Lec 2 Cell Planning Principles lecture notes
- 1. History of Communication Frequency Planning Coverage & Capacity The Cellular Concept Engr. Mian Shahzad Iqbal Lecturer Department of Telecommunication Engineering
- 2. Before GSM: Mobile Telephony Mile stones Electric transmission (Graham Bell) 1st wireless transmissions (Marconi) • • • — — — • • • 1st analog cellular network 1897 1 0 1 0 1 0 1 0 Digital Technology (1st digital switch) 1st public mobile telephone 1876 1946 1970 1982 1992 1st GSM communication (digital cellular network) 1 0 1 0 1 0 1 0
- 3. What is GSM? ETSI: European Telecommunications Standards Institute SMG: Special Mobile Group GSM 900: Global System for Mobiles 900 MHz Band. DCS 1800: Digital Cellular System 1800 MHz Band.
- 4. 1982: Groupe Spécial Mobile (GSM) 1985: List of recommendations are settled and intensely supported by the industry. 1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries: • time-scales for the procurement and deployment, • compatibly of numbering and routing plans, • tariff principles and definition of accounting. 1990: • The GSM specifications for the 900 MHz are frozen. • Specifications start for the 1800 MHz GSM systems. • GSM stands as "Global System for Mobile communications" Development of the GSM Standard
- 5. 30 40 50 60 70 80 90 100 120 140 160 180 200 240 300 MHz 3 4 5 6 7 8 9 10 12 14 16 18 20 24 30 GHz 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.4 AM Marine Short Wave - International Broadcast - Amateur 3 4 5 6 7 8 9 10 12 14 16 18 20 24 30 MHz CB 26 28 VHF LOW Band FM VHF VHF TV 7-13 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.4 3.0 GHz UHF UHF TV 14-69 GPS Cellular GSM1800, GSM1900 Broadcasting Land-Mobile Aeronautical Mobile telephony Terrestrial Microwave Satellite The Application of the Radio Spectrum
- 6. 30 40 50 60 70 80 90 100 120 140 160 180 200 240 300 MHz 3 4 5 6 7 8 9 10 12 14 16 18 20 24 30 GHz 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.4 AM Marine Short Wave - International Broadcast - Amateur 3 4 5 6 7 8 9 10 12 14 16 18 20 24 30 MHz CB 26 28 VHF LOW Band FM VHF VHF TV 7-13 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.4 3.0 GHz UHF UHF TV 14-69 GPS Cellular GSM1800, GSM1900 Broadcasting Land-Mobile Aeronautical Mobile telephony Terrestrial Microwave Satellite The Application of the Radio Spectrum
- 7. GSM Architecture F1 F2 F1' F2' Frequency 1 2 3 4 5 6 7 8 45 MHz BS Transmission Band : 935 – 960 MHZ MS Transmission Band : 890 – 915 MHZ Year Introduced 1990 Access method TDMA Channel Bandwidth 200 kHz Number of duplex channels 125 Users per channel 8 Speech coding bit rate 13 kbps Data coding bit rate 12 kbps Frame size 4.6 ms
- 8. The cellular concept • Earlier systems used single high power transmitter. So no frequency reuse • Cellular concept solve the problem of spectral congestion and user capacity without any major technological changes. • Replaces single high power transmitter with many low power transmitters. • Each base station is allocated portion of available channels. • Distribution to neighbors so that minimize interference.
- 9. Contd.
- 10. • Hexagonal shape is only logical shape. Actual coverage of cell is known as footprint and is determined by measurements and prediction models. Cell must be designed to serve the weakest mobile at edge in footprint. Frequency reuse
- 11. Cell Shape & Coverage Actual Shape: Irregular Shape depending on terrain or result from planning. Theoretical Shape: Hexagon is used for showing a cell footprint.
- 12. S total duplex channels • S=kN k duplex channel allocated to one cell (k<S) • C=MkN =MS N number of cells which use together full channels S. • N is called cluster size M if cluster is repeated M times typically equals to 4,7,12 C total capacity • If N is reduced (cluster size) keeping cell size constant more clusters are required to cover a given region so more capacity is achieved. But increases co channel interference. Frequency reuse
- 13. • Smallest possible value of N is desirable to increase capacity. • Frequency reuse factor of cellular system is given by 1/N as each cell in cluster is only assigned 1/N of total available channels in system. • Number of cells per cluster N can only have values which satisfies eq N=i^2+ij+j^2 Frequency reuse
- 14. • i and j are non negative numbers • Follow the steps to find nearest co channel interferer. 1. Move i cells along any chain of hexagonal. 2. Turn 60 degree anticlockwise or 120 degree clockwise and move j cells. Frequency reuse
- 15. Method of locating co-channel cells in a cellular system. In this example, N = 19 (i.e., I = 3, j = 2). Frequency reuse
- 16. Frequency Reuse „ Small number of radio channel were available for mobile systems. „ Find way to reuse radio channels. „ Mobile telephone system architecture is restricted into cellular concept.
- 17. Numerical „ Total Bandwidth 33MHz. „ Uses two 25Khz simplex channel to provide full duplex voice and control channels. „ Compute the total number of channels avaliable per cell if a system uses: „ 4 cell/cluster „ 7 cell/cluster „ 12 cell/cluster „ If 1 MHz of the allocated spectrum is dedicated to control channels and voice channels in each cell for each of three systems. „ Self practice question 3.4 page no.97.
