The fixed wireless access network refers to the part or all of the service node to the fixed user terminal adopting the wireless mode. Terminals of fixed wireless access systems with or without limited mobility.
The fixed wireless access network is a fixed application of wireless technology, and its working frequency band can be 450MHz, 800/900MHz, 1.5GHz, 1.8/1.9GHz or 3GHz or so.
1. Basic introduction of fixed wireless access network
The fixed wireless access network is mainly a way to provide wireless network communication access services for users in fixed locations or users who only move within a small area. Its user terminals include telephones, fax machines or computers.
Wireless access technology refers to the communication technology that uses microwave, satellite and other transmission methods to connect user terminals to service nodes and provide users with various services. Wireless access technology is divided into two types: fixed wireless access technology and mobile wireless access technology. Among them, the latter is the technology used by the familiar cellular mobile phone system and satellite communication system. The object of mobile wireless access technology service is mobile terminal, that is, to realize the information exchange between mobile terminal and fixed terminal or mobile terminal. For users with fixed locations or user groups that only move within a small range, fixed wireless access technologies can be used.
2. Classification of fixed wireless access networks
According to service objects and network coverage, fixed wireless access networks can be divided into three categories:
Macro area: Also known as a large area, the radius of the network coverage area is from 5 to 55KM, and it is mainly used in rural areas, mountainous areas, coastal areas, and desert areas.
Micro-area: The radius of the network coverage area is between 0.5-5km. This type of product is mainly used in cities, suburbs and rural areas.
Pico area: The radius of the network coverage area is between 50 and 500m. This type of product is mainly used in densely populated areas of large cities.
Because in non-adjacent coverage areas, the same channel can be used by different users at the same time, so the same bandwidth is occupied, and the number of users that the system can accommodate is related to the size of the coverage area.
The connection between the end office and the tandem office of the fixed telephone network is generally connected by optical cables, copper cables and microwave relays. It is generally divided into three sections from the end office to the user: the end office to the transfer box is called the feeder section, which is mainly composed of optical cables, copper Wire cable or microwave relay is completed; from the transfer box to the junction box is called the wiring section, which is mainly completed by copper wire cables: from the junction box to the user is called the lead-in line, mainly using unshielded twisted pair or multi-strand single wire cable.
For example, all the three sections use wireless transmission instead of wired connection, which is the case of the macro area. Its advantages are: economical and cost-effective, and easy installation. The disadvantage is: the system coverage area is too large, and the number of users is small under the same bandwidth and the same multiple access technology, which is suitable for suburbs, mountainous areas or rural areas.
If the two sections of wiring and lead-in lines use wireless transmission instead of wired connection, it is roughly equivalent to the aforementioned micro-district. Low-power systems are often used to solve medium-range communications. Its user capacity is more than 20 times that of macro areas. It is used in new residential areas, communities, suburban areas, large institutions, factories, mines, and reservoir construction sites.
Only the lead-in section replaces the wired connection with wireless transmission. In this case, a low-power system is used. The coverage area is a pico area, and the user capacity is the largest among the three systems.
3. Application mode of fixed wireless access network
According to the application position of the wireless transmission technology in the access network. The fixed wireless access network mainly has the following three application modes. Feeders, distribution lines and service leads.
3.1 All wireless local loop. From the local exchange to the user end all adopt the wireless transmission mode. That is, the feeder, distribution and lead-in lines of copper cables are replaced by wireless.
3.2 Wireless distribution lead/input local loop. Wired transmission from the local exchange to the flexibility point or distribution point. Then connect to the user wirelessly. That is, wiring and drop wires or drop wires are replaced by wireless.
3.3 Wireless feeder/feeder local loop. Wireless transmission from the local exchange to the flexibility point or distribution point. From the flexible point to the use of optical cables, copper cables and other wired methods for each user.
4. Implementation of fixed wireless access network
Divided according to the transmission rate provided to the user. The implementation of fixed wireless access network technology can be divided into narrowband wireless access (less than 64kbit/s), medium broadband wireless access (64~2048kbit/s) and broadband wireless access (greater than 2048kbit/s).
