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Cellular Network Concepts and Design
System Architecture
Instructor: Dr. Mustafa Shakir
Distributed Control over Wireless Links
Packet loss and/or delays impacts controller performance. Controller design should be robust to network faults. Joint application and communication network design.
Automated Vehicles - Cars - UAVs
Joint Design Challenges There is no methodology to incorporate random delays or packet losses into
control system designs.
The best rate/delay tradeoff for a communication system in distributed control cannot be determined.
Current autonomous vehicle platoon controllers are not string stable with any communication delay
Can we make distributed control robust to the network?Yes, by a radical redesign of the controller and the network.
Single Cell ‘Network’
History of Cellular Networks Why cellular networks?
To address requirement for greater capacity
For efficient use of frequency
To address the poor quality of non cellular
mobile networks and increases coverage
replaces a large transmitter with smaller ones in cells
smaller transmitting power
each cell serves a small geographical service area
each cell is assigned a portion of the total frequency
Replacement of huge single cell by a number of small cells
Why Hexagonal Cell StructureNo proper coverage of the area with
theoretical circles. Polygon near to the circleHexagon is selected for further technical
simplicity.
Types of Mobile Communication Cells
The size of a cell is dictated by capacity demand
Macro-cell
large, covering a wide area
range of several hundred kilometers (km) to ten km
mostly deployed in rural and sparsely populated areas
Micro-cell
medium cell, coverage area smaller than in macro cells
range of several hundred meters to a couple of meters
deployed mostly in crowded areas, stadiums, shopping malls
Types of Mobile Communication Cells Contd.
The size of a cell is dictated by capacity demand
Pico-cell
small, covering a very small area
range of several tens of meters
low power antennas
can be mounted on walls or ceilings
used in densely populated areas, offices, lifts, tunnels etc
Mega-cell
-- These cells are formed by LEO and MEO
History of Cellular Networks Why cellular networks?
To address requirement for greater capacity
For efficient use of frequency
To address the poor quality of non cellular
mobile networks and increases coverage
replaces a large transmitter with smaller ones in cells
smaller transmitting power
each cell serves a small geographical service area
each cell is assigned a portion of the total frequency
Replacement of huge single cell by a number of small cells
Why Hexagonal Cell StructureNo proper coverage of the area with
theoretical circles. Polygon near to the circleHexagon is selected for further technical
simplicity.
Description of a Cell
Approximated to be a hexagonal coverage
best approximation of a circular area
Served by a base station
low powered transceiver
antenna system and it
may be divided into 6 equilateral triangles
length of base of each triangle = 0.5R (radius)
different groups of channels assigned to base stations
R
RR
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3
Mathematical Description of a Cell
Area of a cell is:
Perimeter of a cell = 6R
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598.22
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26 R
RRx
RxAreacell
Types of Mobile Communication Cells
The size of a cell is dictated by capacity demand
Macro-cell
large, covering a wide area
range of several hundred kilometers (km) to ten km
mostly deployed in rural and sparsely populated areas
Micro-cell
medium cell, coverage area smaller than in macro cells
range of several hundred meters to a couple of meters
deployed mostly in crowded areas, stadiums, shopping malls
Types of Mobile Communication Cells Contd.
The size of a cell is dictated by capacity demand
Pico-cell
small, covering a very small area
range of several tens of meters
low power antennas
can be mounted on walls or ceilings
used in densely populated areas, offices, lifts, tunnels etc
Mega-cell
-- These cells are formed by LEO and MEO
Capacity Computations
Assume there are N cells, each allocated k different frequency channels. These N cells are said to form a cluster. Total number of channels per cluster is given by
S = k N Total capacity associated with M clusters: C = M k N = M S A cluster may be replicated more times in a given area if the
cells are made smaller (note that power needs to be reduced accordingly).
Capacity of cellular system is directly proportional to “M”, number of times a cluster is replicated.
Capacity versus interference for same size cell and power transmission
Decrease N for More Capacity: If Cluster Size, N is decreased while cell size remains
fixed, more clusters are required to cover the area (M increases). Therefore, Capacity increases.
Increase N for Less Interference: On the other hand, if N is increased (large cluster size)
means that co-channels are now farther than before, and hence we will have less interference.
Value of N is a function of how much interference a mobile or a base station can tolerate.
We should select a smallest possible value of N but keeping S/I in the required limits.
Means of Increasing System Capacity
There are several approaches for increasing
cellular system capacity including:
Cell clustering
Sectoring of cells
Cell splitting
Frequency reuse
Reduction of adjacent cell interference and co-
channel interference
Cell Clusters
Service areas are normally divided into clusters
of cells to facilitate system design and increased
capacity
Definition
a group of cells in which each cell is assigned a
different frequency
cell clusters may contain any number of cells, but clusters
of 3, 4, 5, 7 and 9 cells are very popular in practice
Cell Clusters
A cluster of 7 cells
the pattern of cluster is repeated throughout the network
channels are reused within clusters cell clusters are used in frequency planning
for the network Coverage area of cluster called a ‘footprint’
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Cell Clusters (1)
A network of cell clusters in a densely populated
Town
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Representation Of Cells Through BS
Frequency Plan
Intelligent allocation of frequencies used
Each base station is allocated a group of channels to be
used within its geographical area of coverage called a
‘cell’
Adjacent cell base stations are assigned completely
different channel groups to their neighbors.
base stations antennas designed to provide just the
cell coverage, so frequency reuse is possible
Frequency Reuse Concept
Assign to each cluster a group of radio channels to
be used within its geographical footprint
ensure this group of frequencies is completely different
from that assigned to neighbors of the cells
Therefore this group of frequencies can be reused
in a cell cluster ‘far away’ from this one
Cells with the same number have the same sets of
frequencies
Frequency Reuse Factor
Definition
When each cell in a cluster of N cells uses one of
N frequencies, the frequency reuse factor is 1/N
frequency reuse limits adjacent cell interference
because cells using same frequencies are
separated far from each other
Factors Affecting Frequency Reuse
Factors affecting frequency reuse
include:
Types of antenna used
--omni-directional or sectored
placement of base stations
-- Center excited or edge excited.
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