- 18. Co-Channel and Adjacent Channel Interference „ CCI is interference from two different radio stations on the same frequency. „ ACI is interference caused by extraneous power from a signal in an adjacent channel. „ Caused by inadequate filtering. „ ACI is distinguished from crosstalk.
- 19. Smaller N is greater capacity
- 20. Signal to Interference Formula „ S is desired signal power. „ I Interference power. „ i 0 number of co-channel interfering cells. „ D/R co-channel reuse ratio. „ S/I signal-to-interference ratio. S/I = (D/R)n/i 0
- 21. Cell Size (Max & Min) Large Cells: Low Subscriber Density Unobstructed Terrain Small Cells: High Subscriber Density Urban Terrain
- 22. Frequency Re-Use Repeat Pattern: 3,4, or 7 cell repeat patterns are common. Co-Channel Cells: Cells using same frequency must be positioned far enough so as to avoid Co-Channel Interference.
- 23. Frequency Group A1 Frequency Group A1 Other frequencies Other frequencies Reuse distance D R Wanted signal Interfering signal R The Frequency Reuse Distance
- 24. B4 A4 B3 C4 B2 B1 A2 C2 C3 A1 C1 A1 A3 4*3 Reuse Pattern of 12 cells Distance of frequency reuse Trisectorial Site A1 C1 B1 A3 A2 C2 B2 C3 B3 A4 A1 C4 B4 C1 B1 A2 B2 C2 A3 A3 C2 B2 C1 B1 A2 C3 B3 A4 C4 B4 C3 B3 A4 B4 C4 A4 B4 A2 B2 A4 B4 A2 B2 C3 C1 C3 C1 Frequency Reuse Pattern
- 25. Frequency Plan
- 26. TRAFFIC LIMITED AREA (10000 subscriber per km2) COVERAGE LIMITED AREA (-75 dBm at cell edge) COVERAGE LIMITED AREA (-70 dBm at cell edge) Coverage or Traffic Limitations
- 29. Bi and Trisectorial Site Antennas
- 30. HANDOVER – Serving / Neighbour Cells Best Neighbours: Mobile monitors signal strength from neighboring cells. Handover Criteria: Signal Strength Signal Quality
- 31. Channel assignment strategies •Two types of channel assignment Fixed vs dynamic Fixed: cell is allocated predetermined set of channels. If all channels are occupied then call is blocked. To avoid this problem borrowing strategy is used in which channel is borrowed from neighbor cell supervised by MSC (mobile switching center).
- 32. Dynamic assignment • Voice channels are not allocated to different cells permanently. • Each time serving base station requests a channel from MSC. • MSC plays major role by monitoring reuse distance, cost function and other issues. • MSC needs to collect real time data on channel occupancy, traffic distribution and radio signal strength indications (RSSI) this increases the storage and computational load but provides the advantage of increased channel utilization and decreased probability of blocked calls.
- 33. Handoffs - the basics Handoff is initialized at signal level of about -90dBm and -100dBm
- 34. The umbrella cell approach To avoid frequent handover for fast user. Fast moving user is assigned frequency from umbrella cell and slow moving users are provided treated in micro cells
- 35. Improving coverage and capacity in cellular system • Cell Splitting • Sectoring
- 36. Cell Sectorization Omni Cells: Omni Directional Antenna Sectorized Cells: Directional Antennas. Advantages: Higher Capacity Better Coverage
- 37. Cell Splitting • It is process of dividing a congested cell into smaller cells. • Transmitting power and antenna height is reduced. • It increases the capacity by increasing the number of times that channels are reused.
- 38. Sectoring 120 degree sectoring 60 degree sectoring
- 39. Sectoring • Sectoring improves S/I. • In 7 cell reuse we have S/I equal to 10dB, when n=4 and co channels are 6. • It is improved i,e 23.43dB when co channels are reduced to 2 as in fig. • It helps reducing N for example to attain S/I of 21 dB we need 12 cell reuse (23.34dB), while sectorizing by 60 degrees we can attain this figure by 7 cell reuse,
- 40. • High sensitivity to interference • Requires "secured" Frequency reuse pattern • High isolation from interferences • A few Frequencies intensively reused MACRO - CELL: antenna radiating ‘above’ roofs ---> Wide Coverage (≤ 35 km) MICRO-CELL: Antenna ‘below’ the roofs ---> small coverage PICO-CELL: Antenna inside building ---> Very small coverage EXTENDED - CELL: macro cell with system coverage extension (≤ 120 km) for coasts... CONCENTRIC - CELL: macro cell with system coverage limitation inside another macro Different Types of Cells
- 41. Macrocell Antenna Microcell Antenna Umbrella cell Macrocell Microcell Fast speed vehicle Slow speed vehicle after direction change Pedestrian µ cell 2 µ cell 1 Cell Layering 2 layers model
- 42. Exercise 100 100 100 20 60 100 100 60 60 20 20 20 20 20 20 60 40 20 20 Considering this radio coverage, could you identify the topology of the different areas? Figures indicates Base Stations Erlang capacity
- 43. Solution: Topology of Different Areas 100 100 100 20 60 100 100 60 60 20 20 20 20 20 20 60 40 20 20 Town Rural Suburb Highway