KR20130063756A - Management method of scanning period based on speed of mobile node in wireless networks - Google Patents

Abstract

PURPOSE: A searching period management method of a portable terminal in a wireless network is provided to reduce the number of messages and enable a node to save energy. CONSTITUTION: A speed calculation unit(150) measures the moving speed of a portable terminal using the reception signal strength of a beacon signal. A search period determination unit(160) determines an AP(Access Point) searching period based on the moving speed. The speed calculation unit determines the ranking of the APs according to the strength of the reception signal. The speed calculation unit determines an AP which has the most changed reception signal strength of a beacon signal which is periodically received from each of the AP. The speed calculation unit calculates the moving speed of the mobile terminal using the strength of the reception signal of the large AP which has the strength of the reception signal conversion amount of the beacon signal. [Reference numerals] (110) Control unit; (120) Memory; (130) RF processing unit; (140) Base band processing unit; (150) Speed calculation unit; (160) Search period determination unit

Description

Management method of scanning period based on speed of mobile terminal in wireless network

The present invention relates to a handover of a wireless local area network (WLAN) based on IEEE 802.11, and more particularly, to a method for searching for an access point.

Recently, due to the spread of smart phones, it is necessary to increase the technology of the wireless local area network (WLAN) based on the IEEE 802.11 standard. Wherever people move, WLANs are being built, and various applications are being built on top of them.

In particular, applications such as Voice Over IP (VoIP) must provide services seamlessly while the user is moving. However, the current IEEE802.11 handoff procedure does not guarantee QoS due to latency. 90% of the handoff delay occurs during the discovery process. Therefore, to support seamless handoff, a technique for reducing search delay time is required. This method is a technique for proactively searching for a target access point (AP) to be handed off before a handoff occurs. In the pre-search method, the search is performed every second, causing an unnecessary increase in the number of searches. Existing methods do not consider the moving speed of the mobile node. Even if there is no mobility of the mobile node, the search performs unnecessary message transmission and energy of the mobile node. If the user stays in a conference room or other facility or building with a laptop and smartphone, the terminal searches once per second. This consumes unnecessary energy by periodically searching for neighboring APs even if the mobile node is unlikely to deviate from the current AP without considering mobility.

Accordingly, there is a need for an effective search technique that can reduce the number of unnecessary searches according to the speed of the mobile node.

An embodiment of the present invention provides an access point search method.

One embodiment of the present invention provides a method of calculating a moving speed of a mobile terminal.

One embodiment of the present invention provides a mobile terminal capable of providing an effective handover.

An access point search method according to an embodiment of the present invention comprises the steps of: measuring the moving speed of the mobile terminal using the received signal strength of the beacon signal; And determining an access point search period based on the moving speed.

In an embodiment, the measuring of the moving speed of the mobile terminal using the received signal strength of the beacon signal may include: determining M access points in order of receiving signal strength being strong (M is a positive natural number); Determining an access point having the largest change in received signal intensity of the beacon signal periodically transmitted from each of the M access points; The method may further include calculating a moving speed of the mobile terminal using the received signal strength of the access point having the largest change in the received signal strength of the beacon signal.

In one embodiment, the moving speed of the mobile terminal is after receiving the first distance and the first beacon signal corresponding to the received signal strength of the first beacon signal of the access point having the largest change amount of the received signal strength of the beacon signal The difference in the second distance corresponding to the received signal strength of the second beacon signal of the access point having the largest change in the received signal intensity of the beacon signal is divided by the difference in the reception time between the first beacon signal and the second beacon signal. Can be calculated.

The present invention also provides a computer readable recording medium having recorded thereon a program for performing the access point searching method.

로 주어지며, 여기서 V는 이동 단말의 이동속도이고, T가 1보다 작을 때 T는 1로 주어진다.In one embodiment, the search period T is

Where V is the moving speed of the mobile terminal and T is given when T is less than one.

In one embodiment, Tmax may be 10.

