Influence of raised cosine pulse on modulation signal spectrum in digital modulation system

Digital modulation system uses raised cosine pulse to carry the information on the spectrum of modulation signal. Information is carried on the initial phase of the carrier, and the absolute phases between adjacent symbols are 90 degrees different, so all symbol information can be represented by four absolute phases. For example, 00 corresponds to the initial phase 0, 0 1 corresponds to the initial phase 90, 1 1 corresponds to the initial phase 180, and 10 corresponds to the initial phase 270. In addition, from the constellation diagram, when QPSK has error code, the probability that the symbol falls on adjacent constellation points is always higher than that on non-adjacent stars.