29-04-2013, 04:13 PM
HIGHER ALTITUDE PLATFORM BASED COMMUNICATION SYSTEM
[attachment=53261]
INTRODUCTION
High Altitude Platform based communication system is a low cost communication network that combines the
advantages of satellite based and terrestrial communication systems, especially in case of emergency situations. The
high altitude platform acts as a radio repeater like a satellite. The data sent from a ground station is picked up,
amplified and retransmitted to the designated ground station.
As an alternative to satellites, a high altitude platform based approach can be used. A high altitude platform like
a high altitude balloon or a solar powered airplane going in circles can be used to carry the transponder and all the
other communication gear carried by a satellite. The height of the platform can range from several hundred meters to
kilometers, depending on the application and range. A high altitude platform based communication system has several
advantages over terrestrial and satellite communication methods which makes it superior especially for use in military
and emergency operations. Amongst the main advantages of HAPS over terrestrial and satellite systems is its
propagation environment, having less multipath fading than terrestrial and much less free space loss than satellite,
with a much lower propagation delay a serious issue for voice communications over satellite links. Deployment costs
is another advantage of HAPS over terrestrial and satellite, since it is envisaged that a HAPS system comprising just a
platform and ground facilities could in principle be deployed much faster than a terrestrial network, and much quicker
than a satellite system, at only a percentage of the cost. The access to HAPS reduces the reliability requirements of
components relative to a satellite. If a component fails in a HAPS it can be returned to the ground for repair.
Our project aims to create a HAPS based high performance communication system, using the 2.4 GHz unlicensed
ISM band .
MOTIVATION
Why such a project is done?
The motivation to this project is to create a communication system that will perform well in emergency
situations like floods, earthquakes where the existing communication systems may fail and a complete
communication system is to be deployed as soon as possible. Satellite communication is a viable alternative but it is
costly, complex and may take much time to implement. In such situations, a High Altitude Platform based
Communication System can be deployed and communication can be restored.
USB-SERIAL CONVERTER
This section consist of a PL2303 chip-set based USB to RS232 bridge controller. It interfaces RS232
devices to USB, and creates a virtual serial port for the computer with which we can talk to the microcontroller
through its UART.
MICROCONTROLLER
The microcontroller initializes and configures the RF Transceiver and routes the data from PC to the
RF section and vice versa. An Atmega8 is used for this purpose. It is a 8 bit microcontroller which can run up to 16
MIPS.
RF TRANSCIEVER
The RF transceiver used is nRF24L01 made by Nordic semiconductors. It is a single chip
2.4GHz transceiver with an embedded baseband protocol engine (Enhanced Shock Burst TM). The
nRF24L01 is designed for operation in the world wide ISM frequency band at 2.400 - 2.4835GHz. An MCU
(microcontroller) and very few external passive components are needed to design a radio system with the
nRF24L01. The nRF24L01 is configured and operated through a Serial Peripheral Interface (SPI.) Through
this inter-face the register map is available. The high air data rate combined with its ease of interfacing and
availability makes it the best choice
SYSTEM DESIGN
IMPORTANT MODULES USED
The system can be divided into PC interface section, Microcontroller section, RF section and Antenna
Section. PC interface is handled by the USB to serial converter built around a PL2303 USB Serial controller IC. It has
many features including software and hardware flow control, enhanced baud rates upto 2mbps etc. The
microcontroller chosen is an Atmega8. It is quite powerful and can operate at 16 MIPS. The availability of free and
open source compilers and documentation for this family of microcontrollers was the reason ehy this controller was
chosen for our application.
The RF section is built around a NRF24L01+ chip-set manufactured by Nordic semiconductors. It is an
ISM band transceiver with many built in functions for packet handling and flow control. It can operate at am
maximum bandwidth of 2mbps. It uses Gaussian Frequency Shift Keying (GFSK).
The antennas are custom made biquad antennas. They offer good gain. The radiatoin pattern is not highly
directional, this will help in the orientation of the antenna. The antennas are designed to operate in the 2.4 GHz
spectrum with a gain of 10 Db. The antennas are designed and simulated first before the actual construction. The
design and simulation of the antennas are done using the NEC software.
The system is powered from USB at the ground station and in the high altitude platform, uses Lithium
-Ion polymer batteries which are lightweight and provides adequate power.
ANTENNA
Antennas are very important for any communication system. Antennas should be optimized for
maximum gain. The high altitude communication system uses biquad antennas for transmission and reception.
The uniform radiation characteristics, low sidelobes etc makes biquad antenna an excellent choice for this
system. The antenna is modelled using NEC code and simulated in Qantenna, and the radiation pattens are as
expected in the design.
The Bi-Quad antenna is a simple antenna design that offers many advantages. First is the simplicity of the
design. Biquad antenna can be built with materials found in most hardware stores. It offers good directivity due
to the metallic reflector used in the design. The radiating element are two square with the side length equal to 1/4
midband wavelength, 32mm for 2.440GHz in our case. The theoretical beam width is 70 degrees but can vary
widely with the reflection plane size and shape. Typically, the gain is about 10-12 dBi. Typical use of the biquad
is standalone directional antenna or feeder of a parabolic dish. Polarization of the antenna is 90 degrees from the
position of orientation of the biquad, i.e. horizontal biquad has vertical polarization.
