What is the specific format of the signal sent to the base station when the mobile phone wants to send information?

SMS mode of mobile phone short message

English coding

The default GSM character set is 7-bit encoding and ASCII code is 8-bit encoding. Coding is to convert 8-bit ASCII coding into 7-bit coding.

English decoding

Simply put, it is to convert 7-bit character encoding into 8-bit character encoding.

Chinese coding

Just convert the Chinese encoding of GB23 12 into Unicode encoding, and the code page is CP936.

The principle of GSM is to encode, encrypt and interweave the voice channel on the system channel to form a burst, and then send it after modulation. At the receiving end of the mobile phone, the signal is demodulated, deinterleaved, channel decoded and voice decoded, and then it is restored to a voice signal in the user's mobile phone. GSM system adopts narrowband time division multiple access (TDMA) technology in the transmission process. The bandwidth of each carrier frequency channel is 200KHz, and each frame has 8 time slots. Theoretically, a radio frequency is allowed to make eight calls at the same time, each time slot is 0.577ms long and the frame length is 4.6 15ms, that is, the time is divided into periodic frames, each frame is divided into many time slots, and then it is allocated according to the specific time slot principle. So that the mobile phone users send signals to the base station at specified time intervals in each frame, and the base station receives signals from different mobile phone users at respective specified time intervals, and the base station also sends signals to different mobile phone users at specified time intervals.

The principle of CDMA is that signal transmission is modulated after coding and interleaving, and then despread with high bit rate spreading code sequence. At the receiving end of the mobile phone, the signal is separated and compressed by the Rake receiver in the receiver. At this time, all users' signals become noise because of code mismatch and uncompressed bandwidth, and the useful signals become 9.6Kb/s data signals after decoding and deinterleaving. The principle of CDMA technology is based on spread spectrum technology. CDMA calls all use the same frequency, and a large number of CDMA signals use a spectrum, and each spectrum has a different random code. The bandwidth of the original data signal is expanded and then transmitted by carrier modulation. At the receiving end, the same high-speed pseudo-random code is used to restore the received wideband signal to narrowband signal in the last link to realize communication.