
| TR 38.820 vg10 | NR; 7-24 GHz Frequency Range Study | Rel-16 |
| TR 38.876 vi20 | Technical Report on Air-to-Ground Network for NR | Rel-18 |
| TR 38.922 vj20 | Study on IMT Parameters for NR in Higher Bands | Rel-19 |