Mobile phone

The mobile phone (also called a  wireless phone or  cellular phone) is a short-range, portable electronic device used for mobile voice or data communication over a network of specialized base stations known as cell sites. In addition to the standard voice function of a telephone, current mobile phones may support many additional services, and accessories, such as SMS for text messaging, email, packet switching for access to the Internet, gaming, bluetooth, infrared, camera with video recorder and MMS for sending and receiving photos and video. Most current mobile phones connect to a cellular network of base stations (cell sites), which is in turn interconnected to the public switched telephone network (PSTN) (the exception is satellite phones).

Asymmetric Digital Subscriber Line (ADSL)

Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter - or microfilter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time. Because phone lines vary in quality and were not originally engineered with DSL in mind, it can generally only be used over short distances, typically less than 4km.

Radio frequency (RF)

Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits or electromagnetic radiation

Special properties of RF electrical signals
Electrical currents that oscillate at RF have special properties not shared by direct current signals. One such property is the ease with which it can ionize air to create a conductive path through air. This property is exploited by 'high frequency' units used in electric arc welding. Another special property is an electromagnetic force that drives the RF current to the surface of conductors, known as the skin effect. Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric insulator of a capacitor. The degree of effect of these properties depends on the frequency of the signals.

Frequencies

- Extremely low frequency (ELF)

Frequency = a 3 to 30 Hz

Wavelength = 10,000 km to 100,000 km

Applications : directly audible when converted to sound, communication with submarines

- Super low frequency (SLF)

Frequency = b 30 to 300 Hz

Wavelength = 1,000 km to 10,000 km

Applications : directly audible when converted to sound, AC power grids (50 hertz and 60 hertz)

- Ultra low frequency (ULF)

Frequency = c 300 to 3000 Hz

Wavelength = 100 km to 1,000 km

Applications : directly audible when converted to sound, communication with mines

- Very low frequency (VLF)

Frequency = d 3 to 30 kHz

Wavelength = 10 km to 100 km

Applications : directly audible when converted to sound (below ca. 18-20 kHz; or "ultrasound" 20-30+ kHz)

- Low frequency (LF)

Frequency = e 30 to 300 kHz

Wavelength = 1 km to 10 km

Applications : AM broadcasting, navigational beacons, lowFER

- Medium frequency (MF)

Frequency = f 300 to 3000 kHz

Wavelength = 100 m to 1 km

Applications : navigational beacons, AM broadcasting, maritime and aviation communication

- High frequency (HF)

Frequency = g 3 to 30 MHz

Wavelength = 10 m to 100 m

Applications : shortwave, amateur radio, citizens' band radio

- Very high frequency (VHF)

Frequency = h 30 to 300 MHz

Wavelength = 1 m to 10 m

Applications : FM broadcasting, broadcast television, aviation, GPR

- Ultra high frequency (UHF)

Frequency = i 300 to 3000 MHz

Wavelength = 10 cm to 100 cm

Applications : broadcast television, mobile telephones, cordless telephones, wireless networking,
remote keyless entry for automobiles, microwave ovens, GPR

- Super high frequency (SHF)

Frequency = j 3 to 30 GHz

Wavelength = 1 cm to 10 cm

Applications : wireless networking, satellite links, microwave links, Satellite television,
door openers.

- Extremely high frequency (EHF)

Frequency = k 30 to 300 GHz

Wavelength = 1 mm to 10 mm

Applications : microwave data links, radio astronomy, remote sensing, advanced weapons systems, advanced security scanning

Bluetooth Special Interest Group (SIG)

The Bluetooth Special Interest Group (SIG) is the body that oversees the development of Bluetooth standards and the licensing of the Bluetooth technologies and trademarks to manufacturers. Founded in 1998, it is a privately held trade association headquartered in Bellevue, Washington with Michael W. Foley (Mike) presently its executive director.

Computer

A computer is a machine that manipulates data according to a list of instructions.

The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers. Modern computers are based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space. Today, simple computers may be made small enough to fit into a wristwatch and be powered from a watch battery. Personal computers, in various forms, are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and children's toys.
The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity

Bluetooth

Bluetooth is a wireless protocol utilizing short-range communications technology facilitating data transmission over short distances from fixed and/or mobile devices, creating wireless personal area networks (PANs). The intent behind the development of Bluetooth was the creation of a single digital wireless protocol, capable of connecting multiple devices and overcoming issues arising from synchronization of these devices. Bluetooth uses a very robust radio technology called frequency hopping spread spectrum. It chops up the data being sent and transmits chunks of it on up to 75 different frequencies. In its basic mode, the modulation is Gaussian frequency shift keying (GFSK) . It can achieve a gross data rate of 1 Mb/s. Bluetooth provides a way to connect and exchange information between devices such as mobile phones, telephones, laptops, personal computers, printers, GPS receivers, digital cameras, and video game consoles over a secure, globally unlicensed Industrial, Scientific, and Medical (ISM) 2.4 GHz short-range radio frequency bandwidth. The Bluetooth specifications are developed and licensed by the Bluetooth Special Interest Group (SIG). The Bluetooth SIG consists of companies in the areas of telecommunication, computing, networking, and consumer electronics.

