KR100776824B1 - Method for searching nearest-neighbor in wireless broadcast environment, recording medium thereof, apparatus for searching nearest-neighbor in wireless broadcast environment and system thereof - Google Patents

Abstract

A nearest neighbor query searching method in a wireless broadcasting environment, a recording medium, an apparatus and a system thereof are provided to enable any kind of communication device to search for the nearest neighbor effectively and efficiently wherein the communication device has a limited resource. A nearest neighbor query searching method in a wireless broadcasting environment comprises the following several steps. A client receives a broadcast packet regarding a query generated within a lattice cell of the Voronoi Diagram(610). The client calculates an object distance between a coordinate of an object and a coordinate where a query occurs according to a sequence of objects included in the packet and updates the object distance with the minimum distance(620-640). If the distance between a coordinate of the next object included in the packet and a criterion axis on the Voronoi diagram is larger than the minimum distance, the client sets the object, matched with the minimum distance, as the nearest neighbor(650,660).

Description

{Method for searching nearest-neighbor in wireless broadcast environment, recording medium}, Apparatus for searching nearest-neighbor in wireless broadcast environment and System

1 illustrates a structure of a conventional grid-partition index.

2 shows a structure of packets broadcast in a grid cell to which the present invention is applied.

3 is a block diagram of an apparatus for searching for a nearest point query in a wireless broadcasting environment according to the present invention.

4 is a structural diagram of a near-point query search system in a wireless broadcasting environment according to the present invention.

5 is a flowchart of a method for searching for a nearest point query in a wireless broadcasting environment according to an embodiment of the present invention.

6 is a flowchart of a method for searching for a nearest point query in a wireless broadcasting environment according to another embodiment of the present invention.

7 illustrates an example of a method for searching for the nearest point (NN) according to the present invention.

8A is a graph showing an access time obtained by applying uniform spatial data to the present invention and the prior art.

8B is a graph showing an access time obtained by applying actual spatial data to the present invention and the prior art.

9A is a graph showing tuning time obtained by applying uniform spatial data to the present invention and the prior art.

9B is a graph showing the tuning time obtained by applying the actual spatial data to the present invention and the prior art.

10 is a view showing the access time obtained according to the present invention and the prior art according to the size of the data.

11 is a diagram illustrating tuning time obtained through the present invention and the prior art according to the size of data.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to the search for a nearest point (NN) in a broadcast environment, and more particularly, to a method for searching for a nearest point query in a wireless broadcast environment, a recording medium, an apparatus for searching for a nearest point query in a wireless broadcast environment and a system thereof.

Recent contact (NN) queries are being studied as one of the most important queries in location-based services. The wireless broadcasting method has been in the spotlight in terms of the efficient use of insufficient bandwidth and the scalability of supporting all users listening to the channel, and many indexing methods for efficiently and efficiently performing the nearest point (NN) query have been studied in the wireless broadcasting environment. do.

There are many indexes for performing the nearest point (NN) search in a wireless broadcast environment. Indexing method in a wireless broadcasting environment requires a different index than the conventional on-demand method. That is, in the conventional on-demand method, when a user requests spatial information from a server, the server searches through an index in a spatial database, but in a wireless broadcasting environment, searches through an index in a broadcast channel. Therefore, a new index is required because backtracking is not possible, which was possible in the on-demand method. As such an index, an R-tree, a D-tree, and a grid-partition index using sequential search have been proposed.

1 illustrates a structure of a grid-partition index.

The grid-partition index calculates the nearest point NN in advance using a Voronoi diagram and indexes the space to be indexed. The grid-partition index divides the precomputed space into grids according to certain rules and then indexes only those objects that are likely to be the nearest point (NN) within the grid.

