1447.9 - 1462.9 MHz

Description

The term 'XXI' in 3GPP terminology refers to a specific radio frequency band defined for UTRA Time Division Duplex (TDD) operation. It specifies the frequency range from 1447.9 MHz to 1462.9 MHz, which provides a total of 15 MHz of unpaired spectrum. This band is standardized as 3GPP Band 22, a TDD band used primarily for UMTS (TD-SCDMA) and potentially for LTE-TDD deployments, though its global adoption has been limited compared to FDD bands.

In a TDD system like that used in Band 22, the same block of spectrum (1447.9-1462.9 MHz) is used for both uplink and downlink transmissions, separated in the time domain. The base station and User Equipment (UE) transmit in alternating time slots according to a configured TDD frame structure. For UMTS TDD (TD-SCDMA), this involves specific time slot allocations and synchronization procedures defined in the UTRA specifications. The physical layer parameters, including channel raster, allowed channel bandwidths (e.g., 1.6 MHz carriers for TD-SCDMA), and RF requirements, are detailed in 3GPP TS 25.141 for base station conformance testing.

From a network architecture perspective, deploying Band 22 requires TDD-capable NodeBs (for 3G) or eNodeBs (for 4G LTE-TDD). The band's mid-frequency characteristics (around 1.45 GHz) offer a balance between coverage and capacity; it provides better propagation than higher bands like 2.6 GHz but less coverage than sub-1 GHz bands like 800 MHz. Network planning for TDD bands must carefully manage time synchronization across all cells in the network to avoid uplink-downlink interference and to efficiently allocate time slots based on traffic asymmetry (e.g., more downlink slots for data-heavy usage).

The operation within Band 22 involves the base station and UE adhering to a strict timing advance and guard period scheme to compensate for propagation delays and ensure time slots do not overlap. For LTE-TDD, if deployed, it would use one of the standardized TDD uplink-downlink configurations. While not as widely deployed as some other bands, Band 22 represents an important asset of unpaired spectrum that can be utilized for mobile broadband, especially in regions or by operators who have access to this specific frequency allocation. Its definition ensures that equipment manufacturers can build devices and infrastructure that are interoperable and compliant with global standards, even for regionally specific bands.

Purpose & Motivation

The standardization of the XXI band (1447.9-1462.9 MHz) as Band 22 was motivated by the need to incorporate additional TDD spectrum into the 3GPP framework to support growing mobile data traffic and to provide flexibility for operators with unpaired spectrum allocations. Unlike FDD, which requires paired spectrum blocks, TDD can operate in unpaired bands, making it suitable for spectrum that is not symmetrically available. The 1.4 GHz range was identified in some regions as available for mobile services, and 3GPP provided a standardized band definition to enable its use.

Prior to this, TDD operations for 3G were largely focused on other bands (like Band 34 at 2 GHz). Defining Band 22 expanded the portfolio of standardized TDD spectrum, giving regulators and operators more options for deploying UMTS TDD (TD-SCDMA) or later LTE-TDD networks. This addressed the problem of spectrum fragmentation by ensuring that equipment for this specific frequency range would be built to a common standard, fostering competition and reducing costs.

Furthermore, the creation of Band 22 served the purpose of future-proofing network deployments. By including it in the UTRA specifications from Rel-9 onwards, it ensured that this spectrum could be used not only for 3G TD-SCDMA but also, in principle, for 4G LTE-TDD, as the band is part of the E-UTRA band specifications as well. This allows for technology refarming, where an operator could potentially migrate services from 3G to 4G within the same band. While its use is not global, Band 22 represents the principle of comprehensive spectrum standardization, ensuring that virtually any allocated mobile frequency can be supported within the 3GPP ecosystem with interoperable equipment.

Key Features

• Frequency range: 1447.9 MHz to 1462.9 MHz, providing 15 MHz of unpaired spectrum for TDD operation
• Standardized as 3GPP Band 22 for UTRA TDD (and applicable for LTE-TDD)
• Uses Time Division Duplex, where uplink and downlink share the same frequencies in alternating time slots
• Mid-band frequency offering a balance of coverage and capacity characteristics
• Base station conformance testing requirements defined in 3GPP TS 25.141
• Supports channel bandwidths appropriate for TD-SCDMA (e.g., 1.6 MHz) and LTE-TDD

Evolution Across Releases

Defining Specifications