Signal geolocation system and method

One aspect is a network system including a network sewer and a plurality of gateway hosts coupled to the network server and each including a sectorized antenna and defining a plurality of gateway areas. An overlapping gateway grid includes the plurality gateway areas, each gateway area including sectors. The network system includes a plurality of endpoints, each sending and receiving 10 communication signals to and from at least two gateway hosts, and each comprising an oscillator calibrated with a clocking frequency. The network server determines the location of a target endpoint by sending communication signals between two selected sectorized antennas and the target endpoint to determine one sector from each of the two selected sectorized antennas in which the target endpoint is located, 15 and by calculating the time-of-flight for the communication signal to travel between each of the selected sectorized antennas and the target endpoint.

BACKGROUND

In certain network applications, such as Low Power Wide Area Network (LPWAN) applications, signals are transmitted between endpoint and gateway devices according to established protocols. Often, a single gateway receives multiple signals from multiple endpoints. Because of signal attenuation, and the fact that signals will not always be transmitted directly in the shortest distance between an endpoint and a gateway, it is not always apparent from signal strength, which of multiple received signals is from the closest endpoint. Accordingly, the origin of any particular signal received by a gateway from an endpoint cannot be readily determined. For these and other reasons, there is a need for the present invention.

DETAILED DESCRIPTION

FIG. 1illustrates a system overview of a Low Power Wide Area Network (LPWAN)10in accordance with one embodiment. LPWAN10includes endpoints12(E1, E2, E3. . . EN), gateway hosts14(G1, G2. . . GN) and network server16. In some applications, LPWAN10has a network architecture in which gateway hosts14are transparent bridges relaying messages between endpoints12, also known as end-devices or sensors, and a network server16located in the backend. Gateway hosts14are connected to network server16via standard IP connections18.

In one embodiment, each gateway host14includes one or more antennas. In this way, each endpoint12uses single-hop wireless communication to one or many gateway hosts14. In one embodiment, LPWAN10is a LoRa® or LoraWAN™ system configuration.

All end-point communication, or communication with endpoints12, is generally bi-directional, such that each gateway host14both transmits communication signals to, and receives signals from, endpoints12via the gateway antennas. The architecture of LPWAN10is sometime referred to as a “star-of-stars” topology.

In one embodiment, endpoints12in LPWAN10are battery-operated devices intended for low power operation in order to maximize battery life, while at the same time allowing for substantial wireless transmission distance between endpoints12and gateway hosts14.

Communication signals between endpoints12and gateway hosts14is spread out on different frequency channels and data rates. The selection of the data rate is a trade-off between communication range and message duration. Due to the spread spectrum technology, communication signals with different data rates do not interfere with each other, and instead create a set of “virtual” channels increasing the capacity of the gateway hosts14. In one embodiment, LPWAN10uses data rates range from 0.3 kbps to 50 kbps. In order to maximize both battery life of endpoints12and overall network capacity, network server16manages the data rate and RF output for each sensor12individually by means of an adaptive data rate (ADR) scheme.

FIG. 2illustrates the deployment of a plurality of gateway hosts14in a gateway grid20for a LPWAN10. Gateway grid20includes a plurality of gateway areas24, each gateway area24G1,24G2,24G3. . .24GNcorresponding to one gateway host14(G1, G2, G3. . . GN). Each gateway host14(G1, G2, G3. . . GN) includes at least one antenna15G1,15G2,15G3. . .15GN(In the figure, only the gateway antennas15are labeled, rather than also the corresponding gateway host14, in order to simplify the figure). InFIG. 2, the size of each gateway area24G1,24G2,24G3. . .24GNis determined by the range of each corresponding antenna15G1,15G2,15G3. . .15GNin each gateway host14(G1, G2, G3. . . GN). By spacing each gateway host14(G1, G2, G3. . . GN), and accordingly each corresponding antenna15G1,15G2,15G3. . .15GN, relatively close to each other, all positions within the entire gateway grid20are within range of at least one antenna15of one gateway host14.

