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rf planning


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rf planning

  1. 1. Introduction to RF Planning A good plan should address the following Issues : • Provision of required Capacity. • Optimum usage of available frequency spectrum. • Minimum number of sites. • Provision for easy and smooth expansion of the Network in future. • Provision of adequate coverage.
  2. 2. Introduction to RF Planning In general a planning process starts with the inputs from the customer. The customer inputs include customer requirements, business plans, system characteristics, and any other constraints. After the planned system is implemented, the assumptions made during the planning process need to be validated and corrected wherever necessary through an optimization process. We can summarize the whole planning process under the 4 broad headings • Capacity planning • Coverage planning • Parameter planning • Optimization
  3. 3. CELLULAR ENGINERING OBJECTIVES 1) To provide adequate coverage - Contiguous coverage of the required areas without appreciable holes - Adequate depth of coverage (i.e. outdoor or indoor , 2 W or 1.2 W mobiles ) to meet the company’s marketing plans. 2) To provide adequate network capacity - Accommodating traffic in the busiest hour with only a low probability of blocking (congestion). 3) To accommodate network growth - Extension of coverage in new areas - Expanding the network capacity so that the quality of service is maintained at all times. 4) To achieve a cost effective design - Lowest possible cost over the life of the network while meeting the quality targets.
  4. 4. COST JUSTIFICATION OF CELLULAR RNP The cellular mobile radio system design can be broken down in the following elements, which have a mutual relationship. - Reuse of frequency channels - Co- channel interference reduction - A desired minimum carrier to interference ratio (C/I) - Handover mechanism - Cell Planning Historical perspective - Wireless telephony network design is relatively new business with a 10-15 year history During this period many new tools and techniques have been developed: - More accurate radio coverage prediction - More accurate facility network design - Enhanced field measurement analysis to improve network performance. - New technology applications ( microcells, repeaters, smart antennas systems. ) - Better tools and methods to evaluate and predict traffic conditions
  5. 5. COST JUSTIFICATION OF CELLULAR RNP The challenge of accurate cellular network planning is still a complex task. Potential cost of Opportunities Lost Due to Network Planning problems Lost Subscribers - Lost base subscriber fee revenues - Lost enhanced service fee revenue - Lost airtime revenues (local and long distance) - Damaged reputation will impact competitive strength Cost Considerations That Include in the Design of a quality network - Design optimal network : extensive modeling and numerous revision of design. - Acquire radio site candidates that meet the design criterion. - Manage delays in permitting / zoning of best candidates - Extensive testing of radio site performance (coverage ) before commissioning. - Integration of field measurements in design.
  6. 6. COST JUSTIFICATION OF CELLULAR RNP Design Activity to compensate for Improperly designed or less than than optimal radio site in design. - Modify cell operational parameters (eg. Handover values and location) - Modify output power - Modify equipment (eg. Change antenna ) - Move site location - Add new sites (micro or macro cells)
  7. 7. COST JUSTIFICATION OF CELLULAR RNP An equation for Costing Comparison of Accurate Network Planning Option one : Poor design / no redesign - Weak competitive position - Lost disgruntled subscribers - Earn a poor service reputation (Weak attraction for new subscribers ). Option two : Quality network design - Additional design cost (engineering and equipment ). - Teardown and reinstall cost. Simple equation for characterizing cost /benefits - Quality network performances = ( Cost of engineering , equipment, installation ) – (Lost revenues, cost of engineering, equipment, installation ) - The benefits of quality design should farweigh lost revenues particularly in the fact of competition from new wireless companies.
  8. 8. DESIGN CONSTRAINTS The objective of radio planning is a technical realization of the marketing requirements, taking into account of the following constraints. - Technical requirements from the license conditions. - GSM system specific parameters (e.g. GSM recs 5.05 etc.) - Manufacturer specific features and parameters. - Radio communications principles and fundamentals. - Budgetary factors.
  9. 9. LICENSE CONDITIONS An example of technical requirements following from a license. Coverage requirements. - Class 2 or class 4 coverage of 60 % of the population 12 months from commercial launch. - Class 2 or class 4 coverage of 95 % of the population 36 months from the commercial launch. Quality of coverage - Service to be available in 90 % of the declared area and for 90 % of the time. Grade of Service - Endeavour to achieve 5 % or better Frequency Allocation - One of the major limitations in the GSM 900 system is the number of frequencies available to a GSM network operator. There is a relatively small bandwidth available that has to be divided over all the licensed operators. Most network operators are limited to 30-60 frequencies for handeling all traffic. - GSM 1800 offers 75 MHz bandwidth
  10. 10. MANUFACTURER SPECIFIC PARAMETERS - BTS Transmit power - Receiver sensitivity - Combiner performances - Cable loss - Antenna performance - Availability of frequency hopping and power control - Handover algorithm - Capacity – number of TRX provided.
