Cellular communication technology theory

 

Cellular mobile communication technology has become an extraordinary worldwide success, growing so rapidly that business demands far exceed original forecasts.

Communication Technology 

Introduction

 

Cellular mobile communications have become an extraordinary worldwide success, growing so rapidly that business demands far exceed original forecasts. In most cases, operators are limited to a fixed frequency band, with little hope of adding spectrum and the original analog technology cannot be expanded to keep up with the development of demand. Newer technologies allow for more efficient use of spectrum as well as improved security and convenience for users. Even so, the frequency bands allocated to these new technologies often overlap those used by older technologies, complicating migration strategies.

Europe has traditionally used the 900MHz band while North America has used the 800MHz band. Most Asian countries use both bands at the same time. The main analog standard for 900MHz frequency allocation in Europe is the full access communication system, although some European countries use other standards GSM is a digital system in the 900MHz band that has been adopted as a common standard in Europe and used in many other countries around the world, providing Very useful roaming device. In addition, the GMS standard has been used for 1800MHz (DCS1800). Some countries are establishing independent 1800MHz networks while others are trying to increase their GSM capacity using this frequency band. Because the same protocol is used on both frequency bands, the terms GMS-900 and GSM-1800 are more and more commonly used instead of GSM and DCS1800.

Communication Technology 

The construction of the third-generation mobile communication network must consider the compatibility with the GSM system, make full use of the existing GSM network resources all over the world, and save the existing network construction funds. From this point of view, UMTS can meet the requirements for the development of GSM-based mobile communication networks to the third generation, because UMTS communication has the following characteristics: 

1. It can be directly connected to the GSM infrastructure. Network operators can offer high-speed voice, video, and data services without installing a whole new network. According to market demand, UMTS nodes can be gradually introduced into the existing network and the coverage of UMTS communication can be gradually increased. The advantage of this solution is that if the operator already has a GSM/GPRS network of a certain scale, when upgrading to 3G, the existing network node equipment can be fully utilized, which can not only protect the user's investment in the GSM/GPRS network but also Since the maintenance and management system of the upgraded network node equipment is similar to the original one, it can provide convenience for the maintenance and management of the operator.
2. Support a variety of data connection services. UMTS can transmit multi-packet services between two users or multiple users. This service requires work procedures such as connection establishment, data transmission, and connection release; UMTS can also transfer a single service according to the requirements of a service requester. Information is transmitted to multiple users; UMTS can also provide point-to-point wireless network services. Each data packet in this service is independent of each other, and information transmission between users does not require end-to-end call establishment procedures.
3. Strong anti-fading ability. UMTS technology has greater resistance to fading, which means that it can provide a wider range of performance at the same output power, or reduce power requirements under the same coverage. In addition, the additional bandwidth means that there is a greater ability to support higher bandwidth services and provide more flexible mixed services.
4. Enhanced business processing capability. UMTS overcomes the problems of the traditional communication system, such as insufficient capacity, large voice distortion, easy disconnection, strong power radiation, slow data transmission, etc., and its business capability and performance are greatly increased. UMTS can support general personal communication that provides personal mobility. The system design is universal and compatible with existing equipment. It can provide high-definition voice, high-speed data, multimedia, roaming, and other services, and can support a wide range of variable rate information transmission. Provides higher-speed packet data communication capabilities.
5. Wide range of applications. In a practical implementation of UMTS, some users may not get the highest data transfer rate at all times. Considering the physical limitations of wireless transmission and the economics of network operation, in those remote and densely populated areas, the system can only support low-speed data services. Therefore, UMTS services have to adapt to different data rates and different Quality of Service (QoS). In the early days of UMTS development, traffic mainly came from places such as airports and railway stations. However, users expect the coverage of UMTS to be large enough. To this end, experts are working on the roaming technology of UMTS between different networks. These networks include the GSM system managed by the same operator or other networks with roaming agreements.
6. The call quality and data communication speed are greatly improved. Compared with the traditional communication technology, the most obvious advantage of the UMTS communication technology lies in the call quality and the data communication speed. However, in terms of call quality, current mobile phone consumers are still acceptable. With the development and application of technology, the call quality of the mobile phone in the existing mobile phone network is still further improved. The high speed of data communication is indeed a great advantage, and its maximum data transmission rate reaches 2Mbit/s. In addition, due to the advanced technology, the cost investment is greatly reduced, and the UMTS communication cost is also lower than the current communication cost. As a transitional data communication technology between the existing second-generation mobile communication system and the third-generation mobile communication system, the introduction of UMTS cellular communication technology will inevitably have an impact on the existing network structure and mobile communication equipment, although UMTS technology can greatly improve the data service rate of the existing GSM network, to make UMTS easy to be accepted and popularized by network operators, UMTS must minimize the impact of its existing network structure, and the UMTS system should allow operators to again Utilize existing base station equipment. Furthermore, with UMTS, operators should not need to modify their wireless network plans, and the introduction of UMTS should not affect the quality of mobile communications.

 

 

Microcell Technology

Communication Technology 

In the cellular mobile communication system, the main goal in the initial stage of the operation is to build a large macro cell to obtain the largest possible geographical coverage. The coverage radius of each cell in the macro cell is mostly 1km to 25km, and the base station antenna should be as high as possible. In an actual macro cell, there are usually two special micro areas. One is a "blind spot", which is a shadow area caused by obstacles encountered in the propagation of radio waves, and the communication quality in this area is seriously poor; It supports most of the services in microcells. The solution to the above two "points" often relies on methods such as setting repeaters and splitting cells. In addition to economic reasons, in principle, these two methods cannot be used indefinitely, because the expansion of the system coverage will reduce the communication quality; if the communication quality is improved, the capacity is often sacrificed. In recent years, with the increase of users, the macro cell undergoes cell splitting and becomes smaller and smaller. When the cell is small to a certain extent, the cost of building a site will increase sharply, and the reduction of the cell radius will also bring serious interference. On the other hand, blind spots still exist, and the high traffic in hotspot areas cannot be well absorbed. Microcellular technology was created to solve the above problems.

Microcellular Technology

Communication Technology 

Compared with the macro-cellular technology, the micro-cellular technology has the advantages of small coverage, low transmission power, and convenient and flexible installation. Signal leakage on the roof is small. Microcells can be used as a supplement and extension to microcells. The application of microcells mainly has two aspects: one is to improve coverage and apply to some blind spots that are difficult to cover by microcells, such as MRT and basement; the other is to increase capacity, mainly used in high traffic areas, such as bustling commercial streets, shopping malls, stadiums and so on. Microcells generally form a multi-layer network with microcells when used as an application to improve network capacity. The microcell covers a large area. As the bottom layer of the multi-layer network, the microcell is continuously covered with a small area and superimposed on the macro cell to form the upper layer of the multi-layer network. The microcell and the macro cell are different cells in system configuration and have an independent broadcast channel.

 The number of sites in the microcell layer is large, and the transmission cost accounts for a larger proportion of the entire equipment investment than the microcell base station. It is very important to select a reasonable network structure and transmission method according to the actual situation. Microcells generally have 1 to 2 carrier frequencies. When using PCM transmission, if a star connection is used, the transmission line occupancy rate is very low. Generally, a chain mode is used between microcells, so that 4 to 5 microcells can use a pair of the transmission line is connected to the computer room, which can effectively save costs. Compared with the PCM mode, the HDSL transmission mode using the existing telephone line for transmission is a very economical transmission mode at present, and the microcellular devices also tend to have built-in HDSL transmission devices. Optical fiber and microwave are also more commonly used options when microcells cannot be transmitted in an above-mentioned manner due to special reasons.