How Do Mobile Phones Communicate?

The proposed materials are low cost and easy to use.

• Introductory presentation. 
• Video Link (click link or see below) – This is an overview of the activity by the creators. It is intended for the teacher or volunteer, not the students.
• Printable kit  – The kit contains the following resources:

1. Stickers with the activity logo, for the students to write their name and wear it.
2. Binary code table.
3. Encoding and decoding templates:
   • Encoding templates of the words related to engineering.
   • Encoding templates of the mysterious phrase. (Available in general format, grouped by letters or by words, to adapt the transmission of the phrase to the number of teams of students).
   • Even though the decoding process is intended to be carried out on the blackboard, the printable kit contains additional general decoding templates in case the students want to decode the words/phrases themselves.
4. Stick “I” and circle “O”.
5. Encoded mysterious phrases to decorate the classroom.

All the pictures appearing in the templates belong to https://openclipart.org/, Public Domain Dedication (CC0 1.0)

1. Show Presentation

   The workshop begins with a small introductory presentation.

   The students are organized in groups of 4 or 5 members prior to the start of the activity. The teachers help the different groups throughout the process.

   The objective of this initial step is to introduce:

   • The concept of engineering: definition of engineering and presentation of some examples of well-known works of engineering together with their author, highlighting the role of women. The children would be asked if they know any engineers in their families or close friends.
   • Description of telecommunications engineering: explanation of the definition of “Telecommunications Engineering”. The students learn that Telecommunication engineers are in charge of designing everything related to television, satellites, internet and cell phones.
   • Explain the background of the hands-on activity: in order to start with the Step 2 (hands-on activity), the children are first exposed to the background of the activity. As an example, the instructor asks the children for different languages of the animals and people: dogs communicate with each other through barking, birds communicate through singing and people speak and write in different languages, for example, English and Spanish, using sounds (phonemes) and letters to communicate among each other and create words… But how do mobile phones communicate with each other? The answer is through the use of the mobile phones’ language: the bits. The activity consists of translating several words to the phones’ language; this process is called ENCODING. Then, we will TRANSMIT them, and finally translate them back to our language through DECODING. The encoding and decoding binary table must be displayed to the children, so that they can see the bits as “O” and “I” and use it as a “dictionary”.

2. Hands-on Activity

   First, every student writes their name on a sticker and wears it. Then, several groups must be created, ideally of 3 to 5 children. The groups must sit in separated tables. Every group is provided with one or two words as the messages to encode, transmit and decode. They are common words related to engineering: BIKE, CAR, ROBOT, PHONE, BRIDGE, PLANE, TABLET, OVEN, BOAT and TRAIN. The encoding and decoding templates and the stickers are provided in the printable material.

3. Encoding

   The objective of each group is to encode the given word using the binary coding table provided in the printable material. They should write the encoded letters in the encoding templates (with the words related to engineering).

4. Transmission

   When all the groups have encoded their example word, the transmission begins. For the transmission, cards with a large circle (yellow) and a large stick (blue) will be used, corresponding to “0” and “I” respectively. Each group, in order, transmits the binary code of the letters of their example word by holding up in sequence the corresponding “0” or “I” card. The rest of the groups identify the letters, one of the teachers writes the binary code and the associated letter they have identified on the blackboard, and so on until the word is completed, which is a surprise for the students.

   The example words are objects/machines related to engineering and of very common use: CAR, ROBOT, MOBILE, BRIDGE, AIRPLANE, TABLET, OVEN, BOAT, TRAIN, etc.

   To transmit the encoded word, children must use the cardboards with the “circle” and the “stick” as the 0 (“O”) and 1 (“I”) bit, respectively. The circle and the stick are provided along with the printable material. Each group will have their turn to transmit letter by letter their word to the other members of the class. To transmit the bits, one member of each group is in charge of lifting the stick and another member is the one lifting the circle, so that they show them to the rest of their classmates and to the instructor, following the bit order of the encoded letters; a member of the group indicates the bits to lift. The rest of the members of the team will have the role of supervising that everything is correct. The instructor writes each circle “O” and stick “I” on the blackboard.