According to one or more exemplary embodiments, a method of calculating a moving speed of a mobile terminal includes: periodically receiving a beacon signal; Determining M access points having the largest received signal strength of the periodically received beacon signal; Determining an access point having the largest change amount of received signal strength among the M access points; And calculating the moving speed of the mobile terminal by using the received signal strength of the access point having the largest change amount of the received signal strength.

In one embodiment, the moving speed of the mobile terminal is after receiving the first distance and the first beacon signal corresponding to the received signal strength of the first beacon signal of the access point having the largest change amount of the received signal strength of the beacon signal The difference in the second distance corresponding to the received signal strength of the second beacon signal of the access point having the largest change in the received signal intensity of the beacon signal is divided by the difference in the reception time between the first beacon signal and the second beacon signal. Is calculated.

According to an aspect of the present invention, there is provided a mobile terminal comprising: a speed calculator configured to calculate a moving speed of a mobile terminal using a received signal strength (RSS) of a beacon signal; And a search period determiner configured to determine an access point search period based on the moving speed.

In one embodiment, the speed calculator comprises: a candidate access point determiner for determining M (M is a positive natural number) access points in order of receiving signal strength; A speed measurement access point determination unit for determining an access point having the largest change in the received signal intensity of the beacon signal periodically transmitted from each of the M access points; The apparatus may include a speed calculator configured to calculate a moving speed of the mobile terminal using the received signal strength of the access point having the largest change in the received signal strength of the beacon signal.

로 주어지며, 여기서 V는 이동 단말의 이동속도이고, T가 1보다 작을 때 T는 1로 주어진다.In one embodiment, the search period T is

Where V is the moving speed of the mobile terminal and T is given when T is less than one.

In one embodiment, Tmax may be 10.

According to an embodiment of the present invention, the mobile node can save energy and can reduce the number of messages.

According to an embodiment of the present invention, a seamless VoIP service can be provided.

According to one embodiment of the present invention, the overhead of the search can be minimized to improve the performance of the terminal and increase the battery usage time.

1 is a diagram for explaining a handoff.
2 schematically illustrates a handoff procedure of IEEE 802.11.
3 is a view for explaining the DeuceScan method.
4 is a view for explaining a search method according to an embodiment of the present invention when the speed of the mobile node is high (4a) and when the speed of the mobile node is slow (4b).
5 is a view for explaining a search method according to an embodiment of the present invention.
6 schematically illustrates a mobile terminal according to an embodiment of the present invention.
7 schematically illustrates a speed calculator of a mobile terminal according to an embodiment of the present invention.
Figure 8 shows the ratio (Ratio) of the method and the conventional Deuce method according to an embodiment of the present invention.
9 illustrates a relationship between probe messages according to a moving speed in a method (denoted by idea) and a conventional DeuceScan method (denoted by deuce) according to an embodiment of the present invention.
10 illustrates a relationship between a moving speed and a probe message according to an embodiment of the present invention.
FIG. 11 illustrates a relationship between a moving speed and a probe request in a method (denoted by idea) and a conventional DeuceScan (denoted by deuce) method according to an embodiment of the present invention.

Other advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Unless defined otherwise, all terms (including technical or scientific terms) used herein have the same meaning as commonly accepted by the generic art in the prior art to which this invention belongs. Terms defined by generic dictionaries may be interpreted to have the same meaning as in the related art and / or in the text of this application, and may be conceptualized or overly formalized, even if not expressly defined herein I will not.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention.

In the present specification, the singular form includes plural forms unless otherwise specified in the specification. As used herein, the terms' comprise 'and / or various forms of use of the verb include, for example,' including, '' including, '' including, '' including, Steps, operations, and / or elements do not preclude the presence or addition of one or more other compositions, components, components, steps, operations, and / or components.