The grid-partition index measures and compares distances from query points for objects in the grid when searching for the nearest point NN in the grid. When the object and the query point in the object are the same as in FIG. 1, the search process is shown in Table 1 below.

step Object dis_sd cur_dis min_dis One O4 0.2 1.5 1.5 2 O5 One 1.8 1.5 3 O3 1.2 1.7 1.5 4 O2 2.5 stop ·

The search for the nearest point NN is performed as follows. First, each object is aligned about one axis. The sorted order is O ₁ , O ₂ , O ₃ , O ₄ , O ₅ . When the query is executed and the grid for the query is determined, the distance (dis_sd) from the axis aligned with the grid in the grid is searched for the objects in order, and the distance to the query point (cur_dis) is measured. Find the object with distance (min_dis). At this time, these objects should be read and stored as two lists to search for objects in the grid. If dis_sd is larger than min_dis, the object with the current minimum distance becomes NN, so the search stops. Through this search method, the nearest point (NN) search can be performed without searching all objects.

In the conventional grid-partition index, the search is performed in the order of objects having a close distance to one axis based on the query point, and it is assumed that there is sufficient memory of the client.

Therefore, in the conventional near-point query search method, when the mobile client has limited memory, all information in the grid cannot be stored, so that the search for the closest point (NN) cannot be performed, the access time and tuning time are long, and the use of energy is reduced. There is a problem that is not efficient.

In order to solve the above problems, the first technical problem to be solved by the present invention is to smoothly perform the nearest point (NN) search, reduce the access time and tuning time, and use energy efficiently even if the mobile client has limited memory. The present invention provides a method for searching for a nearest-point query in a wireless broadcasting environment.

A second technical object of the present invention is to provide a computer-readable recording medium having recorded thereon a program for executing a near-point query search method in a wireless broadcasting environment.

The third technical problem to be solved by the present invention is that the mobile station has a limited memory to perform the nearest point (NN) search smoothly, reduce the access time and tuning time, and use the energy efficiently in the near point in the wireless broadcast environment To provide a query search device.

A fourth technical object of the present invention is to provide a near-contact query search system in a wireless broadcast environment including a client and a server including a near-point query search device in the wireless broadcast environment.

In order to achieve the first technical problem, the present invention, in a wireless broadcast environment comprising a server for broadcasting a packet (packet) and the client receiving the packet, in the nearest-contact query searching method executed by the client, Receiving a broadcasted packet for a query occurring in any grid cell of the Voronoi diagram, the object distance, which is the distance between the coordinates of the object and the coordinates from which the query was generated, in the order of the objects contained in the packet. During the operation of updating the minimum distance to the smallest object distance and calculating the object distance, the distance between the coordinates of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is the minimum. If greater than a distance, setting an object corresponding to the minimum distance to the nearest point; The recent offer quality contacts how to navigate in line broadcast environment.

In order to achieve the above second technical problem, the present invention provides a computer-readable recording medium having recorded thereon a program for executing a near-contact query searching method in a wireless broadcasting environment.

In order to achieve the third technical problem, the present invention relates to a packet receiver for receiving a broadcast packet, and a coordinate of the object in order of an object included in the packet, for a query generated in one lattice cell of the Voronoi diagram. An object distance calculator configured to calculate an object distance which is a distance from the coordinates at which the query is generated, a minimum distance setter configured to update a minimum distance to an object distance having the smallest size in a calculation process of the object distance calculator, and included in the packet If the distance between the coordinates of the next object and a predetermined reference axis on the Voronoi diagram is greater than the minimum distance, the nearest point query in a wireless broadcast environment including a closest point setting unit for setting the object corresponding to the minimum distance to the nearest point Provide a navigation device.

In order to achieve the fourth technical problem, the present invention provides a wireless broadcasting system including a server and a client, wherein the server stores the nearest point information in advance in spatial information by using a Voronoi diagram, and specifies the closest point information. A packet receiver configured to generate an index divided into grids according to a rule of the present invention, wherein the client reads the index from a wireless broadcast channel and receives a broadcasted packet for a query generated in the grid cell according to the index; An object distance calculating unit that calculates an object distance, which is a distance between coordinates of the object and coordinates in which the query is generated, in order of objects included, and updating the minimum distance to the smallest object distance in the calculation process of the object distance calculating unit A minimum distance setting unit and coordinates of the next object included in the packet and the Voronoi Following the distance between on the gram predetermined reference axis is greater than the minimum distance, provided the closest point search query system in a wireless broadcast environment in recent years it includes the contact setting portion for setting an object corresponding to the minimum distance to the closest point.

