Principles of Signal Theory

Signal Theory is the study of how information is transmitted between two or more entities, also known as peers, in a communication system. The digital signals are a series of pulses made of denoting on and off or 1’s or 0’s which can be digital or analog waves. Digital signal processing (DSP) is a set of methods aimed at enhancing data integrity when transmitted by removing errors.

Data is made of bits, stored in bytes and is transported in packets. A bit is a binary digit with a single value of either 0 or 1 and is the smallest unit of computer data. A byte is a binary term made of 8 bits and represents a single character, which could be a number, letter or a symbol. Data sent in its entirety is difficult and easily corrupted. However, by breaking it down into smaller packets that are 1 kilobyte or 1024 bits each, data can be transmitted or retransmitted should there be an error. A packet contains a header, a payload and some might also contain a trailer. The header holds 96 bits of instructions about the data such as the packet number in sequential order, protocol and information about the source and destination including port numbers, IP addresses and MAC addresses. The payload holds 896 bits of data that the endpoint device processes, this could be instructions to retrieve or update data from the server if the request is from the client. If the data is a response from the server to the client, the payload could be information to display on a web page. The trailer is the DSP part that is 32 bits at the end of the packet and includes error correction to ensure the correct data arrives at the correct destination.

Synchronous transmission happens in the Network Layer 3 and Data Link Layer 2 as packets or frames are transmitted as a sequence of signals coupled with timing signals to ensure the sender and receiver are in sync. These endpoints have to wait for their timing signals generated by an electronic clock to synchronise and data can be transferred in this window period efficiently at a high rate. The transfer pauses when the timing signals are out of sync. An example is the Ethernet protocol which is used in a LAN whereby the Fast Ethernet offers data transfer rates of up to 100 Mbps, allowing for a continuous stream of signals to be sent. Note by contrast, the standard Ethernet- based LAN speed is up to 10 Mbps.

Asynchronous transmission is when is sent from one endpoint to another without having to wait. The packets are sent in spurts of various lengths as opposed to a continuous stream which is less efficient but more flexible than synchronous transmission.

Error detection is a method that detects corruption to the data caused by channel noise during a data transmission when a 1 becomes a 0, vice versa, in the received code. The error correction ensues as instructed in the trailer of a data packet and rebuilds the data to ensure the binary code is correct.

Bandwidth is the amount of data that is able to be transferred through a medium and is measured in bits per seconds (bps). Nowadays millions or billions of bits per second is the throughput modern networks can handle, offering a higher bandwidth.Bandwidth comes at a price that users pay and internet service providers (ISP) have to manage and limit usage to match the user’s tariff. Fibre optic cables has a higher bandwidth than copper wire because light travels faster than electricity and is less susceptible to background noise interference. Background noise is unwanted electrical energy that degrades transmitting signals, especially over long distances. Whether it is data in the form of text or sound, it can be distorted by noise which is then rectified by error detection and correction.

Telephone communication is speech transported in radio signals over a radio channel. A satellite is a floating device circling in the Earth’s orbit and such a channel offers high, cheap bandwidth that can send and receive signals over a large area. Microwaves are a form of electromagnetic radiation offering wireless communication at a high bandwidth and uses a little bit more energy than radio waves. High frequency radio waves has a radio frequency of 3 to 30 megahertz (MHz) and its high frequency permits fast transmission used by mobile phones.