Hi All!
I was reading how cell phones have inbuilt error correction software that checks the parity bits etc and corrects issues. These issues supposedly come up during transmission where a certain bit that is transmitted gets corrupted and is received as another bit.

In reality, how often does a text message gets messed up? Is it a common occurrence that happens all the time or is it rare?

Are the text messages we receive daily, the first version or are they the corrected/ re-transmitted version?

Ty 4 the replies!

 

ECC (Error Correcting Codes) are universally used in digital radio communications because a radio connection is a fading channel. In the case of mobile phones, where the frequencies used are quite high, multipath is one of the biggest causes.

That is, signals are reflected from objects in the environment and arrive at the antenna of the mobile device at different times, in and out of phase. This leads to destructive and constructive interference as the signals are added they can either decrease signal strength, which leads to fading, or increase it which can lead to distortion.

Mobile phones use a class of error correction called FEC (Forward Error Correction) where extra data is transmitted to avoid needing to retry a damaged packet. In particular they use Turbo Codes which are a fairly modern invention and are extremely efficient. They allow the data transmission to come close to the Shannon Limit, the theoretical capacity of the channel.

Every practical mobile radio data connection has a non-zero BER (Bit Error Rate). That is, mobile data devices, like mobile phones will always suffer from lost data. The extent of this, in the absence of ECC, is determined by things like signal strength and severity of multipath reception. Adding in ECC, in particular FEC, reduces the BER so there are fewer retries to send packets.

Your mobile phone is constantly correcting bit errors and often requiring retries. This is what allows such small devices with small antennas to work well. If not for the ECC, you would need much greater power from the cell site and much larger antennas to successfully communicate.

Now I think maybe you have a misconception. In the case of your text messages, the ECC wouldn't be correcting one character in a message. It is used to make sure the packet that contains that character, among other data, is intact. Because various sorts of compression are used in data transmission, the correction is to the compressed data and until it is decompressed later in the process, a single letter in a text message would not be visible in it.

[EDIT: added omitted word "suffer" and omitted letter "v".]