WO1998008107A1

WO1998008107A1 - Method and system for calculating transmitted signal coverage in an environment model using a receiver area data structure

Info

Publication number: WO1998008107A1
Application number: PCT/US1997/013447
Authority: WO
Inventors: Theodore Xauier Boone; Thomas Eugene Finegan
Original assignee: Motorola Inc.
Priority date: 1996-08-22
Filing date: 1997-07-29
Publication date: 1998-02-26
Also published as: FR2752618A1

Abstract

An environment model (300) is selected (202), wherein the environmental model locates at least one object (306) in relation to a transmitter (302) that transmits a transmitted signal. Thereafter, an initial transmitted signal characteristic is associated (208) with each of a plurality of areas of interest (324) in the environment model (300). A change in direction of the transmitted signal by one of the objects (306) is represented as a transmitter image (336, 436) that transmits an image signal. Signal characteristic contributions by the image signal are calculated only (212) for selected ones of the plurality of areas of interest (344) wherein the signal characteristic associated with the area of interest can be influenced by the image signal by at least threshold amount (220, 222, 224).

Description

METHOD AND SYSTEM FOR CALCULATING TRANSMITTED SIGNAL

COVERAGE IN AN ENVIRONMENT MODEL USING A RECEIVER

AREA DATA STRUCTURE

Cross-Reference to Related Applications

The present invention is related to: • U.S. Patent Application Serial No. 08/656.029, entitled "Method and

System for Calculating a Transmitted Signal Characteristic in an Environmental Model" filed 05/31/96 (attorney docket no. CE04378N);

• U.S. Patent Application Serial No. 08/685,344, entitled "Method and System for Calculating a Transmitted Signal Characteristic in an Environmental Model Having Attenuator Figures" filed 07/23/96

(attorney docket no. CE04347N); and

• U.S. Patent Application Serial No. 08/415,051, entitled "Method for Wireless Communication System Planning" filed 03/31/95 (attorney docket no. CE04227N); each of which is assigned to the assignee herein and incorporated herein by reference.

Field of the Invention

The present invention is related in general to calculating transmitted radio signal characteristics, and more particular to an improved method and system for calculating a transmitted signal characteristic at a plurality of areas of interest in an environmental model using raytracing techniques to model radio signal propagation.

Background of the Invention

In a wireless communications system, such as a cellular telephone system or a personal communications services (PCS) system, base station antennas should be located so that suitable radio signals propagate to every point in the service area. One way to ensure adequate signal coverage in the service area is to copiously locate base station antennas throughout the service area. Because this solution results in redundant or overlapping coverage, the solution is not practical or cost effective. In addition to the expense of the base station equipment, leasing property for the base station equipment adds to the expense of each base station. Therefore, communication systems providers attempt to lower the cost of their systems by using a minimum number of base stations, each located so that its coverage area does not excessively overlap the coverage of another base station.

To correctly locale base station antennas in a radio communications system, it is important to accurately predict signal strength, or any other transmitted signal characteristic, in the service area. If signal propagation cannot be accurately predicted, a system designer may spend too much money as a result of locating base stations too close together, or, conversely, design a system that does not provide adequate radio signal coverage as a result of placing base stations too far apart.

Such radio signal propagation prediction is the goal of many so-called raytracing programs.

One problem with raytracing programs is the amount of computing time required to produce an accurate, high-resolution map showing signal strength of a transmitted signal at various areas of interest in a service area. For example, predicting signal strength among buildings in a downtown area of a city may take a raytracing program days, or even weeks to run. Additionally, this computation time may be inversely proportional to the accuracy of the output of the program. One reason raytracing programs require so much computation time is because modeling a transmitted signal is a complex and tedious process. In the coverage area, propagating signals are reflected by walls of buildings and diffracted by corners of buildings. The raytracing program may represent building walls as panels. Each panel in the model is assigned properties that mimic those of a corresponding wall in the coverage area. Such properties include reflection coefficients and other mathematical expressions that permit modeling of radio wave reflections and radio wave diffractions at a panel corner.

