"Over the air broadcasting" redirects here. For the technology over the air television, see Terrestrial television
Wireless communication (or just wireless, when the context allows) is the transfer of information (telecommunication) between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most common wireless technologies use radio waves. With radio waves, intended distances can be short, such as a few meters for Bluetooth or as far as millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mouse, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones. Somewhat less common methods of achieving wireless communications involve other electromagnetic phenomena, such as light and magnetic or electric fields, or the use of sound.
The term wireless has been used twice in communications history, with slightly different meanings. It was initially used from about 1890 for the first radio transmitting and receiving technology, as in wireless telegraphy, until the new word radio replaced it around 1920. Radio sets in the UK and the English-speaking world that were not portable continued to be referred to as wireless sets into the 1960s.[1][2] The term wireless was revived in the 1980s and 1990s mainly to distinguish digital devices that communicate without wires, such as the examples listed in the previous paragraph, from those that require wires or cables. This became its primary usage in the 2000s, due to the advent of technologies such as mobile broadband, Wi-Fi, and Bluetooth.
Wireless operations permit services, such as mobile and interplanetary communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, etc.) that use some form of energy (e.g. radio waves and acoustic energy) to transfer information without the use of wires.[3][4][5] Information is transferred in this manner over both short and long distances.
History
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Photophone
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Bell and Tainter's photophone, of 1880.The first wireless telephone conversation occurred in 1880 when Alexander Graham Bell and Charles Sumner Tainter invented the photophone, the telephone that sent audio over a beam of light. The photophone required sunlight to operate, and a clear line of sight between the transmitter and receiver, which greatly decreased the viability of the photophone in any practical use.[6] It would be several decades before the photophone's principles found their first practical applications in military communications and later in fiber-optic communications.
Electric wireless technology
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Early wireless
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A number of wireless electrical signaling schemes including sending electric currents through water and the ground using electrostatic and electromagnetic induction were investigated for telegraphy in the late 19th century before practical radio systems became available. These included a patented induction system by Thomas Edison allowing a telegraph on a running train to connect with telegraph wires running parallel to the tracks, a William Preece induction telegraph system for sending messages across bodies of water, and several operational and proposed telegraphy and voice earth conduction systems.
The Edison system was used by stranded trains during the Great Blizzard of 1888 and earth conductive systems found limited use between trenches during World War I but these systems were never successful economically.
Radio waves
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Marconi transmitting the first radio signal across the Atlantic.In 1894, Guglielmo Marconi began developing a wireless telegraph system using radio waves, which had been known about since proof of their existence in 1888 by Heinrich Hertz, but discounted as a communication format since they seemed, at the time, to be a short-range phenomenon.[7] Marconi soon developed a system that was transmitting signals way beyond distances anyone could have predicted (due in part to the signals bouncing off the then unknown ionosphere). Marconi and Karl Ferdinand Braun were awarded the 1909 Nobel Prize for Physics for their contribution to this form of wireless telegraphy.
Millimetre wave communication was first investigated by Jagadish Chandra Bose during 1894–1896, when he reached an extremely high frequency of up to 60 GHz in his experiments.[8] He also introduced the use of semiconductor junctions to detect radio waves,[9] when he patented the radio crystal detector in 1901.[10][11]
Wireless revolution
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The wireless revolution began in the 1990s,[12][13][14] with the advent of digital wireless networks leading to a social revolution, and a paradigm shift from wired to wireless technology,[15] including the proliferation of commercial wireless technologies such as cell phones, mobile telephony, pagers, wireless computer networks,[12] cellular networks, the wireless Internet, and laptop and handheld computers with wireless connections.[16] The wireless revolution has been driven by advances in radio frequency (RF), microelectronics, and microwave engineering,[12] and the transition from analog to digital RF technology,[15][16] which enabled a substantial increase in voice traffic along with the delivery of digital data such as text messaging, images and streaming media.[15]
Modes
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Wireless communications can be via:
Radio
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Radio and microwave communication carry information by modulating properties of electromagnetic waves transmitted through space. Specifically, the transmitter generates artificial electromagnetic waves by applying time-varying electric currents to its antenna. The waves travel away from the antenna until they eventually reach the antenna of a receiver, which induces an electric current in the receiving antenna. This current can be detected and demodulated to recreate the information sent by the transmitter.
