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LTE NB-IoT NPBCH Function | LTE NB NPBCH Physical Layer Processing


This page describes LTE NB-IoT NPBCH function and its basics with respect to LTE-NB IoT Standard. It covers LTE NB NPBCH Physical Layer Processing and NPBCH applications in the system.

Function:
The NPBCH stands for NB-IoT Physical Broadcast Channel. It is used to carry MIB informations to the device in the downlink by eNB (i.e. Base station). This helps device to operate with NB-IoT network.

NPBCH mapping in NB-IoT Frame

Location: As shown in the figure-1, NPBCH uses 640 ms TTI but within the TTI only subframe #0 is used in every radio frame. Following table mentions useful NPBCH informations.

NPBCH information Value
Subframe 0
Subframe periodicity 10 ms
Basic TTI 640 ms
Subcarrier spacing 15 KHz
Bandwidth 180 KHz
Carrier Anchor

LTE NB NPBCH Physical Layer Processing

NPBCH resource mapping

• As shown in the figure-2, 100 REs (Resource Elements) are available for NPBCH in a subframe. NPBCH uses QPSK modulation. Hence 200 encoded bits can be carried in NPBCH subframe.
• TBS of 34 bits along with 16 bits of CRC will give 50 bits during NPBCH processing.
• These 50 bits are encoded by LTE TBCC and will later rate matched to give output of 1600 encoded bits.
• These 1600 encoded bits are segmented into 8 CSBs (Code Subblocks), having 200 bits size. Each of these CSBs are mapped to 100 QPSK symbols.

NPBCH CSBs Transmission

The figure-3 depicts transmission of NPBCH CSBs. On each CSB, a symbol level scrambling is applied to offer robust protection against intercell interference.

Reference: 3GPP 36 series Rel.13, 14, 15



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