Method for predicting radio wave propagation

p0001Method for predicting the Funkwellenausbreitunσ

p0002The invention relates to a method for predicting the radio-wave propagation, in particular in urban areas.

p0003State of the art

p0004The prediction of the radio wave propagation is an important step in the computer-aided planning of mobile networks. In this step, the field distribution of the light emitted from a base station radio wave is calculated at a specified by the designer area. This calculation is performed for each base station of the network to be planned. The calculated field strength values ​​of the base stations form the basis for further planning steps, such as the prediction of the supply situation of the network.

p0005The conventional method for predicting the radio wave propagation based on empirical models such as the Okumura model (OKTJMURA, Y. Ohmori, E., KAWANO, T., FUKUDA, K., "Field Strength and Its Variability in VHF and UHF land-mobile Radio service ", Rev. Elec. Commun. Lab., Vol. 16, 1968, pp. 825-873), which was obtained by the analysis of radio field measurements. the resolution of the field strength calculation with such a process, ie, the resolution of a planar element for which a field strength value can be calculated, is grόßenordnungsmäßig a square of several hundred meters.

p0006With the development of mobile communications, the number of mobile subscribers, especially in the urban areas is increasing rapidly. To cope with the high volume of traffic in urban areas, base stations with low antenna heights and low transmission powers are built close to each other in such areas. This leads to small Zellengrδßen of the base stations, the cell size of a base station Size of the served by this base station area indicated. A cell is called a micro cell, if this has a radius of a few hundred meters up to a maximum of 1 km. In contrast, cells designated with a radius of several kilometers or more than macrocells.

p0007The conventional empirical method for predicting the radio wave propagation are applicable for planning of macrocells. But they are not suitable because the accuracy is not high enough and their resolutions are too coarse for the planning of microcells in urban areas.

p0008For several years, different models and methods for the calculation of the radio wave propagation will be developed in urban areas. Among these methods, which are based on ray tracing methods.

p0009The previously known methods which operate based on the ray tracing method can already provide more accurate results than the empirical method. The resolution of the Feldstärkeprädiktion this method is much finer than that of the empirical method. A significant disadvantage and obstacle to the wide use of these methods is the enormous and Rechenauf. The methods can be just used in studies of radio systems, since these planning steps are not as time-critical. In the radio network planning is the high computation times that are far from interactive response times, by no means acceptable to the planners.

p0010For the planning of microcells in urban areas, an improved method is needed.

p0011The invention is therefore based on the object of proposing a method for predicting the radio propagation, the

p0012• a much better accuracy than the empirical method has, • a much better resolution than the empirical method comprising, and

p0013• cost of computation is so efficient that it can be used in the radio network planning.

p0014The object is achieved by the features of claim 1.

p0015The project presented in the following process fulfills the above criteria for use in the radio network planning.

p0016The radio wave propagation in urban areas characterized by the multipath propagation. Different wave components arrive by reflection and diffraction on different propagation paths and with various maturities at the receiver. The method takes into account all relevant propagation paths, the first time the diffraction effects to objects, and determines the received power of the receiver and the field strength at the receiving antenna by the summation of the different wave components.

p0017The method uses a three-dimensional description of the building structure of the planning area. The relevant propagation paths of the examined antenna beams are determined radiate optically. For this example, a ray tracing algorithm is used which on the MRT (minimum Rendering Toolkit) is based, a gerate- and platform-independent modeling and

p0018Visualization tool (see this FELLNER DW: Extensible image systhesis; In Object-Oriented Programming and Mixed Paradigms, Wisskirchen P., Focus on Computer Graphics, Springer Verlag, February 1996, pp 7-21..).

p0019According to the invention, the method uses a planning tool that allows a separate and flexible modeling of the antenna, the buildings, the characteristic of building surfaces (walls) and the forecast level. The consistent modeling approach for geometric objects of any kind also allows the consideration of diffraction of the antenna beams at objects such as cylinders, for previously existing procedures were not applicable.

p0020For the treatment of reflection and diffraction of the radio wave to buildings and for determining the field parameters, the geometric diffraction theory is used.