On the other hand, the terms '~', '~', '~ block', '~ module', etc. used throughout the present specification may mean a unit for processing at least one function or operation. For example, a hardware component, such as a software, FPGA, or ASIC. However, '~', '~', '~', '~' and 'module' are not limited to software or hardware. '~', '~', '~', '~' And the like may be configured to be in an addressable storage medium or may be configured to reproduce one or more processors. Thus, as an example, '~', '~', '~ block', '~ module', etc. may be configured as software components, object-oriented software components, class components, and task components. Elements, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays And variables. The components and the functions provided within '~', '~', '~ Block', and '~' are divided into smaller number of elements and '~', '~', '~ Block' It can be combined into '~ module' or further separated into '~', '~', '~ block' and '~ module'.

An embodiment of the present invention provides a discovery method for efficient handover in a WLAN environment. For example, an embodiment of the present invention provides a pre-search method for efficient handover of the data link layer (L2).

First, handoff and DeuceScan in a WLAN environment will be described.

Handoff

Handoff in WLAN refers to the process of moving a node's connection from an Old AP to a New AP and is schematically illustrated in FIG. 1.

The 802.11 standard defines a handoff procedure as three steps: scanning, authentication, and reasociation. The discovery step is a process where a node finds a neighboring AP. Send and receive Probe request message and Probe response message. This process is divided into two types: passive scanning and active scanning. A search step will be described with reference to FIG. 2. 2 schematically illustrates a handoff procedure of IEEE 802.11.

First, manual discovery detects the presence of the AP by listening to beacon frames that occur periodically at the AP. This method has the advantage of low overhead, but has the disadvantage of high latency.

There is a second active search to solve the disadvantage of high latency. In active discovery, a node first broadcasts a probe request format, runs a probe timer, and waits for a probe response.

If the probe response is not received within the minimum channel time (MinChannelTime), the mobile station moves to the next channel and performs a search again. If more than one probe response is received within the minimum channel time, the maximum channel time (maxChannelTime) is stopped, the received probe response is processed, and the next channel is moved to search again. After searching all channels, the node selects an AP to connect using information obtained from a beacon frame or probe response. Nodes select APs differently, but they usually select the AP with the highest received signal strength indication (RSSI), because the higher RSSI value means the best performance. .

The authentication phase is a process where a node obtains permission to access an AP. The authentication step is a process in which a node accesses a new New AP from an old AP previously connected. This procedure is used as Inter-Access Point Protocol (IAPP).

DeuceScan

The DeuceScan method will be described with reference to FIG. The DeuceScan method uses a prescan method and provides a handoff method for vehicular networks. It performs partial preliminary exploration, and also caches the information based on geographic and temporal information about previously visited areas.

Each area of the AP and the terminal is divided into triangles, and partial pre-search is performed based on the information stored in the cache when the mobile terminal revisits the corresponding area. When the terminal visits the new region, the neighboring AP information is obtained through the whole channel search. Alpha and beta values increase the success rate of handoffs. Alpha is an additional channel, and DeuceScan basically performs partial prescan for three APs. Beta is used to increase the reliability of partial search.

The performance of DeuceScan is superior to that of SyncScan, which uses handoff and prescan without prior search.

A search method according to an embodiment of the present invention will be described.

Select AP to Manage

The discovery method according to an embodiment of the present invention is a method for supporting an efficient handoff by managing an unnecessary discovery period in a process of pre-discovering an AP to be accessed. Suppose you have a node that uses DeuceScan. The mobile node is moving while managing six APs. Three APs with strong RSSI values are used to compare the information with existing information by drawing a triangle, and the other three APs are used to increase the QoS.

The RSSI value is given by Equation 1 below.

(수식 1)

(Equation 1)

Where G _Tx = transmit antenna gain, G _Rx = receive antenna gain, λ = wavelength,

d = distance between the transmitting and receiving antennas, L = system loss factor (1≥),

P _Tx = transmit power)

Traditional DeuceScan manages these two groups of APs in the same cycle. That is, assuming that the beacon period is one second, six APs are managed once per second. This is not efficient in cycle management. The AP to which the mobile node will connect later will be one of the APs with strong RSSI values. However, the conventional DeuceScan wastes unnecessary time by searching the remaining three APs to guarantee QoS. It also does not consider the speed of the mobile node at all.