In one embodiment, each antenna15G1,15G2,15G3. . .15GNof each gateway host14(G1, G2, G3. . . GN) is configured as a plurality of sectorized antennas. In one embodiment, each gateway antenna15G1,15G2,15G3. . .15GNincludes three discrete sectors such that each sector transmits and receives over approximately a 120-degree radius from the antenna15GNin each gateway area24G1,24G2,24G3. . .24GN. Accordingly, a first sector antenna is configured to transmit and receive over a first sector (a) of each of gateway areas24G1,24G2,24G3. . .24GN, a second sector antenna is configured to transmit and receive over a second sector (b) of each of gateway areas24G1,24G2,24G3. . .24GN, and a third sector antenna is configured to transmit and receive over a third sector (c) of each of gateway areas24G1,24G2,24G3. . .24GN. The dotted lines within each gateway area24G1,24G2,24G3. . .24GNillustrate the approximate 120-degree radius for each sector of the sectorized antenna. As such, any location within gateway grid20is within the range of at least one of the sectorized antennas15G1,15G2,15G3. . .15GNassociated with the gateway host14(G1, G2, G3. . . GN) in that location.

FIG. 3illustrates the deployment of a plurality of gateway hosts14in an overlapping gateway grid30for LPWAN10in accordance with one embodiment. Similar to gateway grid20, overlapping gateway grid30includes a plurality of gateway areas34G1,34G2,34G3,34GN, each gateway area34G1,34G2,34G3,34GNcorresponding to one gateway host14(G1, G2, G3, GN). Each gateway host14(G1, G2, G3, GN) includes at least one gateway antenna15G1,15G2,15G3,15GN. As described previously, the size of each gateway area34G1,34G2,34G3,34GNis determined by the range of each corresponding antenna15G1,15G2,15G3,15GNin each gateway host14(G1, G2, G3, GN). Each gateway area34G1,34G2,34G3,34GNof overlapping gateway grid30overlaps at least a portion of at least one other gateway area34G1,34G2,34G3,34GN. As such, in one embodiment, any location within overlapping gateway grid30is within range of at least two gateway antennas15G1,15G2,15G3,15GN.

FIG. 3illustrates a simplified overlapping gateway grid30, including four exemplary gateway areas34G1,34G2,34G3,34GNin order to clarify the illustration. Other embodiments of overlapping gateway grid30can contain hundreds or thousands of gateway hosts14GNwith the same amount of corresponding gateway antennas15GN. Similar to gateway grid20, the four illustrated gateway areas34G1,34G2,34G3,34GNof gateway grid30respectively include first, second, third and fourth sectorized antennas15G1,15G2,15G3and15GN, and each accordingly have first, second and third sectors (a), (b), and (c), each having a range of approximately 120 degrees.

In the illustration, the overlapping nature of gateway areas34G1,34G2,34G3,34GNis exemplified, and will be explained further, by first, second and third sectors (a), (b) and (c) of third antenna15G3. First sector (a) of third antenna15G3overlaps with part of third sector (c) of second antenna15G2and with part of second sector (b) of first antenna15G1. Second sector (b) of third antenna15G3overlaps with part of third sector (c) of second antenna15G2and with part of first sector (a) of fourth antenna15GN. Third sector (c) of third antenna15G3overlaps with part of first sector (a) of fourth antenna15GNand part of second sector (b) of first antenna15G1. Where more gateway areas34are included in overlapping gateway grid30, they can be arranged similarly to have similarly overlapping sectors.

In one embodiment, LPWAN10determines the physical location, or geolocation, of endpoints12using overlapping gateway grid30, taking advantage of a single target endpoint12being located in sectors of two different overlapping gateway areas34. In order to determine the location of endpoint12, LPWAN10uses bi-directional communication signals between endpoints12and gateway hosts14GN, via the gateway antennas15GN, to calculate the time-of-flight (tof) for the communication signals. Furthermore, using the overlapping gateway grid30, LPWAN10determines direction of the flight for the communication signals. Using the time-of-flight calculation combined with the direction of the flight determination, LPWAN10can accurately geolocate the endpoint12.

