planning part_5 - frequency planning
TRANSCRIPT
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FrequencyFrequencyPlanningPlanning
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Module objectives
DESCRIBE FREQUENCY PLANNING CRITERIA
CALCULATE THE FREQUENCY REUSE FACTOR
DESCRIBE FREQUENCY ALLOCATIONMETHODS
At the end of this module you will be able to
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Content of FrequencyPlanning GUIDELINES
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Frequency Planning GUIDELINES
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Tighter re-use of ownfrequencies
more capacity more interference
Target to minimise
interferences at an
acceptable capacitylevel
First when a completearea has beenfinalised
Automatic frequencyplanning tools
R
D
Frequency PlanBasics
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Why frequency re-use ?
8 MHz = 40 channels 7 traffic timeslots = 280 users
max. 280 simultaneous calls??!
Limited bandwidth available
Re-use frequencies as often as possible
Increased capacity
Increased interferences
Trade-off between interference level and capacity
Allocate frequency combination that creates least overall interference
conditions in the networkInterference is unavoidable
minimise total interferences in network
Frequency PlanBasics
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Criteria
The frequency planning criteria include the configuration
and frequency allocation aspects. The configurationaspects consider the:
Frequency band splitting between the macro and micro base
stations, Frequency band splitting between the BCCH and TCH layers, Frequency band grouping and
Different frequency reuse factors for different TRX layers.
Frequency allocation aspects include
frequency planning thresholds (QOS requirements) C/I requirements Percentage of co-channel and adjacent channel interference
Frequency PlanFrequency Planning Criteria
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Macro - Micro
needed because of inaccurate coverage predictions betweenmacro and micro layers not needed if accurate coverage predictions available in thefuture
BCCH - TCH
needed to ensure a good quality on BCCH frequency (in order toensure signalling)
Frequency PlanFrequency Band Splitting
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Frequency grouping
+ Frequency hopping (coherence bandwidth)+ Intermodulation+ Frequencies assigned to all TRX layers at one time+ Frequencies evenly used
- Limitations for automatic frequency planning algorithms- Fixed frequency reuse factor
f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14
BCCH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
2. TRX 15 16 17 18 19 20 21 22 23 24 25 26 27 283. TRX 29 30 31 32 33 34 35 36 37 38 39 40 41 42
Frequency PlanFrequency Band Grouping
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f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 f15
BCCH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
2. TRX 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
1. Micro 31 32 33 34 35 36 31 32 33 34 35 36 31 32 33
2. Micro 37 38 39 40 41 42 37 38 39 40 41 42 37 38 39
Frequency planning for different TRX layers
different freqency reuse factors for different TRX layers frequency planning for different layers
Frequency PlanDifferent Frequency Reuse Factors for Different TRX Layers
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C/I requirements
- C/Ic = 15 dB, C/Ia = -6 dB (Note Overlay-Underlay concepts)
Interference probability
- 2% co-channel and 5% adjacent channel interference
Frequency separations
- cell/site separations- combiner limitations
Frequency PlanFrequency Allocation Thresholds
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Do not use
Hexagon cell patterns
Regular grids
Systematic frequency allocation
Use
Interference matrix calculation
Calibrated propagation models
Minimise total interference innetwork
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Frequency PlanBest Method
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Frequency PlanRe-Use-Factor
RuF
Average number of cells that have different frequencies
Measure for effectiveness of frequency plan
Trade-off: effectiveness vs. interferences
Multiple RuFs increase effectiveness of FP
Compromise between safe, interference free planning and effective resource
usage
1 3 6 9 12 15 18 21
safe planning(BCCH layer)
normal planning(TCH macro layer)
tight re-use planning(IUO layer)
same frequencyin every cell(spread spectrum)
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Frequency PlanMultiple Re-Use-Factor
Capacity increase with multiple RuFs
e.g. network with 300 cells
Bandwidth : 8 MHz (40 radio channels)
Single RuF =12
NW capacity = 40/12 * 300 = 1000 TRX
Multiple RuF
BCCH layer: re-use =14, (14 frq.) Normal TCH: re-use =10, (20 frq.)
Tight TCH layer: re-use = 6, (6 frq.)
