Method of mapping into triangles an area of wireless lan and portable device thereof

The invention provides a method of mapping into tessellating triangles an area from a set of sample point spaced over the area. First, each point is connected to every other point to create a group of lines. Then the number of intersections of each line is counted. The line or lines with the greatest number of intersections is removed from the group. The counting and line removal steps are repeated until the group is confined to lines with no intersections, these lines defining triangles. The invention has particular application to the division into triangles of an area served by a wireless LAN, in order to display the variation of a radio signal parameter across the area.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to area mapping and in particular to a method of mapping into triangles an area from a set of sample points spaced over the area.

SUMMARY OF THE INVENTION

The invention arose from the need to represent, as a group of tessellating triangles, an area of a building served by a wireless LAN (local area network). The quality of radio coverage over the area will normally vary, and it is helpful to be able to display this variation on a map of the area, for example on a computer display unit. Interpolation procedures are easier and faster to implement if the area is divided into triangles.

According to the invention there is provided a method of mapping into triangles an area from a set of sample points spaced over the area, comprising:(a) connecting each point to every other point such that a group of lines is created,(b) for each line, counting the number of intersections, if any, of that line with any other line,(c) removing from the group the line, or one of the lines, with the greatest number of intersections, and(d) for the remaining lines, repeating steps (b) and (c) until the group is confined to lines with no intersections, the lines defining the triangles.

Preferably, the method is performed by a portable site survey tool provided with software for performing the method. The portable site survey tool may have a display unit capable of displaying the mapped area.

In the preferred method, the sample points are locations in an area served by a wireless LAN, in which case the portable site survey tool is in radio communication with an access point of the LAN.

The variation of a parameter may be mapped over the area of each triangle to provide a variation of the parameter over the area. The parameter is preferably related to quality of radio communication provided by a wireless LAN serving the area.

According to another aspect of the invention there is provided a portable computer serving as a site survey tool and programmed to carry out the inventive method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

When a building is equipped with a wireless LAN, computers within the building communicate by radio with access points of the LAN, the access points being distributed over the area of radio coverage. InFIG. 1, an access point1of a LAN is connected by hard wiring2to the remainder3of the LAN. At the access point1, there is hardware4, routing or bridging firmware5, a wired LAN card6(hardware) at the interface with the remainder3of the wireless LAN and a LAN card7(hardware) at the radio interface8with portable computers. InFIG. 1, a sample area of a building covered by the wireless LAN is being surveyed, so the access point1is in radio communication with a portable computer in the form of a site survey tool9having software10, a personal computer12including a display unit and a wireless LAN card13(hardware) at the radio interface8. It will be appreciated that this radio interface8provides two-way transmission of data between the site survey tool9and the access point1of the LAN.

By the use of the site survey tool9, the quality of radio coverage over a sample area of the building can be detected and shown as a visual presentation on the display unit of the site survey tool9, and also on a display unit of any other computer linked to the LAN.

Referring toFIGS. 2,3and4, suppose the area of the building to be surveyed is that within the polygonal shape whose outline is indicated at12. The outline shape is defined by straight lines drawn between five sample points, and additional sample points are located within the area. The sample points are shown by the flag symbols inFIGS. 2 to 4. A map of the area to be surveyed is entered into the site survey tool software, typically being loaded into the site survey tool9from another computer linked to the access point1. The locations of the sample points are then loaded into the site survey tool software. The site survey tool is then taken to each sample point in turn and a signal parameter is measured at each sample point.

In the described method, two parameters are measured and recorded, namely signal stability and signal throughput. Stability is representative of the variation of signal throughput from an average throughput. Throughput is representative of the rate of received data and is measured in bits per second. Having detected these parameters at the sample points, the software in the site survey tool is able to provide a visual representation (on the display unit of the site survey tool9) of the variation of each parameter over the sample area. This is done by interpolation, using a gradient fill algorithm. The presentation on the display unit is in color, green being used to show a desirable value of the parameter and red being used to show an undesirable value of the parameter, the display showing variations in intensity of green and red and showing any transition between red and green as a progressive variation in hue.

FIG. 2, which shows the variation of stability over the sample area, shows red areas as dark and green areas as light, the transition being shown as a variation of a grey color.

FIG. 3shows the same area but with the illustrated parameter being throughput, andFIG. 4shows a composite presentation where the combination of throughput and stability is represented, with each of these parameters providing a 50% weighting to the combined presentation.

In order to provide the display shown inFIGS. 2 to 4, the sample area is first divided into a group of tessellating triangles, and the invention lies in the way in which the sample area is so divided. Considering the simplified rectangular sample are shown inFIG. 5, a number of sample points, distributed over the area are chosen and the locations of these sample points are fed into the site survey tool9, as indicated at15inFIG. 8. The site survey tool software is then operative to connect every sample point with every other sample point to create, in a list, a group of m lines. This is indicated pictorially inFIG. 6and by the step indicated at16inFIG. 8. Of the m lines, some will have no intersections, some may have only one intersection and some may have multiple intersections with other lines. For each line of the group of m lines, the number of intersections are counted (step17inFIG. 9) and the line with the largest number of intersections is discarded from the group, as indicated at18inFIG. 8. If more than one line has the greatest number of intersections, one of the lines with this greatest number of intersections is discarded. After step18, a decision (step19) is taken as to whether any intersection remains. If there is a remaining intersection (branch20inFIG. 8) steps17and18are repeated until the result of decision19is that no intersection remains. Each individual triangle is then identified by finding, for each line, two further lines connecting the ends of the line to a common third point so that the remaining lines define the tessellating triangle, as indicated pictorially inFIG. 7and by bock23inFIG. 8. Having divided the sample area up into the pattern of tessellating triangles as shown inFIG. 7, the sequence of logic steps terminates, as indicated at24inFIG. 8.

Having divided the sample area up into tessellating triangles, the variation of throughput or stability is mapped over the area of each triangle by a gradient fill routine (which may be linear, logarithmic or any chosen variation), to provide the visual variation of the parameter over the complete area, in the way previously described with reference toFIGS. 2 to 4.