With reference now to FIG. 1, there is depicted a portion of an environment model that may be used by a raytracing program to compute a transmitted signal characteristic at an area of interest in the coverage area. FIG. 1 depicts a transmitted signal reflecting off of a panel, and a resultant transmitter image, or child image, which is used to model the propagating radio signal once it has reflected off of the wall. As shown, transmitter 20 is located relative to panel 22 in environment model 24. Environment model 24 represents a portion of a coverage area that has buildings or other objects that can redirect propagating signals which are radiated from transmitter antenna 20. In the example shown, transmitter 20 may be limited to transmitted energy in a particular direction, or with a particular scope, which may be defined by arc 26, defined by rays 28 and 30. After leaving transmitter 20 transmitted signals propagate toward panel 22 and reflect off of panel 22 with a signal strength determined by the material in panel 22 and the incident angle between the propagating signal and panel 22. Thus, the signal strength of ray 32 depends upon the distance traveled by ray 28, incident angle 36 and the reflection coefficient of panel 22.

Note that the signals from transmitter 20 that reflect off of panel 22, such as ray 32 and 34, may be represented as signals coming from another point source, which in this example is transmitter image or child image 38. Representing reflected signals as signals transmitted from a child image is a means for simplifying the raytracing problem.

When propagating radio signals strike a corner, such as the corner of building 46 in FIG. 2, the transmitted signal is diffracted, as indicated by rays 48 and 50. This phenomenon occurs at the end of a panel, such as the panels that make up building 46. When the radio signal is diffracted, the diffraction corner re-radiates energy received from another source, such as a transmitter. Most of the energy that is re-radiated by diffraction corner 52 is re-radiated more in the direction of ray 48 than in the direction of ray 50.

Because diffracted rays 48 and 50 behave as though they emanated from diffraction corner 52, diffraction corner 52 may be represented by a child image at that same location. Like the use of a child image in modeling reflections from a panel, this use of a child image to model a diffraction corner simplifies the raytracing problem.

With reference now to FIG. 3, there is depicted a more complex environmental model of a communications system service area. If a system designer wants to predict the total signal strength of a transmitted signal that is transmitted from transmitter 60 and received at area of interest 62, the designer must consider power contributed from a signal propagating directly from transmitter 60 to area of interest 62, as well as any reflected or diffracted signal power arriving at area of interest 62. Thus, diffracted signals and signals reflecting off of buildings 64 and 66 may be modeled as rays coming from child or transmitter images, and grandchild images. To make the problem tractable, the number of descendent images such as child image 70 may be limited by a parameter set by the user, or by an algorithm which monitors the power associated with each descendent image.

Typically, a raytracing program will locate descendent transmitter images in the environment model and then calculate total signal strength at area of interest 62 by accounting for contributions from transmitter 60 via ray 68, from child's image 70 via ray 72, from child image 74 via ray 76, and from grandchild image 78 via ray 80. Image 78 is referred to as a grandchild image because that image is a child of a child. That is, grandchild image 78 is energized, or illuminated, or receives energy from, child image 70. Note that grandchild image 78 is not energized by transmitter 60 (the parent image) because the path between transmitter 60 and grandchild image 78 is obstructed by a panel 82. As may be concluded from the discussion above, it doesn't take a very complicated environmental model to require many tedious calculations for determining the signal strength, or other signal characteristic, of a transmitted signal at a selected area of interest. Furthermore, to be most useful, thousands of areas of interest at specified distance intervals may be considered to produce a useful map of signal coverage in a service area.

With reference now to FIG. 4, there is depicted a tree 100, which is a data structure that may be used in raytracing programs to represent relationships between images and aid in the calculation of transmitted signal characteristics over a signal propagation path. In tree 100, each node, such as parent node 102, may point to, or be associated with, a child node, such as child nodes 104 and 106. Similarly, child nodes may point to a grandchild node, and a grandchild node may in turn point to a great grandchild node, such as the relationship between grandchild node 108 and great grandchild node 110. Note that the same node, say node 108, may be a child node with respect to node 104, one level up, and a grandchild node with respect to node 102, two levels up. Thus, node relationships are expressed in relative terms.

