FIXED TELEPHONE, MOBILE TELEPHONE AND SATELLITE COMMUNICATION SYSTEMS

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FIXED TELEPHONE, MOBILE TELEPHONE AND SATELLITE COMMUNICATION SYSTEMS

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FIXED TELEPHONE, MOBILE TELEPHONE AND SATELLITE COMMUNICATION SYSTEMS

  1. 1. Flexible · Affordable · Accessible the people’s university TEL 213/05 Telecommunication Principle Tutorial 4: FIXED TELEPHONE, MOBILE TELEPHONE AND SATELLITE COMMUNICATION SYSTEMS Semester January 2012
  2. 2. the people’s university Flexible · Affordable · Accessible Introduction • Students used to focus on either data communications or voice communications. • Today, the two fields are merging. • Most voice systems are computer controlled and data • networks support voice. • Anyone studying the field of data communications and • networks must learn some basic telecommunications too. • Telecommunications used to be just “voice.”
  3. 3. the people’s university Flexible · Affordable · Accessible Basic Telephone Systems • POTS is the plain old telephone system that connects most • homes and small businesses. • POTS lines were designed to transmit the human voice, • which has a bandwidth less than 4000 Hz. • A telephone conversation requires two channels, each • occupying 4000 Hz.
  4. 4. the people’s university Flexible · Affordable · Accessible Various telephone channels and the assignment of frequencies
  5. 5. the people’s university Flexible · Affordable · Accessible Limitations of Basic Telephone Systems • A 4000 Hz analog signal can only carry about 33,600 bits per • second of information while a 4000 Hz digital signal can • carry about 56,000 bits per second. • If you want to send information faster, you need a signal with • a higher frequency. • POTS cannot deliver faster signals.
  6. 6. the people’s university Flexible · Affordable · Accessible Basic Telephone Systems - Loops • The local loop is the telephone line that runs from the • telephone company’s central office to your home or business. • The central office is the building that houses the telephone company’s switching equipment and provides a local dial tone on your telephone. • If you place a long distance call, the central office passes yourtelephone call off to a long distance provider.
  7. 7. the people’s university Flexible · Affordable · Accessible Local Loops
  8. 8. the people’s university Flexible · Affordable · Accessible Local Access Transport Areas • The USA is divided into a few hundred local access transport • areas (LATAs). • If your call goes from one LATA to another, it is a long distance call and is handled by a long distance telephone company. • If your call stays within a LATA, it is a local distance call and is handled by a local telephone company.
  9. 9. the people’s university Flexible · Affordable · Accessible Trunk • A trunk is a special telephone line that runs between central offices and other telephone company switching centers. • A trunk is usually digital, high speed, and carries multiple telephone circuits. • A trunk is typically a 4-wire circuit, while a telephone line is a 2-wire circuit. • Not associated with a single telephone number like a line is. • A telephone number consists of an area code, an exchange, and a subscriber extension. • The area code and exchange must start with the digits 2-9 to separate them from long distance and operator services.
  10. 10. the people’s university Flexible · Affordable · Accessible •When the telephone company installs a line, it must not proceed any further than 12 inches into the building. This point is the demarcation point, or demarc. •Modular connectors, such as the RJ-11, are commonly used to interconnect telephone lines and the telephone handset to the base. •When the handset is lifted off the base (off-hook), an off- hook signal is sent to the central office.
  11. 11. the people’s university Flexible · Affordable · Accessible Basic Telephone Systems Services • Foreign exchange service (FX) - customer calls a local number which is then connected to a leased line to a remote site. • Wide area telecommunications services (WATS) – discount volume calling to local and long distance sites. • Off premises extensions (OPX) - dial tone at location B comes from the PBX at location A.
  12. 12. the people’s university Flexible · Affordable · Accessible PBX • Private branch exchange (PBX) - a common internal phone switching system for medium to large-sized businesses. • Provides advanced intelligent features to users, such as: 4-digit, special prefixes for WATS (wide area telephone service), FX, etc (private dialing plans) • PBX collects dialed digits and intelligently decides how to route this call for lowest cost
  13. 13. the people’s university Flexible · Affordable · Accessible PBX Advanced Features • Voice mail • Routes incoming calls to the best station set (automatic call distribution) • Provides recorded messages and responds to touch-tone requests (automated attendant) • Access to database storage and retrieval (interactive voice response)
  14. 14. the people’s university Flexible · Affordable · Accessible PBX Components • CPU, memory, telephone lines, trunks • Switching network • Supporting logic cards • Main distribution frame • Console or switchboard • Battery back-up system
  15. 15. the people’s university Flexible · Affordable · Accessible Cordless system •What is cordless system? •History of cordless system. •Frequencies •Performance •Wireless phone handsets •Types of cordless system ● Analog ● Digital
  16. 16. the people’s university Flexible · Affordable · Accessible What is cordless system? • Cordless system is basically general term of cordless telephones and cordless telecommunication systems. •Cord means “wire” , so cordless system means wireless system.