  11. 11. RADIO COMMUNICATION FUNDAMENTALS - Propagation loss - Shadowing - Multipath fading - Power link budgets - Interference effects - The (un)predictability of radio wave propagation
  12. 12. QUALITY OF SERVICE SPECIFICATIONS The service requirement from the marketing should include information on which the technical plan can be based , including : Coverage Quality : Defined as a part of optimizing the business plan (indoor / outdoor coverae, handheld car, mobile set). Interference should be taken into account for coverage quality including margin of 12 dB) : Co channel C/I Adjacent channel C/I Call completion and Dropped call Rates : Dictated by the lisence conditions and quality of the competing network(includes Blocking rates 2% etc.) Service availibility
  13. 13. QUALITY OF SERVICE SPECIFICATIONS Traffic forecast: - Longterm forecast and trends for the network must be developed by the marketing. - Traffic distributions for the existing coverage areas and typical densities may be obtained from the network. Spectral effeciencies : for demonstration within the context of winning maximum points for a mobile license. The spectral efficiency is determined by decisions taken in : - Quality of coverage - Frequency Reuse plan - Use of cell splitting - Design for traffic demend - Feedback into the business plan Customer support measures
  14. 14. DEFINITION OF COVERAGE QUALITY Outdoor coverage: - Default definitions of coverage - Refers to 2 Watt class 4 mobiles in the street - Probability of coverage is 95 % averaged across the cell area. - Coverage probability at the edge of cells is less than this value. In car coverage : - A supplementary level of coverage for highways - Refers to a Class 4 mobile inside car or other vehicles. - Coverage probability is nominally 95% averaged - Coverage is critically dependent on the position of the handheld mobile within the vehicle. 8 Watt Coverage - A Supplementary level of coverage for remote areas. - Refers to class 2 mobile or class 4 with an 8 watt booster and external antenna
  15. 15. DEFINITION OF COVERAGE QUALITY Indoor coverage - Especially good coverage for city centers and stragetic locations - Refers to a class 2 mobile indoors - Building loss is very variables, so indoor coverages can never be guaranteed - Where indoor coverage is provided , outdoor coverage will be nearly 100 %
  16. 16. BLOCKING RATE ( Grade of Service, GOS ) GOS is defined as the probability that a call will be blocked or delayed due to unavailability of the radio resource. Example for license requirement - 5 % Averaged over a defined sub-network (e.g. weighted average by traffic load over the worse 10 cells ) - No cell to be worse than 10% - By a particular date , 8 % of the cells permitted to be between 2 % and 10 % GOS. - By a particular date , 5 % of the cells permitted to be between 2 % and 10 % GOS. - Ultimate target is that no cells should be worse than 2 % GOS.
  17. 17. CALL SUCCESS RATE Call failure may be due to : - Coverage holes - Interference - Congestion - Problem in fixed network - Handover failures - Equipment failures Call success rate is often expressed as the proportion of calls connected and held for 2 min. - Target is normally 90 % at launch of service - Mature networks achieve in excess of 98 % - Only applies within a declared coverage area. By a particular date , 95 % of the calls to the network boundary should be set up within four seconds and held for two min.
  18. 18. RADIO PLANNING METHODOLOGY Overall picture It is important to create an overall picture of the network before going into the detailed network planning. This is the fact the main objective of this presentation. Coverage Capacity and Quality Providing coverage is usually considered as the most important activity of a new cellular operator. For a while , every network is indeed coverage driven. However the coverage is not the only thing. It provides the means of service and should meet certain quality measures. The starting point is a set of coverage quality requirements. To guarantee a good quality in both uplink and downlink direction, the power levels of BTS and MS should be balanced at the edge of the cell. Main output results of the power link budget are: - Maximum path loss that can be tolerated between MS and the BTS. - Maximum output power level of the BTS transmitter.
  19. 19. Introduction to RF Planning • A simple Planning Process Description Business plan. No of Subs. Traffic per Subs. Subs distribution Grade of service. Available spectrum. Frequency Reuse. Types of coverage RF Parameters Field strength studies Available sites Site survey Capacity Studies Plan verification Quality check Update documents Coverage &C/I study Search areas Implement Plan Monitor Network Optimize Network Customer Acquires sites Capacity Studies Coverage plan & Interference studies Frequency plans and interference Studies Antenna Systems BSS parameter planning Data base & documentation of approved sites Expansion Plans.
  20. 20. Introduction to RF Planning Data Acquisition OMC Statistics “A” Interface Drive Test Implemented Planning Data Data Evaluation Implemented Recommendation Recommendations : Change frequency plan Change antenna orientation/Down tilt Change BSS Parameters Dimension BSS Equipment Add new cells for coverage Interference reduction Blocking reduction Augment E1 links from MSC to PSTN
  21. 21. Cell Planning Aspects At the end of it all, a good cell plan should have the following characteristics : · Coverage as required as predicted. · Co Channel and Adjacent Channel interference levels as predicted. · Minimum antenna adjustments during the optimization process. · Minimum changes to the BSS parameters/database during the optimization phase. · Should be well phased, requiring optimization only for short periods in the initial commissioning phase and during · Facilitate easy expansion of the network with minimal changes in the system.
  22. 22. The Basic Cell Planning Process The basic approach to cell planning is to provide good coverage and capacity. Initially, both are not known !! Hence the planning is based on the projections given by the customer. The customer based on market surveys and the company plans, may specify : · Number of sites he want in the city OR · Number of subscribers expected in a city. Base on the inputs from the customer, the initial planning process begins. From these we can determine either the capacity that is possible for a given number of sites OR minimum number of sites needed to provide service to a given number of subscribers. The site density required for a specific capacity should also pass the coverage criteria. This aspect will be covered later in the course.
  23. 23. Cell Planning Aspects · What is the area of coverage needed ? · How many sites are required for this area ? ( cell radius of 1 Km. Means an approximate coverage area of 3 sq. Kms. ) · Do we need so many sites ? Can some site be bigger ? Decide number of sites based on capacity and coverage requirements. · Divide city into clutter types such as . >Urban >Suburban >Quasi Open >Open >Water. · Identify search areas covering all clutter types. · Customer selects a few sample sites.
  24. 24. Cell Planning Aspects · Survey sites with reference to : >Clutter heights >Vegetation levels. >Obstructions. >Sector orientations >Building strengths and other civil requirements · Prepare Power Budgets. · Conduct propagation tests · Calculate Coverage probabilities based on the drive test results. · Verify Power budget sensitivityagainst drive test result , modify planning tools parameters. · Prepare final coverage maps. .