If the environment model in FIG. 3 was represented in a tree structure, transmitter 60 may be represented in tree 100 as parent node

102. Child image 70 in FIG. 3 may be represented as child node 104 in FIG. 4. Child node 104 is associated with parent node 102 because child image 70 derives its energy from transmitter 60. Similarly, child image 74 may be represented in tree 100 by child node 106. Child nodes 104 and 106 have direct links to parent node 102 because child images 70 and 74 are directly energized by rays from transmitter 60 in FIG. 3. Child image 78, however, is energized by a reflection off of building 64. Therefore, child image 78 is represented in tree 100 as grandchild node 108. Any rays emanating from child node 78 that strike additional panels to create additional child images will be represented as a great grandchild node, such as great grandchild node 110. In this manner, the parent image, or transmitter 60, and derivative child images in FIG. 3 may be represented by a tree, such as tree 100 in FIG.4.

To aid in calculating signal characteristics at an area of interest in the environment model, each node in tree 100 may be associated or linked with various types of data, including location of the node, type of node (reflection or diffraction), scope of the node (angles at which rays depart from the image represented by the node).

Many raytracing programs frequently perform calculations to predict transmitted signal characteristics only to find out after the calculation that the calculation did not significantly add to the solution of mapping signal characteristics in the coverage area. Performing calculations that do not significantly impact the solution to the problem wastes time and uses resources inefficiently. Therefore, a need exists for improved method and system that calculates a transmitted signal characteristic at a plurality of areas of interest in an environment model in a faster and more efficient manner while maintaining a high degree of accuracy.

Brief Description of the Drawings

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objects, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: FIG. 1 depicts a transmitted signal reflecting off of a panel, and a corresponding transmitter image according to the prior art;

FIG. 2 depicts diffraction of a transmitted signal according to the prior art;

FIG. 3 illustrates an environment model of a wireless system service area, including a transmitted signal with a propagation path that changes direction due to reflections and diffractions according to the prior art;

FIG. 4 depicts a data structure which may represent transmitter images and their corresponding radio frequency signals that propagate in an environment model; FIG. 5 illustrates a data processing system that may be used to implement the method and system of the present invention;

FIG. 6 is a high-level logical flowchart that illustrates the operation of an embodiment of the method and system of the present invention;

FIG. 7 is a more detailed high-level logical flowchart that illustrates the operation of a portion of the flowchart of FIG. 6 according to the method and system of the present invention;

FIG. 8 depicts a relationship between a receive data structure and areas of interest in an environment model according to the method and system of the present invention; FIGS. 9-12 illustrate the selection of areas of interest in an environment model within the scope of a selected transmitter image in accordance with the method and system of the present invention;

FIGS. 13 and 14 depict the creation of a transmitter image data structure in accordance with the method and system of the present invention; and

FIG. 15 illustrates the selection of areas of interest in an environment model within the scope of a selected transmitter image in accordance with the method and system of the present invention.

Detailed Description of the Invention With reference now to FIG. 5, there is depicted a data processing system 140, which may be used to implement an embodiment of the method and system of the present invention. Data processing system 140 may include processor 142, keyboard 144, display 146, and pointing device 148. Keyboard 144 provides means for entering data and commands into processor 142. Display 146 may be implemented utilizing any known means for displaying textual, graphical, or video images, such as a cathode ray tube (CRT), a liquid crystal display (LCD), an electroluminescent panel, or the like. Pointing device 148 may be implemented utilizing any known pointing device, such as a trackball, joystick, touch sensitive tablet or screen, track pad, or, as illustrated in FIG. 5, a mouse. Pointing device 148 may be utilized to move a pointer or a cursor on display 146.

Processor 142 may be coupled to one or more peripheral devices, such as CD-ROM 150.

Data processing system 140 includes means for reading data from a storage device or other storage means. Such means for reading data may include: a hard disk drive internal or external to processor 142 (not shown); a tape drive (not shown); floppy disk drive 152, which reads and writes floppy disks 154; or CD-ROM 150, which reads and /or writes compact disk 156. Such storage means may be referred to as a computer usable medium for storing computer readable program code in the form of data and software.

