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National-Level Faculty Development Workshop“Challenges for Research in Wireless Communication                   Technologi...
Principles of                 Cellular             Communications                            Cell structure andCellular Te...
 A cell is the basic geographic unit of a cellularsystem. It is also called a footprint.  A cell is the radio area cove...
Determined by the desired                                                     Rreceived signal level by themobile subscrib...
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    Offers best possible non-    overlapped cell radio    coverage   Multiple hexagons can be    arranged next to each  ...
    A group of cells that use a different set of    frequencies in each cell    Only selected number of cells can form a...
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One very powerful transmitter located at the  highest spot in an area would broadcast in a  radius of up to 50 kilometers....
Main limitation of a conventional mobile wireless    communication system is:   Limited availability of FREQUENCY    SPEC...
System capacity at required QoS        The need:with conventional frequency plan       • Optimum                    Out of...
   Reuse allocated RF spectrum or a given set of    frequencies (frequency channels) in a given    large geographical ser...
   Large coverage area, efficient spectrum    utilization and enhanced system capacity are    the major attributes of cel...
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   Cells, which use the same set of frequencies,    are referred to as cochannel cells   Co-channel cells are located su...
Suppose the system has RF                                    spectrum for 100 voice          2            3            cha...
Technical issues for proper design and planning   of a cellular network:   Selection of a suitable frequency reuse patter...
   In a cellular system, the whole    geographical service area is divided into a    number of clusters having finite num...
   The cluster can be replicated many times to    cover the desired geographical area by a    cellular communication syst...
Cells which use the same set offrequencies are referred to ascochannel cells.The interference between cochannelcells is ...
The shift parameters iand j are separated by60 degrees in ahexagonal geometryIt can have anyinteger value 0, 1, 2,….The...
Rules for determining the nearest cochannel cell    using “Shift parameters” (i, j) to lay out a    cellular system is:  ...
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Distance betweentwo adjacent cells,d = √3 RLet D be the distancebetween twoco-channel cells.D = √{3R2(i2+j2+ixj)}D2/(3R2...
By     joining   thecenters of the sixnearest cochannelcells,     a   largehexagon is formedwith radius equalto D, which i...
Asmall hex = (3√3/2)xR2Alarge hex = (3√3/2)xD2Number of cells in largehexagon, L = D2∕R2Number of cells enclosedby large h...
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9                   9        8         10         8            10              2        11             2        7         ...
    Reusing an identical frequency channel in    different cells is limited by co-channel    interference between cells....
   The number of co-channel cells in the vicinity    of the center cell    The type of geographic terrain contour    Th...
C1               C1                       D                   R                R            q=D ∕RThe frequency reuse rati...
•   The real power                                    of the cellular                                    concept is that  ...
   The frequency reuse factor, q can be    determined from the cluster size K as        q = D / R = (3K)   The frequenc...
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   Theoretically, a large value of D is desired to    reduce co-channel interference. Large D can    be obtained by choos...
    Now the challenge is to obtain the smallest K    which can still meet the desired system    performance requirements ...
Advantage: The           Disadvantage: If thefrequency reuse          system is notsystem can               properly desig...
Sources of Interference      Another mobile in the same cell      A call in progress in a neighboring cell      Other b...
On Control Channels      On Voice Channels      Interference leads to   Causes cross talk       missed calls and       whe...
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A channel scanning mobile receiver recordsthree received signals while moving in any oneco-channel cell, under following c...
    If C/I > 18 dB in most of the area being served    by a cell, the system is said to be properly    designed.    If C...
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   When only the mobile unit in the serving cell    transmits (signal recorded is termed as C)    Up to six interference...
Increasing the     Using directional   separation       antennas at thebetween two co-         cell sitechannel cells (D) ...
    The essential principles of cellular    communication include frequency reuse, co-    channel cells, and co-channel i...
T. L. Singal graduated from National Institute of Technology,                Kurukshetra in 1981 . He began his illustriou...
