AO1: Fundamentals of Data Communication

Question 1

What do we use modulation?

Answer 1

To increase the range of the signal.

Can allow the use of smaller antenna as modulation can decrease the low and high bandwidth.

Question 2

What are the three different types of Modulation?

Answer 2

Amplitude Modulation
Frequency Modulation
Phase modulation

Question 3

What are analog waves denoted by?

Answer 3

Sine waves

Question 4

What are digital waves denoted by?

Answer 4

Square waves

Question 5

Which type of signal has the most response to noise?

Answer 5

Analog

Question 6

What is unipolar encoding

Answer 6

Unipolar encoding:
High amplitude is a 1
No Amplitude is a 0.

Question 7

What are the different types of Polar Non-Return to Zero

NRZ

Answer 7

NRZ-L –> Every different bit the voltage switches

NRZ-I –> Voltage switches every time a 1 is encountered.

Question 8

What is RZ encoding?

Answer 8

RZ (Return to Zero) counts all two different bits before making a decision, It has three different voltage levels:
Positive represents 1
Negative Represents 0
Zero Voltage represents: null
This way fewer errors are made when converting digital data to a digital signal.
For example:
if a null and a negative are picked up then it will be translated as a negative.
If a null and a positive are picked up then it will be translated as a negative.

Question 9

What is Bipolar Encoding

Answer 9

Bipolar encoding is similar to RZ,
No voltage (neither positive or negative) is counted as a zero
Any voltage (even negative and positive) is counted as a positive

Question 10

What is block coding?

Answer 10

Block coding is the name given for family of error-correcting codes such as parity bits and

Question 11

What does PCM stand for and how is it used in Analog-to-digital Converison

Answer 11

PCM stands for
Pulse Code Modulation.
It’s the most common method used to convert analog data into a digital format. It involves three different steps:
Sampling:
The sampling signal is sampled at every T interval.
Quantization
Turning the sampling into points over the analog signal with different values
Encoding:
Turning each approximated value into a binary format.

Question 12

What is the difference between parallel transmission and serial transmission?

Answer 12

Parallel:
Sends data that has been organized into groups of fixed lengths to an equal number of data lines. All of the data is sent at the same time.
Disadvantages: Commonly affected by EMI such as crosstalk which leads to fewer data inputs. Which in turn leads to lower speeds. The pins can get easily damaged.
Serial Transmission
Bits are sent one after another in a queued manner. Serial transmission requires only one communication channel rather than multiple like parallel.
Advantages: Can send more data than parallel due to fewer errors as it isn’t heavily affected by EMI like parallel.
Due to the design, most serial transmission media have their pins protected so they aren’t easily broken like parallel.

Question 13

What is synchronous communication?

Answer 13

Synchronous –> occuring at the same
The sender and the receiver are are synchronoised using a clock which clicks at the same speed, which is used as a reference point for data transmission so communication can occur at regular intervals.

Question 14

What is asynchronous communication?

Answer 14

The devices aren’t permanel synced, only during transmission.
This is done with a start bit then ending with a stop bit.
They have seperate clocks. It uses the time inbetween the start bit and the next real bit to synch it’s clock to the speed of the data transmission. The body of the data must already be pre-agreed.