Due to the advantages like long range, lower operating and deployment costs and reduced power consumption, sub-GHz wireless systems are popularly used in low data rate applications like home automation systems, security systems and smart metering etc. These networks are capable to provide a cost-effective solution for low data rate applications from simple point – to –point connections to larger mesh networks. Let us look at some of these sub-GHz wireless communication systems.
Sub-GHz Communications with Transmitters
A number of standard solutions of PHY, MAC, and stack layers are available for sub-GHz applications. Some of these communications are RF, IR, GPS, EnOcean, IO-Home Control Communication and so on.
Radio Frequency communication (RF)
In general, a wireless systems’ designer has two overriding constraints: the system must operate over a certain distance and transfer a certain amount of information within a data rate. The RF modules are very small in dimension and have a widely operating voltage range, i.e., 3V to 12V.
Basically the RF modules are 433 MHz, RF transmitter and receiver modules. The transmitter draws no power when transmitting logic zero while fully suppressing the carrier frequency, and thus, consumes significantly low power in a battery operated mode. When logic one is sent,thecarrier is fully on to about 4.5mA with a 3volts power supply. The data is sent serially from the transmitter, which is then received by the tuned receiver. The transmitter and receiver are duly interfaced to two microcontrollers for data transfer.
Features of RF Module
- Receiver frequency: 433MHz
- Receiver typical frequency: 105Dbm
- Receiver supply current: 3.5mA
- Low-power consumption
- Receiver operating voltage: 5v
- Transmitter frequency range: 433.92MHz
- Transmitter supply voltage: 3v~6v
- Transmitter output power: 4v~12v
RF Transmitter and Receiver’s Working Procedure
In many projects, we use RF modules for transmitting and receiving data because they have high volumes of applications than IR. The RF signals travel in the transmitter and receiver even when there is an obstruction. They operate at a specific frequency of about433MHz.
The RF transmitter receives serial data and transmits the data to the receiver through an antenna which is connected to the 4th pin of the transmitter. When logic 0 is appliedto the transmitter, then there is no power supply in the transmitter. When logic 1 is applied to the transmitter, then the transmitter getson, and there is a high-power supply in the range of 4.5mA with a 3V voltage supply.
IR Transmission Communication: (Infrared Signals)
These sensors can be utilized as a part of measuring the radiation temperature without beingincontact. For different radiation temperature ranges, various filters are available. An infrared (IR) sensor is an electronic device that radiates or locates infrared radiations to sense some parts of its surroundings. The Infrared radiations are undetectable to human eyes.
An infrared sensor can be consideredas a Polaroid that briefly recalls how an area’s infrared radiation shows up. It is very regular for an infrared sensor to be coordinated into movement indicators like those utilized as a feature of private or business security systems. An IR sensor is shown in the figure; basically it has two terminals: positive and negative. These sensors are undetectable to human eyes. They can measure the heat of an object and also identify itsmovement. The wavelength region around 0.75µm to 1000 µm is the IR region. The wavelength region around 0.75µm to 3 µm is called close infrared; 3 µm to 6 µm is called mid infrared; and, higher than 6 µm is called far infrared. IR sensors emit a frequency of 38 KHz.
Types of IR Communication
Point to Point: It requires a line of sight between the transmitter and a receiver. In other words, the transmitter and the receiver should be pointed to each other and there shouldn’t be any obstacles between them. Example is the remote control communication.
Diffuse Point: It doesn’t require any line of sight and the link between the transmitter and the receiver is maintained by reflecting or bouncing of the transmitted signal by surfaces like ceilings, roof, etc. Example is awireless LAN communication system.
IR Transmitter and Receiver Working Procedure
The transmitter of an IR LED inside its circuit emits infrared light for every electric pulse given to it. This pulse is generated as a button on the remote is pressed, thus completing the circuit, andproviding bias to the LED.
IR communication Working Principle
IR Transmission: The LED on being biased emits light of the wavelength of around 940nm as a series of pulses, corresponding to the button pressed. However, along with the IR LED many other sources of infrared light including human beings, light bulbs, sun, etc., interfere withthe transmitted information. A solution to this problem is through modulation. The transmitted signal is modulated using a carrier frequency of 38 KHz (or any other frequency between 36 to 46 KHz). The IR LED is made to oscillate at this frequency for the time duration of the pulse. The information or the light signals are pulse width modulated and are contained in the 38 KHz frequency.
IR Reception: This receiver consists of a photo detector that develops an output electrical signal as light incident on it. The output of the detector is filtered using a narrow-band filter that discards all the frequencies below or above the carrier frequency (38 KHz in this case). The filtered output is then given to the suitable device like a Microcontroller or a Microprocessor which controls thedevices like a PC or a Robot. The output from the filters can also be connected to the Oscilloscope to read the pulses.
Advantages of IR communication
Security: Infrared communication has high directionalityand is capable of identifying the source as a different source emitting radiation of different frequencies, and thus, the risk of information being diffused is eliminated. Safety: Infrared radiation is not harmful to human beings. Hence, infrared communication can be used at any place.
