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Frequency Reuse

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  • 1. Telecom TutorialsMonday, June 03, 2013www.tempustelcosys.comFrequency Reuse
  • 2. Monday, June 03, 2013www.tempustelcosys.comGSM900Upward 890 915 MHzDownward 935 960 MHzTx-Rx difference is 45MHz,carrier space is 200KHz。GSM1800Upward 1710 1785 MHzDownward 1805 1880 MHzTx-Rx difference is 95MHz,carrier space is 200KHz。
  • 3. Monday, June 03, 2013www.tempustelcosys.comGSM900GSM900: FU(n) = 890 + 0.2 n MHzFD(n) = Fu(n) + 45 MHz,1 n 124E-GSM900:FU(n) = 890 + 0.2 (n-1024),974 n 1023FD(n) = Fu(n) + 45 MHzn is called Absolutely Radio Frequency Channel Number.GSM1800Fu(n) = 1710.2 + 0.2 (n-512) MHzFD(n) = Fl(n) + 95 MHz, 512 n 885374 channels
  • 4. Monday, June 03, 2013www.tempustelcosys.comFrequency reuse is referred to as the same frequency is reused aftera certain distance in cellular wireless system. Generally, a limitedfrequency band is divided into many groups, each containing a fewcarriers, which are in turn assigned to adjacent cells
  • 5. Usually, frequency reuse patterns include:Ordinary frequency reuse: “4 3”, “3 3” and more close “2 3”and “1 3”.Dual frequency reuse: BCCH and TCH adopt different frequencyreuse patterns respectively.Concentric: the Underlay and Overlay adopt different frequencyreuse patterns respectively.MRP: different layers adopt different reuse patterns.Monday, June 03, 2013www.tempustelcosys.com
  • 6. “4 3” frequency reuse pattern is that each site is divided into 3sector. 12 frequencies form a group which are distributed to 4different sites. Each site owns 3 frequencies.Monday, June 03, 2013www.tempustelcosys.comA3D2B1C3B2D1D3A2C1B3C2A1B3C2A1A3A1B1D1D3D2C3B2A1C3D2C3C1D2B1C2A1A2C1D3
  • 7. Monday, June 03, 2013www.tempustelcosys.comA3C2B1B3A2C1C3B2A1A3C2B1B3A2C1B3A1C1A1A3A2C3B2A1A3A3C3C1B2A1B2A1A2C1B3“3 3” frequency reuse pattern is that each site is divided into 3 sector. 9 frequenciesform a group which are distributed to 3 different sites. Each site owns 3 frequencies.
  • 8. Monday, June 03, 2013www.tempustelcosys.comA1 B1 C1 A2 B2 C2 A3 B3 C31 1 2 3 4 5 6 7 8 92 10 11 12 13 14 15 16 17 183 19 20 21 22 23 24 25 26 27
  • 9.  The following equation is used to estimate frequency reusedistance:D —— frequency reuse distanceR —— cell radiusN —— frequency reuse factor.N=9 for “3 3”; N=12 for “4 3” For “3/9” frequency reuse, D=5.2R For “4/12” frequency reuse, D=6RMonday, June 03, 2013www.tempustelcosys.com
  • 10. • Co-channel Interference C/I: C/I refers to the interference of another cellusing the same frequency to the current cell. Theratio of carrier to interference is called C/I. GSM specification regulates that C/I >9dB. Inimplementing, it requires C/I>12dB.• Adjacent channel interference C/A C/A refers to interference of adjacent cell tothe current cell. The ratio is called C/A. The GSMspecification regulates that C/A>-9dB.Monday, June 03, 2013www.tempustelcosys.com
  • 11. Where, Pown_cell is the signal strength of current cell; Pi_BCCH isBCCH signal strength of interfering cell i measured by MS.Monday, June 03, 2013www.tempustelcosys.com
  • 12.  In GSM, presume a trunk can support 30 TCHs, GOS=2%,then thetotal traffic will be 22Erl according to Erlang-B table. The totalsubscribers that can be supported will be 733 if the traffic of eachsubscriber is 30mErl.Monday, June 03, 2013www.tempustelcosys.comTRX TCH ( GOS=2% )Rtrunk ( % )1 7 2. 94 372 14 8. 20 573 22 14 . 90 664 30 21 . 93 725 37 28 . 25 756 45 35 . 61 787 53 43 . 06 80
  • 13.  Analyze total traffic and traffic distribution featurewithin the service area Calculate system capacity, the traffic that each cell canprovide and subscriber numbers Calculate the total numbers of TRX s required Determine the total numbers of cells required Determine the TRX configuration mode of each cell. Adjust the configuration (optimization) in combinationwithcell planning and frequency planningMonday, June 03, 2013www.tempustelcosys.com
  • 14. • Analogy of telephone set Prediction mode: Y5 = r X5 where, Y5:predicted subscriber number on 5th year X5:total numbers of telephone set on 5th year r :percentage of mobile phone to telephone set• Social survey and city analogy Based on social survey, compare with the cities where mobilenetwork has been established and where the city scale, economyand customer requirement are similar. Refer to that cities’ subscribersto predict the potential numbers of mobile subscribers of the city.Monday, June 03, 2013www.tempustelcosys.com