T L Singal, Wireless Communications,      ISBN: 978-0-07-068178-1, Tata McGraw-Hill, First Edition, 2010.     www.mhhe.com...
tl.singal@chitkara.edu.inContact No: +91-98145-42041                              52
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Cellular Architecture Design Concepts

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Cellular Architecture Design Concepts

  1. 1. National-Level Faculty Development Workshop“Challenges for Research in Wireless Communication Technologies” Presented by Prof. T. L. Singal May 21-23, 2012 Chitkara University, Punjab 1
  2. 2. Principles of Cellular Communications Cell structure andCellular Terminology cluster Cluster Size andFrequency Reuse Concept System CapacityMethod of Locating Co- Frequency Reuse channel Cells DistanceCo-channel Interference Co-channel Interference and Signal Quality Reduction Methods 2
  3. 3.  A cell is the basic geographic unit of a cellularsystem. It is also called a footprint.  A cell is the radio area covered by a cell-site that is located at its center  A large geographical area is divided into a number of contiguous smaller geographical coverage areas called cells 3
  4. 4. Determined by the desired Rreceived signal level by themobile subscribers from (a) Ideal Cellits base station transmitterin its operating areaIdeal, actual andfictitious cell models (b) Actual Cell R R R R (c) Fictitious Cell 4
  5. 5. 5
  6. 6. 6
  7. 7. 7
  8. 8.  Offers best possible non- overlapped cell radio coverage Multiple hexagons can be arranged next to each other For a given radius (largest possible distance between the polygon center and its edge), the hexagon has the largest area Simplifies the planning and design of a cellular system 8
  9. 9.  A group of cells that use a different set of frequencies in each cell Only selected number of cells can form a cluster Can be repeated any number of times in a systematic manner The cluster size is the number of cells within it, and designated by K 9
  10. 10. 10
  11. 11. One very powerful transmitter located at the highest spot in an area would broadcast in a radius of up to 50 kilometers.Limitations: High power consumption Low capacity Large size of the mobile 11
  12. 12. Main limitation of a conventional mobile wireless communication system is: Limited availability of FREQUENCY SPECTRUM !!!So the big challenge is … to serve large number of mobile users .. within limited allocated frequency spectrum with a specified system quality 12
  13. 13. System capacity at required QoS The need:with conventional frequency plan • Optimum Out of spectrum usage Capacity!!! • More capacity • High quality of Subscriber growth service (QoS) Time • Low cost How to increase capacity & Spectrum utilization ? 13
  14. 14.  Reuse allocated RF spectrum or a given set of frequencies (frequency channels) in a given large geographical service area without increasing the interference Divide the service area into a number of small areas called cells Allocate a subset of frequencies to each cell Use low-power transmitters with lower height antennas at the base stations 14
  15. 15.  Large coverage area, efficient spectrum utilization and enhanced system capacity are the major attributes of cellular communication Frequency reuse is the core concept of cellular communications The design process of selecting and allocating channel groups for all the cellular base stations within a system is called frequency reuse 15
  16. 16. 16
  17. 17.  Cells, which use the same set of frequencies, are referred to as cochannel cells Co-channel cells are located sufficiently physically apart so as not to cause cochannel interference The space between adjacent cochannel cells is filled with other cells that use different frequencies to provide frequency isolation 17
  18. 18. Suppose the system has RF spectrum for 100 voice 2 3 channels Scenario 1: A high power1 7 4 base station covering entire 6 area – system capacity = 100 5 channels Scenario 2: Divide spectrum HPT – High Power Transmitter into 4 groups of 25 channels each; cells (1, 7), (2, 4), (3, 5), LPT – Low Power Transmitter 6 are assigned distinct channel groups – system capacity = 175 channels 18
