5G 3GPP NR Frame Structure


Introduction

The 5G is expected to fulfill the needs and business contexts of 2020 and more.
It is expected to enable a fully mobile 
and connected society, related to the huge growth in connectivity and density/volume of traffic that will be required in the near future to provide and guarantee:

  1. Very high throughput (1 Gbps or more), to support ultra-high-definition video and virtual reality applications.
  2. Very low latency (even less than 1 ms in some cases), to support real-time mobile control and Device to Device (D2D) applications and communications.
  3. Ultra high reliability.
  4. Low energy consumption.
  5. Ultra high connectivity resilience and robustness to support advanced safety applications and services.

So as to meet these complicated or even at sometimes contradictory requirements, 5G will involve both an evolution of traditional 4G-LTE networks and a new radio access technology, globally standardized by the 3rd Generation Partnership Project (3GPP) as NR (New Radio).

5G 3GPP NR Frame Structure 

The 3GPP technical provide the specifications for the PHY layer. Both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) will be supported.
The waveform is Orthogonal Frequency Division Multiplexing (OFDM) with a cyclic prefix.
Different numerologies will be used in order to address the different use cases of 5G.
The frame structure follows a time and frequency grid similar to that of LTE, with a higher number of configurable parameters. The subcarrier spacing is 15 × 2 n kHz, n ∈ Z, n ≤ 4.

In Release 15, at most, there will be 3300 sub-carriers, for a maximum bandwidth of 400 MHz. A frame lasts 10 ms, with 10 subframes of 1 ms.
It will be possible to multiplex different numerologies for a given carrier frequency 
and the whole communication must be aligned on a subframe basis. A slot is composed of 14 OFDM symbols.
There are multiple slots in a subframe, and their number is given by the numerology used since the symbol duration is inversely proportional to the subcarrier spacing.

Mini-slots are also supported: they can be as small as 2 OFDM symbol and have variable length, and can be positioned asynchronously with respect to the beginning of the slot (so low-latency data can be sent without any waiting for all slot duration).

5G 3GPP NR Frequency Ranges

In Release 15 NR, the operating bands are divided into two frequency ranges; Frequency Range 1 (FR1) and Frequency Range 2 (FR2).
The definition of the frequency ranges is shown below:
The physical layer and higher layers designs are frequency agnostic, but separate radio performance requirements are specified for each frequency range. Furthermore, different testing methodologies are used in FR1 and FR2.

In FR1, the supported subcarrier spacings are {15, 30, 60} kHz. The supported and maximum transmission bandwidth configuration NRB for each bandwidth and subcarrier spacing are following:
In FR2, the supported subcarrier spacings are {60, 120} kHz. The supported and maximum transmission bandwidth configuration NRB for each bandwidth and subcarrier spacing are as following

5G NR Time Frame Structure

In the time domain, the physical layer transmissions are organized in radio frames. The radio frame’s duration is 10 ms. Each radio frame is divided into 10 subframes, each with a duration of 1 ms. Each subframe is further divided into slots. The number of slots in a subframe depends on the subcarrier spacing as shown below:

For Example, Frame Structure in for Subcarrier Spacing of 120 kHz with Normal CP.

5G NR Frequency Frame Structure

In the frequency domain, transmissions are organized in resource blocks, a resource block occupies 12 subcarriers.

References:

  1. Cisco, “Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update”.
  2. “Five disruptive technology directions for 5G,” IEEE Communications Magazine.
  3. 3GPP TS 38.101.
  4. 3GPP TS 33.501.

 

 

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