US20070265020A1 - Method and system for determining the speed and position of a mobile unit - Google Patents

Abstract

Apparatus and methods are disclosed for estimating the position and velocity of mobile wireless transmit/receive units (WTRUs) in a wireless communication system. Network stations use directional communication beams to divide service areas into sectors to provide communication services to the WTRUs. A WTRU saves pertinent information such as sector ID, received power and time of reception of the several received signals. The collected information is sent to the network, where it is used to estimate the WTRU's position, speed and direction of travel, which information can then be used to improve radio resource management.

Description

CROSS REFERENCE TO RELATED APPLICATION
• This application claims priority from U.S. Provisional Patent Application No. 60/392,413 filed on Jun. 28, 2002; U.S. patent application Ser. No. 10/330,637, filed Dec. 27, 2002; and U.S. patent application. Ser. No. 11/261,238, filed Oct. 28, 2005, which are incorporated by reference as if fully set forth.
BACKGROUND OF THE INVENTION
• The present invention is directed to wireless communication systems. More particularly, the invention is related to a cellular system using a plurality of smart antennas for determining the speed and distance of a wireless transmit receive unit (WTRU).
• In current wireless system deployments, the speed and position of WTRUs are determined using many different methods. For example, global positioning system (GPS) may be used for those WTRUs with GPS capability. Alternatively, the network may determine the speed and position using triangulation techniques. Each of these techniques generally have undesirable drawbacks. For example, the GPS affixes significant expense and complexity to a WTRU. A WTRU that is equipped with a GPS is basically a device with two receivers, one for interfacing with the cellular system and the second for the reception of the positioning satellites. The additional receiver increases the battery consumption and uses up valuable WTRU resources.
• Another method for WTRU position determination employs triangulation techniques that require the use of additional primary stations and/or extra hardware in each primary station to support the triangulation.
• It would desirable to provide an improved WTRU tracking mechanism which is able to effectively locate a WTRU when it is in communication with a primary station.
SUMMARY
• The present invention comprises a method and system where a common channel (such as a beacon channel) is swept over a specified coverage area of a sectorized cell. An idle wireless transmit/receive unit (WTRU) saves pertinent information such as received power and time of reception of the last several readings of the common channel. On the WTRU's next access, the information is sent to the network to determine the WTRU's location, its direction of travel and a speed estimate which is valuable for radio resource management.
• The communications system preferably includes a plurality of WTRUs and means to calculate a speed and distance of each of the plurality of WTRUs using stored information. Each WTRU preferably has a receiver that is configured to monitor a selected channel while in an idle state, a memory to store information regarding the selected channel and a transmitter to send the stored information from the WTRU at an appropriate time.
• In one embodiment a wireless communication network in which communication services for WTRUs is provided by network stations that transmit wireless communication signals in directional beams such that beams are from time to time transmitted to each area serviced by the respective network station, each beam including beam identifying information. The network preferably includes at least one network station and at least one WTRU.
• A preferred network station has a transmitter configured to transmit wireless communication signals in directional beams from a known location such that beams are from time to time transmitted to each area serviced by the network station, each beam including beam identifying information.
• A preferred WTRU has a receiver configured to receive a plurality of network station transmitted directional beams, including beam identifying information for each of the received beams. The WTRU receiver is preferably configured to measure respective received signal strength for each of the plurality of beams received. The WTRU has an associated memory configured to store respective beam identifying information data with respective measured received signal strength data. The WTRU also preferably has a transmitter configured to transmit to the network station stored beam identifying information data and received signal strength data for the plurality of received beams. The memory and the transmitter of the WTRU is preferably configured to transmit sets of beam identifying information data and received signal strength data for a selected number, no less than three, of successively received beams. The beam identifying information data for each beam preferably includes a direction of the beam, a time the beam was sent and a transmit power of the beam.
