Key focus: Bandwidth Part (BWP): Allocates segments of spectrum for flexible resource allocation in 5G NR networks, enhancing efficiency and adaptability. Know the difference between bandwidth part and transmission bandwidth
Introduction
The 3rd Generation Partnership Project (3GPP), in its Release 15, specified the new radio-access technology called 5G New Radio (5G NR). The 5G NR continues to evolve in the subsequent releases that addresses performance improvements and new use cases.
In the release 15, new features for 5G NR were introduced so as to support a varied range of devices, services and deployments. Once such new basic feature in 5G NR is the Bandwidth Part (BWP).
5G NR Frequency ranges
3GPP defines the frequency ranges for 5G NR operation, as specified in Table 1 (illustrated in Figure 1).
Operating bands
Within each Frequency Range (FR), the 3GPP defines operational bands. 3GPP 5G NR defines 60 operating bands in FR1 and 7 bands in FR2 (refer section 5.2 in [1]). These operating bands represent specific frequency ranges that come with their own unique radio frequency requirements (for example: some of these bands are designated for use in Frequency Division Duplexing (FDD), Time Division Duplexing (TDD), Supplemental Up Link (SUL), Supplemental Down Link (SDL) communication). The width of these operating bands can vary significantly, ranging from just a few megahertz to several gigahertz. Different mobile network operators might be allocated (typically by respective governments through spectrum auction) different portions of the available spectrum within a given operational band.
To cater to the diverse spectrum allocation scenarios while keeping implementation complexities in check, the New Radio (NR) technology supports a wide range of channel bandwidths (a.k.a Base station (BS) channel bandwidth) spanning from 5 MHz to 2 GHz. In this context, “channel bandwidth” refers to the width of an NR carrier, the fundamental component of the 5G system.
Channel bandwidth
The base station’s channel bandwidth enables the use of a single NR RF carrier in either the uplink or downlink. The user equipment (UE) may support different channel bandwidth than the BS.
The UE connects to the BS. The UE receives information about the cell’s channel bandwidth from the network. The network also provides the UE with details regarding the location and extent of a Bandwidth Part (BWP). The core concept is that a User Equipment (UE) can employ a wide-bandwidth when a significantly large data is required to be transmitted/received, but operate with a limited bandwidth during other periods of limited activity.
Bandwidth Part (BWP)
As we know, 5G NR defines scalable Orthogonal Frequency Division Multiplexing (OFDM) using numerology \(\mu = \left\{ 0,1,2,3,4 \right\}\) that defines the subcarrier spacings (SCS) as \( \Delta f = 2^{\mu} \times 15 \; kHz\). A resource element is the smallest time-frequency resource over one subcarrier of a single OFDM symbol. A resource block (RB) is a block of \( N_{sc}^{RB} = 12 \) subcarriers over which the transmissions are scheduled (Figure 2).
In a broad sense, a BWP can be described as a collection of contiguous Resource Blocks (RBs) configured within a given channel bandwidth. The BWP provides a flexible mechanism for adapting to varied bandwidth ranges in order to aid in reduction of power consumption.
Another reason is to cater to devices with varying bandwidth capabilities by setting up different BWPs for each device. A Base Station (BS) might have the ability to accommodate an exceptionally broad channel bandwidth, even though certain User Equipment (UEs) may not have the capability to handle it. The concept of Bandwidth Part (BWP) offers a way to dynamically allocate radio resources, ensuring that a UE’s signals are limited to a portion of the BS’s channel bandwidth that aligns with the UE’s capabilities.
Point A, illustrated in Figure 3, functions as a standardized reference across all resource grids within the frequency. It acts as the central marker for subcarrier 0 within a common resource block 0 of the lowest resource grid and it can reside outside the carrier’s bandwidth. Each individual resource grid (RG) adheres to a distinct 5G NR numerology and commences at a frequency offset from point A.
As shown in Figure 3, the bandwidth part consists of contiguous set of RBs for a particular numerology on a given carrier and starts at an offset RB_{start} from the reference Point A.
Transmission bandwidth
5G NR defines another concept called transmission bandwidth that is closely related with bandwidth part. While BWP refers to a portion of the overall channel bandwidth that is allocated for specific communication purposes, transmission bandwidth refers to the range of frequencies that are used to transmit signals. It encompasses the total frequency range used for communication, including both the data-carrying portion and any guard bands or additional spectrum used for various purposes.
In short, the BWP refers to a specific allocated portion of the transmission bandwidth, while the transmission bandwidth encompasses the entire range of frequencies used for communication.