Data processing system 140 may also be coupled to a network which permits the transfer of data and software between data processing systems. Using such a network, programs can be loaded into data processing system 140. The components of data processing system 140 discussed above may each be implemented utilizing any one of several known off-the- shelf components. For example, data processing system 140 may be implemented utilizing any general purpose computer or so-called workstation, such as the workstation sold under the name "Model 712/60" by Hewlett-Packard Company of Palo Alto, CA.

Referring now to FIGs. 6 and 7, there is depicted a high-level logical flowchart that illustrates the operation of an embodiment of the method and system of the present invention. As illustrated, the process begins at block 200 and thereafter passes to block 202 wherein an environment model of at least a portion of the wireless communications system is selected. An example of such an environment model is shown in FIG. 8. As shown in FIG. 8, the environment model locates objects, such as buildings, in relation to a transmitter. The term "objects" includes buildings and other structures (which may be modeled with panels) that can redirect a propagating radio frequency signal transmitted from a transmitter antenna. Such a redirection of the radio frequency signal occurs through reflection or diffraction. Objects in the environment model are used to simulate structures that are made of various materials. The differences in materials are modeled with coefficients used to calculate characteristics of reflected or diffracted signals. Thus, depending upon the material of the panel, characteristics of reflected or diffracted signals are affected in different ways.

In environment model 300, transmitter 302 is located near building 304. Buildings 306, 308, and 310 are also shown located relative to transmitter 302. Once the environment model of the service area has been selected, the next step in the process is to select areas of interest in the environment model, as illustrated at block 204. One method of selecting or defining areas of interest includes overlaying a grid, such as grid 312, on environment model 300, as shown in FIG. 8. In order to reduce the number of calculations in the raytracing problem, a signal characteristic, such as signal strength, is calculated at a point located in each area of interest.

The size of the area of interest selected by the user determines the resolution in the output of the raytracing program which maps the signal characteristic over the area covered by the environment model. For example, the area of interest may represent a 10 meter by 10 meter square, and the signal strength over this area of interest may be approximated to the signal strength at a point in the center of the area of interest. Smaller areas of interest will provide higher resolution in the output of the raytracing program while larger areas of interest provide a lower resolution output.

Although grid 312 is used to select areas of interest in the example shown in FIG. 8, areas of interest may be selected randomly, or along selected streets or walkways representing high traffic areas in the coverage area. While using a grid is a convenient way of dividing the coverage area into areas of interest, using a grid to select areas of interest is not required.

Next, the process creates a receive area data structure that represents the selected areas of interest in the environment model, as depicted at block 206. In a preferred embodiment, such a data structure is a binary tree having its leaves associated with individual areas of interest and its nodes associated with groups of areas of interest.

For example, receive area data structure 314, which may also be referred to as receive tree 314, is shown in FIG. 8. Root node 316 represents all areas of interest in environment model 300. Group node 318 represents the bottom half of environment model 300, which extends the entire width of grid 312. And as further illustrated in FIG. 8, group node 320 is associated with all areas of interest in the lower left quarter of environment model 300. As the process of subdividing areas of interest in model 300 continues, individual areas of interest are eventually represented as leaf nodes in receive tree 314. As an example, leaf node 322 is shown associated with area of interest 324. To simplify the receive tree, areas of interest that fall within buildings may be omitted as leaves in the tree. In receive area data structure 314, nodes that have descendants may be referred to as parent nodes, and nodes without descendants may be referred to as leaf nodes. The top node in the tree may be referred to as the root node.

