Wireless Communications 1 2 3
Megahertz (MHz)
1,000,000 (1 million) hertz.
Gigahertz (GHz)
1,000,000,000 (1 billion) hertz.
Kilohertz (kHz)
1000 Hz
wireless wide area network (WWAN)
A WAN that uses cellular phone technologies and encompasses any geographical region, including the entire globe.
non-return-to-zero, invert-on-ones (NRZ-I)
A binary signaling technique that changes the voltage level only when the bit to be represented is a 1; a variation of NRZ-L
polar non-return-to-zero (polar NRZ)
A binary signaling technique that increases the voltage to represent a 1 bit but drops to negative voltage to represent a 0 bit
non-return-to-zero (NRZ)
A binary signaling technique that increases the voltage to represent a 1 bit but provides no voltage for a 0 bit
Return to Zero (RZ)
A binary signaling technique that increases the voltage to represent a 1 bit, but the voltage is reduced to 0 before the end of the period for transmitting the 1 bit, and there is no voltage for a 0 bit.
Barker code (or chipping code)
A bit pattern used in a DSSS transmission. The term chipping code is used because a single radio bit is commonly referred to as a chip
Wi-Fi
A certification label awarded to IEEE 802.11 WLAN-compatible wireless devices that pass all interoperability tests performed by an organization called the Wi-Fi Alliance. The acronym is often thought to stand for Wireless Fidelity, but this is a common misconception. The name was chosen by the alliance purely for marketing reasons and is not an acronym at all.
baud
A change in a carrier signal.
American National Standards Institute (ANSI)
A clearinghouse for standards development in the United States.
Psuedo-Random Code
A code that is usually derived through a number of mathematical calculations as well as practical experimentation.
quadrature amplitude modulation (QAM)
A combination of phase modulation with amplitude modulation to produce 16 different signals.
de facto standard
A common practice that the industry follows for various reasons.
USB
A common way of connecting peripherals such as flash drives, Wi-Fi NICs, printers, and other peripherals to a computer. Stands for Universal Serial Bus.
mixer
A component that combines two inputs to create a single output.
amplifier
A component that increases a signal's intensity.
filter
A component that is used to either accept or block a radio frequency signal
antenna
A copper wire, rod, or similar device used to send and receive radio signals that has one end up in the air and the other end connected to the ground through a receiver
Repeater
A device commonly used in satellite communications that simply "repeats" the signal to another location.
smartphone
A device that combines a cellular phone with the capabilities of a personal digital assistant (PDA). These devices provide the user with the ability to enter appointments in a calendar, write notes, send and receive email, play games, watch videos, and browse websites, among other functions.
wireless network interface card (wireless NIC)
A device that connects to a computer or other digital device to transmit and receive network data over radio waves. It includes an antenna for wireless communication between networked devices
RFID reader or RFID interrogator
A device that emits electromagnectic energy to power a typical RFID tag and can transmit to and read the data stored in the tag's memory.
wireless access point (wireless AP or just AP)
A device that receives the signals and transmits signals back to wireless network interface cards (NICs), typically in a WLAN. APs connect wireless devices to a wired network such as the Internet.
modem (MOdulator/DEModulator)
A device used to convert digital signals into an analog format, and vice versa.
3G (third generation)
A digital cellular technology that can send data at up to 21 Mbps over the cellular network.
4G (fourth generation)
A digital cellular technology, often called LTE (Long Term Evolution), that can transmit and receive data at speeds over 20 Mbps when users are moving fast to well over 100 Mbps when users are moving slowly or are stationary.
Frequency Shift Keying (FSK)
A digital modulation technique that changes the frequency of the carrier signal in response to a change in the binary input signal.
Phase Shift Keying (PSK)
A digital modulation technique that changes the starting point of a wave cycle in response to a change in the binary input signal.
quadrature phase shift keying (QPSK)
A digital modulation technique that combines quadrature amplitude modulation with phase shift keying.
amplitude shift keying (ASK)
A digital modulation technique whereby a 1 bit is represented by the existence of a carrier signal, whereas a 0 bit is represented by the absence of a carrier signal
detector
A diode that receives a light-based transmission signal.
high-pass filter
A filter that passes all signals that are above a maximum threshold
low pass filter
A filter that passes all signals that are below a maximum threshold.
bandpass filter
A filter that passes all signals that are between the maximum and minimum threshold, that is, within the pass-band.
optical fiber
A glass strand, about the thickness of a human hair, that carries data signals encoded in a laser beam
constellation diagram
A graphical representation that makes it easier to visualize signals using complex modulation techniques such as QAM. It is generally used in laboratory and field diagnostic instruments and analyzers to aid in design and troubleshooting of wireless communications devices
Telecommunications Industries Association (TIA)
A group of more than 600 companies that manufacture or supply the products and services used in global communications
fixed broadband wireless
A group of wireless technologies intended for communications between fixed points such as buildings or communication towers
emitter
A laser diode or a light-emitting diode that transmits a light-based signal.
diffused transmission
A light-based transmission that relies on reflected light.