• A preferred network station also a receiver configured to receive sets of beam identifying information data and received signal strength data from WTRUs and an associated controller configured to estimate the position, speed and direction of movement of a particular WTRU using beam identifying information data and received signal strength data for a plurality, preferably at least three, of received beams received from the particular WTRU in a data set. The network station controller is preferably configured to calculate a signal pathloss from the beam identifying information data and received signal strength data, for each of the plurality of beams; estimate, from a calculated pathloss, a distance from the network station known transmission location to the WTRU for each of the plurality of beams; estimate, from a network station known transmission location and respective estimated distances, a position of the WTRU each of the plurality of beams; and estimate a WTRU's speed and direction of movement using the plurality of position estimates in combination with the times the respective beams were sent. The estimate of the distance from the network station to a WTRU is preferably made using at least one of an environmental factor, a cost-231 Hata model, a plane earth propagation model or a free space model.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1A is a diagram of a communication system in accordance with the teachings of which incorporates the present invention.
• FIG. 1B is a diagram of a convergence area of a primary station of the system illustrated inFIG. 1A.
• FIG. 2 is a flow diagram of a method for determining speed and distance of a WTRU in accordance with the teachings of the present invention.
• FIG. 3 is an example of the WTRU Cartesian coordinate representation of the coverage area illustrated inFIG. 1B.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• The present invention will be described with reference to the drawing figures wherein like numerals represent like elements throughout. Referring toFIG. 1A, acommunication network10 generally comprises one or moreprimary stations14, each of which is capable of wireless communication with a plurality ofWTRUs16. Each WTRU16 communicates with either the closestprimary station14 or theprimary station14 which provides the strongest communication signal. WTRUs in general are well known in the art and are used as vehicle telephones or hand held cell phones. Generally such WTRUs are also known as mobile units. Primary stations are also known as base stations.
• Eachprimary station14 broadcast and receives signals through thecoverage area100 via the primary stations'antenna21. Theantenna21, through its antenna array, shapes the antenna's radiation pattern into the form of abeam24. Thebeam24 is swept throughout acoverage area100 as shown inFIG. 1B. Thecoverage area100 comprises a plurality of sectors S₁. . . S_N. The base station controller20 coordinates communications among multipleprimary stations14 by means of anetwork path26 which may be a land line or wireless link. Thecommunication network10 may optionally be connected to a public switched telephone network (PSTN)22 via aPSTN network path28. Although thewireless communication system10 is shown employing separate units for thenetwork26 and theprimary stations14, these functions may be physically combined with abase station14 to form a “master primary station.”
• With reference toFIG. 1A. andFIG. 2, a WTRU16 traverses (step301) through one or more sectors of thecoverage area100 of aprimary stations14, which is swept by abeam24. The WTRUs16 are configured to monitor one or more common channels when in an idle state (step310), for example, the beacon channel which is broadcast by aprimary station14 throughout of thecoverage area100. Common channels by design are meant to be received by all WTRUs within the coverage area. As the idle (turned-on, but not active in user information exchange) WTRU16 stays stationary or moves about the coverage area, it will store information about and from the beacon channel (step320). This information may include the time, signal path loss, sector ID, beacon transmit power, received power and received interference level. TheWTRU16 later uplinks the information it has collected from the common channel to the primary stations14 (step330). The information will then be used by the network to determine the speed, distance and direction of the mobile (step340).
• When theWTRU16 acquires a common channel, the common channel may also contain information from theprimary station14 that will assist thebase station controller20 determine the WTRU's location. For example, thenetwork20 will instruct theprimary stations14 to systematically sweep thebeam24 in a deterministic fashion throughout the coverage area to carve out sectors (seeFIG. 1B). Thebase station controller20 can append the common channels with a sector ID or beam number which indicates the sector the beam is transmitting in. TheWTRU16 later uplinks the time stamped information to thebase station controller20. Thebase station controller20 can then use the sector id or beam number received by theWTRU16 along with the calculated path loss to calculate the location of the WTRU16 relative to theprimary station14. The pathloss is based upon the transmission power of theprimary station14 and the received power at theWTRU16. An appropriate environmental model is then applied to compensate for the effects of the terrain. For example, if the environment were rural, then the base station controller would use a rural environment model in its calculations.
• The position of the primary station is known and the network can translate the relative position into an absolute position. It should be noted that the position of the primary station is not an absolute position, it is a relative value to a known reference point using an X,Y grid or Cartesian coordinate system. The X axis represents the east and west direction and the Y axis represent the north and south direction. The grid values are usually in meters or kilometers. An example of the WTRU Cartesian coordinate representation for a coverage area is illustrated inFIG. 3.
• To locate the position of a WTRU (WTRU_X, WTRU_Y), the ΔX and ΔY distances are first determined as the X and Y distance from the primary station and the WTRU. The WTRU_X of the WTRU's position can be found in Equation 1:
  WTRU_—X=ΔX+PS_position_—X;  Equation 1
  where ΔX is the X distance from WTRU to the PS and PS_position_X is the X coordinate of the PS. The WTRU_Y of the WTRU position can be found by Equation 2:
  WTRU_—Y=ΔY+PS_position_—Y;  Equation 2
  where ΔY is the Y distance form WTRU to the PS and PS_position_Y is the Y coordinate of the PS.
• The distance from the Primary Station to the WTRU can be found from Equation 3:
  Distance_—TO_—WTRU=√{square root over ((ΔX²)+)}(ΔY²);  Equation 3
  where ΔX and ΔY are the values from above equations. The azimuth angle from the PS to the WTRU can be found from Equation 4:
  Azimuth(WTRU)=tan⁻¹(ΔY/ΔX)  Equation 4
  where Azimuth is the azimuth angle in degrees.
• Referring toFIG. 3, aexemplary coverage area30, is referenced by a Cartesian coordinate system with the reference point (RP)32 located at the origin (0,0). APS14 is located at coordinates (−5,2) and aWTRU16 is located at (−1,5). The azimuth angle Φ38 is the angle from thePS14 to theWTRU16. To calculate the distance from thePS14 to theWTRU16, the ΔX and ΔY values must be obtained. The ΔX and ΔY values are the X and Y distances from thePS14 to theWTRU16, respectively, which were obtained from calculations using pathloss and known PS transmit power and received power at theWTRU16. The ΔX is equal to 4 and the ΔY is equal to 3.Equation 3 is the used to determine that the distance from PS toWTRU16, which is 5 meters. The azimuth angle Φ38 is determined fromEquation 4 which is approximately 39 degrees.
• The distance calculation is dependent upon the pathloss calculation and environmental variables, such atmospheric conditions. A typical propagation in free space model for determining the distance based on the pathloss and environment is shown in Equation 5:
  Distance=10^{(Pathloss−32.4−20 log(f))/20};  Equation 5
  where f is the center carrier frequency in MHz; distance is in Km and the pathloss is in dB. Another method to calculate distance is the plane earth propagation model, which is illustrated by Equation 6:
  Distance=10^{(pathloss+20 log(HbHm)/40};  Equation 6
  where Hb is the height of the base station antenna (meters); Hm is height of mobile station antenna (meters) and the distance is in meters. In yet another method to calculate distance is the cost-231 Hata model for pathloss calculation is illustrated by Equations 7:
  Pathloss=46.3+33.9 log(f)−13.82 log(Hb)−a(Hm)+(44.9−(6.55 log(Hb)))*log(distance)+Cm;  Equation 7
  and for distance, Equation 8:
  Distance=10^{(Pathloss−46.3−33.9log(f)+13.82log(Hb)−a(Hm)−Cm/44.9−6.55log(Hb)))};  Equation 8
  where Hb and Hm are the base station's and the WTRU's antenna heights in meters; f is the center frequency in MHz; the distance is in Km; a is a correction factor in dB for the antenna height of the mobile for a medium small urban city and is illustrated in Equation 9:
  (Hm)=(1.1 logf−0.7)Hm−1.56 logf+0.8;  Equation 9
  where the value of Cm changes depending on suburban or rural environments. For the suburban environmental model the Cm value is 0 dB and for the metropolitan environmental model, a 3 dB value is used.
• As the WTRU moves about the coverage area, thenetwork20 can then calculate the speed and direction of theWTRU16 by comparing WTRU's16beam24 acquisition measurements. For example, to obtain an approximate speed determination, a simple equation such as the change in position divided by the change in time is shown in Equation 10:
  speed=Δposition/Δtime;  Equation 10
  where Δ position is change in position and Δtime is the change in time.
• A further breakdown ofEquation 1 is illustrated by Equation 11:
  speed=(P_n−P_n−1)/(T_n−T_n−1);  Equation 11
  where P_nand T_nrepresent the current position and the current time of theWTRU16 and P_n−1and T_n−1represent a previous position and its associated time.
• It should be noted that the estimate of speed depends on the accuracy of the position estimates. The position estimates may become inaccurate if thecoverage area100 is large or if theWTRU16 is near the furthermost perimeter of the cell. However, if thecoverage area100 is relatively small and theWTRU16 is close to the center of the cell, the estimate will be highly accurate. The size of the sector will also impact the position estimate; more sectors will slice the coverage area into more positional determinable locations.
• To obtain the direction of the WTRU, the system may simply use the current and previous locations of the WTRU. First the distance is calculated using the equations above and inFIG. 3.
• In order to achieve the most efficient assignment of resources, it is highly desirable to produce an estimate of the position and speed of theWTRU16 when it first comes into thecoverage area100. This allows thecommunication network10 to employ admission algorithms and efficiently assign communication resources.
• In another embodiment, the communications system may utilize neighboring primary stations or neighboring cells to more accurately estimate the position of aWTRU16. When theWTRU16 accesses aprimary station14, the communications may be monitored up by neighboring primary stations which also use adaptive antenna receivers. The linked receiving primary stations are then able to determine the location of theWTRU16 using simple triangulation techniques to more accurately calculate the WTRU's position.
• In an alternative embodiment, three or more WTRU beacon measurements are taken by the WTRU and reported back to the communications system. This allows for better determination of the speed and the direction of the WTRU.
• While the present invention has been described in terms of the preferred embodiment, other variations which are within the scope of the invention as outlined in the claims below will be apparent to those skilled in the art.

