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Wireless# Guide to Wireless Communications

Chapter 3

Understanding Radio Frequency Communications

Wireless# Guide to Wireless Communications

Objectives

  • List the components of a radio system
  • Describe how different factors affect the design of a radio system
  • Discuss why standards are beneficial and list the major telecommunications standards organizations
  • Explain the radio frequency spectrum

Wireless# Guide to Wireless Communications

Components of a Radio System

  • Components include:
  • Filters
  • Mixers
  • Amplifiers
  • Antennas

Wireless# Guide to Wireless Communications

Filters

  • Filter
  • Removes unwanted RF signals
  • RF filter
  • Either passes or rejects a signal based on frequency
  • Types of filters
  • Low-pass filter
  • High-pass filter
  • Bandpass filter

Wireless# Guide to Wireless Communications

Filters (continued)

Wireless# Guide to Wireless Communications

Filters (continued)

  • Filters are also found in transmitters
  • Used to eliminate some unwanted frequencies
  • That result from the process of modulating the signal before transmission
  • Intermediate frequency (IF) signal
  • Resulting output from the modulation process
  • IF signal is filtered through a bandpass filter
  • To remove any undesired high- or low-frequency signals

Wireless# Guide to Wireless Communications

Filters (continued)

Wireless# Guide to Wireless Communications

Mixers

  • Combine two radio frequency inputs to create a single output
  • Output is in the range of the highest sum and the lowest difference of the two frequencies
  • Sum and differences are known as the sidebands of the frequency carrier
  • Shield transmitted signal from “stray” signals
  • Used to convert an input frequency to a specific desired output frequency

Wireless# Guide to Wireless Communications

Mixers (continued)

Wireless# Guide to Wireless Communications

Mixers (continued)

Wireless# Guide to Wireless Communications

Amplifiers

  • Increase the amplitude of an RF signal
  • RF signals tend to lose intensity (amplitude)
  • When they move through circuits, air, or space
  • Amplifier is an active device
  • Must be supplied with electricity
  • Increases a signal’s intensity or strength
  • By using the input signal to control a circuit that “shapes” the output
  • To reflect the shape of the input signal exactly

Wireless# Guide to Wireless Communications

Amplifiers (continued)

Wireless# Guide to Wireless Communications

Antennas

  • Transmit or receive an RF signal

Wireless# Guide to Wireless Communications

Antennas (continued)

Wireless# Guide to Wireless Communications

Design of a Radio System

  • Designers of radio communications systems
  • Need to consider how the systems will be used

Wireless# Guide to Wireless Communications

Multiple Access

  • Only a limited number of frequencies are available for radio transmission
  • Conserving the use of frequencies is important
  • Conserving a frequency
  • Share a frequency among several individual users
  • Methods that allow multiple access
  • Frequency Division Multiple Access (FDMA)
  • Time Division Multiple Access (TDMA)
  • Code Division Multiple Access (CDMA)

Wireless# Guide to Wireless Communications

Multiple Access (continued)

Wireless# Guide to Wireless Communications

Multiple Access (continued)

  • Frequency Division Multiple Access (FDMA)
  • Divides the bandwidth of a channel into several smaller frequencies bands
  • Cable television is transmitted using FDMA
  • Crosstalk
  • Causes interference on the other frequency and may disrupt the transmission

Wireless# Guide to Wireless Communications

Multiple Access (continued)

Wireless# Guide to Wireless Communications

Multiple Access (continued)

  • Time Division Multiple Access (TDMA)
  • Divides the transmission time into several slots
  • Each user is assigned the entire frequency for the transmission
  • For a fraction of time on a fixed, rotating basis
  • Advantages
  • Uses the bandwidth more efficiently
  • Allows both data and voice transmissions to be mixed using the same frequency

Wireless# Guide to Wireless Communications

Multiple Access (continued)

Wireless# Guide to Wireless Communications

Multiple Access (continued)

  • Code Division Multiple Access (CDMA)
  • Used primarily for cellular telephone communications
  • Uses direct sequence spread spectrum (DSSS)
  • With a unique digital spreading code (PN code)
  • Before transmission occurs
  • High-rate PN code is combined with the data to be sent
  • Imprints a unique address on the data
  • The longer the code is, the more users will be able to share the same channel
  • Number of chips in the code
  • Determines the amount of spreading or bandwidth

Wireless# Guide to Wireless Communications

Multiple Access (continued)

