Analysis of Core Technology of PHS Network PHS is actually a supplement and extension of the fixed local telephone network. It changes the last line of fixed telephone from cable connection to wireless connection for communication. It is composed of central office equipment RT, air traffic controller ATC, base station controller RP and mobile phone PS. It can realize all functions of fixed telephone network. For example, transfer calls, three-way calling, language mailbox, etc. In addition, it also has some functions of mobile phones. For example, cross-zone roaming, wireless Internet access, location alarm and ISDN and other services. Its biggest feature is the low cost of fixed phones and the versatility of mobile phones, which is the root cause of its rapid development and popularity. The core technology of PHS is the use of micro-cell and channel dynamic allocation technology, which greatly improves the frequency utilization rate and system capacity. The time division duplex mode TDD is adopted between the PHS base station and the mobile phone. The wireless channel is based on the time division multiple access TDMA structure. The voice coding uses 32kbit / s AD PCM. The wireless interface uses data V5 interface technology, which strengthens the system's resistance Interference ability improves the quality of voice communication and enhances the confidentiality of the system. PHS product technology has made breakthrough progress in terms of business side, network side, wireless side, and terminal compared to PHS products 5 years ago. So far, PHS has formed a service provider (SP), network A complete industrial chain consisting of operators, equipment providers, terminal vendors and users. If the PHS technology is the same technology as it was 6 years ago, it will not achieve rapid development in the Chinese telecommunications market. Various signs indicate that after 6 years of development in China, PHS has undergone qualitative changes in all aspects. Communication frequency selection and multiple access technology PHS connects the local hand-off machine LS with the personal handheld phone PS system through the V5 data interface technology on the existing local telephone network, and combines it with the air traffic controller ATC, so as to realize the rapid and effective use of the original fixed telephone network Development of wireless communication systems for mobile services. PHS uses 1.9GHz as the cell phone communication frequency of its cell site. The wireless access channel of PHS, that is, the multi-carrier frequency time division duplex mode TDD is used between the base station and the mobile phone, and the wireless channel is based on a time division multiple access TDMA structure. In the multi-frequency sub-band, a frequency is dynamically allocated to each base station and every moment. The wireless access method of PHS system adopts TDMA / TDD. TDMA divides time into periodic, non-overlapping frames. Each frame is divided into several non-overlapping time slots, and then according to a certain time slot allocation principle, each mobile station sends a signal to the base station according to the specified time slot in each frame, under the conditions of timing and synchronization, The base station can receive the signals of each mobile station in each time slot without confusion. At the same time, the signals sent by the base station to multiple mobile stations are arranged in sequence in predetermined time slots for transmission. As long as each mobile station receives in the designated time slot, it can distinguish the signals sent to it among the combined signals. Thus, the multiple access communication transmission method is realized. Microcell and channel dynamic allocation technology PHS uses the micro-cell system to form a network. It divides the entire service area into many micro cells. These micro cells are organically combined to meet the needs of the entire wireless access mobile communication. In order to solve the shortage of frequency resources, PHS uses dynamic channel allocation technology in frequency resource allocation. The system does not allocate a fixed frequency for each cell separately, but allocates the best in the cell station as the call is established. Frequency and channel. The frequency selected for each moment of the same carrier frequency device may be different. In this way, the PHS system does not need to perform frequency planning during network construction and optimization, which saves a lot of manpower and material resources, and can effectively avoid co-frequency interference and neighboring when multiple operating companies jointly use limited frequency resources. Frequency interference, thereby improving the utilization of frequency resources. It does not need a lot of basic construction work like GSM and CDMA systems for frequency planning, base station site selection, and computer room construction. It is an effective means of using the existing local telephone network for wireless communication. Therefore, the PHS system organically combines microcell technology and channel dynamic allocation technology, which not only improves the frequency utilization rate, but also greatly increases the wireless channel resources of the system. V5 interface technology This technology is proposed to adapt to multiple transmission media, multiple access configurations, and service development within the access network. It can support ordinary telephone services and IS? DN dedicated line services. According to the different transmission rates, the V5 interface can be divided into V5.1 and V5.2 interfaces, of which V5.1 has multiplexing functions, V5.2 has integrated functions and dynamic allocation of time slots. As the data interface of the local switch and the access network, the characteristics of the V5 interface technology are mainly manifested in the following aspects: it is a fully open interface, which is manifested in the network operator can freely choose the equipment of different manufacturers to effectively optimize the combination to improve Network function; can support different access methods, through a full range of open interfaces, local switches can accept a variety of different access network equipment and support different access methods, so that the network is developing in the direction of wired and wireless; Provide comprehensive business digital services, such as voice, image, data and other business development; information transmission is safe and reliable, because the V5 interface transmits data stream information, it is not easy to lose, and encryption is convenient, which increases the security and reliability of the network Reduce costs, due to the large amount of data through the V5 interface, correspondingly reducing the cost of transmitting information per line. The V5 interface technology is adopted by the PHS system because of its wider business adaptability and higher degree of standardization. It is also the foundation of PHS's multiple functions such as wireless Internet access, cross-region roaming, and online billing. The V5 interface structure has three layers: physical layer, data link layer and network layer. Due to the rapid development of Xiaolingtong, various manufacturers have launched various styles and models of mobile phones, and they are constantly updated in technology. Therefore, the development of Xiaolingtong technology is changing rapidly, and it is developing in the direction of updating to meet the needs of users. . However, there are still some problems in the development of PHS. For example, in theory, a base station for contacting mobile phone signals must be built every 100 to 500 meters, and many base stations must be deployed to eliminate network blind spots. Another hidden concern of PHS is the frequency band problem. Although from the perspective of the technology contained in the protocol standard, the PHS technology system is not as good as CDMA, and even has a certain gap with GSM. But the PHS technology system also has its own advantages, which are unmatched by other systems. First of all, using TDMA / TDD system, as long as a continuous frequency band can work; secondly, for PHS, expansion only needs to add the corresponding base station, adjust the antenna or position of some base stations, you can achieve efficient expansion; but for GSM, In terms of CDMA, the expansion of each cell ’s base station in the neighboring cell must be adjusted, and other neighboring cells must also be adjusted. In addition, for data service support, PHS can provide very high rates as long as the network side RAS is added. Internet access, while GSM requires GPRS, as opposed to overlaying a network to provide data services, CDMA also requires a lot of changes to support high-speed data services, and high-speed data services will affect its capacity on a large scale; at the same time, In the use of wireless intelligent technology, PHS base stations are currently at the forefront.
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