p0021The computational complexity of the method is mainly through the search^" the ray paths determined. In particular, the search for the diffraction edges consumes a significant portion of the computing time. In this method, an algorithm is used by the diffraction edges are obtained quickly and keeps to a minimum the number of intersection calculations between rays and objects in the cell.

p0022The method can be used in a frequency range in which the wavelength of the radio signal is substantially less than the dimensions of the building.

p0023Description of the building structure

p0024Buildings and other occurring in the metropolitan area objects, such as trees, be as specific variants of a generic object type, represented by a base class T_OBJECT represented. The core functionality of the base class and thus the functionality of all geometric objects includes the following methods: boundingVolume () returns the enveloping body. intersectO calculates the first intersection point between the object and a beam. The result is true if and only if this within a given distance (usually the date next found object) exists checkintersect () takes only a simple test for the existence of the intersection, the example for Illumination beam is sufficient and can be done much faster than its calculation in most cases. By default, however, this method is based on intersectO. checkBoxlntersect () is used to initialize spatial data structures for accelerating the intersection calculations. The method determines whether the object has a non-empty intersection with an axis-parallel cuboid. By default, this box is compared with the enveloping body of the object. surface normal () computes the normal to the surface at a given point of the object surface (facing outwards). triangulate () takes one parameter for quality control and produces a surface approximation, which is suitable for visualization using planar facets.

p0025What is new is that the entire scene as well as all sub-scenes are consistently treated as geometric objects. A Subszene, described by the class t_Scene, in a lot of geometric objects are included, is also derived from the base class t_Object and thus also provides the above methods.

p0026Sub-scenes are always automatically generated when an included scene description is processed or when a group of n objects (n> l) included. Covering body of sub-scenes are automatically calculated by the method unifyO Class t_BVol combining two encasing body to.

p0027The concept of extensibility is also surface properties of particular importance, since it can be just as efficiently address the changing needs of radio wave calculation. For example, be realized as a derivative of the existing class enhanced by electrostatic properties surface - its basic functionality such as membership of an object does not have to be modeled again. The ray tracing algorithm

p0028Non-trivial scenes are usually already organized hierarchically been designed to be. In addition to obvious advantages in handling, this results in a particular case, a considerable acceleration of ray tracing.

p0029Responsible is the minimum Rendering Toolkit (MRT) implemented algorithm for determining the intersection of ray and the scene:

p0030First, it is checked whether the examined antenna beam the enveloping body of the scene, which was calculated when generating the scene cuts and sends in case an intersection there exists the request intersectO all objects contained in it, either elementary objects or turn his scenes , Because this is done on each level of hierarchy, the number of such tests is of the order of the logarithm of the number of objects when the hierarchy reflects the spatial structure with sufficient accuracy.

p0031The present city models lack such a hierarchy. To make the effect are still usable, it is subsequently produced by a quadtree-based method, because this takes account of the predominantly two-dimensional extent. Contains a scene being viewed too many objects, is the scene - if it contains at least four objects - recursively divided into up to four sub-scenes. This has the advantage that no longer the objects of the entire scene must be checked for intersections with the antenna beams, but it is first checked for each Subszene enabling enveloping body, whether the Subszene forms an intersection with the antenna beam. If for one or more sub-scenes an intersection exists, must be considered in the following only the objects of these sub-scenes.

p0032The computation required is minimized dramatically.

p0033To determine the allocation to the sub-scenes, the center of the envelope is determined for all objects, and for the entire scene each. By comparing coordinates the membership of objects following to exactly one of the four quadrants.

p0034Calculation of field parameters

p0035The modeling of an antenna via three-dimensional position, transmission power, transmission frequency and an optional radiation, passed through a Ante Rien chart. The key to the use of abstract realization of an antenna is the strengthO method. After entering an emission it provides the field strength E at one meter. All necessary calculations as well as the consideration of the radiation are encapsulated in the class, so that a redefinition of the antenna without changes in other parts of the program is possible.

p0036A major problem is choosing the right antenna beams to find the relevant propagation paths. So far, the beam distribution is based on an imaginary sphere around the antenna. By specifying the areas for azimuth and elevation angle to parts of the sphere can be selected; the density can be influenced by appropriate increments.