4.1 Narrowband Fixed Wireless Access Network Technology
Narrowband fixed wireless access networks are characterized by low-speed circuit-switched services. Its data transmission rate is generally less than or equal to 64kbit/s. The more commonly used techniques are as follows:
4.1.1 Microwave point-to-point systems. The ground microwave line-of-sight transmission system is used to realize point-to-point signal transmission in the access network. This method is mainly used to connect the remote concentrator or user multiplexer with the switch.
4.1.2 Microwave point-to-multipoint systems. Use microwave as the transmission means to connect user terminals and switches. Most practical systems use TDMA multiple access technology to realize point-to-multipoint connection at present.
4.1.3 Fixed cellular systems. Transformed from a mobile cellular system. The mobile exchange and the user's mobile phone in the mobile cellular system are removed. Keep the base station equipment in it. And increase the fixed user terminal. Users of this type of system mostly use TDMA or CDMA and their mixed methods to access the base station. It is applicable to the wireless access service that can be activated quickly in an emergency.
4.1.4 Securing cordless systems. Transformed from a mobile cordless system. Just change the omnidirectional antenna to a high gain sectoral antenna.
4.2 Medium and Broadband Fixed Wireless Access Network Technology
The medium broadband fixed wireless system can provide users with a wireless access rate of 64-2048kbit/s. Open ISDN and other access services. Its system structure is similar to the narrowband system. It consists of base station controller, base station and subscriber unit. The interface between the base station controller and the switch is generally a V5 interface. Fiber optic or wireless connections are usually used between the controller and the base station. Users of this type of system mostly adopt TDMA access mode. Work in the frequency band of 3.5GHz or 10GHz.
4.3 Broadband Fixed Wireless Access Network Technology
Narrowband and medium broadband wireless access is based on circuit switched technology. Its system structure is similar. But the broadband fixed wireless access system is based on packet switching. It mainly provides video services. At present, it has developed from providing one-way broadcasting service to providing two-way video service. Such as video on demand (VOD) and so on. The technologies it adopts mainly include direct broadcast satellite (DBS) system, multi-channel multipoint distribution service (MMDS) and local multipoint distribution service (LWDS).
4.3.1 Direct broadcast satellite system. It is a one-way transmission system. That is, the synchronous satellite broadcasting system commonly used at present. It mainly transmits one-way analog TV broadcasting services.
4.3.2 Multi-channel multi-point distribution service. It is a one-way transmission technology. Communication with the headend needs to be achieved through another separate channel, such as a telephone line.
4.3.3 Local multipoint distribution service. It is a two-way transmission technology. Support services such as broadcast TV, VOD, data and voice.
5. Application of fixed wireless access network
5.1 Sparsely populated rural areas, marginal areas and rural areas
In such areas, if users are connected to the local telephone network in a wired way, no matter whether it is buried cables or erected open wires, the investment is large and the benefits are low. Using wireless local loop is a better solution. The initial development of the wireless local loop was initiated to solve the problems of the rural telephone network.
5.2 Emerging business districts and residential areas in the city
In such areas, the demand for telephones is great. The original local telephone network can no longer meet the requirements, and the new local telephone network will require a large investment and a long time. Using the wireless local loop can quickly meet the needs of its economic development in a short time.
5.3 In places where it is difficult to install wires
In such areas limited by geographical or climatic conditions, it is difficult to bury cables, or it is not easy to erect open wires, the only solution is to use wireless local loops.
5.4 Land-time application or emergency measures
Wireless access is suitable for quickly providing the required communication capability and capacity in some emergency situations, and it can also be used as a temporary or transitional means to postpone the construction of the wired access network as a long-term solution.
As the telecom market is opening up, new telecom operators can use wireless access to enter the market quickly and economically. The initial investment is small and the effect is quick. They can flexibly expand the scale according to user needs and avoid blindly spending money online. put in. Then make realistic investment decisions based on market developments and build a permanent network of appropriate size.