  25. 25. A typical Power Budget RF Link Budget UL DL Transmitting End MS BTS Tx Rf power output 33 dBm 43 dBm Body Loss -3 dB 0 dB Combiner Loss 0 dB 0 Db Feeder Loss(@2 Db/100 M) 0 dB - 1.5 dB Connector loss 0 dB - 2 Db Tx antenna gain 0 dB 17.5 dB EIRP 30 dBm 57 dBm
  26. 26. A typical Power Budget RF Link Budget UL DL Receiving End MS BTS Rx sensitivity -107 dBm -102 dBm Rx antenna gain 17.5 dBm 0 dB Diversity gain 3 Db 0 dB Connector Loss - 2 dB 0 dB Feeder loss - 1.5 dB 0 dB Interference degradation 3 dB 3 Db margin Body loss 0 dB -3 dB Duplexer loss 0 dB 0 dB Rx Power -121 dBm -96 dBm Fade margin 4 dB 4 dB Reqd Isotropic Rx. Power -117 dBm -92 dBm Maximum Permis. Path los 147 Db 149 dB
  27. 27. Summary · A good RF Planning ensures that the mobiles receive certain minimum signal strength for specified percentage of time over a specified area of coverage. · The MS receive signal strength depends on the path loss depends on the path loss between the MS and the BTS. · The path loss in a mobile environment includes : > Free space path loss >Additional Loss due to Topography of the site ( clutter Factor ) >Confidence level required. (Probability of area coverage ) · In general RF Planning means the understanding of : > Propagation Models > Coverage aspects > Link Budgets ( Power Budgets) > Antenna considerations > Frequency planning and reuse aspects.
  28. 28. Urban Propagation Environment This is the most common and yet unpredictable propagation environment for a mobile system. Building Penetration: Building are responsible for the reflection and shadowing of signals. Trees and foliages also contribute to shadowing as well as scattering of radio signals. Attenuation of signals by building is measured by taking the difference between the median signal level in front of the building and inside the bu9ilding. Obviously, the building attenuation depends on the type of construction and the material used as well as how big or small it is. Typically the attenuation values may cause the signal levels to vary by – 40 to +80 Db The negative value implies that the signal is attenuated and the positive values implies that the increase in the signal level. Windows and Doors in general give a good penetration of RF signals. Another important factor is the angle of arrival of RF signals in to the building. Generally, a building facing the BTS site has better penetration than the one that is side facing and without windows. The furniture used in the building also contributes to attenuation. Typically a furnished building gives a loss of 2-3 dB more than an empty one.
  29. 29. Propagation Environment Some Typical values for Building Attenuation Type of building Attenuation in dBs Farms, Wooden houses, Sport halls 0-3 Small offices,Parking lots,Independent 4-7 houses,Small apartment blocks Row Houses, offices in containers, Offices, Apartment blocks 8-11 Offices with large areas 12-15 Medium factories, workshops without roof tops 16-19 windows Halls of metal, without windows 20-23 Shopping malls, ware houses, buildings with 24-27 metals/glass
  30. 30. Propagation Models • Classical Propagation models :- • Log Distance propagation model • Longley – Rice Model (Irregular terrain model ) • Okumara • Hata • Cost 231 – Hata (Similar to Hata, for 1500-2000 MHz band • Walfisch Ikegami Cost 231 • Walfisch-Xia JTC • XLOS (Motorola proprietary Model ) • Bullington • Du path Loss Model • Diffracting screens model
  31. 31. Propagation Models • Important Propagation models :- • Okumara Hata model (urban / suburban areas )( GSM 900 band ) • Cost 231 – Hata model (GSM 1800 band ) • Walfisch Ikegami Model (Dense Urban / Microcell areas ) • XLOS (Motorola proprietary Model )
  32. 32. Okumara Hata Models In the early 1960 , a Japanese scientist by name Okumara conducted extensive propagation tests for mobile systems at different frequencies. The test were conducted at 200, 453, 922, 1310, 1430 and 1920 Mhz. The test were also conducted for different BTS and mobile antenna heights, at each frequency, over varying distances between the BTS and the mobile. The Okumara tests were valid for : • 150-2000 Mhz. • 1-100 Kms. • BTS heights of 30-200 m. • MS antenna height, typically 1.5 m. (1-10 m.) The results of Okumara tests were graphically represented and were not easy for computer based analysis. Hata took Okumaras data and derived a set of empirical equations to calculate the path loss in various environments. He also suggested correction factors to be used in Quasi open and suburban areas.
  33. 33. Hata Urban Propagation Model The general path loss equation is given as :- Lp = Q1+Q2Log(f) – 13.82 Log(Hbts) - a(Hm)+{44.9-6.55 Log(Hbts)}Log(d)+Q0 Lp = L0 +10r Log (d) path loss in dB F = frequency in Mhz. D = distance between BTS and the mobile (1-20 Kms.) Hbts = Base station height in metres ( 30 to 100 m ) A(hm)={ 1.1log(f) - 0.7 } hm - {1.56log(f) - 0.8} for Urban areas and = 3.2{log(11.75 hm)2 - 4.97 for dense urban areas. Hm= mobile antenna height (1-10 m) Q1 = 69.55 for frequencies from 150 to 1000 MHz. = 46.3 for frequencies from 1500 to 2000 MHz. Q2 = 26.16 for frequencies from 150 to 1000 MHz.
