3G MOBILE COMMUNICATIONS
This section presents some specific aspects related to the planning of third generation cellular networks for mobile communication services (UMTS, CDMA2000, HSDPA, HSUPA, etc.).
The relationship between capacity and coverage in third generation cellular systems (based on CDMA) requires study both aspects of the network together
The usual way of this study is based on the performance of traffic simulations (Monte Carlo), which is randomly generated traffic load, placing users in the study area, and analyzes the network behavior presence of the load.
If it is not desired to undertake the study based on simulation, it is posible to obtain estimations of the network coverage through a simplified study based on classical techniques, ie, link budget and calculations of link propagation attenuation. This analysis has some limitations, and the results are less accurate than those obtained by simulation. Typically, the simplified study carried out as a first approach to network planning, which is then precise through simulation-based study. The simplified study based on link budget and calculation of attenuation is considered separately for uplink and downlink.
Xirio introduces a simplified approach for calculating coverage of third generation mobile stations by calculating the sensitivity using load parameters from the base station, number of users, etc.
Then, steps of access network planning process are listed, highlighting in each of them, and when necessary, the points to which the user must pay special attention in these networks planning.
NEEDS ANALYSIS - CONFIGURATION
•Cartography. Depending on the service area for the network on project, this type of studies may require the use of rural, urban or mixed cartography.
When the stations are located in rural areas, terrain models of 100 and 25 meter resolution are often used. For simulating the effect of multipath losses in the coverage of these stations over urban areas, it is usually used a morphography layer in which the user can include additional losses associated with each urban area.
If the stations are located within an urban area, is advisable to use urban mapping for radio planning. It is adequate a terrain model of between 1 and 2 meter resolution. In this case it would not be added any additional losses to the propagation.
Finally, it is possible to use multiple layers of altimetry to perform mixed calculations, where the station is located in proximity to an urban center and the user wants to analyze the propagation toward its interior.
•Calculation methods. Different mobile communication technologies work in very different frequency bands and require many customisations when defining a calculation method applicable to their planning. Here are some proposals for specific environments and technologies:
oRural environment. Planning in such environments is usually performed using deterministic methods such as UIT-R Rec.P.526 or Deygout method, provided that cartography of the rural area where the network is deployed is available. In these cases it is necessary to consider that the simulation results assure the levels exceeded in 50% of time and locations, so that, in order to ensure higher percentages it will be necessary to use the "fading margin", which is configurable in parameters of the calculation method.
Together with these methods, and if morphographic layers are available, it is customary to introduce additional losses associated with the terrain, especially to see the effects of multipath in urban environments.
In cases where no precise morphographic layers from the service area are available, it is possible to use empirical methods such as Okumura-Hata, particularized for rural settings.
oUrban environment. Planning for urban or mixed areas (rural-urban) can be done by empirical methods (the Okumura-Hata method is an adequate approximation of the range of the signal into a radius from the base station) or deterministic if precise enough urban cartography is available (1 or 2 meters resolution). As a deterministic method, can be used as ITU-R Rec. 1411, Xia-Bertoni or modulated Okumura-Hata method to obtain the signal propagation in city taking into account the diffractions on the buildings roofs, and reflection effects in buildings.
Whether using empirical methods, or detailed urban cartography, the use of corrections due to terrain use (clutter) is discouraged, since it would be introducing redundant correction on estimates of propagation.
Quality objectives for these networks require to ensure a minimum coverage for a certain percentage of time and locations. These minimum percentages are translated into signal margin over the estimated average value in the simulations, which is obtained from a statistical distribution that simulates the effects of fading of the received signal by the mobile terminal in a given propagation environment. Therefore, in order to ensure higher percentages it will be necessary to use the "fading margin" configurable in the parameters of the calculation method.
•Link budget. Since the simplified study based on link budget and calculation of attenuation must be study separately for each transmission path (uplink and downlink), Xirio incorporates into coverage and link studies the ability to select the path under study as well as specific parameters (load factor base station, number of users, etc) in sectors and receivers for the dynamic calculation of the reception sensitivity from them, as well as specific 3G parameters in link and coverage studies.
•Stations and sectors. Mobile communications networks are typically composed of a stations distribution in a cellular mesh. Each station can consist of one or more sectors. The way to define these entities in Xirio is to define a site as the transmitting station location and as many transmitter as sectors. Particularly for third generation mobile communications is necessary to specify parameters like bit rate, load factor, etc. to establish a dynamic sensitivity that characterizes calculation.
•Best server by signal. The user has to give the criteria that Xirio will use to determine the desired sector (best server) at each location. This will be the sector to which the mobile would be linked at every location in normal conditions. The usual approach is to work with a better server by signal, that is, the mobile would be linked to the transmitter which provides the highest signal level.