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Understanding Waves and Wireless Technology

Learn about waves, frequencies, and wireless signals in this comprehensive guide. Explore the properties and behaviors of different wave types.

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Understanding Waves and Wireless Technology

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  1. Ch. 2 – 802.11 and NICsPart 3 – 802.11 PHY Cisco Fundamentals of Wireless LANs version 1.1 Rick Graziani Cabrillo College Spring 2005 Note: Includes information which is in Cisco online curriculum Module 2 and Module 3

  2. Topics • Overview of Waves • EM Spectrum • 802.11 PHY Physical Layer Technologies • PLCP • PMD • 802.11 Technologies • FHSS – 802.11 • DSSS- 802.11 • HR/DSSS – 802.11b • OFDM – 802.11a • ERP – 802.11g • Comparing 802.11a, 802.11b, 802.11g Rick Graziani graziani@cabrillo.edu

  3. Overview of Waves

  4. Overview of Waves • Wave is a “disturbance or variation” that travels through a medium. • The medium through which the wave travels may experience some local oscillations as the wave passes, but the particles in the medium do not travel with the wave. • Just like none of the individual people in the stadium are carried around when they do the wave, they all remain at their seats. Rick Graziani graziani@cabrillo.edu

  5. Waves • Waves are one way in which energy can move from one place to another. • The waves that you see at the beach are the result of the kinetic energy of water particles passing through the water. • Other types of energy (such as light, heat, and radio waves) can travel in this way as well. www.ewart.org.uk Rick Graziani graziani@cabrillo.edu

  6. Waves • The distance between 2 peaks (or 2 troughs) is called a wavelength • The deepest part of a trough or the highest part of a peak is called the amplitude • The frequency is the number of wavelengths that pass by in 1 second www.ewart.org.uk Rick Graziani graziani@cabrillo.edu

  7. Longitudinal Waves • Longitudinal sound waves in the air behave in much the same way. • As the sound wave passes through, the particles in the air oscillate back and forth from their equilibrium positions but it is the disturbance that travels, not the individual particles in the medium. • Rick talks in a loud voice. • When he talks he causes the air near his mouth to compress. • A compression wave then passes through the air to the ears of the people around him. • A longitudinal sound wave has to travel through something - it cannot pass through a vacuum because there aren't any particles to compress together. • It has a wavelength; a frequency and an amplitude. www.ewart.org.uk Rick Graziani graziani@cabrillo.edu

  8. Transverse Waves interactive activity 3.1.1 • Transverse waves on a string are another example. • The string is displaced up and down, as the wave travels from left to right, but the string itself does not experience any net motion. • A light wave is a transverse wave. • If you look at the waves on the sea they seem to move in one direction .... towards you. • However, the particles that make up the wave only move up and down. • Look at the animation, on the right, although the wave seems to be moving from left to right the blue particle is only moving up and down. Rick Graziani graziani@cabrillo.edu

  9. Sine waves • The sine wave is unique in that it represents energy entirely concentrated at a single frequency. • An ideal wireless signal has a sine waveform • With a frequency usually measured in cycles per second or Hertz (Hz). • A million cycles per second is represented by megahertz (MHz). • A billion cycles per second represented by gigahertz (GHz). Rick Graziani graziani@cabrillo.edu

  10. Sine waves • Amplitude – The distance from zero to the maximum value of each alternation is called the amplitude. • The amplitude of the positive alternation and the amplitude of the negative alternation are the same. • Period – The time it takes for a sine wave to complete one cycle is defined as the period of the waveform. • The distance traveled by the sine wave during this period is referred to as its wavelength. • Wavelength – Indicated by the Greek lambda symbol λ. • It is the distance between one value to the same value on the next cycle. • Frequency – The number of repetitions or cycles per unit time is the frequency, typically expressed in cycles per second, or Hertz (Hz). Go to interactive activity 3.1.2 Amplitude and Frequency Rick Graziani graziani@cabrillo.edu