  34. 34. Path Loss & Attenuation Slope The path loss equation can be rewritten as : Lp = L0 + { 44.9 – 6.55 + 26.16 log (f) – 13.83 log (hBTS)-a(Hm) Where L0 is = [69.55 + 26.16 log (f) – 13.82 log ( HBTS ) – A (Hm) Or more conveniently Lp = L0 + 10 log(d) is the SLOPE and is = {44.9 – 6.55 log(hBTS)}/10 Variation of base station height can be plotted as shown in the diagram. We can say that Lp 10 log(d) typically varies from 3.5 to 4 for urban environment. When the environment is different, then we have to choose models fitting the environment and calculate the path loss slope. This will be discussed subsequently.
  35. 35. Non line of Sight Propagation Here we assume that the BTS antenna is above roof level for any building within the cell and that there is no line of sight between the BTS and the mobile We define the following parameters with reference to the diagram shown in the next slide: W the distance between street mobile and building Hm mobile antenna height hB BTS antenna height Hr height of roof hB difference between BTS height and roof top. Hm difference between mobile height and the roof top.
  36. 36. Non line of Sight Propagation • The total path loss is given by: • Lp = LFS+LRFT+LMDB • LFS= Free space loss = 32.44+20 log(f) + 20 log(d) • Where, • LFS = Free space loss. • LRFT = Rooptop diffraction loss. • LMDB = Multiple diffraction due to surrounding buildings. • LRFT = -16.9 – 10 log(w) +10log(f) +20log(^Hm)+L(0) Where hm=hr-hm L( ) = Losses due to elevation angle. L( ) = -10 + 0.357 ( -00) for 0< <35 2.5 +0.075 ( -35) for 35< <55 4.0 +0.114 ( -55) for 55< <90
  37. 37. Non line of Sight Propagation • The losses due to multiple diffraction and scattering components due to building are given by : LMBD = k0 + ka +kd.log(d) +kf.log(f) – 9.log(w) Where K0 = - 18 log (1+ hB) Ka = 54 – 0.8 ( hB) Kd = 18 – 15 ( hB/hr) Kf = - 4 +0.7 {f/925) – 1 } for suburban areas Kf = - 4 +1.5 {f/925) – 1 } for urban areas W= street width hB= hB –hr For simplified calculation we can assume ka = 54 and kd = 18
  38. 38. Choice of Propagation Model Environment Type Model Dense Urban Street Canyon propagation Walfish Ikegami,LOS Non LOS Conditions, Micro cells COST231 Macro cells,antenna above rooftop Okumara-Hata Urban Urban Areas Walch-ikegami Mix of Buildings of varying heights, vegetation, Okumara-Hata and open areas. Sub urban Business and residential,open areas. Okumara – Hata Rural Large open areas,fields,difficult terrain with Okumara-Hata obstacles.
  39. 39. Calculation of Mobile Sensitivity. The Noise level at the Receiver side as follows: NR= KTB • Where, • K is the Boltzmann’s constant = 1.38x10-20 (mW/Hz/0Kelvin) • T is the receiver noise temperature in 0Kelvin • B is the receiver bandwidth in Hz.
  40. 40. Signal Variations Fade margin becomes necessary to account for the unpredictable changes in RF signal levels at the receiver. The mobile receive signal contains 2 components : • A fast fading signal (short term fading ) • A slow fading signal (long term fading )
  41. 41. Probability Density Function The study of radio signals involve actual measurement of signal levels at various points and applying statistical methods to the available data. A typical multipath signal is obtained by plotting the RSS for a number of samples. We divide the vertical scale in to 1 dB bin and count number of samples is plotted against RF level . This is how the probability density function for the receive signal is obtained. However, instead of such elaborate plotting we can use a statistical expression for the PDF of the RF signal given by : P(y) = [1/2 ] e [ - ( - y – m )2 / 2 ( )2 Where y is the random variable (the measured RSS in this case ), m is the mean value of the samples considered and y is the STANDARD DEVIATION of the measured signal with reference to the mean . The PDF obtained from the above is called a NORMAL curve or a Gaussian Distribution. It is always symmetrical with reference to the mean level.
  42. 42. Probability Density Function Plotting the PDF : Plotting the PDF 0 -20 -40 -60 -80 -100 SAMPLES RSS RSS A PLOT OF RSS FOR A NUMBER OF SAMPLES
  43. 43. Probability Density Function Plotting the PDF : Plotting the PDF Bin Numbers P(x) ni/N NORMAL DISTRIBUTION P(x) = ni/N Ni = number of RSS within 1 dB bin for a given level.
  44. 44. Probability Density Function A PDF of random variable is given by : P(y) = [ ½ ] e [ - (y-m)2 / 2( )2 ] Where, y is the variable, m is the mean value and is the Standard Deviation of the variable with reference to its mean value. The normal distribution (also called the Gaussian Distribution ) is symmetrical about the mean value. A typical Gaussian PDF :
  45. 45. Probability Density Function The normal Distribution depends on the value of Standard Deviation We get a different curve for each value of The total area under the curve is UNITY
  46. 46. Calculation of Standard Deviation If the mean of n samples is “m”, then the standard deviation is given by: = Square root of [{(x1-m)2 + …..+( xn-m)2 }/(n-1)] Where n is the number of samples and m is the mean. For our application we can re write the above equation as : = Square root of [{RSS1-RSSMEAN)2+…..+(RSSN-RSSMEAN)2/(N-1)}]
  47. 47. Confidence Intervals The normal of the Gaussian distribution helps us to estimate the accuracy with which we can say that a measured value of the random variable would be within certain specified limits. The total area under the Normal curve is treated as unity. Then for any value of the measured value of the variable, its probability can be expressed as a percentage. In general, if m is mean value of the random variable within normal distribution and is the Standard Deviation, then, The probability of occurrence of the sample within m and any value of x of the variable is given by : P= By setting (x-m)/ = z, we get, P=
  48. 48. Confidence Intervals The value of P is known as the Probability integral or the ERROR FUNCTION The limits (m n )are called the confidence intervals. From the formula given above, the probability P[(m- ) < z < (m+ )] = 68.26 % ; this means we are 68.34 % confident. P[(m- ) < z < (m+ )] = 95.44 % ; this means we are 95.44 % confident P[(m- ) < z < (m+ )] = 99.72 % ; this means we are 99.72 % confident. This is basically the area under the Normal Curve.
