Scalable Ad Hoc Wireless Geocast

Get the Flash Player to see this video.

Geocast : Applications in Mobile GeoGames and Public Safety

Scalable Ad Hoc Wireless Geocast is a network protocol for addressing messages to receivers in a geographic area, like "180 Snyder Ave." or "Dodge Park".  Geocast is designed for wireless, GPS-enabled devices, like the iPhone, but could run on almost any PDA-scale device that can provide its geographic position.

Geocast has two important characteristics.   First, Geocast is an ad hoc network protocol.  Communication between Geocast-enabled devices is peer-to-peer and requires no fixed infrastructure, like towers, routers, or access points.  This permits Geocast-enabled devices to communicate instantaneously in challenging environments, like remote locations where fixed infrastructure may be unavailable or unreliable.

Second, Geocast is highly scalable.  It can handle high traffic between tens to thousands of devices, even in urban settings.  Plus Geocast can use fixed communication tiers, like a cellular network, for efficient transport of messages over long distances.

Geocast was invented in Research to enable a novel military training technology for the U.S. Army known as OneTESS. Two key requirements of OneTESS were that the wireless network protocol be ad hoc and highly scalable. Geocast was studied extensively in simulation and was successfully tested in a field trial at the Army National Training Center at Fort Irwin in the Mojave Desert.

Our prototype of Geocast on the iPhone includes a novel GeoGame application, public safety applications, and a GeoTexting application, all built upon an implementation of the Geocast network framework.



Public SafetyGeocast Query Result

In emergencies, first responders need to locate and alert people with instructions appropriate to their location and situation.

Suppose there is a disaster at a school (green dot in the green circle). Using a command console, like a laptop (at blue dot), authorized personnel can issue a GeoQuery to the area.  GeoQuery causes contacted phones (red dots) to automatically send Geocast to command center,  which can plot position of receiver.

When searching in collapsed structures, knowing lat/long location of a phone is not always enough due to sensor imprecision.  In these cases, commander can send GeoAlarm message which causes devices in defined Geocast region to set off loud alarm that can help rescuers find trapped individuals.

Commander can also issue GeoAlert messages to devices in Geocast region, which results in dialog pop-up.  Message can be tailored to specific areas within emergency response area.

GeoAlert Message

Because Geocast is a peer-to-peer, ad hoc protocol, it works even if infrastructure is damaged or absent and it can achieve better coverage in more challenging situations than can a broadcast-based system.  Its scalability means it works even if there are 1000s of units in the effected area.



 iTESS: A GeoGaming Application

GeoGame Interface

GeoGames are a novel class of augmented-reality video games that require strenuous physical activity.  iTESS is a hide-and-go-seek GeoGame played with virtual munitions (or water balloons) in a large outdoor area like a forest or park.  The object of iTESS is to avoid being "hit" by virtual munitions shot by other gamers.

The map shows a game situation.  Blue dot and uncertainty halo show gamer's approximate position.  Numbers in upper-right show available munitions and number of permitted simultaneous shots.  Shots take significant time to travel from “mortar battery” to target (e.g, 10-15 secs) just like in reality, because game is being played outdoors and gamers need sufficient time to run.

The gamer taps the screen to direct a virtual UAV (unmanned aerial vehicle, green circle at right) to move and search for other gamers.  Gamers found in the "look-down circle" beneath the UAV are shown as red dots. The UAV is implemented by sending GeoQueries to the look-down circle.

Here, the UAV has located a target (red dot), but the gamer is already targeted by an incoming round (red shaded circle containing gamer's blue dot).
The gamer then has 10 seconds to run out of the circle before the shell “lands”. 

GeoGame InterfaceSimultaneously, the gamer can point gray cross hair at gamers in UAV range and launch munitions. 

Gamers that do not run out of red target circle in time are hit and their game is over, while other "live" gamers can continue to play.

iTESS can augment existing simulation games, like paintball or laser tag, with new kinds of weapons and can simulate other types of interactions, like medical engagements.


How does Geocast work?

Within one wireless channel, the originator transmits a message, labeled with a unique serial number, to all nodes within the originator's range.  Any participant that receives the message enqueues it for re-transmission.

Each time a copy of the same Geocast message is received, the receiver records statistics, including the copy count, the location of the sender, the distance from the target Geocast region, etc.

When a re-transmission reaches the head of the queue, the sender makes heuristic decision whether to re-transmit or drop the message.  The technical paper entitled "A Tiered Geocast Protocol for Long Range Mobile Ad Hoc Networking" listed below gives the details of the heuristic algorithm for re-transmission




More about OneTess

One Tess Equipment

The Army wants to train its troops as realistically as possible without using live fire weapons.  The aim of OneTESS is to replace live fire with electronic simulations in which weapons fire "electronic bullets" and engagements are mediated by a wireless data network.

Small PDA-scale devices and sensors, like GPS and compasses, are carried by soldiers and mounted on weapons and vehicles to sense and respond to action in realistic battlefield environments.

Sensor data, such as trigger pull, tuble angle, and unit positions are sent via the wireless data network to appropriate computational devices, simulation results are computed, and then engagement results are transmitted out to units and soldiers,  who take simulated damage.

After a battle scenario is enacted with OneTESS units, all locally-collected situational data are transmitted to a central collector where it can be presented for after-action review and further learning.