Positioning method for long-thin fleet

(a) Field of the Invention

The invention relates to a positioning method, particularly to a positioning method for long-thin fleet.

(b) Description of the Related Art

Global positioning systems (GPS) are well known and not only can be built in a current commercialized portable electronic device but also can be extensively used in various mobile devices, such as a mobile phone. However, when the portable electronic device uses GPS, power consumption of the device becomes so high that its battery power is quickly used up within a very short time. Therefore, GPS is not suitable to turn on for a long time.

Furthermore, the majority of mobile devices have limited supply of electric power. For example, during the movement of a fleet, if GPS is turned on for a long time, additional power charging equipment is required. If the fleet is a bike fleet, users usually cannot have additional power charging equipment to result in increasing inconvenience.

One object of the invention is to use a motion track (a path along which the fleet moves) of a fleet and cooperation among members of the fleet for positioning without additional charging equipment and without downloading map data in advance to further reduce the number of global positioning systems of the members to be turned on. Thus, the operable time of the network of the whole fleet can be further prolonged.

One embodiment of the invention provides a positioning method for a long-thin fleet, which moves along a direction and has a motion track and a leading member being in the forefront of the motion track. The method comprises a positioning step, acquiring positioning data through a GPS in a preset period of time; and a transmitting step, transmitting a periodic signal to members of the fleet through a wireless network system; wherein the leading member proceeds the positioning and transmitting steps and the motion track is connected according to the positioning data.

Since GPS requires consuming a lot of electric power during positioning and the battery on a mobile device only has limited electric power, the present invention uses the grouping characteristic of mobile devices and wireless communication to have the devices cooperate with each other while positioning. Thus, the number of global positioning systems of the members to be turned on can be reduced to achieve the similar speed of positioning and the similar positioning precision within a certain range or area.

Other objects and advantages of the invention can be better understood from the technical characteristics disclosed by the invention. In order to clarify the above mentioned and other objects and advantages of the invention, examples accompanying with figures are provided and described in details in the following.

FIG. 1A shows a schematic diagram illustrating a positioning method for long-thin fleet according to one embodiment of the invention.

FIG. 1B shows a schematic diagram illustrating a positioning method for long-thin fleet according to one embodiment of the invention.

FIG. 2 shows a schematic diagram illustrating positions for the long-thin fleet according to one embodiment of the invention.

FIG. 3 shows a flow chart illustrating a positioning method for long-thin fleet according to the invention.

Please refer to FIG. 1A . FIG. 1A shows a schematic diagram illustrating a positioning method of long-thin fleet according to one embodiment of the invention. The long-thin fleet 100 includes a plurality of members C 1 ˜C 9 and has a motion track W and a leading member K. The leading member K is in the forefront of the motion track W. In other words, the members C 1 ˜C 9 follow the leading member K and move along the motion track W to advance toward a direction D

In this embodiment, the leading member K and the members C 1 ˜C 9 all carry mobile devices, such as mobile phones, and use the Wi-Fi wireless Ad Hoc network system to make the long-thin fleet 100 a long-thin network on the motion track. Thus, the leading member K and the members C 1 ˜C 9 can perform signal transmission in the long-thin network.

It should be noted that the leading member K acquires positioning data every a preset period of time through a global positioning system (hereinafter referred to as “GPS”) and transmits a periodic signal to the members C 1 ˜C 3 within the signal reachable range through the Wi-Fi wireless Ad Hoc network system in the mobile device.

The periodic signal includes time data T, the positioning data P corresponding to the time data T and the motion track W corresponding to the time data T. The motion track W is formed by connecting a plurality of positioning data acquired by the leading member K every a period of time. The arc line in the figure shows the signal reachable range of the leading member K. In other words, the transmission radius of the leading member K through the Wi-Fi antenna is R 1 .

Then, for the members C 1 ˜C 3 within the range of the transmission radius R 1 , an algorithm is used to calculate the distances between the members C 1 ˜C 3 and the leading member K according to the positioning data and the motion track W to calculate the relative positions on the motion track W. Thus, the members C 1 ˜C 3 can realize their locations without the need of turning on their GPS for positioning.

