Comparison of IoT connectivity technologies
Every single thing – or device – on the Internet of Things will be connected. However, to save power or transmission cost the connected devices may only intermittently exchange data packages, or items may stream data continuously at a suitable speed – either over a fixed line or wirelessly.
In a Peer-2-peer system every device can initiate the call to another item connected. Each device will know the addresses of other equipment. In client/server systems the client is waiting for a call from the server to respond to.
Network Structure (Topology)
Wired systems are often organised in a Star topology connecting a group of items to one central hub likewise internet devices connected to a router. A star of stars constitutes a structure in larger networks.
The number of connections required can be reduced by connecting along a Daisy Chain topology where every device is listening for relevant messages on a common bus routed from one device to the next in a chain.
Wireless systems can apply the Star topology where a single device forms the common access point – such as a base station for mobile phones within range, or a WiFi network with connected devices.
A further advantage of wireless systems is the ability to connect to any item within vicinity in a so-called Mesh topology. The routing for transmitting between two devices may vary dependent on the present signal strength, availability or power priorities. The robustness is much higher than in a strictly hierarchical network if the connection dynamically can be optimised by re-routing through the mesh.
In certain environments a wired connection will be considered more stable, less noise sensitive and the electronics less expensive – besides the cost of rolling out and maintaining the wiring. Several wired connectivity solutions have been optimised towards commercial or industrial purposes. USB and an industrial Profi-bus (Siemens proprietary standard) are typical examples of wired connectivity. Analog (older) sensors may simply be a measurement of a variable resistance or inductance through a wire.
Bandwidth of wired connectivity
Internet equipment without the need for portability is cabled via 8-wire Ethernet and a RJ45 connector one cable from the router to each of the devices. The hub or switch can detect the supported bandwidth of each device.
Cabled connectivity is available through a selection of multiple technologies. High-speed connections are obtained via fiber optic cable with a laser-diode and a light sensor in each end of the fiber. The speed is higher than through coaxial cables, which in turn offers higher bandwidth than twisted paired wires, of which there are four sets in an Ethernet cable. A metallic screen wrapped around the cable may shield the system from electrical noise and allow higher bandwidth.
Parallel connections establishing one physical wire per bit in an e.g. 16 or 32 bit address system are seen between system component in computer systems.
Several good reasons justify abandoning the wire and instead connect devices wirelessly. The rationale may be combinations of remote access or lack of physical infrastructure, need for mobility, convenience when installing without the laborious wiring, or simply avoiding damaging the wire. Wireless connectivity is based on transmission of radio waves, where a high frequency carrier wave is modulated as if a light source changes colour slightly in a recognisable pattern. Certain systems divide a time-slice for each device gaining access, others use variations in frequency (channels) or coding form.
The higher frequency the higher data rate is possible to transmit. However, lower frequencies usually penetrate building elements like concrete walls more easily. The data rate and necessary signal strength for staying connected constantly or intermittently have a strong impact on power consumption.
A comprehensive list of all available wireless technologies is available at https://www.link-labs.com/blog/complete-list-iot-network-protocols.
Long Range Cellular
The 3G, 4G (or Long Term Evolution LTE), 5G networks are divided into cells within each a large number of mobile products share access to the same base station. When the mobile device is moving or the signal is degraded, the device tries connecting to the nearest base station in reach (Figure 18). IoT or M2M (machine2machine) optimised cellular radio units can be commanded into deep sleep for minimal power consumption and then waking up for transmitting a burst of data when required. New Narrow Band standards NB-IoT and LTE-M are specialised sub-specifications offering power saving and lower bandwidth on the existing cellular network for applications requiring less expensive equipment than a standard mobile connection. A M2M network over Cellular comes with subscription and data rate cost.
Low Power Wide Area Network
LP-WAN systems optimise range but minimises bandwidth and power dissipation when transmitting. For instance a Sigfox signal will connect up to hundreds of kilometres in direct line of sight from the base station. The transmission is using an ultra-narrow-band principle only sending 12 bytes per message and up to 140 messages a day to minimise the load of many units connected.
LoRa is another proprietary network currently rolling out worldwide with low power dissipation. The protocol can be implemented on the radio spectrum allocated regionally for open applications.
Short range Wireless Area Network (WLAN)
WiFi – a Wireless Access Point is sharing a connection between devices having logged in using ID & Password. The WiFi router is typically connected via Ethernet to the network backend. The router in the star topology decides the network activity of each device in the network.
Alternatively two devices may engage in a direct network structure where each can initiate the communication to another device. They may then change frequency to avoid interference from others communicating on the same channel.
Short Range wireless connectivity for small devices
Bluetooth was originally defined to support different purposes each guided by a specific profile, for instance audio transmission to speakers or headsets. Lately newer profiles specify IoT specific data transmission of e.g. biometric parameters as blood pressure or glucose content.
Bluetooth release BLE-4 has special attention to optimisation for low energy (LE) demand in small battery operated devices. Bluetooth devices are often bridged via a master device to another network type such as WiFi or Ethernet for overcoming the short-range barrier when connecting individual rooms or larger areas.
Profibus and other legacy wired standards are replacing the physical layers and moving into wireless to reuse existing communication protocols and logic without the need for a wire.
Other purely wireless standards developed for consumer or industrial applications include Zigbee, Z-Wave, EnOcean, Thread, 6LowPAN etc. all short range high bandwidth for connecting devices.
Contact less / near field technologies
Near Field Communications (NFC) was designed for sending small data bursts, for instance credentials for financial transactions or exchanging identification prior to establishing a connection over e.g. BT or WiFi.
Continue reading: System Architecture Layers