NW cap. = (1 +2 +1)* 300 = 1200 TRX
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Co-cell separation
e.g. 3 (4 for GSM1800)
600 (800 ) kHz spacing between frequencies in the same cell
Co-site separation
e.g. 2
400 kHz spacing between frequencies on the same site
Co-channel interferences from neighbouring sitesAdjacent channel interferences from neighbouring sites
Frequency PlanConstraints
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Frequency PlanManual Allocation
A1 B1 C1 D1 E1 F1 G1 H1 A2 B2 C2 D2BCCH 1 26 3 28 5 30 7 32 9 34 11 36
TCH 25 2 27 4 29 6 31 8 33 10 35 12
E2 F2 G2 H2 A3 B3 C3 D3 E3 F3 G3 H3
BCCH 13 38 15 40 17 42 19 44 21 46 23 48
TCH 37 14 39 16 41 18 43 20 45 22 47 24
With Frequency Groups: 8 groups, 6 ARCFN each
A1 B1 C1 D1 E1 F1 G1 H1 I1 L1 A2 B2 C2 D2 E2 F2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
G2 H2 I2 L2 A3 B3 C3 D3 E3 F3 G3 H3 I3 L3 M3 N3
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
O3 P3 Q3 R3 M4 N4 O4 P4 Q4 R4 M5 N5 O5 P5 Q1 R5
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
BCCH
BCCH TCH
TCH
With Separated Bands: 10 groups BCCH, 6 TCH, 3 ARCFNeach
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Allocation Criteria
Take into account both: theoretical dominance area and
planner's knowledge of the site
Starting point:
critical site or critical area
"cluster approach"?
"dynamic" BCCH allocation
No more than 60-70 sites!!!
Conclusion
Method 1 is simpler than method 2
Method 2 is more accurate
(RuFBCCH > RuFTCH, intracell HO)
C/I C/A C/I C/A
groups x x x x
sub-bands x
TCHBCCHsimplicity
Frequency PlanManual Allocation
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Frequency allocation algorithms implemented inplanning tools
Compute compatibility matrix across total cell area
(heavy computing!) Allocate same frequencies in sufficiently separatedcells
Allocate frequencies until traffic needs of all cells aresatisfied
Boundary condition: minimise total networkinterferences
No closed solution available for this problem
Iterative procedure
Frequency PlanAutomatic Allocation
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Interferenceparameters setting
Separationparameters setting
Interference matrix calculation
Separation matrix calculation
Frequency allocation Analyzeresults
Frequency PlanAutomatic Allocation
Choose the following parameters for all network layers
Co-cell separation
Co-site separation
Target level for co-channel + adj channel interference
Frequency band allowed
Algohorithm:
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Frequency PlanAutomatic Allocation
Interference matrix
Element (i,j) = amount of interference caused on cell i by cell j
Comparison parameter = co-channel (adj channel) C/I
Separation matrix
Element (i,j) = minimum channel separation between cell i and cell j
Comparison parameter = maximum C/I (C/A) probability
Co-site, co-cell and adj-cell separations manually set
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Frequency PlanAutomatic Allocation
Evaluation criteria
Check the avg co-channelinterferenceparameter
Check the channel distribution Check the contraints violationlist
Use the Interference Analisystool
Automatic frequency
plan
Manual analysis and errorcorrection
Finalresult
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A
BC
15km
internationalborderline
Frequency PlanFrequency Coordination
Regulations for international boundaries
18 dB V/m at borderline
18 dB V/m at 15km distance from border for preferential frequencies
Set of preferential and reserved frequencies must be mutuallyagreed between operators
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Intermodulation interference can be avoided by
Ensuring that the base station site equipment quality is such high that the
intermodulation does not exist, Grouping the frequencies such that the intermodulation products do not cause
interference or Allocating the frequencies such that the intermodulation products do not cause
interference or
its complex influence on the frequency planning can be made easier by
Preventing the power control (only for the downlink intermodulation products) or
Directing the intermodulation products to the BCCH frequencies (there is nodownlink power control on the BCCH).
Frequency PlanIntermodulation
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Exercises / Questions Is the frequency grouping of the reuse factor 15 enough to
maximise the performance of the frequency hopping?
Does the 1800 MHz GSM network cause interference to the 900MHz networks?
Why does the frequency band have to be split?
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References
1. J. Lempiinen, M. Manninen, Radio Interface System Planningfor GSM/GPRS/UMTS, Kluwer Academic Publishers 2001.