-In the previous sequence, we saw that the role of the modulator found within the transmitter was to build a signal from the original binary information to be transmitted. This sequence aims at having a closer look at how this signal can be built and looking at the impact of the signal formation on the transmission chain. No matter how the signal is built, the principle is identical. We associate a different physics symbol to each bit or group of bits to be transmitted. We will start this sequence by introducing a few signals. Here, two different signals for a same binary sequence to be transmitted. In the first case, 0s are coded with a low level and 1s are coded with a high level. This is level coding. It is a NRZ-type signal meaning Non Return to Zero. This signal can be found in GPS systems. The two levels can be two voltage levels. In the second signal example, coding is done via an edge. 0s are coded with a rising edge and 1s are coded with a falling edge. This signal is called Manchester type. It can be found in the Ethernet for example. You see that, for a same binary sequence, we have formed two different signals with different appearances. In both cases, a physics symbol codes one bit. But we could imagine a physics symbol coding several bits. Like here, where a physics symbol codes a group of two bits. So there are four possible physics symbols to code the four possible groups that can be formed with two bits, that is to say 00, 01, 11 and 10. The duration of this physics symbol is the symbol duration. You see here that it increased since we coded two bits in one symbol. We can go further and code three bits in a symbol like here. So we will need eight different levels, here we have a level coding, to code the eight possible groups of three bits to form eight symbols. We note that the symbol duration increased again since we code three bits with one symbol. The signal dynamics also increased. The signal dynamics is the difference between the minimal and maximal amplitude of the signal. If we want to keep the same distance between each levels, and we increase the number of levels, the signal dynamics increases. The minimal distance between symbols will impose the bit error rate we get, which measures the quality of the transmission. The bit error rate is linked to the minimal distance between the symbols. The energy dedicated to transmission is linked to the signal dynamics. Later on, we will see that the number of bits put in a symbol is linked to the band used by the signal. This is something you do not know yet, but we will talk about it later on. The band used by the signal will depend on the number of bits put in a symbol.