Low Power WAN Technologies: Next Step for the IoT ecosystem
The Internet of Things (IoT) ecosystem thus far has been deeply dependent on Wi-Fi (based on the IEEE 802.11 Wireless LAN standards) and in case of wearables, Bluetooth. When we connect any wearable such as a smartwatch with a mobile device, it is generally connected via Bluetooth. The mobile device acts as a gateway for the internet connectivity and smartwatch as a Thing connected to the internet. With the growing use of such wirelessly connected devices, the development of the Internet of Things (IoT) has been rapidly increasing and consequently the calls for standardization of the component technologies have also been increasing.
IoT devices are an integral part of smart cities, smart buildings and smart homes which need a faster and secure connection. Many communication technologies such as Wi-Fi, Bluetooth, ZigBee and 2G/3G/4G cellular are prevalent and available today but depending on the application, factors such as range, data requirement, security and power demands and battery life will dictate the choice of one or some form of a combination of these communication technologies and standards. Most of these technologies work on either high power consumption or short range. IoT devices for smart home automation such as a smart doorbell, surveillance cameras, and smart thermostats, for example, work on Wi-Fi so as to increase the range as compared to the Bluetooth and/or Bluetooth Low Energy (LE). Bluetooth LE (and ZigBee, for that matter) offer very low power consumption compared to Wi-Fi – but this comes at a cost of significantly reduced range.
In wireless communication, antenna size is inversely proportional to the used frequency, the higher the frequency is, the smaller the antenna and vice versa. If the frequency decreases, the size of the antenna increases. Use of higher frequency bands will allow smaller modules, which is important for IoT applications where size is an important factor, such as wearables. Conversely, lower frequencies provide better coverage and are more suitable for extended coverage applications where antenna and module size is not an issue.
IoT devices have major application in industry as well such as consumer processes, for example to monitor hazardous fluid tanks and vending machines used for privacy/data verification for cashless payments. Some agricultural applications such as monitoring of soil, temperature and weather conditions also use IoT devices which need to be connected to the internet. These IoT devices need long-range communication and low power consumption. The problem is that the cellular services consume much higher power. So, a solution for long range, low power consumption, low cost, low data requirements and security for IoT devices is Low Power Wide Area Network (LPWAN).
LPWAN technologies and standards are designed to create either a private wireless sensor network or to create a wireless cellular network provided by a cellular network service provider such as T-Mobile and AT&T. The LPWAN services provided by mobile operators are deployed on existing standards so that there is no need for investing in gateway technology. There are several well-known Standard Developing Organizations (SDOs) such as European Telecommunications Standard Institute (ETSI), Third Generation Partnership Project (3GPP), Institute of Electrical and Electronics Engineers (IEEE), and Internet Engineering Task Force (IETF) are working towards the open standards for LPWA technologies. Further, multiple industry alliances are built around individual LPWA technologies to promote new standards. LoRa Alliance, Weightless-SIG and DASH7 Alliance are a few examples of such Special Interest Groups (SIGs). 3GPP, one of the most influential SDOs today, also offers multiple licensed solutions such as Long Term Evolution (LTE) enhancements for Machine Type Communication (eMTC), Extended Coverage GSM (EC-GSM) and Narrow Band IoT (NB-IoT).
Long Term Evolution (LTE) enhancements for Machine Type Communication (eMTC) also known as LTE-M
LTE-M is a Low Power Wide Area (LPWA) technology standard published by 3GPP in the release 13 specifications. LTE-M supports IoT through lower device complexity and provides extended coverage while allowing the reuse of the LTE installed infrastructure. This technology is evolved by 3GPP releases to support an extended battery life for a wide range of machine type communication through the use of Power Saving Mode (PSM) and extended idle-mode Discontinuous Reception (eDRX), and connected mode eDRX, cellular IoT (CIoT) control plane and Evolved Packet System (EPS) optimization for small data transmission.
