Introduction to analog cellular mobile communication system (1G)

The simulated cellular mobile communication system is a cell-based, large-capacity public mobile phone system. It adopts the Frequency Multiplexing Technology and has many users and wide coverage. It has been widely used in the world. This section describes the composition, working principle, and working process of the simulated cellular mobile communication system. Through the introduction, readers can not only understand the characteristics of the simulated cellular network, but also lay the foundation for understanding various digital cellular network systems in the future.

1. Composition of a simulated Cellular Mobile Communication System

Similar to other mobile communication systems, the analog cellular mobile communication system is also composed of three parts: the mobile phone exchange board (mtso), the base station (BS) and the Mobile Station (MS. Among them, the mobile phone exchange board and the base station are generally connected through a wired line, and the base station and the mobile station are connected through a wireless link through an air interface.

1. Mobile phone exchange

The mobile phone exchange board is used to automatically connect and exchange calls between mobile users and local users or between mobile users. In addition to the general function of program-controlled telephone exchange, it also has some unique features of mobile communication, such as identification and registration of mobile stations, channel distribution, transit switching, roaming and call processing. Therefore, the mobile phone exchange board is usually composed of dedicated programmable switches suitable for mobile communication. However, some software and hardware can also be added to a general program-controlled switch to achieve control, connection, and exchange of mobile phones. The hardware refers to the switching network, processor, data terminal, and other devices; software includes system operating procedures (such as call processing, connection and control), device status testing and maintenance procedures (such as route management, fault detection, diagnosis and Handling) run the Management Program (such as traffic statistics, records, and billing.

2. Base Station

The base station consists of RF components (RF racks and receiving and transmitting antennas), data racks, Line Monitoring racks, and maintenance test racks. When the base station uses a 120 ° Sector radiation mode, three RF racks, one data rack, one line detection rack, and one maintenance test Rack are required. Each RF rack has a maximum capacity of 16 wireless channels, that is, 16 Receiver/sender machines. When the base station uses an omnidirectional antenna, it must be equipped with at least four racks, namely one RF rack, one data rack, one line monitoring rack, and one maintenance test rack.

The data shelf consists of five parts: the data devices and controllers connected to the data link of the mobile phone exchange board, the establishment of the radio, positioning receiver and voice channel data receiver, respectively, to complete different functions. Data devices and controllers have backup devices. The main function of the Line Monitoring rack is to provide audio signal circuit interfaces for the mobile phone exchange board and the RF rack, and conduct line monitoring, including monitoring single-tone sending, receiving, and signaling code. The function of maintaining the test shelf is to test the status of various devices to maintain the good running status of the devices.

3. Mobile Server

There are two main types of mobile phones and mobile phones. The main difference is that the power size is different, and the functions, composition, and working principles are the same. The mobile station consists of three parts: Control Unit, logic unit, and receiving/sending machine.

The User Control Unit includes the transmitter, receiver, keyboard, indicator light, and buzzer. Unlike ordinary landlines, in order to reduce the time used by wireless channels and avoid misdialing, the mobile station does not immediately issue the numbers dialed by the user in one place, it is displayed on the screen and saved to the register. The called number is issued quickly only when the user confirms that the dial is correct and presses the send key. Once the connection succeeds, both parties can call. If it fails, the display displays the corresponding content for the user to process.

The logical unit is the main control component of the mobile station. It is mainly composed of a single-chip microprocessor. It is used for the compilation/Decoding of broadband data signaling, controlling the start of the transmitter, detecting and forwarding the monitoring audio. Various analog signals obtained by measurements, such as signal level, noise level, transmit power, static noise detection results, voltage of the voltage controlled oscillator, and the operating status of the Frequency Synthesizer Phase-Locked Loop, after A/D (module/Number) transformation, the processing result is sent to the single-chip microprocessor for processing. The controlled components in the sender can realize the intelligent functions of mobile devices similar to computers.

The receiving/sending machine is mainly composed of a transmitter, a receiver, and a shared frequency synthesizer. The vehicle carrier can adopt dual-space diversity to reduce the effect of fading. That is, the mobile station is equipped with two antennas, one of which is used for receiving and transmitting, and the other is used for diversity, multiple-choice switch diversity is adopted. Mobile phones cannot receive data in diversity, and a public antenna is used for receiving/sending data.

On the mobile platform, there is also a voice signal processing circuit, which is mainly composed of the instantaneous frequency offset control circuit, the compression and expansion circuit, and the aggravation and Depressurization circuit.