Accordingly, the search method according to an embodiment of the present invention considers the moving speed of the mobile node. If the distance between the AP and the distance between the AP and the other AP can be measured at the speed of the mobile node, it is possible to separately manage an AP having a low probability of handoff in the distance.

This will be described in more detail with reference to FIG. 4. 4 is a diagram showing two cases when the speed of the mobile node is high (4a) and when the speed of the mobile node is slow (4b). The mobile node manages the surrounding APs. 4 exemplarily shows management of six APs. In the case of Fig. 4A, the moving speed of the mobile node is high. In this case, all APs will be managed in the same manner as the existing APs. This means that if the moving speed is high, the probability of leaving the transmission radius of the currently connected AP is high. For this reason, the mobile node manages the entire AP to increase the QoS.

In the case of Fig. 4B, the figure shows a case where the moving speed is slow. Although the mobile node manages six APs, it manages only three APs (AP2, AP3, AP5 in the drawing) that have the strongest signal strength and are most likely to be connected later because of the slow moving speed. The search speed of the remaining three APs is selected by measuring the moving speed based on the signal strengths obtained from the three APs.

5 shows a simple example. If the node is fast, the AP advance search is performed in the unit of 1 second as shown in 5 (a). But if you think it's slow

It means that there is little probability of escape from the current AP. As shown in FIG. 5 (b), by performing a prescan skipping one cycle, search execution time of 6, 7, and 9 can be saved. In addition, using the manual search can save energy of the mobile terminal.

Calculate the speed of a mobile node

RSSI value is used to measure the distance between the node and the managed AP. The distance d between the AP and the mobile node may be obtained from Equation 1 described above. When receiving continuous beacon signals from the same AP, it is possible to know the time between successive beacon signals (for example, the beacon transmission period of the AP that periodically transmits the beacon signal), and also to the AP when transmitting the beacon signal. The distance between mobile nodes can be obtained from Equation 1 above. Therefore, the moving speed of the mobile node can be easily obtained.

The speed of the mobile node can be obtained from each of the APs managed by the mobile node. First, M APs are selected in order of the largest RSSI value, for example, three APs having the largest RSSI values (search period calculation). Candidate AP to be used). The largest value of the movement speeds obtained from the candidate APs may be determined as the movement speed of the mobile node. Alternatively, the moving speed obtained from the AP having the largest change in the RSSI value among the candidate APs may be determined as the moving speed of the mobile node for the search period calculation.

On the other hand, when there is only one AP connected to the mobile node, the moving speed of the mobile node obtained using the AP may be determined as the moving speed for calculating the discovery period.

Search frequency setting

An embodiment of the present invention determines the period in consideration of the moving speed of the mobile node. Accordingly, an embodiment of the present invention proposes an algorithm that can differentially distribute speed.

The search period T is obtained by the following formula (2).

(수식 2)

(Equation 2)

In Equation 2, v is a moving speed of the mobile node, and Tmax is a constant. However, when the search period T is less than 1 as a result of the calculation, the search period T is 1. In Equation 2, the corresponding period T can be obtained by substituting the moving speed of the mobile node for v.

The constant Tmax can be the maximum search period that can be tolerated when the mobile node is not moving, for example Tmax = 10.

It uses more detailed cycles from 1 second to 10 seconds, and when there is no mobility, it is more efficient by using a 10-second cycle, and searches can be performed once every 10 seconds, so that higher QoS can be supported than when a handoff occurs later.

<Table 1> below shows the search period according to the moving speed obtained using Equation 2 above.

As shown in Table 1, when the moving speed of the mobile node is less than 0.1 m / sec, the search is performed once every 10 seconds, and as the moving speed increases, the maximum value approaches 1. This is more efficient than DeuceScan's periodic management. In addition, its advantages can be further highlighted in buildings with low mobility or in residential buildings.

6 illustrates a configuration of a mobile terminal 100 according to an embodiment of the present invention having the above-described search function. Referring to FIG. 6, the controller 110 controls the overall operation of the mobile terminal. For example, processing and control of voice communication, data communication, video communication, Internet connection, real-time message transmission, program download and upload, and the like, and in addition to the usual functions, determine the speed of the mobile terminal according to an embodiment of the present invention. It performs a function for controlling for determining a search period.