Free-space optical
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An 8-beam free space optics laser link, rated for 1 Gbit/s at a distance of approximately 2 km. The receptor is the large disc in the middle, and the transmitters are the smaller ones. To the top and right corner is a monocular for assisting the alignment of the two heads.Free-space optical communication (FSO) is an optical communication technology that uses light propagating in free space to transmit wireless data for telecommunications or computer networking. "Free space" means the light beams travel through the open air or outer space. This contrasts with other communication technologies that use light beams traveling through transmission lines such as optical fiber or dielectric "light pipes".
The technology is useful where physical connections are impractical due to high costs or other considerations. For example, free space optical links are used in cities between office buildings that are not wired for networking, where the cost of running cable through the building and under the street would be prohibitive. Another widely used example is consumer IR devices such as remote controls and IrDA (Infrared Data Association) networking, which is used as an alternative to WiFi networking to allow laptops, PDAs, printers, and digital cameras to exchange data.
Sonic
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Sonic, especially ultrasonic short-range communication involves the transmission and reception of sound.
Electromagnetic induction
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Electromagnetic induction only allows short-range communication and power transmission. It has been used in biomedical situations such as pacemakers, as well as for short-range RFID tags.
Services
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Common examples of wireless equipment include:[17]
Electromagnetic spectrum
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AM and FM radios and other electronic devices make use of the electromagnetic spectrum. The frequencies of the radio spectrum that are available for use for communication are treated as a public resource and are regulated by organizations such as the American Federal Communications Commission, Ofcom in the United Kingdom, the international ITU-R or the European ETSI. Their regulations determine which frequency ranges can be used for what purpose and by whom. In the absence of such control or alternative arrangements such as a privatized electromagnetic spectrum, chaos might result if, for example, airlines did not have specific frequencies to work under and an amateur radio operator was interfering with a pilot's ability to land an aircraft. Wireless communication spans the spectrum from 9 kHz to 300 GHz.[citation needed]
Applications
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Mobile telephones
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One of the best-known examples of wireless technology is the mobile phone, also known as a cellular phone, with more than 6.6 billion mobile cellular subscriptions worldwide as of the end of 2010.[19] These wireless phones use radio waves from signal-transmission towers to enable their users to make phone calls from many locations worldwide. They can be used within the range of the mobile telephone site used to house the equipment required to transmit and receive the radio signals from these instruments.[20]
Data communications
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"Wireless Internet" redirects here. For all wireless Internet access, see Wireless broadband . For mobile wireless Internet, see Mobile broadband
Wireless data communications allow wireless networking between desktop computers, laptops, tablet computers, cell phones, and other related devices. The various available technologies differ in local availability, coverage range, and performance,[21] and in some circumstances, users employ multiple connection types and switch between them using connection manager software[22][23] or a mobile VPN to handle the multiple connections as a secure, single virtual network.[24] Supporting technologies include:
citation needed
] Standardized as IEEE 802.11 a, b, g, n, ac, ax, Wi-Fi has link speeds similar to older standards of wired Ethernet. Wi-Fi has become the de facto standard for access in private homes, within offices, and at public hotspots.[25] Some businesses charge customers a monthly fee for service, while others have begun offering it free in an effort to increase the sales of their goods.[26]Wireless data communications are used to span a distance beyond the capabilities of typical cabling in point-to-point communication and point-to-multipoint communication, to provide a backup communications link in case of normal network failure, to link portable or temporary workstations, to overcome situations where normal cabling is difficult or financially impractical, or to remotely connect mobile users or networks.