  49. 49. The Concept of Normalized Standard Deviation The probability that a particular sample lies within specified limits is given by the equation : P= We define z = (x-m)/ as the Normalized Standard Deviation. The probability P could be obtained from Standard Tables (available in standard books on statistics ). A sample portion of the statistical table is presented in the next slide..
  50. 50. Calculation of Fade Margin To calculate the fade margin we need to know : Propagation constant(g) >From formulae for the Model chosen >Or from the drive test plots Area probability : >A design objective usually 90 % Standard Deviation(s) >Calculated from the drive test results using statistical formulae or >Assumed for different environments. To use Jakes curves and tables.
  51. 51. Calculation of Edge Probability and Fade Margin From the values of s and g we calculate : r= s / g Find edge probability from Jakes curves for a desired coverage probability, against the value of on the x axis. Use Jakes table to find out the correlation factor required – Look for the column that has value closest to the edge probability and read the correlation factor across the corresponding row. Multiply s by the correction factor to get the Fade Margin. Add Fade Margin to the RSS calculated from the power budget
  52. 52. Significance Of Area and Edge Probabilities Required RSS is – 85 dBm. Suppose the desired coverage probability is 90 % and the edge probability from the Jakes curves is 0,75 This means that the mobile would receive a signal that is better than – 85 dBm in 90 % of the area of the cell At the edges of the cell, 75 % of the calls made would have this minimum signal strength (RSS).
  53. 53. In Building Coverage Recalculate Fade Margin. >Involves separate propagation tests in buildings. >Calculate and for the desired coverage ( say 75 % or 50% ) >Use Jakes Curves and tables to calculate Fade Margin. >Often adequate data is not available for calculating the fade margin accurately. >Instead use typical values. Typical values for building penetration loss : Area 75 % coverage 50 % coverage Central business area < 20 dB < 15 dB Residential area < 15 dB < 12 dB Industrial area < 12 dB < 10 dB In Car 6 to 8 dB
  54. 54. Fuzzy Maths and Fuzzy Logic The models that we studied so far are purely empirical. The formulas we used do not all take care of all the possible environments. Fuzzy logic could be useful for experienced planners in making right guesses. We divide the environment into 5 categories viz., Free space, Rural, Suburban, urban, and dense urban. We divide assign specific attenuation constant values to each categories , say Fuzzy logic helps us to guess the right value for , the attenuation constant for an environment which is neither rural nor suburban nor urban but a mixture, with a strong resemblance to one of the major categories. The following simple rules can be used :  Mixture of Free space and Rural :  Mixture of Rural and Suburban :  Mixture of Suburban and Urban :  Mixture of Urban and Dense urban :
  55. 55. Cell Planning and C/I Issues The 2 major sources of interference are: • Co Channel Interference. • Adjacent Channel Interference. The levels of these Interference are dependent on • The cell radius ® • The distance cells (D) The minimum reuse distance (D) is given by : D = ( 3N )½ R Where N= Reuse pattern = i2 + i j + j2 Where I & j are integers.
  56. 56. Cell Planning and C/I Issues R D
  57. 57. Cell Planning and C/I Issues Assuming the cells are of the same size . All cells reansmit the same power. The path loss is not free space and is governed by the attenuation constant . By geometry, for every cell there are 6 interfering cells in the first layer. The reuse distance Dand cell radius R are related to the c/I as given below (D/R) = 6 (C/I) The C/I is in absolute value.
  58. 58. Cell Planning and C/I Issues Co Channel Interference C/I for Omni Cells D/R = 3N C/I = 10 Log [ 1/m (D/R ) ], where m is the number of interferers. M= 1 to 6 for the first layer of interfering cells. Assuming = 3.5, m = 6 (worst case ), we calculate the theoretical C/I available for various reuse plans as shown below : N D/R = 3N C/I = 10 Log [ 1/6 (D/R) ] 3 3 8.917 dB 4 3.46 13.29 dB 7 4.58 21.80 dB 9 5.19 25.62 dB 12 6 29.99 dB
  59. 59. Cell Planning and C/I Issues Adjacent Channel Interference : Adjacent Chl Interference = - 10 Log [1/m (D/R) ]+ Where is the isolation offered by post modulation filters Minimum value of is 26 dB , as per EIA standards. If ( C/I ) for co channel interference is 10 dB, then for adjacent channel interference it is 36 dB.
  60. 60. Frequency Planning Aspects The primary objective of frequency planning is to ensure that, given the limited RF spectrum, we achieve the required capacity (traffic channels), keeping the interference within specified limits. There are two types of frequency planning : >Frequency planning based on Reuse patterns (manual) >Frequency planning based on heuristic algorithm (automatic) Manual planning is done by dividing the available frequencies in to a number of frequency groups (as per a selected reuse pattern ) and assigning frequencies to various sectors / cells. Suppose we have “n” frequencies . For a 3 cell repeat pattern with 3 sectors, we have 9 frequency groups, each group having n/9 frequencies. The sectors are labeled A1,A2,A3,B1,B2,B3 and so on.. Assuming that an operator has 32 frequencies, say, from ARFCN 63 to 94, the frequencies could be grouped as shown in the table opposite.