Next, the process associates an initial value with each leaf and group node in the receive area data structure, as illustrated at block 208. If the goal of the raytracing program is to map signal strength, this initial value associated with the nodes and the leaves is an initial power value, which may be the noise floor power measured in the modeled service area. As an example, this initial value may be set to -110 dBm (Decibels referenced to one milliwatt). After initializing the binary receive tree, the process generates and selects the first image, which typically represents the transmitter itself, in a transmit image tree, as depicted at block 210. At this point in the first time through the process, only the root node, or transmitter image, exists in the transmit image tree. Next, the process determines whether or not the selected transmitter image power exceeds a threshold power based on the root node power in the receive tree, as illustrated at block 212. This threshold may be a calculated threshold, such as one that is a percentage of the power associated with the root node. The threshold power may be either above or below the root node power (e.g., 80% of the root node power or

120% of the root node power). Of course, at the beginning of the signal characteristic calculations, the selected image, which on the first time through this loop is the line of sight image of the transmitter, always exceeds the power at the root node because the root node is initialized to the power of the noise floor in the modeled area.

If the selected image power does not exceed the threshold based on the root node power in the receive tree, the process of calculating signal characteristics in an environment model is terminated, as illustrated at block 214. Thus, if the power of the selected image does not exceed the threshold based on the root node power, then the selected image cannot significantly affect signal strength at any area of interest in environment model 300. By comparing the power of the selected transmitter image with the root node power in the receive tree, the power of the selected transmitter image is effectively compared with each area of interest in environment model 300 to determine whether or not its power is high 5 enough to affect at least one of the areas of interest in model 300. By making this power comparison early in the process, and without considering the scope of the selected image, the raytracing problem is quickly terminated when none of the remaining transmitter images can affect a signal characteristic by a significant amount at any area of interest ιo in the environment model.

Once it is determined that the selected transmitter image power exceeds a threshold based on the root node power in the receive tree, the process maps the selected transmitter image in the transmit tree onto the receive area binary tree, calculates and changes the power associated with

15 selected areas of interest, and sets the power associated with each parent node in the receive tree equal to the minimum power associated with that node's descendants, as illustrated at block 216. These steps listed in block 216 may be referred to as mapping the transmitter image onto the receive tree. The process of mapping the transmit image onto the receive

20 tree is illustrated in more detail in FIG. 7.

Referring now to FIG. 7, the mapping process begins at block 218 and thereafter passes to block 220. As illustrated in block 220, the process determines the irradiated scope of the selected image and selects only areas of interest that are irradiated by the selected image. Thus areas of

25 interest behind buildings are not selected. This selecting step is best illustrated with reference to FIG. 9.

FIG. 9 shows environment model 300 with transmitter 302 located near building 304. Buildings 306, 308 and 310 are also shown in environment model 300. If transmitter 302 uses an omni-directional x antenna, the areas of interest affected by a signal that propagates directly from transmitter 302 are shown bound by a polygon 326. Notice how all areas of interest within polygon 326 are in the upper half of environment model 300 because transmitter 302 does not transmit through building 304. In FIG. 9, each area of interest has been shown with a point at its

35 center. In one embodiment, the area of interest is selected if a line may be drawn directly from transmitter 302 to the point in the center of the area of interest. Points in the shadows of buildings are not selected.

Next, from the selected areas of interest in polygon 326, the process selects areas of interest having an associated power that is less than the power of the selected transmitter image by at least a threshold, as depicted at block 222. This further reduces the number of calculations by determining that signal strength calculations should not be performed for areas of interest whose power cannot be affected by more than a threshold, or a predetermined percentage of the existing minimum power, when receiving a signal from the selected transmitter image that has a known maximum power. When the raytracing program is considering signal power propagating directly from the transmitter, this step does not produce any time savings. However, when considering weaker images created as a result of several reflections, and considering them after more powerful images have already been mapped to increase the power associated with certain areas of interest, this step can save a considerable number of calculations. Thus, calculations that cannot add significantly to the amount of signal power received in an area of interest are not performed. The threshold used in this comparison need not be the same as the threshold used in the comparison described in relation to block 212. Thus, if a different threshold is used, it may be referred to as a second threshold.

The second threshold may be selected by the system designer at the time the raytracing program is initiated, or this second threshold may be a calculated threshold that is calculated at some later time during the operation of the raytracing program. A calculated threshold includes a threshold that is a percentage of the power that is already associated with an area of interest.

