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EPL 476 Fundamental Concepts in Wireless Networks

EPL 476 Fundamental Concepts in Wireless Networks. Cellular Networks. Prior Cellular Networks Telephone service provided by high power transmitter Typical system 25 channels with an effective radius 80km Cellular Networks Lower power transmitter of 100w

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EPL 476 Fundamental Concepts in Wireless Networks

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  1. EPL 476Fundamental Concepts in Wireless Networks

  2. Cellular Networks • Prior Cellular Networks • Telephone service provided by high power transmitter • Typical system • 25 channels with an effective radius 80km • Cellular Networks • Lower power transmitter of 100w • Due to low coverage of the transmitter • the area can divided into multiple cells • Each cell is served by Base Station • Transmitter, receiver, and control unit

  3. What is a Cell? • Cell is the Basic Union in The System • defined as the area where radio coverage is given by one base station. • A cell has one or several frequencies, depending on traffic load. • Fundamental idea: Frequencies are reused, but not in neighboring cells due to interference.

  4. Shape of Cell? • Design Decision • Shape of Cell to cover the area • Square • Hexagonal,

  5. Frequency Reuse • Transmission Power • Carefully controlled to allow communication within the cell using a given frequency band while limiting the power at that frequency that escapes the cell into adjacent cells. • The same frequency is not used in the adjacent cells • The objective is to use the same frequency band in multiple cells at some distance from one another. • At the same cell multiple frequency bands are assigned, the number of bands depending on the traffic expected.

  6. Frequency Reuse • A key design • Determine the minimum separation between two cells using the same frequency band so that the two cells do not interfere with each other.

  7. Frequency Reuse • A key design • D=minimum distance between centers of cells that use the same frequency band • R=radius of cell • d= distance between centers of adjacent cells • N=number of cells in repetitious pattern • K= total number of frequency allotted for the system. • Frequencies for each cell = K / N

  8. Frequency Reuse • In hexagonal cell pattern the following values of N are possible: • N=1,3,4,7,9,12,13,16,19,21…..

  9. Problem • Assume a system of 32 cells with a cell radius of 1.6km, a total of 32 cells, a total frequency bandwidth that supports 336 traffic channels, and a reuse factor of N=7. • What is the geographic area covered? • How many channels are per cell? • What is the total number of concurrent calls that can be handled? • Repeat with 0.8km and 128 cells.

  10. Solution • What is the geographic area covered? • Find the area for each cell area of hexagonal=6.65k total geographic area= 6.65*32=213k • How many channels are per cell? • For N=7 the number of channels per cell is 336/7=48. 48 channels per cell.

  11. Solution • What is the total number of concurrent calls that can be handled? • 48 channels per cell* 32 cells=1536 channels

  12. Mobile Radio Propagation Effects • Signal Strength • The strength of the signal between the base station and the mobile unit must be strong enough to maintain signal quality at the receiver but not so strong to create too much cochannel interference with channels in another cell using the same frequency band. • Fading • Even if the signal is within an effective range, signal propagation effects may disrupt the signal and cause errors

  13. Mobile Radio Propagation Effects • Path loss information HATA

  14. Mobile Radio Propagation Effects • Path loss information HATA

  15. Path Loss Problem • Let fc = 900MhHz, ht =40m, hr= 5m and d = 10km. Estimate the path loss for a medium-size city.

  16. Traffic Engineering • Consider a cell that has L potential of customers (L mobile units) and that is able to handle N simultaneous users • If L <= N • No-blocking system • If L >= N • Blocking system

  17. Traffic Engineering • Blocking System • What is the degree of blocking? • What is the probability the call is blocked? • What is the capacity (N) is needed to achieve a certain upper bound on the probability of blocking A=λh A=traffic intensity λ=the mean rate of calls attempt per unit time h=the mean holding time per successful call

  18. Traffic Engineering A=λh λh=ρN A= ρN A=is the average number of channels required λ=the mean rate of calls attempt per unit time h=the mean holding time per successful call ρ=is server utilization

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