The Internet of Things is proliferating into applications across broad domains, connecting personal and home devices, industrial machines, and cloud software platforms. Wireless technology is an integral part of connecting these devices, and a variety of standards are available to implement them. The choice of protocol and frequency band largely depends on the power and communication range constraints of the deployment. In this article, we will take a look at a few of the commonly used wireless protocols and frequencies.
Typical RF Communication System
An RF communication system includes a source of data, a hardware subsystem made of the transmitter, the medium of transmission (air), a receiver, and a destination to collect the data. Typically, a transmitter and receiver, called a transceiver, are mounted into a single package, as most systems need bi-directional data flow. The hardware subsystem is made of the RF transceiver chipset, host processor, and antenna.
The data is modulated by the transmitter using one of the modulation techniques like Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), On-Off Keying (OOK), Direct-Sequence Spread Spectrum (DSSS), or Frequency-hopping Spread Spectrum (FHSS). The reverse process of demodulation is carried out by the receiver using the same modulation technique of the transmitter to extract the digital data. The processing unit is called the baseband processor, used to manage all the radio functions related to the protocol.
The host processor is a microcontroller or microprocessor device that communicates with the RF module. Some SoC RF modules are available with a built-in controller.
The antenna consists of a radiating element that converts the modulated electrical signals from the transmitter to electromagnetic waves and converts the incoming electromagnetic waves to electrical signals. Antenna size is directly proportional to the wavelength (λ) of the radio signal. There are various types of antennae, and the selection is based on the size, protocol, and form factor. Combo antennas can handle multiple RF protocols, hence are suitable for multiprotocol SOC chipsets.
To know more about antennas, please refer Tech Spotlight: PCB Design for Surface-Mounted Chip Antennas and Tech Spotlight: How to Place an Antenna for Optimal RF Performance
Classification of RF Protocols
The designer has to choose from the many protocols based on the specifications of communication range, bandwidth, transmitting power, receiver sensitivity, power consumption, and battery life.
The radio frequency range suitable for IoT varies and ranges from 400 kHz to 10 GHz. They may be classified as licensed (cellular), forbidden (defense) and unlicensed (Wi-Fi/BLE). The unlicensed bands are the most popular for IoT applications. Device manufacturers can use frequencies in this spectrum freely by following product specifications and regulations set by the authorities. The ISM band (433/915/2400 MHz), is globally reserved for Industrial, Scientific and Medical applications.
Wireless networks are also classified by the network topology used to connect the devices. The network topology is an arrangement of a network that defines the way different nodes are interconnected and connected with each other. There are many network topologies available, but the widely adopted topologies in IoT are:
- Star Topology: Each node connects to a central node, which can also act as the gateway to the Internet.
- Mesh Topology: Each node connects to any number of nodes, and any node can be the central node for the nodes around it.
From an IoT application point of view, we can classify the protocols by the requirements for Communication Range. As shown in Figure 1, we have classified RF protocols based on their communication range below:
- Long Range
- Short / Medium Range
- Ultra-Short Range
Figure 1. Classification of RF Protocols
The long-range communication protocol provides high availability of a network in a large coverage area typically beyond 1km. Long-range RF communication is associated with the higher power required to transmit and receive the signals. The primary challenge is to transfer the signals over long distances with minimum power consumption enabling battery-operated IoT installations. The long-range protocols include Cellular, LoRa WAN, and Sigfox.
IoT applications widely use the existing cellular networks like 3G and 4G LTE for data communication. 3G uses 2100 MHz and offers 384 Kbps-10Mbps data rate and the 4G LTE delivers a high data rate of 3Mbps-10 Mbps at 2700 MHz. They are suited for applications like video surveillance. However, they are not suited for a majority of the IoT applications due to their high power consumption and cost of implementation. Cellular modems use ceramic Surface-Mount Technology (SMT) LTE antennas.
In the 3rd Generation Partnership Project (3GPP), new protocols Cat-M1 and NB-IOT were introduced to adapt the existing 4G LTE networks for IoT and M2M communication. The LTE Cat-M1 (LPWA) works on 1.4 MHz and provides data rates up to 1Mbps. The NB-IOT (Cat-M2) works on 180 KHz frequency and provides data rates up to 250Kbps.
