Solar-Powered “Connect-on-Demand” Satellite/Radio Link for Tanzanian Schools (George and Vickie Rock and Dow Chemical Company)

Proposal

February 19, 2010

ECE 480 – Design Team #3 – Spring 2010

ManagementRodney K. Singleton

WebmasterEric Hatch

Document Prep.Michael Edward Moulton

Presentation Prep.Rafael Robert Ocampo

Lab CoordinatorLuis Alfredo Garcia

Team 4 SupportJoe Larsen

FacilitatorSelin Aviyente

TABLE OF CONTENTS

Executive Summary...... Page 2

Background...... Page 3

Design Criteria...... Page 4

Conceptual Design...... Page 5

Design Evaluation...... Page 8

Risk Analysis...... Page12

Project Management Plan...... Page 13

Approximate Costs...... Page 14

Executive Summary

One of today’s basic necessities is that of a reliable source of electricity, which is still not available to all places of the globe. This is what makes the internet link for public schools in Tanzania so unique; being that the country lacks a reliable power grid. In order to power the VSAT to link Tanzanian students to the World Wide Web, solar cells were utilized for the power source. That being said, concerns about the quantity of sunlight being sufficient to run the satellite link and computer systems are raised. With this in mind, Dow Chemical Company has challenged the College of Engineering at MSU to design a solar-powered, “connect on-demand” satellite/radio link in order for Tanzanian students to access the web while keeping energy efficiency a priority. With this new design in place, the system will draw minimum power from the batteries while optimizing the time of its usage. This will allow the Tanzanian users to gain the most out of their internet while staying well within their power limitations.

Background

It is well known that a quality education is critical for helping the people of developing countries rise out of poverty. While there are many schools in developing countries, such as Tanzania, many lack financial resources. The lack of financial capital results deficiencies of textbooks for students to use. In order to avoid the cost of purchasing textbooks, MSU's Department of Engineering, Department of Telecommunications, Information Studies, and Media have taken an interest in providing internet to provide education material comparable to information given in text books. While this will lower costs in the long run, up front equipment costs can be very expensive. Resources must be used as efficiently as possible;including power used to operate networking equipment.

The goal of creating on-demand wireless internet in Tanzania is closely related to earlier ECE 480 projects. These projects provided multi-seat computer systems at the Tanzanian schools. The first one being installed at BarakaPrimary School was powered by solar panels. The second location was at ManyaraSecondary School,which was powered by the local power grid using an Uninterrupted Power System (UPS). Design Team 3’s internet-on-demand design system is being installed at Rift Valley Secondary School in conjunction with Design Team 4’s multi-seat computer system, both being powered by the local grid and UPS system.

To connect these schools to the internet, a terminal (VSAT) is placed at Baraka. This device communicates with an orbiting satellite. In order to connect Rift Valley and Manyara to the Baraka VSAT terminal, wireless Ethernet bridges are utilized. The wireless bridge between Manyara and Baraka is based off the WiFi standard, while the wireless bridge connecting Rift Valley and Baraka will be based off of the Worldwide Interoperability for Microwave Access (WiMAX) standard.

A technical difficulty with the network design being described is power consumption at BarakaPrimary School. As Baraka is the hub to the internet, the networking equipment at Baraka must constantly be on, even if the internet is not being used. To preserve the life of the solar batteries at Baraka, the networking equipment must be powered down when not in use. Unfortunately in doing so, internet users at Rift Valley and Manyara are unable to access the internet when the Baraka networking equipment is powered down. To rectify this situation, Manyara and Rift Valley users must send a signal to Baraka to boot-up the networking equipment so that internet access is available to the schools.

The goal for team 3 is to produce a solution that provides internet-on-demand so that the internet networking equipmentis used more efficiently. To do this, the VSAT will power on with a request from any of the schools, making internet use independent of the operations at Baraka; which is the main hub. Resources will only be used to power the networking equipment when the network is in use by an end user. By using the networking equipment efficiently,solar power can be conserved resulting in lengthening the life span of the solar batteries. The end result is the basis of our project, using power most efficiently at Baraka with emphasis placed on longevity the solar power equipment, while still being able to provide internet to any user at any of the schools when requested. Also in the event that the connect-on-demand system fails, an override will be included that will revert network management to its current state.

Design Criteria

Low power consumption (priority: 1) – The new integrated system will be running off of solar power during the day, and at night will operate off of battery power. Once battery power reaches 40% the battery life will be preserved by shutting down power to the whole network. The system design itself will consume very little power at Baraka where solar power is used.