  61. 61. Frequency Planning Aspects Say, for 32 frequencies (ARFCN 63 –94 ), for a 3*3 reuse pattern, the frequencies are grouped as shown below A1 A2 A3 B1 B2 B3 C1 C2 C3 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 OR A1 B1 C1 A2 B2 C2 A3 B3 C3 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94
  62. 62. Frequency Planning Aspects The Frequency reuse could be done in either of 2 ways mentioned in the tables in the previous slide :
  63. 63. Frequency Planning Aspects Directional reuse : In a sectorised site, a group of channels (ARFCN) is transmitted in the direction of antenna orientation , This is based on tri cellular platform consisting of 3 identical cells as shown in the diagram in the last slide. Every cell is considered as an omni logically. The cells are excited from the corners, separated by 1200 The axes of the diagram represent the 3 directions of reuse. These are designated as { f(00)}, {f(1200)} and {f(2400)} Because we use directional antennas, the worst co channel interference will be from only one interfering station in the same direction
  64. 64. Frequency Planning Aspects We form a generic combination of the tricell pattern using 7 such pattern, as shown in fig. Down. From this we can see that each of three axes has three parallel layers. This result in a total of six or multiples of six frequency GROUPS. While assigning frequencies to individual calls we have to take the directions of reuse into account.
  65. 65. Antenna Considerations · Uniform coverage in all cells · Alignment with hexagonal pattern · Space availability · Connectivity to BSC/MSC Urban areas may have the following conditions : · Several sites may be needed. · Frequency reuse is unavoidable · In building penetration is must · Building act as RF shield and contain coverage. · Buildings reflect signals and provide coverage to areas where LOS would have failed. · Such additional paths improve in building penetration. · Antenna at a very high point may not meet in building coverage requirements
  66. 66. Tackling Multipath Fading In general we have the following methods to combat Multipath fading: · In time domain Interleaving and coding · In Freq. Domain Frequency hopping · In spatial domain Space diversity · In the polarization domain Polarization diversity The last two are related to Antenna Systems.
  67. 67. Diversity Antenna Systems A diversity antenna System essentially has : · Two or more antenna · A combiner circuitry. Signals A and B should have minimum correlation between them typically the correlation coefficient <0.7
  68. 68. Diversity Antenna Systems Antenna Spacings : Separation D/ 900 Mhz 1800Mhz Horizontal 10 3.3 m 1.7 m Vertical 17 5.7 m 2.8 m >Figures in the table are of minimum required separation >If space is not a constraint, larger separation is always recommended. >Horizontal separation is preferred because it provides low correlation values. >However, horizontal separation suffers from angular dependence (demonstrated in the diagram, next page ). >Vertical separation does not suffer much from the angular dependence. >It also requires minimum supporting fixtures and does not occupy a lot of space. >But as the distance increases the correlation between the RF signal at the antenna points increases rapidly, thereby negating the very advantage of space diversity.
  69. 69. Diversity Antenna Systems Space diversity can be achieved using: · 3 antenna system · 2 antenna system The 3 antenna system provides very good spatial separation between the two receive antenna and avoids the use of duplexers. This reduces the risk of generating intermodulation products. The 2 antenna system is preferred where the space for the antenna structure is limited or where the operators want to use less number o antenna.
  70. 70. Diversity Antenna Systems Advantages of dual polarization : · Reduced support structure for the antenna · Reduced weight · Slim towers and hence quicker construction and low cost. · Cost of one dual polarized antenna is generally lower than the cost of two space diversity antenna. Choice of Dual Polarized type H/V type : · As most mobile are held at an angle 450, H/V is more likely to cause balanced signals at the two branches. · The diversity performance is less dependent on the mobile location Slant type · Correlation between the two elements is angular dependent. · Unbalanced signals at the two arms of the receive antenna, since one of the signal could be at the same angle as the mobile
  71. 71. General Antenna Specifications Typical parameters of importance : · Polarization Linear polarization :Evector contained in one plain Horizontal polarization :H Vector parallel to the horizontal plane Vertical Polarization : E Vector parallel to the vertical plane Circular / Elleptical Polarization The extremity of the E or H field describes a circle or an ellipse in the direction of propagation · Radiation pattern This is a plot of electric field intensity as a function of direction from the antenna, measured at the fixed distance.
  72. 72. General Antenna Specifications When the main radiation lobe of the antenna is intentionally adjusted above or below its plane of propagation, the result is known as a beam tilt. When tilted downward, we get the Downtilt. Down tilt can be done in two ways : Electrical down tilt Mechanical down tilt
  73. 73. RADIO PLANNING METHODOLOGY Overall picture It is important to create an overall picture of the network before going into the detailed network planning. This is the fact the main objective of this presentation. Coverage Capacity and Quality Providing coverage is usually considered as the most important activity of a new cellular operator. For a while , every network is indeed coverage driven. However the coverage is not the only thing. It provides the means of service and should meet certain quality measures. The starting point is a set of coverage quality requirements. To guarantee a good quality in both uplink and downlink direction, the power levels of BTS and MS should be balanced at the edge of the cell. Main output results of the power link budget are: - Maximum path loss that can be tolerated between MS and the BTS. - Maximum output power level of the BTS transmitter.
  74. 74. RADIO PLANNING METHODOLOGY These values are calculated as a result of design constraints. - BTS and MS receiver sensitivity. - MS output power level - Antenna Gain - Diversity reception - Losses in combiners, cables etc. The cell ranges are derived with propagation loss formulas such as Okumara Hata or Walfisch Ikegami, which are simply to use . Given a maximum path loss, differences in the operating environment and the quality targets will result in different cell ranges. The traffic capacity requirement have to be combined with the coverage requirements, by allocating frequencies. This also may have impact on the cell range.