Directed transmission
A light-based transmission that requires the emitter and detector to be directly aimed at one another.
wireless local area network (WLAN)
A local area network that is not connected by wires but instead uses wireless technology. Its range extends to approximately 330 feet (100 meters) and has a data rate of 600 Mbps and higher. Today's WLANs are based on IEEE 802.11a/b/g/n/ac/ad standards.
Frequency
A measurement of radio waves that is determined by how frequently a cycle occurs
Digital Modulation
A method of encoding a digital signal onto an analog carrier wave for transmission over media that does not support direct digital signal transmission.
analog modulation
A method of encoding an analog signal onto a carrier wave.
Passband
A minimum and maximum threshold that spells out which range of frequencies will pass through a filter
Institute of Electrical and Electronics Engineers (IEEE)
A nonprofit organization that creates standards related to electrical and electronics products and devices that are adopted by manufacturers worldwide. IEEE's core purpose is to foster technological innovation and excellence for the benefit of humanity
Internet Society (ISOC)
A professional-membership organization of Internet experts that comments on policies and practices and oversees a number of other boards and task forces dealing with network policy issues
Wi-Fi Hotspot
A public Wi-Fi network that is available at many stores, coffee shops, auto repair shops, fast-food outlets, etc., for use by its customers. Individuals can also use some smartphones to create a private Wi-Fi hotspot.
Frequency Division Multiple Access (FDMA)
A radio transmission technique that divides the bandwidth of the frequency into several smaller frequency bands
adaptive array processing
A radio transmission technique that replaces a traditional antenna with an array of antenna elements.
band
A range of radio frequencies. Frequency bands are defined by each country's regulatory agencies, such as the FCC in the United States, and each range is allocated for a specific radio communications purpose.
802.16 (WiMAX)
A set of standards for fixed and mobile broadband wireless communications that allows computers to communicate at up to 75 Mbps and at distances of up to 35 miles (56 kilometers) in a point-to-point configuration. This set of standards also allows the use of both licensed and unlicensed frequencies.
electromagnetic (EM) wave
A signal composed of electrical and magnetic forces that in radio transmission usually propagates from an antenna and can be modulated to carry information
analog signal
A signal in which the intensity (amplitude or voltage) varies continuously and smoothly over a period of time
dibit
A signal unit that represents 2 bits.
Tribit
A signal unit that represents 3 bits.
Quadbit
A signal unit that represents 4 bits.
binary phase shift keying (BPSK)
A simple digital modulation technique that uses four phase changes to represent 2 bits per signal change
piconet
A small network composed of two or more Bluetooth devices that are exchanging data with each other.
ZigBee
A specification based on IEEE 802.15.4 developed by the ZigBee Alliance, an organization that creates protocols and specifications for devices used for home automation that can wirelessly control lighting, as well as security and energy systems, in homes and industries.
WiGig
A specification for connecting computers, communication, and entertainment devices over short ranges, using the 60 GHz band at multi-gigabit speeds, developed by an alliance of companies.
frequency hopping spread spectrum (FHSS)
A spread spectrum technique that uses a range of frequencies and changes frequencies during the transmission.
direct sequence spread spectrum (DSSS)
A spread spectrum technique that uses an expanded, redundant code to transmit each data bit
de jure standard
A standard that is controlled by an organization or body.
European Telecommunications Standards Institute (ETSI)
A standards body that develops telecommunications standards for use throughout Europe
Internet Engineering Task Force (IETF)
A standards body that focuses on the upper levels of telecommunications protocols and Internet technologies
circuit switching
A switching technique in which a dedicated and direct physical connection is made between two transmitting devices—for example, between two telephones during a call
amplitude modulation (AM)
A technique that changes the height of a carrier wave in response to a change in the height of the input signal.
frequency modulation (FM)
A technique that changes the number of wave cycles in response to a change in the amplitude of the input signal.
phase modulation (PM)
A technique that changes the starting point of a wave cycle in response to a change in the amplitude of the input signal. This technique is not used in analog modulation.