p0037In the urban area, this method is problematic because the forecast level is very large compared to the antenna height. The constant pitch of the spherical coordinates in this case leads to an oversupply of the near and an undersupply of remote receiving cells. This is where a new strategy, in which the radiation emitted so be that they would impinge on open ground in uniform grid.

p0038In order regardless of the selected antenna beam in any case to find all the diffraction edges, which are visible from the antenna, it is possible, submit them directly diffraction cone. It is the so-called Edge shooting method was used, and initially each building edge is checked whether it comes as a diffraction edge in question, ie, whether it is convex and on a side facing the antenna building area is. Then it is determined for several lying on this edge points, whether they are visible from the antenna; can then directly from these points a diffraction cone generated.

p0039Since diffracted antenna beams to many receiving sites make a significant contribution to the total field strength, it is very important that the corresponding diffraction edges are found. this is ensured by applying the Edge-shooting method.

p0040When ray tracing reduced by propagation, reflection and diffraction beam power is carried. It is a meaningful criterion for termination of ray tracing as the previously used maximum number of reflection and diffraction.

p0041The amplitude of the reflected or diffracted beam is to the Geometric Theory of Diffraction (see, for example OKUMURA ​​Y. Ohmori E., KAWANO T., K. FUKUDA:. Field Strength and its variability in vhf and uhf land-mobile radio service; Rev. Elec Communication Lab. 16 (1968), pp. 233-333) determined from the amplitude of the incident beam by the multiplication by a reflection or diffraction coefficient. The use of empirical reflection and diffraction coefficient is optionally available. The attenuation of a beam in a homogeneous medium is carried multiplying the amplitude at the beginning of the beam path marked with a divergence factor.

p0042A key concept in the simulation model is the forecast level, the registers at each intersection with the beam path the field strength. The forecast level is not necessarily a flat plane, but can follow the ground surface, the height of the forecast level can be set on the floor by the user. Normally, the amount of the forecast level is equal to the antenna height of the receiver.

p0043As for the zy plane parallel rectangular prognosis level is modeled as specialized geometric object. This extension to arbitrary (eg, non-planar) forecast levels without changing the rest of the algorithms is possible. By implementing a geometric object forecast levels can be full members of a scene, and there is a consistent treatment of the intersection of search and visualization.

p0044When initializing a screen size is specified, based on which the forecast level divides into squares reception for accumulation of incident rays. To access the resulting matrix suitable methods are provided.

p0045The use of a purely two-dimensional forecast level has the disadvantage that the plane parallel to the ground receiving squares, are difficult to make by the beams when they are further away from the transmitting antenna or if they are about the same height of the transmitting antenna. Particularly striking is this circumstance, when the reception squares exactly located on antenna height. Intersections with the antenna beams then come not before.

p0046One solution to this problem is to forecast the level of an additional third dimension, ie a certain height, to give. The result is a three-dimensional prediction level with a certain thickness. The individual receiving the squares will receive blocks that are easy to make in general then by the antenna beams.

p0047Unlike a two-dimensional plane can forecast as well as with a lower radiance a nationwide feed of antenna beams can be achieved, resulting in a significant reduction of the computation time.

p0048With the news disturbing () is the forecast level indicated that it was hit by a jet. will pass the point of impact, the field strength and the beam direction. From the point of impact, the forecast level determines the associated reception Square and registered in the characterized by strength and direction of the beam.

p0049Due to the simulation model i is st necessary, each evaluated by several rays striking a reception square on the same propagation only one. It is immaterial which is selected. In practice, it seems sufficient, similar rays compare to that effect by their strength and direction, if so not all theoretically possible cases are covered.

p0050The elimination of similar rays done internally by each receiving a square beam list is assigned. Each of the function disturbing () reported beam is only stored if not already exist, a similar. As comparison criteria are the absolute difference of the field strength and the dot product of the direction vectors whose interval limits can be set by the user.

p0051The method Calco eventually causes the forecast level, summarize the accumulated radiation to field strength values ​​and to put these in the result matrix. Since the amplitude and the path length of each individual beam which arrives receiving square, are registered, one can compute the impulse response of the radio channel and the associated parameters, such as the delay spread for the received square.

