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04_20.pptx

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04_20.pptx

  1. 1. Dibrugarh University Institute of Engineering & Technology PRESENTATION ON FDMA & TDMA Prepared by Arunangshu Chetia roll.no: CSE-04/20
  2. 2. FREQUENCY- DIVISION MULTPILE ACCESS ⬥ Implemented at the media access control(MAC) layer ⬥ The user is assigned a specific frequency band in the electromagnetic spectrum, and during a call that user is the only one who has the right to access the specific band 2
  3. 3. ⬥Total system bandwidth is divided into narrow frequency slots. Each user is allocated a unique frequency band or channel ⬥ A user is free to transmit or receive all the time on its allocated radio channel, but the cost of transceiver is high, as each has to be designed on a different band 3
  4. 4. GRAPH REPRESENTATION • Each user transmits with no limitations in time, but using only a portion of the whole available frequency bandwidth. • Different users are separated in the frequency domain
  5. 5. Numbers of Channels in FDMA ⬥ Let Btotal be the total system bandwidth, Bguard be the guard band at edge, and Bch the single radio channel bandwidth. Then the number of channels in a FDMA system: ⬥ N = (Btotal - 2Bguard)/Bch 5
  6. 6. Numbers of Channels in FDMA ⬥ Example: ⬥ AMPS uses FDMA/FDD with Btotal = 12.5 MHz, Bguard = 10 kHz and Bch = 30 kHz ⬥ N = 12.5 x 1062(10 × 103)/30 × 103 ⬥ N=416 6
  7. 7. TIME DIVISION MULTIPLE ACCESS 7
  8. 8. IN TWO OR THREE COLUMNS ⬥ Time division multiple access (TDMA) is digital transmission technology that allows a number of users to access a single radio- frequency (RF) channel without interference by allocating unique time slots to each user within each channel. ⬥ The TDMA digital transmission scheme multiplexes three signals over a single channel. ⬥ The current TDMA standard for cellular divides a single channel into six time slots, with each signal using two slots, providing a 3 to 1 gain in capacity over advanced mobile-phone service (AMPS). Each caller is assigned a specific time slot for transmission. 8
  9. 9. How TDMA Works? TDMA relies upon the fact that the audio signal has been digitized; that is, divided into a number of milliseconds-long packets. It allocates a single frequency channel for a short time and then moves to another channel. The digital samples from a single transmitter occupy different time slots in several bands at the same time. The access technique used in TDMA has three users sharing a 30-kHz carrier frequency. The reason for choosing TDMA for all these standards was that it enables some vital features for system operation in an advanced cellular or PCS environment. 9
  10. 10. The Advantages of TDMA ⬥ In addition to increasing the efficiency of transmission, TDMA offers a number of other advantages over standard cellular technologies. First and foremost, it can be easily adapted to the transmission of data as well as voice communication. TDMA offers the ability to carry data rates of 64 kbps to 120 Mbps (expandable in multiples of 64 kbps). ⬥ • It is the most cost effective technology for upgrading analog to digital. • It provides the user with extended battery life and talk time. • It is the only technology that offers an efficient utilization of hierarchal cell structures like pico, micro and macro cells. • Dual band 800/1900 MHz 10
  11. 11. The Disadvantages of TDMA ⬥ One of the disadvantages of TDMA is that each user has a predefined time slot. However, users roaming from one cell to another are not allotted a time slot. ⬥ Another problem with TDMA is that it is subjected to multipath distortion. A signal coming from a tower to a handset might come from any one of several directions. It might have bounced off several different buildings before arriving 11
  12. 12. FDMA vs TDMA • Frequency division is very simple: all transmitters sharing the medium have output power spectra in non overlapping bands. -Many of the problems experienced in TDMA due to different propagation delays are eliminated in FDMA. • The major disadvantage of FDMA is the relatively expensive and complicated band pass filters required. - TDMA is realized primarily with much cheaper logic functions. • Another disadvantage of FDMA is the rather strict linearity requirement of the medium.

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