It should be noted that, in the positioning method for long-thin fleet according to the invention, the Wi-Fi wireless Ad Hoc network systems of the members C 1 ˜C 3 each set a back-off time of the members C 1 ˜C 3 to have the members C 1 ˜C 3 count down according to its own back-off time and determine one member having the shortest back-off time in the members C 1 ˜C 3 as a relay member M 1 . In this embodiment, the member C 3 is the farthest away from the Wi-Fi wireless Ad Hoc network system of the leading member K and thus is the relay member M 1 .

After the countdown of the back-off time of the relay member M 1 is finished, GPS of the relay member M 1 is automatically turned on for positioning to acquire the current positioning data of the relay member M 1 . The relay member M 1 transmits the periodic signal to the members C 1 ˜C 7 within the signal reachable range through the Wi-Fi wireless Ad Hoc network system. In other words, the members C 1 ˜C 2 receive the periodic signal transmitted by the relay member M 1 before the countdown of the back-off time of the relay member M 1 is finished. As shown in the figure, the relay member M 1 has a transmission radius R 2 through the Wi-Fi antenna and also has a corresponding motion track W 2 .

In one embodiment, a user can determine the length of the back-off time according to the distance between each of the members C 1 ˜C 3 and the leading member K but the invention is not limited to this example. For example, if the signal transmission radius of the Wi-Fi antenna of the leading member K is 100 meters, the member having a distance of 100 meters with the leading member K sets its back-off time to 2 μs (micro seconds); the member having a distance of 70 meters with the leading member K sets its back-off time to 3 μs; and the member having a distance of 50 meters with the leading member K sets its back-off time to 5 μs.

In another embodiment, a user can determine the back-off time based on the remained power of the mobile devices of the members C 1 ˜C 3 . For example, the member having the more remained power of the mobile device has the shorter back-off time. Thus, since it is very power consuming during positioning by the GPS of the mobile device, the condition of a member having low remained power becoming the relay member M 1 can be prevented.

When the members C 4 ˜C 7 receive the periodic signal, the distances between the members C 4 ˜C 7 and the relay member M 1 are calculated according to the corresponding positioning data in the periodic signal through an algorithm and then the positions of the members C 4 ˜C 7 are calculated further according to the motion track W 2 . In other words, the members C 4 ˜C 7 within the transmission radius R 2 calculate the distances between the members C 4 ˜C 7 and the relay member M 1 according to the positioning data of the relay member M 1 and the motion track W 2 through an algorithm to calculate the relative positions on the motion track W 2 .

The Wi-Fi wireless Ad Hoc network systems of the members C 4 ˜C 7 each set a back-off time of the members C 4 ˜C 7 according to their own positions to have the members C 4 ˜C 7 count down according to their own back-off time and one member having the shortest back-off time in the members C 4 ˜C 7 is determined to be a relay member M 2 . In this embodiment, the member C 7 is the farthest away from the Wi-Fi wireless Ad Hoc network system of the relay member M 1 and thus is the relay member M 2 . As shown in the figure, the relay member M 2 has a transmission radius R 3 through the Wi-Fi antenna and the relay member M 2 also has a corresponding motion track W 3 .

By the same steps described previously, in this embodiment, the members C 8 ˜C 9 can determine the last relay member M 3 to be the member C 9 and calculate the positions according to the distances with the relay member M 2 and the motion track W 3 . The rest of principle is the same as that previously described and thus it will not be given hereinafter. At the time, the leading member K and the members C 1 ˜C 9 keep repeating the above steps to carry out positioning.

It should be noted that the leading member K, the relay members M 1 and M 2 have the corresponding motion tracks W, W 2 and W 3 , respectively, but the motion tracks W, W 2 and W 3 have the same moving path and direction. Thus, the motion track W can be considered to include the motion tracks W 2 and W 3 .

In this embodiment, the relay member M 1 positioned on the motion track W receives the periodic signals transmitted by the leading member K and the relay member M 2 . Similarly, the members C 1 ˜C 2 positioned between the leading member K and the relay member M 1 receive the periodic signals transmitted by the leading member K and the relay member M 1 . Thus, except the leading member K and the relay member M 3 at the end, the relay members M 1 and M 2 , the members C 1 , C 2 , C 4 ˜C 6 and C 8 positioned on the motion track W receive the periodic signals from its predecessor(s) and successor(s).