PSM mode is similar to power-off, but the User Equipment (UE) (IoT devices) remains registered with the network. The UE requests the PSM simply by including a timer (T3324) with the desired value in attach request, Tracking Area Update (TAU) or Routing Area Update (RAU) request. The T3324 will be the time the UE listens to the paging channel after having transitioned from connected to idle mode. When the timer expires, the UE enters PSM. The UE can also include a second timer, which is an extended T3412 in order to remain in PSM for longer than the T3412 broadcast by the network. The network accepts PSM by providing the actual value of the T3324 (and T3412) to be used in the attach/TAU/RAU accept procedure. The maximum duration, including T3412, is about 413 days.
The extended idle-mode Discontinuous Reception (eDRX) is another mechanism that reduces power consumption by extending the sleeping cycle in idle mode. It allows the device to turn part of its circuitry off during the extended DRX period to save the power. The main difference between PSM and eDRX is that in PSM mode UE should exit PSM and issue periodic TAU/RAU with the same frequency as the extended idle mode DRX cycle, thus causing additional signaling for the network and power consumption in the UE. In the eDRX mode, UE can request the use of extended idle-mode DRX cycle (eDRX) during an attach request, tracking area updating (TAU) or routing area updating (RAU) procedure by including the eDRX parameters IE.
Further, in order to optimize the transmission of a small amount of data, 3GPP rel-13 introduces optimized EPS procedures for small data. Depending on the application needs and traffic data cellular service provider will choose the optimized technique best suited to reduce the power consumption. The control plane CIoT EPS optimization aims to concentrate the data transfer and control plane procedures in the Mobile Management Entity (MME). The MME connects the UE (using control plane CIoT optimizations with a Packet Data Network (PDN) connection) either to the Packet GateWay (PGW) via the Serving GateWay (SGW) or directly to a new network element called SCEF (service capabilities exposure function) that connects to the MME via the radio interface. The user plane CIoT EPS optimization avoids the need to renegotiate the UE-eNB security association at idle active transition by introducing the concept of suspending and resuming a Radio Resource Control (RRC) connection. The user plane CIoT EPS optimization provides the UE with the usual user plane connectivity and is suitable both for applications involving lower data volumes transfer and for applications where the possible range of data volume transmission is unpredictable and can vary quite significantly in frequency and volume. The control plane CIoT EPS optimization, on the other hand, is more suitable for applications involving lower data volumes transfer as it uses the system control plane resources.
The IoT devices operating according to the LTE-M standard connects to the cheaper LTE network as they are half-duplex and narrower bandwidth of 1.4 MHz licensed spectrum between 450 MHz to 3.5 GHz. The maximum data rate of LTE-M devices is only 100 kb/sec which makes it much cheaper for IoT devices. LTE-M is suitable for both static sensor applications and also for the applications which require voice, mobility and higher throughput. Some of the applications include:
IoT devices which involve tracking sensors such as tracking children or animals, remote health monitoring and wearables. To protect threatened species, their behavior and which habitat is best suited for them needs to be fully understand. So, LTE-M network provides cost effective technology for wildlife tracker IoT devices.
IoT devices which require high mobility and low data rate such as event-triggered location tracking IoT devices in which only location needs to be transmitted.
Wearables such as smart watches often require voice support, mobility and high throughput to communicate with the internet.
The security requirements for these applications are high as personal data is involved. So, LTE-M powered IoT devices enjoy all the security features provided by LTE.
Extended Coverage GSM (EC-GSM)
EC-GSM is a 3GPP rel-13 feature based on enhanced GPRS (eGPRS) and designed as a high capacity, long range, low energy and low complexity cellular system for IoT communications. GSM can be deployed on either side of WCDMA (Wideband Code Division Multiple Access) or LTE carriers. EC-GSM IoT does not require any additional frequency planning since the system is supported on top of existing GSM deployments. The most commonly used spectrum bands for GSM are 800-900 MHz and 1800-1900 MHz. It uses variable data rate with a peak rate of 240 kbps using modulation techniques such Gaussian Minimum Shift Keying (GMSK) and 8-array Phase Shift Keying (8-PSK). GMSK is a digital frequency modulation scheme in which frequency of the carrier is modulated by passing the data stream first through the Gaussian filter which reduces the sideband power to minimize the inter-channel interference. In Phase Shift Keying (PSK) modulation phase of the carrier is changed according to the digital data. 8-PSK uses eight different phase angles to represent a combination of three bits. The optimization techniques PSM and eDRX are the software features for the core network. EC-GSM also supports security framework comprising Ciphering, Mutual authentication and integrity protection for user data and control plane.