  75. 75. COVERAGE PLANNING STRATEGIES The selection of site configurations, antenna and cables in the core of the coverage planning strategy. The right choice will provide cost saving and guarantees smooth network evolution. Some typical configurations are : - 3 sector site for (sub)urban areas - 2 sector site for road coverage. - Omni site for rural areas. These are not the ultimate solutions, decisions should be based on careful analysis. Cell Range and Coverage Area : For any site configurations, the cell ranges can be determined given the equipment losses and gains. The site coverage areas can be calculated then and these will lead to required number of sites for a given coverage region. This makes it possible to estimate the cost, eg. Per km2, to be used for strategic decisions After getting the overall picture, the actual detailed radio network planning is done with a RNP tool.
  76. 76. RADIO PLANNING METHODOLOGY - Marketing specifications - Define design rules and parameters. - Set performance targets. - Design nominal cell plan. - Implement cell plan. - Produce frequency plan. - Optimize network. - Monitor performances.
  77. 77. METHODOLOGY EXPLAINED Define design rules and parameters - Identify design rules to meet coverage and capacity targets efficiently - Acquire software tools and databases - Calibrate propagation models from measurements. Set performance targets - Clear statement of coverage requirements (rollout and quality) - Forecast traffic demand and distribution. - Test business plan for different roll out scenarios and quality levels. Design nominal cell plan. - Use computer tool to place sites to meet coverage an d capacity targets. - Verify feasibility of meeting service requirements - Ensure a frequency plan can be made for the design. - Estimate equipment requirement and cost. - Develop implementation and resource plans (including personal requirements) - Radio plan will provide input to fixed network planning.
  78. 78. METHODOLOGY EXPLAINED Implement Cell plan - Identify physical site locations near to nominal or theoretical locations, using search areas. - Modify nominal design as theoretical sites are replaced with physical sites - Modify search areas in accordance with envolving network. Produce Frequency Plan - Fixed Cluster configration, can be done manually. - Flexible, based on interference matrix using an automatic tool.
  79. 79. METHODOLOGY EXPLAINED Optimize the network - Campaign of measurements - Analyze results - Adjust network parameters such as : antenna directions, handover parameters, and frequencies. Expand the network - In accordance with rollout requirements - In accordance with forecast traffic levels - To improve coverage quality. - To maintain blocking performances.
  80. 80. RF Planning Process 1 Understand the Customers requirements Coverage requirements In building coverage experiments Initial Roll out plans Pre determined number of sites ? 2 Survey Traffic Distribution and Pattern Growth areas High density business/ residential areas Propagation tests for in building coverage estimates and model calibrations 3. Prepare Planning Tool Get Digitized maps Load maps in the planning tool. Use survey data and run the programme.
  81. 81. RF Planning Process 4. Draft Plan Divide the city into number of regions- Busy business areas Areas that need excellent inbuilding coverage areas Use appropriate model and link budgets to calculate the number of sites required per region. 5. Fine Tune plan. Perform more with drive test, confirm plan predictions. Review plan with customer and fine tune the plan.
  82. 82. RF Planning Process Understanding Customer Requirements : What are the boundaries for the network ? Are there any special pockets to be covered due to Govt. requirements ? What are the areas in which medium to average in building coverage is acceptable ? What are the areas where excellent in building coverage is needed ? Areas with high growth potential · Need colonies under development · High revenue areas · Shopping malls , offices complex, industrial estates etc.
  83. 83. RF Planning Process Initial Implementation Strategy : High usage, high revenue users first ? High end residential and business areas ? Street coverage first ? Special areas like 5 star hotel, commercial building with fine in building coverage ? High way coverage critical ? Total coverage on day one ? Number of sites more than the competition ? Any Budget Limitations ? Give an ideal plan to start with. Let the customer cut corners. Not an easy job !!
  84. 84. RF Planning Process City Surveys : · Basically a scouting exercise Looking for :- Major traffic routes Markets Business Centres Shopping malls General customer behaviors Telephone density Congested areas with narrow lanes Narrow water canals/lakes/ponds General city layout Prestigious residential areas. VIP areas Parks/ playground/open areas. General Building types.. Multistoried, Row houses, apartments, colonies etc. Airport coverage
  85. 85. RF Planning Surveys In building Coverage Surveys : · Classify Buildings- Hotel/restaurants Commercial Industrial Residential Shopping malls/markets · Propagation tests in a number of buildings in each variety. · Rf signal on road Vs. inside building gives building penetration loss. · Repeat tests in as many buildings as possible to get an estimate of building loss for the area. · In building coverage affected mostly in ground floor/basement · Typical values (examples only) : > Hotel restaurants 15 dB > Commercial buildings 20 dB > Shopping malls 15 dB > Industrial Estates 12-15 dB > Residential buildings 15-20 dB > Old/Historical buildings 25-30 dB
  86. 86. RF Propagation Test Kits Battery powered Transmitter. 10 or 20 Watts output : frequency in GSM 900/1800 Mhz. Portable mast Adjustable upto 5 m. With 1 m antenna on top, effective height above ground is 6 m. Transmit antenna High gain omni or directional antenna as required Receiver TEMS mobile Hand held mobile phone with RS232 connection to a laptop. Or an accurate portable RF sensitivity meter / CW receiver if model calibration is required. Positioning system GPS system, with PCMCIA card Computer Laptop PC with TEMS software and GPS software Cables accessories Calibrated cable lengths (10 m) of low loss feeder with known attenuation values; 12 Volts battery with appropriate cable to connect to transmitter. Power meter, VSWR meter.