  11. Relationship between time and frequency • The inverse relationship between time (t), the period in seconds, and frequency (f), in Hz, is indicated by the following formulas: t = 1/f (time = 1 / frequency) f = 1/t (frequency = 1 / time) Examples: 1 second • t = 1/f 1 second = 1 / 1 Hz (1 cycle per second) • f = 1/t 1 Hz = 1 / 1 second ½ second • t = 1/f ½ second = 1 / 2 Hz (2 cycles per second) • f = 1/t 2 Hz = 1 / ½ second 1/10,000,000th of a second • t = 1/f 1/10,000,000th of a second = 1 / 10,000,000 Hz (cycles/sec) = 1 / 10 MHz • f = 1/t 10 MHz = 1 / 1/10,000,000th of sec Rick Graziani graziani@cabrillo.edu

  12. Sine waves • One full period or cycle of a sine wave is said to cover 360 degrees (360°). • It is possible for one sine wave to lead or lag another sine wave by any number of degrees, except zero or 360. • When two sine waves differ by exactly zero° or 360°, the two waves are said to be in phase. • Two sine waves that differ in phase by any other value are out of phase, with respect to each other. Go to interactive activity 3.1.2 Amplitude, Frequency, and Phase 180° Phase Shift Rick Graziani graziani@cabrillo.edu

  13. Analog to digital conversion • Analog wave amplitudes are sampled at specific instances in time. • Each sample is assigned a discrete value. • Each discrete value is converted to a stream of bits. Go to interactive activity 3.1.3 Rick Graziani graziani@cabrillo.edu

  14. Bandwidth • There are two common ways of looking at bandwidth: • Analog bandwidth • Digital bandwidth • Analog bandwidth • Analog bandwidth can refer to the range of frequencies . • Analog bandwidth is described in units of frequency, or cycles per second, which is measured in Hz. • There is a direct correlation between the analog bandwidth of any medium and the data rate in bits per second that the medium can support. Rick Graziani graziani@cabrillo.edu

  15. Bandwidth • Digital bandwidth • Digital bandwidth is a measure of how much information can flow from one place to another, in a given amount of time. • Digital bandwidth is measured in bits per second. • When dealing with data communications, the term bandwidth most often signifies digital bandwidth. Rick Graziani graziani@cabrillo.edu

  16. EM (Electromagnetic) Spectrum

  17. Basics of EM waves • EM (Electromagnetic)spectrum a set of all types of radiation when discussed as a group. • Radiation is energy that travels in waves and spreads out over distance. • The visible light that comes from a lamp in a house and radio waves that come from a radio station are two types of electromagnetic waves. • Other examples are microwaves, infrared light, ultraviolet light, X-rays, and gamma rays. Rick Graziani graziani@cabrillo.edu

  18. Basics of EM waves • All EM waves travel at the speed of light in a vacuum and have a characteristic wavelength (λ) and frequency (f), which can be determined by using the following equation: • c = λ x f, where c = the speed of light (3 x 108 m/s) • Wavelength x Frequency = Speed of light • Speed of light = 180,000 miles/sec or 300,000 kilometers/sec or 300,000,000 meters/sec Rick Graziani graziani@cabrillo.edu

  19. Basics of EM waves • wavelength (λ), frequency (f), speed of light (c) • A wave of 1 cycle per second, has a wavelength of 300,000,000 meters or 300,000 kilometers or 180,000 miles. • Speed of a bit doesn’t go beyond the speed of light, Dr. Einstein says we all go “poof” (my words, not his) • Speed is a function of increasing the number of waves, bits, in the same amount of space, I.e. bits per second 300,000 kilometers or 180,000 miles 150,000 km 150,000 km Rick Graziani graziani@cabrillo.edu

  20. Basics of EM waves • Other interesting calculations Rick Graziani graziani@cabrillo.edu

  21. Size of a Wave

  22. Size of a Wave • It’s important to visualize the physical size of a wireless signal because the physical size determines: • How that signal interacts with its environment • How well it is propagated from antenna to antenna • The physical size of the antenna (the smaller the signal size, the smaller the antenna) Rick Graziani graziani@cabrillo.edu