Gaussian frequency-shift keying (GFSK)

Gaussian Frequency-Shift Keying (GFSK) is a type of Frequency Shift Keying modulation that utilizes a Gaussian filter to smooth positive/negative frequency deviations, which represent a binary 1 or 0. It is used by DECT, Bluetooth, Cypress WirelessUSB, Nordic Semiconductor and z-wave devices. For Bluetooth the minimum deviation is 115 kHz.

In a GFSK modulator, everything is the same as an FSK modulator except that before the baseband pulses (-1, 1) go into the FSK modulator, it is passed through a gaussian filter to make the pulse smoother so to limit its spectral width. Gaussian filtering is one of the very standard ways for reducing the spectral width, it is called "pulse shaping".
If we use -1 for fc-fd and 1 for fc+fd, once when we jump from -1 to 1 or 1 to -1, the modulated waveform changes rapidly, which introduces large out-of-band spectrum. If we change the pulse going from -1 to 1 as -1, -.98, -.93 ..... .96, .99, 1, and we use this smoother pulse to modulate the carrier, the out-of-band spectrum will be reduced.
The Fourier transform of a Gaussian curve results in a Gaussian curve.

Digital

A digital system uses discrete (that is, discontinuous) values to represent information for input, processing, transmission, storage, etc. By contrast, non-digital (or analog) systems use a continuous range of values to represent information. Although digital representations are discrete, the information represented can be either discrete, such as numbers, letters or icons, or continuous, such as sounds, images, and other measurements of continuous systems.
The word digital comes from the same source as the word digit and digitus (the Latin word for finger), as fingers are used for discrete counting.
The word digital is most commonly used in computing and electronics, especially where real-world information is converted to binary numeric form as in digital audio and digital photography. Such data-carrying signals carry electronic or optical pulses, the amplitude of each of which represents a logical 1 (pulse present and/or high) or a logical 0 (pulse absent and/or low)

ISM band

The industrial, scientific and medical (ISM) radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific and medical purposes other than communications. In general, communications equipment must accept any interference generated by ISM equipment

The ISM bands are defined by the ITU-R in 5.138, 5.150, and 5.280 of the Radio Regulations. Individual countries' use of the bands designated in these sections may differ due to variations in national radio regulations. Because communication devices using the ISM bands must tolerate any interference from ISM equipment, these bands are typically given over to uses intended for unlicensed operation, since unlicensed operation typically needs to be tolerant of interference from other devices anyway. In the United States of America, ISM uses of the ISM bands are governed by Part 18 of the FCC rules, while Part 15 Subpart B contains the rules for unlicensed communication devices, even those that use the ISM frequencies. Thus, designers of equipment for use in the United States in the ISM bands should be familiar with the relevant portions of both Part 18 and Part 15 Subpart B of the FCC Rules.

The ISM bands defined by the ITU-R are (bands in italics are subject to local acceptance):
6.765–6.795 MHz (centre frequency 6.780 MHz)
13.553–13.567 MHz (centre frequency 13.560 MHz)
26.957–27.283 MHz (centre frequency 27.120 MHz)
40.66–40.70 MHz (centre frequency 40.68 MHz)
433.05–434.79 MHz (centre frequency 433.92 MHz) in Region 1
902–928 MHz (centre frequency 915 MHz) in Region 2
2.400–2.500 GHz (centre frequency 2.450 GHz)
5.725–5.875 GHz (centre frequency 5.800 GHz)
24–24.25 GHz (centre frequency 24.125 GHz)
61–61.5 GHz (centre frequency 61.25 GHz)
122–123 GHz (centre frequency 122.5 GHz)
244–246 GHz (centre frequency 245 GHz)

For many people, the most commonly encountered ISM device is the home microwave oven operating at 2.45 GHz. However, in recent years these bands have also been shared with license-free error-tolerant communications applications such as wireless LANs and cordless phones in the 915 MHz, 2450 MHz, and 5800 MHz bands. Because licensed devices already are required to be tolerant of ISM emissions in these bands, unlicensed low power uses are generally able to operate in these bands without causing problems for licensed uses. Note that the 915 MHz band should not be used in countries outside Region 2, except those that specifically allow it such as Australia and Israel, especially those that use the GSM-900 band for cellphones. The ISM band is also widely used for Radio-frequency identification (RFID) applications with the most commonly used band being the 13.56 MHz band used by systems compliant with ISO/IEC 14443 including those used by biometric passports and contactless smart cards.

DSL : Digital subscriber line

DSL or xDSL, is a family of technologies that provide digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop, although in recent years, the term digital subscriber line has been widely adopted as a more marketing-friendly term for ADSL, which is the most popular version of consumer-ready DSL. DSL uses high frequency, while regular telephone uses low frequency on the same telephone line.

