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All Rights Reserved, Copyright © 2015 Osaka Institute of Technology

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Construction of a Wireless Ad-Hoc network using

an Autonomous Mobile Robot

Ubiquitous Network System Lab.

Yuki Yamazoe, Satoshi Nakajima, Susumu Matsui*

Osaka Institute of Technology

2 All Rights Reserved, Copyright © 2015 Osaka Institute of Technology

Background and System Configuration

Ø  In the time of an disaster, there are needs of a monitoring the dangerous or a pollution area where a person can't enter.

Ø  Instead of a person, a mobile robot enter such area, and it’s possible to collect much information.

Ø  It is expected that a wireless network infrastructure can’t be used at such area, so we consider the system to connect a mobile robot and monitoring center by ad-hoc network.


Dangerous or polluted area

Mobile Robot

Wireless network infrastructure

Ad-Hoc Network

Moving Control

Collect much informationMonitoring Center


Issues

Ø  In the case that the distance between the monitoring center and the mobile robot is far away, or the mobile robot enter a building, the mobile robot can’t communicate to the monitoring center directly.

Ø  So we construct the multi-hop environment by some relay robots.


Dangerous or polluted area

Mobile Robot

Multi-Hop

Monitoring Center Relay Robot

Ø  Moving control of the mobile robot (head robot) is performed from the monitoring center, but it's difficult to do moving control of the relay robot from the monitoring center.

Ø  We consider autonomous moving control method of the relay robot.


The assumption about the topography

Ø  The various topography and structure were considered in a disaster area or in a building, for example some obstacles, corners, steps, but as first step of our research we consider a flat plane where there are no obstacles, corners, steps.


Head RobotMonitoring Center

Relay Robot

The area with some obstacles, corners, steps

The area with no obstacles, no corners, no steps

Monitoring CenterRelay Robot

Head Robot

Corner

Obstacle

StepFlat plane


Autonomous moving control method

Ø We introduce a autonomous moving control method using RSSI. Ø Control the position of the relay robot as it stay at the area that the

RSSI value is in the range(greater than Threshold_min and less than Threshold_max).


RSSI

RSSI Received Signal Strength Indicator

Distance

Threshold_Max

Threshold_Min

Stay at this area

Head RobotRelay Robot

Threshold range

Too nearToo far


Autonomous moving control method by RSSIØ  There is relay robot pool near the monitoring center. Ø  A relay robot measures the RSSI between the robots, and when it'll be below the

Threshold_min, begins to move. Ø  To exchange position information between the robots, the relay robot determine the moving

direction of itself. Ø  The relay robot stay at an area that the RSSI is in the range.


Pool of relay robot

Threshold_min < RSSI RSSI < Threshold_min

Moving

By more than one relay robots moving in sequence, the multihop connection is maintained

Head Robot

Head Robot

Relay Robot

Threshold_min < RSSI < Threshold_max

RSSI < Threshold_min

RSSI < Threshold_min

Position information


RSSI vs. Throughput

Item Specification

Protocol UDP/TCP

Measurement tool NetPerf

Data length 1400Byte

Measurement time 30 sec

Height of antenna 2m

WiFi IEEE802.11g

RTS-CTS not use -90 -85 -80 -75 -70 -65 -60

UDP TCP

v  The throughput falls suddenly in the range where the RSSI value is less than -80dBm.

Threshold_min -75dBm

Threshold_max -65dBm

Condition

Value of Threshold


Ø  To determine the threshold, we measure the throughput.


Route stabilization of ad hoc networkØ  We use the OLSR for ad-hoc routing protocol. In OLSR, a route is built by an

exchange of the Hello message. Ø  The Hello message is sent by a broadcast. The transmission rate of the broadcast

is the most low speed of the wireless LAN. Ø  So, it is able to happen that the Hello message sometimes reaches, but user data

never to reach.


Very low RSSI: for example -85dBm

Hello message sometimes reaches

User data never to reach


Route stabilization of ad hoc network



Suitable RSSI: for example -70dBm

Built route

Desirable route

Ø  We use the OLSR for ad-hoc routing protocol. In OLSR, a route is built by an exchange of the Hello message.

Ø  The Hello message is sent by a broadcast. The transmission rate of the broadcast is the most low speed of the wireless LAN.

Ø  So, it is able to happen that the Hello message sometimes reaches, but user data never to reach.

Ø  In such case, even if a relay robot exists in the location of suitable RSSI place, the built route by the Hello message not use the relay robot.


Route stabilization of ad hoc network


Ø  In such case, even if a relay robot exists in the location of suitable RSSI place, the built route by the Hello message not use the relay robot.

Ø  To built the desirable route (use suitable relay robot), we develop the mechanism that a Hello message with bad RSSI is blocked.


Hello message

Suitable RSSI: for example -70dBm

BlockBlock

Hello message Hello message

Ø  We use the OLSR for ad-hoc routing protocol. In OLSR, a route is built by an exchange of the Hello message.

Ø  The Hello message is sent by a broadcast. The transmission rate of the broadcast is the most low speed of the wireless LAN.

Ø  So, it is able to happen that the Hello message sometimes reaches, but user data never to reach.


Prototype System

Ø  We develop the prototype system using Kobuki and RaspberryPi. Ø  Kobuki is mobile robot for researches sold from Yujin Robotics. Ø  We use ROS (Robot Operating System) for moving control of the Kobuki.


Item Specification

Robot kobuki+RaspberryPiOS UbuntuRobot Control ROSWiFi IEEE802.11gAd-Hoc OLSRv2

Specification of Proto-System

Kobuki

RaspberryPiMobile Battery

USB Camera


Software structureØ  Blue line is moving control of head robot from the monitoring center. Ø  A relay robot executes its moving control by RSSI getting by iw command and

position information of head robot and itself getting by odometry information from ROS.


Kobuki Control

ROS

Kobuki Position

Ubuntu

OLSRv2

Kobuki Operation

ROS

Ubuntu

OLSRv2

RSSI Kobuki Position

Autonomous Moving Control

ubuntu

OLSRv2

Relay Robot Head RobotMonitoring Center

iw command

odometry information ( Wheel rotating information)


Hello message blocking mechanism

Ø  The Hello message that OLSR program should receive is redirected by iptables to Hello Message Block program.

Ø  Hello Massage Block program checks the RSSI of the Hello message sender. Ø  If the RSSI is below the threshold, the Hello message is blocked. Ø  If the RSSI is beyond the threshold, the Hello message is forwarded to OLSR.


OLSRv2

iptables(redirect)

Hello Message

Block

Hello Message

Check the RSSI of Hello message sending robot

RSSI > Threshold

Forward to OLSR

Block the Hello Message

Yes No


Demonstration



Demonstration


Movie from Head Robot

Position Information

RSSI Value


Conclusion

Ø We consider the system to monitor various information by a moving robot instead of a person in disaster area.

Ø  Several relay robots are installed between the head robot and monitoring center and these are connected by ad-hoc network.

Ø  The relay robot moves autonomously by RSSI value and position information of neighbor robot.

Ø  Stabilization of ad-hoc network is performed by Hello message blocking mechanism.

Ø We develop a prototype system using Kobuki and RaspberryPi and confirm the proposed method.


This work was supported by JSPS KAKENHI Grant Number 25330121.

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