  23. Speed of Light Speed of light = 186,000 miles/sec or 300,000,000 meters/sec (approx.) Start here End here 1 second 186,000 miles Mile: 0 Mile: 186,000 1 mile • 5,280 feet per mile; so 186,000 miles = 982,080,000 feet • 63,360 inches per mile; so 186,000 miles = 11,784,960,000 inches Rick Graziani graziani@cabrillo.edu

  24. Wavelength http://eosweb.larc.nasa.gov/EDDOCS/wavelength.html All About Wavelength • Speed of the wave = Frequency x Wavelength • Wavelength = Speed of the wave or speed of light / Frequency • Speed of light = • 186,000 miles/sec or • 982,080,000 feet/sec or • 11,784,960,000 inches/sec • Wavelength = Speed of the wave or speed of light/ Frequency • 10.93 feet = 982,080,000 feet per sec / 90,000,000 cycles per sec Rick Graziani graziani@cabrillo.edu

  25. Speed of Light Speed of light = 186,000 miles/sec Mile: 0, beginning of rope Mile: 186,000, end of rope Length of rope 186,000 miles long 0 seconds After 1/2 second After 1 second 0 second 1 second 1 second • Length of rope 186,000 miles long traveling at the speed of light, 186,000 miles/second • In 1 second we would see the entire length of rope go by. Rick Graziani graziani@cabrillo.edu

  26. Speed of Light – 1 Hz Speed of light = 186,000 miles/sec Mile: 0, beginning of rope Mile: 186,000, end of rope Length of rope 186,000 miles long 186,000 miles 0 second 1 second • So, if 1 Hz is 1 cycle per second, traveling at the speed of light…. • The length of the wave would be 186,000 miles long (300,000,000 meters). Rick Graziani graziani@cabrillo.edu

  27. Speed of Light – 2 Hz Speed of light = 186,000 miles/sec Mile: 0, beginning of rope Mile: 186,000, end of rope Length of rope 186,000 miles long 93,000 miles 0 second 1 second • 2 Hz is 2 cycles per second, traveling at the speed of light…. • The length of each wave would be 186,000/2 or 93,000 miles long (150,000,000 meters). Rick Graziani graziani@cabrillo.edu

  28. Speed of Light – Let’s do inches 11,784,960,000 inches 6,000,000,000 inches • 11,784,960,000 inches in a mile • 1 Hz wave = 11,784,960,000 inches (11 billion inches) • 2 Hz wave = 11,784,960,000 / 2 = 6 billion inches (give or take) • What would a wave the size of 11 GHz wave be? Rick Graziani graziani@cabrillo.edu

  29. Speed of Light – Lets do inches Mile: 186,000, end of rope Length of rope 186,000 miles long Mile: 0, beginning of rope Length of rope 11.8 billion inches long 1 2 11 billion … 1 inch 0 second 1 second • What would a wave the size of 11 GHz wave be? • Size of the rope divided by the number of pieces = size of each piece • About 1 inch! (11,784,960,000 in. per sec / 11,000,000,000 pieces or cycles or Hz) • Same as slicing up the 186,000 mile rope into 11 billion equal pieces. • Each piece is 1 inch, 11 billion pieces equal 11 billion inches, the size of our rope traveling at 186,000 miles per second. Rick Graziani graziani@cabrillo.edu

  30. Speed of Light – Lets do inches Mile: 186,000, end of rope Length of rope 186,000 miles long Mile: 0, beginning of rope Length of rope 11.8 billion inches long 1 2 1 billion … 11.8 inches 0 second 1 second • What would a wave the size of 1 GHz wave be? • 11 inches! (Actually, 11.8 inches because we rounded off values.) (approx.: 11,784,960,000 inches per sec / 1,000,000,000 cycles per sec) • Same as slicing up the 186,000 mile rope into 1 billion equal pieces. • Each piece is 11 inches, 1 billion pieces equal 11 billion inches, the size of our rope traveling at 186,000 miles per second. Rick Graziani graziani@cabrillo.edu