The process of selecting areas of interest within the scope of the selected transmitter image, and selecting some of these areas of interest that are already associated with a high power level compared to the power 5 level of the selected transmitter image, may be thought of as dividing the areas of interest into two groups — a group that may be referred to as a bypass group and another that may be referred to as a calculate group. Areas of interest in the bypass group are outside the scope of the selected transmitter image, or are already associated with a high power level

10 compared to the level of the selected transmitter image, which means that the effect of the transmitter image on these high power areas is not worth calculating. Areas of interest in the calculate group are ones that may be significantly affected by a signal from the selected transmitter image.

15 Once the calculate group is identified, the process calculates the power of the transmitted signal received at the remaining areas of interest by considering the path losses over the propagation path that is represented by the selected transmitter image, as illustrated at block 224. These path losses include path losses resulting from the signal

20 propagation distance, as well as path losses incurred during reflections and diffractions. Path losses incurred in reflections usually consider the type of material the signal is reflecting off of, and the incident angle at which the propagating signal strikes the panel and leaves the panel.

Once the transmitted signal power that is received at the selected 2 .5 areas of interest has been calculated and added to the appropriate leaf nodes, the receive area data structure is adjusted in response to the these changes in power. As illustrated at block 226, the process sets the power associated with each group node equal to the minimum power of the group node's children, or descendants. In this manner, the lowest power

∞ level associated with any leaf node will be propagated up through branches belonging to intermediate group nodes, all the way to the root node. Thus, the root node represents the lowest power level associated with any leaf in the receive tree.

After the appropriate areas of interest have been modified to reflect

.35 power received from the selected image and the receive tree has been updated, the mapping subroutine returns to the main program, as illustrated at block 228.

Referring again to FIG. 6, after the mapping is complete, the process creates all descendent images of the selected transmitter image in the transmit tree, as depicted at block 232. Such transmitter images are created by identifying panels and diffraction corners illuminated by the selected image.

For example, with reference to FIGS. 10, 11 and 12, transmitter images 336, 338 and 340 are created because signals from transmitter 302 strike panels belonging to buildings 306 and 308, and a diffraction corner on the corner of building 306. These transmitter images may be referred to as first order transmitter images because they are illuminated by rays directly from the transmitter 302. In FIG. 12 only the most powerful diffracted rays — i.e., rays that bend around the diffraction corner — are used to define the scope of the diffraction corner. Also note that this is not a complete set of transmitter images that descend from transmitter 302. For example, another image should be created because of signals directly from transmitter 302 reflect off of a second wall of building 308. Also, the left hand corner of building 306 will also act as a diffraction corner. Once the new transmitter images have been added to the transmitter image tree, the transmitter image tree looks like transmitter image tree 400 in FIG. 13. Transmitter image 402 represents transmitter image 302 in environment model 300. Transmitter image 402 has three descendants, which are shown in FIGS. 10-12 and represented in transmitter image tree 400 by transmitter images 436, 438 and 440.

Transmitter image 442 represents other descendent images not shown in the figures herein. Thus, as indicated by block 230 in FIG. 6, the transmitter image tree grows as descendants of a selected transmitter are added, following the mapping of the selected transmitter image. Once new descendent images have been added to the transmit tree, the process selects from all unmapped transmitter images in the transmit tree the image having the greatest power, or the image having the most influence on signal characteristics associated with areas of interest in the environment model, as illustrated at block 232. In the example shown in these figures, the most powerful image is probably image 336 because it is associated with a panel that is the closest to transmitter 302. Image 336 in environment model 300 corresponds to transmitter image 436 in transmitter image tree 400.

After selecting transmitter image 336, the process iteratively returns to block 212, wherein the process determines whether or not the power associated with the selected image exceeds a threshold power based on the root node power in the receive tree. Presumably the answer to this question will be yes because the power associated with the root node in the receive tree will still be set at the noise floor level because several areas of interest in model 300 were not affected by the power calculations done in relation to the areas of interest selected in FIG. 9. Thus, the process continues to block 216 wherein image 336 is mapped onto the receive area tree.