The memory 120 may include a ROM, a RAM, a flash memory, and the like. The ROM may store microcodes of various programs and various reference data for processing and control of the controller 110. In particular, it is possible to store a program for controlling the moving speed of the mobile node using the AP and thus determining the AP discovery period. The RAM is a working memory of the controller 110 and stores temporary data generated while executing various programs.

The RF unit 130 lowers the frequency of the radio frequency signal received through the antenna to the baseband processor 140, and raises the baseband signal from the baseband processor 140 and transmits the signal through the antenna. The baseband processor 140 processes the baseband signal transmitted and received between the RF unit 130 and the controller 110. For example, in case of transmission, channel coding and spreading of data to be transmitted may be performed, and in case of reception, function of despreading and channel decoding of a received signal may be performed.

The speed calculator 150 calculates the speed of the mobile node based on the received signal strength as described above, and the search period determiner 160 searches for the AP based on the moving speed of the distributed node calculated by the speed calculator 150. Determine the cycle.

7 schematically illustrates a configuration of a speed calculator according to an embodiment of the present invention. Referring to FIG. 7, the speed calculator 150 may include a candidate AP determiner 151, an AP determiner 153 for speed measurement, and a speed calculator 155. The candidate AP determiner 151 determines, as a candidate AP, the top three APs having a large received signal strength when there are several APs managed by the mobile node. The speed measuring AP determiner 153 determines the AP having the largest received signal strength change among the candidate APs or the AP having the largest change in received signal strength among the APs as the speed measuring AP. The speed calculator 155 calculates the speed of the mobile terminal using the speed measuring AP.

Compare effects

When the transmission range of the AP is 30m, the number of probe message transmissions according to the moving speed is compared and summarized in <Table 2> below.

According to one embodiment of the present invention, as shown in Table 2, the number of searching, that is, generating a probe message is 60 times when moving to 0.1 m / sec. In contrast, in the case of the conventional DeuceScan, 600 scans are performed. The difference in probe messages is 1080. When the moving speed is increased to 1.1 m / sec, according to an embodiment of the present invention, the number of searches occurs 54 times, and the same DeuceScan occurs 54 times. This means that the same performance as the DeuceScan method can be achieved at high speeds. At slower speeds, the difference is noticeable, no probe messages are generated, and data rates can be increased.

Figure 8 shows the ratio (Ratio) of the method and the conventional Deuce method according to an embodiment of the present invention. When the speed is 1.0m / sec, the same ratio of 100% can be seen. This can be said to have the same performance as Deuce above 1.0m / sec.

When it is calculated that it is out of the transmission range of 30m, the difference of the probe message is shown in FIG. As can be seen in the graph of Fig. 9,

The speed is remarkable difference, but the same performance is shown for speeds of 1.0 m / sec or more.

As shown in FIG. 10, it can be seen that a large gain can be obtained even when the speed is slow even in the difference between probe messages.

simulation

Evaluation of the method according to an embodiment of the present invention was performed using NS-2. It is aimed at people walking in IEEE802.11 WLAN environment. The 802.11 standard, DeuceScan method is compared with the method of the present invention. The node is an environment in which the node moves from the origin (0,0) to the destination (400,400). <Table 3> below shows the environment.

11 shows the simulation results. When the speed is 0.1m / sec, the number of probe packets is close to 100, but as the speed increases, it shows the same performance as the DeuceScan method. In other words, it means that if you are slow, you can benefit a lot.

In an embodiment of the present invention, for example, to solve a problem of L2 handover, the UE performs pre-search according to speed. The terminal detects the presence of the AP and the period of the beacon message periodically transmitted by the AP after searching all channels using the active search technique. The terminal maintains the latest information through the beacon message and defines the order of neighboring APs based on the RSSI value in the beacon message. In addition, the movement speed of the AP is measured based on the RSSI value and reflected in the period selection of the next discovery process of the terminal. Classes are managed in terms of the moving speed. After measuring the moving speed, the next cycle is selected according to the class.

