Lego Robotic I Project

The Lego Robotic I (LeRoI) Project is responsible for the development of LEGO based robotic systems used in studying the spatial characteristics of radio-wave propagation.

Project Summary:

Understanding the complex nature of radio-wave propagation is essential to developing wireless communication systems. The UnWiReD Laboratory's activities in radio-wave propagation research are focused on characterizing the spatial, temporal, and frequency dimensions of radio channels. This understanding guides the development of communication technologies that exploit the multidimensional nature of the radio channel.

The execution of measurement campaigns that study the spatial dimension of radio channels is a tedious task requiring measurement repetition with high accuracy. An autonomous measurement system makes such campaigns feasible by tasking specialized robots with measurement execution.

Figure 1 shows a computer simulation of a standing-wave radio channel on one floor of an office building. The superimposed white grid shows a spatial sampling pattern that would be used in actual field measurements to reconstruct the radio channel as observed at the center of the grid. The sweeping of this grid pattern is the responsibility of an antenna positioning robot.

The configuration of a measurement system for studying the multidimensional radio channel is illustrated in Figure 2. This system is based on the UnWiReD Lab's software defined digital transceiver testbed which supports communication over multiple transmit and receive antenna in a 20MHz band of radio spectrum centered at frequencies in the 2 to 5 GHz range. The testbed is capable of exploring space, time, and frequency dimensions of the radio channel simultaneously. In particular, the testbed is a platform that is well suited to studying channel scenarios experienced by communication systems employing advanced technologies such as Orthogonal Frequency Division (OFDM), Multiple-Input Multiple-Output (MIMO), and Space-Time Coding as well as commercial technologies (e.g. the IEEE 802.11g Wireless LAN standard).

At the heart of the measurement system in Figure 2 are two identical positioning robots, LeRoI TX and LeRoI RX . Each LeRoI unit has the ability to position an antenna within a 3-dimensional space with high precision and accuracy. Figure 3 shows a proof-of-concept robot that has the ability to position an antenna in a 60cm x 60cm plane with 1.59mm accuracy. A LeRoI unit, or Lego Robotic I, is named named for it's ability to position an antenna at points in a grid so that we can "see" the spatial variation of propagating radio signals much like the grid of cones and rods in the eye allows us to see patterns of light.

Figure 3: A 2-dimensional proof-of-concept positioning robot based on LEGO components. Note the yellow RCX microcomputer on the right side of the robot, the infrared tower above it and the black control wirelines connecting the RCX brick to the robot's motors and sensors.

LeRoI units are built using LEGO pieces coming mainly from the Mindstorms and Technics series. Structural components are designed both in computer simulation and on the lab bench. Computer simulation using LeoCAD allows great flexibility in evolving ideas for a design because of the unlimited number of available parts and ease of manipulating pieces. Figure 4 shows a motor and rail assembly designed on the computer. Figure 5 shows an implementation of the motor and rail assembly as tested on the lab bench.

Figure 4: Computer aided design of a basic motor and rail assembly.	Figure 5: Implementation of the motor and rail assembly.

LeRoI movements are controlled by a LEGO Mindstorms RCX microcomputer (RCXm) running the Java based operating system LeJOS. The RCXm regulates motor speed and monitors sensor values via signals traveling to and from the robot over flexible wireline. The RCXm in turn communicates with a Personal Computer (PC) via an infrared link. The PC coordinates both the robot and radio hardware during measurements. Command and control and algorithms executed by the RCXm are written on the PC in the Eclipse Java development platform. These algorithms are then compiled and uploaded to the RCXm via the infrared link. Below is a link to a video demonstration of the system in action.

The choice to use a pervasive software architecture like Java allows remote control and monitoring of LeRoI operation via the internet. This is a great convenience to the test engineer who must often run tests overnight or in situations where human activity in the vicinity of the measurement equipment is undesirable.

The LeRoI design is highly configurable due to the modularity of Java and LEGO. It is very cost effective in terms of infrastructure and engineering time investments. The software is freely available Open Source Software and the LEGO components are commercially available at costs far below that of industrial grade components.

For more information on this project or to inquire about current activities of the group please contact David Browne.

References and Links:

D. Kabolis, "Study of Indoor Radio Wave Propagation by FDTD Simulation", MSc Thesis, University of Linköping, 2001.