wireless systems and networks radio frequency
- 1. College of Education School of Continuing and Distance Education 2014/2015 – 2016/2017 DCIT 413 Wireless Systems and Networks Week 3 – Radio Frequency Communications Lecturer: Prof F.A. Katsriku Contact Information: fkatsriku@ug.edu.gh
- 2. Goals and Objectives • At the end of the session, the student will be able to: – List the components of a radio system – Describe the factors that affect the design of a radio system – Discuss why standards are beneficial and list the major telecommunications standards organizations – Explain the radio frequency spectrum Dr Jamal-Deen Abdulai, CSD Slide 2
- 3. Dr Jamal-Deen Abdulai, CSD Session Outline • Topics to be covered in this session are: – Components of a Radio System – Multiple Access Technologies – Transmission Direction – Understanding Standards – Telecommunications Standards Organizations – Regulatory Agencies – Radio Frequency Spectrum Slide 3
- 4. Dr Jamal-Deen Abdulai, CSD Components of a Radio System • Components include: – Filters – Mixers – Amplifiers – Antennas Slide 4
- 5. Dr Jamal-Deen Abdulai, CSD Filters • Filter: removes unwanted RF signals • RF filter – Either passes or rejects a signal based on frequency • Types of filters – Low-pass filter: maximum frequency is set and all signals below that value are allowed – High-pass filter: minimum frequency is set and all signals above that level are allowed – Bandpass filter: sets a range called a passband and signals that fall within the passband are allowed Slide 5
- 6. Dr Jamal-Deen Abdulai, CSD Filters Figure 3-2 Low-pass filter Figure 3-3 High-pass filter Figure 3-4 Bandpass filter Slide 6
- 7. Dr Jamal-Deen Abdulai, CSD Filters • Filters are also found in transmitters – Used to eliminate some unwanted frequencies called harmonic oscillations • 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 Slide 7
- 8. Dr Jamal-Deen Abdulai, CSD Filters Figure 3-5 Filter function in a radio transmitter Slide 8
- 9. Dr Jamal-Deen Abdulai, CSD Mixers • 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 Slide 9
- 10. Dr Jamal-Deen Abdulai, CSD Infrared Light Figure 3-7 Mixer output Figure 3-6 Mixer symbol Slide 10
- 11. Dr Jamal-Deen Abdulai, CSD Mixers Figure 3-8 AM radio sidebands Slide 11
- 12. Dr Jamal-Deen Abdulai, CSD Amplifiers • 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 – Uses this electricity to increase a signal’s intensity or strength • Then output an exact copy of the input signal with a higher amplitude Slide 12
- 13. Dr Jamal-Deen Abdulai, CSD Antennas • Antennas: transmit or receive an RF signal – Antennas will be discussed in greater detail in Chapter 4 Figure 3-11 Antenna symbol Slide 13
- 14. Dr Jamal-Deen Abdulai, CSD Antennas Table 3-1 Radio system components and their symbols Slide 14
- 15. Dr Jamal-Deen Abdulai, CSD Design of a Radio System • Designers of radio communications systems – Need to consider how the systems will be used – Other considerations: • Multiple user access • Transmission direction • Switching • Signal strength Slide 15
- 16. Dr Jamal-Deen Abdulai, CSD 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 multiple users • Methods that allow multiple access – Frequency Division Multiple Access (FDMA) – Time Division Multiple Access (TDMA) – Code Division Multiple Access (CDMA) Slide 16
- 17. Dr Jamal-Deen Abdulai, CSD Multiple Access Figure 3-12 Multiple access Slide 17
- 18. Dr Jamal-Deen Abdulai, CSD Multiple Access • Frequency Division Multiple Access (FDMA) – Divides the bandwidth of a channel into several smaller frequencies bands – Most often used with analog transmissions – Cable television is transmitted using FDMA – Drawback of FDMA: Crosstalk • Causes interference on the other frequency and may disrupt the transmission Slide 18
- 19. Dr Jamal-Deen Abdulai, CSD Multiple Access Figure 3-13 Frequency Division Multiple Access (FDMA) Slide 19
- 20. Dr Jamal-Deen Abdulai, CSD Multiple Access • 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 Slide 20
- 21. Dr Jamal-Deen Abdulai, CSD Multiple Access Figure 3-14 Time Division Multiple Access (TDMA) Slide 21
- 22. Dr Jamal-Deen Abdulai, CSD Multiple Access • 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 – Spreads the signal over a wide frequency band – 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 Slide 22
- 23. Dr Jamal-Deen Abdulai, CSD Multiple Access Figure 3-15 CDMA spreading of a data signal by a PN code Slide 23
- 24. Dr Jamal-Deen Abdulai, CSD Multiple Access • Code Division Multiple Access (cont’d) – Spreading process is reversed at the receiver • Code is de-spread to extract the original data bit transmitted Figure 3-16 De-spreading a CDMA signal to recover the data bits Slide 24
- 25. Dr Jamal-Deen Abdulai, CSD Multiple Access • Code Division Multiple Access (cont’d) – 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 Slide 25
- 26. Dr Jamal-Deen Abdulai, CSD 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 Slide 26
- 27. Dr Jamal-Deen Abdulai, CSD Transmission Direction Figure 3-18 Simplex transmission Slide 27
- 28. Dr Jamal-Deen Abdulai, CSD Transmission Direction Figure 3-19 Half-duplex transmission Slide 28
- 29. Dr Jamal-Deen Abdulai, CSD Transmission Direction • 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 Slide 29
- 30. Dr Jamal-Deen Abdulai, CSD Transmission Direction Figure 3-20 Full-duplex transmission Figure 3-21 Using a single antenna in full-duplex RF communications Slide 30
- 31. Dr Jamal-Deen Abdulai, CSD 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 Slide 31
- 32. Dr Jamal-Deen Abdulai, CSD Switching Figure 3-22 Telephone call switching Slide 32
