Uplink operating band

Description

In 3GPP specifications, an operating band is a range of frequencies designated for a specific duplex mode and direction. The uplink operating band is the part of an FDD operating band allocated for uplink transmission, i.e., from the user equipment (UE) to the base station (eNodeB or gNB). This definition is fundamental to the physical layer and radio frequency (RF) requirements, as it determines the spectral resources available for the terminal-to-network link. For TDD bands, the same frequency range is used for both uplink and downlink, but the term 'uplink operating band' is specifically defined for FDD operation, where separate frequency ranges are used for each direction.

The uplink operating band is characterized by its frequency range, duplex spacing, and channel bandwidth options. For example, in LTE Band 1 (FDD), the uplink operating band is 1920–1980 MHz, while the downlink is 2110–2170 MHz. The duplex spacing of 190 MHz allows simultaneous transmission and reception using a duplexer. The UE must be capable of transmitting within the specified uplink band with a certain maximum output power, typically 23 dBm for power class 3. The base station receives these transmissions and must meet sensitivity and blocking requirements defined in specifications like 36.104 and 37.104.

The uplink operating band is crucial for interference management and coexistence. Since the uplink transmissions from many UEs can create interference in adjacent bands, regulatory bodies and 3GPP define strict limits on out-of-band emissions and spurious emissions. The UE must also support power control to minimize interference while maintaining sufficient signal quality at the base station. The uplink band is paired with a downlink band, and the duplex spacing is standardized to ensure global roaming and equipment interoperability.

In carrier aggregation, multiple uplink operating bands can be combined to increase uplink throughput. The UE may transmit on multiple component carriers simultaneously, each within its own uplink operating band. This requires advanced RF front-end designs to handle multiple transmit chains and avoid intermodulation interference. Similarly, dual connectivity allows the UE to transmit to two different base stations, potentially using different uplink operating bands.

The definition of uplink operating band has evolved over releases. Initially, it was simply 'the part of the operating band designated for uplink.' In Rel-13, the wording was refined to 'part of the (FDD) operating band designated for uplink transmission,' explicitly mentioning FDD and transmission. This clarification helps distinguish from TDD bands and emphasizes the transmission aspect. The term is used across numerous specifications, including 21.905 (vocabulary), 36.104 (LTE BS radio transmission and reception), 37.104 (NR BS radio transmission and reception), and others, highlighting its importance in both LTE and 5G NR.

Purpose & Motivation

The concept of an uplink operating band exists to clearly define the spectrum resources allocated for terminal-to-base-station transmissions in FDD systems. By separating uplink and downlink into distinct frequency ranges, FDD enables simultaneous transmission and reception without the need for complex time synchronization, which simplifies network planning and improves spectral efficiency. The uplink operating band ensures that UEs transmit only within authorized frequencies, minimizing interference to other services and adjacent bands.

Before the formalization of operating bands, early mobile systems used less structured frequency allocations, which led to interoperability issues and inefficient spectrum use. 3GPP's definition of operating bands, including uplink and downlink parts, brought order to spectrum management, enabling global roaming and multi-band device support. It also allowed regulators to assign spectrum in a harmonized way, fostering economies of scale.

The uplink operating band is particularly important because the UE's transmit power is limited, and the uplink is often the coverage-limiting link. By specifying the exact frequency range, 3GPP ensures that base station receivers can be designed with appropriate sensitivity and selectivity, and that UE transmitters meet regulatory requirements. This definition also facilitates coexistence studies and interference mitigation techniques, which are essential for deploying new technologies alongside legacy systems.