Enhanced 4G LTE coverage for Machine-Type Communications and Internet of Things
Support for Machine-Type Communications (MTC) and Internet of Things (IoT) in cellular networks is being drastically improved with the recent launches of products based on 3GPP Release 13. Improvements have been introduced in both 2G GSM networks and 4G LTE networks as well as in the form of a new radio interface optimized for narrow frequency band allocations. These are referred to as EC-GSM, LTE-M and NB-IoT, respectively. In this blog post we focus on the 4G LTE improvements for MTC/IoT known as LTE-M in the areas of low device cost, long battery life, and deep coverage.
You’ll find a link to a more detailed introduction to the new terminology at the end of the post.
Low device cost
Low device cost is facilitated in Release 13 by the introduction of the new low-complexity device category M1 (Cat-M1) aimed at applications with relatively relaxed requirements on data rate and latency compared to the 4G device categories used in smartphones and mobile broadband modems. Cat-M1 is associated with both reduced peak rate and transmit/receive bandwidth. Cat-M1 devices can be implemented with a single receive antenna (whereas other 4G devices have at least two), a lower power class (with a maximum transmission power of 100 milliwatts instead of 200 milliwatts) and half-duplex operation, which means that the device is not required to transmit and receive at the same time. Using these simplifications, device complexity can be substantially reduced to be roughly on par with that of a 2G GSM device.
Long battery life
Long battery life comes with the introduction of extended discontinuous reception, allowing the device to switch off its receiver (and transmitter) circuitry completely during long periods without data activity. The device can either be kept in connected mode or be moved to idle mode. Release 13 introduces a suspend/resume mechanism for idle mode which reduces the need for signaling during transition back from idle to connected mode. All these mechanisms can be supported by both Cat-M1 and ordinary 4G devices. In addition, Cat-M1 devices can achieve even longer battery life thanks to the simplifications for reduced complexity mentioned in the previous paragraph. Assuming infrequent data traffic, these features should allow for a battery life of many years without the need to recharge the battery.
Deep coverage is the result of the introduction of two new coverage-enhancement modes referred to as CE modes A and B. The improved coverage is expected to be needed by some MTC/IoT devices with challenging coverage conditions, for example water/gas/electricity metering devices installed in basements. The coverage enhancement is mainly achieved through repetition techniques. In ordinary 4G operations, each transmission spans just 1 millisecond, but in the CE modes each transmission can be repeated tens, hundreds or even thousands of times to improve the chances of successful transmission. CE mode A is optimized for moderate coverage enhancement, whereas CE mode B provides extremely deep coverage. Support for at least CE mode A is mandatory for Cat-M1, but both CE modes can also be supported by ordinary 4G devices.
Until now, it has been somewhat unclear exactly how deep coverage Cat-M1 in CE mode B can provide, but now a group of companies – including Ericsson – has conducted a thorough joint-effort evaluation, which is described in detail in the white paper Coverage Analysis of LTE-M Category-M1. The conclusion is that Cat-M1 in CE mode B can fulfill the same coverage requirement that was assumed in the design of EC-GSM and NB-IoT (a coupling loss of 164 dB) and that LTE should therefore be well equipped to provide the coverage necessary for MTC/IoT applications with challenging coverage conditions.
More on LTE for MTC/IoT
Further LTE enhancements for MTC/IoT are introduced in 3GPP Release 14 in the form of improved support for higher data rates, multicast, positioning, voice service and mobility, as described in this 3GPP work item summary.
Visit Diversifying Cellular for Massive IoT for an introduction to Ericsson’s product offerings in this area and check out our popular post on Cellular IoT alphabet soup for an introduction to the terminology.