  19. 19. Technical issues for proper design and planning of a cellular network: Selection of a suitable frequency reuse pattern Physical deployment and radio coverage modeling Plans to account for the expansion of the cellular network Analysis of the relationship between the capacity, cell size, and the cost of the infrastructure 19
  20. 20.  In a cellular system, the whole geographical service area is divided into a number of clusters having finite number of cells. The K number of cells in a cluster (cluster size) use the complete set of available frequency channels, N. Each cell in the cluster contains J = (N/K) number of channels only Therefore, N = J x K; where J ≤ N 20
  21. 21.  The cluster can be replicated many times to cover the desired geographical area by a cellular communication system Let M be the number of clusters in the system, then overall system capacity, C is given as C=MxN→C=MxJxK (N = J x K) When K is reduced, J is proportionally increased since N = J x K is constant. To increase C, M is increased. But reducing K will increase co-channel interference! 21
  22. 22. Cells which use the same set offrequencies are referred to ascochannel cells.The interference between cochannelcells is referred to as cochannelinterference.The space between adjacentcochannel cells are filled with cellsusing different frequencies. 22
  23. 23. The shift parameters iand j are separated by60 degrees in ahexagonal geometryIt can have anyinteger value 0, 1, 2,….These can be used todetermine the locationof cochannel cells 23
  24. 24. Rules for determining the nearest cochannel cell using “Shift parameters” (i, j) to lay out a cellular system is: Step 1: Move i cells along any side of a hexagon. Step 2: Turn 60 degrees anticlockwise Step 3: Move j cells.where i and j are shift parameters and can have integer value 0, 1, 2, 3, and so on … 24
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  26. 26. Distance betweentwo adjacent cells,d = √3 RLet D be the distancebetween twoco-channel cells.D = √{3R2(i2+j2+ixj)}D2/(3R2) = i2+j2+i x j 26
  27. 27. By joining thecenters of the sixnearest cochannelcells, a largehexagon is formedwith radius equalto D, which is alsothe cochannel cellseparation. 27
  28. 28. Asmall hex = (3√3/2)xR2Alarge hex = (3√3/2)xD2Number of cells in largehexagon, L = D2∕R2Number of cells enclosedby large hexagon,L = K+6x[(1 ∕3)x K] = 3 xKK = D2∕ (3 x R2)K = i 2 + j2 + i x j 28
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  31. 31. 9 9 8 10 8 10 2 11 2 7 11 3 7 3 1 12 1 6 12 4 6 4 9 5 98 5 10 8 10 2 11 27 11 3 7 1 3 12 1 126 4 6 4 5 5 31
  32. 32.  Reusing an identical frequency channel in different cells is limited by co-channel interference between cells. The co-channel interference can become a major problem in cellular communication. It is desirable to find the minimum frequency reuse distance D in order to reduce this co- channel interference. 32
  33. 33.  The number of co-channel cells in the vicinity of the center cell The type of geographic terrain contour The antenna height The transmitted power at each cell siteNOTE: As long as the cell size is fixed, co- channel interference is independent of transmitter power of each cell. 33
  34. 34. C1 C1 D R R q=D ∕RThe frequency reuse ratio, q is also referred as the co-channel reuse ratio the co-channel reuse factor co-channel interference reduction factor 34
  35. 35. • The real power of the cellular concept is that  Interference is D not related to the absolute distance between cells 6  but related to 6 5 1 the ratio of the R distance5 1 7 between co- 7 4 2 channel (same frequency) cells4 2 3 to the cell radius 3 35
  36. 36.  The frequency reuse factor, q can be determined from the cluster size K as q = D / R = (3K) The frequency reuse factor determines the minimum distance for repeating a set of frequencies The spectrum efficiency is most significantly influenced by the frequency reuse factor 36
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  38. 38.  Theoretically, a large value of D is desired to reduce co-channel interference. Large D can be obtained by choosing large cluster size K. However, when K is too large, the number of channels assigned to each of K cells becomes small since N is fixed. As K increases, system capacity per cell and hence spectrum efficiency reduces significantly. 38