Forward Error Correction (FEC)
A technique that is used to correct bit errors in transmissions by sending extra redundant bits that are used to calculate which bit was lost or changed during transmission, so the receiving equipment can correct the error. This saves time in the case of single-bit errors because no re-transmission is required.
Spread Spectrum Transmission
A technique that takes a narrow signal and spreads it over a broader portion of the radio frequency band.
Code Division Multiple Access (CDMA)
A technique that uses spread spectrum technology and unique digital codes to send and receive radio transmissions
radio frequency identification (RFID)
A technology developed to replace barcodes that uses small tags placed on product packaging and boxes that can be remotely activated and read by sensors. The data about the product is then transferred directly to an information- processing system for inventory control, location tracking, and item counting.
Near Field Communication (NFC)
A technology similar and sometimes compatible with RFID that can store data that can be used to configure and activate a connection between two devices over Bluetooth or Wi-Fi. NFC tags are similar to RFID tags and can also store web addresses and may contain commands to be executed by a smartphone or tablet, such as opening a web browser and automatically entering an address
Voice over Internet Protocol (VoIP)
A technology that allows voice telephone calls to be carried over the same network used to carry computer data.
digital convergence
A technology used to transmit data as well as video signals over a television cable connection
digital subscriber line (DSL)
A technology used to transmit data at high speeds over a telephone line
Time Division Multiple Access (TDMA)
A transmission technique that divides the bandwidth into several time slot
wireless personal area network (WPAN)
A very small network that typically extends to 33 feet (10 meters) or less. Due to its limited range, WPAN technology is used mainly as a replacement for cables. See also piconet and Ultra Wide Band.
Oscillating signal
A wave that illustrates the change in a carrier signal.
sine wave
A wave that illustrates the change in a carrier signal.
Ultra Wide Band (UWB)
A wireless communications technology that allows devices to transmit data at hundreds of megabits or even gigabits per second at short distances—up to 6 feet (2 meters) at the higher speeds and up to 150 feet (50 meters) at lower speeds.
wireless metropolitan area network (WMAN)
A wireless network that covers a large geographical area such as a city or suburb. The technology is usually based on the IEEE 802.16 (WiMAX) set of standards and can span an entire city, covering distances of up to 35 miles (56 kilometers) between transmitters and receivers or repeaters.
Bluetooth
A wireless standard that enables devices to transmit data at an effective rate of 721.2 Kbps over short distances of up to 33 feet (10 meters). Bluetooth is popular for short- distance communications between wireless devices such as smartphones, laptops, speakers, headsets, printers, smartwatches, and keyboards.
light spectrum
All the different types of light that travel from the Sun to the Earth.
radio frequency (RF) communications
All types of radio communications that use radio frequency waves
International Telecommunication Union (ITU)
An agency of the United Nations that sets international telecommunications standards and coordinates global telecommunications networks and services
continuous wave (CW)
An analog or sine wave that is modulated to eventually carry information, becoming a carrier wave
carrier wave
An analog wave having a frequency that a receiver is tuned to. Although the term is commonly used to refer to any wave at a particular frequency that is used to transmit a wireless signal, technically speaking, a wave is only a carrier if some kind of data is encoded into it. Until data is encoded onto the wave, it is more correct to refer to it as a continuous wave (CW)
directional antenna
An antenna that radiates the electromagnetic waves in one direction only. As a result, it can help reduce or eliminate the effect of multi path distortion if there is a clear line of sight between the two antennas.
American Standard Code for Information Interchange (ASCII)
An arbitrary coding scheme that uses the numbers from 0 to 127 to represent alphanumeric characters and symbols.
radio wave (sometimes called radio-telephony)
An electromagnetic wave created when an electric current passes through a wire and creates a magnetic field in the space around the wire.
Unicode
An international encoding standard that is capable of supporting numeric character codes to represent all the different languages and scripts in the world, such as Arabic, Hebrew, multiple Chinese and Japanese scripts, Sanskrit, etc.
T1
An older wired technology used to transmit data over special telephone lines at 1.544 Mbps.
International Organization for Standardization (ISO)
An organization to promote international cooperation and standards in the areas of science, technology, and economics
cycle
An oscillating sine wave that completes one full series of movements.
Unlicensed National Information Infrastructure (U-NII)
An unregulated band approved by the FCC in 1996 to provide for short-range, high-speed wireless digital communications
Industrial, Scientific and Medical (ISM) band
An unregulated radio frequency band approved by the FCC in 1985
Digital Signal
Data that is discrete or separate.