- 33. Dr Jamal-Deen Abdulai, CSD Switching Demonstrated, excerpt from the series “The Crowns” Slide 33
- 34. Dr Jamal-Deen Abdulai, CSD Switching Figure 3-23 Packet switching Slide 34
- 35. Dr Jamal-Deen Abdulai, CSD Switching • 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 • Only packets affected must be resent, not entire message Slide 35
- 36. Dr Jamal-Deen Abdulai, CSD 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) – Affects radio signal strength – Also called noise • Signal-to-noise ratio (SNR) – Compares signal strength with background noise – When strength of a signal is well above the noise, interference can be filtered out Slide 36
- 37. Dr Jamal-Deen Abdulai, CSD Signal Strength Figure 3-24 Sources of EMI or noise (interference) Slide 37
- 38. Dr Jamal-Deen Abdulai, CSD Signal Strength Figure 3-25 Signal-to-noise ratio (SNR) Slide 38
- 39. Dr Jamal-Deen Abdulai, CSD Signal Strength • To reduce the interference of noise – Boost the strength of the signal – Use of filters on the receiving end • Attenuation – A loss of signal strength • Multipath distortion – As a radio signal is transmitted, the electromagnetic waves spread out – Waves travel different paths between transmitter and receiver • Arrive at different times and out of phase Slide 39
- 40. Dr Jamal-Deen Abdulai, CSD Signal Strength Figure 3-26 Multipath interference or distortion Slide 40
- 41. Dr Jamal-Deen Abdulai, CSD Signal Strength Figure 3-27 Effect of multipath distortion in a signal Slide 41
- 42. Dr Jamal-Deen Abdulai, CSD Signal Strength • 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 Slide 42
- 43. Dr Jamal-Deen Abdulai, CSD Understanding Standards • Standards for telecommunications have been in place almost since the beginning of the industry – Standards have played an important role in the rapid growth of the industry Slide 43
- 44. Dr Jamal-Deen Abdulai, CSD The Need For Standards • Standards – Commonly accepted technical specifications • Telecommunications requires standards exist for the design, implementation, and operation of the equipment • A lack of standards between devices would prevent communications from taking place Slide 44
- 45. Dr Jamal-Deen Abdulai, CSD 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 Slide 45
- 46. Dr Jamal-Deen Abdulai, CSD Types of Standards • De Facto Standards – Not official standards – Common practices that industry follows • De jure Standards – Also called official standards – Controlled by an organization or body – Process for creating standards can be very involved • Consortia – Industry-sponsored organizations that promote a specific technology Slide 46
- 47. Dr Jamal-Deen Abdulai, CSD Telecommunications Standards Organizations • United States Standards Groups – American National Standards Institute (ANSI) – 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) Slide 47
- 48. Dr Jamal-Deen Abdulai, CSD Telecommunications Standards Organizations • International Standards Groups – International Telecommunications Union (ITU) – International Organization for Standardization (ISO) Slide 48
- 49. Dr Jamal-Deen Abdulai, CSD Regulatory Agencies • Enforcing telecommunications regulations is important for RF spectrum management and open standards for multiple vendors. • Federal Communications Commission (FCC) – Primary regulatory agency for telecommunications in the United States • National Communication Authority – Primary regulatory agency for telecommunications in Ghana – Responsibilities • Develops and implements regulatory programmes • Processes applications for licenses and other filings • Analyzes complaints and conducts investigations • Take part in congressional hearings • Represents the United States in negotiations • Regulates radio and television broadcast stations Slide 49
- 50. Dr Jamal-Deen Abdulai, CSD Radio Frequency Spectrum • Radio frequency spectrum – Range extends from 10 KHz to over 30 GHz – Spectrum is divided into 450 different sections (bands) • Radio frequencies of 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 Slide 50
- 51. Dr Jamal-Deen Abdulai, CSD Radio Frequency Spectrum Table 3-3 Radio frequency bands Slide 51
- 52. Dr Jamal-Deen Abdulai, CSD Radio Frequency Spectrum • 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) Slide 52
- 53. Dr Jamal-Deen Abdulai, CSD Radio Frequency Spectrum Table 3-4 Unregulated bands Slide 53
- 54. Dr Jamal-Deen Abdulai, CSD Radio Frequency Spectrum • 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 • Currently used in limited radar and position-location devices Slide 54
- 55. Dr Jamal-Deen Abdulai, CSD 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 Slide 55
- 56. Dr Jamal-Deen Abdulai, CSD Summary • 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 Slide 56
- 57. Dr Jamal-Deen Abdulai, CSD Summary • 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 Slide 57
- 58. Dr Jamal-Deen Abdulai, CSD Review Questions • List and describe the three types of data flow. • List and discuss the advantages of standard. • What is switching? What type of switching is used with telephone transmissions, and what type is used for data transmission. • Explain multipath distortion and how it can be minimized. • What are the functions of NCA in Ghana? Slide 58
- 59. Dr Jamal-Deen Abdulai, CSD References • All materials in this slide are the sole property of Cengage Learning 2014 • Chapter 3: Olenewa J. L. (2014). Guide to Wireless Communications. (3rd ed.), Boston, MA 02210, USA: Course Technology • Chapters 2 & 3: Hucaby D. (2016). CCNA Wireless 200-355 Official Cert Guide. (1st ed.) Cisco Press . • Ciampa M. (2002). Guide to Wireless Communications. (1st ed.), Thomson Course Technology. Slide 59