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5G NR Frame Structure: Updated 2023

Updated: May 17, 2023

5G NR Frame Structure: Updated 2023

The 5G NR (New Radio) Frame Structure is a key component in the design and implementation of 5G networks. This article will provide a comprehensive guide to understanding the 5G NR Frame Structure and its significance in the world of wireless communication. We will explore the design, features, and various aspects involved in creating a 5G NR Frame Structure that allows for high-speed, low-latency communication between devices.


5G NR Frame Structure
5G NR Frame Structure: Updated 2023

5G NR (New Radio) is the latest cellular network technology that promises faster download and upload speeds, lower latency, and better connectivity than its predecessors. Its frame structure is the basic building block of the 5G NR system, which is responsible for transmitting and receiving data between the user equipment (UE) and the base station (BS).

The radio frame can be further divided into four different types, depending on the subcarrier spacing (SCS) used for transmission. These are:

  1. Type 1: 15 kHz SCS

  2. Type 2: 30 kHz SCS

  3. Type 3: 60 kHz SCS

  4. Type 4: 120 kHz SCS

  5. Type 5: 240 kHz SCS

Each subframe within a radio frame has a unique identification number called a radio frame number (RFN). This number ranges from 0 to 9 and indicates which subframe within the radio frame is being transmitted or received.


The subframe, on the other hand, consists of a number of symbols, each with a duration of 66.67 microseconds (µs). The number of symbols in a subframe varies depending on the length of the cyclic prefix (CP) used. The CP is a guard interval that is inserted between two consecutive symbols to prevent inter-symbol interference.


In addition to the subframes, the 5G frame structure also includes different channels that are used for transmitting different types of data. These channels include the physical downlink control channel (PDCCH), the physical downlink shared channel (PDSCH), and the physical uplink control channel (PUCCH), among others.


In summary, the 5G frame structure is a complex but essential component of the 5G NR system. By understanding its basic building blocks, you can gain a better understanding of how data is transmitted and received in 5G NR networks.


Understanding the 5G Frame Structure


The 5G Frame Structure is specified in the 3GPP (3rd Generation Partnership Project) specification (38.211). It is a hierarchical structure that determines how data is transmitted and received in a 5G network. The primary components of the 5G NR Frame Structure include:

  1. Numerology: This defines the subcarrier spacing and symbol duration for different types of transmissions in the network.

  2. Radio Frame and Subframe: These are the basic time units used in the 5G NR Frame Structure, with a Radio Frame lasting 10ms and a Subframe lasting 1ms.

  3. Slot: This is a smaller time unit within a Subframe, which contains a specific number of OFDM (Orthogonal Frequency Division Multiplexing) symbols.

  4. Resource Block: This is the basic frequency domain unit in the 5G NR Frame Structure, containing a set number of subcarriers.

  5. Resource Grid: This is a time-frequency grid that represents the resources available for data transmission in a 5G network.

Numerology and Subcarrier Spacing


One of the unique features of 5G NR compared to its predecessor, LTE (Long-Term Evolution), is the support for multiple numerologies, or different subcarrier spacings. In LTE, there was only one type of subcarrier spacing: 15 kHz. However, in 5G NR, there are various possible numerologies, ranging from 15 kHz to 960 kHz. These different numerologies allow for more flexibility and adaptability in the network, catering to various use cases and scenarios.


Numerology and Subcarrier Spacing
Numerology and Subcarrier Spacing

Radio Frame, Subframe, and Slot


The 5G Frame Structure uses a hierarchical approach, with a Radio Frame being the largest time unit and lasting 10ms. Each Radio Frame is divided into Subframes, which last 1ms. Subframes are further divided into Slots, which contain a specific number of OFDM symbols depending on the numerology being used. The number of Slots within a Subframe can vary, allowing for different transmission configurations to accommodate various use cases.


Radio Frame, Subframe, and Slot
Radio Frame, Subframe, and Slot


Resource Block and Resource Grid


Each Resource Block in the 5G Frame Structure contains 12 subcarriers. The Resource Grid is a time-frequency grid that represents the available resources for data transmission in the network. The Resource Grid is composed of multiple Resource Blocks, with the total number of Resource Blocks in the grid depending on the bandwidth being used.


NR Resource Block and Resourse grid
NR Resource Block and Resourse grid


5G NR Frame Structure Configurations and Variations

Due to the support for multiple numerologies, there are several possible configurations for the 5G Frame Structure. Each configuration is determined by the subcarrier spacing being used, as well as the specific requirements of the network and its use case. Some of the possible configurations include:

  1. Normal CP (Cyclic Prefix) Configuration: This is the most common configuration, with a fixed number of 14 OFDM symbols per Slot regardless of the numerology being used.

