Cellular Network Concepts and Design System Architecture Instructor: Dr. Mustafa Shakir

Distributed Control over Wireless Links Automated Vehicles - Cars - UAVs Packet loss and/or delays impacts controller performance. Controller design should be robust to network faults. Joint application and communication network design.

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 Structure No proper coverage of the area with theoretical circles. Polygon near to the circle Hexagon 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 Structure No proper coverage of the area with theoretical circles. Polygon near to the circle Hexagon 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

Mathematical Description of a Cell Area of a cell is: Perimeter of a cell = 6R

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 1 2 5 6 7 4 3 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’

Cell Clusters (1) A network of cell clusters in a densely populated Town 1 2 5 6 7 4 3

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.