Peripherals
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Peripheral devices in computing can also be connected wirelessly, as part of a Wi-Fi network or directly via an optical or radio-frequency (RF) peripheral interface. Originally these units used bulky, highly local transceivers to mediate between a computer and a keyboard and mouse; however, more recent generations have used smaller, higher-performance devices. Radio-frequency interfaces, such as Bluetooth or Wireless USB, provide greater ranges of efficient use, usually up to 10 feet, but distance, physical obstacles, competing signals, and even human bodies can all degrade the signal quality.[32] Concerns about the security of wireless keyboards arose at the end of 2007 when it was revealed that Microsoft's implementation of encryption in some of its 27 MHz models were highly insecure.[33]
Energy transfer
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Wireless energy transfer is a process whereby electrical energy is transmitted from a power source to an electrical load that does not have a built-in power source, without the use of interconnecting wires. There are two different fundamental methods for wireless energy transfer. Energy can be transferred using either far-field methods that involve beaming power/lasers, radio or microwave transmissions, or near-field using electromagnetic induction.[34] Wireless energy transfer may be combined with wireless information transmission in what is known as Wireless Powered Communication.[35] In 2015, researchers at the University of Washington demonstrated far-field energy transfer using Wi-Fi signals to power cameras.[36]
Medical technologies
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New wireless technologies, such as mobile body area networks (MBAN), have the capability to monitor blood pressure, heart rate, oxygen level, and body temperature. The MBAN works by sending low-powered wireless signals to receivers that feed into nursing stations or monitoring sites. This technology helps with the intentional and unintentional risk of infection or disconnection that arise from wired connections.[37]
Categories of implementations, devices, and standards
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See also
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References
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Further reading
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It is no exaggeration to say that modern society is supported by communication technologies such as mobile phones, Wi-Fi, radios, transportation IC cards, and television broadcasting. The communication we refer to here is communication using electricity—telecommunication. Telecommunication has undergone various technological innovations since its invention more than 250 years ago. It is even continuing to progress today especially with digitalization including 5G and IoT.
In this way, telecommunication has already become a part of our social infrastructure. Nevertheless, it is not easy to grasp an overall view of telecommunication due to its wide-ranging specifications and applications. For example, there are explanations of the technical aspects such as the signal form (digital and analog), the signal direction (duplex and simplex), and the transmission path (whether or not there is a cable), but it is rare to see comprehensive coverage of telecommunication-related content.
Accordingly, we wanted in this article to focus on wireless communication and to provide the basic materials to understand wireless communication together with the technical aspects while introducing our communication-related components and modules. This article is aimed at beginners who need wireless knowledge and those who have an interest in communication itself. We hope this article will be useful to those who want to broadly know and understand wireless communication knowledge.
Note: This article attempts to give an outline explanation of wireless communication. Accordingly, we have not fully explained some areas and left out other areas altogether. We plan to cover those areas little by little in the future.
Put simply, wireless communication is wireless telecommunication that uses electromagnetic waves (radio waves), magnetic fields, and electric fields, whereas optical communication uses light without using wires or cables. Among the various methods of wireless communication, telecommunication that uses radio waves enables long-distance communication in the order of kilometers or more and allows lots of data (information)*1 to be transmitted. Therefore, radio waves are used in most wireless communication systems. We would like to focus our explanation mainly on radio waves in this series.
Wireless communication systems that use radio waves are configured to use space as the transmission path (or communication channel) and to send data on radio waves as signals*1 from transmitters to receivers (Fig. 1).
Fig. 1: Configuration of a Simple Model for a Wireless Communication System*1: We consider “data,” “information,” and “signals” here as follows.
・Data: A collection of symbols and codes that represent facts
・Information: Data including audio, text, and images that can be interpreted by humans and used in ways such as to determine things and take actions
・Signals: Data or information transmitted over time across transmission paths (communication channels) such as space or cables
We do not distinguish between “information” and “data” from here on for convenience. We use the expression of “data” unless otherwise specified.
Table 1 summarizes the approximate categories of wireless communication that transmit data using radio waves and the typical applications of each category. Wireless communication is used in various fields. The applications and types of wireless communication are also wide-ranging.
We should note here that wireless communication is also being developed beyond the boundaries of these categories in recent years. For example, various countries have begun satellite mobile communication services that incorporate satellite communication into mobile communication (smartphones equipped with a function to connect to satellites).
Categories of Wireless Communication
Typical Applications
Mobile communication
Mobile phones
Aviation communication
Radio altimeters, radars for air traffic control
Satellite communication
Satellite broadcasting, GPS, weather observation
Ship communication
LF beacons, MF/HF/VHF wireless communication
Broadcast communication
AM/FM radio broadcasting (audio), television broadcasting (video)
Fixed communication (microwave communication)
Long-distance telephone call relays, television relays
Wireless network communication
Bluetooth®, UWB, Wi-Fi, Wi-MAX, LPWA, etc.
(Supplementary Information to the Terms in Table 1)Term
Description
Global Positioning System (GPS)
A satellite positioning system for the entire earth.