According to an embodiment of the present invention, efficient handoff is performed at the second layer of the WLAN.

Shows search cycle management by speed. Handoff is an important factor for seamless VoIP service and real-time streaming service of mobile users. Handoff

The delay rate should be within 50ms. However, the 802.11 standard does not guarantee QoS. The present invention can reduce the waste of unnecessary periods by managing the search period according to the speed. We also use NS-2 to perform a performance analysis of the existing and proposed approaches.

Respectively. The proposed scheme reduces handoff delay rate and traffic, and the node can save energy. This method reduces the handoff delay rate or the number of probe packets compared to the previous method. For this reason, the proposed method is effective in managing cycles and saving energy when compared to other methods.

Claims (13)

In the access point search method,
Measuring a moving speed of the mobile terminal using the received signal strength of the beacon signal; And,
And determining an access point search period based on the moving speed. The method according to claim 1,
Measuring the moving speed of the mobile terminal using the received signal strength of the beacon signal:
Determining M access points in order of receiving signal strength being strong (M is a positive natural number);
Determining an access point having the largest change in received signal intensity of the beacon signal periodically transmitted from each of the M access points; And,
And calculating a moving speed of the mobile terminal using the received signal strength of the access point having the largest change in the received signal strength of the beacon signal. The method according to claim 2,
The moving speed of the mobile terminal,
The change in the received signal strength of the beacon signal has the largest change in the received signal strength of the beacon signal received after receiving the first beacon signal and the first distance corresponding to the received signal strength of the first beacon signal of the access point having the largest change. And calculating a difference of a second distance corresponding to a received signal strength of a second beacon signal of an access point by dividing a difference in a reception time between the first beacon signal and the second beacon signal. The method according to claim 1,
Measuring the moving speed of the mobile terminal using the received signal strength of the beacon signal:
The difference between the first distance corresponding to the received signal strength of the first beacon signal received from the access point and the second distance corresponding to the received signal strength of the second beacon signal received to the access point after receiving the first beacon signal And calculating by dividing by a difference in reception time between the first beacon signal and the second beacon signal. The computer-readable recording medium which recorded the program which performs the method of any one of Claims 1-4. The method according to any one of claims 1 to 4,
The search period T is

Where V is the moving speed of the mobile terminal and T is 1 when T is less than 1. 7. The method of claim 6, wherein Tmax is 10. Periodically receiving a beacon signal;
Determining M access points having the largest received signal strength of the periodically received beacon signal;
Determining an access point having the largest change amount of received signal strength among the M access points; And,
And calculating a moving speed of the mobile terminal using the received signal strength of the access point having the largest change in the received signal strength. The method according to claim 8,
The moving speed of the mobile terminal,
The change in the received signal strength of the beacon signal has the largest change in the received signal strength of the beacon signal received after receiving the first beacon signal and the first distance corresponding to the received signal strength of the first beacon signal of the access point having the largest change. And calculating a difference of a second distance corresponding to a received signal strength of a second beacon signal of an access point by dividing a difference of a reception time between the first beacon signal and the second beacon signal. A speed calculator configured to calculate a moving speed of the mobile terminal using the received signal strength of the beacon signal; And,
And a search period determiner configured to determine an access point search period based on the moving speed. The method of claim 10,
The speed calculating unit:
A candidate access point determination unit for determining M (M is a positive natural number) access points in order of receiving signal strength;
A speed measurement access point determination unit for determining an access point having the largest change in the received signal intensity of the beacon signal periodically transmitted from each of the M access points; And,
And a speed calculator configured to calculate a moving speed of the mobile terminal using the received signal strength of the access point having the largest change in the received signal strength of the beacon signal. The method according to claim 10 or 11,
The search period T is

Where V is the moving speed of the mobile terminal and T is given as 1 when T is less than 1. The method of claim 12,
Tmax is a mobile terminal of 10.

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