Technical standards and network structure of PHS communication system

In my country, wireless local calls based on PHS use 1.9GHz as the air wireless communication frequency, and the frequency range is 1900~1920MHz. PHS adopts TDMA/TDD multi-access and duplex mode, adopts π/4-QPSK modulation and 32kb/s ADPCM voice coding, and adopts microcell and channel dynamic allocation technology, which can effectively improve frequency utilization and improve the communication capacity of the system. [3].

Similar to mobile cellular networks, PHS-based wireless local phone networks also consist of three major parts: core switching and transmission networks, base stations and their related control equipment, and wireless terminals.

The above briefly introduces some developments in PHS network technology. In fact, the current PHS network cannot provide high communication rates and meet the requirements of future multimedia communications. With the development of communication technology, academia and business circles are also seeking some methods to improve the performance of PHS systems, making the network gradually evolve into future IP-based broadband communication networks.

PHS networking development and evolution of the core network

The traffic of the PHS system is carried by local switches. From this perspective, the evolution and fixation of the core network of the PHS system The development of the telephony core network is consistent. It is mainly reflected in two aspects: one is the development of backbone transmission systems, and the other is the evolution of core switching networks. For the former, large-capacity optical fiber networks are currently and will be mainly used to carry the load. With the maturity of technology and the development of equipment manufacturing industry, it is gradually evolving towards intelligent all-optical networks; for the latter, this is currently the case for international and domestic operations. We discussed and paid much attention to the topic with equipment manufacturers. Everyone agreed that the future network should have the function of separating call control and service provision, and the separation of transmission media and call access, and thus introduced the concept of soft switching. By establishing a next-generation network with softswitch as the core, it can not only complete comprehensive services of voice, data, wireless communications and multimedia services, but also realize the integration of PHS system, 3G and existing wired networks, and achieve an effective combination of wired and wireless communications. , and ultimately achieve the goal of personal communication.

The structure of the soft switching network based on the PHS system is given. It provides various accesses such as TG/SG (Relay Gateway/Signaling Gateway), AG (Access Gateway), IAD (Integrated Access Device), MSAG (Multimedia Service Access Gateway), etc., and is compatible with existing fixed , mobile, and multimedia terminals to interoperate; it provides an effective platform to improve PHS user access and provide new value-added services, thereby effectively attracting existing and potential network users. The biggest feature of wireless communication is that the signal is affected by the wireless channel and various refraction and reflection waves, so the signal performance is poor when receiving. This problem can be compensated by using various technologies at the base station and wireless terminals respectively; however, since wireless terminals are used by users, new technologies and devices will inevitably increase the size and cost of wireless terminals, so a more realistic method is to increase Signal processing capabilities at the base station, thereby improving network performance.

The PHS system adopts micro-cell technology and initially uses low-power base stations for coverage. The signal coverage effect is relatively poor and switching is frequent. At present, in addition to using indoor distribution systems and repeaters to improve PHS signal coverage, there are two main ways to improve system performance through base stations: one is to increase the transmission power of the base station to improve the coverage of the system, and the other is to bundle technology to achieve an increase in system capacity. Increasing the transmit power is certainly helpful in improving the call phenomenon caused by frequent handovers and improving signal penetration, but it will also increase electromagnetic radiation. Although bundling technology can increase the number of channels, as the number of bundling increases, Increasing its implementation technology and cost will also be larger. In addition, how to better utilize bundled base stations to effectively absorb traffic is also a problem that needs to be studied.

With the development of signal processing technology, it is an effective way to improve the performance of the system by processing the correlation of signals received by the base station antenna. In this regard, Japan and other countries have conducted relevant research and discussions, proposed base stations that use SDMA (Space Division Multiple Access)/TDD communication methods, and conducted relevant experimental tests and achieved good results. Compared with the traditional TDMA/TDD method, the base station of the SDMA/TDD PHS system using adaptive beamforming technology can perform better interference suppression [8].

Adaptive beamforming technology began in the 1950s and was first used in military and radar systems. After decades of vigorous development, it has gradually matured and begun to be applied in civilian systems. Array antennas using adaptive beamforming can Effectively eliminating the time, frequency and space selective fading of mobile communication systems is of great significance for improving the performance of communication systems. With the rapid development of modern signal processing technology and the continuous improvement of the computing power of digital signal processing chips, the cost of using adaptive antenna systems has been greatly reduced, which also laid the foundation for its practical application [8, 9].

In addition, it is also a good choice to use diversity sending and receiving technology to increase the capacity of the system. This can be combined with space-time coding technology that is currently widely studied in the communications industry. Various studies and simulations have shown that its ability to improve system reception performance is very obvious. Currently, finding a more practical application solution is a problem that needs to be studied. PHS system mobile phones are small handheld phones designed for mobile users. In order to make it easy for users to use and carry, the size and processing power of mobile phones are subject to many restrictions. Despite this, as people demand for broadband multimedia services, the processing power and functions of mobile phones still need to be continuously enhanced to meet the requirements of future multimedia communications.

The current PHS system mobile phones mainly implement voice communication, and some also provide wireless Internet data services. The recent interoperability of text messages among major operators has also greatly promoted the development of PHS services; in order to achieve future The demand for broadband services such as images [4] requires the structure of current communication terminals to be improved to meet the development of future communications. Figure 3 shows the general structure of the communication terminal as follows. Terminal equipment can process multiple services at the same time, thereby fully realizing multimedia services. Among them, the business identification and driver module is an important part of realizing multimedia terminal. This is because there are different processing and coding methods for different services: for example, for real-time services such as voice, voice codecs (such as G.721, G.729, etc.) need to be used; for images, videos, etc. Services must be implemented using H.261, H.263 or MPEG standards. Therefore, only by knowing the current business that needs to be processed can the correct recovery of data be effectively achieved. In the above implementation process, in order to save terminal costs and improve the flexibility to adapt to various services, software radio can be used. In this way, under the condition that the system structure is relatively universal and stable, various functions can be realized through software, making system improvement and upgrade very convenient.

In addition, while implementing PHS terminals that support multimedia communications, it is also an important development trend to realize machine-card separation in the development of PHS terminals. This is because machine-card separation can use smart cards to store user information and Data confidentiality greatly improves the security and convenience of PHS terminals. This is currently a hot topic for equipment manufacturers and communication operators.