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LTE-M Frame Structure | LTE-M downlink,uplink frame structure

This page describes LTE-M frame structure and its constituents. It mentions both LTE-M downlink frame structure and LTE-M uplink frame structure.

Introduction:
LTE-M follows 3GPP specifications similar to LTE technology. LTE-M stands for Long Term Evolution for Machine-Type Communications. It is mainly developed to fulfill cellular IoT device objectives such as low device cost, deep coverage, longer battery life, higher cell capacity and so on. There are different categories of LTE-M devices viz. Cat-0, Cat-M1 and Cat-M2 as per different 3GPP releases. LTE-M Cat-0, Cat-M1 and Cat-M2 follow 3GPP TS 36 series of rel.12, rel.13 and rel.14 respectively. Let us understand constituents of LTE-M frame structure.

LTE-M Frame Structure

LTE-M Frame Structure

The figure depicts LTE-M frame structure similar to LTE technology. As shown one hyperframe cycle consists of 1024 hyperframes. Each hyperframe consists of 1024 frames. One Frame consists of 10 subframes. One subframe consists of two slots each having 0.5ms duration. Hence each subframe has duration of 1 ms where as one frame has duration of 10ms. Each slot occupies either 7 symbols (for normal CP) and 6 symbols (for extended CP). Each subframe is uniquely identified by H-SFN (range 0-1024) , SFN (range 0-1024)and SN (range 0-9). H-SFN stands for Hyper System Frame Number. SFN stands for System Frame Number. SN stands for Subframe Number

Normal CP makes system robust in propagation conditions with delay spread upto 4.7 µs where as Extended CP in delay spread upto 16.7 µs.

LTE-M PRB Pair

Smallest resource unit used by LTE-M device is one PRB pair mapped over two slots. One PRB pair spans 12 subcarriers with 15 KHz subcarrier spacing. This gives total bandwidth of 180 KHz for 12 subcarriers. The figure depicts 12 subcarriers over 14 symbols for normal CP operation used as PRB pair in LTE-M. There is one more unit called RE (Resource Element) which refers to one subcarrier in one symbol.



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