High Speed DataCommunication: The data rate of Infrared communication is about 1Gbps and can be used for sending information like video signal.
Radio Frequency Identification Communication (RFID)
RFID or Radio Frequency Identification System is a technology based identification system that helps identifying objects just through the tags attached to them, without requiring any line of sight between the tags and the tag reader. All that is needed is a radio communication between the tag and the reader.
A Basic RFID System
The RFID System consists of mainly three components such as:
An RFID tag: It consists of a silicon microchip attached to a small antenna and mounted on a substrate and encapsulated in different materials like plastic or glass veil and with an adhesive on the back side, which is used to attach the tags to objects.
A Reader: It consists of a scanner with antennas to transmit and receive signals and is responsible for communication with the tag and receives the information from the tag.
A Processor or a Controller: It can be a host computer with a microprocessor or a microcontroller which receives the reader input and processes the data.
Types of RFID Systems
Active RFID system: In these systems, the tags havetheir own power sources like external power supplies units or batteries. The only constraint is the life time of the power devices. These systems can be used for larger distances and to track high-value goods like vehicles.
Passive RFID system: These are thesystems wherein the tags get power through the transfer of power from a reader antenna to the tag antenna. They are used for short-range transmission.
Here, we are mostly concerned with the passive RFID system as it is most widely used in regular applications like in retail market organizations.
A Passive RFID System Using Induction Coupling Method
In this approach, the RFID tag gets power from areader throughan inductive coupling method. The reader consists of a coil connected to an AC supply such that a magnetic field is formed around it. The tag coil is placed in the vicinity of the reader coil and an electromotive force is induced to it by virtue of Faraday’s law of induction.
The EMF causes a flow of current in the coil, thus producing a magnetic field around it. By the virtue of Lenz law, the magnetic field of the tag coil opposes the reader’s magnetic field and there is a subsequent increase in the current through the reader coil. The reader intercepts this asload information. This system is suitable for very short distance communication. The AC voltage appearing across the tag coil is converted to a DC by using a rectifier and filter arrangement.
A Passive RFID System Using EM Wave Propagation Method
The antenna present in the reader transmits electromagnetic waves which are received by the antenna present in the tag as potential difference across the dipole. This voltage is rectified and filtered to get the DC power. The receiver antenna is kept at a different impedance thatcauses it to reflect a part of the received signal. This reflected signal is received by the reader and monitored accordingly.
Active RFID System’s Working Principle
In the active RFID system, the reader sends signal to the tag using an antenna. The tag receives this information and resends this information along with the information in its memory. The reader receives this signal and transmits itto the processor for further processing.
Passive RFID System’sWorking Principle
In a passive RFID system, the RFID card (tag) is swiped against the RFID reader, a carrier signal of 125 KHz is sent to the tag coilthat receives this signal and transmits itto the processor for further processing.
Global Positioning System Communication (GPS)
GPS or Global Positioning System is a satellite navigation system that furnishes location and time information in all climate conditions to the user. The GPS is used for navigationof planes, ships, cars and trucks as well.This systemoffers critical abilities to military and civilian users around the globe. GPS provides continuous real time, 3-dimensional positioning, navigation and timing worldwide.
How does a GPS System Work?
The GPS system consists of three segments:
- The space segment: the GPS satellites
- The control system: operated by the U.S. military
- The user segment, which includes both the military and civilian users and their GPS equipment.
The space segment is the number of satellites in the constellation. It comprises 29 satellites circling the earth every 12 hours at an altitude of 12,000 miles. The function of the space segment is utilized to route/navigate signals and to store and retransmit the route/navigation message sent by the control segment. These transmissions are controlled by highly-stable atomic clocks on the satellites. The GPS Space Segment is formed by a satellite constellation with enough satellites to ensure that the users have, at least, 4 simultaneous satellites in view from any point on the Earth surface at any time.
The control segment comprises a master-control station and five monitoring stations outfitted with atomic clocks, which are spread around the globe. The five monitoring stations monitor the GPS satellite signals and then send that qualified information to the master control station wherein the abnormalities are revised and sent back to the GPS satellites through the ground antennas. The Control segment can also be referred to as a monitoring station.
The user segment comprises a GPS receiverthat receives signals from the GPS satellites and determines how far away it isfrom other satellite. This segment is mainly used by the U.S military, missile guidance systems, and the civilian applications of GPS are there in almost every field. Most of the civilian use this for transportation surveys, natural resources’identification and for agricultural purpose and mapping too.
Sub-GHz Communication with Transceiver Protocols: (below 1GHz)
These communication networks include GSM, EnOcean, IO-Home Control, ONE-NET and Z-Wave Communication. Let us look on in brief about all these communications.
Global System for Mobile Communication Protocol: (GSM)
A GSM is a mobile communication modem.It stands for global system for mobile communication (GSM). The idea of GSM was developed at Bell Laboratories in 1970. At present, it is the most widely used mobile communication system in the world. GSM is an open and digital cellular technology used for transmitting mobile voice and data services and operatesat 850MHz, 900MHz, 1800MHz and 1900MHz frequency bands.
