Mobile Sensor Swarms

In this approach, ultra-low complexity sensor swarm paradigms are developed and implemented. Emergent behavior of many extremely simple swarm agents is utilized to generate robust and fully autonomous navigation and tracking behavior.

This expert consultant is developing and implementing low complexity swarm algorithms to perform robust sensing using mobile agents. Our current implementations are primarily based on the following platforms.

1. VEX mobile robot
2. Hovercraft

In addition, we explore the use of air-borne blimps with the same navigation principles.

The Navigation Principle
Radio beacons generated using packet transmissions via IEEE 802.15.4 / Zigbee based wireless nodes [Tmote] are used to guide the navigation path of the mobile swarm agents. Each mobile agent is fitted with two directional antennas in its left and right sides. These antennas are directly coupled to two separate Tmote nodes (Master and Slave nodes).

By comparing the received signal strength (RSSI) values in the master and slave nodes (via the left and right antennas respectively), the mobile agent can navigate towards an attractive beacon, or navigate away from a repel beacon. Details including the beacon type (attractive or repel) and Beacon ID are included in the data payload of the packet being transmitted by the wireless radios at the beacons.

Leader - Follower Operation
In one of the navigation modes, the swarm of agents follow one leader. The leader navigates over a predetermined path marked by multiple waypoint beacons. Followers swarm around the leader, attracting towards the leader using its attractive beacon while responding to repel beacons from its peers and the leader to avoid collisions.

Directional Antennas on Mobile Agents
Tmote nodes have a built-in patch antenna, which radiates almost in an omni-directional pattern. Placing the master and slave nodes in the two sides of the agent and using some shielding in the middle gives some directionality.

However, this does not provide enough distinction between the RSSI values received over the left and right directions, for the successful navigation of the agent using the above principle. Hence, we designed an approximately parabolic shaped directional antenna using an Aluminum sheet, and placed the Tmote nodes in its focal point. This apparatus is proven to give good directionality, and thus accurate and robust navigation of agents.

High-Gain External Antennas at Waypoint Beacons
Although the omni-directional radiation pattern of the built-in antennas of the Tmote wireless nodes are desired for the waypoint beacons, its transmission gain is not sufficient for the beacons to be heard from a considerable distance by the Leader mobile agent.

Hence, we fitted the Tmote nodes at waypoint beacons with a high gain external antenna with an omni-directional pattern. One can in-deed further increase the RSSI at the receiver nodes by placing these waypoint beacon antennas high above the ground.

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