Cellular IoT -- Comparison of CIoT technologies

Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim Sachs

October 15, 2018

Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim SachsOctober 15, 2018

Editor's Note: Growing requirements for increased availability of IoT devices coincide with the emergence of cellular technologies well suited for the IoT. For developers, the need has never been more acute for more detailed information about cellular technologies and their application to the IoT.  Excerpted from the book, Cellular Internet of Things, this series introduces key concepts and technologies in this arena.

In an earlier series, the authors described the evolving landscape for cellular, its role in the IoT, and technologies for massive machine-type communications (mMTC) and ultra reliable low latency communications (URLLC).


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Adapted from Cellular Internet of Things, by Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim Sachs.


Chapter 9. The competitive Internet of Things technology landscape (Cont.)

By Olof Liberg, Marten Sundberg, Eric Wang, Johan Bergman, Joachim Sachs



The different CIoT technologies EC-GSM-IoT, NB-IoT, and LTE-M have been extensively analyzed in Chapters 3-8. Here we summarize and compare the performance and characteristics. For NB-IoT we consider in this summary only in-band and stand-alone deployment options for simplicity. The performance of guardband mode of operation is to a large extent similar to the in-band performance. The full NB-IoT performance analysis including guardband operation can be found in Chapter 8. Coverage and Data Rate

The data rate in uplink and downlink for all CIoT technologies are summarized in Figures 9.7 and 9.8 for different coupling losses. All of those technologies have introduced extended coverage features, which enable an operation at a coupling loss of up to 164 dB. This is a significant extension of coverage range compared to what can be found in Global System for Mobile Communications (GSM), UMTS, or Long-Term Evolution (LTE) networks today. For EC-GSM-IoT the 164 dB coupling loss is based on a device with an output power of 33 dBm, as it is common in GSM networks. However, this means that a 10 dB higher device output power is needed for full extended range in EC-GSM-IoT compared to the device output power for NB-IoT and LTE-M for achieving the same uplink coverage. When looking more into details of the extended coverage results in Chapters 4, 6, and 8, it is seen that NB-IoT can operate at a lower control channel block error rate than EC-GSM-IoT and LTE-M at 164 dB MCL, making it more robust at extreme coverage. It can be noted that LTE-M and EC-GSM-IoT can apply frequency hopping, which provides some additional coverage robustness due to added frequency diversity.

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FIGURE 9.7 Coverage and physical layer data rate for uplink.

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FIGURE 9.8 Coverage and physical layer data rate for downlink.

Figures 9.7 and 9.8 also provide the physical layer data rates values for the different CIoT technologies. The instantaneous peak physical layer data rate specifies the achievable data rate of the data channels only. The other data rate values in the tables refer to the effective physical layer data rates for the transmission of a single message, where also the latencies for scheduling and control signaling is taken into account in the transmission time of the message. In this comparison it is assumed that half- duplex operation is used for all technologies but it should be noted that LTE-M devices can also be implemented with support for full-duplex operation which will achieve higher data rates (with peak rates close to the instantaneous peak physical layer data rates). These rates are provided for devices with different coupling loss to the base station: peak physical layer data rate corresponds to device with an ideal error free connection to a base station. Physical layer data rates at 144 dB coupling loss corresponds to the normal cell edge of the GSM or LTE radio cell, and 154 and 164 dB correspond to 10 and 20 dB of coverage extension compared to the cell edge of GSM.

What can be seen is that LTE-M can achieve significantly higher data rates in uplink and downlink compared to NB-IoT or EC-GSM-IoT. This is, in particular, the case for devices, which are within normal coverage of the radio cell. When devices are located in extended coverage areas, the uplink is limited by device output power, and all CIoT technologies make us of repetitions to achieve the required link quality. In extreme coverage situations like at 164 dB coupling loss, the achievable data rates for different technologies become quite similar when using the same output power. EC-GSM-IoT has at the 164 dB MCL a higher data rate than the other technologies due to the 10 dB higher output power of the device. Within the same LTE carrier, LTE-M has in general higher data rates than in-band NB-IoT.

All three technologies fulfill the 3GPP requirement on achieving 160 bps at the MCL of 164 dB. Latency

The latency of the CIoT technologies has been evaluated with respect to an exception report, which is an infrequent high-important IoT message contained in an 85 byte IP packet, which is being transmitted from a device over the CIoT network. All technologies, LTE-M, NB-IoT, and EC-GSM-IoT, fulfill the 3GPP latency target of 10 s first defined in Release 13, as depicted in Figure 9.9. When a device is within normal coverage, LTE-M can achieve somewhat lower latencies due to the higher data rates provided by LTE-M. In extended coverage, EC-GSM-IoT can provide the lowest latency due to the higher device output power, which can provide higher data rates. Stand-alone NB-IoT has a lower latency compared with in-band NB-IoT due to the higher power used for downlink channels.

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FIGURE 9.9 Latency for exception report. Battery Lifetime

The battery lifetime has been analyzed for all CIoT technologies, assuming two AA batteries with a joint capacity of 5 Wh. A power amplifier efficiency of 45%-50% has been assumed for all three IoT technologies.

Overall, all CIoT technologies apply mechanisms to save battery lifetime for infrequent transmission of messages, as it is common for many IoT services. The main principles are that devices only become active for the transfer of data, and otherwise are put into a battery-saving sleep state. Efficient procedures have been defined, which minimize the signaling overhead associated with the data transfer. This is particularly important for small messages because any signaling overhead can then account for a significant part of the energy consumption.

For a daily report of a 200 byte message, the battery lifetimes for the different CIoT technologies is depicted in Figure 9.10. The results for different message sizes and periodicities of IoT data transfers are summarized in Table 9.5. Overall, all technologies enable battery lifetimes of 10 years, and for some cases even significantly longer. The biggest challenge for long battery lifetime is when a device is located in a very bad coverage position. In the extended coverage mode, very low data rates are used and many repetitions are applied for the data transfer. In this situation a device requires an extended effort for data transmissions, which reduces the opportunity for resting in a battery-saving sleep state. Accordingly, the battery lifetime is significantly reduced at the MCL of 164 dB for all CIoT technologies. With such a large coupling loss, a battery lifetime of 10 years can only be achieved, if data transfer events of a device occur rarely, like once per day. For more frequent data transfer events, like one message every 2 h, battery lifetimes of 1-3 years are achievable at a MCL of 164 dB.

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FIGURE 9.10 Battery lifetime for a device with a daily report of a 200 byte message.

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Table 9.5 Battery lifetime

All three technologies fulfill, or indicate a potential of fulfilling, the 3GPP requirement on achieving 10 years battery life at the MCL of 164 dB.

Continue reading on page two, Device Complexity >>



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