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

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. Receiver unit on a robot
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
Centralized Network
Mobile Ad Hoc Network (MANET)

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
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 b,g,a
HiperLAN/II
ZIgBee
WiMax (near future)

10. Hardware Structure, different network layers
Baseband Processor
RF transceiver
MAC controller
physical
MAC
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
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
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.: /
Fax.: /