Question

For this task you will have to design a system for text message communication after a major disaster, for example, after a major earthquake, tsunami, or hurricane. This system is motivated by the difficulties experienced in getting emergency help after a major disaster has rendered land-based communications useless in a large radius in the disaster area. For example, after Hurricane Katrina, most land-based communications systems failed immediately or shortly after the disaster [1]. This text message system would provide an alternative method for people to send short messages with the outside world (and perhaps receive replies), including with emergency personnel. As another example, after the March 2011 Japan earthquake and tsunami, twitter and email became important ways for people to find each other after transportation and cellular systems failed. This system could allow people to send messages announcing where they are, and if they need emergency assistance. This system would potentially allow emergency personnel to coordinate rescue operations.

Design Restrictions

One of the major problems with communications after a disaster is that everyone wants to communicate -- systems become overwhelmed with requested bandwidth and blocked by high traffic. You may, in your system design, restrict people to short text messages (like Twitter's 140 characters, for example), which forces them to communicate only the most critical information. You may restrict the number of messages per user (However, emergency personnel must not have a restriction on the number of messages they may send). In this manner, your system can limit the total bit rate of messages that are being generated.
Your system is allowed to use any ISM band (for example, the 83 MHz of bandwidth from 2400 to 2483 MHz). Assuming that this system will be used as an alternative communication system when all power is out, we can assume that 802.11 access points have all failed, cordless phones don't work, and thus the major sources of interference in these bands are gone. You don't necessarily need to meet FCC requirements for ISM band operation -- I assume that if your system is sufficiently beneficial to the public, the FCC would be willing to make an exception for your system during disaster situations.
You may not rely on electric power from the grid -- we can assume power has been lost, and will be out for days or weeks. You may not rely on cellular voice or data systems, or paging infrastructure, or telephone lines, or broadband internet services, anywhere within the disaster area. You may assume that these exist outside of the disaster area. Whatever (wireless device) equipment (which I term the user device) that you expect people to have in a major disaster, you must ask them to buy it today (not during the disaster). So a very low price for the user device is important, and it should be of a size that they can put in their emergency kit and forget about (until they need it). You might expect a small fraction of people (eg, hospitals, emergency personnel) to own more larger or more expensive equipment, which I refer to as infrastructure devices. To be specific, when needed in your system design, consider that a major earthquake strikes Salt Lake County, and no ground communications exist in the county, and ground communications are possible but significantly impaired in neighboring counties. This should include technical specifications of how the system will work:

1.    Description of the user device(s), including components of the hardware
2.    Description of the any communication link, including link budget, modulation, multiple access mechanism, transmit power and receiver sensitivity, etc.
3.    Evaluation of the probability of blocking, or probability that a user's message will be lost by your system
4.    Power source(s) for any user or infrastructure devices
5.    An approximate cost for the devices
6.    Robustness of the system: Why will this system be able to operate after a large-scale disaster?

Summary

The question belongs to Computer Science and it is about designing a text message communication system. The communication system must have specifications which can handle high surge of communication requests during the time of emergencies. So, the system has to have restrictions on the number of messages being sent, or the number of characters in the message, etc. The solution covers these and others in much detail.

Total Word Count 581

 

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