Packet Switching
Data transmission that is broken into smaller units.
RFID tag
Device embedded in or attached to an object that contains a chip and antenna. The chip is powered by the energy emitted by an RFID reader and can then transmit information contained in its memory back to the reader
smartwatch
Device that functions as a regular watch but also connects via Bluetooth to the owner's smartphone. Some of these devices can run applications that link directly to the same app on the smartphone, while others only display email messages, notifications, and calls from the smartphone. A few models are equipped with speakers and microphones that allow you to answer a call without having to use the smartphone and others give you the ability to respond to text messages using your voice, directly from the watch.
wireless residential gateway (often called a wireless router)
Device used to set up a Wi-Fi network in a home or small office. These devices are used to connect a home or small office to the Internet and are often supplied by the service provider, integrated with a cable modem.
Voltage
Electrical pressure
guard band
Frequency space in which no signal is transmitted. Intended to prevent interference between two transmitters using adjacent channels
wireless communications
Generally refers to any type of communications that does not require the use of wires or cables. In this sense, smoke signals and police radio may be understood as forms of wireless communications, but for the purpose of this book, wireless communications is defined as the wireless transmission of digital data while connected to some type of network
Consortia
Industry-sponsored organizations that have the goal of promoting a specific technology
electromagnetic interference (EMI)
Interference with a radio signal; also called noise
infrared light
Light that is next to visible light on the light spectrum and that has many of the same characteristics as visible light.
switching
Moving a signal from one wire or frequency to another.
PN code
Pseudo random code; a code that appears to be a random sequence of 1's and 0's but actually repeats itself. Used in CDMA cellular telephone technology.
Official standards
See de jure standards.
unregulated bands
See license exempt spectrum.
non-return-to-zero-level (NRZ-L)
See polar non-return-to-zero.
Crosstalk
Signals from close frequencies that may interfere with other signals.
radio module
Small radio transceiver built onto microprocessor chips and embedded into Bluetooth devices, which enable them to communicate.
link manager
Special software in Bluetooth devices that helps identify other Bluetooth devices, creates the links between them, and sends and receives data
harmonics
Stray oscillations that result from the process of modulating a wave and that fall outside the range of frequencies used for transmission. Harmonics also occur when a signal goes through a mixer and must be filtered out at several points before the signal is finally fed to the antenna for transmission.
line of sight
The direct alignment as required in a directed transmission.
radio frequency spectrum
The entire range of all radio frequencies that exist
Wavelength
The length of a wave as measured between two positive or negative peaks or between the starting point of one wave and the starting point of the next wave.
signal-to-noise ratio (SNR)
The measure of signal strength relative to the background noise.
bits per second (bps)
The number of bits that can be transmitted per second. digital data.
Hertz (Hz)
The number of cycles per second.
Internet Architecture Board (IAB)
The organization responsible for defining the overall architecture of the Internet, providing guidance and broad direction to the IETF. The IAB also serves as the technology advisory group to the Internet Society and oversees a number of critical activities in support of the Internet.
intermediate frequency (IF)
The output signal that results from the modulation process.
Federal Communications Commission (FCC)
The primary U.S. regulatory agency for telecommunications.
Modulation
The process of changing a carrier signal.
sidebands
The range of frequencies, above and below the carrier frequency of the transmitted signal, in which a signal is transmitted
phase
The relative starting point of a wave, in degrees, beginning at 0 degrees.
hopping code
The sequence of changing frequencies used in FHSS.
Half-duplex transmission
Transmission that occurs in both directions but only one way at a time.
Simplex transmission
Transmission that occurs in only one direction.
narrow-band transmission
Transmission that uses one radio frequency or a very narrow portion of the frequency spectrum.
full-duplex transmission
Transmissions in which data flows in either direction simultaneously.
license exempt spectrum
Unregulated radio frequency bands that are available in the United States to any users without a license
Multipath Distortion
What occurs when the same signal reflects and arrives at the receiver's antenna from several different directions and at different times.
packet
a smaller segment of the transmitted signal
Institute of Electrical and Electronics Engineers (IEEE)
a standards body that establishes standards for telecommunications
noise
see electromagnetic interference (EMI)
amplitude
the height of a carrier wave
attenuation
the loss of signal strength
baud rate
the number of times that a carrier signal changed per second
bandwidth
the range of frequencies that can be transmitted