Durability/Robustness (priority: 2)– Certain precautions need to be taken into consideration given the fact that this design will be installed in a hot climate with very little moisture. Steps must be taken to ensure that dust or any particulate matter enters the system and causes malfunctions. Furthermore, steps will be taken to account for any animals (i.e. rats, millipedes, termites… etc) that might interfere with system functionality.

Low maintenance (priority: 3) – With the assumption that there will betrained technicians in the area;a user-friendly design will be implemented. Problems could occur leading to network error. In order to minimize this possibility, the design must be robust;however, it should also include an override for possible error.

Safety (priority: 4) – Added protection will be beneficial to prevent any damage to the network or user. Hardware components should be protected preventing any interaction between the system and the user so that both are safe and secure.

Low cost (priority: 5) –MSU’s interests in Tanzania are most concerned with developing a concept that provides the end user an internet terminal at the lowest cost. Down the road, the internet would be provided by 3G cellular data cards. The 3G coverage in Tanzania is currently underdeveloped, and is why a VSAT with wireless bridges must be used at this time. Since the “internet-on-demand” system being designed will be outside the scope of a multi-seat system, MSU hopes the Tanzanian government adopts the 3G system. Therefore, cost of this specific project is not a primary concern,being that it will not be the adopted method for providing internet to these terminals.

Conceptual Design

Design Overview

Figure 1 shows a FAST diagram representing the overall functionality of our design; this was the basis leading to the conception to our design. Figure 2 illustrates the system design - anything connected in blue is a typical network connection. The signals dealing with the proposed control system are in red. First, a user would try to access the internet, then a software program will detect if the internet is accessible at that moment. If not, the software will locally cache TCP packets and at the same time initiate the AM radio link to activate the network. The AM receiving end will demodulate the signal and send it to a decoder. Whenthe AM signal is decoded and the source of the request is determined, a microcontroller will power up the necessary networking equipment, providing that specific location with internet. The microcontroller will also be used to determine solar batter life, shut the system down when not in use for a specific amount of time, and implement a curfew at certain times of day when internet is known not to be used, i.e. night hours.

Figure 1: FAST Diagram

Figure 2: Design Diagram

End user software

At the end user machine (Lenovo S10/20), software will be running that will capture and analyze packets originating from the client machine. If the packet is determined to have originated from a user input, the application will send a request to turn on the wireless network bridge at Baraka. If the end user computer does not have internet connectivity then the packets generate, they will be cached in memory until a network connection has been established. To determine if a request is user generated, the software will examine the destination port of TCP headers. To determine if the computer has a network connection, the software will check the IP address.

Also, a component of the software will generate a composite of sinusoids consisting of three separate frequencies to be transmitted over the AM radio link. The computer itself will initiate the software and send the sinusoidal signal via USB port to the AM transmitter.

Radio link

To let the microcontroller know that a user is making an internet request from one the satellite schools (Manyara or Rift Valley); a tone signal will be transmitted from one of these schools to Baraka via AM radio. Since this radio will be sending much less data and will be at a lower frequency than the internet link, it will consume less power at the satellite school than if the WiFi or WiMAX. More importantly, it will consume less power at the Baraka end because there only needs to be a receiver and decoder. The signal being transmitted will be a summation of tones. When a user tries to access the internet, the computer program will send a short signal composed of three tones. Each satellite school will have its own tones so the microcontroller knows which link to establish. This signal will be amplitude modulated and transmitted to Baraka. At Baraka, the signal will be received, demodulated, and decoded. Once the signals are decoded, the microcontroller will know which school sent the request.

AM radio

The AM radio will operate at 433 MHz. This frequency is advantageous because it is unlicensed worldwide. It is usually used for short range applications such as car door openers and tire pressure meters. This frequency will allow us to test the system in America and install it in Tanzania. 433 MHz is also advantageous because it allows for a directional antenna. At very low frequencies, directional antennas would not be practical because the size of an antenna is proportional to the inverse of the frequency. The wavelength of a 433 MHz wave is about 70 cm. This is a workable size for a direction antenna.

The radio will be implemented using an off the shelf transmitter and receiver. The transmitter, only having a range on the order of 100 meters by itself, will be amplified with a radio frequency amplifier of our design.

Antennas

Directional antennas will be implemented if needed at the satellite schools to lower the transmitting power. These antennas will most likely be simple two or three element Yagi-Uda arrays of our design. If the transmitting power is high enough on its own, monopoles will be used at the satellite schools. Baraka's receiving antenna will be an omni-directional monopole since it requires receiving signals from multiple sources.