  39. 39.  Now the challenge is to obtain the smallest K which can still meet the desired system performance requirements in terms of capacity per cell, spectrum utilization efficiency and received signal quality (minimum co-channel interference). This involves estimating co-channel interference and selecting the minimum frequency reuse distance D to reduce co channel interference (and hence small K). 39
  40. 40. Advantage: The Disadvantage: If thefrequency reuse system is notsystem can properly designed,drastically increase co-channelthe spectrum interference mayefficiency, thereby, occur due to theincreasing the simultaneous use ofsystem capacity. the same channel. Co-channel Interference is the majorconcern in the concept of frequency reuse. 40
  41. 41. Sources of Interference  Another mobile in the same cell  A call in progress in a neighboring cell  Other base stations operating in the same frequency band or  Any non cellular system which inadvertently leaks energy into the cellular frequency band 41
  42. 42. On Control Channels On Voice Channels Interference leads to Causes cross talk missed calls and where the blocked calls due to subscriber hears error in the digital signaling interference in the background due to an undesirable transmission. Interference is more pronounced in urban areas due to greater RF noise floor and the large number of base stations and mobiles.  Capacity cannot be increased. 42
  43. 43. 43
  44. 44. A channel scanning mobile receiver recordsthree received signals while moving in any oneco-channel cell, under following conditions:  When only serving cell transmits (signal recorded is termed as C)  Cell-sites of all six co-channel cells only transmit (signal recorded is termed as I)  No transmission by any cell site (signal recorded is termed as N) 44
  45. 45.  If C/I > 18 dB in most of the area being served by a cell, the system is said to be properly designed. If C/I < 18 dB and C/N > 18 dB in some areas, the system is said to have co-channel interference problem. If both C/I and C/N < 18 dB and C/I is approximately same as C/N in a given area, the system is said to have radio coverage problem. If both C/I and C/N are < 18 dB and C/I < C/N in a given area, the system is said to have both co-channel interference as well as radio coverage problem. 45
  46. 46. 46
  47. 47.  When only the mobile unit in the serving cell transmits (signal recorded is termed as C) Up to six interference levels are obtained at the serving cell site from six mobile units transmitting in six co-channel interfering cells. (the statistical average signal recorded is termed as I) No transmission by any mobile unit (signal recorded is termed as N) 47
  48. 48. Increasing the Using directional separation antennas at thebetween two co- cell sitechannel cells (D) Lowering the Use of diversityantenna heights scheme at at the cell site receiver 48
  49. 49.  The essential principles of cellular communication include frequency reuse, co- channel cells, and co-channel interference Various cell parameters based on regular hexagonal cellular pattern include cluster, frequency reuse distance, reuse factor Co-channel interference reduction methods aim at maintaining desired signal quality and cell capacity 49
  50. 50. T. L. Singal graduated from National Institute of Technology, Kurukshetra in 1981 . He began his illustrious career with Avionics Design Bureau at HAL, Hyderabad and worked on design and development of Air-Route Surveillance Radar Communication System. Then he led R&D group in a Telecom company and successfully developed Multi-Access Wireless Communication Systems.He executed international assignment as Senior Network Consultant with Flextronics International Inc. USA during 2000- 02. He was associated with Nokia, AT&T, Cingular Wireless and Nortel Networks, for optimization of 2G/3G Cellular Networks in USA. Since 2003, he is in teaching profession in engineering colleges in India. He has number of technical research papers published in the IEEE Proceedings, Journals, and International/National Conferences. He has authored two text- books `Wireless Communications’ and `Analog & Digital Communications’, published by renowned publisher Tata McGraw-Hill. 50
  51. 51. T L Singal, Wireless Communications, ISBN: 978-0-07-068178-1, Tata McGraw-Hill, First Edition, 2010. www.mhhe.com/singal/wc 51
  52. 52. tl.singal@chitkara.edu.inContact No: +91-98145-42041 52
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