  31. RADM Grace Hopper • Grace Hopper, “Mother of Cobol” • The size of a nanosecond, 11.8 inches • The distance the speed of light travels in a billionth of a second. Rick Graziani graziani@cabrillo.edu

  32. Size of a 2.4 GHz WLAN wave Mile: 186,000, end of rope Length of rope 186,000 miles long Mile: 0, beginning of rope Length of rope 11.8 billion inches long 1 2 2.4 billion … 4.8 inches 0 second 1 second • Same as slicing up the 186,000 mile rope into 2.4 billion equal pieces. • Each piece is 4.8 inches or 12 cm (.12 meters) (approx.: 11,784,960,000 inches per sec / 2,450,000,000 cycles per sec) • 2.4 billion pieces equal 11 billion inches, the size of our rope traveling at 186,000 miles per second. Rick Graziani graziani@cabrillo.edu

  33. Size of a 5.8 GHz WLAN wave Mile: 186,000, end of rope Length of rope 186,000 miles long Mile: 0, beginning of rope Length of rope 11.8 billion inches long 1 2 5.8 billion … 2 inches 0 second 1 second • Same as slicing up the 186,000 mile rope into 5.8 billion equal pieces. • Each piece is 2 inches or 5 cm (.05 meters) (approx.: 11,784,960,000 inches per sec / 5,800,000,000 cycles per sec) • 5.8 billion pieces equal 11 billion inches, the size of our rope traveling at 186,000 miles per second. Rick Graziani graziani@cabrillo.edu

  34. Basics of EM Waves

  35. Basics of EM waves • EM waves exhibit the following properties: • reflection or bouncing • refraction or bending • diffraction or spreading around obstacles • scattering or being redirected by particles • This will be discussed in greater detail later in this module. • Also, the frequency and the wavelength of an EM wave are inversely proportionally to one another. Rick Graziani graziani@cabrillo.edu

  36. Basics of EM waves • There are a number of properties that apply to all EM waves, including: • Direction • Frequency • Wavelength • Power • Polarization • Phase. Rick Graziani graziani@cabrillo.edu

  37. EM Spectrum Chart • One of the most important diagrams in both science and engineering is the chart of the EM spectrum . • The typical EM spectrum diagram summarizes the ranges of frequencies, or bands that are important to understanding many things in nature and technology. • EM waves can be classified according to their frequency in Hz or their wavelength in meters. • The most important range for this course is the RF (Radio Frequency) spectrum. Rick Graziani graziani@cabrillo.edu

  38. EM Spectrum Chart • The RF spectrum includes several frequency bands including: • Microwave • Ultra High Frequencies (UHF) • Very High Frequencies (VHF) • This is also where WLANs operate. • The RF spectrum ranges from 9 kHz to 300 GHz. • Consists of two major sections of the EM spectrum: (RF Spectrum) • Radio Waves • Microwaves. • The RF frequencies, which cover a significant portion of the EM radiation spectrum, are used heavily for communications. • Most of the RF ranges are licensed, though a few key ranges are unlicensed. Rick Graziani graziani@cabrillo.edu

  39. EM Spectrum Chart Nasa.gov Rick Graziani graziani@cabrillo.edu

  40. Nasa.gov Rick Graziani graziani@cabrillo.edu

  41. www.britishlibrary.net Rick Graziani graziani@cabrillo.edu

  42. Licensed Frequencies • Frequency bands have a limited number of useable different frequencies, or communications channels. • Many parts of the EM spectrum are not useable for communications and many parts of the spectrum are already used extensively for this purpose. • The electromagnetic spectrum is a finite resource. • One way to allocate this limited, shared resource is to have international and national institutions that set standards and laws as to how the spectrum can be used. • In the US, it is the FCC that regulates spectrum use. • In Europe, the European Telecommunications Standards Institute (ETSI) regulates the spectrum usage. • Frequency bands that require a license to operate within are called the licensed spectrum. • Examples include amplitude modulation (AM) and frequency modulation (FM) radio, ham or short wave radio, cell phones, broadcast television, aviation bands, and many others. • In order to operate a device in a licensed band, the user must first apply for and be granted the appropriate license. Rick Graziani graziani@cabrillo.edu