Decoder

The decoder will be implemented using analog circuitry of our design. The received, demodulated signal will first pass through band pass filters. A peak detector and comparator will create a logical 1 if this frequency is received. These bits will be go through a logical AND gate to make sure all three tones are present. If all three tones are present, a logical 1 will be sent to the microcontroller. The reason for three signals being sent is to ensure the microcontroller does not receive an undesired signal.

Microcontroller

In the design, a microcontroller will be used to handle all switching functions at the site of the satellite link at Baraka. The hardware will be plugged into outlet boxes. The microcontroller will decide whether to turn on/off the satellite link based on four different inputs:

  • The first input is an alert from the battery system, determining the 40% threshold voltage. If 40% or lower is detected, the microcontroller will turn off the system and go into an idle state. The microcontroller will then wait for another alert from the battery system, determining if battery voltage is at 60%. If so, the microcontroller will power up the network if a request is made.
  • The second input will be a signal from either Baraka, Manyara or Rift Valley requesting access to the internet. Whenever a user from either of these locationsgeneratesinternet packets, the microcontroller will tell the satellite to and respective routers to turn on.
  • The third input will be a reset timer which will be clocked internally through the microcontroller. As soon as the microcontroller receives a high value to turn on the system, the clock will reset and count down 15 minutes. After the countdown is complete, the microcontroller will realize that the system is not being used and it will power down the system.
  • The last input is another timing signal based on what time of the day it is. The microcontroller will be synchronized to an external clock at Baraka. When that clock reads 11pm, the microcontroller will shut down the system for the night and enter in a hibernation mode. The external clock will then begin a countdown until a specified time the next day. When the countdown ends, it will send a high signal to the microcontroller, causing the microcontroller to relay the message for the system to turn on when request are made.

Outlet Boxes

The hardware that is to be turned on and off will be plugged into outlet boxes. Each outlet box will have an outlet, a relay, and a manual switch. The outlets have to be 240VAC English outlets. This is what is currently used in Tanzania. The relays, controlled by the microcontroller, are latch-type relays. This way, a current doesnot have to be running through the relay coil the entire time the relay is connected. This will save power at the Baraka end. The switch will act as a manual override to the control system. This way, if the control system does fail, the hardware can be manually switched on and off.

Power Supplies

Baraka has a system of 24 volts; from the 24 volts a power supply will be implemented to supply 5 volts. The 5 volts will run the microcontroller and the AM receiver. In both Rift Valley and Manyara the 240 volts AC will be taken to make a power supply to power the AM transmitter.

Design Evaluation

The following table provides an overview of possible designs. This is later broken down in examining solutions for the software, wireless bridges, and radio link that could be used.

Design Justification Table
Parallel Antennas (Remote turn on) / Parallel Antennas -
Router monitoring network usage / Router monitoring network usage
Low Power Consumption
(At Baraka) / Only new hardware would be low power microcontroller, receiver, and relays. Power consumed would be very low.
Wireless bridges would be turned off when not in use. / This would require a low power microcontroller, receiver, and router to place software on.
The router would be an additional device that would have to be powered. But the wireless bridges could be powered off when not in use. / This would require a low power microcontroller and router to place software on.
The router would always be on as would the wireless network bridges
Durability/Robustness / Microcontroller, relays, and decoder will be placed inside of a protective case.
Transmitter, receiver, and antennas will be exposed to the elements so smaller cases might have to be fabricated. / Microcontroller, relays, and decoder will be placed inside of a protective case.
Transmitter, receiver, and antennas will be exposed to the elements so smaller cases might have to be fabricated. / All equipment would be housed inside of a protective case
Low Maintenance / There will be an ability to remotely connect to administer software, but hardware will be designed to require as little servicing as possible / As long as there are no hardware failures almost all aspects of this system could be accessed remotely. / All components, other than relays and the microcontroller could be administered remotely as they would be software.
Safety / All components would be placed in a protective case. To prevent harm to antennas they would be placed on poles or roofs with limited access / All components would be placed in a protective case. To prevent harm to antennas they would be placed on poles or roofs with limited access / All hardware would be placed in a protective case to restrict physical access.

In determining the software that can be used to detect user generated requests there are several options available. These range from developing an application using only modules or libraries to handle low level details to modifying currently existing software to accommodate the system requirements. The table below presents three options Scapy and a shell script would require the most testing and development time, but would allow for the most control over how the system works. Tinyproxy is a piece of software which is considered to be very stable and mature. Time would have to be invested in learning the functionality of existing code.