As image 336 in FIG. 10 is mapped onto the receive area tree, the areas of interest within polygon 344 are selected as candidates for a power calculation. As each of the selected areas of interest in polygon 344 are considered in the mapping subroutine, some selected areas of interest near transmitter 302 will probably not have a power calculation done to determine the power received from image 336 because some of the areas near transmitter 302 may already be associated with a high level of power received directly from transmitter 302.

Because all selected areas of interest in the lower half of environment model 300 did not receive power directly from transmitter 302, these bottom half selected areas of interest will each have signal power calculations done to determine the amount of transmitted signal energy received from selected image 336.

Note that transmitted signal power received from a transmitter image involves calculating signal path losses due to reflections or diffractions, or other losses experienced by the signal along its propagation path. For example, all selected areas of interest in polygon 344 in FIG. 10 receive power from the transmitted signal after it has bounced off of building 306.

After transmitter image 336 has been mapped onto receive tree 314, images that descend from transmitter image 336 are added to transmitter tree 400, so that transmitter tree 400 looks like transmitter image tree 400 depicted in FIG. 14. Note that transmitter image 436 has descendent images 442 and 446. Image 442 is shown in FIG. 15 and results from energy reflecting off of building 310. Transmitter image 446 represents other images that are not shown in the environment model figures herein.

As shown in block 232 of FIG. 6, the process once again selects the most influential image, which in this example is the most powerful image, from the group of all unmapped images. This most influential image becomes the "selected image" for the next pass through the loop beginning at block 212. The process iteratively loops until the answer to the question in block 212 is "No."

As indicated above, aspects of this invention pertain to specific method functions implementable on computer systems. In an alternate embodiment, the invention may be implemented as a computer program product for use with a computer or data processing system. Those skilled in the art should readily appreciate that a program defining the functions of the present invention can be delivered to a computer in many forms, which include, but are not limited to; (1) information permanently stored in non-writable storage media (e.g., read only memory devices such as ROM chips, or CD-ROM discs 154 which are readable by a computer I/O attachment such as CD-ROM reader 150); (2) information alterably stored on writable storage media (e.g., hard disk drives and floppy disks 154); or (3) information conveyed to a computer through communication media, such as a network, the public switched telephone network, a fiber optic cable, and transmitted radio frequency signals. It should be understood, therefore, that such media, when carrying computer readable instructions that direct the method functions of the present invention, represent alternate embodiments of the present invention.

Although the method and system of the present invention has been described with an example that calculates signal strength in a service area, those persons skilled in the art should recognize that other signal characteristics, such as bit error rate, or a signal delay spread, may be calculated.

The method and system of the invention described above accurately and quickly predicts transmitted signal characteristics at a plurality of areas of interest in an environment model of a communications system service area. While viewing or analyzing the output of the present invention, wireless communication system designers are able to provide communications systems that provide quality communications services without the cost of overdesigning the system with excessively overlapping signal coverage between cell sites. Raytracing performed according to the present invention may also expose signal coverage problems, which may then be corrected before customers are annoyed by poor communications services.

The foregoing description of a preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

ClaimsWhat is claimed is:

1. A method for calculating a transmitted signal characteristic at a plurality of areas of interest in an environment model, said method comprising the steps of:

selecting an environment model that locates at least one object in relation to a transmitter that transmits a transmitted signal;

associating a transmitted signal characteristic with each of said plurality of areas of interest in said environment model;

representing a change in direction of said transmitted signal by said at least one object as a transmitter image that transmits an image signal;

dividing said plurality of areas of interest into a calculate group and a bypass group, wherein said bypass group includes areas of interest that cannot be influenced by said image signal by at least a threshold amount; and

calculating signal characteristic contributions by said image signal only for said plurality of areas of interest in said calculate group, wherein unnecessary calculations of said signal characteristic associated with said areas of interest in said bypass group are avoided.

2. The method for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 1 wherein said signal characteristic is signal strength.

3. The method for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 1 wherein said at least one object is a building.

4. The method for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 1 wherein said change in direction of said transmitted signal by said at least one object includes a reflection of said transmitted signal by said at least one object.