Please also refer to FIG. 1B . FIG. 1B shows a schematic diagram illustrating a positioning method for long-thin fleet according to one embodiment of the invention. In one embodiment of the invention, if one of the members C 1 ˜C 9 overpasses the leading member K, for example, the member C 2 passes over or is ahead of the leading member K, the member C 2 can only receive the periodic signal from the leading member K at its back because the member C 2 is beyond the signal reachable range of the relay member M 1 . At the time, the overpassing member C 2 resets a new back-off time to carry out countdown. After the countdown is finished, the previously mentioned positioning step and transmitting step are executed. That is, the mobile device of the member C 2 turns on GPS automatically to perform positioning and the periodic signal is transmitted to the members positioned within the signal reachable range of the member C 2 through the Wi-Fi wireless Ad Hoc network system of the member C 2 .

It should be noted that, when the leading member K receives the overpassing member C 2 and the relay member M 1 , the member C 2 replaces the leading member K as a new leading member K′. Thus, each member in the long-thin fleet 100 can replace the leading member and repeatedly perform the previously mentioned steps for positioning, transmitting, calculating positions and determining relay members through the mobile device.

In this embodiment, the distances between the members C 1 ˜C 3 and the leading member K, the distances between the members C 4 ˜C 7 and the relay member M 1 , and the distances between the members C 8 ˜C 9 and the relay member M 2 can be calculated by the time of arrival (TOA) algorithm.

For example, please also refer to FIG. 2 , showing the positions of the leading member K, the member C 2 and the relay member M 1 . The arrow indicates the motion track W. It is assumed after the leading member K and relay member M 1 finish positioning, the periodic data is transmitted to the member C 2 at the time T 1 and T 2 . The member C 2 receives the periodic data of the leading member K and the relay member M 1 at the time T 3 and T 4 . Thus, the following equation (1) and (2) is used to calculate d C2 K and d M1 C2 .

d C2 K =c× ( T 3− T 1)  (1)

d M1 C2 =c× ( T 4− T 2)  (2)

In the above equations, d C2 K is the distance between the leading member K and the member C 2 ; d M1 C2 is the distance between the member C 2 and the relay member M 1 ; and c is the speed of light (3×10 8 m/s).

Then, the following equation (3) is used to calculate the position P C2 — T3 .

√{square root over (( P C2 — T3 −P K — T1 ) 2 )}= d C2 K   (3)

√{square root over (( P C2 — T4 −P M1 — T2 ) 2 )}= d M1 C2   (4)

P K — T1 is the position of the leading member K at the time T 1 ; P C2 — T3 is the position of the member C 2 at the time T 3 ; P M1 — T2 is the position of the relay member M 1 at the time T 2 ; and P C2 — T4 is the position of the member C 2 at the time T 4 . Thus, after the leading member K and the relay member M 1 use GPS to complete positioning to acquire the corresponding positioning data, the position of the member C 2 at each timing can be calculated through the equations (1)˜(4) and the motion track W of the leading member K. Assumed that the position of member C 2 is (X i , Y i ), the distance between leading member K and member C 2 is d i , motion track W (W={(X 1 , Y 1 ), (X 2 , Y 2 ), . . . , (X n , Y n )}) is a set of all track points in the coordinates of X-axis and Y-axis which is from leading member K. Motion track W includes at least two track points and contains up to all track points collected in the Wi-Fi transmission radius. (X 1 , Y 1 ) is shown the latest position of leading member K; and (X n , Y n ) is shown the oldest position of leading member K. (X i , Y i ) can be solved by the following equation (a) and (b), where X i is between X j and X j+i ; and Y i is between Y j and Y j+1 .

d i = ( X i - X 1 ) 2 + ( Y i - Y 1 ) 2 ( a ) ( X i - X j ) ( Y i - Y j ) = ( X j - X j + 1 ) ( Y j - Y j + 1 ) ,

⁢ j = 1 ~ ( n - 1 ) ( b )