5. Decoding

   Every time an encoded letter is written on the blackboard, the students must decode them using the binary coding template and say the solution out loud. Then the instructor writes each letter on the blackboard, when the word is finished, the kids say it out loud.

   We call it “the mysterious phrase” since the students don’t know it. In this case, each group transmits a word or a group of letters from the phrase: “TELECOMMUNICATIONS HELP US EVERYDAY”.

6. Collaborative phrase

   The final step is to repeat the encoding, transmission and decoding steps to communicate a complete phrase. Each group is in charge of communicating a word or, alternatively, a set of letters.

   Next, the same exercise is performed encoding, transmitting and decoding a sentence collaboratively. We call it “the mysterious phrase” since the students don’t know it. In this case, each group transmits a word or a group of letters from the phrase: “TELECOMMUNICATIONS HELP US EVERYDAY”. In the end, they all read it together, turning into a surprise for them.

   “TELECOMMUNICATIONS HELP US EVERYDAY”

   The instructors would call this phrase, “the mysterious phrase”, since the children do not know it and thus we arouse their curiosity

   Depending on the number of groups, it can be more convenient either to transmit the phrase by words or by sets of letters. If the phrase is transmitted by words, the order would be the following:
   1) TELECOMMUNICATIONS
   2) HELP
   3) US
   4) EVERYDAY

   The alternative option is to break the phrase into a set of letters and blank spaces so that the activity is adapted to the number of teams. The encoded phrase is provided along with the printable material, as a gift to the children, so that they can decorate their classroom and always remember what they have learnt during this activity.

7. Conclusions

   In this final step, the instructor explains to the children that, in real life, the “circle” and the “stick” are not cardboards, but changes made to radio waves. In general, waves cannot be seen. However, some of them are visible: the light. The instructor can use their phone flashlight to represent the circle (0, no light) and the stick (1, light). In this way, children will understand how the bits are communicated in reality. As an option, the instructor can use a Li-Fi app that we may provide.

The activity can be easily adapted to the number of participants, their age and to the available time. Ideally, the duration of the activity is approximately 1h30min.

The activity consists of encoding, transmitting and decoding a message, with the objective of understanding how information is sent through a wireless communications system. We exemplify it with the use of mobile phones, which are well known to them.

We have presented this workshop to students between 6 and 10 years old during the 2021-22 academic year, using very simple materials, with great acceptance and participation by students and teachers. We obtained very satisfactory results in public schools in the region of Madrid (Spain).

The theory behind “HOW DO MOBILE PHONES COMMUNICATE?” is linked to the basic processes related to the digitalization, such as the source encoding and decoding, and to the transmission.

There are two types of messages: analog and digital. People can communicate through voice or images, for example, which are analog, that is, they can take any value (voice level, color intensity, etc.). Digital messages only take a few values, in the binary case “0” and “1”.

The process of “translating” analog messages to digital has many advantages. For example, the effects of distortion, noise and delay in transmission are qualitatively different. In the analog case, the quality of the signal is degraded, while in the digital case bit errors are produced. However, it is easier to regenerate the original message with a low probability of error if it can only take one of two possible values.

The relative immunity to disturbances is what justifies digital communications. In addition to other added advantages such as the compatibility of different types of information, storage, computation, and the possibility of compressing the message to be transmitted, facilitating more efficient encryption and detecting/correcting errors (channel coding), among others.

Once the bits are created, they need to be transmitted through the air to a receiver that can be quite distant. We transmit by changing the characteristics of a radio wave according to the message to be transmitted. In a simplified way, we can transmit the wave when we want to signal a “1”, and not transmit at all to signal a “0”. Even though we do not see them, the receiver will be able to decide if there is a wave or not, then being able to receive and decode the message.

Thanks to the IEEE Communications Society (ComSoc) and it’s members who created this hands-on activity:

• Lianet Mendez-Monsanto Suarez, Universidad Carlos III de Madrid, Spain
• Raquel Perez Leal, Universidad Carlos III de Madrid, Spain
• Ana Garcia Armada, Universidad Carlos III de Madrid, Spain