Typically, the download speed of consumer DSL services ranges from 256 kilobits per second (kbit/s) to 24,000 kbit/s, depending on DSL technology, line conditions and service level implemented. Typically, upload speed is lower than download speed for Asymmetric Digital Subscriber Line (ADSL) and equal to download speed for the rarer Symmetric Digital Subscriber Line (SDSL).

Digital camera

A digital camera (or digicam for short) is a camera that takes video or still photographs, or both, digitally by recording images on a light-sensitive sensor. Many compact digital still cameras can record sound and moving video as well as still photographs. In the Western market, digital cameras outsell their 35 mm film counter parts. 

Digital cameras can include features that are not found in film cameras, such as displaying an image on the camera's screen immediately after it is recorded, the capacity to take thousands of images on a single small memory device, the ability to record video with sound, the ability to edit images, and deletion of images allowing re-use of the storage they occupied.

Digital cameras are incorporated into many devices ranging from PDAs and mobil phones (called camera phones) to vehicles. The Hubble Space Telescope and other astronomical devices are essentially specialised digital cameras.

Printer

In computing, a printer is a peripheral which produces a hard copy (permanent human-readable textand/or graphics) of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cableor, in most newer printers, a USB cable to a computer which serves as a document source. Some printers, commonly known as network printers, have built-in network interfaces (typically wireless orEthernet), and can serve as a hardcopy device for any user on the network. Individual printers are often designed to support both local and network connected users at the same time.

In addition, a few modern printers can directly interface to electronic media such as memory sticks ormemory cards, or to image capture devices such as digital cameras, scanners; some printers are combined with a scanners and/or fax machines in a single unit. Printers that include non-printing features are sometimes called Multifunction Printers (MFP), Multi-Function Devices (MFD), or All-In-One (AIO) printers.

A printer which is combined with a scanner can function as a kind of photocopier if so designed. MostMFPs include printing, scanning, and copying among their features. Printers are designed for low-volume, short-turnaround print jobs; requiring virtually no setup time to achieve a hard copy of a given document. However, printers are generally slow devices (30 pages per minute is considered fast; and many consumer printers are far slower than that), and the cost-per-page is relatively high. In contrast, theprinting press (which serves much the same function), is designed and optimized for high-volume print jobs such as newspaper print runs--printing presses are capable of hundreds of pages per minute or more, and have an incremental cost-per-page which is a fraction of that of printers.

The printing press remains the machine of choice for high-volume, professional publishing. However, as printers have improved in quality and performance, many jobs which used to be done by professionalprint shops are now done by users on local printers; see desktop publishing. The world's first computerprinter was a 19th century mechanically driven apparatus invented by Charles Babbage for his Difference Engine.

Personal computer

A personal computer (PC) is any computer whose original sales price, size, and capabilities make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator.

Today a PC may be a desktop computer, a laptop computer or a tablet computer. The most commonoperating systems are Microsoft Windows, Mac OS andLinux, while the most common microprocessors are x86-compatible CPUs. Software applications for personal computers include word processing, spreadsheets,databases, games, and a myriad of personal productivity and special-purpose software. Modern personal computers often have high-speed or dial-up connections to the Internet, allowing access to the World Wide Web and a wide range of other resources.

A PC may be a home computer, or may be found in an office, often connected to a local area network. The distinguishing characteristics are that the computer is primarily used, interactively, by one person at a time. This is in contrast to the batch processing or time-sharing models which allowed large expensive systems to be used by many people, usually at the same time, or large data processing systems which required a full-time staff to operate efficiently.

While early PC owners usually had to write their own programs to do anything useful with the machines, today's users have access to a wide range of commercial and non-commercial software which is easily installed.

Laptop

A laptop computer or notebook computer is a small mobile computer, typically weighing 3 to 12 pounds (1.4 to 5.4 kg), although older laptops may weigh more.

Laptops usually run on a single main battery or from an external AC/DC adapter that charges the battery while it also supplies power to the computer itself, even in the event of a power failure. This very powerful main battery should not be confused with the much smaller battery nearly all computers use to run the real-time clock and backup BIOS configuration into the CMOS memory when the computer is without power.

Laptops contain components that are similar to their desktop counterparts and perform the same functions, but are miniaturized and optimized for mobile use and efficient power consumption, although typically less powerful for the same price. Laptops usually have liquid crystal displays and most of them use different memory modules for their random access memory (RAM), for instance, SO-DIMM in lieu of the larger DIMMs. In addition to a built-in keyboard, they may utilize a touchpad (also known as a trackpad) or a pointing stick for input, though an external keyboard ormouse can usually be attached.

Telephone

The telephone (from the Greek words tele (τηλέ) = far and phone (φωνή) = voice) is a telecommunications device that is used to transmit and receive sound (most commonly speech), usually two people conversing but occasionally three or more. It is one of the most common household appliances in the world today. Most telephones operate through transmission of electric signals over a complex telephone network which allows almost any phone user to communicate with almost