Sigfox is a private network provider similar to telephony or cellular service providers, aimed at serving customers in the IoT space. It uses sub-GHz ISM bands, (868 to 869 MHz or 902 to 928 MHz) and supports long range up to 50km using the star topology. The flexible Dipole antenna is suitable for Sigfox devices. Although Sigfox communication is bi-directional, the payload from the base station to the node is very low. It is used for remote sensing, where low amounts of data have to be transmitted sporadically with high battery life requirements.
LoRaWAN is a Low Power Wireless WAN communication protocol in the sub-GHz frequency range (433/ 868/ 915 MHz). It has a typical data rate of 0.3-50 Kbps and can cover up to 15km range. The higher distance is achieved by dynamically lowering data rates. The dipole antenna is suitable for LoRaWAN. It is designed to provide Low Power, low-cost, secure and full-duplex communication for IOT, M2M, Smart City, and Industrial Applications.
Wireless Local Area Network (WLAN) includes Wi-Fi and Wireless Personal Area Network (WPAN) includes ZigBee, Z-Wave, and Bluetooth for communication range between 10 to 1000 Meters. For a small size network and low bandwidth requirement, WPAN protocols are used. An antenna with maximum radiation-efficiency, high-gain, and compact size are preferred for short and medium-range protocols.
Wi-Fi as defined in IEEE 802.11 standard acts as a wireless replacement to Ethernet. The 802.11-b/g/n operates on 2.4GHZ and provides 150-200 Mbps data rate in the home or office environment typically at a range of 50 meters. The latest 802.11-ac standard works on 5GHz and provides 500Mbps-1Gbps data rate. Wi-Fi uses the star network topology, and the access point can be used as a gateway to the Internet. Each access point can connect to a maximum of 250 devices, and most commercially available solutions support up to 50 devices. For Wi-Fi, dual-band 2.4GHz and 5GHz PCB, SMT, or flexible cable antennas are used.
ZigBee uses IEEE 802.15.4 standard physical and link layer, operating at ISM 2.4 GHz band and provides a range of up to 300 feet. Ceramic 2.4GHz antennas are preferred for ZigBee due to the small form factor. It supports mesh topology, hence the network can be extended over a long distance using multi-hop operations. The protocol is highly interoperable and includes standard libraries of data models, security, and network management procedures. ZigBee has features such as low power consumption, node discovery, duplicated packet detection, route discovery, sleep mode and reliability. It is widely used in smart home and building automation applications.
Z-Wave is a low power wireless technology designed for IoT Home Automation applications. It offers low-latency and reliable communication. It supports Mesh topology with a maximum of 232 nodes in a single network. It works on 868 MHz for the Europe region, and 915 MHz for North America and Australia, providing a 100-Kbps data rate. The ultra-thin ceramic antenna can be used for Z-wave.
Bluetooth Low Energy (BLE) is meant for low-power applications, using 2.4 GHz band, and provides up to a 25Mbps data rate with a maximum range of 20m. A Ceramic SMT 2.4GHz antenna offers easy integration and outstanding performance for Bluetooth.
The latest iteration of Bluetooth, BLE 5.0, supports low data rate applications and an extended range up to 150 meters. Features like beaconing and location services have helped to deploy it in a wide range of fitness and automotive applications. It can support star topology. The latest versions support mesh topology, which helps to extend the network using many-to-many device networking suitable for home automation applications.
Near Field Communication (NFC) is an Ultra-Short Range Radio communication protocol.
NFC uses the ISO/IEC 18000-3 standard and the 13.56 MHz ISM frequency band. It provides a data rate of 100-420 Kbps and a range up to 20cm. [NFC devices can work as an NFC tag or as an NFC reader.] Some NFC devices can read (ISO 15693 compliant) passive high-frequency RFID tags, which also works on 13.56 MHz. It uses loop inductor antenna made up of a conductor coil, that when energized generates a magnetic field to establish the RF communication channel.
NFC provides full-duplex communication over the detection range from metallic and non-metallic substrates. It is used for contactless payment, fast synchronizing, and digital content access applications.
Global Positioning System:
GPS is a simplex communication protocol and works on 1575.42 MHz (L1) and 1227.60 MHz (L2) frequency. Global navigation satellite system provides time and geolocation details to a GPS receiver. To find accurate location GPS receiver needs at least three satellites to calculate longitude and latitude information also known as triangulation. It offers critical navigation system to civil, military, marine, airlines and commercial users around the world. GPS location is used in mobile applications like Google Maps, and Find Me. GPS patch antennas are widely used in GPS devices.