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

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

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

Example 1, AIBO

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

Example 3, Khepera

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

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

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

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

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

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

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

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

Multi-channel scheme: CDMA, OFDM

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

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

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