GSM system was developed as a digital system using time division multiple access (TDMA) technique for communication purpose. A GSM digitizes and reduces the data, then sends it down through a channel with two different streams of client data, each in its own particular time slot. The digital system has an ability to carry 64 Kbps to 120 Mbps of data rates.
There are various cell sizes in a GSM system such as macro, micro, Pico and umbrella cells. Each cell varies as per the implementation domain. There are five different cell sizes in a GSM network: macro, micro, Pico and umbrella cells. The coverage area of each cell varies according to the implementation environment.
A GSM network consists of the following components:
A Mobile Station: It is the mobile phone which consists of the transceiver, the display and the processor and is controlled by a SIM card operating over the network.
Base Station Subsystem: It acts as an interface between the mobile station and the network subsystem. It consists of the Base Transceiver Station which contains the radio transceivers and handles the protocols for communication with mobiles. It also consists of the Base Station Controller which controls the Base Transceiver station and acts as an interface between the mobile station and mobile switching center.
Network Subsystem: It provides the basic network connection to the mobile stations. The basic part of the Network Subsystem is the Mobile Service Switching Centre that provides access to different networks like ISDN, PSTN etc. It also consists of the Home Location Register and the Visitor Location Register which provides the call routing and roaming capabilities of GSM. It also contains the Equipment Identity Register which maintains an account of all the mobile equipment wherein each mobile is identified by its own IMEI number. The IMEI stands for International Mobile Equipment Identity.
EnOcean Wireless Communication Transceiver Module
The EnOcean is anenergysaving wireless technology used primarily for building automation systems.EnOcean-based products (such as sensors and light switches) can perform without batteries and are engineered to operate maintenance-free. The radio signals from these sensors and switches can be transmitted wirelessly over a distance up to 300 meters in the open and up to 30 meters inside building.It mostly works as a unidirectional protocol without handshaking.
The transmission frequencies used for the devices include902 MHz, 868.3 MHz and 315 MHz.
The Parameters of the EnOcean Transceiver
- EnOceantechnology transceivers support UART and SPI protocol.
- EnOcean technology transceivers have SoC.
- EnOceantechnologytransceivers support Amplitude shift keying(ASK) modulation technique.
- The transmission distance is 20m.
IO-Home ControlCommunication Transceiver Module
IO-home controlisa highly secure wireless technology included in a wide range of home equipment marketed by partner brands specializing in the residential sector.It provides security and energy savings every day by making the automated or motor-operated equipment of your home in a veryefficient way including roof windows, roller shutters, interior and exterior solar screens, gates, garage doors, entrance doors, alarms, lighting, heating, cooling and ventilation systems, etc.
The transmission frequencies used for the devices are 433 MHz, 868 MHz and 915 MHz.The new version module is ADF7022.
The Parameters ofIO-Home Control Transceiver
- IO-homecontrol transceivers support UART and SPI protocol.
- IO-homecontroltransceivers haveSoC.
- IO-homecontroltransceiverssupportAmplitudeShift Keying (ASK) Modulationtechnique.
- The transmission distance is veryshort: 20m.
- An IO-homecontrol transceiver’s voltage is 1.8-3.6V.
ONE-NET Communication Transceiver Module
ONE-NET is an open source standard for wireless networking system. ONE-NET was designed for low-cost, low-power (battery-operated) control networks for applications such as home automation, security & monitoring, device control, and sensor networks. ONE-NET supports star, peer-to-peer and multi-hop topology.
The transmission frequencies used for the devices are 868 MHz and 915 MHz.
The parameters ofONE-NET Transceiver
- The ONE-NET transceivers support UART and SPI protocol.
- The ONE-NET transceivers have SoC.
- The ONE-NET transceivers use Amplitude shift keying (ASK) modulation.
- The transmission distance is 500m.
- A ONE-NET transceiver’s voltage is 1.8-3.6V.
Z-Wave Communication Transceiver module
Z-Wave developed by Zensys is a two-way RF mesh networking technology that targets home control and energy management applications. Like Zigbee, Bluetooth Z-Wave offers a low latency, low-power, cost-effective solution. Z-Wave comes as a single-chip solution with CPU, flash memory and radio. It works in the sub-1-GHz band at frequencies of 908.42 MHz in the U.S. and 868.42 MHz in Europe,and 865.2MHz in India.
Z-Wave’s mesh network architecture uses source routing and can support up to 232 nodes on a single network. These networks can be combined and coexist with other common home networks, including Bluetooth and Wi-Fi without interference.
The parameters of Z-Wave Transceiver
- Z-Wave transceivers support UART and SPI protocol.
- Z-Wave transceivers have SoC.
- Z-Wave transceivers usebinary phase shift keying (BPSK)modulation.
- The transmission distance is 30m.
- Z-Wavetransceiver’s voltage is 2.1-3.6V.