Showing posts with label Communication System. Show all posts

A Mathematical Theory of Communication

Satellite Based Train Monitoring System

Presentation on Satellite Based Train Monitoring System

Introduction

Transportation is a large & important part of the economy & the need for transportation increase continuously. Train is one of the main & biggest transportation system in Bangladesh. Everyday thousands of people travel in train to different destinations. For good customer service it is their responsibility to have a good management system.

So it is necessary for them to have a clear idea about the actual position, speed, time to reach destination of a particular train at every instant.

But unfortunately there is no such system that could give them clear idea about the situation. What they do is, they divide the total network in kilometer blocks & approximates the position of a particular train.

Existing Monitoring System

The existing conventional monitoring system most of the times relay on the oral communication through telephonic and telegraphic conversations. In our railway system, when train crosses a station & sets for next station the rail track between the two station is locked & no other train are permitted to enter in that locked section. A station can only senses a train within its 1200 ft. range.

When a train crosses this limit a station can only tell the train is somewhere between the two station but cannot tell in which particular position & at what speed the train is heading to the next station. This miscommunication may lead to wrong allocation of the track for trains, which ultimately leads to the train collision.

When a train passes a station it blocks the total link up to next station. If the train makes too late to reach the next station then they check the link manually. If problem exists it takes hours to know for them about the problem.

In our project we have implemented a Satellite based Train Monitoring System that would give the status of a train at any instant. This status can be viewed by the train control room as well as any passenger who want to access it.

Objectives:

To monitor the status of a particular train at any instant.
This system will also provide a way to minimize the accidents & helps to minimize the human errors which cause accidents.
Passengers who will travel by train can know the status of their train by internet at any time. This would help him to make decision about his traveling.
The monitoring could be done from various points which will reduce human errors.

Project Overview

GPS (global positioning system) is a device that can give its own longitude, latitude, speed etc. from the orbiting satellites. There are 24 satellites orbiting our earth. These satellites transmit transparent data to earth. A GPS receives the data from the satellites those can be viewed by the device & calculates its status.

Fig: AVL VT310 GPS-GPRS module.

Fig: Flow Diagram of GPS based train monitoring system

Fig: Position updating in Google Map from client end

In our system we will use GPS-GSM/GPRS module to collect the position information of a train at every instant & passes this information to a web-server via man –machine interface.

As new data being inserted to the database, it will update the location information containing speed, distance from a particular station etc. of the train at the client end when requested.

Man machine interface can also become a useful tool for preciously locating a train in a track. An operator in the train will continuously update the track number in the computer connected with the GPS.

With the introduction of man machine interface , our system should look somewhat like this:

The data served by GPS & from the computer will be accumulated by the server & the server will be able to give accurate position with track number & will make the decision when & in which track the train should arrive at the next crossing.

Important Attributes:

Our system will be cost effective. This system

will reduce the work force required;
will definitely reduce train accident;
Late running of trains can be prevented to large extend.

Conclusion

The implementation of our proposed system will contribute a lot in automation of our railway system. The introduction of digital maps could make the system even better & as the positions could be accurately measured.

We have made a small step in making our train controlling & monitoring system automatic & error free. We have to go a long way to make it fully functional. Our government has a big role to play in these regards.

Submitted by BY Rajesh Mozumder and Jiban Chandra Bhowmik

Design & Construction of 2.4GHz Axial Mode Helical Antenna to Establish WLAN

Presentation on Design & Construction of 2.4GHz Axial Mode Helical Antenna to Establish WLAN

What is an Antenna?

An antenna is a transducer that converts electrical energy to electromagnetic energy in case of transmission and converts electromagnetic energy to electrical energy in case of receiving antenna. Apart from their different functions, transmitting and receiving antennas have similar characteristics, which mean that their behavior is reciprocal.

How Antenna Radiates

There must be a time varying current i.e. acceleration or deceleration of charge to create radiation. To create acceleration or deceleration the wire must be curved, bent, discontinuous or truncated. Two EM Fields – Induction & Radiation Induction Field is liable for storing energy and Radiation Field is liable for radiating that stored energy.

Antenna Parameters

Resonant Frequency
Gain
Directivity
Radiation Pattern
Impedance
Efficiency
Bandwidth
Polarization
Reciprocity

Helical Antenna Theory

D = Diameter of helix

C = Circumference of helix = πD

S = Spacing between turns

α = Pitch Angle = tan-1 (S/πD)

n = Number of turns

L = Axial length = nS

a = Radius of helix wire conductor

The Gain of Helical Antenna is, G=11.8+10*log{(C/l) 2*N*S} dB
The HPBW of Helical Antenna- HPBW = 52/C_λÖ(nS_λ) degrees
The input impedance is R = 140C/λ Ω

Design of 2.4 GHz Helix

Circumference, C = πD = λ = 12.5 cm

Pitch Angle, α = arctan (S/πD) =14°

Diameter, D = C/π = 3.97887 cm

Spacing between the turns, S = C tan α = 3.12 cm

Number of Turns, N = 28

Gain, G = 19.3 dBi

HPBW = 19.7 degree

Antenna Length, L = NS = 783 cm

Terminal Impedance, Z = 150 Ohm

Conductor Diameter, d ≥ 0.005λ = 0.625 mm

Problem with 2.4GHz Helix

All the equations developed by John D. Kraus were for the helix in the air.
But we build our antenna in a PVC pipe.
The dielectric constant of dry air that is 1.000056 at 60Hz frequency and 30°C temperature whereas the dielectric constant for PVC concrete tube is 3.5 for 60Hz which at 2.4GHz is 1.5 approximately
Suspension Factor = 1/√ ε_r = 1/√1.5 = 0.8164
So, we build our antenna for 2.4/0.8164=2.92GHz

Design for 2.92GHz Antenna

For this design the required parameters are

Frequency, f = 2.92GHz

Wavelength, λ = 10.27 cm

Circumference, C = λ = 10.27cm

Diameter, D = 3.27 cm

Spacing between Turns, S = 2.56 cm

Pitch Angle, α = 14°

Number of Turns, N = 28

Conductor Diameter, d ≥ 0.005 λ ≥ 0.5135 mm

We used conductor of 1.26mm.

