Extend IoT Device Battery Life with LTE-M Power Consumption
LTE-M, or Long-Term Evolution for Machines, is a low-power, wide-area (LPWA) cellular technology specifically designed for Internet of Things (IoT) applications. It is a variant of the 4G LTE standard and is optimized for low-power, low-cost, and extended-coverage IoT devices.
LTE-M Power Consumption Advantages
According to IndustryARC, the LTE-M Devices Market size is forecast to reach $6.2 billion by 2026, growing at a CAGR of 25.4% in the period 2021-2026. The steadily increasing market size could be attributed to the significant advantages that LTE-M offers for IoT deployments. In comparison to traditional cellular networks, LTE-M provides better coverage and penetration. LTE-M is an ideal connectivity solution for applications in underground or hard-to-reach areas. LTE-M technology also offers improved power efficiency, allowing IoT devices to operate for extended periods on battery power. This makes it ideal for applications where power consumption is a critical factor, such as remote monitoring, asset tracking, smart meters, wearables, and industrial automation.
Moreover, LTE-M supports voice capabilities, which enables IoT devices to incorporate voice communication functionalities when required. It also provides reliable connectivity, enhanced security features, and support for mobility, allowing devices to seamlessly switch between cellular towers without interruption.
What are the Enabling Technologies of the IoT?
IoT devices rely on wireless communication technologies like Wi-Fi, Bluetooth, Zigbee, NFC, or cellular networks to connect and exchange data with each other and the internet. Without wireless connectivity, an IoT ecosystem is incapable of the data exchange and intelligence necessary for the successful implementation of IoT applications across various industries and domains. A device’s chosen form of wireless communication protocol is a crucial part of its design and is integral to overall functionality. How can developers determine whether LTE-M is the ideal connectivity solution for their design?
LTE-M vs Cat-M
In the consumer world, there seems to be confusion about the interchangeable nature of LTE-M and Cat-M. For clarification, LTE-M and Cat-M are two terms often used interchangeably to refer to the same technology: LTE-M1 or Long Term Evolution for Machines Category M1. It is important to note that there is no significant technical difference between LTE-M and Cat-M. They both represent the same technology and offer the same capabilities and features. The term "Cat-M" is derived from the 3GPP (Third Generation Partnership Project) release naming convention, while "LTE-M" is a more common term used in the industry. LTE-M and Cat-M are synonymous and refer to the same technology, LTE-M1, which provides optimized cellular connectivity for IoT devices with low power consumption and wide coverage.
LTE-M vs NB-IoT
LTE-M is but one of two cellular IoT standards that are expanding the use of cellular communications to a wide range of applications and connected devices. Another popular cellular IoT standard is NB-IoT, or narrowband IoT. Allied Market Research valued the global NB-IoT market at $634.3 million in 2021. While both are positioned as the successors of older cellular standards, they are not one and the same.
Figure 1: There are some significant differences between LTE-M and NB-loT.
Source: Qorvo
Both LTE-M and NB-IoT are forms of machine-to-machine (M2M) communication, also known as machine-type communications (MTC). M2M helps enable applications such as smart cities, environmental monitoring, asset tracking, and more. Of course, operators already use older 2G and 3G networks for some IoT applications, like fleet tracking. However, LTE‑M and NB‑IoT are different because they’re optimized for IoT devices that communicate small amounts of data over long periods of time. In turn, they’re simpler than other cellular standards, with much less overhead.
When compared to each other (Figure 1), each has its own strengths and areas of applicability. It's important to note that the choice between LTE-M and NB-IoT depends on specific use cases and requirements. However, here are some reasons why LTE-M may be considered advantageous in certain scenarios:
Data Rates: LTE-M offers higher data rates compared to NB-IoT. This makes it suitable for applications that require relatively higher throughput, such as firmware updates, voice-over (VoLTE) for IoT devices, or applications involving periodic transmission of larger data packets.
Latency: LTE-M generally has lower latency compared to NB-IoT. This lower latency is beneficial for applications that require real-time or near real-time communication, such as remote-control applications or real-time monitoring.
Mobility: LTE-M supports mobility, allowing IoT devices to move and maintain connectivity while on the move. This is advantageous for use cases involving mobile IoT devices, such as asset tracking or vehicle tracking.
Voice Support: LTE-M supports voice services, which can be useful for certain IoT applications that involve voice communication, such as voice-controlled devices or voice-enabled services.
