LTE NB-IoT NPUSCH Function, LTE NB NPUSCH Format-1, NPUSCH Format-2

This page describes LTE NB-IoT NPUSCH function with location and its basics with respect to LTE-NB IoT Standard. It covers NB-IoT NPUSCH formats and mentions difference between NPUSCH format-1 and NPUSCH format-2.

NPUSCH channel is used to transport uplink user data and control information from upper layers. Moreover NPUSCH carry HARQ Ack for NPDSCH. NB-IoT uses only one PRB as maximum device scheduled bandwidth.

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

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

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

NPUSCH supports two transmission formats depending on data it carries viz. format-1 and format-2. Let us understand difference between NPUSCH format-1 and NPUSCH format-2.

NPUSCH format-1

Slot format for NPUSCH format-1

• This format-1 is used for carrying uplink data and uses same LTE turbo code for error correction.
• It supports UE bandwidth allocation smaller than one PRB where as LTE has min. bandwidth allocation of 1 PRB.
• 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.
• It supports single layer transmission where as LTE supports multiple spatial multiplexing layers.
• It uses same slot structure as legacy PUSCH with 7 OFDM symbols per slot ( as shown in the figure-1) and middle symbol as DMRS used for channel estimation.

NPUSCH format-2

Slot format for NPUSCH format-2

• It is used for signaling HARQ Ack for NPDSCH.
• It uses repetition code for error correction.
• NPUSCH format-2 has 7 OFDM symbols per slot as shown in the figure-2.
• It supports 3.75 KHz or 15 KHz numerology.
• It uses middle three symbols as DMRS used for channel estimation.
• It uses single tone transmission.

Reference: 3GPP 36 series

NB-IoT Related Stuff


This tutorial section on LTE basics covers following sub topics:
LTE tutorial  LTE features  LTE terminologies  Frame  TDD FDD  Channel types  PHY  stack  throughput  CA   cell search  network entry  Timers  PSS vs SSS  Security   LTE Bands  EARFCN  Hotspot  router  What is VoLTE  VoLTE originating call flow  VoLTE UE attach and registration procedure 

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