# Mathematical Contest in Modeling, 2000

## The event

The Mathematical Contest in Modeling is an annual event, sponsored by the Consortium for Mathematics and Its Applications, in which students at colleges and universities all over the world are asked to develop and analyze mathematical models of open-ended, practical problems for which no direct solutions are known. Participants work in teams of three and are permitted to use libraries, computers, and other inanimate sources of knowledge and inspiration. The organizers of the contest propose three problems; over the three days of the contest, each team selects one of these problems, designs, implements, and analyzes a model, and writes a substantial report presenting its results.

The sixteenth Mathematical Contest in Modeling was held on February 4-7, 2000. Grinnell's teams this year were:

• Rachel Heck 2001, Andrew Kensler 2001, and Eric Nana Otoo 2001(faculty sponsor: Marc Chamberland).
• Alex Ford 2001, Noah Hoffman-Smith 2001, and Morgan Page 2002 (faculty sponsor: Marc Chamberland).
• Shekhar Shah 2001, Wei Zhao 2000, and Jamal Rogers 2000 (faculty sponsor: Mark Montgomery).
• Oleksiy Andriychenko 2001, Dmitry Krivin 2001, and Zorka Milin 2000 (faculty sponsor: Mark Montgomery).

## The problems

Here are the problems that COMAP posed this year:

### Problem A: Air traffic control

Dedicated to the memory of Dr. Robert Machol, former chief scientist of the Federal Aviation Agency

To improve safety and reduce air traffic controller workload, the Federal Aviation Agency (FAA) is considering adding software to the air traffic control system that would automatically detect potential aircraft flight path conflicts and alert the controller. To that end, an analyst at the FAA has posed the following problems.

Requirement A: Given two airplanes flying in space, when should the air traffic controller consider the objects to be too close and to require intervention?

Requirement B: An airspace sector is the section of three-dimensional airspace that one air traffic controller controls. Given any airspace sector, how do we measure how complex it is from an air traffic workload perspective? To what extent is complexity determined by the number of aircraft simultaneously passing through that sector (1) at any one instant? (2) during any given interval of time? (3) during a particular time of day? How does the number of potential conflicts arising during those periods affect complexity?

Does the presence of additional software tools to automatically predict conflicts and alert the controller reduce or add to this complexity?

In addition to the guidelines for your report, write a summary (no more than two pages) that the FAA analyst can present to Jane Garvey, the FAA Administrator, to defend your conclusions.

### Problem B: Radio channel assignments

We seek to model the assignment of radio channels to a symmetric network of transmitter locations over a large planar area, so as to avoid interference. One basic approach is to partition the region into regular hexagons in a grid (honeycomb-style), as shown in Figure 1, where a transmitter is located at the center of each hexagon.

An interval of the frequency spectrum is to be allotted for transmitter frequencies. The interval will be divided into regularly spaced channels, which we represent by integers 1, 2, 3, ... . Each transmitter will be assigned one positive integer channel. The same channel can be used at many locations, provided that interference from nearby transmitters is avoided. Our goal is to minimize the width of the interval in the frequency spectrum that is needed to assign channels subject to some constraints. This is achieved with the concept of a span. The span is the minimum, over all assignments satisfying the constraints, of the largest channel used at any location. It is not required that every channel smaller than the span be used in an assignment that attains the span.

Let s be the length of a side of one of the hexagons. We concentrate on the case that there are two levels of interference.

Requirement A: There are several constraints on frequency assignments. First, no two transmitters within distance 4s of each other can be given the same channel. Second, due to spectral spreading, transmitters within distance 2s of each other must not be given the same or adjacent channels: Their channels must differ by at least 2. Under these constraints, what can we say about the span in Figure 1?

Requirement B: Repeat Requirement A, assuming the grid in the example spreads arbitrarily far in all directions.

Requirement C: Repeat Requirements A and B, except assume now more generally that channels for transmitters within distance 2s differ by at least some given integer k, while those at distance 4s at most must still differ by at least one. What can we say about the span and about efficient strategies for designing assignments, as a function of k?

Requirement D: Consider generalizations of the problem, such as several levels of interference or irregular transmitter placements. What other factors may be important to consider?

Requirement E: Write an article (no more than 2 pages) for the local newspaper explaining your findings.

## Results

The team of Alex Ford, Noah Hoffman-Smith, and Morgan Page earned the Meritorious rating from COMAP's judges. The team consisting of Rachel Heck, Andrew Kensler, and Eric Nana Otoo received Honorable Mention. Both the team of Shekhar Shah, Wei Zhao, and Jamal Rogers and the team of Oleksiy Andriychenko, Dmitry Krivin, and Zorka Milin were ranked as Successful Participants.

This year, 495 teams submitted complete entries. Twelve of these entries were judged Outstanding; seventy-six, Meritorious. One hundred thirty-five received Honorable Mentions in COMAP's report. The remaining 272 teams were classified as Successful Participants.

This document is available on the World Wide Web as

```http://www.math.grinnell.edu/mcm-2000.xhtml
```