4G/LTE - MTC

MTC (Machine Type Communication)

MTC stands for Machine Type Communication. This is mainly designed to use LTE for M2M (Machine to Machine) or IoT (Internet of Things). Usually these application requires not that much throughput (in most case it needs very low throughput).

Why do you need this kind of special technique ? Does this mean that current LTE cannot achieve such a low throughput ?

Of course there is no problem with the current LTE to work for such a low throughput application. But the issue is not with the low throughput, but with some other constraints. In practical point of view, this kind of application would need following characterstics.

• Low Throughput (usually just a couple of hundreds of bps in DL and less than 100 bps in UL)
• Low Cost (As low as an EGPRS modem)
• Low Energy Consumption

As I said there is no problem with achieving Low Throughput with the current LTE implementation, but there would be limitation to achieve Low Cost, Low Energy Consumption as required in this area (Actually Low Throughput itself is not a goal of the design. It is more like a result of design/implementation that meets MTC criteria illustrated below.

Then how to achieve these critical requirement. The easies way we can think of is to reduce the complexity of LTE and this is the main motivation of MTC and it is one of major topics in Rel 13. I think this would be more important feature/topic in 5G than in 4G (Current LTE).

In LTE, the main idea to achieve the low cost solution is

• i) Use the narrowest BW 1.4
• ii) Use Single Antenna (SISO)
• iii) Make some changes on Physical layer processing to reduce (simplify) baseband processing

You may say 'item i) and ii) has been supported from the day 1 of LTE. So we don't have to do anything (effort /changes) on network side ?'

Only in terms of throughput in a good signal condition, you may say like it. But with BW 1.4 and single antenna, it is very difficult to apply techniques to improve the reliable data connection (e.g, Spatial Diversity, Frequency Diversity etc). So we may need to change some specification to compensate this restriction.

Also, we may need to change some lower layer specification due to item iii) as well.

As of now (Apr 2015), no TS document yet, but you can get pretty details information from following documents.

• RP-141865
• TR 36.888

Followings are some of the Objective of MTC discussed in RP-141865

• Reduced Complexity in Category and Channel Bandwidth
• Reduced UE bandwidth of 1.4 Mhz in downlink and uplink
• Bandwidth reduced UEs should be able to operate within any System Bandwidth
• Frquency Multiplexing of bandwidth reduced UEs and non-MTC UEs should be supported
• The UE only needs to support 1.4 Mhz RF bandwidth in downlink and uplink
• Reduced maximum transmission power
• Reduced support for downlink transmission mode
• Reduced maximum transport block size for unicast and/or broadcast signaling
• Reduced support for simultaneous reception of multiple transmissions
• Relaxed transmit/receive EVM requirement
• Reduced physical control channel processing (e.g, reduced number of blind coding attempts)
• Reduced physical data channel processing (e.g, relaxed downlink HARQ time line or reduced number of HARQ processes
• Reduced support for CQI/CSI reporting modes
• Relative LTE Coverage Improvement (around 15 dB improvement for FDD) - Refer to RP-1418165 for details
• Reduced power consumption/Ultra-long battery life - Refer to RP-1418165 for possible techniques
• Half Duplex FDD, full Duplex FDD and TDD should be supported

Now (as of Rel 13) we can see the real implementation of these criteria because LTE MTC specification is released. See how these general criteria turns into reality in LTE : LTE BL/CE (M1) and LTE NB pages.

Reference :

[1] 22.368 - Service requirements for Machine-Type Communications (MTC) Stage 1 

[2] TR 36.888 - Study on provision of low-cost Machine-Type Communications (MTC) User Equipments (UEs) based on LTE