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Internet of Things (IoT) is undoubtedly one of the major revolutions that the wireless industry has seen and it is likely to be the key element in driving the future of cellular technology as well. With widespread adoption of the internet, it is evident that every device and every human is being connected to each other today. IoT is the key enabler for this by delivering machine-to-machine (M2M) communication on a massive scale. Ericsson predicts there will be around 28 Billion connected devices by 2021, of which more than 15 billion will be connected M2M and consumer-electronics devices.

Connectivity is the foundation for IoT, and the type of access required will depend on the nature of the application. Many IoT devices are served by radio technologies such as Bluetooth that operate on unlicensed spectrum and are ideal for short-range connectivity for a home or indoor environment. In order to achieve wide area connections of IoT devices, two alternatives are available. On one hand, there are the current proprietary LPWA technologies, such as SigFox and LoRa, which typically operate on unlicensed spectrum. On the other hand, there are 3GPP standardized cellular IoT technologies such as NB-IoT and eMTC which typically operate on licensed spectrum. We are going to talk about the latter set of IoT technologies in this paper.

Cellular IoT (CIoT) is defined as a set of technologies under the 3GPP standardization that enables IoT connectivity using the licensed frequencies while co-existing with the legacy cellular broadband technologies, such as LTE. Owing to its capabilities, numerous services are envisioned for cellular IoT, including utility meters, vending machines, automotive (fleet management, smart traffic, real time traffic information to the vehicle, security monitoring and reporting), medical metering and alerting. But, LTE was primarily designed for mobile communication and there are numerous requirements of the M2M communication systems and applications that LTE needs to deliver. Some of the major requirements are as follows:

Cost Reduction: The cost of LTE supporting cellular modules embedded on phones are not considered very expensive with respect to the other components on a typical smartphone. For M2M, the cost of the communication unit has to be drastically reduced to be integrated with IoT devices because devices such as wearable devices and smart meters lie in a lower price range as compared to phones. Various cost reduction techniques have been considered by the Third Generation Partnership Project (3GPP), including reduced computational complexity, reduced data rate, single antenna support, and half duplex operations.

Reduced Power Consumption: This is another important aspect of the battery powered IoT devices because millions of them are deployed in various locations across the world. Regular changing of batteries in these devices is not at all feasible. Enhanced Coverage: There exists IoT applications where devices are sometimes located in remote or not so easily reachable locations such as basements and deep indoors, where there are high chances of path loss between the transmitter and the receiver. Thus, M2M communication services may require a 15–20 dB coverage enhancement with respect to regular cellular services. Scalability: In order to enable a Massive IoT market, networks need to scale efficiently and be able to support millions of devices.

Diversity: Every IoT application will have a different set of requirements in terms of cost, latency, data rate and performance. LTE based M2M communication should be able to handle such diverse set of requirements from different applications. In order to meet the above requirements, 3GPP release two new technologies namely, NB-IoT and eMTC that share the spectrum with the already existing LTE. Section II and Section III of the paper gives a brief introduction to these two technologies in terms of its functionalities and architecture while section IV thoroughly analyzes the difference between them in terms of performance and other parameters. Finally, in the Section IV, we conclude the paper with a brief note on our understanding about their differences followed by the references.

ENHANCED MACHINE TYPE COMMUNICATION (EMTC)

In the Release 13 standardization, 3GPP released a favorable cellular LPWA technology eMTC which is also called LTE Cat-M1. This was done with an intention to minimize the cost, complexity and power consumption over the legacy UE’s proposed in the previous releases for machine type communication (category 0). eMTC achieves this by extending most of the existing LTE physical layer procedures and introducing a set of new features to it. An eMTC UE adopts a narrowband operation for transmitting and receiving signals over the physical channels where the maximum channel bandwidth is limited to 1.08 MHz (or 6 LTE RB’s) out of the available 1.4MHz. The two remaining PRB’S of 180KHz each are used as guard bands to mitigate the interference levels.

The value of 6 RB’S is used to make sure that eMTC can use the same signals and channels used by a regular LTE UE to perform all the cell search and random access procedures. The physical channel and signals are always constrained within the 1.08 MHz irrespective of the cell bandwidth by using a new frequency unit called a narrowband. This also ensures that eMTC coexists with other UE’s and can be controlled by the same eNB with just minor software updates and no other infrastructure changes. In terms of the downlink control channel, eMTC has introduced a few new mechanisms in the Release 13. Instead of the legacy control channel (PDCCH), a new control channel called MTC Physical Downlink Control Channel MPDCCH is introduced. This new control channel spans up to six RBs in the frequency domain and one subframe in the time domain. The mechanism is handled in a way that it removes the necessity to decode PCFICH and have no Physical Hybrid Automatic Retransmission Request (ARC).

Indicator Channel (PHICH) as well. With the deployment of the eMTC network, series of multiple narrowband regions can be configured. That is, it is possible to configure 6 PRBs each within the LTE carrier for narrowband Physical Downlink Shared Channel (PDSCH) and MPDCCH for data scheduling purposes. Cat-M1 devices are can achieve a maximum throughput of up to 1 Mbps in both uplink and downlink operations for massive IoT. eMTC targets 15 dB coverage enhancement with respect to legacy LTE, which results in 155.7 dB maximum coupling loss between transmitter and receiver. This ensures coverage for IoT devices deployed in remote regions or locations. Thus, we see that eMTC enhances the legacy MTC mechanisms to reduce cost and extend coverage while also seamlessly coexisting with the existing LTE. eMTC is standardized to ensure that for Massive IoT deployment and coverage, it supports long battery life of about 10 years with a 5 Watt-Hour battery system for effective utilization. This technology uses power savings management (PSM) and extended discontinuous reception (eDRX) as its power savings mechanisms to achieve long battery life for Cat-M1 devices.

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