  17. 17. the people’s university Flexible · Affordable · Accessible Cordless telephone with base
  18. 18. the people’s university Flexible · Affordable · Accessible Definition: • A cordless telephone or portable telephone is a telephone with a wireless handset that communicates via radio waves with a base station connected to a fixed telephone line, usually within a limited range of its base station (which has the handset cradle). The base station is on the subscriber premises, and attaches to the telephone network the same way a corded telephone does.
  19. 19. the people’s university Flexible · Affordable · Accessible • Current cordless telephone standards, such as PHS and DECT, have blurred the once clear-cut line between cordless and mobile telephones by implementing cell handover, various advanced features, such as data-transfer and even, on a limited scale, international roaming.
  20. 20. the people’s university Flexible · Affordable · Accessible • Unlike a corded telephone, a cordless telephone needs mains electricity to power the base station. The cordless handset is powered by a rechargeable battery, which is charged when the handset sits in its cradle.
  21. 21. the people’s university Flexible · Affordable · Accessible Limitations: • Residential – a single base station can provide in-house voice and data support • Office A single base station can support a small office Multiple base stations in a cellular configuration can support a larger office • Telepoint – a base station set up in a public place, such as an airport
  22. 22. the people’s university Flexible · Affordable · Accessible Frequencies • In the US, seven frequency bands have been allocated by the FCC for uses that include cordless phones. These are: 1. 1.7 MHz (1.64 MHz to 1.78 MHz & up to 5 Channels, AM System) 2. 43–50 MHz (Base: 43.72-46.97 MHz, Handset: 48.76- 49.99 MHz, allocated in 1986 for 10 channels, and later 25 Channels, FM System) 3. 900 MHz (902–928 MHz) (allocated in 1990) 4. 1.9 GHz (1880–1900 MHz) (used for DECT communications outside the U.S.)
  23. 23. the people’s university Flexible · Affordable · Accessible 5. 1.9 GHz (1920-1930 MHz) (developed in 1993 and allocated U.S. in October 2005) 6. 2.4 GHz (allocated in 1998) 7. 5.8 GHz (allocated in 2003 due to crowding on the 2.4 GHz band).
  24. 24. the people’s university Flexible · Affordable · Accessible Types (standards) of Cordless telephone • Digital cordless phones (i) Digital Enhanced Cordless telecommunication(DECT) (ii)Personal Handy-Phone System(PHS) • Analog cordless phones The main distinction among types of cordless phones is the way to transmit their signals.
  25. 25. the people’s university Flexible · Affordable · Accessible Application of DECT • Domestic cordless telephony, using a single base station to connect one or more handsets to the public telecoms network. • Enterprise premises cordless PABXs and wireless LANs, using many base stations for coverage. Calls continue as users move between different coverage cells, through a mechanism called handover. Calls can be both within the system and to the public telecoms network. • Public access, using large numbers of base stations to provide high capacity building or urban area coverage as part of a public telecoms network. • “Fido”
  26. 26. the people’s university Flexible · Affordable · Accessible Features of DECT Typical abilities of a domestic DECT Generic Access Profile (GAP) System include: • Multiple handsets to one base station and one phone line socket. This allows several cordless telephones to be placed around the house, all operating from the same telephone jack. • Interference-free wireless operation to around 100 metres (109 yards) outdoors, much less indoors when separated by walls . - For instance, generally immune to interference from other DECT systems, Wi-Fi networks, video senders, Bluetooth technology, baby monitors and other wireless devices.
  27. 27. the people’s university Flexible · Affordable · Accessible Mobile Telephone Systems
  28. 28. the people’s university Flexible · Affordable · Accessible Early Cellular Telephone Systems – Advanced Mobile Phone System (AMPS)
  29. 29. the people’s university Flexible · Affordable · Accessible Problem with AMPS
  30. 30. the people’s university Flexible · Affordable · Accessible New Mobile Telephone Switching Office (MTSO) Systems
  31. 31. the people’s university Flexible · Affordable · Accessible FDMA in Mobile Phones • Frequency division multiple access (FDMA) systems are like frequency division multiplexing in that they allow many users to share a block of spectrum by simply dividing it up into many smaller channels. • Each channel of a band is given an assigned number or is designated by the center frequency of the channel. • One subscriber is assigned to each channel. Typical channel widths are 30kHz, 200kHz, 1.25MHz and 5MHz.