Low Frequency (LF)
Also called long wave.
The frequency range is 30 kHz to 300 kHz.
Medium Frequency (MF)
Also called medium wave.
The frequency range is 300 kHz to 3,000 kHz (3 MHz).
High Frequency (HF)
Also called short wave.
The frequency range is 3 MHz to 30 MHz.
Very High Frequency (VHF)
Also called ultra-short wave.
The frequency range is 30 MHz to 3,000 MHz (3 GHz).
Microwaves
Also described as Super Very High Frequency (SHF).
The frequency range is 3 GHz to 30 GHz.
Amplitude Modulation (AM)
A type of communication technology that
transmits analog audio over long distances.
Frequency Modulation (FM)
A type of audio communication technology similar to AM.
[Reference]
FM broadcasts have a reach of about 100 km.
However, AM broadcasts can go beyond that and even
reach overseas. Nevertheless, AM broadcasts are more
susceptible to the impact of noise.
The basic model configuration of wireless communication systems (and wired communication systems) is as in Fig. 2. We describe its constituent elements in Table 2. Figure 1 in “1. What Is Wireless Communication?” is an even more simplified illustration of this basic model.
We call the data transmitted through a transmission path a “signal.” We refer to the unnecessary components that negatively affect these signals and make it difficult to transmit the data we want to send to the recipient “noise.” In practice, noise may occur in both transmitters and receivers and then cause interference with the operation of devices and other problems. In other words, we can call a communication system completely unaffected by this noise the ideal communication system.
Constituent Elements
Description
Sender
The person sending data
Data
Audio, text, still images, videos, etc.
Transmitter
The device that converts the information you want to pass along
the transmission path into signals
Transmission path (communication channel)
The medium in which signals are transmitted from the transmitter
to the receiver
(the transmission path is a wire or cable in wired communication)
Receiver
The device that converts the signals passed along the transmission
path into data
Recipient
The person who received data
Fig. 3 shows a configuration that describes the modulation and demodulation that are the basic functions of a wireless communication system. It is based on the basic model of the communication system in Fig. 2.
If you try to directly transmit data as radio waves, you will not be able to send it over long distances. For this and other reasons, wireless communication requires an operation called “modulation” that converts data into convenient signals in the transmitter to enable the transmission of data over long distances. On the other hand, an operation called “demodulation” that returns the modulated signals back to the original data is required in the receiver.
Table 3 summarizes the typical modulation technologies and adoption examples. Many of the terms are unfamiliar in general. However, we would like you to think of these modulation technologies as those that support part of our current lifestyle infrastructure such as mobile phones and radio and television broadcasts here. We plan to explain the details on a separate page at a later date.
Typical Modulation Technologies
Adoption Examples
Analog
Amplitude modulation (AM)
Radio (medium-wave broadcasting,
short-wave broadcasting)
Frequency modulation (FM)
Radio (community broadcasting)
First-generation mobile telephones
Digital
Amplitude shift keying (ASK)
RFID
Remote keyless entry
Frequency shift keying (FSK) modulation
RFID
Remote keyless entry
Wi-SUN
Phase shift keying (PSK) modulation
Terrestrial digital broadcasting
Satellite broadcasting
Second, third, and enhanced third-generation
mobile phones
WiGig (IEEE802.11ad)
Zigbee
Wi-SUN
Amplitude phase shift keying (APSK) modulation
BS8K broadcasting
BS4K broadcasting
Spread spectrum (SS) modulation
Direct sequence (DS)
Third generation mobile phones
Wi-Fi (IEEE802.11b/11g)
WiGig (IEEEB02.11ad)
Zigbee
Frequency hopping (FH)
Bluetooth®
Chirp
LoWaWAN (LPWA)
Quadrature amplitude modulation (QAM)
Terrestrial digital broadcasting
Fourth-and fifth-generation mobile phones
WiGig (IEEEB02.11ad)
Ultra-wideband (UB) modulation
Smartphone position detection
Orthogonal frequency-division multiplexing (OFDM) modulation
Terrestrial digital broadcasting
Generation 4 and 5 mobile phones
Wi-Fi (IEEE802.11b/11g)
Wi-Fi 4 (IEEE802.11n)
Wi-Fi 5 (IEEE802.11ac)
Wi-Fi 6 (IEEE802.11ax)
WiGig (IEEEB02.11ad)
Wi-SUN
LTE-M/LTE-Cat.M1 (LPWA)
NB-IoT (LPWA)
Radio waves are a form of energy like motion and heat. They are also called electromagnetic waves. (In fact, light is a type of electromagnetic wave.) Radio waves are defined as electromagnetic waves with a frequency of 3,000 GHz or less in Japan’s Radio Law and the Radio Regulations annexed to the International Telecommunication Convention. (We will explain later how to calculate the frequency.)