It should be noted that the above distance calculation method can carry out calculation through the coordinates of the members. For example, when the coordinate of the position P K — T1 of the leading member K at the time T 1 is (X K T1 , Y K T1 ) and the coordinate of the position P C2 — T3 of the member C 2 at the time T 3 is (X C2 — T3 , Y C2 — T3 ), the equation (3) can be rewritten into the following equation (5):

√{square root over (( P C2 — T3 −P K — T1 ) 2 )}=√{square root over (( X K —T1 −X C2 — T3 ) 2 +( Y K — T1 −Y C2 — T3 ) 2 )}{square root over (( X K —T1 −X C2 — T3 ) 2 +( Y K — T1 −Y C2 — T3 ) 2 )}= d C2 K .  (5)

In another embodiment, the distances between the members C 1 ˜C 3 and the leading member K, the distances between the members C 4 ˜C 7 and the relay member M 1 , and the distances between the members C 8 ˜C 9 and the relay member M 2 can be calculated by the received signal strength (RSS) algorithm. The equation of energy propagating in air of the periodic signal of Wi-Fi is shown in the following equation (6):

In the above, P r represents the received power, P t represents the emitting power, d represents the distance, G t represents the emitting antenna gain, λ represents the wavelength of the periodic signal of Wi-Fi, L is the systematic loss factor, and π represents the ratio of the circumference of a circle to its diameter. The parameters except the distance d can be measured in advance.

If the leading member K transmits the periodic signal at the time T 1 , after the member C 2 receives the periodic signal at the time T 3 , the signal strength P r can be measured. According to the equation (6), the distance between the leading member K and the member C 2 can be calculated to be d C2 K . Then, according to the positioning data of the leading member K in the periodic signal and the equation (3), the position P C2 — T3 of the member C 2 at the time T 3 can be calculated.

Please refer to FIG. 1B again. The positioning method according to the invention can determine whether a member overpasses the leading member K or not based on the positions of each member and the leading member K or the distances between each member and the leading member K. It is assumed that the signal transmission radius of Wi-Fi antenna is 100 meters, the distance d K C2 between the member C 2 and the leading member K is 30 meters, and the distance d M1 K between the leading member K and the relay member M 1 is 50 meters. Since the member C 2 is positioned within the signal reachable ranges of the leading member K and the relay member M 1 , the distance d M1 C2 between the member C 2 and the relay member M 1 is compared with the distance d M1 K between the leading member K and the relay member M 1 . If the distance d M1 C2 is larger than the distance d M1 K the member C 2 overpasses the leading member K and the member C 2 becomes a new leading member K′.

Please refer to FIG. 3 . FIG. 3 shows a flow chart illustrating a positioning method for long-thin fleet according to the invention. The positioning method comprises the following steps:

Step S 301 : turning on GPS of the leading member or the relay member for positioning to acquire positioning data;

Step S 302 : transmitting a periodic signal to members within a signal reachable through Wi-Fi;

Step S 303 : according to time data, positioning data corresponding to the time data and motion track corresponding to the time data in the periodic signal, calculating corresponding positions by members;

Step S 304 : determining a back-off time according to distances or the quantity of the battery power and performing countdown by members;

Step S 305 : determining whether the periodic signal is received or not before the countdown of the back-off time is complete, jumping to step S 306 if not, and jumping to step S 307 ;

Step S 306 : becoming a relay member and jumping to step S 301 ; and

In conclusion, since the battery power on a mobile device is limited, the present invention uses the grouping characteristic of mobile devices and wireless communication to have the devices cooperate with each other while positioning. Thus, the number of global positioning systems of the members to be turned on can be reduced to achieve the similar speed of positioning and the similar positioning precision within a certain range or area.

Although the present invention has been fully described by the above embodiments, the embodiments should not constitute the limitation of the scope of the invention. Various modifications or changes can be made by those who are skilled in the art without deviating from the spirit of the invention. Any embodiment or claim of the present invention does not need to reach all the disclosed objects, advantages, and uniqueness of the invention. Besides, the abstract and the title are only used for assisting the search of the patent documentation and should not be construed as any limitation on the implementation range of the invention.