  32. 32. the people’s university Flexible · Affordable · Accessible FDMA Process 1. A base station can receive radio signals in a given band of spectrum 2. The band of frequency is broken up into smaller bands (subbands) 3. Each transmitter (user) transmits to the base station using radio waves in its own subband 4. When a user is assigned to a subband, it transmits to the base station using a sine wave with the center frequency in that band 5. When the base station is tuned to the frequency of the desired user, it receives no portion of the signal transmitted by another in-cell user. 6. Multiple local transmitters in a cell do not interfere with one another.
  33. 33. the people’s university Flexible · Affordable · Accessible Time division Multiplexing (TDMA)
  34. 34. the people’s university Flexible · Affordable · Accessible TDMA Process 1. Time is broken into time slots (small, equal-length intervals) 2. Assume there are N users in the cell 3. Base station groups N consecutive slots into a frame 4. Each user is assigned one slot per frame. This slot assignment stays fixed as long as the user communicates with the base station (the length of the phone conversation) 5. In each time slot, the assigned user transmits a radio wave using a sine wave at the center frequency of the frequency band assigned to the base station.
  35. 35. the people’s university Flexible · Affordable · Accessible Code division Multiple Access (CDMA)
  36. 36. the people’s university Flexible · Affordable · Accessible CDMA Method 1 (frequency hopping Method) 1. Each user is assigned a frequency hopping pattern (a fixed set of frequency values) 2. Time is divided into slots 3. In the first time slot, a given user transmits to the base station using the first frequency in its frequency hopping sequence. 4. In the next time interval, it transmits using the second frequency value in its frequency hope sequence, and so on. This way the transmit frequency keeps changing in time.
  37. 37. the people’s university Flexible · Affordable · Accessible Satellite Movement
  38. 38. the people’s university Flexible · Affordable · Accessible Satellite Formulas
  39. 39. the people’s university Flexible · Affordable · Accessible Satellite Formulas Kepler’s third Law:
  40. 40. the people’s university Flexible · Affordable · Accessible Example – Satellite Calculations
  41. 41. the people’s university Flexible · Affordable · Accessible Solution
  42. 42. the people’s university Flexible · Affordable · Accessible Communication Satellites • Communication satellites are not originators of the signal to be transmitted • Act as relay stations for earth sources • The satellite contains a receiver that picks up the transmitted signal, amplifies it, and translates it to another frequency (uplink – 6GHz). The signal is then retransmitted to the receiving stations on earth (downlink – 4 GHz). Known as transponder.
  43. 43. the people’s university Flexible · Affordable · Accessible Satellite Bands and Frequencies As C Band is full, most modern satellite systems use the Ku Band:
  44. 44. the people’s university Flexible · Affordable · Accessible The C Band
  45. 45. the people’s university Flexible · Affordable · Accessible Example • A mobile transponder operates in the C band. Assume a local oscillator frequency of 2GHz. – What is the uplink receiver frequency if the downlink transmitter is on channel 4? – What is the maximum theoretical date rate if one transponder is used for binary transmission?
  46. 46. the people’s university Flexible · Affordable · Accessible Solution • The downlink frequency of channel 4 is 3840 MHz. The downlink frequency is the difference between the uplink frequency fu and the local oscillator frequency, fLO • The bandwidth of one transponder channel is 36MHz. For binary transmission, the maximum theoretical data rate or channel capacity C for a given bandwidth B is: • • C=2B • =2(36)=72Mbps
  47. 47. the people’s university Flexible · Affordable · Accessible TDMA, FDMA, CDMA • To maximize the use of the available spectrum in satellite transponders and to ensure access for as many users as possible, all satellites use some form of multiplexing. • Frequency-division multiplexing (FDMA) was used in early satellites. Time division multiple access (TDMA) is used in newer satellites.
  48. 48. the people’s university Flexible · Affordable · Accessible TDMA, FDMA, CDMA • TDMA assigns each user a time slot on the full bandwidth of the transponder channel. Modulation methods are BPSK and QPSK, although multilevel QAM (16 QAM, 32 QAM, 256 QAM) is used to increase digital transmission speeds at a given bandwidth. • Code-division multiple access (CDMA) spreads the signals of multiple users over the full transponder channel bandwidth and sort them by the use of pseudorandom codes. CDMA also provides security and provides multiple access while conserving spectrum.
  49. 49. the people’s university Flexible · Affordable · Accessible Thank you!

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