Principles of Signal Theory

BTEC National

Signal Theory

• Data is represented in digital format based on binary (base 2) principles

• Digital signals are discrete.

Data

• The smallest element of data is the ‘bit’ or ‘binary digit.’

• This can be represented by a ‘0’ or a ‘1’.

• When bits are grouped together they can be more useful units of data. For example 8 bits form a byte

Converting Denary to Binary

• To convert denary to binary you must firstly know the ‘base 2’ rules. (This is similar to the units, tens, hundreds you were taught at primary school)

128 64 32 16 8 4 2 1

Converting Denary to Binary

128 64 32 16 8 4 2 10 0 1 0 1 1 1 1 =

47

We work this out by looking at the headingsAnd adding the numbers up.

= 32 + 8 + 4 + 2 + 1 = 47. Therefore 47 is represented as 00101111 (byte format)

Concept of a packet

• In networking, data must be formed in a suitable ‘package’ to be able to be transported across the network.

• The actual format of the package is different for different types of network. However the term ‘data packet’ is always used to describe the package

Concept of a packet

• A data packet should minimally contain the source and destination address, data and error control.

Source Address

Destination Address

Data Error Control

The source address is sent so the recipient knows who has sent the data. The destination address is used to find the right recipient. Data is the ‘actual message’. Error control is sent to help identify problems with the data once it has been received.

Asynchronous versus synchronous transmission

• Asynchronous transmission means that device 2 (the receiver) must acknowledge receipt of the data before device 1 (the sender) will send more.

• In synchronous transmission both devices (sender and receiver) will synchronise with each other before the data is sent.

Bandwidth

• This is generally defined as the quantity of data that can be sent through data transmission over a specified period of time.

• Bandwidth is usually quoted in (from slow to fast)– Bits per second (bps)– Kilo bits per second (kbps)– Mega bits per second (mbps)– Giga bits per second (gbps)