Terminology » Mobile Communication » LTE NB-IoT NPUSCH: Format-1 vs Format-2

LTE NB-IoT NPUSCH: Format-1 vs Format-2

This page describes the LTE NB-IoT NPUSCH (Narrowband Physical Uplink Shared Channel) function, its location, and basics with respect to the LTE-NB IoT Standard. It covers NB-IoT NPUSCH formats and highlights the difference between NPUSCH format-1 and NPUSCH format-2.

Function: The NPUSCH channel is used to transport uplink user data and control information from upper layers. Moreover, NPUSCH carries HARQ-ACK (Hybrid Automatic Repeat Request - Acknowledgement) for NPDSCH (Narrowband Physical Downlink Shared Channel). NB-IoT uses only one PRB (Physical Resource Block) as the maximum device scheduled bandwidth.

Table-1 shows useful parameters related to the NB-IoT NPUSCH channel.

NPUSCH information	Value
Subframe	Any
RU	1, 2, 4, 8, 32 ms
Repetitions	1, 2, 4, 8, 16, 32, 64, 128
Subcarrier spacing	3.75 KHz, 15 KHz
Bandwidth	3.75, 15, 45, 90, 180 KHz
Carrier	Any

Difference between NB-IoT NPUSCH Format-1 and Format-2

NPUSCH supports two transmission formats depending on the data it carries: format-1 and format-2. Let’s understand the differences between them.

NPUSCH Format-1

Slot format for NPUSCH format-1

Format-1 is used for carrying uplink data and uses the same LTE turbo code for error correction.
It supports UE (User Equipment) bandwidth allocation smaller than one PRB, whereas LTE has a minimum bandwidth allocation of 1 PRB.
The maximum transport block (TB) size is 1000 bits.
It supports multi-tone transmission based on LTE numerology. Here, NB-IoT UE is allocated with 3 and 6 tone formats.
It also supports single-tone transmission based on either 3.75 KHz or 15 KHz numerology. LTE uses only 15 KHz.
It uses π/2 - BPSK or π/4 - QPSK for single-tone transmission to reduce PAPR (Peak-to-Average Power Ratio).
It supports single-layer transmission, whereas LTE supports multiple spatial multiplexing layers.
It uses the same slot structure as legacy PUSCH with 7 OFDM symbols per slot (as shown in the figure above) and the middle symbol as DMRS (Demodulation Reference Signal) used for channel estimation.