These radio waves are emitted from wireless devices. However, it is not easy to actually visualize them. Accordingly, we have explained the occurrence and transmission of radio waves from the phenomenon that occurs when sinusoidal alternating current is passed through a conductor rod such as metal to make it easier to picture.
Figure 4 shows how radio waves travel at that time. In fact, radio waves extend out three-dimensionally. However, we focus on radio waves that travel when the conductor is vertically oriented here to reveal how they are transmitted. The electric field*2 and magnetic field*2 are maintained at right angles (orthogonally) to each other. Changes in the magnetic field create an electric field. Changes in the electric field then create a magnetic field. The repetition of this process allows radio waves to be transmitted as sinusoidal vibrations. We give below the main properties of radio waves.
[1] Radio waves are traverse waves. The amplitude (strength) of the electric field and magnetic field changes perpendicularly to the direction of travel, and the electric field and magnetic field then also transmit the radio waves perpendicularly to each other.
[2] The speed at which the radio waves are transmitted is the same as that of light.
[3] Radio waves have no transmission medium. (The air vibrates and is transmitted as waves. We then feel the sound when those waves enter our ears. The air at this time is referred to as the transmission medium.)
The properties of [3] are far from our everyday senses. Nevertheless, it is believed that radio waves, or electromagnetic waves, that are transmitted even in a vacuum such as outer space propagate while electric fields (space that electrical forces act) and magnetic fields (space that magnetic forces act) vibrate.
Incidentally, we stated that radio waves are electromagnetic waves with a frequency of 3,000 GHz or less at the beginning of this column. We can calculate this frequency (f) [Hz] using the formula of f = c/λ assuming the radio wave length (m) in Fig. 4 and the speed of light c (3 × 108 m/s). Electromagnetic waves are classified into several types depending on their frequency and wavelength (Fig. 5).
Fig. 5: Classification of Electromagnetic Waves by Frequency and Wavelength*2: Electric field and magnetic field: An electric field refers to a space where an electric force acts. A magnetic field refers to a space where a magnetic force acts. Fig. 6 is an image that indicates with arrowed lines the range of the electric field generated by the application of voltage and the range of the magnetic field generated around the magnet.
Fig. 6: Image of the Range Covered by Electric Field and Magnetic Field[Advanced Supplementary Information]
We often see an image of the transmission of radio waves that simply combines the phenomena of changes in the magnetic field creating an electric field and changes in the electric field creating a magnetic field in explanations of radio waves for beginners (Fig. 7). If you want to seriously study radio waves such as in relation to antennas, instead of such an image, it is important to have an image of the vectors that represent the strength of the electric and magnetic fields with arrows in Fig. 4—the electric field vector*3 and the magnetic field vector*3. (The image in Fig. 4 is derived from Maxwell’s equations*4.) According to this image, the radio waves used in satellite broadcasting, for example, are explained as circularly polarized radio waves that travel in a spiral pattern while the magnetic field vector in Fig. 4 rotates to the left or right.
*3: Electric field vector and magnetic field vector:
Both these vectors are vectors that represent the clockwise rotation and speed of rotation. (They are also called “rotation vectors” in this sense.) This does not mean that both indicate the direction in which an object or something else moves like with a velocity vector.
*4: Maxwell’s equations: These are the basic equations relating to electromagnetic fields that express all the relationships between electricity and magnetism. Coulomb’s law, which beginners to electromagnetism learn, can also be derived from these equations.
Index: Wireless Mechanism (2)
5. Data Transmission Direction: Duplex (Full Duplex and Half-duplex) and Simplex
5.1 Duplex Transmission
5.2 Simplex Transmission
6. What Is a Communication Protocol?
Column: History and Evolution of Wireless Communication