LTE-M: The Future of LTE for the M2M Industry

M2M covers wide variety of applications, including in-house smart meters, wearables, asset tracking, smart agriculture, and more. These applications require longer battery life with remote connectivity. Additionally, many of these applications need to send small amount of data at infrequent time intervals. Customers call for a module which will offer data connectivity but at a lower cost. With the 2G sunset for AT&T in North America looming, customers are looking to migrate to the most suitable technology.

LTE offers connectivity to outside world and to the cloud. It also offers longevity, ensuring the life of design for years to come. However, LTE is specifically designed to target higher data rates around 100Mbps and to reduce latency. LTE makes use of higher modulation techniques and receiver diversity to deliver these requirements. The negative side of this is very high operational cost and complex hardware requirements. With these limitations in mind, one may wonder how LTE can cater to the M2M industry successfully.

3GPP concentrates on M2M with Rel 12 & Rel 13:

The 3^rd Generation Partnership Project (3GPP) is a collaboration responsible for developing the LTE standards which are globally applicable. 3GPP defines requirements and architectural specifications for cellular technologies such as LTE, and tries to reinvent it with each revision or Release. The first LTE standard was Release 8, and since then 3GPP has been moving in the direction suitable for smartphones. With the introduction of Rel. 12 and Rel. 13, they are taking note of the special requirements of IoT and making modifications fitting to them.

LTE Requirements of IoT:

1. Reduce Cost: Traditionally, LTE modems need to support architecture with high complexity techniques for modulation, Multiple-Input-Multiple-Output (MIMO), and diversity to help high resolution and data-centric applications. This adds complexity to the design and in return considerably increases the cost. Most of the IoT applications do not require this intricacy and would prefer a lower cost module. LTE needs to have a simplified chipset and reduce the cost.
2. Improve Battery Life: As mentioned before, LTE does employ a large number of complex techniques which increases the power consumption of the device resulting in frequent charging. Many M2M applications operate on a battery and want a technology which would last for years using that. Also, in many applications it is not practically possible to change the batteries frequently and not a cost optimized option either. In this matter substantial modifications are necessary to make LTE consume lesser power and make it last longer.
3. Omnipresent Coverage: Although LTE has good network coverage in dense areas, it lacks in the remote fields, which represents a significant drawback since many applications deploy their units in the remote areas. The oil industry, smart agriculture, and asset tracking are a few examples where coverage area becomes an important issue. Therefore, a few features need to be introduced in order to enhance the network coverage.

3GPP LTE Rel. 12 Enhancement for IoT:

3GPP has understood the requirements of M2M applications and is taking steps in LTE development to address those concerns. They have decided to introduce a new device Category, Cat-0, which will adhere to M2M specifications. It will be referred to as LTE-M, or LTE for Machine Type Communications (MTC).

1. Peak Rates of 1Mbps: It has been decided to reduce the peak rate requirements for M2M applications. Higher rate requirements need complex circuitry which results in increased cost and power consumption. By decreasing the throughput requirements these issues can be addressed. The decreased throughput makes LTE ideal for applications which require infrequent transmissions and lower payload.
2. Half-Duplex Systems: LTE offers a full-duplex system for communication. Which means it can handle incoming and outgoing communications simultaneously. The full-duplex requirement adds a lot of cost overhead on the system. Therefore, an option for supporting half-duplex devices has been provided. With half-duplex systems costs can be considerably decreased by removing the extra switches and filters.
3. One Receive Antenna: LTE requires a deployment of two receive antennas to provide the diversity. This has been changed to deploying only one receive antenna. This will help in cost reduction as well as power consumption.
4. Power Saving Modes: To further increase the battery life of the device new Power Saving Modes (PSM) have been introduced. These make the devices sleep whenever operation is not required and wake up less frequently and after longer duration. This will help in reducing the battery consumption significantly.

3GPP LTE Rel. 13 Enhancement for IoT:

To further address the M2M issues 3GPP has suggested more enhancements to the Cat-0 devices described below:

1. Reduced Bandwidth: LTE supports a bandwidth of 20MHz. With Rel. 13 the Cat-0 would be subjected to support only 1.4MHz in the receive bandwidth.
2. Max Transmission Power Reduced: The maximum transmission power for LTE is defined at 23dbm. This has been reduced to 20dbm in case of Cat-0 devices. The reduction in maximum power requirements will reduce the power consumption which will in turn help in the conservation of the battery, making it last longer.

Along with these, other coverage and power saving modes enhancements have been suggested as well. With all these changes it is expected to drop the cost of the LTE devices by 50-60% and be comparable to that of GPRS devices.

What’s Available Today: LTE Cat-1 Devices (Baby-Step towards IoT)

Even though Rel. 12 is fully defined it is not commercially deployed, and Rel. 13 is still at the development stage. It will take a lot of effort from the carriers’ side to implement the changes defined for MTC and deploy them. We are looking at 2017 for these changes to take effect according to the current timeline. While we wait for them, we still have Cat-1 devices defined in the current specifications which are not exactly optimized for M2M applications, but are certainly a step towards it. These devices provide a significant improvement in terms of power consumption and cost compared to the high end LTE solutions, as well as lesser overhead on the carriers to build the resources required for the deployment.

References:

1. Nokia White Paper: Nokia LTE M2M “Optimizing LTE for the IoT”