Wireless# Guide to Wireless Communications

Multiple Access (continued)

Wireless# Guide to Wireless Communications

Multiple Access (continued)

Wireless# Guide to Wireless Communications

Multiple Access (continued)

  • Code Division Multiple Access (CDMA) (continued)
  • Advantages
  • Can carry up to three times the amount of data as TDMA
  • Transmissions are much harder to eavesdrop on
  • A would-be eavesdropper must also know the exact chip in which the transmission starts

Wireless# Guide to Wireless Communications

Transmission Direction

  • Simplex transmission
  • Occurs in only one direction
  • Rarely used in wireless communication today
  • Except for broadcast radio and television
  • Half-duplex transmission
  • Sends data in both directions
  • But only one way at a time
  • Used in consumer devices such as citizens band (CB) radios or walkie-talkies
  • User must hold down the “talk” button while speaking

Wireless# Guide to Wireless Communications

Transmission Direction (continued)

Wireless# Guide to Wireless Communications

Transmission Direction (continued)

Wireless# Guide to Wireless Communications

Transmission Direction (continued)

  • Full-duplex transmission
  • Allows data to flow in both directions simultaneously
  • Example: A telephone system
  • If the same antenna is used for wireless transmission and reception
  • A filter can be used to handle full-duplex transmissions
  • Full-duplex wireless communications equipment
  • Sends and receives on different frequencies

Wireless# Guide to Wireless Communications

Transmission Direction (continued)

Wireless# Guide to Wireless Communications

Transmission Direction (continued)

Wireless# Guide to Wireless Communications

Switching

  • Involves moving the signal from one wire or frequency to another
  • Circuit switching
  • Type of switching used by telephone systems
  • A dedicated and direct physical connection is made between the caller and the recipient
  • Direct connection lasts until the end of the call
  • Packet switching
  • Used by data networks
  • Data transmissions are broken into packets
  • Each packet is sent independently

Wireless# Guide to Wireless Communications

Switching (continued)

Wireless# Guide to Wireless Communications

Switching (continued)

Wireless# Guide to Wireless Communications

Switching (continued)

  • Packet switching advantages
  • Allows better utilization of the network
  • Allows multiple computers to share the same line or frequency
  • If a transmission error occurs
  • It usually affects only one or a few packets

Wireless# Guide to Wireless Communications

Signal Strength

  • Strength of the signal in a radio system
  • Must be sufficient for the signal to reach its destination
  • With enough amplitude to be picked up by the antenna
  • And for the information to be extracted from it
  • Electromagnetic interference (EMI)
  • One factor that affects radio signal strength
  • Also called noise
  • Signal-to-noise ratio (SNR)
  • Compares signal strength with background noise

Wireless# Guide to Wireless Communications

Signal Strength (continued)

Wireless# Guide to Wireless Communications

Signal Strength (continued)

Wireless# Guide to Wireless Communications

Signal Strength (continued)

  • When signal strength falls near the level of noise
  • Interference can take place
  • To reduce the interference of noise
  • Boost the strength of the signal
  • Use of filters when receiving the signal
  • Attenuation
  • A loss of signal strength
  • Multipath distortion
  • As a radio signal is transmitted, the electromagnetic waves spread out

Wireless# Guide to Wireless Communications

Signal Strength (continued)

Wireless# Guide to Wireless Communications

Signal Strength (continued)

Wireless# Guide to Wireless Communications

Signal Strength (continued)

Wireless# Guide to Wireless Communications

Signal Strength (continued)

  • Directional antenna
  • Used to minimize multipath distortion
  • Radiates electromagnetic waves in one direction only
  • Other methods to reduce multipath distortion
  • Use an amplifier in front of receiver to increase SNR
  • Transmit the same signal on separate frequencies

Wireless# Guide to Wireless Communications

Understanding Standards

  • Standards for telecommunications have been in place almost since the beginning of the industry

Wireless# Guide to Wireless Communications

The Need For Standards

  • Standards
  • Commonly accepted technical specifications
  • Telecommunications requires standards
  • For the design, implementation, and operation of the equipment
  • A lack of standards between devices would prevent communications from taking place

Wireless# Guide to Wireless Communications

Advantages and Disadvantages of Standards

  • Advantages
  • Guarantee device interoperability
  • Create competition
  • Competition results in lower costs for consumers and improvements in products
  • Competition also results in lower costs for manufacturers
  • Help consumers protect their investment in equipment
  • Disadvantages
  • Can be a threat to industries in large countries
  • Although standards are intended to create unity
  • They can have the opposite effect

