I have secondary informatins to protected and must be coded in the transmission channel. I'm looking for ideas or matlab codes that explain how to encode this informations.
Channel coding is used to correct errors introduced during transmission. If you want to protect your information use encryption alogorithms. However, some authors proposed a combination of cryptography and simple channel codes to make security and forward error correction.
Dear Benadjina, channel coding does not protect information. For this, you must use cryptography. Best regards,
Channel coding is used to correct errors introduced during transmission. If you want to protect your information use encryption alogorithms. However, some authors proposed a combination of cryptography and simple channel codes to make security and forward error correction.
Channel coding is necessary for error detection and correction and there are sveral methods such as turbo code convolutional code ldpc code and so on another methods to protect the transmitted data by encryption algorithms
Dear Benadjina,
Channel coding is used to detect and correct errors as the colleagues hinted. So, channel coding improves effectively the S/N ratio and affect's processing gain.
There are two types of channel coding; the block coding and the convolutional coding. Turbo coding and low density parity check LDPC achieves the highest processing gain.
I order to protect the information from being intercepted one encrypts the data. There are two types of ciphers; the block cipher and the stream cipher.
In encryption process one mix the plain text with cipher key which is a random or a pseudo number to render the plain text unintelligible.
Best wishes
Hello Benadjina
I agree with Adbelhalim, Zainab, Mustapha.
Channels are not our friends, channels carry information in an imperfect way.
Therefore information carried across channels needs protection of TWO TYPES:
-1) one is against channel error
This is called channel coding, error protection
-2) one is against unauthorised "listening", and hacking of information not intended for the recipient
For instance a radio channel can be listened to by aynone in the area of coverage, even unauthorised listeners.
To protect the information against unauthorised interception, you may want a form of conditional access or encryption, an here I agree with all previous contributors.
Channel coding is highly dependent on the physical features of the channel, it needs to be tuned to it, for maximum robustness.
Let me give an illustrative example: it's called Gray coding.
Assume you have a system transmitting words of 2 bits say [b1;b2], representing one of four directions N, S, W E.
Assume you have a single bit error at worst, from your channel.
It is easy to see that the worst would be to read after channel transmission South instead of North, or West instead of East, but that errors leading to read East instead of North or South are less bad. Then you could have 00 for N, 11 for S, 01 for W and 10 for E.
It's called Gray code protection: an error shifts you to a "neighbour state".
Similarly assume a three state system A, B C, with 2 bit words: the assume A is coded by 00, B is coded by 01 and C is coded by 10. Then if you read 11, an error has occurred on the channel: the "forbidden state" 11 is used to detect errors. Now the probable correct word was either 10 or 01 if you assume only one bit was erroneous. If you know that B is much more frequent than C, then you may assume B was sent...
Note also that error patterns are not always isolated bits inverted (0 becomes 1 or vice-versa), but there are packet errors, depending on the channel and its physical properties.
Also note that illegal interception of digital signals dates back the Chappes Telegraph, with first illegal known interception in this optical and digital system performed by a trader on the stock exchange of Lyon, who used information from the Paris stock exchange before other traders in Lyon got the values.
Bad behaviours are not new...
Information Theory is a very interesting domain. This is where these topics are discussed.
Hope it helps
- Badges
- Science topic