Existing Network Infrastructure: LTE-M can leverage existing LTE networks, making it easier for network operators to deploy and manage. This compatibility with existing infrastructure can provide cost and operational advantages in certain deployments.
Low Power Design for LTE-M and NB-IOT
A new IoT environment was created with the release of 3GPP rev 12 and 13 standards. Two new features were added to help reduce the power consumed by dedicated Low Power Wide Area Network (LPWAN) modems connecting to the cellular network:
Power Saving Mode (PSM)
Extended Discontinuous Reception (eDRX)
Power Saving Mode (PSM)
PSM works by dropping your modem into a deep sleep mode for a programmed length of time. Under PSM, your modem negotiates timing with the cellular network’s eNode base station. This negotiation happens when modem registers itself (Attach) or during a Tracking Area Update (TAU).
Right before the modem drops into deep sleep, it notifies the eNode base station. When your modem comes out of deep sleep, the eNode base station and your modem have preserved the existing connection, so a reattach is not needed. This saves significant energy.
The disadvantage of PSM is that your modem is not reachable from the cellular network while it is in deep sleep. The 3GPP standard specifies that the eNode base station needs to store any attempts to communicate with your modem, but the cache size of 100 characters is very limited, and implementations of caching is not always consistent between cellular carriers. If there is a large amount of traffic, messages could be dropped by the eNode base station.
The PSM standard allows you to negotiate two important timing parameters:
Active Time (T3324 timer)
Time between TAU (T3412 timer)
By manipulating these timing parameters, significant power savings can be achieved.
Extended Discontinuous Reception (eDRX)
eDRX works by controlling the interval and number of paging checks your modem performs. During a page check your modem briefly turns on its radio and listens for a signal from the eNode base station. If the base station has a message for your modem, it will signal your modem at that time. A paging check is very brief:
32 ms for CAT-M1 with 1.28 second wait between each page check
8 ms for NB-IoT with 2.56 second wait between each page check
The eDRX standard allows you to negotiate two important timing parameters:
Paging Time Window Length (i.e, number of paging checks per window)
between 1 and 16 paging checks per window
Length of time between windows
5.12 secs to 2622.44 secs for CAT-M1
20.48 secs to 10485.76 secs for NB-IoT
By manipulating these timing parameters, significant power savings can be achieved while retaining responsiveness to external network messaging.
The disadvantage of eDRX mode is that not as much internal hardware can be shut down while in deep sleep mode. eDRX quiescent current will be higher than PSM. It means there is a tradeoff between total battery lifetime vs responsiveness to external requests. Since a device that is designed to respond to external requests is by nature going to be more energy intensive, the designer should pick a higher energy storage system for this sort of application.
Network Considerations While in Power Savings Mode
Care must be taken when designing a network that includes a device that utilizes either PSM or eDRX. For example, it might be tempting to leave a communication socket open with the network and use a popular protocol such as MQTT to communicate between the device and the network. Due to the intermittent nature of downlink communications, however, such a strategy might not work as expected. If the network publishes data destined for the end device and the device is in a sleep cycle, the data would not be delivered in a timely manner, or perhaps not at all if the network does not queue the data. Different cellular carriers implement queuing and caching of downlink data differently, so a solution might work differently on different networks. A better communications strategy (for the MQTT example) would be to disconnect MQTT sessions in between sleep cycles, and only establish the MQTT connection when the device is actively communicating. Alternatively, a RESTful API that does not rely on network timing could be utilized for communication.
Designing an LTE-M/Cat-M Product
There are several key steps to ensure the successful development of an LTE-M product:
Identify Use Case and Requirements
Hardware Selection
Software Development
Power Management
Network Connectivity
Testing and Certification
Integration and Deployment
Field Testing and Optimization
Scalability and Upgrades
Throughout the design process, developers will need to collaborate with network providers, chipset vendors, and other stakeholders to ensure compatibility and maximize the potential of LTE-M technology. It’s important to regularly review the design to address any challenges or opportunities that arise during development.
When navigating the complexities of developing an LTE-M device, it is highly beneficial for developers to utilize a comprehensive engineering service firm like Connected Development. Our extensive IoT, LTE-M, and M2M experience positions us to provide you with an accelerated development process and successful deployment of your LTE-M product. If you’re interested in developing a customized solution and collaborating with a team of expert connected systems engineers for your LTE-M device design, contact Connected Development today!
Resources:
Power Management Trade-offs: Hard Shutdown vs PSM and eDRX Technologies