Wireless# Guide to Wireless Communications

Types of Standards

  • De Facto
  • Not really standards at all
  • Common practices that industry follows
  • De jure
  • Also called official standard
  • Controlled by an organization or body
  • Process for creating standards can be very involved
  • Consortia
  • Industry-sponsored organizations that promote a specific technology

Wireless# Guide to Wireless Communications

Telecommunications Standards Organizations

  • United States Standards Groups
  • American National Standards Institute (ANSI)
  • Electronic Industries Alliance (EIA)
  • Telecommunications Industries Association (TIA)
  • Internet Engineering Task Force (IETF)
  • Internet Architecture Board (IAB)
  • Internet Society (ISOC)
  • Institute of Electrical and Electronics Engineers (IEEE)
  • Multinational Standards Groups
  • European Telecommunications Standards Institute (ETSI)

Wireless# Guide to Wireless Communications

Telecommunications Standards Organizations (continued)

  • International Standards Groups
  • International Telecommunications Union (ITU)
  • International Organization for Standardization (ISO)

Wireless# Guide to Wireless Communications

Telecommunications Standards Organizations (continued)

Wireless# Guide to Wireless Communications

Regulatory Agencies

  • Enforcing telecommunications regulations is important
  • Regulations must be enforced by an outside agency
  • Federal Communications Commission (FCC)
  • Primary regulatory agency for telecommunications in the United States
  • Responsibilities
  • Develops and implements regulatory programs
  • Processes applications for licenses and other filings
  • Analyzes complaints and conducts investigations
  • Represents the United States in negotiations
  • Regulates radio and television broadcast stations

Wireless# Guide to Wireless Communications

Radio Frequency Spectrum

  • Radio frequency spectrum
  • Entire range of all radio frequencies that exist
  • Range extends from 10 KHz to over 30 GHz
  • Spectrum is divided into 450 different sections (bands)
  • Radio frequencies of other common devices include:
  • Garage door openers, alarm systems: 40 MHz
  • Baby monitors: 49 MHz
  • Radio-controlled airplanes: 72 MHz
  • Radio-controlled cars: 75 MHz
  • Wildlife tracking collars: 215 MHz–220 MHz
  • Global positioning system: 1.227 GHz and 1.575 GHz

Wireless# Guide to Wireless Communications

Radio Frequency Spectrum (continued)

Wireless# Guide to Wireless Communications

Radio Frequency Spectrum (continued)

Wireless# Guide to Wireless Communications

Radio Frequency Spectrum (continued)

  • International spectrum allocations are established by the ITU
  • License exempt spectrum
  • Unregulated bands
  • Radio spectra available without charge to any users without a license
  • Devices from different vendors may attempt to use the same frequency (disadvantage)

Wireless# Guide to Wireless Communications

Radio Frequency Spectrum (continued)

Wireless# Guide to Wireless Communications

Radio Frequency Spectrum (continued)

  • Recent developments that have had an impact on the crowded radio frequency spectrum
  • Adaptive array processing
  • Replaces a traditional antenna with an array of antenna elements
  • Ultra-wideband transmission (UWB)
  • Uses low-power, precisely timed pulses of energy
  • That operate in the same frequency spectrum as low-end noise

Wireless# Guide to Wireless Communications

Summary

  • Radio frequency system hardware components
  • Filters, mixers, amplifiers, and antennas
  • Filter is used either to accept or block a radio frequency signal
  • Mixer combines two inputs to create a single output
  • Amplifier increases a signal’s intensity or strength
  • Multiple access methods
  • FDMA
  • TDMA
  • CDMA

Wireless# Guide to Wireless Communications

Summary (continued)

  • Types of data flow
  • Simplex
  • Half-duplex
  • Full-duplex
  • Switching involves moving the signal from one wire or frequency to another
  • Electromagnetic interference (EMI) is sometimes called noise
  • Signal-to-noise ratio (SNR)
  • Measure of signal strength relative to background noise

Wireless# Guide to Wireless Communications

Summary (continued)

  • Standards for telecommunications
  • In place almost since the beginning of the industry
  • Radio frequency spectrum
  • The entire range of all radio frequencies that exist
  • Recent developments that have had an impact on the crowded radio frequency spectrum
  • Adaptive array processing
  • Ultra-wideband transmission

Wireless# Guide to Wireless Communications