  87. 87. RF Planning Tool Planning Tool preparation and Model Calibration : There are many planning tool available toaday : PLANET (MSI) Cell Cad (LCC) Odessy (Aethos) Asset (Aircom) NetPlan (Motorola) A planning tool Should be : Easy to use Compatible with tools like TEMS Minimum hardware requirements. Economical. Maps collected from authorized sources. 1:50000 or 1:25000 scale 50 m resolution for macro Less than 30 m resolution for Micro cell planning using “Ray tracing Tool” Maps are digitized under 3 categories : LandUse Digital Terrain Map Vectors (Roads, Railways, etc.)
  88. 88. RF Planning Tool Planning Tool preparation and Model Calibration : Most Planning tools use corrections for the land use or clutter. Propagation Model tuned by assigning the values to · Clutter factor (Gain or Loss due to clutter ) · Clutter Heights (for diffraction modeling) Different types of clutter are defined in these models/ tools 1. Dense Urban 2. Urban 3. Suburban 4. Suburban with Dense Vegetation 5. Rural 6. Industrial area 7. Utilities (marshalling yards, docks, container depots etc. ) 8. Open area 9. Quasi Open Area 10. Forest 11. Water Too many clutter type definitation complicate planning process 10 to 15 is typical.
  89. 89. RF Planning Tool Planning Tool preparation and Model Calibration : DTM · Provided by the map vendor · Provides contour information as a digital map. Vectors · Highways · Main Roads · Railways · Canals / water ways. · Coast line · Rivers. Each categories is digitized as different layer Displayed separately if required Map information is set up in the planning tool. Model calibration carried out.
  90. 90. Model Calibration All tools have provision for manipulating clutter values. Different tools have different directory structures and means of handling geographical data. The procedure mainly talks about ensuring correct data header files to include. · BTS location · EIRP of BTS · Antenna Type · BTS antenna height · Description of surrounding area. Procedure uses a general core model equation : · The equation has constant k1 to k6 and a constant of clutter, kclutter · Initial values for the constants are set as per the model chosen (say Okumara Hata ) · PLANET programme is run repeatedly to make RMS error values for all data files ZERO or a minimum. · For each run of the programme, the values of k1 to k6 are manipulated. · This completes model calibration.
  91. 91. Link Budget and other Steps Key Points To be Considered : Coverage Probability Expected inbuilding coverage Edge probability Fade margin required Maximum permissible path loss ( from the link Budget ) What is the radius of the cell ? Number of sites required (from coverage point of view ) Is the number of sites calculated as above adequate for capacity ? Decide on more sites for capacity.
  92. 92. Capacity Calculations Capacity calculations : Check if number of sites is enough to give capacity. Depends on · Spectrum available · This decides the site configuration. · Availability of features like frequency hopping etc. If Capacity is not met, add more sites. If number of site is not OK with the customer, then :- Recalculate site density, for 50 % in building coverage in place of 75 %
  93. 93. Fine Tune The Plan Use Planning tool to return Coverage predictions Iterate the process in consultation with the customer. Finalize Plan and document it. Search Areas Planner issues search areas for each site location with information on : · Location · Lat/Long · Antenna heights · Specific target areas if any · Size of search areas Size acquisition team scouts for buildings. 3-5 alternatives preferred.
  94. 94. Site Selection Central Business area Small Search areas (100 m) Avoid near field obstruction. Antenna at or slightly above the average clutter height. Orientation is critical. Try solid structure (lift room ) for antenna mounting. This helps reduce backlobe radiation problems Avoid towers on building tops. This reduces interference to neighbouring cells. Residential suburban areas : Larger search areas (200 m) Location not very critical. Antenna 3-5 metres above average clutter height. Antenna orientation less critical.
  95. 95. Site Selection Industrial area : A suitable central location. Avoid proximity to electrical installations like towers, transformers etc. Towers are common Quasi / open Highways Larger search areas (500 m) Limited by terrain and not the clutter. Hilly areas need care. Highways need closer search areas along road. Tall sites give better coverage.
  96. 96. Extending Cell Range Extended cell range reduces number of sites. Cell range improvement achieved through : · BTS transmit power enhancement · BTS sensitivity enhancement · Combination of both
  97. 97. Extending Cell Range Increasing BTS transmit EIRP: To maximize BTS O/P power, single carrier cells can be used. This will avoid the combination losses of multiple carrier cells. The output power at the top of the cabinet could be set to 40 Watt, giving an increase in signal strength of 3 Db. For cells with more than aone carrier, air combination can be implemented so that the combination loss is minimized. Another way to maximize Tx and Rx signals is to implement lowloss feeder cable. A typical 7/8 “ Andrewscoaxial cable has an attenuation of 3.92 dB/100 m. If a 5/8” Andrews cable with an attenuation of 2.16 dB/100 m is used, then an increase of 1.6 dB can be obtained per 100m.
  98. 98. Extending Cell Range Improving BTS receiver sensitivity : Better devices in the BTS receiver. Using Mast Head amplifiers with very low noise figures. Better RF cables.
  99. 99. Extending Cell Range Improvement in the transmit side gives 2 dB advantage. MHA’s extend the BTS receiver sensitivity to –110 dBm instead of the usual – 107 dBm. Overall improvements result in 4-5 dB advantage in path loss, leading to extended coverage. This improves quality of coverage. Experiments with MHA’s have shown improvements · In areas with 50 % probability to approximately 70 % probability. · In areas with 70 % probability to approximately 85 % probability. · In areas with 85 % probability to approximately 95 % probability. · In areas with 95 % probability to approximately 98 % probability.