p0052visualization

p0053The result of the field strength distribution can be represented as two-dimensional. The field strength values ​​are visualized by greyscale or color values, their assignment is given to the fixed field intensity intervals by a legend.

p0054Since the entire musical genre by special modeling approach as a full MRI object, it can be displayed in three dimensions without detours with the appropriate methods. For identification of the antenna location while an additional object is created, which models an abstract antenna. The forecast level receives a texture with which the field strength distribution is shown. For a photorealistic visualization using ray tracing or interactive through hiking. This is particularly suitable for the practical use for easy interpretation of the results is very important.

p0055In the following the invention will be explained in more detail with reference to drawings. Here, from the drawings and their description inventive features and advantages of the invention.

p0056Figure 1 illustrates a plurality of different propagation paths of an antenna beam from a transmitting antenna on a building roof to a receiver in a street; Figure 2 shows a schematic representation of a side view of different propagation paths of the antenna beams to impinge on the forecast level;

p0057Figure 3 is a plan view of the schematic representation of Figure 2;

p0058Figure 4 is a two-dimensional visualization of the simulated field distribution.

p0059Figure 1 illustrates a plurality of different propagation paths from antenna beams from a disposed on a building roof 7 transmitting antenna 1 to a receiver 2 in a street. There are four antenna beams shown only four antenna beams, two of which, each reflected on a building 3 or 6, reach the receiver 2 indirectly.

p0060The other two investigated antenna beams are both bent on building 5, wherein one of the beams after diffraction at building 5 reaches the receiver. 2 The remaining beam reaches by the diffraction at the building 5 with a portion of its power to the receiver, the other part is reflected on the building 4, and only then reaches the receiver second

p0061At the receiver 2 so take five more or less strong antenna beams from different directions and with different Laufzeitverzδgerung. The inventive method allows, as shown schematically, to track the propagation paths of each beam and to take account of reflections and diffractions, and to determine the power losses of the beam during its course. At the receiver site, the remaining beam power and maturity may be determined each investigated beam, so that a resultant field strength and an associated timing diagram at the receiver 2 results. As shown in Figures 2 and 3 is in the planning area for which the radio wave propagation to be examined, determined a forecast level 9, which is set at a certain height above the ground. Preferably, the height of the forecast level corresponds to 9 of the height at which usually the receiver 2 stop (eg, 1 to 2 meters above the ground). The forecast level 9 is, for example, square 10, divided into individual receiving squares, the size of the squares depends on the topography and the building density of the study area. In the city center, the size of the receiving squares will be smaller than in the slightly built suburbs.

p0062Starting from a fixed antenna location 1 in the reception squares incident beam power and reception quality (impulse response) is now being investigated, said the planning area (eg urban) existing objects (eg buildings, trees, water surfaces, etc.) presented as three-dimensional objects and in the calculation be included.

p0063The antenna 1 for example is now a beam 12 sent the 10 directly hits the examined reception square, with its direction angle, duration and beam power is registered by receiving square. Given each beam is the instantaneous field strength E and runtime or run length s carried during ray tracing.

p0064A steel 11 is also sent from the antenna 1, however, does not apply directly to the investigated reception square, but is reflected from the object 8 and then passes as a reflected beam 11 'for receiving square 10th

p0065For the two impinging Receptionist square beams 11 'and 12 in the reception square whose power and run time is registered, said with this information statements about Reception quality in the investigated reception square can be made.

p0066Figure 4 shows a way of visualization of

p0067Simulation results in the form of a two-dimensional

p0068Representation.

p0069The planning area and the objects in it are

p0070Floor plan shown. One can see the location of the

p0071Transmitting antenna and the resulting field strengths within the

p0072Planning area, the field strength values ​​E in dB microvolts / m as

p0073Grayscale or color values ​​are shown.

p0074Using such a representation to areas in

p0075make radio shadow light and optimize the antenna site accordingly.

p0076drawing Legend

p0077antenna

p0078receiver

p0079building

p0080building

p0081building

p0082building

p0083building

p0084object

p0085forecast level

p0086Reception square, 11 'antenna beam antenna beam