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# Signal Theory - Communications Technology. Analogue signals are converted to digital using sampling, basically at least two samples are made per cycle, and the more samples the higher quality of the digital output.

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Introduction

Task 2 - P5 Table of Contents Signal Theory 2 Frequency 2 Phase Difference 2 Amplitude 2 Wavelength 2 How Analogue Signals are converted to Digital Signals 3 Data Sizes 3 Synchronous & Asynchronous 4 Bandwidth 5 Error Detection & Error Correction 5 Checksum 6 CRC (Cyclic Redundancy Check) 6 Reed-Solomon 6 Comparison of Mediums 6 Data Compression 7 Huffman Encoding 7 Lossy 7 Loss-Less 8 RLL - Run Length Limited 8 JPEG - Joint Photographic Experts Group 8 Table of Figures Figure 1 - Sine Wave 2 Figure 2 - Analogue Signal With Sampling 3 Figure 3 - Digital Signal After Sampling 3 Figure 4 - Asynchronous Packet 4 Figure 5 - Synchronous Packet 4 Figure 6 - Shannon's Law Formulae () 5 Figure 7 - Reed-Solomon Error Detection 6 Figure 8 - Huffman Tree Diagram [] 7 Figure 9 - JPEG Image [] 8 Task 2a - P5 Signal Theory Figure 1 - Sine Wave Frequency Frequency is the number of cycles per second; this is measured in Hertz (Hz). This is calculated by the reciprocal of time (1/T ). Phase Difference Phase Difference is two Sine waves with the same frequency but the two waves are delayed in time; the delay in time is measured in degrees. ...read more.

Middle

Different types of noise can conflict with the signal; there are different types of noise such as: White Noise Pink Noise Johnson Noise Error Detection & Error Correction Parity Bit - RS232 There are a few types of error correction types; I will explain what these are and which ones are more efficient. With RS232 - Serial you had a parity bit; this was part of the packet when you sent data. This worked by calculating the odd or even numbers. For example if the parity bit looks for an even number of 0's and there is an odd number it will detect that there is an error and flip a bit to make it even. However this is bad because RS232 has a limitation of one bit detection, when more than one bit flips over and it won't detect any errors because it will show that it is even. Another downfall is that there is no retransmission on RS232 so the packet can't be requested if there is an error that cannot be fixed. Checksum Checksum is where you have a fixed size of data which can be compared to rule out any accidental errors in transmission, this is done by calculating how many 1 bits they are and it will compare it with the sender, if the amount of 1 bits match you will have a successful transmission. ...read more.

Conclusion

This is a very complex method. There are two different variations of data compression one is lossy and one is loss-less. Huffman Encoding uses Loss-Less compression. Lossy With file formats such as JPEG, MP3, MPEG, and PNG you can afford to drop and lose some bits here and there and quality won't decrease noticeably. Loss-Less This is used with data compression where if you lose one bit your data will be corrupted. RLL - Run Length Limited Run length limited is a loss-less compression method, this is a simple method of reducing a file size for use in media such as CDs, DVDs and Flash Drives. RLL simply counts how many ones and zero's they are in a binary code. For example if you had this code "000111001 11110000 1101011 00" RLL would change it to this: "3,0s;3,1s;2,0s;1,1s;4,1s;4,0s;2,1s;1,0s;1,1s;1,0s;2,1s;2,0s" JPEG - Joint Photographic Experts Group JPEG is a compressed image format that is a lossy form; JPEG can easily be a fifth of the original file format which would usually be a .BMP or .TIF file. You cannot use JPEG in: CAD-CAM Applications Images that have had mask and or shadow effects added Images containing 256 colours or less. [4] Figure 9 - JPEG Image [5] 1 http://en.wikipedia.org/wiki/Shannon-Hartley_theorem 2 http://en.wikipedia.org/wiki/Cyclic_redundancy_check 3 http://en.wikipedia.org/wiki/Huffman_coding 4 http://www.prepressure.com/library/compression_algorithms/jpeg 5 http://vesta.astro.amu.edu.pl/Library/WWW/Tutorial1/graphics/jpeg_graphics.html ?? ?? ?? ?? Antony Bond Unit 10 - Communications Technology P5 1 ...read more.

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