Diameter of the Ground Plane ≥ 0.75 λ ≥ 7.7cm

We used the Flat Circular Aluminium Ground Plane of 15cm Diameter.

Design for 2.92GHz Helix Antenna

For this design the required parameters are

Frequency, f = 2.92GHz

Wavelength, λ = 10.27 cm

Circumference, C = λ = 10.27cm

Diameter, D = 3.27 cm

Spacing between Turns, S = 2.56 cm

Pitch Angle, α = 14°

Number of Turns, N = 28

Conductor Diameter, d ≥ 0.005 λ ≥ 0.5135 mm

We used conductor of 1.26mm.

Diameter of the Ground Plane ≥ 0.75 λ ≥ 7.7cm

We used the Flat Circular Aluminium Ground Plane of 15cm Diameter.

Using the parameters stated previously,

Gain, G = 19.3 dBi
HPBW = 19.7 degree
FNBW = 43.5 degree
Antenna Length, L = 757 cm
Terminal Impedance, Z = 150 Ohm

We used a Cu strip triangle of 72mm base and 17mm in perpendicular of it.

WLAN

A wireless LAN (WLAN) is a wireless local area network, which permits a network connection between two or more computers without using wires. It uses radio communication to accomplish same functionality that a wired LAN has. We used Ad-hoc network that uses IEEE 802.11b standard of 2.4GHz band. An ad-hoc network is a network where stations communicate only peer to peer (P2P). We used a wireless NIC that enables a client station capable of sending and receiving RF signals.

Before finishing, want to say something about our aspirations and the reasons for why we had to see our fancy hopes fritter away and our dreams were shattered like a shield……

Submitted by Shaikat Debnath And Kaisar Jamil

DESIGN, CONSTRUCTION AND PERFORMANCE ANALYSIS OF YAGI-UDA ANTENNA IN ULTRA HIGH FREQUENCY REGION

Presentation on DESIGN, CONSTRUCTION AND PERFORMANCE ANALYSIS OF YAGI-UDA ANTENNA IN ULTRA HIGH FREQUENCY REGION

INTRODUCTION

An antenna is a transducer designed to transmit or receive electromagnetic waves.
Transmission-transmits electromagnetic energy into space.
Receiption-receives electromagnetic energy from space.

Radiation through antenna

Eletromagnetic wave results due to acceleration of charges.
This time varying electric field has associated time varying magnetic field.
They comprise electromagnetic field.

OBJECTIVES

To become familiar with different types of antenna and antenna parameters.
To observe the performance of different types of antenna in terms of radiation pattern.
To design & implement two Yagi-Uda as transmitting & receiving antenna with three and five directors.
To compare the directivity between these two antennas.
To compare the designed antenna with the lab antenna using radiation pattern & MATLAB.
To observe the performance of designed antenna using mobile.

METHODOLOGY

DESIGN, CONSTRUCTION AND PERFORMANCE ANALYSIS OF YAGI-UDA ANTENNA IN ULTRA HIGH FREQUENCY REGION

Reasons of selecting Yagi-Uda antenna in Ultra High Frequency region

Yagi-Uda is a directive antenna.
The size of antenna decreases with increasing the frequency.
We can test the antenna in lab.
We can compare our designed antenna with lab antenna in terms of radiation pattern.

Different antenna parameters

Radiation pattern-The graph that describes the field strength versus direction at a fixed distance .Radiation patterns are taken at one frequency, one polarization.
Directivity-is the ratio of radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions.
Bandwidth-The bandwidth of an antenna is the range of frequencies over which it is effective, usually centered on resonant frequency.
Polarization-is the orientation of the electric field of radio wave with respect to the earth’s surface and is determined by the physical structure of antenna.
Main lobe-The direction of maximum radiation
Side lobe-The direction of minimum radiation.
Input impedance

Za-Antenna
Impedance
Za=Ra+jXa
Ra=Rr+Rl
Generator impedance
Zg=Rg+jXg

Elements of Yagi-Uda antenna

The Yagi antenna's overall basic design consists of a “resonant” fed dipole with one or more parasitic elements. These parasitic elements are called the “reflector” and the “director”.
The driven element of a Yagi is the feed point where the feed line is attached from the transmitter to the Yagi to perform the transfer of power from the transmitter to the antenna.
The directors are the shortest of the parasitic elements and are used to provide the antenna with directional pattern.
The reflector is the element that is placed behind of the driven element; its length is approximately 5% longer than the driven element. It's length will vary depending on the spacing.

Design of a Yagi-Uda antenna

While designing the antenna we consider some criterions

The length of the driven element
The length of the directors
The length of reflector
Spacing between directors
Spacing between reflector & driven element
Spacing between driven element & director
The type of driven element used

Range of length of different elements
Length of reflector=0.47 λ - 0.52 λ
Length of driven element=0.45λ - 0.49λ
Length of directors=0.4λ - 0.45λ
Range of spacing between different elements
Spacing between reflector & driven element=0.16λ - 0.35λ
Spacing between driven element & nearest
Director=0.2 λ -0.3λ
Spacing between directors=0.2λ - 0.3 λ
Range of diameter of elements=0.001λ - 0.003λ
Directivity Calculation