capacity planning exercise

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Capacity planning exercise. M.Sc. Mika Husso 9.2.2007. Traffic reviewed …. The unit of traffic is E [erlang] Single line or sever can handle up to 1 E traffic. Offered Traffic (total traffic created by subcribers) A=  h = call intensity * mean service time - PowerPoint PPT Presentation


  • Capacity planning exerciseM.Sc. Mika Husso9.2.2007

  • Traffic reviewed The unit of traffic is E [erlang]Single line or sever can handle up to 1 E traffic.Offered Traffic (total traffic created by subcribers)A= h = call intensity * mean service timeCarried Traffic (or served traffic) = Total amount of traffic the network is able to serveLost Traffic (or rejected traffic)= Offered Traffic Carried TrafficPotential traffic: Offered traffic if there would be no restrictions on the use of the service.

  • Traffic reviewedIn practice, it is not feasible for mobile network to have the capacity to handle any possible load at all times.Fortunately, not all subscribers place calls at the same time and so it is reasonable to size the network to be able to handle some expected level of load.> planner has to design the network to meet a predefined blocking probability (e.g. 2 %), which depends on the desired GoS

  • Capacity planning process (TDMA/FDMA)1. Considering the available resources (number of carriers etc.) and the GoS requirements (blocking prop., )2. Estimating the amount of Offered Traffic on each area 3. Estimating how many cells (BSs) and how many traffic channels per cell are needed to serve the offered traffic on the area with the given blocking propability (e.g. 2 %)-> Determining the CAPACITY based cell area (and radius)4. Checking if also COVERAGE can be granted for the capacity based cell (i.e. can the signal reach the user/BS without attenuating too much?)-> if not the cell radius is decreased so that COVERAGE can be granted

  • 1. Considering the resourcesThere are available resourcesNumber of carriers (channels)Multiplexing (TDMA, FDMA, CDMA)Duplexing (TDD, FDD)There are also requirements for GoSBlocking propabilityCall dropping propability

  • 2. Estimating the traffic Offered voice traffic from a user group can be predicted as follows

    , whereN is the number of personsC denotes the penetrationT is the average traffic generated by one userF denotes the area coverage probability (users not on the network coverage area cant offer traffic)

  • Estimating the trafficThe traffic offered by each user is:A = H Erlangs, whereH is the average holding time of a call is the average number of calls requested/time unit by the user For exampleH = 2 minutes and = 0.8 calls / hour -> A = 2 * (0.8/60) 26.7 mErlang

  • Traffic estimatePenetration CP = 0.25Offered traffic per user: TO,1=TO,2=20 mErlangCoverage probability: F1=0.8 (Pedestrian), F2=0.95 (Vehicular)Distance between pedestrians S1=4 mDistance between vehicles S2=25 mNumber of people in a car 2=1 (1=1)Number of pedestriansN1 = 1 Ls/S1 = 110000/4=2500Number of carsN1 = 2 Ls/S2 = 110000/25=400Traffic offered by pedestrian usersT1=F1CP TO,1 N1 = 0.80.250,022500=10 ErlangTraffic offered by vehicular usersT2=F2CP TO,2 N2 = 0.950.250,02400=1.9 ErlangOffered traffic A= T1+T2 = 11.9 Erlang

  • 3. Estimating the number of BSs neededAssuming we have estimated a total traffic of 20 Erlang on a given area, how many BSs do we need if the smax number of tranceivers (channels) on a BS is 5 and the desired blocking level is 3 %?Using Erlangs B formula (or table) We need 27 channels, which can serve a total of 20.31 Erlang (from the Erlang B table) We need 27 / 5 = 5.4 -> 6 Base Stations (using 5 transceivers in a BS)

  • 4. Can coverage be granted?Will be dealt with in the coverage planning exerciseBased on the calculation of a link budgetCan the signal be received with adequate power?If the signal attenuates too much, the maximum distance between BS and user (i.e. cell radius) must be reduced

  • Example of capacity planningSystem parametersPenetration (all user groups): 25 %Offered traffic/user (all user groups): 20 mErlangCoverage probability target: vehicular users 95%, 1 user/car, pedestrian users 80%Multiple access method: FDMA, 28 TRX/cell Blocking probability target: 2 %Service area divided into 4 homogenous Regions with spatially uniformly distributed usersIn Region A the vehicular generated traffic is handled by macrocells and pedestrian generated traffic by microcells, in other Regions all traffic is handled by macrocellsApproach: Minimum excess capacity, starting from Region with highest traffic density, cells possibly overlapping to adjacent Regions will reduce the area in these to be covered correspondingly

  • Geometry of the service areaRegion types:A: dense cityB: cityC: suburbanD: rural

  • Parameters of the Regions in the Service AreaBasic assumption: Vehicles, pedestrians, and traffic are assumed to be spatially uniformly distributed in each Region.

    RegionSize, L1L2-area of o3ther RegionsBlock size, LB1LB2Vehicle spacing, SvPedestrian spacing, SpA55 km2 = 25 km20.20.2 km225 m4 mB1515 25 km2 = 200 km20.250.25 km250 m10 mC4040 225 km2 = 1375 km20.1250.25 km2200 m125 mD120120 1600 km2 = 12800 km222 km21000 m550 m

  • Choosing the cell structureAn ideal cell would have a circular shape.To get complete coverage a certain overlapping must be allowed. Minimum overlapping with hexagonal structure, which is the most common in theoretical investigations Another possible cell structure giving complete coverage is the quadratic cell structure In this example the quadratic cell structure gives easier calculations and will be used FROL = Fractional Overlapping

  • Estimating the population in the regions

  • Estimating the offered traffic

  • Estimating the amount of traffic channels and BSs to be used

  • Dimensioning cells

  • Dimensioning cells

  • Dimensioning cells

  • Dimensioning cellsWhen region B is dimensioned, it usually partly overlaps regions A, C and D and therefore also serves some of their offered traffic> When dimensioning regions A, C and D the traffic already served by region B should not be served again (equipment should be minimized)Otherwise the dimensioning process is done exactly as for region BWhen the next region is dimensioned (in this case D), the traffic served by it in other regions should also not be served again

  • Macrocell layout (capacity planning)

  • Dimensioning microcellsThe procedure is similar, butIn the city area, buildings cause significant attenuation to the signalTo minimize equipment, the BSs should generally be located at the street crossingsUsually pedestrian originated traffic on the area is served using microcells and vehicular originated using macrocells

  • Microcell layout (capacity planning)