Diagram of 5G NR frame structure

Compared to LTE (subcarrier spacing and symbol length), NR supports a wide range of subcarrier spacing (in LTE, there is only 15 Khz subcarrier spacing).

In 3GPP38.211, there is a summary of NR subcarrier spacing types.

The specific subcarrier spacing types are shown in the following figure:

Figure 1.1 Subcarrier spacing types supported by NR

(In the frequency domain, 1 RB = 12 subcarrier spacing)

As shown in the figure below, the time slot length varies due to different subcarrier spacing. Generally, as the subcarrier spacing increases, the time slot length decreases.

Figure 2.1 Time slot length under normal CP

(Each time slot has 14 symbols)

Figure 2.2 Length of time slot in case of extended CP

(Each time slot has 12 symbols)

Different subcarrier spacings support different physical channel capabilities, as shown in the following figure:

Figure 3.1 Capabilities of supporting physical channels

Figure 4.1 OFDM symbol length calculation

Although 5GNR supports multiple subcarrier spacings, the lengths of radio frames and subframes are the same under different subcarrier spacing configurations. The radio frame length is 10ms and the subframe length is 1ms .

So what are the differences in the structure of the radio frame under different subcarrier spacing configurations? The answer is that the number of time slots contained in each subframe is different. Under normal CP conditions, the number of symbols contained in each time slot is the same, which is 14 .

• Subcarrier spacing = 15Khz (normal CP )

In this configuration, a subframe has only one time slot, so a radio frame contains 10 time slots.

The number of OFDM symbols contained is 14.

Figure 5.1 Subcarrier spacing = 15Khz (normal CP )

• Subcarrier spacing = 30Khz (normal CP )

In this configuration, a subframe has 2 time slots, so a radio frame contains 20 time slots.

The number of OFDM symbols contained is 14.

Figure 5.2 Subcarrier spacing = 30Khz (normal CP )

• Subcarrier spacing = 60Khz (normal CP )

In this configuration, a subframe has 4 time slots, so a radio frame contains 40 time slots. 1 time slot contains

The number of OFDM symbols is 14.

Figure 5.3 Subcarrier spacing = 60Khz (normal CP )

• Subcarrier spacing = 120Khz (normal CP )

In this configuration, a subframe has 8 time slots, so a radio frame contains 80 time slots. 1 time slot contains

The number of OFDM symbols is 14.

Figure 5.4 Subcarrier spacing = 120Khz (normal CP )

• Subcarrier spacing = 240Khz (normal CP )

In this configuration, a subframe has 16 time slots, so a radio frame contains 160 time slots.

The number of OFDM symbols contained is 14.

Figure 5.5 Subcarrier spacing = 240Khz (normal CP )

• Subcarrier spacing = 480Khz (normal CP )

In this configuration, a subframe has 32 time slots, so a radio frame contains 320 time slots.

The number of OFDM symbols contained is 14.

Figure 5.6 Subcarrier spacing = 480Khz (normal CP )

• Subcarrier spacing = 60Khz (Extended CP )

In this configuration, a subframe has 4 time slots, so a radio frame contains 40 time slots. 1 time slot contains

The number of OFDM symbols is 12.

Figure 5.7 Subcarrier spacing = 60Khz (Extended CP )

3GPP 38.211 (starting from 2.0.0) defines many different timeslot formats. This concept is similar to the traditional LTE TDD subframe configuration, but there are many differences:

1. In the NR time slot format, the uplink and downlink services use symbols as the switching point (in LTE TDD, the uplink and downlink services use subframes as the switching point)

2. Compared with LTE TDD uplink and downlink subframe configurations, there are more uplink and downlink symbol configuration types in the NR time slot format (not good news for FPGA or DSP engineers)

3. 38.211-Table 4.3.2-3 applies only to DCI with SFI_RNTI (i.e. DCI 2_0)

Although all time slot formats look like TDD structures, these can also be deployed in FDD mode.

This article is translated by Yu Bingcai. The original English manuscript comes from: http://www.sharetechnote.com/. The original author’s permission has been obtained.