In the previous tutorial, various physical and media access control (MAC) protocol for Personal Area Network (PAN), Home Area Network (HAN) and Local Area Network (LAN) were discussed. In this tutorial, physical and MAC protocols based on RFID and mobile standard will be discussed.
There are the following RFID based protocol stacks –
There are the following common mobile standards which are evolving to accommodate IOT applications –
RFID and WSN- Radio Frequency Identification (RFID) is a radio frequency based identification and tracking technology. RFID is a method of uniquely identifying items wirelessly i.e. using radio waves. Based on various regulated ISM bands, the technology uses tags (with in-built microchips) that have unique identification number. The tags could be read using an RFID reader. So, an RFID system comprises a tag, a reader & an antenna. The reader sends an interrogating (base station signal or the reader signal) signal to the tag via the antenna, and the tag responds with its unique information.
RFID can be used in variety of applications such as for attendance tracking, inventory management and access control (RFID tags restrict access to only pre-approved person). There are two types of RFID tags –
• Active tag – It has an on-board battery and periodically transmits its ID signal.
• Battery Assisted Passive (BAP) tag – It has a small battery on board and is activated when in the presence of a RFID reader.
Fig. 1: Table listing frequency and range of RFID
RFID & Wireless Sensor Networks (WSN) are both important technologies in the IOT domain. Wireless sensor networks, sometimes called Wireless Sensor and Actuator Networks, are spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location.
Wireless sensor network is needed to monitor large areas and complex activities like when single sensor is not capable to monitor large areas. In wireless sensor network, tens to thousands of sensor nodes get interconnected with each other using wireless technologies to monitor physical or environmental conditions. These sensor nodes can be connected using various topologies like star, mesh & cluster technologies. These sensor nodes collect data from the physical environment and pass that information to the gateway then gateway does some protocol conversion and forward the information to the communication network. Then the cloud gets the information through the network. The communication between sensor nodes in a WSN can be either direct or multi hop.
The sensor nodes in a WSN network are of constrained nature like low power communication, but gateway nodes have sufficient power & processing resources. Most of the communication in WSN is based on the IEEE 802.15.4 standard or IEEE 802.11 (Wi-Fi) standards with 2.4 GHz radio frequency. For Example Xbee series 1 (WSN) supports IEEE 802.15.4 standard to communicate with the network. The popular network topologies used in WSN are star, mesh & cluster network.
Fig. 2: Image showing WSN Network Topologies
RFID can only be used for object identification. And sensor network used for sensing & monitoring the environmental condition. So, when RFID is integrated with WSN network, both technologies can be utilized in a better way with more productive results. By merging these two technologies, a smart network with sensing capability, multi hop communication and embedded Intelligence can be designed.
The integration of RFID with WSN network is possible in the following ways:
• Integration of RFID tags with sensors: RFID tags connected with the sensors called sensor tags, can sense the data from the surrounding and the RFID reader can read this sensed data from the tag. There is limitation in this integration that the communication capabilities are limited to only single hop.
• Integration of RFID tags with WSN nodes: To overcome the single hop limitation i.e. to extend the communication capabilities, the sensor tag can be equipped with wireless transceiver, small flash memory and computational capabilities. In such a way, the multi hop communication can be extended with other nodes and wireless devices. The sensor nodes in this way will create a mesh network. Long range communication is possible using this method because large number of sensor nodes are connected and communicated with each other.
• Integration of RFID readers with WSN nodes: This type of integration is also done to increase the range of RFID tag readers. Multi hop communication is possible because of this integration. Just like RFID tags, RFID readers will also be equipped with wireless transceiver and microcontroller, the sensor tag data will be reached to the reader. The data from the readers will ultimately reaches to the central gateway or base station that forwards the data to the communication network then to the server/cloud.
DASH7 – DASH7 is a wireless protocol used for active RFID tags. Compared to Zigbee, DASH7 is more scalable, has greater network coverage and greater data rates. It is not only a physical and MAC layer protocol but also includes IPv6 addressing for network layer. The protocol uses unique identifiers along with 16-bit network identifiers for addressing in the IOT network. The data is communicated using 255-byte long frames that include addresses, sensor data and multiple fields.
This protocol stack has been designed for retail and industrial IOT applications where the IOT network would be spanning over a long distance. Like, one of the use case of DASH7 includes tracking of inventory items in a supply chain.
Near Field Communication (NFC) – Near Field communication (NFC) is a very short range data communication typically at a distance of 10 cm or less with the help of contactless RF (radio frequency) communication technology. So, NFC is also based on RFID technology. The technology allows a simple, rapid, intuitive, and easily securable communication between two electronics devices. However, this technology is based on RFID but it uses two-way communication unlike RFID. It uses variations in the magnetic field to provide communication between two NFC enabled devices. NFC operates over same frequency as RFID operates i.e. 13.56 MHz.
To implement NFC technology, there are two modes of operations – Active mode and Passive mode.
• Active mode: In Active mode, both the devices generate magnetic field. Today’s many mobile devices (android as well as IOS) are available in market which uses Active NFC. One major use of NFC in mobile devices is storing and transferring the credit card information. For example, with android apps like Google wallet, one can simply tap the mobile device to pay at stores.
• Passive mode: In this mode, only one device generates the field and the other uses load modulation to transfer the data. For example, student ID cards can use NFC technology. If a student tap the card on the bus, the card is passively transferring information through NFC to the bus system’s active card reader, which allows the bus system to realize the identity of a student from a particular school and then allow to enter in bus.
The passive mode is useful in battery powered devices because it uses less power and the IOT devices also require less power to operate.
Fig. 3: Table listing frequency and range of Near Field Communication (NFC)
The following existing mobile standards are also evolving and adapting to find applications in an IOT scenario –
GPRS (General Packet Radio Service) – As the demand for wireless data services is increasing on the market, operators have to develop their own data and services in the field, and strive to stay ahead in the fierce competition. Traditional GSM networks can only support 9.6 kbps data transmission rate, which cannot meet the user demand for high-speed wireless data services. GPRS (General Packet Radio Service) is architected for traditional GSM network, a standardized packet switched data service which can provide up to 115 kbps rate of the packet data services, including so that pictures, voice and video, multimedia services in a wireless network transmission becomes a reality.
GPRS is considered to be the second generation mobile communication. Unlike GSM (which uses circuit switching), GPRS is a packet switching technology with high speed, low cost data rates and “always on connectivity”. With the rapid development of wireless data transmission technology, GPRS wireless data services have become the best destination.
Fig. 4: Table showing GPRS data rates
GSM (2G/3G/4G/5G) – GSM (Global System for Mobile communications) is an open, digital cellular technology used for transmitting mobile voice and data services. Terrestrial GSM networks cover more than 90% of the world’s population. GSM satellite roaming has also extended service access to areas where terrestrial coverage is not available. The existing GSM network spanning across the globe can be utilized for IOT applications as it will be highly cost effective. There is readily available hardware infrastructure which can be adapted to suit the IOT applications just by upgrading software solutions.
The next generation GSM (5G) will be equipped with features like Software-defined Networking (SDN) and Network Function Virtualization (NFV) which are under development to support mobile technology for IOT solutions.
Fig. 5: Table listing frequency and range of GSM (2G/3G/4G/5G)
CDMA – Code Division Multiple Access (CDMA) is another popular mobile networking standard. The existing CDMA network are undergoing transformation to evolve as LTE Cat M1 standard to support variety of IOT applications.
In the next tutorial, Network or Adaption Layer protocols will be discussed.