The EC-GSM is a cheaper option as it uses the lower frequency band of GSM technology. It is useful for agricultural-based IoT devices as they don’t require high data rate and are generally no handover is required in such cases. EC-GSM is a 2G based technology specifically designed for IoT devices to be deployed in rural areas with limited 3G or 4G connectivity. This technology will be more helpful in improving agricultural problems in rural areas. The environmental sensors (IoT devices) collect weather data and agronomic data to be sent over EC-GSM network and helps to tackle problems like food security such as climate change and water availability. The only drawback of this technology is that it is based on out dated 2G network.
Narrow Band IoT (NB-IoT)
Narrowband IoT (NB-IoT) is a 3GPP Release 13 feature that uses various principles and building blocks of the existing LTE physical layer and higher protocol layers. NB-IoT has been designed to offer extended coverage compared to the traditional GSM networks. New physical layer signals and channels, such as synchronization signals and physical random access channel, are designed to meet the demanding requirement of extended coverage and ultra-low device complexity. It is not compatible with 3G but can co-exist with GSM, GPRS, and LTE. In existing LTE network connectivity is supported by Packet Data Network (PDN) attach request but NB-IoT comes with a new capability of connectivity without PDN. UEs supporting CIoT (Cellular Internet of Things) remains attached without PDN connection, which may be useful for cases where huge numbers of devices would keep a connection inactive for a very long period of time and rarely transmit data over it. When a UE is attached without PDN connection, only SMS service is available for any data transmissions and applications are constrained by this sole capability. The SMS could be used also to trigger PDN connection establishment.
The 3GPP Enhanced Coverage feature is an integral characteristic of NB-IoT, as it increases the depth of radio coverage to enable IoT devices to operate in remote locations. This feature increases the power level of signaling channels together with the ability to repeat transmissions. The NB-IoT supports eDRX and PSM as is done by LTE-M. NB-IoT reuses the LTE design extensively, including the numerologies, downlink orthogonal frequency-division-multiple-access (OFDMA), uplink Single-Carrier Frequency Division Multiple-Access (SC-FDMA), channel coding, rate matching, interleaving, etc. This significantly reduces the time required to develop full specifications. NB-IoT can be deployed inside a GSM carrier of 200 KHz, inside a single LTE of 180 KHz or inside an LTE guard band. NB-IoT is ideal for simple static sensor applications which require very low throughput, low data rate and no voice capability. It provides partial mobility and data rate of 20-65 Kb/s. Some of the applications include:
Smart Street Lights which are static and needs to send the data at low rate. Smart Street Lights with embedded sound sensor which can detect gunshots and automatically report it to 911 department without depending on citizen involvement
Parking sensors to monitor and report the availability of parking spaces which can reduce the time spent by cars which emits the greenhouse gases.
Waste Management to monitor the status of waste containers to optimize the collection of waste works that can work on NB-IoT cellular network architecture.
Smart Water Management includes smart water meters which communicates with water service providers giving details of water consumption on daily basis. It helps in leak detection, supply and demand management and fair services to the customers.
Smart Energy Meters are also ideal for NB-IoT technology. Smart Energy Meters measures the energy consumption on daily basis and communicates with electricity department as well as the customer over the internet.
These three standards are the cornerstones of "Mobile IoT " and are in the process of deployment in existing mobile network architecture. NB-IoT and LTE-M in particular are widely launched and deployed by the number of mobile operators across North America (T-Mobile and AT&T respectively), East Asia and in many European countries - though their potential for IoT specifically is as yet underutilized and in a classic cause-and-effect scenario, under-researched. But as emerging technologies go, LPWANs remain closer to fruition than most.