5G NR Numerology

Do you still remember that picture? It was the description of one PRB (Physical Resource Block) in 4G LTE. One PRB contains 12 subcarriers and 7 symbols.
Are we still use that modulation in 5G NR? Based on 3GPP TS38.802 OFDMA is still being used for 5G NR modulation, then the concept of one PRB also not changed. We might see the new approach of transmitting the Radio signal in Higher Frequency. 5G NR will be operating in two main frequency:

1. sub-6 GHz for operating frequency below 6 GHz
2. mmWave for operating frequency above 6 GHz

In higher frequency, it's hard to guarantee there is no Inter Carrier Interference (ICI) if we still using default Sub Carrier Spacing (SCS) with the length 15 kHz between subcarrier. In order to mitigate this problem, there are several SCS were introduced in 5G NR Release 14.
f(n) = 15 kHz * 2^n ; where (n is non-negative integer),

One Numerology corresponds to one subcarrier spacing in frequency domain

Maximum channel bandwidth per NR carrier is 400 Mhz in Rel 15. All details for channel bandwidth up to 100 Mhz per NR Carrier are to be specified in Rel 15.

At least for single numerology case, candidates of the maximum numbers of the subcarrier are 3300 or 6600 in Rel 15. Subframe Duration is fixed to be 1 ms. One TTI duration corresponds to a number of consecutive symbols for one transmission in the time domain (TR 38.804 5.4.7). The combination of one numerology and one TTI duration determines how the transmission is made on the physical layer. Frame Length is fixed to be 10 ms. Scalable numerology should allow the subcarrier spacing from 15 Khz to 480 Khz. The number of subcarrier per PRB is 12. The number of OFDM symbols per slot may vary depending on subcarrier spacing. Slot Aggregation (data transmission scheduling to span one or multiple slots. All numerologies align on symbol boundaries every 1 ms in NR carrier (regardless of subcarrier spacing and CP-overhead).No explicit DC subcarrier is reserved for both Downlink and Uplink.

5G NR should be able to use more than one numerologies in one NR work frequency

A slot is defined as 7 or 14 OFDM symbols for the same subcarrier spacing of up to 60kHz with normal CP and as 14 OFDM symbols for the same subcarrier spacing higher than 60kHz with normal CP. A slot can contain all downlink, all uplink, or {at least one downlink part and at least one uplink part}. Slot aggregation is supported, i.e., data transmission can be scheduled to span one or multiple slots.

Mini-slots having the following lengths are defined. At least above 6 GHz, mini-slot with length 1 symbol supported. Lengths from 2 to slot length -1. For URLLC, at least 2 is supported
From 3GPP RAN Meeting, there are several discussion from each vendor about supports SCS and maximum BW for one NR system in two domains operating frequency which is not fixed in the current study [Rel.14].

For sub 6GHz, 15k, 30k, and 60k are included in all companies proposals. For above 6GHz (mmWave), 60k, 120k and 240k are included in most companies proposals. Wider SCS will bring us more symbols can be transmitted over one TTI duration so higher data rate can be achieved with this approach.

Source :
Ray KHASTUR
LTE Senior RNO Consultant at P.I.Works, Inc.