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
22.214.171.124 Short-Range Radio Solutions
In this section we provide an overview of the most promising unlicensed short-range radio communication technologies for the IoT, which are IEEE 802.15.4, Bluetooth Low Energy (BLE) and Wi-Fi HaLow. The choice to focus on these is made based on the following properties of those technologies: they address the communication requirements of IoT, they target an IP-based IoT solution according to Figure 9.5 and the right-hand side in Figure. 9.4, and they are based on open standards and are expected to reach a substantial economy of scale. We also address the capillary network architecture where any of these solutions may be used to provide the short-range connectivity within a larger network context.
126.96.36.199.1 IEEE 802.15.4
One of the early standards for 6LoWPAN is IEEE 802.15.4 [10e12]. It was standardized in 2003 at a time of intense research on wireless sensor networking technologies [13,14], and it is applicable for a wide range of IoT use cases, ranging from office automation, connected homes to industrial use cases. Several application-specific protocol stacks have been developed, which build on parts of the IEEE 802.15.4 standard (mostly the physical layer and to some extend the medium access control (MAC)) , including ZigBee, WirelessHART, ISA-100, and Thread.
IEEE 802.15.4 has been specified for the three frequency bands of 868 MHz (for Europe), 915 MHz (for United States), and 2.4 GHz (global) [16e18]. In the 2.4 GHz band, IEEE 802.15.4 has 16 channels available of 2 MHz bandwidth. It uses offset quadrature phase shift keying with DSSS and a spreading factor of 8. A gross data rate of 250 kbps is achievable, see References [16,18]. In 868 MHz one channel of 600 kHz is available, which uses differential binary phase shift keying modulation and DSSS with a spreading factor of 15. The achievable data rate at 868 MHz is 20 kbps [16,18]. In the 915 MHz 10 channels are available with a gross data rate of 40 kbps, see Reference .
IEEE 802.15.4 uses carrier-sense multiple access with collision avoidance (CSMA-CA) for access to the radio channel; this can be complemented with optional Automatic Repeat Request (ARQ) retransmissions. Typical coverage ranges are in the order of 10e20 m . Two different topologies are supported: star topology and mesh (or peer-to-peer) topology. Two types of devices are defined: full-function devices that provide all MAC functionality and can act as network coordinator of the local network, and reduced function devices that can only communicate with a full-function device and are intended for very simple types of devices. The network can operate in beaconed mode, which allows a set of devices to synchronize to a superframe structure that is defined by the beacon transmitted by a local coordinating device. The channel access in this case is slotted CSMA-CA. In non- beacon mode, unslotted CSMA-CA is applied. In case of direct data transmission, a device transmits data directly to another device. In indirect data transmission, data is transferred to a device, e.g., from a network coordinator. When beacon transmission is active, the network coordinator can indicate the availability of data in the beacon; the device can then request the pending data from the network coordinator. In nonbeaconed transmission, the network coordinator buffers data and it is up to the device to contact the network coordinator for pending data.
In Reference  the performance of IEEE 802.15.4 has been evaluated in an experiment with an ideal link and devices placed at 1 m distance. It has been found that for a configuration at 2.4 GHz with a theoretical gross data rate of 250 kbps, a net data rate of 153 kbps was measured for direct transmission (from the device), and a net data rate of 66 kbps for indirect transmission (towards the device). Furthermore, it has been shown that the effective data rate and delivery ratio decrease with an increasing number of devices.
A major step for broader relevance of IEEE 802.15.4 for the IoT has been to address end-to-end IP-based communication. To this end the IETF working group 6LoWPAN has been chartered in 2005 and it has developed IETF standards for header compression and data fragmentation. The maximum physical layer payload size of 802.15.4 is limited to 127 bytes, which is further reduced by various protocol headers and optional security overhead and can leave as little as 81 bytes available for application data within an IEEE 802.15.4 frame. IETF has developed standards that provide header compression and IP packet fragmentation that enable the transmission of IPv6 over 802.15.4 networks [17,19e22]. In addition, the RPL routing protocol has been developed to enable IP mesh routing over IEEE 802.15.4 [17,22,23]. In 2014 the Thread group was formed with the objective to harmonize the usage of IEEE 802.15.4 together with 6LoWPAN for home automation.
IEEE 802.15.4 has been extended in IEEE 802.15.4g to address smart utility networks with an objective to improve coverage and support higher data rates [24e26]. To this end multiple new physical layers have been defined which can be used from a common MAC layer. Physical layer implementations are multirate frequency shift keying (MR-FSK), multirate orthogonal frequency-division multiplexing (MR-OFDM), and multirate offset quadrature phase shift keying (MR-OQPSK). MR-FSK has a benefit of good transmit power efficiency because of constant signal envelop, MR-OFDM enables higher data rates for frequency selective fading channels, and MR-OQPSK has the benefit of the original IEEE 802.15.4 modulation with cost-effective and easy design. A physical layer agnostic management protocol is based on a common signaling mode to allow a network configuration with interference coordination among multiple IEEE 802.15.4 transmitters .
Bluetooth has been developed as a technology for wireless short-range connectivity [27,28] and has established itself as a leading technology for personal area networking. With the release of the Bluetooth core specification 4.0  in 2010 a novel transmission mode called Bluetooth Low Energy (BLE) was introduced, which considerably reduces power consumption compared with Bluetooth classic. BLE has been a significant first step to expand the Bluetooth ecosystem towards IoT.
BLE uses the 2.4 GHz ISM band. The spectrum is divided into 40 channels, with 2 MHz channel spacing, of which 37 are data channels and 3 are used as advertising channels. Frequency hopping is applied to mitigate the impact of interference. The modulation is based on Gaussian Frequency Shift Keying and a data rate of up to 1 Mbps can be achieved over-the-air. A master-slave architecture has been adopted to assign asymmetric roles to devices; peripheral devices perform only a minimum amount of functions to enable ultra-low power consumption, while central devices perform coordination functions. BLE has short connection setup and data transfer times so that applications can transfer authenticated data within a few milliseconds. BLE allows connection-oriented or connectionless communication. It supports fragmentation and reassembly of large data packets into small radio frames, which are then transmitted over the radio interface. This enables BLE to support data services with large packets (e.g., IP packets).
An analysis of BLE for building automation use cases has been performed in References [16,30e32]. With a single-hop deployment, the range for BLE in an indoor deployment setup is in the order of 10 m, and around five BLE gateways are needed to provide coverage in a 1000 m2 office floor .
In 2014 the Bluetooth Special Interest Group (BT SIG), the standardization forum for Bluetooth, published the Internet Protocol Support Profile , which enables IP connectivity for BLE devices. Further, IETF has standardized a standard for end-to-end IPv6 connectivity over BLE , including header compression. This enables that end-to-end IP-based IoT services can be provided via BLE systems .
A further evolution of BLE has occurred recently with the launch of Bluetooth 5, the Bluetooth core specification 5.0 [36,37]. It comprises quadrupling of the communication range at low data rates (i.e., 125 kbps) and the doubling of the peak data rates (to 2 Mbps). The BT SIG has also announced that the development of an extension of BLE for mesh networking is ongoing, which would further increase the range of BLE, see e.g., Reference .
The next installment in this series continues the discussion of short-range radio solutions with a look at Wi-Fi and capillary networks.
Reprinted with permission from Elsevier/Academic Press, Copyright © 2017