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&#39;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; and U.S. patent application Ser. No. 10/330,637, filed Dec. 27, 2002, now U.S. Pat. No. 7,123,924, 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&#39;s next access, the information is sent to the network to determine the WTRU&#39;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&#39;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 in  FIG. 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 is illustrated in  FIG. 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 to  FIG. 1A , a communication network  10  generally comprises one or more primary stations  14 , each of which is capable of wireless communication with a plurality of WTRUs  16 . Each WTRU  16  communicates with either the closest primary station  14  or the primary station  14  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. 
   Each primary station  14  broadcast and receives signals through the coverage area  100  via the primary stations&#39; antenna  21 . The antenna  21 , through its antenna array, shapes the antenna&#39;s radiation pattern into the form of a beam  24 . The beam  24  is swept throughout a coverage area  100  as shown in  FIG. 1B . The coverage area  100  comprises a plurality of sectors S 1  . . . S N . The base station controller  20  coordinates communications among multiple primary stations  14  by means of a network path  26  which may be a land line or wireless link. The communication network  10  may optionally be connected to a public switched telephone network (PSTN)  22  via a PSTN network path  28 . Although the wireless communication system  10  is shown employing separate units for the network  26  and the primary stations  14 , these functions may be physically combined with a base station  14  to form a “master primary station.” 
   With reference to  FIG. 1A . and  FIG. 2 , a WTRU  16  traverses (step  301 ) through one or more sectors of the coverage area  100  of a primary stations  14 , which is swept by a beam  24 . The WTRUs  16  are configured to monitor one or more common channels when in an idle state (step  310 ), for example, the beacon channel which is broadcast by a primary station  14  throughout of the coverage area  100 . 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) WTRU  16  stays stationary or moves about the coverage area, it will store information about and from the beacon channel (step  320 ). This information may include the time, signal path loss, sector ID, beacon transmit power, received power and received interference level. The WTRU  16  later uplinks the information it has collected from the common channel to the primary stations  14  (step  330 ). The information will then be used by the network to determine the speed, distance and direction of the mobile (step  340 ). 
   When the WTRU  16  acquires a common channel, the common channel may also contain information from the primary station  14  that will assist the base station controller  20  determine the WTRU&#39;s location. For example, the network  20  will instruct the primary stations  14  to systematically sweep the beam  24  in a deterministic fashion throughout the coverage area to carve out sectors (see  FIG. 1B ). The base station controller  20  can append the common channels with a sector ID or beam number which indicates the sector the beam is transmitting in. The WTRU  16  later uplinks the time stamped information to the base station controller  20 . The base station controller  20  can then use the sector id or beam number received by the WTRU  16  along with the calculated path loss to calculate the location of the WTRU  16  relative to the primary station  14 . The pathloss is based upon the transmission power of the primary station  14  and the received power at the WTRU  16 . 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 in  FIG. 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&#39;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     =           (     Δ   ⁢           ⁢     X   2       )     +       ⁢     (     Δ   ⁢           ⁢     Y   2       )         ;           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 (Δ Y/ΔX )  Equation 4 
where Azimuth is the azimuth angle in degrees.
 
   Referring to  FIG. 3 , a exemplary coverage area  30 , is referenced by a Cartesian coordinate system with the reference point (RP)  32  located at the origin (0,0). A PS  14  is located at coordinates (−5,2) and a WTRU  16  is located at (−1,5). The azimuth angle Φ 38  is the angle from the PS  14  to the WTRU  16 . To calculate the distance from the PS  14  to the WTRU  16 , the ΔX and ΔY values must be obtained. The ΔX and ΔY values are the X and Y distances from the PS  14  to the WTRU  16 , respectively, which were obtained from calculations using pathloss and known PS transmit power and received power at the WTRU  16 . 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 to WTRU  16 , which is 5 meters. The azimuth angle Φ 38  is determined from Equation 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 (patloss+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−46.3−33.9 log(f)+13.82 log (Hb)−a(Hm)−Cm/(44.9−6.55 log(Hb))) ;  Equation 8
 
where Hb and Hm are the base station&#39;s and the WTRU&#39;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 log  f −0.7) Hm −1.56 log  f +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, the network  20  can then calculate the speed and direction of the WTRU  16  by comparing WTRU&#39;s  16  beam  24  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=Δ position/Δtime;  Equation 10
 
where Δ position is change in position and Δtime is the change in time.
 
   A further breakdown of Equation 1 is illustrated by Equation 11:
 
speed=( P   n   −P   n−1 )/( T   n   −T   n−1 );  Equation 11
 
where P n  and T n  represent the current position and the current time of the WTRU  16  and P n−1  and T n−1  represent 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 the coverage area  100  is large or if the WTRU  16  is near the furthermost perimeter of the cell. However, if the coverage area  100  is relatively small and the WTRU  16  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 in  FIG. 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 the WTRU  16  when it first comes into the coverage area  100 . This allows the communication network  10  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 a WTRU  16 . When the WTRU  16  accesses a primary station  14 , 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 the WTRU  16  using simple triangulation techniques to more accurately calculate the WTRU&#39;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.