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It is possible that two independent GPS units might be accurate enough (as ViennaMike suggests) if both are sufficiently similar, get a lock from the same location, follow roughly the same paths (so the accumulated differential GPS errors are roughly the same) and are re-synchronised at regular intervals.

This might be significantly assisted though if you also had some sort of proximity measure between the two devices.

Start them off a fixed distance from each other, sync both their differential GPS locks & calibrate the proximity thresholds (starting distance, too close threshold and too far threshold). You can then use the proximity sensor distance to say if the gps locks are drifting too much (they are getting closer than they should be or further apart).

One option which I believe could provide both rough proximity information and data communication between the two UAVs would be Bluetooth. Once the two devices are paired, you may be able to get both intra-device communication and rough proximity information from one pair of radios.

Searching on Bluetooth Proximity led me to see the use of RSSI (Received Signal Strength Indicator) as a measure of proximity and thus onto Bluetooth Indoor Positioning using RSSI and Least Square Estimation ^# which may be able to give you some interesting ideas for this.

^{# Stack Exchange thinks that the original link http://202.175.25.24/papers/2010/fcc2010yapeng.pdf is invalid, so won't let me use it as a link, so I have used the google wrapped link.}

It is possible that two independent GPS units might be accurate enough (as ViennaMike suggests) if both are sufficiently similar, get a lock from the same location, follow roughly the same paths (so the accumulated differential GPS errors are roughly the same) and are re-synchronised at regular intervals.

This might be significantly assisted though if you also had some sort of proximity measure between the two devices.

Start them off a fixed distance from each other, sync both their differential GPS locks & calibrate the proximity thresholds (starting distance, too close threshold and too far threshold). You can then use the proximity sensor distance to say if the gps locks are drifting too much (they are getting closer than they should be or further apart).

One option which I believe could provide both rough proximity information and data communication between the two UAVs would be Bluetooth. Once the two devices are paired, you may be able to get both intra-device communication and rough proximity information from one pair of radios.

Searching on Bluetooth Proximity led me to see the use of RSSI (Received Signal Strength Indicator) as a measure of proximity and thus onto Bluetooth Indoor Positioning using RSSI and Least Square Estimation ^# which may be able to give you some interesting ideas for this.

^{# Stack Exchange thinks that the original link http://202.175.25.24/papers/2010/fcc2010yapeng.pdf is invalid, so won't let me use it as a link, so I have used the google wrapped link.}

It is possible that two independent GPS units might be accurate enough (as ViennaMike suggests) if both are sufficiently similar, get a lock from the same location, follow roughly the same paths (so the accumulated differential GPS errors are roughly the same) and are re-synchronised at regular intervals.

This might be significantly assisted though if you also had some sort of proximity measure between the two devices.

Start them off a fixed distance from each other, sync both their differential GPS locks & calibrate the proximity thresholds (starting distance, too close threshold and too far threshold). You can then use the proximity sensor distance to say if the gps locks are drifting too much (they are getting closer than they should be or further apart).

One option which I believe could provide both rough proximity information and data communication between the two UAVs would be Bluetooth. Once the two devices are paired, you may be able to get both intra-device communication and rough proximity information from one pair of radios.

Searching on Bluetooth Proximity led me to see the use of RSSI (Received Signal Strength Indicator) as a measure of proximity and thus onto Bluetooth Indoor Positioning using RSSI and Least Square Estimation ^# which may be able to give you some interesting ideas for this.

^{# Stack Exchange thinks that the original link http://202.175.25.24/papers/2010/fcc2010yapeng.pdf is invalid, so won't let me use it as a link, so I have used the google wrapped link.}

It is possible that two independent GPS units might be accurate enough (as ViennaMike suggests) if both are sufficiently similar, get a lock from the same location, follow roughly the same paths (so the accumulated differential GPS errors are roughly the same) and are re-synchronised at regular intervals.

This might be significantly assisted though if you also had some sort of proximity measure between the two devices.

Start them off a fixed distance from each other, sync both their differential GPS locks & calibrate the proximity thresholds (starting distance, too close threshold and too far threshold). You can then use the proximity sensor distance to say if the gps locks are drifting too much (they are getting closer than they should be or further apart).

One option which I believe could provide both rough proximity information and data communication between the two UAVs would be Bluetooth. Once the two devices are paired, you may be able to get both intra-device communication and rough proximity information from one pair of radios.

Searching on Bluetooth Proximity led me to see the use of RSSI (Received Signal Strength Indicator) as a measure of proximity and thus onto Bluetooth Indoor Positioning using RSSI and Least Square Estimation ^# which may be able to give you some interesting ideas for this.

^{# Stack Exchange thinks that the original link http://202.175.25.24/papers/2010/fcc2010yapeng.pdf is invalid, so won't let me use it as a link, so I have used the google wrapped link.}

It is possible that two independent GPS units might be accurate enough (as ViennaMike suggests) if both are sufficiently similar, get a lock from the same location, follow roughly the same paths (so the accumulated differential GPS errors are roughly the same) and are re-synchronised at regular intervals.

This might be significantly assisted though if you also had some sort of proximity measure between the two devices.

Start them off a fixed distance from each other, sync both their differential GPS locks & calibrate the proximity thresholds (starting distance, too close threshold and too far threshold). You can then use the proximity sensor distance to say if the gps locks are drifting too much (they are getting closer than they should be or further apart).

One option which I believe could provide both rough proximity information and data communication between the two UAVs would be Bluetooth. Once the two devices are paired, you may be able to get both intra-device communication and rough proximity information from one pair of radios.

Searching on Bluetooth Proximity led me to see the use of RSSI (Received Signal Strength Indicator) as a measure of proximity and thus onto Bluetooth Indoor Positioning using RSSI and Least Square Estimation ^# which may be able to give you some interesting ideas for this.

^{# Stack Exchange thinks that the original link http://202.175.25.24/papers/2010/fcc2010yapeng.pdf is invalid, so won't let me use it as a link, so I have used the google wrapped link.}

It is possible that two independent GPS units might be accurate enough (as ViennaMike suggests) if both are sufficiently similar, get a lock from the same location, follow roughly the same paths (so the accumulated differential GPS errors are roughly the same) and are re-synchronised at regular intervals.

This might be significantly assisted though if you also had some sort of proximity measure between the two devices.

Start them off a fixed distance from each other, sync both their differential GPS locks & calibrate the proximity thresholds (starting distance, too close threshold and too far threshold). You can then use the proximity sensor distance to say if the gps locks are drifting too much (they are getting closer than they should be or further apart).

One option which I believe could provide both rough proximity information and data communication between the two UAVs would be Bluetooth. Once the two devices are paired, you may be able to get both intra-device communication and rough proximity information from one pair of radios.

Searching on Bluetooth Proximity led me to see the use of RSSI (Received Signal Strength Indicator) as a measure of proximity and thus onto Bluetooth Indoor Positioning using RSSI and Least Square Estimation ^# which may be able to give you some interesting ideas for this.

^{# Stack Exchange thinks that the original link http://202.175.25.24/papers/2010/fcc2010yapeng.pdf is invalid, so won't let me use it as a link, so I have used the google wrapped link.}