  2. Extended CP Configuration: In this configuration, the number of OFDM symbols per Slot is reduced to 12, allowing for longer Cyclic Prefix durations and improved performance in certain scenarios.

TDD DL/UL Common Configuration

In addition to the different numerologies and configurations, the 5G NR Frame Structure also supports flexible TDD (Time Division Duplex) DL/UL (Downlink/Uplink) configurations. This flexibility allows for more efficient use of network resources and improved performance in various use cases.


SS/PBCH Block

The SS/PBCH (Synchronization Signal/Physical Broadcast Channel) Block is a critical component of the 5G NR Frame Structure, responsible for providing essential information and synchronization signals to devices within the network. The SS/PBCH Block is transmitted in a specific time-frequency location within the Resource Grid, with the location depending on the numerology and other network parameters.


Slot Format and Resource Allocation

The Slot Format in the 5G NR Frame Structure defines how the OFDM symbols within a Slot are allocated for various purposes, such as downlink, uplink, or flexible use. This flexible allocation allows for more efficient use of network resources and improved performance in different scenarios.


Frequency Domain Resource Allocation

The frequency domain resource allocation in the 5G NR Frame Structure is determined by the number of Resource Blocks and their specific location within the Resource Grid. The maximum transmission bandwidth configuration, or NRB, for both FR1 (Frequency Range 1, sub-6 GHz) and FR2 (Frequency Range 2, millimeter-wave) bands are defined in 3GPP specifications 38.101-1 and 38.101-2, respectively.


Time Domain Resource Allocation

The time domain resource allocation in the 5G NR Frame Structure is determined by the numerology, Slot Format, and specific network requirements. The allocation of resources in the time domain allows for more efficient scheduling and improved network performance.


Conclusion

Understanding the 5G NR Frame Structure is essential for anyone working in the field of wireless communication, as it determines how data is transmitted and received in a 5G network. By utilizing multiple numerologies and flexible configurations, the 5G NR Frame Structure allows for high-speed, low-latency communication that can cater to a wide range of use cases and scenarios. With its hierarchical design, flexible resource allocation, and support for TDD DL/UL configurations, the 5G NR Frame Structure is a key component in the future of wireless communication.


FAQ for 5G NR Frame Structure


Q: What is 5G frame structure? A: 5G frame structure is a way of organizing the transmission of data in 5G networks. It defines the way data is divided into smaller units and transmitted over the air.

Q: What is the basic unit of data in 5G frame structure? A: The basic unit of data in 5G frame structure is called a slot. A slot is a small unit of time that can carry a certain amount of data.

Q: How many slots are there in a 5G frame? A: The number of slots in a 5G frame depends on the configuration. There can be 14 slots in a frame with a duration of 10 ms, or 28 slots in a frame with a duration of 20 ms.

Q: What is a subframe in 5G frame structure? A: A subframe is a part of a frame that contains a certain number of slots. In 5G NR, a subframe can contain either one slot or two slots.

Q: What is the purpose of the 5G frame structure? A: The purpose of the 5G frame structure is to efficiently transmit data over the air in a way that minimizes interference and maximizes the use of available bandwidth.

Q: How does the 5G frame structure differ from that of previous cellular technologies? A: The 5G frame structure differs from that of previous cellular technologies in several ways. It allows for more flexibility in terms of slot and subframe configuration, and it uses a more advanced modulation scheme to transmit data more efficiently.

Q: What is the maximum data rate that can be achieved with 5G frame structure? A: The maximum data rate that can be achieved with 5G frame structure depends on several factors, including the bandwidth available and the modulation scheme used. In ideal conditions, data rates of up to 20 Gbps are possible.

Q: What are the different types of subframes in 5G frame structure? A: There are three types of subframes in 5G frame structure: data subframes, control subframes, and special subframes. Data subframes carry user data, control subframes carry control information, and special subframes are used for synchronization and other purposes.

Q: How is synchronization maintained in 5G frame structure? A: Synchronization in 5G frame structure is maintained through the use of special subframes that contain synchronization signals. These signals are used by devices to synchronize their transmissions with the network.

Q: What is the duration of a 5G frame? A: The duration of a 5G frame can vary depending on the configuration. It can be either 10 ms or 20 ms in length.

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