Rail vehicle obstacle avoidance and vehicle localization

1. A method, comprising:

transmitting, from at least two vehicle beacons on a first vehicle, a ranging signal to at least two external beacons, wherein the transmitting the ranging signal to the at least two external beacons comprises:

transmitting, from a first beacon of the at least two vehicle beacons on the first vehicle, a first ranging signal to a first and a second external beacon of the at least two external beacons on a second vehicle; and

transmitting, from a second beacon of the at least two vehicle beacons on the first vehicle, a second ranging signal to the first and the second external beacon of the at least two external beacons on the second vehicle;

receiving, at the at least two vehicle beacons, a return signal from the at least two external beacons, wherein the receiving the return signal from the at least two external beacons comprises:

receiving, at the first and the second beacon of the at least two vehicle beacons on the first vehicle, a first return signal from the first external beacon of the at least two external beacons, and

receiving, at the first and the second beacon of the at least two vehicle beacons on the first vehicle, a second return signal from the second external beacon of the at least two external beacons;

determining, by a processor based on the return signal from the at least two external beacons, a position of each of the external beacons with respect to the at least two vehicle beacons of the first vehicle;

determining, by the processor, whether the at least two external beacons are associated with the second vehicle on a same track as the first vehicle; and

determining, by the processor, a separation distance between the first vehicle and the second vehicle.

2. The method of claim 1 , wherein:

the determining the position of each of the external beacons with respect to the at least two vehicle beacons of the first vehicle comprises:

determining, by the processor, whether the at least two external beacons are associated with the second vehicle on a different track from the first vehicle.

3. The method of claim 1 , wherein:

the determining the position of each of the external beacons with respect to the at least two vehicle beacons of the first vehicle comprises:

determining, by the processor, whether the at least two external beacons are associated with a track below the first vehicle.

4. The method of claim 1 , further comprising:

determining, by the processor, an inter-beacon distance based on the first return signal and the second return signal received by comparing a signal transit time for each of the first return signal and the second return signal at the first and the second beacon of the at least two vehicle beacons on the first vehicle.

5. A method, comprising:

measuring a value of an inter-beacon distance between each beacon of two or more beacons on a first vehicle, and each beacon of a set of two or more beacons on a second vehicle, thereby generating first through fourth measured inter-beacon distance values;

calculating an inter-vehicle distance from the first vehicle to the second vehicle based on the first through fourth measured inter-beacon distance values;

comparing the calculated inter-vehicle distance, and the first through fourth measured inter-beacon distance values to a set of vehicle configuration models;

calculating, based on the set of vehicle configuration models, modeled values corresponding to the first through fourth measured inter-beacon distance values;

determining whether the measured and calculated inter-beacon distance values converge; and

performing a safety operation based on the determination.

6. The method of claim 5 , further comprising:

adjusting an inter-track distance before calculating the modeled value of each inter-beacon distance.

7. The method of claim 5 , wherein the performing the safety operation comprises applying brakes of the first vehicle.

8. The method of claim 5 , further comprising determining whether the first vehicle and the second vehicle are on a same track.

9. The method of claim 8 , further comprising determining that the first vehicle and the second vehicle are not on the same track, and incrementing an inter-track separation distance in response to the determination that the first vehicle and the second vehicle are not on the same track.

10. The method of claim 5 , wherein the performing the safety operation comprises:

transmitting to the second vehicle, information related to a second vehicle position.

11. A system for calculating vehicle position, the system comprising:

a set of first beacons on a first vehicle, each first beacon on the first vehicle configured to transmit a corresponding coded pulse;

a set of second beacons external to the first vehicle, each second beacon configured to receive each coded pulse and to transmit a corresponding reply pulse; and

an obstacle avoidance computer of the first vehicle, the obstacle avoidance computer configured to

based on the reply pulses received by each first beacon, determine a plurality of inter-beacon distances between corresponding first beacons of the set of first beacons and second beacons of the set of second beacons, and

calculate a position of a second vehicle by determining a chord from the plurality of inter-beacon distances.

12. The system of claim 11 , wherein the obstacle avoidance computer of the first vehicle is further configured to initiate a safety operation based on the position of the second vehicle.

13. The system of claim 11 , further comprising:

a second vehicle obstacle avoidance computer configured to calculate a second vehicle position based on a time-of-flight measurement based on the coded pulse from each first beacon.

14. The system of claim 13 , wherein the second vehicle obstacle avoidance computer is further configured to initiate motion of the second vehicle upon determining the second vehicle position.

15. The system of claim 14 , wherein:

the second vehicle obstacle avoidance computer is further configured to cause each second beacon of the set of second beacons to transmit coded pulses to a set of third beacons external to the first vehicle and the second vehicle, and receive response pulses from the set of third beacons, and refine the second vehicle position based on a time-of-flight measurement based on the response pulses from the set of third beacons.

16. The system of claim 11 , wherein:

each second beacon is configured to include the coded pulse in the reply pulse before transmitting the reply pulse.

17. The system of claim 11 , further comprising a range-finding system configured to perform an inter-vehicle distance measurement for the obstacle avoidance computer of the first vehicle.

18. The method of claim 1 , wherein the determining, by the processor, the separation distance between the first vehicle and the second vehicle comprises:

measuring an inter-beacon distance for each vehicle beacon of the at least two vehicle beacons on the first vehicle, with respect to each external beacon of the at least two external beacons on the second vehicle; and

calculating the separation distance based on the inter-beacon distances from the first vehicle to the second vehicle.

19. The method of claim 18 , further comprising:

comparing the separation distance, and the measured inter-beacon distances, to a set of vehicle configuration models.

20. The method of claim 19 , further comprising:

calculating, based on the set of vehicle configuration models, a modeled value of each inter-beacon distance.