Modeling a Cellular Network

Transcription

1 Modeling a Cellular Network Concept: A cellular network is composed of a matrix of small grids, each of which communicates with a cell phone using radio signals. (hands-on, outside, 50 minutes) Materials For the class: Ball (e.g. basket ball, soccer ball, tennis ball) Outdoor area for students to spread out STEM journal Engage Ask how many students own a cell phone. Begin a discussion to see how many have a basic understanding of how it works and integrates into the general telephone infrastructure. (It is helpful to keep in mind that a cell phone is a small radio transmitter and receiver (or transceiver), not unlike a radio station and radio receiver. The following description can be found on the Wikipedia site Communication Networks/Cellular Networks: Cellular phones, or mobile phones, are a very common sight today. Cellular phones connect wirelessly to a local base station, which receives the phone signal and transmits it into the phone network. Roaming occurs when the mobile phone is moving from one cell to another. Cellular phones, in addition to transmitting voice data, also transmit and receive control data. The control data tells the phone how far it is from the base station. If a phone is moving from one cell to another, the distance from the new base station becomes smaller than the distance to the old base station. In this case, the new base station begins to handle the call and the old base station stops communicating with the phone.) Draw on the board or project this image of a cellular network so students can get a sense of the geometry and spatial arrangement of the individual cells that make up a network. If the opening discussion did not bring out the central concept of how a cellular network works, summarize it for students using the image you drew or projected. Tell students you would like them to model such a network and how it works. This activity will be done outside and will use a student for each radio mast transceiver. A ball will be used to represent a radio packet of information that is transferred back and forth between the cell phone and the network transceivers. Explore Take students outside on a flat and fairly level surface. Assign a student to be the cell phone with others representing individual radio mast transceivers. The transceivers should spread out and arrange themselves to look something like the image you showed them in the classroom. If your group is too large, do this activity in two sections or have students take turns. Once the transceivers are in place, have the cell phone slowly walk through the field of transceivers,

2 much like a car would drive along a road with the passenger talking on a cell phone. (Put in a pitch for not talking on a cell phone while driving.) As the cell phone moves through the field, he or she should gently toss the ball to the nearest transceiver and wait for the ball to be tossed back. This could be repeated once or twice as the cell phone pauses. As the cell phone continues to walk and move into range (i.e. closer) of a new transceiver, the ball is again gently tossed to the new transceiver. This transaction can continue as the cell phone walks through the entire field of transceivers. Let more students be the cell phone and maybe even rearrange the pattern of transceivers. Be sure to establish your guidelines for safety and fairness. At some point, after all have had a chance to participate in this activity, have students return to the classroom for a summary discussion. Students could use their STEM journals to diagram and describe the cell network they modeled outside. How was our model like a real cellular network and how was it different? How could we make it more realistic? How would our model work if there were several cell phones in operation at the same time in the same area? Extend If there is time available, students can extend their exploration of the topic with the following resources: Mobile Networks Are Necessary to Deliver a Connected World Introduction to Cellular Systems How Cell Phones Work The Cell Phone Technology Additional Background Information Cellular Network Telecommunication Portal on Wikipedia Mobile Phone Telecommunications Service

3 Neighborhood Communications Infrastructure Survey Concept: Some aspects of the urban communications infrastructure can be seen by walking around the local neighborhood. (field trip, about 60 minutes or time available) Materials STEM journal Engage Tell students they will be taking a field trip to the neighborhood around the school. They are to be observing their surroundings carefully and looking for evidence of objects, systems or processes that can be considered part of the communications infrastructure of the town or city in which the school is located. Brainstorm what some of these items might be. (utility poles, overhead wires, signs for buried cables, telecom utility trucks, mail trucks, mail boxes, people using cell phones, cell phone towers and antennas, etc.) What form of communication have they used so far today? How much of that communication was dependent on computers? Explore Make the necessary arrangements for taking students outside. Group students in pairs and have them take their STEM journals. Tell students to record items they see and to share a spotted item with others nearby. Make this exploration of the neighborhood together and ensure the safety of everyone. Once you get back to the classroom, hold a discussion with students so they can report on the communications infrastructure items they found on the walk. When reporting an item, ask students how that item fits into the larger network of facilitating communication to and among different parts of the town or city. For example, what role does a utility pole play within the communications infrastructure? (It suspends telephone lines and telecommunications cables out of he way over streets and highways.) Students can save this information to add to their city design for the course project. Extend If there is time available, students can extend their exploration of the topic with the following resources: Have students print out a Google map of the neighborhood they surveyed then add selected communications infrastructure items they found to the map. Electric Power Distribution Undergrounding Additional Background Information Telephone Lines How the Radio Spectrum Works

