As China's fixed-line operators (China Telecom and China Netcom) have a long history and have invested in fixed-line construction for many years, the fixed-line access layer resources are very rich, mainly reflected in the physical basic networks such as access layer computer rooms, pipes, poles, optical cables and copper cables, as well as SDH circuits in the access layer. At present, the basic schematic diagram of China fixed network access layer network structure is shown in figure 1.

Figure 1 Network Structure Diagram of Fixed Network Access Layer

Due to the wide geographical area, the network structure between urban and rural areas is slightly different, and the copper cable distance of rural users is longer, so the construction of optical fiber access networks using small-capacity SDH networking is relatively more. As can be seen from the figure, the end office in fixed network resources has good accessibility to users, but the users are basically copper cables. In addition, the use of the module office also makes the optical cable of the user terminal scarce.

The SDH ring used by optical fiber access network is generally 155M system. 155M system has both integrated equipment and rack equipment. In addition to being placed in the office of the end office module, a small number of DSLAM are moved to the ONU access computer room.

Mobile base stations have strong access characteristics.

There are some differences in network structure between mobile communication network and fixed communication network. The wired access layer of mobile communication network is aimed at base stations, business halls and large group customers. At the access layer, the ring network consists of target nodes. Because of the high profit of mobile communication, the security requirements of base station networking are high. Generally, two nodes in a ring network are connected to two different sink nodes. And with the gradual rise of wireless data services, the bandwidth requirements for base station nodes are also very high (see Figure 2).

Fig. 2 schematic diagram of network structure of mobile base station access network

Fixed communication network takes users as the end point. The end of its access layer is usually star access, and the ONU node of the optical fiber access network with the end office as the center enters star radiation.

Generally speaking, the transmission and access resources of the mobile communication network are completely centered on the base station, and its networking characteristics directly reflect the characteristics of the mobile communication network:

(1) The base station needs more bandwidth.

At present, in the central city, many base stations have purchased the carrier frequency setting of10/10, and the required bandwidth is generally 4-6 E 1. In the early stage of 3G construction, considering the shadow sail of wireless data demand, high-rate technologies such as HSDPA will be gradually loaded into base station power, and HSDPA is mainly divided into *. Table 1 gives the bandwidth requirements of 3G base stations at the initial stage of 3G construction.

Table 1 3G Base Station Bandwidth Requirements Table

(2) The requirements for the base station computer room are higher.

Because the base station room involves antenna placement and feeder length (the longer the feeder, the greater the signal loss), so the base station room is generally located at a higher floor. At the same time, the environment requirements of the base station computer room are high, and power supply, battery, temperature and humidity, fire protection, security and so on should be configured. Therefore, mobile communication operators have experienced long-term trouble and tempering in the site selection of base station rooms.

(3) The base station requires high security.

At present, the profit of mobile communication service is the highest, so the security requirements of base station networking are also improved accordingly. More and more attention has been paid to the security of mobile communication operators' base station networking. The backbone layer, convergence layer and access layer of base station networking are all optimized and transformed towards physical ring and dual-node connection. In the access ring, the traffic of the same node will have different traffic to two different aggregation nodes. Therefore, the completeness of the network is improved to the maximum extent. And considering that the number of nodes in the future scalable access loop is generally controlled at 4-6 nodes (slightly more in suburbs and rural areas).

(4) The well level of base station equipment is frequent.

Because the wireless base station is set around the traffic and traffic distribution, with the gradual development of mobile communication, the increase of the number of users, the increase of traffic, the change of mobility and other factors will affect the upgrade and expansion of base station equipment. Among them, the most obvious performance is the upgrade of base station carrier frequency capacity and the construction of base station site, in addition to the adjustment of the ownership relationship between base station and BSC. Therefore, the frequent changes of base stations put forward higher requirements for the service bearing network of base stations-transmission and access networks. The access network of the base station is required to be more scalable.

3. Problems caused by fixed network access resources accessing base stations

Fixed network is not built around the networking of base stations from the beginning, so using the existing fixed network access resources to access base stations will bring a series of problems:

(1)ONU has certain restrictions on entering the computer room.