FIG. 4illustrates two exemplary gateway areas34G1and34G3from overlapping gateway grid30in accordance with one embodiment. Although overlapping gateway grid30includes many more gateway areas34, just two are illustrated to simplify the example. Endpoint12is located in overlapping sectors of gateway areas34G1and34G3. Specifically, endpoint12is located in second sector (b) of first gateway area34G1, and in first sector (a) of third gateway area34G3. Because antennas15G1and15G3are sectorized, LPWAN10can accurately determine the direction of endpoint12using just these two antennas, and accordingly, LPWAN10can determine direction using just two gateway hosts14. Then, by calculating the distance of endpoint12from the respective antennas15G1and15G3, LPWAN10can accurately determine precise location.

Because communication signals between endpoint12and antenna15radiate generally in a signal arc (S) within any given sector, the distance between the endpoint12and antenna15can be calculated by finding the distance between the antenna15and a signal arc (S), which passes through endpoint12. Two such arcs SG1and SG3, respectively from antennas15G1and15G3, are each illustrated passing through endpoint12inFIG. 4. Determining the location of the intersection of the two arcs SG1and SG3, also locates the target endpoint12.

In one embodiment, in order to determine the distance between a signal arc (S) and a respective antenna15GN, time-of-flight calculations are used for the communication signal.FIG. 5illustrates time sequencing for calculating time-of-flight in order to determine the distance between endpoint12and the antenna15according to one embodiment. Both the gateway14and the endpoint12have an independent track of time. In one embodiment, each endpoint12is integrated with a highly accurate clock. In one embodiment, the clock in endpoint12is an oscillator that is calibrated with software to control a highly accurate clocking frequency. Because gateway14is directly coupled to network server16, it uses a network clock. As such, there is a network clock timeline50, represented in the upper portion ofFIG. 5, and an endpoint clock timeline55, represented in the lower portion ofFIG. 5.

In one embodiment, the process for time-of-flight calculation begins when network16sends a first communication signal to endpoint12via gateway antenna15at time t0, representing the network time when the first communication signal is sent. The first communication signal includes a time packet that stores this sent time t0. The first communication signal including the time packet is then received by endpoint12. The time at which endpoint receives the packet containing sent time t0, is represented on timeline55, but because the first communication signal including the time packet will take time to transport from antenna15to endpoint12, the network time relative to point in time when endpoint12receives the packet is:
t0+ttof(d),  1.0)
where ttof(d)is the time-of-flight for the first communication signal with the time packet to travel down from the antenna15to the endpoint12.

Once received, endpoint12will then prepare a time packet to be sent back up to the gateway antenna15in a second communication signal. The period of time from when endpoint12receives the packet containing time sent t0until the packet is sent back up to gateway antenna15is represented by prepare time a ∂t. Because endpoint12is equipped with a highly accurate clock, prepare time a ∂t is accurately recorded by endpoint12, and then added to the data packet that is sent back up to gateway antenna15in the second communication signal. As such, the time packet that is send up from endpoint12to gateway antenna includes the information in expression 1.0, that is, t0+∂t. Again, because the second communication signal including the time packet will take time to transport up from endpoint12to antenna15, the network time relative to when gateway antenna15receives the packet in the second communication signal is:
t0+ttof(d)+∂t+ttof(u),  2.0)
where ttof(u)is the time-of-flight for the second communication signal with the time packet to travel up from the endpoint12to the antenna15.