2. Control and signaling of analog cellular mobile communication system

The analog cellular mobile communication system uses a multi-access method, with a frequency interval of 25 kHz and 45 MHz for upstream and downstream channels, the capacity of the entire cellular network is very large.

The large-capacity and fully-automated analog cellular mobile communication system must constantly monitor the quality of communication channels and perform automatic failover for cross-region channels, in addition to handling the main calls and calls of mobile users, it also provides services for roaming users. Therefore, system control is complicated.

1. System Control Structure

The control of the simulated cellular network system involves the transmission and exchange of voice and signaling between public telephone networks, mobile phone exchange bureaus, base stations, and mobile stations. The system has both wireless channels and wired channels, and there are audio channels and control channels.

The base station has both a wireless channel and a wired channel. It transfers and transmits information between the wireless network and the wired network, including the signaling exchange between the wireless network and the wired network. The mobile phone exchange Board plays a role in control and coordination, manages and allocates wireless channels, and coordinates the work of base stations and mobile stations. It uses the standard signaling of the local telephone network for the signaling exchange with the local telephone network.

2. control signals and functions

The control signal mainly monitors audio and signaling sound. The monitoring audio is used for channel distribution and monitoring of mobile users' call quality. It uses three single voices, namely, 5970, 6000, and 6030hz, out-of-band voice. The monitoring audio is also used by the base station to determine whether to switch over the Channel.

The signaling sound is a 10 kHz audio signal, which is transmitted from the mobile station to the base station in the reverse voice channel. It is mainly used in the following two processes: first, when the mobile station receives the base station's ringing signal, in the reverse voice channel, the system sends a signaling tone to the base station, indicating that the ringing is successful. Once the user starts the call, the system stops sending the message. Second, before the mobile station switches over the channel, under the control of the mobile phone exchange board, the base station sends a new voice channel instruction to the original voice channel. After receiving the instruction, the mobile station sends the signaling voice confirmation message. The system implements relevant control through these two control signals.

3. digital signaling

Because of its large capacity, the cellular mobile communication system uses a dedicated control channel to transmit digital signals. As shown above, there are five transmission channels: forward and reverse voice channels, forward and backward control channels, and wired channels. The digital signals transmitted over different channels and their formats are different, which are not described in detail here.

3. Simulate the working process of the cellular mobile communication system

The main process of simulating a cellular mobile communication system includes the following parts.

1. Initial status (standby)

After the mobile device is powered on, it will scan and search the control channel, lock it on the strongest channel, and maintain monitoring. This process will be repeated as the mobile station moves or the Channel Changes, to ensure that the mobile station keeps tracking the base station with the strongest signal.

2. The mobile station is called

The call process for a mobile station includes paging, base station selection, paging response, voice channel allocation, ringing, and calling. After receiving the called mobile user number, the mobile phone exchange board converts it to the identification number of the mobile station and sends a paging command to enable base stations in the service area to call the mobile user through the forward control channel. If the mobile station starts up, it will find the call signal, and select the idle Base Station with the strongest signal to send the identification code on the reverse control channel, which will be sent to the mobile phone exchange board. After receiving a paging response, the mobile phone exchange Board allocates a voice channel. The base station sends a ringing signal to the control channel and the mobile station can disconnect the phone. It can be seen that the mobile station has been working until it is called, but the user does not feel it.

3. Mobile Station main call

The main call process is to dial before calling, and then press the send key to send the call number and user identification code to the base station through the reverse channel. The base station notifies the mobile phone exchange Board through the wired data line, the mobile phone exchange board first allocates a voice channel for the base station and the mobile station, and then sends a ringing tone to the called user. Call after the phone rings.

4. End-to-End disconnection

After the call ends, you must promptly remove the cables (including wireless and wired links) and release the channels as soon as possible to ensure the normal operation of the system. The disconnection process determines which of the following is the first link between a mobile user and a local user, regardless of the main call or call.

The analog cellular mobile communication system uses the frequency division multiple access method, so that each user occupies a frequency point. Although the Frequency Multiplexing Technology can be adopted, the network capacity still cannot meet the needs of rapid growth. At the same time, the Mobile Station of the simulated cellular mobile communication system uses 10-Bit fixed digital encoding, which is easy to use and has poor security. Therefore, in most parts of the world, analog cellular mobile communication systems have been replaced by more advanced digital mobile communication systems.