Claims (22)

1. A method for determining a position, speed and direction of movement of a wireless transmit/receive unit (WTRU), the method comprising:

the WTRU receiving from a network station a plurality of the transmitted directional beams, including beam identifying information for each of the received beams;

for each of the plurality of received beams, the WTRU measuring the respective received signal strength and storing respective beam identifying information data with respective measured received signal strength data; and

the WTRU transmitting to the network station stored beam identifying information data and received signal strength data for the plurality of received beams to thereby enable the network station to estimate the position, speed and direction of movement of the WTRU using beam identifying information data and received signal strength data for the plurality of received beams received from the WTRU.

2. The method according toclaim 1 wherein the WTRU receiving, measuring, storing and transmitting steps are performed with respect to a selected number of no less than three directional beams successively transmitted from the network station.

3. The method according toclaim 1 wherein the storing of beam identifying information data for each beam includes storing a direction of the beam, a time the beam was sent and a transmit power of the beam.

4. The method according toclaim 3 wherein the WTRU receiving, measuring, storing and transmitting steps are performed with respect to a selected number of no less than three directional beams successively transmitted from the network station.

5. The method according toclaim 1 wherein the WTRU receiving and transmitting steps are performed with respect to a wireless communication network which is one of: an IEEE 802.11, an IEEE 802.16, a GSM or a 3GPP compliant network system using predetermined frame formats.

6. A method for determining a position, speed and direction of movement of a wireless transmit/receive unit (WTRU), the method comprising:

transmitting wireless communication signals from a network station in directional beams from a known location such that beams are from time to time transmitted to each area serviced by the network station, each beam including beam identifying information to thereby enable WTRUs to receive identified beams and measure and store respective received signal strength; and

receiving from a WTRU by the network station stored beam identifying information data and received signal strength data for the plurality of received beams; and

estimating the position, speed and direction of movement of the WTRU using beam identifying information data and received signal strength data for the plurality of received beams received from the WTRU.

7. The method according toclaim 6 wherein the receiving step is performed with respect to a selected number of no less than three directional beams successively transmitted from the network station.

8. The method according toclaim 6 where the beam identifying information data for each beam includes a direction of the beam, a time the beam was sent and a transmit power of the beam, wherein the estimating the position, speed and direction of movement of the WTRU includes:

calculating a signal pathloss from the beam identifying information data and received signal strength data, for each of the plurality of beams;

estimating, from the calculated pathloss, a distance from the network station known transmission location to the WTRU for each of the plurality of beams;

estimating, from the network station known transmission location and the respective estimated distances, a position of the WTRU each of the plurality of beams; and

estimating the WTRU's speed and direction of movement using the plurality of position estimates in combination with the times the respective beams were sent.