The present invention provides an energy and memory efficient nearest point (NN) search algorithm considering limited resources of a mobile client in a mobile broadcasting environment.

The present invention uses the index used in the grid-partition index based on the grid-partition index to change the nearest point (NN) search method to a memory-efficient method.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the present invention. However, embodiments of the present invention illustrated below may be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below.

2 shows a structure of packets broadcast in a grid cell to which the present invention is applied.

As shown in FIG. 2, the lattice G ₂ is associated with O ₁ , O ₂ , O ₃ , O ₄ and O ₅ , so that these objects are composed of sub-indexes. In the present invention, as shown in FIG. 2, the nearest point query is searched using objects (eg, O ₁ , O ₂ , O ₃ , O _4, etc.) included in the packet.

In the present invention, since the objects are sequentially searched according to the order of broadcasting on the channel, even limited memory can be sufficiently performed. A search example of this method is shown in Table 2 below.

step Object dis_sd cur_dis min_dis One O ₁ -3.5 3.7 3.7 2 O ₂ -2.5 2.7 2.7 3 O ₃ -1.2 1.7 1.7 4 O ₄ -0.2 1.5 1.5 5 O ₅ -One 1.8 1.5

In this case, (-) indicates that the position of the object is located on the left side of the y axis compared to the query point.

In Table 2 above, objects are searched according to the broadcast packet order. There are three packets in the grid G _{2 where the} current query point is located, and the broadcast order of these packets is P ₁ , P ₂ , and P ₃ . The search proceeds to the object order (O ₁ , O ₂ , O ₃ , O ₄ , O ₅ ) in each packet. The search stops performing when the distance between the object and the predetermined reference axis is greater than the current minimum distance (dis_sd> min_dis). In this case, the object having the current minimum distance is set as the nearest point NN.

In this case, the distance used may be calculated as the Euclidean distance.

과

이 있다고 할 때, 다음과 같이 유클리디안 거리(Euclidean distance)가 정의된다.n row vectors

and

Given this, the Euclidean distance is defined as

For example, for three-dimensional space, n = 3.

3 is a block diagram of an apparatus for searching for a nearest point query in a wireless broadcasting environment according to the present invention.

The packet receiver 310 receives a broadcasted packet with respect to an inquiry generated in one grid cell of the Voronoi diagram. Preferably, the packet receiver 310 may receive the next packet that is broadcast when all packets are not received in the grid cell.

The object distance calculator 320 calculates an object distance which is a distance between the coordinates of the object and the coordinates at which the query is generated in the order of the objects included in the received packet. Preferably, the object distance may be obtained as an Euclidean distance between the coordinates of the object and the coordinates at which the query is generated.

The minimum distance setting unit 330 updates the minimum distance to the smallest object distance in the calculation process of the object distance calculating unit 320.

The nearest point setting unit 340 sets the object corresponding to the current minimum distance as the nearest point if the distance between the coordinates of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is greater than the current minimum distance. do. Preferably, the predetermined reference axis may be either the x-axis or the y-axis that passes through the coordinate where the query occurred in the two-dimensional coordinate space. Preferably, the closest point setting unit 340 may set the object corresponding to the current minimum distance as the closest point when all packets in the grid cell are received.

4 is a structural diagram of a near-point query search system in a wireless broadcasting environment according to the present invention.

4 is a wireless broadcasting system including a server 450 and a client 400.

The client 400 includes a packet receiver 410, an object distance calculator 420, a minimum distance setter 430, and a nearest point setter 440.

The packet receiver 410 reads the index 451 of the server 450 in the wireless broadcast channel, and receives a broadcast packet for a query generated in the grid cell according to the index. Preferably, the packet receiver 410 may receive the next packet to be broadcast when all packets are not received in the grid cell.