4 Public Utilities How the Postal Service Works

5 Telephone Tube Concept: When sound is confined to travel through a narrow tube, it does not decrease in volume very much. (hands-on, outside or inside, informal time as available) Materials For the classroom: Drain pipe (4 in. x 10 ft. corrugated drain solid; commonly found in hardware stores; several sections) Couplings (alternative: duct tape) STEM journal If commercial drain pipe is not available to you, use a garden hose with, or without, a funnel at each end. Engage Ask students how many times a day they talk on the telephone. Make a line plot on the board of the results. How many have used a telephone that had a rotary dial - like this one. What kind of telephone did people use before electricity was discovered? How could you communicate with a friend over a distance without shouting? Have you ever seen a playground that had a tube with flared bells at either end for speaking into? If you can easily access the Internet, show students this photograph of a speaking tube. Explore Let students explore speaking into the telephone tube during unstructured times. Establish guidelines for use regarding speaking levels, sharing, and cleanliness. (Students should not hold the end of the tube directly against their mouths; it should be held a small distance away to avoid cross contamination.) Challenge students to see how softly they can whisper into the tube and still have their partner understand what was said. One fun way to check this is to ask one s partner to hold up x number of fingers and look for the response. At some point after all have had a chance to use the telephone tube, you might hold a discussion about the reason the sound travels so well from one end to another. (The sound waves coming from the speaker s mouth are confined to the inside of the tube and do not disperse to the surrounding air, as they normally would. As a result, the sound can travel a greater distance without fading.) Extend If there is time available, students can extend their exploration of the topic with the following resources: Sound an interactive simulation Basics of Sound MythBusters Rubens Flaming Tube

6 Additional Background Information Speaking Tube Pictorial examples of speaking tubes Sound

7 Transmitting Radio Waves Concept: Radio waves, or electromagnetic radiation, can be produced with a spark and can be detected with a simple AM radio. (hands-on, one class periods) Materials For the class: Portable AM radio with loudspeaker For each group: C-cell battery (D-cells work too) Metal screw (about 2 3 inches long) Two copper wires, stripped about 1 on both ends Tape (masking or electrical; 3 pieces about 1 long) Battery holder (optional) Portable AM radio with speaker (optional) For each student: STEM journal Engage Display a portable radio that has a loudspeaker and tune in a radio station, either AM or FM. Ask students how the radio is able to produce the sound that is sent out by a radio station. (The radio is super sensitive to the radio waves - electromagnetic radiation - that is produced by the antenna of the radio station. The radio is able to recreate the signal the station generates and broadcasts as a weak radio wave.)ask students if they know of any other devices that work on the same principle. (TV, WiFi networks, cell phones, walkie-talkies) Tell students they are going to build a simple transmitter that works on the same principle as a radio station. Explore Show students how to attach two wires to a C-cell battery, one at each end, using tape. Tape one of the free ends to the top of a screw; see graphic below. Turn on the AM radio. (If you only have one radio, students can make their transmitters and take turns broadcasting to the one radio.) When you scrape the free end of the other wire across the threads of the screw, you will hear static on the radio. Students should use their fingers to hold the taped wires to the ends of the battery since the attachment is not very strong. Using a battery holder eliminates this problem. Caution students not to touch and hold the loose wire from one end of the battery to the opposite end of the battery; the wire can become very hot with a new battery. Challenge students to see how far away they can use their transmitters from the radio and still produce an audible sound. (The spark that is produced when the loose wire is scraped against the screw generates electromagnetic radiation, radio waves. The sound is very noisy and contains no real information, unlike the signal from a radio station.)

8 Extend If there is time available, students can extend their exploration of the topic with the following resources: Radio Waves & Electromagnetic Fields (an interactive simulation of how electron movement in an antenna is transmitted to a receiver) Guglielmo Marconi Wireless Telegraphy (a YouTube video showing the history of the discovery and first use of radio signals; 14:21 minutes) Additional Background Information Spark Gap Transmitter How Radio Works

9 Communicating With Flashlights Concept: Signals can be sent over distances using light and a code. (hands-on, outside or inside, 60 minutes) Materials For each student: Standard flashlight (one that is bright enough to be easily visible outside in daylight) Morse code chart (available for downloading and printing here) STEM journal Engage Ask if any students know one of the internationally recognized symbols for distress (SOS). Do any of them know the Morse code sequence for SOS? ( ) Continue the discussion with: Have they seen any movies where SOS is used? Do they know any other letters of the alphabet in Morse code? Who might use Morse code today? In what form is SOS usually transmitted? (sound or light) Tell students they are going to get a chance to send and receive Morse code transmitted by light. Display a flashlight and demonstrate how it can be turned on and off quickly. Pass out a Morse code chart to each student and review it with him or her. By sending and receiving a short message encoded using Morse code, they will be modeling a communication network that relies on light. In today s urban, and even rural, communities, the coded messages that are sent using light are found in the fiber optic networks of the telecom industry. Explore Let students find a partner to work with when they go outside for this activity. Each should have a flashlight, a Morse code chart and their STEM journal. Explain your boundaries, safety expectations and time frame. Students should be tasked with taking turns sending a very short coded message to their partner and receiving one also, recording it In their STEM journals. If time allows, students could form a network of three and try to re-send a message to a third party that they received from the originator. Upon return to the classroom, hold a discussion about the experience of signaling with flashlights. What were the advantages and disadvantages? How could the effectiveness be improved? How far from each other could students get and still send and received a signal? How was a 3-person network like a communications network in a city? Extend If there is time available, students can extend their exploration of the topic with the following resources: Flag Semaphore Ocean City Beach Patrol

10 Morse Code Sound Morse Code Generator The Telegraph A History Additional Background Information How Do I Send an SOS Distress Signal? International Code of Signals