How to control the power amplifier of GSM mobile phone?

1.GSM modulation mode is GMSK. GMSK modulation refers to gaussian minimum shift keying, which is a digital modulation. To some extent, it can be understood as frequency modulation, but the frequency change is carried out in a discrete (discontinuous) way, while frequency modulation is pure analog modulation, and the frequency change is continuous. GMSK adopts digital modulation, and one of its key technologies is time division multiple access (each user selects a carrier frequency in a certain time slot and can only receive information at a specific time). GSM system has several important features: good anti-theft and copying ability, large network capacity, rich number resources, clear call, strong stability, sensitive information, few dead calls and low power consumption of mobile phones. Therefore, its voice is clear and easy to keep secret, and it can provide many data transmission services.

CDMA uses HPSK modulation, which is also a digital modulation technology. My understanding of HPSK is very general, except that it uses complex spread spectrum to balance the amplitude of I/Q channel. Then, by delaying the Q branch of the PN sequence by 1 PN chip and extracting by a factor of 2, the zero-crossing rate of the I/Q constellation change of the signal is reduced. Specific examples can refer to the block diagram in WCDMA or cdma2000 protocol, and detailed explanations can also be found in monographs. In a word, the principle of CDMA technology is based on spread spectrum technology, that is, the information data with a certain signal bandwidth to be transmitted is modulated by a high-speed pseudo-random code with a bandwidth much larger than the signal bandwidth, so that the bandwidth of the original data signal is expanded, and then it is modulated by a carrier wave and sent out. The receiver uses the same pseudo-random code to correlate with the received bandwidth signal, and changes the broadband signal into the narrowband signal of the original information data, that is, despreading, thus realizing information communication.

In addition, GSM adopts GMSK modulation, and nonlinear power amplifier can be used to improve efficiency. When CDMA adopts HPSK modulation, linear power amplifier must be used to reduce distortion.

2。 Working mode of PLL

I can't explain this clearly. The information I found on the Internet is better than mine. Please have a look:

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3。 The basic structure of mobile phone can be divided into three parts according to the processing of different frequency signals: RF, IF and BF. Radio frequency is responsible for receiving and transmitting high-frequency signals, and baseband is responsible for signal processing and storage. IF is an intermediate bridge between RF and baseband, which enables signals to be smoothly converted from high-frequency signals to baseband signals.

Mobile phone IF module generally consists of three units: wireless receiving unit, signal synthesizing unit and wireless transmitting unit. The wireless receiving unit consists of RF front-end, mixer, IF amplifier and demodulator. The signal synthesis part comprises a distributor and a phase-locked loop; The wireless transmitting unit consists of power amplifier, AGC amplifier and modulator.

When an intermediate frequency (IF)IC receives a signal, the signal (about 800 Hz ~ 3 GHz) received from the antenna is amplified, filtered and synthesized, then the RF signal is restored to baseband, and then the baseband signal is processed. When IF IC transmits signals, the baseband below 20KHz is up-converted into RF signals and then transmitted.

4。 Network structure of national GSM mobile communication network

The national GSM mobile phone network adopts a three-level network structure, which consists of a large-area first-level tandem center, a provincial second-level tandem center and a mobile service local network end office. Its connection with PSTN (Public Telephone Network) is shown in Figure 4-2. As can be seen from the figure, the three-level network structure constitutes a completely independent digital mobile communication network. The structure of the analog mobile communication network is established by mixing with the PSTN network (see Figure 4-3 for its connection with the PSTN network). It establishes a secondary tandem center in the province and an end office in the local mobile service network without a primary tandem center. Inter-provincial communication is realized by the long-distance telephone network of PSTN network. Of course, in order to realize automatic roaming between provinces, the analog mobile phone network must establish its own national signaling network. In addition, the analog mobile communication network is accessed by the end office number of the PSTN network, marked by the prefix "9", so it can be said that the analog mobile communication network is part of the PSTN network, and the GSM digital mobile communication network overlaps with the PSTN network. Of course, the public telephone network still has its international export bureau, while the GSM digital mobile communication network does not, and international communication still needs the help of the international bureau of the public telephone network.

See Figure 4-4 for the network structure between GSM mobile communication network of China Unicom and GSM mobile communication network and PSTN network of Ministry of Posts and Telecommunications (called public communication main network for short). In the location of China Unicom GSM Mobile Exchange Bureau, there is an inter-network interface office between China Unicom and the main network, and the two interface offices are interconnected in pairs one by one. Voice connections and signals required by various services (including local, automatic long distance, mobile and international services, etc.). ) Unicom GSM customers are connected with GSM and PSTN customers in the main network through the inter-network interface office.

2 network structure of GSM mobile communication network in the province

The GSM mobile communication network in the province consists of the local mobile service network in the province, and there are several mobile service tandem centers (secondary tandem centers) in the province. The tandem center is a tennis net structure, and the tandem center and the mobile end office form a star network. According to the size of business volume, the secondary tandem center can be a separate tandem center (that is, there are no customers, all of them have interfaces to the base station, which are only used for tandem), or it can be used as a mobile terminal office (connected to the base station and able to take customers). The GSM mobile communication network in the province should generally have two or three mobile tandem offices, with a maximum of four. Each mobile terminal office should be connected with at least two secondary tandem centers in the province, as shown in Figure 4-5. If the traffic between any two mobile exchange offices is heavy, a dedicated voice line can be established.

3. Network structure of mobile service LAN

The whole country can be divided into several mobile service local networks, and the principle of division is that the area with 2 or 3 long-distance area codes is a mobile service local network. Each mobile service local network should be provided with an HLR (HLR can be added if necessary, which can be physical or virtual, that is, several mobile service local networks share the same physical HLR, which is divided into several areas, and each mobile service local network is managed by a service terminal (see Figure 4-6), one or more mobile service switching centers (MSC) and several mobile service local networks.

In the local network of mobile service, each MSC is connected to the long-distance office where the office is located and the local telephone tandem office where the office is located. In the area of long-distance multi-office system, MSC should be connected with the senior long-distance office in this area. When there is no local telephone tandem office or the traffic is large enough, MSC can also connect to the local local telephone terminal office. When an MSC covers several long-distance numbering areas, it can also be connected with local tandem offices and long-distance offices in these long-distance numbering areas.

Each MSC is the entrance office of the digital mobile communication network, and the entrance office has the function of inquiring the call route for the call of the mobile terminal and the function of routing the call to the destination of their terminal-the called mobile station.

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5。 Phase error (GMSK) and frequency error are two important parameters to characterize the modulation quality of GSM mobile phones. The measurement of phase error can reflect the problems of I/Q baseband signal generator, filter, modulator and amplifier in transmitter circuit. In the actual system, excessive phase error will make the receiver unable to demodulate correctly under some boundary conditions, which will eventually affect the working frequency range. The measurement of frequency error can reflect the performance of frequency synthesizer/PLL and other components. Excessive frequency error reflects that there is frequency conversion when the signal is sent, and the synthesizer can't identify the signal quickly. In the actual system, because of the large frequency error, the receiver can't lock the frequency, which eventually leads to interference with other mobile phones.

In the European GSM telecommunications standard, it is stipulated that the peak value of phase error is not more than 20 degrees and the effective value is not more than 5 degrees. When there is a problem with the phase error index, it will affect the voice quality (increased distortion or grunting), and in serious cases, it will make the mobile phone leave the GSM service network.