Robot Communication over Wireless Ad Hoc Network

1. Robot Communication over Wireless Ad Hoc Network M.Sc. Feng Xu 03.02.2005

2. Agenda • Why communication among robots is necessary • 3 examples • Two categories network: centralized network and ad hoc network • Properties of ad hoc network, and examples • Current Main Stream Techniques • Hardware structure for the communication node • Constrains for portable devices: energy, space, computing ability • MAC protocol, CSMA/CA • Current two hot research directions on MAC layer • Directional communication • Dynamic multi-channel allocation • 3 means to close the gap between theory and realization • Summary

3. Why communication among Robots • Goal of RoBoCup: To fully develop autonomous humanoids that can win against human world champion soccer team by 2050 • Each robot player should have more powerful individual ability over human player • Communication among robots is necessary for the high level coordination (deliberation-based high level behavior control!) • In special robot application scenarios like war field and emergency field, communication among robots can significantly enhance their ability • Contrariwise, robots with wireless communication module can help simulate or experiment the wireless network

4. Example 1, AIBO

5. Example 2, BiM-2 Receiver on a PCB Receiver unit on a robot Seattle University RoboCup Team, USA

6. Example 3, Khepera

7. Two Categories of Network Mobile Ad Hoc Network (MANET) Centralized Network

8. Properties of Ad Hoc Network, examples • MANET is a decentralized wireless network without pre-built infrastructure • Each node acts as host and router simultaneously, and signals may be transmitted via multi hop to the destination • The network topology may change rapidly and unpredictably due to movements, joining and leaving of nodes at any moment • MANET may operate in a standalone fashion, or may be connected to other existent network as its extension Properties: Examples: • Conferencing and home networking • Wireless sensor network • Multi-hop extensions for cellular telecommunication systems • And networks of vehicles, robots

9. Current Main Stream Techniques • Bluetooth • WLAN: IEEE 802.11 b,g,a • HiperLAN/II • ZIgBee • WiMax (near future)

10. Hardware Structure, different network layers Baseband Processor MAC controller RF transceiver MAC physical Hardware structure for each node Host other high layers OSI/ISO Reference Model

11. Constrains for Portable Devices • Physical space • Limited energy (battery powered devices) • Limited computing power

12. CSMA/CA • MAC protocol: carrier sense multiple access with collision avoidance • Prerequisites: Omnidirectional communication on single frequency channel RTS, CTS, data and NAV setting Resulted space allocation condition Basic media access process

13. Current hot research topics • Goals: • Increase resource efficiency, the resource mainly means frequency band • Make the communication link more robust • Means: • Directional communication to increase the space reuse factor • Multi-channel dynamic allocation scheme

14. Smart Antenna, directional antenna • Smart Antenna • Realized by antenna array and additional array signal processing unit • Enable various advantages on network, but also consume much additional resource like space, energy and computing power • Directional Antenna • The directivity is attributed to the directional property of the antenna element itself • With the mechanical turning assistance, or multiple directional antennas equipped on each node with proper orientation, each node can communicate on the direction it wishes • Less additional resource is needed comparing to SM, however, less improvement is anticipated

15. Multi-channel scheme: CDMA, OFDM

16. Theoretical Research, Practical application, 3 means close the gap • Theoretical research: • New schemes are firstly put forward on the physical layer • Higher layers (MAC, network layers) need adapting to the modifications • Cross-layer optimization • Close the gap between theoretical research and practical application • In practice, many constrains are imposed • Rely on the chip layer improvement • Use the simplified scheme to make it more practical • The combination of aforementioned 2 means

17. Summary • To reach the goal of RoBoCup, the communication ability among robots is necessary • To communicate efficiently and effectively, a network called mobile ad hoc network is meaningful for the robot team • Contrariwise, robot team with communication ability can help contribute to the network system improvement • Many constrains are imposed on the portable devices due to its limited resource • Numerous new schemes are put through on the physical layer to increase transmission data rate and communication link robustness • Cross-layer optimization is important for the whole system performance • 3 means to close the gap between theoretical research and practical application

18. Thank you for your attention! Heinz Nixdorf Institut Universität Paderborn Schaltungstechnik Prof. Dr.-Ing. Ulrich Rückert Fürstenallee 11 33102 Paderborn Feng Xu Tel.: 0 52 51/60 6396 Fax.: 0 52 51/60 6351 Email: xu@hni.upb.de http://wwwhni.upb.de/sct