Contiguous spectrum

Description

Contiguous spectrum is a fundamental spectrum arrangement concept in 3GPP specifications, defined as spectrum consisting of a contiguous block of spectrum with no sub-block gap(s). In other words, all the frequency resources allocated to a given operating band or carrier configuration are adjacent to one another, forming an unbroken range of frequencies. This is in contrast to non-contiguous spectrum, where two or more sub-blocks of spectrum are separated by one or more sub-block gaps — unused frequency ranges that may be occupied by other operators, other services, or simply left vacant for regulatory reasons.

The concept appears across a wide range of 3GPP specifications, including the UTRA (25.104, 25.141), E-UTRA (36.101, 36.104, 36.823), NR (38.104, 38.141, 38.174, 38.819), and multi-RAT/base station conformance specifications (37.104, 37.141, 37.145, 37.802, 37.812). It is used to define the operating bands, channel bandwidths, carrier aggregation configurations, and RF requirements for both user equipment and base stations. For example, in carrier aggregation, multiple component carriers can be aggregated either contiguously (adjacent in frequency within the same operating band) or non-contiguously (separated by gaps, possibly across different bands).

From an RF engineering perspective, contiguous spectrum is generally simpler and more efficient to manage. A single wide contiguous block allows a single wideband carrier or a set of adjacent carriers to be transmitted and received with a single radio chain, reducing the complexity of filters, duplexers, and power amplifiers. It also simplifies the definition of out-of-band emissions, spurious emissions, and adjacent channel leakage ratio (ACLR) requirements, because there are no internal gaps that need to be protected. Regulatory and coexistence analyses are also more straightforward when the operator's spectrum is contiguous.

However, real-world spectrum assignments are often fragmented due to historical licensing, refarming, or the presence of incumbent services. 3GPP therefore defines both contiguous and non-contiguous spectrum configurations and specifies the corresponding RF requirements for each. The distinction affects parameters such as the maximum output power, the allowed operating band combinations, the carrier aggregation bandwidth classes, and the test procedures for base station and UE conformance. In NR, for instance, the concept of contiguous spectrum is closely tied to the definition of a single wideband carrier, the use of a single FFT, and the placement of guard bands.

The term has remained stable in its definition since its introduction in Release 10, with only minor editorial changes. It is a foundational concept for understanding how 3GPP manages spectrum, how carrier aggregation is configured, and how RF requirements are derived for both legacy and new radio technologies.

Purpose & Motivation

Contiguous spectrum exists as a formal concept to distinguish between spectrum arrangements that have no internal gaps and those that do. This distinction is essential because RF requirements, transmitter and receiver architectures, and coexistence analyses differ significantly depending on whether an operator's spectrum is contiguous or fragmented. By defining the term precisely, 3GPP ensures that equipment vendors, operators, and regulators share a common understanding of the spectrum being used and can apply the correct conformance tests and deployment rules.

Historically, early cellular systems typically operated within a single contiguous block of spectrum per operator. As spectrum became scarcer and more fragmented due to auctions, refarming, and the introduction of new services, the need to support non-contiguous spectrum arrangements grew. The formal definition of contiguous spectrum, introduced in Release 10 alongside the maturation of carrier aggregation, provided a clear baseline against which non-contiguous configurations could be specified. It also helped standardize the way multi-carrier and multi-band operation is described in 3GPP specifications.

Today, the concept remains relevant for both legacy systems such as UTRA and E-UTRA and for NR, where wide contiguous blocks are preferred for high-throughput deployments, especially in mid-band and millimeter-wave frequencies. Understanding contiguous spectrum is therefore a prerequisite for anyone working on spectrum planning, RF design, or carrier aggregation in 3GPP networks.