5. The method for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 1 wherein said change in direction of said transmitted signal by said at least one object includes a diffraction of said transmitted signal by said at least one object.

6. The method for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 1 wherein said threshold amount is a percentage of said transmitted signal characteristic value associated with each of said selected ones of said plurality of areas of interest.

7. The method for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 2 further including the step of terminating signal characteristic contribution calculations if a most powerful image signal does not exceed power associated with any of said plurality of areas of interest by at least a threshold amount.

8. The method for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 1 further including the steps of:

building a list of transmitter images; and

adding new transmitter images to said list of transmitter images, wherein said new transmitter images are descendants of a most influential transmitter image in a group of transmitter images used in calculating said signal characteristic contributions.

9. A system for calculating a transmitted signal characteristic at a plurality of areas of interest in an environment model comprising:

means for selecting an environment model that locates at least one object in relation to a transmitter that transmits a transmitted signal;

means for associating a transmitted signal characteristic with each of said plurality of areas of interest in said environment model;

means for representing a change in direction of said transmitted signal by said at least one object as a transmitter image that transmits an image signal;

means for dividing said plurality of areas of interest into a calculate group and a bypass group, wherein said bypass group includes areas of interest that cannot be influenced by said image signal by at least a threshold amount; and

means for calculating signal characteristic contributions by said image signal only for said plurality of areas of interest in said calculate group, wherein unnecessary calculations of said signal characteristic associated with said areas of interest in said bypass group are avoided.

10. The system for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 20 wherein said signal characteristic is signal strength.

11. The system for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 20 wherein said at least one object is a building.

12. The system for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 20 wherein said change in direction of said transmitted signal by said at least one object includes a reflection of said transmitted signal by said at least one object.

13. The system for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 20 wherein said change in direction of said transmitted signal by said at least one object includes a diffraction of said transmitted signal by said at least one object.

14. The system for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 20 wherein said threshold amount is a percentage of said transmitted signal characteristic value associated with each of said selected ones of said plurality of areas of interest.

15. The system for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 21 further including means for terminating signal characteristic contribution calculations if a most powerful image signal does not exceed power associated with any of said plurality of areas of interest by at least a threshold amount.

16. A computer program product for calculating a transmitted signal characteristic at a plurality of areas of interest in an environment model comprising:

a computer usable medium having computer readable program code means for selecting an environment model that locates at least one object in relation to a transmitter that transmits a transmitted signal;

a computer usable medium having computer readable program code means for associating a transmitted signal characteristic with each of said plurality of areas of interest in said environment model;

a computer usable medium having computer readable program code means for representing a change in direction of said transmitted signal by said at least one object as a transmitter image that transmits an image signal;

a computer usable medium having computer readable program code means for dividing said plurality of areas of interest into a calculate group and a bypass group, wherein said bypass group includes areas of interest that cannot be influenced by said image signal by at least a threshold amount; and a computer usable medium having computer readable program code means for calculating signal characteristic contributions by said image signal only for said plurality of areas of interest in said calculate group, wherein unnecessary calculations of said signal characteristic associated with said areas of interest in said bypass group are avoided.

17. The computer program product for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 30 wherein said signal characteristic is signal strength.

18. The computer program product for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 30 wherein said at least one object is a building.

19. The computer program product for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 30 wherein said change in direction of said transmitted signal by said at least one object includes a reflection of said transmitted signal by said at least one object.

20. The computer program product for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 30 wherein said change in direction of said transmitted signal by said at least one object includes a diffraction of said transmitted signal by said at least one object.

21. The computer program product for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 30 wherein said threshold amount is a percentage of said transmitted signal characteristic value associated with each of said selected ones of said plurality of areas of interest.

22. The computer program product for calculating a transmitted signal characteristic at a plurality of areas of interest according to claim 31 further including computer usable medium having computer readable program code means for terminating signal characteristic contribution calculations if a most powerful image signal does not exceed power associated with any of said plurality of areas of interest by at least a threshold amount.