Sub-block of Spectrum

Description

In 3GPP terminology, a sub-block refers to one contiguous allocated block of spectrum used for transmission and reception by the same User Equipment (UE). This concept is defined in specifications such as 25.104 (UTRA), 36.101 (E-UTRA), and 38.101 (NR). A sub-block is characterized by its contiguity in frequency and its allocation to a single UE, meaning that the UE can transmit and receive within that block without hopping or switching to other blocks. Multiple sub-blocks may exist within a single RF bandwidth, allowing for flexible spectrum utilization and aggregation.

The sub-block concept is particularly relevant for carrier aggregation (CA) and dual connectivity (DC), where a UE can operate on multiple component carriers (CCs) simultaneously. Each CC may correspond to a sub-block, and the UE's RF front-end must support the transmission and reception of multiple sub-blocks. The sub-block definition ensures that the UE's transmissions are confined to specific contiguous spectrum segments, which simplifies RF design and reduces interference. It also enables the network to allocate resources efficiently, as sub-blocks can be assigned based on the UE's capabilities and the available spectrum.

In the context of RF requirements, sub-blocks are used to specify parameters such as sub-block bandwidth, which is the bandwidth of one sub-block. This parameter is critical for defining the UE's RF performance, including adjacent channel leakage ratio (ACLR) and spectrum emission mask. The 3GPP specifications define sub-block bandwidth for various operating bands and CA configurations, ensuring that UEs meet regulatory and performance requirements. For example, in LTE, the sub-block bandwidth for intra-band contiguous CA is defined as the aggregated channel bandwidth of the component carriers.

Sub-blocks also play a role in the definition of RF bandwidth, which is the maximum bandwidth supported by the UE's RF front-end. The RF bandwidth may contain multiple sub-blocks, each allocated to different UEs or used for different purposes (e.g., uplink and downlink). The network scheduler must ensure that sub-blocks are allocated without causing inter-sub-block interference, which is managed through guard bands and filtering. In NR, the concept of sub-blocks is extended to support flexible numerology and wider bandwidths, including millimeter wave bands.

The sub-block concept has evolved over releases, with the definition initially focusing on base station usage and later clarifying UE transmission and reception. This evolution reflects the growing complexity of UE capabilities and the need for precise spectrum allocation in advanced cellular systems. Overall, sub-blocks provide a foundational element for spectrum management, enabling efficient and flexible use of radio resources in multi-carrier and multi-band deployments.

Purpose & Motivation

The sub-block concept was introduced to provide a clear and standardized way to describe contiguous spectrum allocations for UEs. In early cellular systems, spectrum allocation was often described in terms of channels or carriers, but as systems became more complex with carrier aggregation and multiple frequency bands, a more granular definition was needed. Sub-blocks allow operators to allocate spectrum in contiguous chunks, simplifying RF design and reducing interference.

Before sub-blocks, the lack of a formal definition led to ambiguities in RF requirements and testing. Equipment vendors needed a precise way to specify the spectrum segments that a UE could transmit and receive in, especially for CA scenarios. The sub-block definition addresses this by defining a contiguous block for a single UE, which can be tested and certified. It also enables the network to manage spectrum more efficiently by allowing multiple sub-blocks within an RF bandwidth.

The sub-block concept is essential for supporting advanced features like intra-band contiguous CA, where multiple component carriers are aggregated into a single contiguous block. It also facilitates spectrum sharing and coexistence by providing a common language for describing spectrum usage. As networks evolve towards 5G and beyond, sub-blocks remain a key concept for spectrum flexibility and efficiency.