LTE provides an ideal platform for machine to machine, [email protected] communications. Using low bandwidth and low data rates, with new LTE categories, LTE is able to support this form of communication using LTE-M
The LTE-M variant of LTE enables the enormous coverage of the LTE networks to be utilised for M2M communications without the need for installing a new network.
LTE-M has been tailored to meet the needs of IoT M2M communications with the introduction of new low data rate categories, and with careful design of the remote nodes, this enables enormous battery lifetimes extending to many years to be achieved.
Associated with the introduction of LTE-M are new categories that were introduced in the Release 13 (Rel 13) of the 3GPP standards. These categories include LTE Cat 1.4MHz and LTE Cat 200kHz.
LTE-M key issues
There are several requirements for LTE M2M applications if the cellular system is to be viable in these scenarios:
- Long battery life : Many M2M devices will need to be left unattended for long periods of time in areas where there may be no power supply. Maintaining batteries is a costly business and therefore any devices should be able to have a time between battery changes of up to ten years. This means that the LTE-M system must be capable of draining very little battery power.
- Wide spectrum of devices: Any LTE machine to machine system must be able to support a wide variety of different types of devices. These may range from smart meters to vending machines and automotive fleet management to security and medical devices. These different devices have many differing requirements, so any LTE-M system needs to be able to be flexible.
- Low cost of devices: Most M2M devices need to be small and fit into equipment that is very cost sensitive. With many low cost M2M systems already available, LTE-M needs to provide the benefits of a cellular system, but at low cost.
- Large volumes - low data rates: As it is anticipated that volumes of remote devices will be enormous, the LTE-M must be structured so that the networks are be able to accommodate vast numbers of connected devices that may only require small amounts of data to be carried, often in short peaks but with low data rates.
- Enhanced coverage : LTE-M applications will need to operate within a variety of locations - not just where reception is good. They will need to operate within buildings, often in positions where there is little access and where reception may be poor. Accordingly LTE-M must be able to operate under all conditions.
Rel 12 updates for LTE-M
A number of updates were introduced in 3GPP Rel 12 to accommodate LTE-M requirements.
These updates mean that the cost of a low cost M2M modem could be 40 to 50% that of a regular LTE devices, making them comparable with EGPRS ones.
To accommodate these requirements a new a new UE category has been implemented LTE Category 0. These categories define the broad capabilities of the device so that the base station is able to communicate properly. Read more about LTE UE categories.
These low cost LTE-M, M2M modems have limited capability and are:
- Antennas: There is the capability for only one receive antenna compared to two receive antennas for other device categories.
- Transport Block Size: There is a restriction on the transport block size These low cost LTE-M devices are allowed to send or receive up to 1000 bits of unicast data per sub-frame. This reduces the maximum data rate to 1 Mbps in both the uplink and the downlink.
- Duplex: Half duplex FDD devices are supported as an optional feature - this provides cost savings because it enables RF switches and duplexers that are needed for the full performance modems to be removed. It also means there is no need for a second phase locked loop for the frequency conversion, although having only one PLL means that switching times between receive and transmit are longer.
LTE-M features planned for Rel 13
There are several features that are being proposed and prepared for the next release of the 3GPP standards in terms of LTE M2M capabilities. These include some of the following capabilities:
- Reduce bandwidth to 1.4 MHz for uplink and downlink
- Reduce transmit power to 20dBm
- Reduce support for downlink transmission modes
- Relax the requirements that require high levels of processing, e.g. downlink modulation scheme, reduce downlink HARQ timeline
The UE category for this is being termed 'Cat 1.4MHz'.
There is an additional enhancement for LTE-M under Rel 13 with a reduced bandwidth option of 200kHz in the uplink and downlink - often termed Narrowband or NB lte_m. By reducing the bandwidth and also the data rate, further simplification of the modem can be achieved. The UE category of this is being termed 'Cat 200kHz.'
It is possible to summarise the various UE categories and options for LTE-M modems and systems.
|Comparison of Capabilities and Modem Complexities for LTE-M|
'Cat 1.4 MHz'
|Downlink peak rate (Mbps)||150||1||1||0.2|
|Uplink Peak Rate (Mbps)||50||1||1||0.144|
|Number of antennas||2||1||1||1|
|UE receive bandwidth (MHz)||20||20||1.4||0.2|
|UE transmit power (dBm)||23||23||20||23|
|Relative Modem Complexity||100%||40%||20%||<15%|
One of the key measurements for any machine node is the modem complexity. As this falls, so does the battery consumption. It can be seen that LTE Cat 1.4MHz and LTE Cat 200kHz have very lower complexity modems when compared to a Cat 4 modem.
Accordingly LTE Cat 1.4MHz and LTE Cat 200kHz will be widely used for LTE-M and M2M applications.
LTE-M enables LTE to provide a service tailored to meet the needs of the many IoT and M2M applications that are now being developed. With IoT nodes expected to reach 20 to 30 billion devices in a few years, it was necessary that LTE address this sector of the market and provide a suitable solution. This has been achieved using LTE-M.
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