  43. ISM (Industrial, Scientific, and Medical) & U-NII (Unlicensed National Information Infrastructure) • Some areas of the spectrum have been left unlicensed. • This is favorable for certain applications, such as WLANs. • An important area of the unlicensed spectrum is known as the industrial, scientific, and medical (ISM) bands and the U-NII (Unlicensed National Information Infrastructure) • ISM – 802.11b, 802.11g • U-NII – 802.11a • These bands are unlicensed in most countries of the world. • The following are some examples of the regulated items that are related to WLANs: • The FCC has defined eleven 802.11b DSSS channels and their corresponding center frequencies. ETSI has defined 13. • The FCC requires that all antennas that are sold by a spread spectrum vendor be certified with the radio with which it is sold. • Unlicensed bands are generally license-free, provided that devices are low power. • After all, you don’t need to license your microwave oven or portable phone. Rick Graziani graziani@cabrillo.edu

  44. Fourier synthesis (More than we need…) • When two EM waves occupy the same space, their effects combine to form a new wave of a different shape. • For example, air pressure changes caused by two sound waves added together. • Jean Baptiste Fourier is responsible for one of the great mathematical discoveries. • He proved that a special sum of sine waves, of harmonically related frequencies, could be added together to create any wave pattern. • Harmonically related frequencies are simply frequencies that are multiples of some basic frequency. • Use the interactive activity to create multiple sine waves and a complex wave that is formed from the additive effects of the individual waves. • Finally, a square wave, or a square pulse, can be built by using the right combination of sine waves. • The importance of this will be clarified when modulation is discussed. Rick Graziani graziani@cabrillo.edu

  45. Fourier synthesis Go to interactive activity 3.3.3 Whatis.com • Fourier synthesis is a method of electronically constructing a signal with a specific, desired periodic waveform. • It works by combining a sine wave signal and sine-wave or cosine-wave harmonics (signals at multiples of the lowest, or fundamental, frequency) in certain proportions. Rick Graziani graziani@cabrillo.edu

  46. http://www.sfu.ca/sonic-studio/handbook/Fourier_Synthesis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Fourier_Synthesis.html Sound Example:Addition of the first 14 sine wave harmonics resulting in the successive approximation of a sawtooth wave. Rick Graziani graziani@cabrillo.edu

  47. 802.11 Physical Layer Technologies PLCP PMD Note: The information presented here is just to introduce these terms and concepts. Many of the “how’s” and “why’s” are beyond the scope of this material. Don’t get lost in the detail!

  48. 802.11 Physical Layer Technologies • We have looked at the data link layer, now we will look at the physical layer. • As you can see there are multiple physical layer technologies involved with both similarities and differences between them. • The job of the PHYs is to provide the wireless transmission mechanisms for the MAC. • By keeping the PHY transmission mechanisms independent of the MAC it allows for advances in both of these areas. Rick Graziani graziani@cabrillo.edu

  49. 802.11 Physical Layer Technologies • The physical layer is divided into two sublayers: • PLCP (Physical Layer Convergence Procedure) • PMD (Physical Medium Dependent) • All of this is needed to help ensure that the data goes from the receiver to the transmitter over this “hostile” wireless environment with noise, and all kinds of “mean, nasty ugly things”. (Arlo Guthrie) Rick Graziani graziani@cabrillo.edu

  50. 802.11 Physical Layer Technologies • PLCP (Physical Layer Convergence Procedure) • All PLCPs provide the interface to transfer data octets between the MAC and the PMD. • “Primitives” (fields) that tell the PMD when to begin and end communications. • The PCLP is the “handshaking layer” that enables the MAC protocol data units (MPDUs), fancy name for MAC frame, to be transmitted between the MAC over the PMD. Rick Graziani graziani@cabrillo.edu

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