This LTE-M tutorial covers LTE-M features, LTE-M Architecture, LTE-M Protocol Stack, LTE-M Frame Structure, LTE-M Channel Types, LTE-M RRC Resume Procedure etc.
What is LTE-M technology?
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. LTE-M along with NB-IoT are two LPWA (Low Power Wide Area) technologies designed and developed for IoT applications to transmit/receive small amounts of data using lower bandwidth at low costs. There are number of applications in which these technologies are being used which include smart buildings/cities, healthcare, people/asset/animal tracking, pollution monitoring 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. Following are the features supported in LTE-M Cat-M1 devices. LTE-M cat-M1 (i.e. LTE-M1) uses LTE installed network. It has been deployed in number of countries across the world by various operators in different frequency bands. Some of the countries are Mexico, United States, Canada, North America, Sri Lanka, UAE, Japan , Singapore, New Zealand, Switzerland, Australia and so on. LTE-M uses bands 1, 2, 3, 4, 5, 7, 8, 11, 12, 13, 18, 19, 20, 26, 27, 28, 31, 39, 41 under release 13 and bands 25 and 40 under release 14.
|LTE-M Cat-M1 Features||Description|
|Bandwidth||1.4 MHz (Maximum 6 PRBS are allocated in DL/UL equivalent to 1.08 MHz)|
|Peak Data Rate (DL/UL)||1 Mbps|
|Duplex modes||HD-FDD, FD-FDD, TDD|
|Number of receive antennas||1|
|Transmit power||20 dBm|
|Advanced power saving modes||PSM, eDRX|
|Coding scheme (DL/UL)||Turbo code|
|Spatial Layers (Max. in DL/UL)||1|
|Maximum TBS (DL/UL)||1000 bits|
|CE Modes||Mode-A(Mandatory), Mode-B (Optional) >>.|
|LTE-M Device Categories||Cat-0, Cat-M1, Cat-M2 >>.|
LTE-M focuses on three main features in comparison to NB-IoT as follows.
➤Higher uplink/downlink speed of up to 1 Mbps.
➤VoLTE support for voice calls
➤Mobility support for devices in movement
The figure depicts LTE-M architecture in roaming scenario. Both user plane and control plane are shown which are used for transport of data and control informations.
LTE-M Protocol Stack
The figure depicts LTE-M Protocol Stack layers. Both user plane and control plane protocol layers are shown in the figure. Refer LTE Protocol Stack >> for functions of each of these layers.
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. 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).
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.
Refer LTE-M Frame >> for more information.
LTE-M Channel Types
LTE-M supports set of downlink and uplink channels and signals. The mapping between logical channels, transport channels and physical channels is also shown. As mentioned PSS, SSS and RS are used as downlink signals where as PDSCH, MPDCCH and PBCH are used as downlink channels.
PRACH, PUSCH and PUCCH are used as uplink channels as shown in the figure. RS and DMRS are used as reference signals in uplink. Refer LTE-M Channel Types >> for more information.
LTE-M RRC Resume Procedure
The figure depicts LTE-M RRC Resume procedure.
The above LTE-M tutorial covers basic overview of LTE-M technology, one can follow links in each of the above sections to know more about it.
NB-IoT Related Stuff
LTE RELATED LINKS
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