9. The method according toclaim 8 wherein the distance from the network station known transmission location to the WTRU is estimated using one of: an environmental factor, a cost-231 Hata model, a plane earth propagation model or a free space model.

10. The method according toclaim 8 wherein the receiving step is performed with respect to a selected number of no less than three directional beams successively transmitted from the network station.

11. The method according toclaim 6 wherein the transmitting directional beams is performed by a network station of a wireless communication network which is one of: an IEEE 802.11, an IEEE 802.16, a GSM or a 3GPP compliant network system using predetermined frame formats; and the estimating step is performed by the network.

12. A wireless transmit receive unit (WTRU) comprising:

a receiver configured to receive from a network station a plurality of transmitted directional beams, including beam identifying information for each of the received beams;

a memory associated with said receiver;

said receiver configured to measure the respective received signal strength for each of the plurality of received beams and to storing respective beam identifying information data with respective measured received signal strength data in said memory; and

a transmitter configured to transmit to the network station stored beam identifying information data and received signal strength data for the plurality of received beams to thereby enable the network station to estimate the position, speed and direction of movement of the WTRU using beam identifying information data and received signal strength data for the plurality of received beams received from the WTRU.

13. The WTRU according toclaim 12 wherein the transmitter is configured to transmit beam data in sets with respect to a selected number of no less than three directional beams successively transmitted from the network station.

14. The WTRU according toclaim 12 wherein receiver is configured to store beam identifying information data for each beam that includes a direction of the beam, a time the beam was sent and a transmit power of the beam.

15. The WTRU according toclaim 14 wherein the transmitter is configured to transmit beam data in sets with respect to a selected number of no less than three directional beams successively transmitted from the network station.

16. The WTRU according toclaim 15 configured for use in a wireless communication network which is one of: an IEEE 802.11, an IEEE 802.16, a GSM or a 3GPP compliant network system using predetermined frame formats.

17. A wireless transmit receive unit (WTRU) configured a network station for a wireless communication network comprising:

a transmitter configured to transmit wireless communication signals in directional beams from a known location such that beams are from time to time transmitted to each area serviced by the WTRU, each beam including beam identifying information to thereby enable user WTRUs to receive identified beams and measure and store respective received signal strength; and

a receiver configured to receive from a user WTRU stored beam identifying information data and received signal strength data for a plurality of beams transmitted by the WTRU and received by the user WTRU; and

a processor configured to estimate the position, speed and direction of movement of the user WTRU using the beam identifying information data and received signal strength data for the plurality of beams received by the user WTRU.

18. The WTRU according toclaim 17 wherein the receiver is configured to receive from a user WTRU stored beam identifying information data and received signal strength data for sets of a selected number of no less than three directional beams successively transmitted from the WTRU.

19. The WTRU according toclaim 17 wherein:

the transmitter is configured to transmit and the receiver is configured to receive beam identifying information data for each beam that includes a direction of the beam, a time the beam was sent and a transmit power of the beam; and

the processor is configured to estimate the position, speed and direction of movement of the user WTRU by:

calculating a signal pathloss from the beam identifying information data and received signal strength data, for each of the plurality of beams;

estimating, from the calculated pathloss, a distance from the WTRU known transmission location to the user WTRU for each of the plurality of beams;

estimating, from the WTRU known transmission location and the respective estimated distances, a position of the user WTRU each of the plurality of beams; and

estimating the user WTRU's speed and direction of movement using the plurality of position estimates in combination with the times the respective beams were sent.

20. The WTRU according toclaim 19 wherein the processor is configured to estimate the distance from the WTRU known transmission location to the user WTRU by using one of: an environmental factor, a cost-231 Hata model, a plane earth propagation model or a free space model.

21. The WTRU according toclaim 19 wherein the receiver is configured to receive from a user WTRU stored beam identifying information data and received signal strength data for sets of a selected number of no less than three directional beams successively transmitted from the WTRU.

22. The WTRU according toclaim 17 configured as a network station of a wireless communication network which is one of: an IEEE 802.11, an IEEE 802.16, a GSM or a 3GPP compliant network system using predetermined frame formats; and the estimating step is performed by the network.

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