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April 19, 2023 1
Mobile Computing COE 446
Network PlanningTarek Sheltami
KFUPMCCSECOE
http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm
Principles of Wireless Networks
K. Pahlavan and P. Krishnamurth
April 19, 2023 2
Outline
Network topology Cell hierarchy Cell Fundamentals Signal to interference ratio
calculation
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Wireless Network Topology The main benefit and elements of a cellular
network planning by relating the bandwidth, number of cells, frequency of reuse factor and capacity of the network
The number of simultaneous users using the system is given by:
A cellular topology reduces the coverage of both of MTs and BS
The reduction of the size of coverage lowers the required transmitted power, which increases the battery lifetime and reduces the sizes of MTs and BSs
The larger the number of cells, the larger the capacity and the smaller the size of mobile devices
m(W / N)n
B
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Wireless Network Topology.. We need a fixed network infrastructure to
interconnect the cells and ensure that the entire system works in a coordinated manner
The more number of cells, the more number of handoffs and the more complex the design of network
We need to address the following technical issues for planning a cellular network:
Selection of frequency reuse pattern Physical deployment and radio coverage
modeling The growth of the network Analysis of the relationship between the
capacity, cell size and cost of infrastructure
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Wireless Network Topology.. Cellular Hierarchy
Three reasons for hierarch1. To extend the coverage to the areas that are
difficult to cover by a large cell2. To increase the capacity of the network for
those areas that have a high density of users3. Some applications need certain coverage The cellular hierarchy is classified as follows:1. Femtocells: the smallest unit of the cellular
hierarchy used for connection of personal equipments (notebooks, notepads,..). They cover few meters, where all these devices in physical range of the user
2. Picocells: small cells inside a building that support indoor network such as WLANs. They cover few tens of meters
April 19, 2023 6
Wireless Network Topology.. Cellular Hierarchy
3. Microcells: cells cover the inside streets with antennas mounted at heights lower than the rooftop of building along the streets. They cover hundreds of meters and are used in urban areas
4. Macrocells: traditional cellular network. They cover areas on the order of kilometers and their antenna are mounted above the rooftop of typical buildings in the coverage area.
5. Megacells: cover nationwide areas with range of hundreds of kilometers and mainly used for satellites
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Cell Fundamentals In practice cells are of arbitrary shape (close to
circle) Mathematical analysis is easier to analyze the
topology For cell of the same shape to form tessellation
so that there are no ambiguous areas that belong to multiple cells or to no cell
The cell shape can be only of three types regular polygons: equilateral triangle, square, or regular hexagon
A hexagon cell is the closest approximation to circle of these three and has been used traditionally for system design
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Triangular and rectangular cells
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Arranging regular hexagons that can cover a given area without creating ambiguous regions
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Cell Fundamentals..
In order to investigate the effects of interference, which changes with distance, there is a need to come up with a way of determining distances and identify cells
In order to maximize the capacity, cochannel cells must be places as far apart as possible for a given cluster size
It can be shown there only that six cochannel cells for a given reference cell at this distance
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Cell Fundamentals..
L
L
D3N
R
DL = distance between cochannels, N = cluster size, and RL = cell radius
This quantity is also referred to as cochannel reuse ratio
Values of N are taken from: i2 + ij + j2, i and j are integers
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If we take i = 2 and j = 1, we see that N = 4 + 2 + 1 = 7. Selecting a cell A, we can determine its cochannel cell by moving two units along one face of the hexagon and more unit in a direction 60o or 120o to this direction. Clusters of size N = 7 can be created as in figure page 13 .
Example
Cell Fundamentals..
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Hexagonal cellular architecture with a cluster size of N =7
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Cell Fundamentals..
The number of cells in a cluster N determines the amount of cochannel interference and also the number of frequency channels available per cell.
With fixed-channel allocation, each cluster uses Nc channels and each cell uses Nc/N, where Nc= channel available for the entire system
It desirable to maximize the number of channels allocated to a cell, therefore, N should be as small as possible
But, reducing N increases the Sr
Actual deployment is far more complication because of irregular differing cell sizes and propagation mechanisms
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Signal-to-Interference Ratio Calculation
It is given as:
Where, Pdesired is the strength of the signal from the desired BS and PPinterference, i is the signal strength from the ith interference BS
The signal strength falls as some power of the distance α called the power-distance gradient or path loss gradient
desiredr
int erference, ii
PS
P
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Signal-to-Interference Ratio Calculation..
The transmitted power Pt, after a distance d in meters, the signal ratio will be proportional to Ptd-α
In most simple case, the signal strength falls as the square of the distance in free space (α=2)
If we have BS1 and BS2 located in an area with same transmit power Pt and an MT is at distance of d1 from BS1 and d2 from BS2
April 19, 2023 18
Signal-to-Interference Ratio Calculation..
Let us assume that the MT is trying to communicate with BS1, then the signal from BS2 is interference
The larger the ratio d2/d1, the better the performance
)(1
2
2
1
d
d
dKP
dKPS
t
tr