Scientific planning of 3G wireless network

In order to be able to create the largest market, the most users and the continued appeal of users, 3G mobile communication network must have: high coverage and stable network signal, the system needs to be able to have a certain capacity to face possible high traffic impact, the network must be continuously profitable.

At present, 2G Wireless access network has been quite mature, network coverage and network quality have reached a relatively high user satisfaction, in the 3G network construction, how to make full use of existing network resources, improve user satisfaction, save network investment, it is also our network planning process need to focus on the content.

First, 3G network planning in the core issues

The interference between the community and the community will have an impact on the coverage and capacity of CDMA networks. In the design of CDMA system, the following problems should be considered in the design of network coverage and capacity.

1. Wireless Link Budget problem

Link budget can only provide a rough path loss value, in the actual engineering design, only as a reference value, and can not be used to guide engineering construction.

According to our practical engineering experience, to get accurate path loss values that can be used to guide network construction, we must adopt appropriate propagation model, and modify the model parameters in different terrain conditions, and get the model correction coefficients that reflect the influence of wireless environment on radio signals in different regions. In this way, the coverage range of the cell can be predicted more accurately, the link-level simulation calculation is carried out, and the pilot-frequency pollution is controlled. (Computer science)

2. Capacity and interference issues

The QoS and capacity of CDMA systems are greatly influenced by interference, which makes both coverage and capacity change at the same time. In other words, at the beginning of the design, it is necessary to determine the load limit of the network to avoid the serious interference caused by the increase of load traffic.

The actual capacity and interference planning should pay attention to the following aspects.

(1) The influence of NodeB end transmitting power on capacity and disturbance

The NodeB end transmitting power will affect the network coverage and network capacity, and the traffic volume of each user will affect the whole network capacity, at the same time, the NodeB transmitter power too large will also have an important influence on the wireless network.

(2) The effect of soft switching on capacity and disturbance

Another factor that affects network capacity is soft switching and the extra overhead it requires, at which point the base station needs additional CE units, additional transmission links are required for the Abis interface, additional rake demodulator is required for mobile stations, and additional links are required for different fan sections within the base station. At the same time, soft switching of the selected chain will cause additional interference to the system, even if the activation focus does not include additional links, but it will still cause additional interference to the system.

In order to overcome the negative effect of soft handoff on the network, it is necessary to control too many soft handoff areas in the 3G engineering design stage.

① Select Station site according to network design requirements

When considering the NodeB base station of the common station, the location of the original GSM base station is not ideal, the height is not suitable (too high or too low), the antenna installation position is limited, and the surrounding buildings are blocked and so on to avoid using the site as far as possible. In order to avoid the system soft switch scope control improper, virtually wasted the system later CE resources.

② set the neighbor list reasonably

The neighbor list settings should be adjusted periodically initial system load user, in order to improve the service quality of the system, the neighbor list should be set more, with the increase of the number of users on the Internet, base station coverage area narrowed, the neighbor list should be shortened to reduce the system soft switching area and system search time. In addition, reasonable adjustment of soft switching parameters can also reduce excessive soft switching to some extent.

(3) The influence of mixed service on capacity and disturbance

More consideration of user behavior and the variability of user Terminal Services characteristics, realistic business capacity estimation for a variety of mixed services is a challenging task in network design.

The discontinuous (or intermittent burst) data service demand brings dynamic traffic load to the wireless interface of the network, meanwhile, it is relatively difficult to provide services that meet the strict delay requirements for all kinds of real-time service in the mixed-service network. This dynamic rate selection needs to allocate the corresponding wireless Link resources for different business requirements. This is also a factor that must be considered in order to balance capacity and coverage in 3G network design.

In CDMA networks, the index of whether the mobile phone can access the network is not RSSI (receiving end level) but Ec/io. In other words, when a region of interference signal intensity is strong, although the phone's reception level is very high, and the mobile phone is not normal access to the network. In order to avoid the interference, the following aspects should be paid attention to in the 3G design planning stage.

(1) Reasonable planning station site, antenna, transmitting power and so on, control over the area coverage area.

(2) in the low traffic area to solve the coverage and the use of repeater extension network signal, to carry out strict design before the survey, reasonable design, strict construction and audit. Avoid hasty construction and the later difficult to solve the impact of network quality.

(3) The indoor coverage is mainly to absorb the traffic volume, to solve the indoor signal blind area, and indoor traffic volume is the main source of network traffic, therefore, in the solution of indoor coverage, the first thing to consider is the priority to use the existing indoor coverage system, while taking appropriate means to reduce the possible interference.

3. Impact of "far-near effect" on site selection

Because of the high sensitivity of CDMA network to jamming, the interference caused by the communication on the uplink is higher than the noise of the whole cell. When the user is far away from NodeB, in order to maintain a certain quality of the call, NodeB will improve the transmission power, thus causing interference to other communities. This is also the "far-near effect problem" in CDMA.

At the same time, in the 3G network, in the high traffic volume, high data service area, the number of NodeB will be far more than the number of base stations in 2G network, it is more important to choose a reasonable station site. Therefore, in the construction of the network, the choice of NodeB station site near the user will reduce the network interference, on the contrary, it will increase network interference. When choosing a site, network designers generally need to adhere to the following principles: NodeB location As far as possible in the hot traffic area, switching or soft switch area should be as low as possible.