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Understanding 5G NR Resource Blocks and Bandwidth Parts

Updated: Jun 30

Understanding 5G NR Resource Blocks and Bandwidth Parts
Understanding 5G NR Resource Blocks and Bandwidth Parts

In 5G New Radio (NR) technology, resource blocks and bandwidth parts play a crucial role in defining how data is transmitted and received over the network. This article explores the specifics of resource blocks, their allocation, and the significance of bandwidth parts in the 5G framework as outlined by 3GPP TS 38.211, TS 38.212, and TS 38.331.


Resource Blocks in 5G NR

Definition and Structure

In 5G NR, resource blocks are defined only in the frequency domain. Each resource block occupies 12 consecutive subcarriers, and its bandwidth depends on the subcarrier spacing. Table 1 presents the bandwidth occupied by a single resource block for each subcarrier spacing.

Table 1: Bandwidth Occupied by a Single Resource Block

Subcarrier Spacing

Resource Block Bandwidth

15 kHz

180 kHz

30 kHz

360 kHz

60 kHz

720 kHz

120 kHz

1.44 MHz

240 kHz

2.88 MHz


Common Resource Blocks

Common resource blocks are the set of resource blocks that occupy the entire channel bandwidth. These blocks are numbered from 0 upwards, starting from the lower side of the channel bandwidth. The reference point for common resource blocks is known as 'Point A,' which corresponds to the center of subcarrier 0 of Common Resource Block 0 (CRB0).


Locating 'Point A'

After completing a band scan, a User Equipment (UE) does not immediately know the position of 'Point A.' The UE identifies the location of a Synchronization Signal/Physical Broadcast Channel (SS/PBCH) Block but must determine the position of 'Point A' relative to this block. This can be achieved using a frequency offset or an Absolute Radio Frequency Channel Number (ARFCN).


Frequency Offset Approach

The frequency offset approach involves using information from the Master Information Block (MIB) and System Information Block 1 (SIB1):

  • OffsetToPointA: Specifies the Resource Block offset between CRB0 and the Common Resource Block overlapping with the start of the SS/PBCH.

  • ssb-SubcarrierOffset: Defines the 4 Least Significant Bits of the subcarrier offset.


ARFCN Approach

The ARFCN approach signals an integer representing a frequency at the lower side of the channel bandwidth, using SIB1 or dedicated signaling.


Bandwidth Parts

Bandwidth Part Definition

A Bandwidth Part (BWP) is a contiguous set of resource blocks within a carrier. It allows the network to flexibly manage resources by configuring different parts of the bandwidth for various purposes, such as data transmission, control signaling, and more.


Configuration and Usage

BWPs are crucial for optimizing resource allocation and managing interference. For example, in a 20 MHz channel bandwidth, the maximum number of resource blocks differs based on subcarrier spacing:

  • 15 kHz: Up to 106 Common Resource Blocks.

  • 30 kHz: Up to 53 Common Resource Blocks.

  • 60 kHz: Up to 24 Common Resource Blocks.


Specifying Usable Resource Blocks

The SIB1 message provides the FrequencyInfoDL-SIB parameter structure, which includes instances of scs-SpecificCarrierList for each supported numerology. The offsetToCarrier value specifies the number of Resource Blocks between Point A and subcarrier 0 within the lowest usable Resource Block. The carrierBandwidth value specifies the number of Resource Blocks available for that numerology.

Table 2: FrequencyInfoDL-SIB Parameter Structure

Parameter

Description

offsetToCarrier

Number of Resource Blocks between Point A and subcarrier 0 of the lowest usable Resource Block

carrierBandwidth

Number of Resource Blocks available for that numerology

scs-SpecificCarrierList

Specific carrier list for each supported numerology

Conclusion

Understanding the structure and allocation of resource blocks and bandwidth parts in 5G NR is essential for optimizing network performance and ensuring efficient use of available spectrum. By leveraging the detailed specifications provided by 3GPP, network operators can effectively manage resources, reduce interference, and enhance the overall user experience.


References

  • 3GPP. (n.d.). TS 38.211 V15.2.0: NR; Physical channels and modulation. Retrieved from 3GPP

  • 3GPP. (n.d.). TS 38.212 V15.2.0: NR; Multiplexing and channel coding. Retrieved from 3GPP

  • 3GPP. (n.d.). TS 38.331 V15.2.0: NR; Radio Resource Control (RRC) protocol specification. Retrieved from 3GPP

For further reading and access to the complete list of specifications, visit the 3GPP website at www.3gpp.org.

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