Views:27 Author:Site Editor Publish Time: 2019-12-06 Origin:Site
Trunked communication is a mobile communication system that implements communication through base station relays. It is a communication system between public mobile communication and ordinary walkie-talkies. Co-frequency simulcast network refers to the arrangement of multiple co-frequency repeaters in the same area, thereby increasing the coverage of the wireless communication network and improving the reliability of communication in the coverage area.
The coverage distance of the wireless communication network is not only related to the transmitting power and receiving sensitivity of the device itself, but also related to the terrain and the height of the base station antenna. After a lot of actual comparison tests, the communication distance of PDT digital trunking system is better than analog trunking system.
Because the simulcast system uses the same frequency technology, in order to obtain clear voice quality in the overlapping coverage area, the system must ensure that the wireless signals received by the terminal must meet the requirements of the same frequency, phase, amplitude and minimum field strength. The phase error of digital simulcast system exceeding 1/8 symbol will cause a rapid rise in bit error rate and frame loss rate.
★ According to empirical data, covering the same area, the number of base stations required by the cluster system is 1/3 less than that of the simulcast system.
The user capacity of the trunking system is directly related to the number of base stations and the number of channels in the system. For the same number of channels, the more base stations, the lower the user capacity of the system.
"User mobility management" is an important part of the cluster system, and its quality directly affects the use efficiency of the cluster system. When a user talks, the cluster system allocates the channel resources of the base station according to the registration situation of the base station where the user is located, which can maximize the channel utilization rate.
The simulcast system does not have a "user mobility management" function. When a user talks, each base station allocates channel resources regardless of the presence of a user, and the channel resource utilization rate is very low. In order to increase the system user capacity and meet the requirements of multiple concurrent calls, the system needs more frequency resources. The simulcast system uses few frequency resources, so the number of concurrent calls is also small.
★ With the same number of carrier systems in the trunking system and simulcast system, the user capacity provided by the trunking system is much larger than the simulcast system.
The same-frequency system uses the same-frequency technology. In addition to the factors of expanding the coverage area and the lack of frequency resources, there is also an important reason that users can switch base stations arbitrarily and keep on line during a call.
The PDT digital trunking system adopts mature handover technology and has achieved continuous line crossing of the base station during the call. If the mobile station moves to a base station without the distribution of the group members during the call, the base station can also immediately allocate a call channel.
The voice call services of the trunking system can be differentiated according to different levels, and the priority call rights of important users can be guaranteed to ensure smooth command and dispatch at critical times. Although the digital simulcast system can also perform group calls, the number of groups should not be too much. If the group lacks permission settings, the call channel will often be occupied.
★The trunking system has solved the problem of disconnected calls. The hierarchical communication mode can ensure the smooth flow of command and dispatch instructions.
Short data services are receiving more and more attention. The efficient uploading of GPS positioning data, the timely sending of Chinese short messages, the application of simple status information, and the rapid query of text information have become important means to improve the efficiency of command dispatch and police management.
GPS positioning has become an indispensable function for police officers in their daily service work. The full application of police officer's position information can help the command center to perform rapid dispatch and efficient management of police resources.
Users are very concerned about the success of sending short data services, but only if the "user mobility management" is very accurate can short data be sent to the receiver quickly and accurately. Since the simulcast system does not have the function of "user mobility management", when sending short data, it can only be sent in all base stations in the entire network, and the channel resource utilization efficiency is very low. If there are many users using short data services, it will seriously affect the basic Voice call service.
★Since the simulcast system does not have the "user mobility management" capability, the applications of GPS positioning services and short data services are severely restricted.