In one embodiment, it is assumed that the time-of-flight for the first communication signal is the same down to the endpoint12as it is for the second communication signal back up from the endpoint12. Accordingly, the time, expressed as trec,that the network receives the communication after it is initially sent from the gateway14via antenna15to the endpoint12and back up to the antenna15can also be expressed as:
trec=t0+2ttof+∂t,3.0)
where ttofrepresents the time-of-flight for both the first communication signal with the time packet to travel down from the antenna15to the endpoint12and for the second communication signal with the time packet to travel up from the endpoint12to the antenna15.

With this information contained in the data packet of the second communication signal received by gateway14via antenna15, gateway14can calculate time-of-flight ttoffor the first and second communications, from which the distance between the antenna15and the endpoint12can be derived. In order to calculate time time-of-flight ttoffor the communications, equation 3.0 above is solved for time-of-flight ttofas follows:
ttof=(trec−t0−∂t)/2  4.0)

Because it is known that the communication signals travel is electromagnetic propagation at the speed of light, which travels 1 meter in 3.34 ns, the distance between the endpoint12and the gateway14is:
DE−G=(trec−t0−∂t)/2*1m/3.34ns,5.0)
where DE−Gis the distance between the endpoint12and the gateway14.

As illustrated inFIG. 4, any endpoint12in overlapping gateway areas, such as gateway areas34G1and34G3, is within one sector of each gateway area. As previously discussed, endpoint12ofFIG. 4is located in second sector (b) of gateway area34G1, and in first sector (a) of gateway area34G3. Accordingly, the distance between antenna15G1and target endpoint12is calculated using equation 5.0 and the distance between antenna15G3and target endpoint12is also calculated using equation 5.0.

Furthermore, because the location of each gateway14and gateway antenna15is known, the relative location of the target endpoint12can be calculated by determining the intersection of the signal arcs SG1and SG3of the communication signals between endpoint12and antenna15.

FIG. 6illustrates the intersection of the signal arcs SG1and SG3passing through target endpoint12. The radius of a sphere lying respectively on each of these arcs SG1and SG3can be calculated by using equation 5.0 above:
rG1=(trec−t0−∂t)/2*1m/3.34ns; and  6.1)
rG3=(trec−t0−∂t)/2*1m/3.34ns,6.2)
where rG1is the radius of a sphere having a surface passing through endpoint12and having a center point at gateway antenna15G1and rG3is the radius of a sphere having a surface passing through endpoint12and having a center point at gateway antenna15G3. The coordinates of the respective center points of such spheres are identified on an xyz-axis as (XG1, YG1, ZG1) and (XG3, YG3, ZG3). The coordinates of the target endpoint12is identified on an xyz-axis as (X12, Y12, Z12). Because the location of the gateway antenna is known to the network server16when LPWAN10is deployed, and the radius of the spheres has been calculated using equation 5.0 above, the location of the endpoint12can be calculated by using the calculation for the intersection of two spheres:
(rG1)2=(XG1+X12)2+(YG1+Y12)2+(ZG1+Z12)2; and  7.1)
(rG3)2=(XG3+X12)2+(YG3+Y12)2+(ZG3+Z12)27.1)
By solving equations 7.1 and 7.2 for (X12, Y12, Z12), the xyz-axis coordinates for the location of endpoint12is determined.

Because LPWAN10employs an overlapping gateway grid30with sectorized antennas15GN, it can accurately calculate geolocations of target endpoints12using just two gateway hosts14. Prior systems using other configurations require more gateways and more complex calculations.

Also, using sectorized antennas15GNhelps to reduce, and in some cases eliminated multipath effects that are common is other systems. In any signal communication between endpoints and antennas, the precise path of the communication is difficult to predict, and will often not be in a straight line between the two. For example, if there is a structure, such as a building, between the endpoint and antenna, the communication path will bounce off the structure and other objects while traveling between the endpoint and antenna. When non-sectorized antennas are used, with a single antenna radiating communication signals in a 360 degree radius, it is more likely for this multipath communication to occur. By using sectorized antennas, LPWAN10decreases this multipath effect.