The object distance calculator 420 calculates an object distance which is a distance between the coordinates of the object and the coordinates at which the query is generated in the order of the objects included in the received packet. Preferably, the object distance may be obtained as an Euclidean distance between the coordinates of the object and the coordinates at which the query is generated.

The minimum distance setting unit 430 updates the minimum distance to the smallest object distance in the calculation process of the object distance calculating unit 420.

The nearest point setting unit 440 sets the object corresponding to the current minimum distance as the nearest point if the distance between the coordinates of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is greater than the current minimum distance. . Preferably, the closest point setting unit 440 may set the object corresponding to the current minimum distance as the closest point when all packets in the grid cell are received. The closest contact setting unit 440 may output the information on the set closest contact as a query result.

The server 450 previously stores the nearest point information in the spatial information using the Voronoi diagram, and generates an index 451 in which the closest point information is divided into grids according to a predetermined rule. The wireless transmitter 452 of the server 450 broadcasts the generated index.

5 is a flowchart of a method for searching for a nearest point query in a wireless broadcasting environment according to an embodiment of the present invention.

First, in response to a query occurring in one grid cell of the Voronoi diagram, a broadcast packet is received (step 510).

When the packet is received, the minimum distance is determined by calculating the minimum distance by calculating the coordinates of the object in the order of the objects included in the received packet and the distance of the query, that is, the distance of the query. Update to a distance (steps 530-540). Preferably, the object distance may be calculated as the Euclidean distance between the coordinates of the object and the coordinates from which the query is generated. That is, when the currently calculated object distance is smaller than the previously set minimum distance (step 530), the value of the minimum distance is set as the currently calculated object distance (step 540).

In operation 550, it is determined whether a distance between the coordinate of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is greater than the current minimum distance. Preferably, in this step (550), the predetermined reference axis may be either the x-axis or the y-axis passing through the coordinate where the query was generated in the two-dimensional coordinate space.

At this time, if the distance between the coordinates of the next object included in the packet and the predetermined reference axis on the Voronoi diagram is greater than the current minimum distance, the object corresponding to the current minimum distance is set as the nearest point (step 560).

On the other hand, if the distance between the coordinates of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is not greater than the current minimum distance, the object distance operation is performed on the next object (steps 550 and 520).

6 is a flowchart of a method for searching for a nearest point query in a wireless broadcasting environment according to another embodiment of the present invention.

First, in response to a query occurring in one grid cell of the Voronoi diagram, a broadcasted packet is received (step 610).

When the packet is received, the minimum distance is determined by calculating the minimum distance by calculating the coordinates of the object in the order of the objects included in the received packet, and the object distance that is the coordinate where the query is generated, that is, the distance from the query point (step 620). Update to distance (steps 630-640).

In operation 650, it is determined whether the distance between the coordinate of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is greater than the current minimum distance.

At this time, if the distance between the coordinates of the next object included in the packet and the predetermined reference axis on the Voronoi diagram is greater than the current minimum distance (step 650), it is determined whether all packets in the grid cell have been received (step 655). On the other hand, if the distance between the coordinates of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is not greater than the current minimum distance, the object distance operation is performed on the next object (steps 650 and 620).

In this case, when all packets in the grid cell are received (step 655), an object corresponding to the current minimum distance is set as the nearest point (step 660).

On the other hand, if all packets in the grid cell have not been received (step 655), the next packet is received (step 610).

7 illustrates an example of a method for searching for the nearest point (NN) according to the present invention.

The algorithm of FIG. 7 obtains an object associated with a grid cell and compares the distance between these objects and a query point to find the nearest point NN. In the algorithm of FIG. 7, the input is the coordinate p (x, y) of the query point and the output is a pointer ptr to the data object.

The algorithm starts by pointing to the grid cell containing the query point (line 1). In order to initialize the current shortest distance, that is, the minimum distance min_dis, is set to infinity (line 2). The algorithm repeats the interval (lines 4-16) receiving packets in the order in which they are broadcast on the channel within the grid cell until the nearest point NN is found.

