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WIRELESS COMMUNICATION SYSTEM
Figure 1: Block diagram of Wireless communication System
Wireless communication refers to the transmission and reception of information between devices over a distance, without requiring any wires, cables or other electrical conductor. Wireless communication system consists of a transmitter, channel and a receiver. The transmitter is the device that sends out signal or data. The signal (information) is transmitted through vacuum or air in the form of electromagnetic waves like radio frequencies, infrared, satellite, etc. Then receiver picks up the signal and communication is accomplished and we get the desired output signal. Now-a-days, the wireless communication has become an integral part of our life which allows user to communicate even from remote areas. Let us discuss about some popular wireless communications.
Types of wireless communication
Different types of wireless communication include Satellite communication, Radio Frequency(RF) communication, Infrared (IR), microwave, Wi-Fi, Bluetooth, etc.
* Satellite communication
Satellite communication is widely spread over the world which allows user to stay connected almost anywhere on the earth. When a signal is sent, the satellite amplifies the signal and sent it back to the receiver antenna located on the surface of earth. Space segment and ground segment are the two main components of satellite communication. The ground segment contains fixed or mobile transmission, reception and the space segment is satellite itself.
* Radio frequency communication
Radio frequency communication refers to the propagation of radio waves from transmitter to receiver. Radio waves refer to electromagnetic waves with a frequency range from 3 KHz to 300GHz. RF transmission occurs at the speed of light.
* Infrared communication
In infrared communication, the communication between devices takes place through IR (electromagnetic energy) radiation. IR radiation lies between microwaves and visible light. For a successful IR communication, a transmitter and a receiver are required. The transmitter transmits the IR signal and it is captured by the receiver.
* Microwave communication
Here the data or information can be transferred using two methods. First one is Satellite method. In satellite method data is transmitted through satellite. The transmitter and receiver on earth send and receive signals with a frequency ranging from 11 GHz to 14 GHz and with a sped from 1 Mbps to 10 Mbps. Second method is terrestrial method. In terrestrial method two microwave towers with a clear line of sight and a frequency range of 4GHz to 6GHz is used.
* Wi-Fi communication
Wi-Fi stands for Wireless Fidelity. In Wi-Fi communication, radio signals are transmitted from antennas and these signals are picked by the receiver such as computer, phones etc. The range of Wi-Fi depends upon the environment, indoor or outdoor ranges. Frequency range of Wi-Fi varies from 2.4GHz to 5GHz.
* Bluetooth communication
Bluetooth communication uses radio waves for exchanging data over a short distance. It operates at a frequency between 2.4GHZ to 2.485 GHz. The range of Bluetooth devices is up to 10 meters.
Have you ever thought about, how to establish a simple communication between two devices which are located miles apart without using internet. This can be accomplished by “LoRa” communication technique. LoRa transceivers can communicate over a long range. In this tutorial let us discuss about the various aspects of LoRa technology. Also we will get a basic idea about its features, architecture, protocol stack, transceiver and applications etc.
What is LoRa???
LoRa stands for Long Range wireless technology. LoRa technology is used as WAN (Wide Area Network) technology (LoRaWAN). Wide Area Network is designed for a large topographical area such as a country, continent, or even whole of the world. WAN transmit data over wireless links such as satellites or high speed phone lines. World’s most popular WAN is internet.
LoRa refers to a low power-long range communication. Low power-long range communication is acheived by low frequency operation. Lower the frequency, less power is required to transmit/receive data within a specified range. In LoRa Spread Spectrum modulation used. This modulation type uses wide band FM pulses. Frequency increase or decrease over certain time period is used to encode the data to be transmitted. LoRa will enable public or private networks to connect multiple applications running in the same network.
LoRa Features
* Range : LoRaWAN can achieve range up to 15Km.
* Frequency bands : Uses 868 MHz (EU) and 915 MHz (America) frequencies in ISM band.
(ISM band : Industrial, Scientific and Medical radio bands are portions of radio spectrum reserved internationally for the use of radio frequency (RF) energy for industrial, scientific and medical purposes)
* Standard : Uses IEEE standard 802.15.4g (Technical standard which defines the operation of low rate wireless area network)
* Capacity: LoRa module simultaneously transmits and receives data on a same channel without any interference.
* Battery life : Better and Longer battery life up to 10 years.
LoRa network architecture
Figure 1: LoRa Network Architecture
LoRa network architecture consists of LoRa gateways, network servers and end-devices. A gateway is a device used to connect two networks, especially a connection to internet. End-device is a source or destination device in a network system. The devices in the network are connected in a star of stars topology. Communication between gateways and end devices are carried at different data rates and different frequency channel frequency channels. LoRa technology supports data rate from 0.3 Kbps to 50 Kbps.
LoRa frame structure
LoRa frame structure consists of two parts: uplink part and downlink part. Uplink is the transmission from end-devices and gateways. Downlink is the transmission from gateways to end-devices. Different classes supported in LoRa network are Class A, Class B and Class C.
* CLASS A
Class A frame has one uplink slot followed by two downlinks.
* CLASS B
In Class B, it will get extra DL slot at specified interval.
* CLASS C
Class C is ideal for applications requiring more downlink transmissions but it utilize more power compared to other classes.
LoRa Protocol stack
Figure 2: LoRa Protocol Stack
Protocol Stack of LoRa technology consists of Application Layer, MAC (Media Acess Control) layer, PHY (physical) Layer and RF (Radio Frequency) Layer.
* Data from application layer required to establish connection between gateways and end-devices and are carried as MAC payload. (Payload is the part of transmitted information that is the actual intended data)
* Using MAC payload, MAC layer constructs the MAC frame.
* Physical layer take care of power, frequency, modulation, signalling between end-devices and gateways.
* RF layer modulates PHY frame on required RF carrier and transmits on to the air.
LoRa Transceiver Chip
Transceiver chip based on LoRa technology is used for low power and long range wireless communication.
Above figure shows typical components in a LoRa Transceiver chip. Transceiver chip consists of UART, LoRa protocol stack, LoRa radio layer, processor, interfaces (I2C, SPI) and GPIO’s. For control applications the microcontroller unit is interfaced using UART. GPIOs are used to interface user defined hardware components like switches, LEDs etc. Radio layer is interfaced with antenna of different frequency bands such as 868 MHz and 15 MHz. The transceiver chip requires crystal for running the processor and real time clock.
Applications of LoRa Technology
* Home security
* Radiation leak detection
* Smart lighting
* Precision farming
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