Concepts of & cell sectoring and micro cell
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The document discusses concepts related to cellular network sectoring and microcells. It explains that cells can have square or hexagonal shapes, with hexagons providing equidistant antennas. Frequency reuse allows the same frequencies to be used in different cells by controlling base station power to limit interference. Common frequency reuse patterns include reuse factors of 1, 3, 7, etc. Capacity can be increased through methods like frequency borrowing, cell splitting, cell sectoring, and microcells which use smaller cell sizes.
Concepts of & cell sectoring and micro cell
- 1. CONCEPT OF & CELL SECTORING AND MICRO CELL By Kundan Kumar
- 2. Shape of Cells Square Width d cell has four neighbors at distance d and four at distance d Better if all adjacent antennas equidistant Simplifies choosing and switching to new antenna Hexagon Provides equidistant antennas Radius defined as radius of circum-circle Distance from center to vertex equals length of side Distance between centers of cells radius R is R Not always precise hexagons Topographical limitations Local signal propagation conditions Location of antennas 2 3
- 4. Frequency Reuse Power of base transceiver controlled Allow communications within cell on given frequency Limit escaping power to adjacent cells Allow re-use of frequencies in nearby cells Use same frequency for multiple conversations 10 – 50 frequencies per cell E.g. N cells all using same number of frequencies K total number of frequencies used in systems Each cell has K/N frequencies Advanced Mobile Phone Service (AMPS) K=395, N=7 giving 57 frequencies per cell on average
- 5. Characterizing Frequency Reuse D = minimum distance between centers of cells that use the same band of frequencies (called cochannels) R = radius of a cell d = distance between centers of adjacent cells (d = R) N = number of cells in repetitious pattern Reuse factor Each cell in pattern uses unique band of frequencies Hexagonal cell pattern, following values of N possible N = I2 + J2 + (I x J), I, J = 0, 1, 2, 3, … Possible values of N are 1, 3, 4, 7, 9, 12, 13, 16, 19, 21, … D/R= D/d = N3 N
- 8. Principles of Cellular Frequency Reuse Typical frequency reuse plan for 7 different radio frequencies, based on hexagonal cells. In fact some problems in cellular frequency assignment are solved using map coloring theory.
- 9. Principles of Cellular Frequency Reuse (con’t) Frequency 're-use' distance is the closest distance between the centers of two cells using the same frequency (in different clusters) is determined by the choice of the cluster size C and the lay-out of the cell cluster.
- 10. Co-Channel Interference (CCI) CCI arises in cellular systems where the available frequency channels are divided into different sets. Each set being assigned to a specific cell and with several cells in the system using the same set of frequencies. CCI limits the system capacity This interference generally happens in places where population is high.
- 11. The Capacity of Cellular Network Why do we need more capacity? Reach more users at the same time Share more information throughout the network. New technologies will require more complex solutions and these solutions can be achieved with maximum space available.
- 12. The Capacity of Cellular Network (con’t) The capacity of cellular systems can be increased by; Frequency borrowing Cell splitting Cell sectoring Microcells
- 13. Frequency Borrowing RF bandwidth is the most important constraint in wireless systems. So to increase the capacity, frequency of Radio Signals and wireless systems shall be increased. To do this, frequencies are taken from adjacent cells by congested cells.
- 14. Cell Splitting The unit area of RF coverage for cellular network is called a cell. In each cell, a base station transmits from a fixed cell site location, which is often centrally located in the cell. In base stations where the usage of cellular network is high, these cells are split into smaller cells.
- 16. Cell Splitting (con’t) The radio frequencies are reassigned, and transmission power is reduced. A new cell site must be constructed when a cell is split Cell splitting is one of the easy and less costly solution when increasing the capacity of cellular network. Splitting the cells into smaller ones also lead to a new solution called cell sectoring.
- 17. Cell Sectoring Sectorization consists of dividing an omnidirectional (360 degree) view from the cell site into non-overlapping slices called sectors. When combined, sectors provide the same coverage but they are considered to be separate cells. Also considered as one of easy and inexpensive capacity increasing solution.
- 18. Sectoring In basic form, antennas are omnidirectional Replacing a single omni-directional antenna at base station with several directional antennas, each radiating within a specified sector. achieves capacity improvement by essentially rescaling the system. less co-channel interference, number of cells in a cluster can be reduced Larger frequency reuse factor, larger capacity
- 20. Sectoring Examples Only two cochannel cell S/I improvement 7.2dB Capacity 12/7 First type handoff Trunking efficiency low Urban area not good Example 3.9
- 22. DAYANANDA SAGAR COLLEGE OF ENGINEERING, BANGALORE Repeater Extend coverage range Directional antenna or distributed antenna systems
- 23. Microcells As the splitting of cell idea evolves, the usage of smaller cells become efficient and it leads the creation of microcells. The aim of creating microcells are increasing the capacity of cellular network in areas where population is high.
- 24. Microcells (con’t) Typical comparison can be made like this; Cells typically range in size from two to twenty kilometers in diameter. Microcells range from about a hundred meters to a kilometer in diameter.
- 25. Micro Cell Zone Concept Large control base station is replaced by several lower powered transmitters on the edge of the cell. The mobile retains the same channel and the base station simply switches the channel to a different zone site and the mobile moves from zone to zone. Since a given channel is active only in a particular zone in which mobile is traveling, base station radiation is localized and interference is reduced.
- 26. Micro Cell Zone Superior to sectoring, any base station channel may be assigned to any zone by the base station Same channel No handoff Only the active zone
- 27. DAYANANDA SAGAR COLLEGE OF ENGINEERING, BANGALORE Example 2.33 times capacity gain
- 28. Questions
- 29. Question1 How can Cellular network capacities will be improve in the future? A: There are lots of solutions for improving the capacity of the Network. But the one of the most logical one is, using the logical solution cell in the sector with adaptive antennas. And using more cells where the number of subscriber is bigger.
- 30. Question 2 Why we need the frequency reuse? What are the reasons? A: We need frequency reuse because we have a bandwidth. If we use same frequency in every cell, the other cells make interference. Hence the specific frequency is trying to not use by the other cells.