At present, the fixed-line ONU access to the computer room is generally based on renting low-rise (L building) houses. However, using low-rise residential buildings for base station access will bring a series of problems, such as antenna erection and excessive attenuation caused by too long feeder. And because the base station computer room needs to build a series of supporting systems, the room rent is generally 50 square meters.

(2) The transmission capacity of the existing optical fiber access network is insufficient.

At present, the optical fiber access network is basically organized by 155M loop, and some devices adopt integrated devices. Due to the small bandwidth of fixed-line services carried by optical fiber access networks, the loop utilization rate of optical fiber access networks is generally maintained at around 50%. At this time, if the existing optical fiber access network loop is used to access the base station, there will be a serious shortage of capacity. In addition to the daily carrier frequency expansion, especially the use of HSDPA high-rate services, the demand for bandwidth will further increase. Therefore, the existing 155M loop optical fiber access network has insufficient access capacity.

(3) The existing optical fiber access network has insufficient security considerations.

At present, the loop optical fiber of optical fiber access network is basically laid along the main road, and the access to the surrounding base stations can only rely on the access computer room for star radiation. At this time, the network will have a heavy ring chain and ring tree, which will cause certain hidden dangers to the security of the base station access ring. In addition, at present, optical fiber access networks are all organized around end offices, and single-node uplink also leads to single uplink routing and insufficient security considerations.

(4) The distance between end offices is too far.

At present, fixed network access networks are all built around end offices. If the base station is connected, considering the safety, the access loop will be connected to two different convergence nodes, but at present, the distance between the end offices is about 5-6 kilometers, which leads to the access loop being too large.

(5) At present, the development of fixed network is relatively stable, and frequent cutover will have a certain impact on the existing network.

At present, the fixed-line access service realized to users through optical fiber access network and modular office is relatively stable, mainly because the development of fixed-line network has tended to be full. If the existing circuit is used to carry the base station, hybrid networking and frequent handover will have a certain impact on the existing fixed network services. Therefore, using the existing optical fiber access loop to carry the base station load will affect the stability of fixed network services to some extent.

4 Suggestions for fixed network access resources to access base stations

From the above analysis, it can be seen that there are some problems in accessing the base station by using the existing fixed network resources. Considering the practical significance of the reorganization of operators and the utilization of fixed resources in the future, it is necessary to make corresponding construction adjustments when using fixed network resources to access base stations:

(1) It is suggested that the base station loop be networked independently.

It is suggested that the base station set up a separate ring network, on the one hand, it will not affect the existing optical fiber access network services. On the other hand, it is also convenient to maintain and manage the base station. In addition, the access loop of the base station should be able to reach the computer rooms of the two convergence nodes.

(2) Increase the meeting node computer room.

In terms of fixed network resources, the regional access network is basically set around the end office. Due to the characteristics of the fixed network, the average coverage radius of the end office is generally about 3 kilometers, and it is too far to use the end office as the gathering node computer room. Therefore, after the convergence of mobile communication, the convergence nodes of mobile communication transmission network should be placed in the end office computer room, and the convergence node computer room should be appropriately increased. You can re-select a new convergence node computer room, or you can choose an existing access computer room with a large area and reasonable geographical location.

(3) Clean up the tube hole resources and lay the optical fiber.

For base station access, the most abundant and reliable fixed network access resources are physical basic resources such as pipelines and telephone poles. However, due to the characteristics of fixed network, a large number of large-core copper cables are laid in the pipes and poles at the end of fixed network. Therefore, gradually cleaning up the pipe hole resources and laying optical cables have become the key to the base station ring network.

5. Adopt large-capacity SDH equipment.

3G base stations require large bandwidth capacity, so large-capacity SDH equipment should be used for independent networking of base stations, and 622M equipment can be used in urban areas. 155M equipment can be used in suburbs and rural areas. And the number of branches and nodes on the ring should be strictly controlled, and the number of nodes should be controlled at 4-6.

(4) The urban access layer can be equipped with optical cables with increased cores.

Urban access layer networking can make use of the current situation of fixed-line optical junction boxes to lay large-core access layer backbone optical cables in urban trunk sections, and base station access loops can be built based on network junction boxes. This not only standardizes the use of optical fiber, but also improves the utilization rate of optical fiber to some extent.