Introduction to Signals

Analogue v's Digital

Analogue and Digital signals are used because they send out information through electric signals. The information can range form audio to video and it is then sent out in electric signals. Analogue signals are translated into electric pulses that vary in amplitude. In digital technology the information sent out is translated into binary so that each bit is representative of of two different amplitudes. The limitation of analogue is that recordings can suffer from distortion and noise. The limitation of digital signal is that  Digital systems are often more expensive than analogue.

Binary, Bits and Bytes
A bit is the smallest piece of computer data. a bit can either represent 0 or 1 by using the electrical states inside computer chips that store and process bits or magnetic bits in disk drives. A byte is 8 bits put together to represent decimal numbers 0 through to 255 by assuming each collections of bits is double the value of the previous group.  Binary is a set of 0 and 1s, 0 being off and 1 being on. Computers can only make calculations using binary.

Synchronous and Asynchronous Transmission
Asynchronous happens outside of real time because the signal is sent at a different clock rate to other signals. Synchronous is when signals in the network are sent at the same time based on one reference clock. The limitation of Asynchronous is important messages arrive at a later time than preferred. The limitation of synchronous is that when signals are based on one reference clock meaning the clock may not have the correct time displayed on it.  

Error Detection and Correction
Error detection occurs when noise or impairments are found in the data during transmission. The error is then found. Error detection makes data transmission more reliable. Error correction is when data that is transmitted contains errors are changed and reconstructed so that the data is clear from any errors. This ensures sent messages do not contain any errors on the receiving side. The limitation of error detection is that it can only find an error but it cannot rectify the error. The limitation of error correction is that the data may not be displayed correctly because of the changes made to the data during the correction process.

Data Transmission
Bandwidth is the speed of which electronic signals travel through a wire, cable or channel. In analogue transmission bandwidth is measured in Hertz or cycles per second. In digital transmission bandwidth is measured in BPS or Bits Per Second. Noise is electrical energy that can disrupt both signals and data while also lowering them in quality. Noise occurs in both digital and analogue hardware. Data compression occurs when users wish to to transfer or store data using less bits. The techniques used to compress data include; CCITT,ARC and ZIP these are the most common ways of compressing data. The limitation of bandwidth is that if the bandwidth is slow then devices will not be as efficient. The limitation of data compression is that it can take a while to compress data particularly large pieces.

Channel Types
A communication channel is a connection between a transmitter and the receiver that data can pass through. There are two types of communication channel which are guided and unguided. Guided is a wired connection and contains wires like twisted pair and fiber optic. These help to make the connection between a transmitter and receiver much quicker and secure. An guided connection is a connection between a transmitter and receiver that contains no wires. So that means things like satellites, radio broadcast and terrestrial microwave are needed to make the connection possible. A limitation of a guided channel is that there are more wires to trip on meaning a higher trip hazard risk. A limitation of unguided channel is that you could lose connection at any moment to this channel especially with satellites.