Wireless Control of a Multihop Mobile Robot Squad UoC Lab. 임 희 성

Introduction WMMRC(Wireless, mobile, multihop robot control) - Without any fixed network infrastructure - Freely and dynamically self-organize - Communicate with each other using the multihop capabilities of the neighbor nodes (when nodes are not within proximity) - Leader : Control the actions of the squadron Collect the position information & Transmit movement commands

Introduction Single Leader - Number of hops between leader and all the robots Multiple Path - Increase in the robustness of wireless control system - Not beneficial if all the nodes are moving

Communication Constrained Control

Wireless Communication - Control packet & Measurement packet - A Controller cannot act in real-time, if information is late or missing ∴ To cope with the dynamic nature of mobile networks, new theory is required. State feedback controller Communication Constrained Control

PID-Controller Tuning for Delay Jitter Jitter margin theorem - Amount of additional delay that a control system can tolerate without becoming unstable - Regular controller can be tuned to tolerate additional delay caused by the communication in a networked control loop - PID Controller :

State estimation with Regular control - To use an estimator to estimate the output of the controlled process during packet drops caused by the network - Kalman Filter : Efficient recursive filter that estimates the state of a linear dynamic system from a series of noisy measurements - If a packet is dropped, the output is predicted using only the process model PID-Controller Tuning for Delay Jitter

Efficient routing protocol - Be capable of establishing and maintaining a path between a source and a destination - Keep the overhead and memory requirement low - To minimize both the number of path losses and the length of recovery Routing Protocol and Prioritization

Single routing protocol (AODV : Ad hoc on-demand distance vector) - Try to find a route with the shortest distance - Establish only when there is information to be sent from one node to the other - Maintain as long as they are required for communication Multipath routing protocol (LMNR : Localized multiple nexthop routing protocol) - Extend to the AODV for multiple loop-free and link-disjoint paths - Use cost function and enable each node to choose from multiple available paths based on the cost Routing Protocol and Prioritization

Broadcast-type routing protocol (SIRP : Sink initiated routing protocol) - Similarly to LMNR(multiple paths to the leader) - Proactive protocol - Limit network-wide initialization to the squad leader - Broadcast interval is an important parameter Routing Protocol and Prioritization

Prioritization - Genuine requirement in many sensor network application - Relax controller design requirements by equalizing packet delays for a different number of hops Our Proposal - Forwarded hop-based prioritization strategy - The prioritization of a packet is increased for every hop - Base on distance traveled

Simulation

Constitution - WMMRC simulation case on PiccSIM - Consist of a group of wireless, mobile robots, collaborating in an ad hoc fashion - Each robot localizes itself and sends its position information to the leader robot - The leader then calculates the desired path and sends control signals - Squad of 25 robots / Equip with and IEEE radio module / Communicate only with its nearest neighbors / Speed of robots depends on the control(less than 1.5m/s) - Ricean Propagation model Simulation

ISE(Integral of square error) - The ISE cost is a measure for the tracking error of the robots - Calculate as the integral of the squared difference between the desired robot location and the actual location, summed over all the robots - The cost is calculated as an average of only the instances when the communication link is working Simulation

Results

- Multipath routing decreases the network performance - Multipath routing(LMNR) has slower recovery from link breaks compared to single path(AODV) ∵ All the robots are moving - In light of network performance, AODV better than LMNR, and SIRP has the worst performance although its routing overhead is lowest of all of them - Using prioritization, the control cost is smaller for both control structures Results

Conclusion