 Basics 1
We won't explain the difference between bits and bytes here. Perhaps we'll briefly talk about ASCII code. It's one of the first examples of how letters are assigned to numbers. It still exists today, albeit as part of a global
code.
The original ASCII code is content with 127 characters, so it only needs 7 bits. It dates back to a time when computers still had to pay particular attention to memory space. It includes numbers, uppercase and lowercase
letters, and special characters before, between, and at the end.
As more and more special characters were added - just think of accented letters - it was expanded to 8 bits. With the advent of networking, the need to transmit characters from as many languages as possible became
clear, so two bytes (16 bits) per character were sacrificed. The Chinese script, for example, benefits greatly from this Unicode character set.
Therefore, if digital data is transmitted over an analog telephone network, a so-called demodulator is required. In its oldest form, this is a modem to which a telephone receiver is connected. Therefore, if zeros and ones
are to be transmitted in oscillations, they can have either different amplitudes or different frequencies.
By combining the changes in both parameters, you can even use multiple connections (channels) simultaneously (multiplexing). This book, of course, focuses primarily on radio transmission. Frequencies play an
important role there anyway. They are divided into tiny ranges and allocated piecemeal, so to speak; in the case of UMTS, even for billions of dollars.
So, when you switch between different stations on your car radio, you're essentially just changing the frequency with the same transmission hardware. When transmitting bits and bytes, individual frequencies can be further
divided into time slots. The processes described up to this point are also typical for mobile networks.
As with any data transmission, it's not just speed that counts, but also the synchronization between sender and receiver. This includes the receiver noticing when an important message needs to be retrieved and whether it
can keep up during transmission—i.e., whether the transmission is transmitted sequentially, bit by bit.
Just as with bus systems, there are multiple start and stop bits that simultaneously allow the receiver to synchronize to the sender's timing cycle, regardless of whether the sender sends bit strings of varying lengths
(asynchronous) or always the same length in fixed frames (synchronous). With the latter transmission method, fewer bits are required for control. However, the channel is used less efficiently.
Just as with bus systems, there are multiple start and stop bits that simultaneously allow the receiver to synchronize to the sender's timing cycle, regardless of whether the sender sends bit strings of varying lengths
(asynchronous) or always the same length in fixed frames (synchronous). With the latter transfer method, fewer bits are required for control. However, the channel is used less efficiently.
Control of transmitted data is urgently needed. Since sufficient interference is already possible with wired connections, wireless transmission, which is never possible without a line network, presents additional sources of
error. The problem is generally solved by additional bits, which, however, result from the data already transmitted (redundancy). Read more about this in our book on CAN bus and the like.
Control of transmitted data is urgently needed. Since sufficient interference is already possible with wired connections, transmission via radio, which is never possible without a wired network network, there are additional
sources of error. The problem is generally solved by additional bits, which, however, result from the data already transmitted (redundancy). Read more about this in our book on CAN bus and the like.
Since a radio signal is easier to tap than any wire, security and possibly even coding are essential. You've probably already used the simplest form of source coding when you ended a text message with 'Best regards.'
Channel coding is more fun. We use it, for example, to improve speech output on our websites. If a letter is spoken too briefly, we modify the text using software so that the letter appears twice or an 'h' is added. However,
this type of coding is intended to detect errors here.
Line coding is often applied by the router itself, for example, in data traffic between a router and a smartphone, depending on the quality of the signal transmission. This determines whether one bit or even more than one is
sent per symbol. '0' would then be sent as '000' and '1' as '001'. Of course, this must be agreed upon beforehand with the communication partner.
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