LTE MOBILE COMMUNICATIONS

This section presents some specific aspects related to LTE cellular networks planning using Xirio-Online. The LTE features and the complexity of its radio interface require addressing the planning of such systems differently from other mobile systems.

A proper LTE planning involves analyzing both network coverage and capacity of the system facing the traffic demand of users. The presence of bigger traffic load limits the system's behavior since radio resources to meet demand are limited. Similarly, a higher level of interference between cells is generated as their load increases.

When traffic loads are known, the LTE network simulation can be performed statically, obtaining coverage and interference levels throughout the service area. If real data on the traffic load are not available, it is necessary to conduct a capacity study to determine it.

Capacity studies can be based on random traffic generators (Monte Carlo), however, such simulations are particularly expensive in computing time and may not faithfully recreate the behavior of the system. The calculation of capacity introduced by Xirio-Online is an evolution within the existing mobile communication simulations focuses on obtaining an overall average behavior of the network in a very short calculation time..


Xirio-Online allows to make the following LTE specifics calculations, based on user requirements:

- Static coverage of the network. The RSRP results provides a shadow of the LTE network reference signals coverage.

- Static analysis of SINR interference . Initially the traffic load supported by each base station is not known. Thereby Xirio-Online performs a static analysis of SINR interference from traffic load set in LTE parameters of sectors.

This calculation provides, through a shadow of coverage, and without a capacity analysis, an approximate idea of ​​the network coverage in the loading conditions defined by the user.

- Analysis of capacity. From a distribution of users in environments, and the prior static analysis of SINR interference, Xirio-Online obtains an approximate result of the demand for network resources.

Here are the steps in the planning process, highlighting in each of them, and where necessary, the issues to which the user must pay special attention for planning LTE networks:

1. Needs Analysis - Configuration

- Cartography: This type of study may require the use of mapping rural, urban or mixed, depending on the service area for the network to plan.

When stations are located in rural areas, models of the terrain between 100 and 25 meter resolution are often used. To simulate the effect of multipath losses, and coverage of these stations on urban areas, a layer of morphography with clutter which includes losses associated with each village is often used.

If the stations are located within an urban area, it is recommended to use urban cartography for radio planning. A terrain model from 1 to 2 meters is an adequate resolution. In this case, additional losses would not be added to propagation.

Finally, it is also possible to employ multiple layers of altimetry to perform mixed calculations, where the station is located near an urban center and the propagation toward inside that urban center is wished to analyze.

- Calculation Methods: Different mobile communications technologies operate in very different frequency bands and require quite a particularizations when defining a method of calculation applicable to planning. Here are some concrete proposals for specific environments and technologies:

- Rural environment. Planning in such environments is usually performed using deterministic methods such as ITU-R Rec 526 or Deygout method, only if cartography is available for the network deployment area. In this cases, it is necessary to consider that the simulation results ensure the levels exceeded in 50% of time and locations, so that in order to ensure higher rates will be necessary to use the "Fade Margin", configurable in the parameters of the calculation method.
Together with these methods, and if morfographic layers are available, it is customary to introduce additional losses associated with the ground, especially for the effects of multipath in urban environments.

In cases where precise cartography of the service area is not available, it is possible to employ empirical methods such as Okumura-Hata, particularized for rural environments.

- Urban environment. Planning in urban areas or mixed (rural-urban) areas can be performed by using empirical methods (Okumura-Hata method is a sufficient approximation of the signal range of a base station in to a radius), or deterministic methods if urban cartography precise enough is available (1 or 2 meter resolution). As deterministic methods you can use methods such as ITU-R 1411, Xia-Bertoni or Okumura-Hata modulated, for propagation simulation in town taking into account the diffraction over the roofs of buildings, and the effects of reflection in buildings.

Whether using empirical methods or detailed urban cartography, it is not advisable to use corrections due to land use (clutter), as it would be introducing a redundant correction on estimates of propagation.


Quality objectives for these networks impose ensuring minimum coverage for a certain percentage of time and locations. These minimum percentages are translated into a signal margin, regarding the estimated mean value in the simulations, obtained from a statistical distribution that simulates the effects of fading of the received signal by the mobile terminal in a given propagation environment, so, in order to ensure higher rates it will be necessary to use the "Fade Margin" that is configurable in the parameters of the calculation method.

2. Parameterization of stations

- Stations and sectors: LTE communications networks are typically composed of a distribution of stations in a cellular mesh. Each of the stations may be composed of one or several sectors. In Xirio-Online these entities can be detemined by defining a site as a transmitter location, and as many transmitters objects as sectors. In the case of LTE communications it is necessary to specify parameters such as bit rate type, load factor, etc.. to establish a sensitivity in a dynamic way that characterizes the calculation..

3. Network Planning

- Best server by signal: The user must define the criteria used by Xirio-Online to determine the desired sector (best server) at each point. The mobile terminal will be linked to that sector at each point under normal conditions. The usual approach is to work with a criteria of better server by signal, that is, the mobile terminal will be linked to the sector from which would receive a higher signal level.

The result is a static coverage area of RSRP signal level. In scenarios with low traffic demand, as for example in rural environments, the result obtained in this stage may be sufficient. Otherwise it will be necessary to conduct a study of interference and network capacity.

4. LTE network interference

- Specific parameters of the LTE network. In order to obtain an interference calculation, it is necessary to set some specific LTE parameters of the sectors and of the mobile terminal.

In case of using static ICIC when stations are being parameterized, it will be necessary to configure each sector with a different static ICIC label. In this way, mitigating the effect of intercell interference is achieved. In the following link you can see the different use of the LTE bandwidth made by each label for each of the frequency reuse schemes available in Xirio Online.

This calculation is specially optimized for base stations with three sectors. If the base station is composed of a single sector, it is advisable to ensure, as far as possible, that adjacent cells have different labels.

The LTE interference result consists of a series of global coverage shadows, and some individual reports and graphs for each sector.

5. Network capacity

- Cartography. For calculations in urban environments it is advisable to use an additional digital elevation model in capacity calculations. Normally the distribution of mobile terminals in the study scenario vary from indoor to outdoor, and it will be necessary to have proper cartography to take into account this effect. From the Multi-transmitter study the user can access to configure this cartography.

- Parámetros de capacidad LTE. - Parameters of LTE capacity. The distribution of users/terminals in the scenario under study is done by defining environments. In each environment, you can configure different types users/terminals with their respective densities for indoor and outdoor. Settings of these LTE capacity parameters are done from the parameters window of the multi-transmitter study.

The capacity results consists of a report and a detailed graphical of the demand for network resources.

Once the capacity calculation is done, it is advisable obtaining the final SINR coverage area. For doing so, we must perform a second calculation of interference, adjusting the sectors traffic load according to the obtained capacity statistics.

 

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