During each iteration, we read the object from the packet and compute the distance between the query point and the object, that is, the object distance (cur_dis) (lines 5-8). The minimum distance min_dis is updated when the current entity distance cur_dis <minimum distance min_dis (lines 13-16).

This process stops running if the distance (dis_sd)> minimum distance (min_dis) between the next object and the predetermined reference axis (line 9-12).

In addition, this process can be set to stop performing when all packets in a grid cell have been read.

Experimental measurements through performance evaluation of the present invention are shown through FIGS. 8A-11. The performance evaluation assumes that the mobile client has limited memory, and compares the R-tree and grid-partition index with the present invention.

R-tree and grid partition index (grid-partition index) are the same as the conventional method to apply to the client environment of limited resources, but modified to be performed in a limited environment.

The modified R-tree and the grid-partition index are represented by the prior art 1 (BASE in R-tree) and the prior art 2 (BASE in FP), respectively.

The two key performance measurement factors for indexing techniques in the broadcast method are access time, which is the time to obtain the result value, and tuning time, which is the time when the user consumes power in the active mode. Measured.

The data set used contains 5922 objects each, using uniform data with uniform distribution and Skewed Data, the location of Greek cities and towns on the R-tree portal website. It was.

8A is a graph showing an access time obtained by applying uniform spatial data (uniform data) to the present invention and the prior art.

8B is a graph showing an access time obtained by applying actual spatial data (skew data) to the present invention and the prior art.

As shown in Figures 8A and 8B, the present invention exhibits shorter access times than the two conventional methods. This is because the two conventional methods cannot collect enough information in a memory-limited situation, and thus the access time is increased due to a situation in which necessary information is read again in the next broadcasting cycle. On the contrary, the present invention stores only the coordinates of the nearest point NN computed immediately upon reading and shows good performance even in an extremely limited environment.

9A is a graph showing tuning time obtained by applying uniform spatial data (uniform data) to the present invention and the prior art.

9B is a graph showing tuning time obtained by applying actual spatial data (skew data) to the present invention and the prior art.

The tuning time is the longest in the prior art 1 (BASE in R-tree), and the remaining two methods show almost the same performance. The performance of the prior art 1 (BASE in R-tree) is the worst because the sequential search in the R-tree to read packets that do not need to read. In addition, the present invention seems to have to read more packets at first glance compared to the conventional grid-partition index method, but in reality, the present invention only needs to read information in the grid cell once. In the method of the grid-partition index of the prior art 2, it is necessary to repeat reading in the next cycle, so the performance of the two cases is almost the same.

10 is a view showing the access time obtained according to the present invention and the prior art according to the size of the data.

10 also shows a short access time when the present invention is compared with the other two methods (prior art 1, 2).

11 is a diagram illustrating tuning time obtained through the present invention and the prior art according to the size of data.

What is unique about the present invention is that the tuning time is increased when the size of data increases.

It can be seen that the performance is much improved compared to the prior art 2 (grid-partition index method). This is because the conventional grid-partition index method reads more objects because more objects need to be read in the next cycle as data increases.

Table 3 below is a table comparing the amount of memory of the client used in the present invention and the prior art.

Way Memory capacity Prior Art 2 (grid partition index) Information of all objects in grid cell (number of all objects in grid cell * 6 bytes) The present invention One pointer to one coordinate and minimum distance (ie 6 bytes)

Referring to Table 3, the conventional grid-partition index requires a lot of memory to the client by storing the information of the objects in the grid, while the present invention requires the information of the current nearest point (coordinates, pointers). Saves only) and asks the client for the right amount of memory.

Preferably, in the wireless broadcasting environment of the present invention, a program for executing the nearest-contact query searching method on a computer may be recorded and provided on a computer-readable recording medium.

The invention can be implemented via software. When implemented in software, the constituent means of the present invention are code segments that perform the necessary work. The program or code segments may be stored on a processor readable medium or transmitted by a computer data signal coupled with a carrier on a transmission medium or network.