[attachment=53261]
INTRODUCTION
High Altitude Platform based communication system is a low cost communication network that combines the
advantages of satellite based and terrestrial communication systems, especially in case of emergency situations. The
high altitude platform acts as a radio repeater like a satellite. The data sent from a ground station is picked up,
amplified and retransmitted to the designated ground station.
As an alternative to satellites, a high altitude platform based approach can be used. A high altitude platform like
a high altitude balloon or a solar powered airplane going in circles can be used to carry the transponder and all the
other communication gear carried by a satellite. The height of the platform can range from several hundred meters to
kilometers, depending on the application and range. A high altitude platform based communication system has several
advantages over terrestrial and satellite communication methods which makes it superior especially for use in military
and emergency operations. Amongst the main advantages of HAPS over terrestrial and satellite systems is its
propagation environment, having less multipath fading than terrestrial and much less free space loss than satellite,
with a much lower propagation delay a serious issue for voice communications over satellite links. Deployment costs
is another advantage of HAPS over terrestrial and satellite, since it is envisaged that a HAPS system comprising just a
platform and ground facilities could in principle be deployed much faster than a terrestrial network, and much quicker
than a satellite system, at only a percentage of the cost. The access to HAPS reduces the reliability requirements of
components relative to a satellite. If a component fails in a HAPS it can be returned to the ground for repair.
Our project aims to create a HAPS based high performance communication system, using the 2.4 GHz unlicensed
ISM band .
MOTIVATION
Why such a project is done?
The motivation to this project is to create a communication system that will perform well in emergency
situations like floods, earthquakes where the existing communication systems may fail and a complete
communication system is to be deployed as soon as possible. Satellite communication is a viable alternative but it is
costly, complex and may take much time to implement. In such situations, a High Altitude Platform based
Communication System can be deployed and communication can be restored.
USB-SERIAL CONVERTER
This section consist of a PL2303 chip-set based USB to RS232 bridge controller. It interfaces RS232
devices to USB, and creates a virtual serial port for the computer with which we can talk to the microcontroller
through its UART.
MICROCONTROLLER
The microcontroller initializes and configures the RF Transceiver and routes the data from PC to the
RF section and vice versa. An Atmega8 is used for this purpose. It is a 8 bit microcontroller which can run up to 16
MIPS.
RF TRANSCIEVER
The RF transceiver used is nRF24L01 made by Nordic semiconductors. It is a single chip
2.4GHz transceiver with an embedded baseband protocol engine (Enhanced Shock Burst TM). The
nRF24L01 is designed for operation in the world wide ISM frequency band at 2.400 - 2.4835GHz. An MCU
(microcontroller) and very few external passive components are needed to design a radio system with the
nRF24L01. The nRF24L01 is configured and operated through a Serial Peripheral Interface (SPI.) Through
this inter-face the register map is available. The high air data rate combined with its ease of interfacing and
availability makes it the best choice
SYSTEM DESIGN
IMPORTANT MODULES USED
The system can be divided into PC interface section, Microcontroller section, RF section and Antenna
Section. PC interface is handled by the USB to serial converter built around a PL2303 USB Serial controller IC. It has
many features including software and hardware flow control, enhanced baud rates upto 2mbps etc. The
microcontroller chosen is an Atmega8. It is quite powerful and can operate at 16 MIPS. The availability of free and
open source compilers and documentation for this family of microcontrollers was the reason ehy this controller was
chosen for our application.
The RF section is built around a NRF24L01+ chip-set manufactured by Nordic semiconductors. It is an
ISM band transceiver with many built in functions for packet handling and flow control. It can operate at am
maximum bandwidth of 2mbps. It uses Gaussian Frequency Shift Keying (GFSK).
The antennas are custom made biquad antennas. They offer good gain. The radiatoin pattern is not highly
directional, this will help in the orientation of the antenna. The antennas are designed to operate in the 2.4 GHz
spectrum with a gain of 10 Db. The antennas are designed and simulated first before the actual construction. The
design and simulation of the antennas are done using the NEC software.
The system is powered from USB at the ground station and in the high altitude platform, uses Lithium
-Ion polymer batteries which are lightweight and provides adequate power.
ANTENNA
Antennas are very important for any communication system. Antennas should be optimized for
maximum gain. The high altitude communication system uses biquad antennas for transmission and reception.
The uniform radiation characteristics, low sidelobes etc makes biquad antenna an excellent choice for this
system. The antenna is modelled using NEC code and simulated in Qantenna, and the radiation pattens are as
expected in the design.
The Bi-Quad antenna is a simple antenna design that offers many advantages. First is the simplicity of the
design. Biquad antenna can be built with materials found in most hardware stores. It offers good directivity due
to the metallic reflector used in the design. The radiating element are two square with the side length equal to 1/4
midband wavelength, 32mm for 2.440GHz in our case. The theoretical beam width is 70 degrees but can vary
widely with the reflection plane size and shape. Typically, the gain is about 10-12 dBi. Typical use of the biquad
is standalone directional antenna or feeder of a parabolic dish. Polarization of the antenna is 90 degrees from the
position of orientation of the biquad, i.e. horizontal biquad has vertical polarization.