The computer-readable recording medium includes all kinds of recording devices in which data is stored which can be read by a computer system. Examples of computer-readable recording devices include ROM, RAM, CD-ROM, DVD ± ROM, DVD-RAM, magnetic tape, floppy disks, hard disks, optical data storage devices, and the like. The computer readable recording medium can also be distributed over network coupled computer devices so that the computer readable code is stored and executed in a distributed fashion.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those of ordinary skill in the art that various modifications and variations can be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, according to the present invention, even if the mobile client has limited memory, it is possible to smoothly perform the nearest point (NN) search, reduce the access time and tuning time, efficiently use energy, and have limited resources. Any type of communication device that is present has the effect of effectively and efficiently searching for the nearest point.

Claims (10)

In a wireless broadcasting environment including a server for broadcasting a packet and a client for receiving the packet, the method for searching for the nearest-contact query executed by the client, Receiving a packet that is broadcast, for a query occurring in any grid cell of the Voronoi diagram; Updating the minimum distance to the smallest object distance while calculating an object distance, which is a distance between the coordinates of the object and the coordinates at which the query is generated, in the order of the objects included in the packet; And In the operation of calculating the object distance, if the distance between the coordinates of the next object included in the packet and a predetermined reference axis on the Voronoi diagram is greater than the minimum distance, the object corresponding to the minimum distance is set to the nearest point. A method for searching for a nearest point query in a wireless broadcasting environment comprising the steps of: The method of claim 1, The object distance is And a Euclidean distance between the coordinates of the object and the coordinates at which the query is generated. The method of claim 1, Setting to the nearest point is Setting an object corresponding to the minimum distance to the nearest point when all packets are received in the grid cell, and receiving the next packet that is broadcast when all packets are not received in the grid cell. Near-point query search method in a wireless broadcasting environment. The method of claim 1, Setting to the nearest point is And the predetermined reference axis is either one of an x-axis and a y-axis that pass through the coordinates at which the query is generated in a two-dimensional coordinate space. A computer-readable recording medium having recorded thereon a program for executing the method of any one of claims 1 to 4. A packet receiver for receiving a broadcast packet for a query generated in one grid cell of the Voronoi diagram; An object distance calculator configured to calculate an object distance which is a distance between the coordinates of the object and the coordinates at which the query is generated in the order of the objects included in the packet; A minimum distance setting unit updating the minimum distance to an object distance having the smallest size in the calculation process of the object distance calculating unit; And And a closest point setting unit configured to set an object corresponding to the minimum distance as the nearest point if the distance between the coordinates of a next object included in the packet and a predetermined reference axis on the Voronoi diagram is greater than the minimum distance. Near-point query navigation device in the environment. The method of claim 6, The object distance is And a Euclidean distance between the coordinates of the object and the coordinates at which the query is generated. The method of claim 6, The packet receiving unit If not receiving all packets in the grid cell, receives the next packet to be broadcast, The closest contact setting unit The apparatus of claim 1, wherein, when all packets are received in the grid cell, an object corresponding to the minimum distance is set as the nearest point. The method of claim 6, The closest contact setting unit And the predetermined reference axis is any one of an x-axis or a y-axis that passes through the coordinate where the query is generated in the two-dimensional coordinate space. In the wireless broadcasting system comprising a server and a client, The server is Using the Voronoi diagram, the nearest contact information is stored in advance in the spatial information, and the index generated by dividing the nearest contact information into a grid according to a predetermined rule is generated. The client is A packet receiver which reads the index from a wireless broadcast channel and receives a broadcasted packet for a query generated in the grid cell according to the index; An object distance calculator configured to calculate an object distance which is a distance between the coordinates of the object and the coordinates at which the query is generated in the order of the objects included in the packet; A minimum distance setting unit updating a minimum distance to an object distance having a smallest size in a calculation process of the object distance calculating unit; And And a closest point setting unit configured to set an object corresponding to the minimum distance as the nearest point if the distance between the coordinates of a next object included in the packet and a predetermined reference axis on the Voronoi diagram is greater than the minimum distance. Near-point query search system in the environment.

Images