Patent Publication Number: US-2005143090-A1

Title: Location aided wireless signal characteristic adjustment

Description:
FIELD OF INVENTION  
      The present invention relates to control of signal parameters in wireless communication systems. More particularly, the invention relates to adjusting received signal characteristics based on location information.  
     BACKGROUND  
      In wireless communication systems, parameter measurement is essential to the efficient operation of the system. These parameters include, bit error rates (BERs), block error rates (BLERs), signal to interference ratio (SIR) measurements, Doppler shifts, etc. To illustrate, in many wireless communication systems, the block error rate is used to determine whether transmission power levels need to be increased or decreased. A high BLER results in an increase in power and a low BLER results in a decrease in power. The use of the BLER measurements helps the wireless system maintain an efficient trade off between transmission power levels and system capacity.  
      A delay exists in adjusting for significant changes in the signal characteristics. For example, it takes many (e.g., 40) frames to complete an automatic frequency control (AFC) adjustment, and a number of frames for power control to correct for a deep fade (depending on the delay and averaging parameters). The fade may actually be over by the time the Doppler frequency compensation or power level converges to the correct value.  
      Accordingly, it is desirable to have alternate approaches to adjusting wireless signal characteristics.  
     SUMMARY  
      A wireless communication system uses location information in order to provide signal control parameters based on the anticipated movement of a wireless transmit receive unit (WTRU). A signal connection is established between a WTRU and a base station, and a location of the WTRU is obtained. The location is correlated with a database to obtain the anticipated movement of the WTRU.  
      In a particular embodiment of the invention, the correlation of the location includes mapping the location to a database and correlating the location and the database to obtain anticipated movement of the WTRU. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S)  
       FIG. 1  is a diagram showing an illustrative wireless signal propagation environment.  
       FIG. 2  is a flow chart for location aided wireless measurements.  
       FIG. 3  is a simplified diagram of a location aided wireless measurement system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
      The present invention is useful in wireless communication systems, such as in conjunction with a third generation partnership program (3GPP) wideband code division multiple access (W-CDMA) system. Hereafter, a WTRU includes but is not limited to a user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. A base station includes but is not limited to a Node-B, site controller, access point or other interfacing device in a wireless environment.  
       FIG. 1  is an illustration of applying location aided channel condition measurements. As illustrated in  FIG. 1 , a WTRU  20  (indicated at positions  20 A through  20 G) is traveling along a highway in a cell serviced by a base station  22 , which is in turn in operative communication with a radio network controller (RNC)  23  which has access to a database  24 . The database  24  includes a correlation between locations and relative signal strengths and between locations and anticipated future locations (travel paths).  
      As the WTRU  20  travels along the highway as illustrated by the arrow (from generally left to generally right), from position  20 A to position  20 B, a localized obstruction  31 , such as a building, causes a deep fade. The deep fade would likely result in a short duration high BER, high BLER and low SIR. The effects of obstruction  31  diminish, at position  20 C. As the WTRU  20  continues along the highway, it encounters a dense wooded area  33 , at positions which include  20 D and  20 E. Due to the varying nature of the wooded area  33 , each position  20 D,  20 E may encounter differing channel conditions. At position  20 F, the WTRU  20  continues along the highway in a transverse direction with respect to base station  23 , towards position  20 G in a longitudinal position with respect to base station  23 , the WTRU  20  begins to experience a Doppler shift as it moves at a fast rate away from the base station  23 . At position  20 H, the WTRU  20  moves to a handover zone, which results in another Doppler shift as a result of a handover. After handover, another Doppler shift occurs. Prior to handover the WTRU  20  is moving quickly away from the base station  22 . After handover, the WTRU  20  is moving quickly towards the neighboring cell&#39;s base station.  
      In accordance with one aspect of the present invention, the base station  22  is able to correlate its database with an anticipated path of the WTRU  20 . Thus if a WTRU  20  had moved from position  20 A to position  20 B, one could conclude that it is likely that the WTRU  20  will follow the roadway. The base station  22  correlates the present and previous locations, e.g. locations  20 A and  20 B with the data in the database  24 , and determines anticipated locations for the WTRU, such as location  20 C.  
      The RNC can anticipate future locations o f the WTRU  20  by, for example, (a) using the location and direction of motion to project the future path based on linear or non-linear extrapolation, or (b) employing a statistical approach in which, given the present location and direction of travel, and based on past behavior of previous WTRUs at that location and moving in that direction, empirically determining the probability of this WTRU  20  passing through a specified location, or (c) correlating the WTRU  20 &#39;s path with known paths of the area (such as from a map) and determining that the WTRU  20  is following a known path. The base station  22  uses the anticipated locations to provide signal control parameters in accordance with the anticipated locations.  
      While the above description has the base station  22  making the correlations, it is understood that the location of the database and the specific part of the network which makes the determinations of anticipated location and signal parameters may be elsewhere on the network. For example, the determination of anticipated location may be made by the RNC  23  or the database  24  can be at the base station  22 .  
       FIG. 2  is a flow diagram of location aided measurements. A base station  23  acquires a WTRU  20  (step  41 ), typically by establishing communications with the WTRU  20  or through a handoff (indicated as step  42 ). The base station and WTRU  20  establish signal parameters (steps  44  and  45 ) based on signal measurements. The WTRU  20  provides the base station  22  or RNC  23  with GPS location, or location information for the WTRU  20  is otherwise determined by the base station  22 /RNC  23  (step  46 ). The base station  23  then compares the location of the WTRU  20  as provided in step  46  with the database  24  (step  47 ). The comparison of the location of the WTRU  20  with the database  24  provides an indication of the environmental effects on the signals transmitted to and from the WTRU  20  and are correlated with the signal parameters determined in steps  44  and  45 . As the WTRU  20  progresses, the WTRU  20  provides the base station  23  with updated position information. The base station makes estimates of changes in signal parameters based on the new positions (step  49 ), and is able to provide estimates as to future locations of the WTRU  20  (step  51 ).  
      Optionally, the WTRU  20  provides directional movement data to the base station  22 /RNC  23 , such as by global positioning system (GPS) sensing (step  53 ). This data concerning movement is correlated by the base station  23  with data from the database  24  so as to provide more precise indications of movement of the WTRU  20 . Optionally, the WTRU  20  may also interpolate between GPS readings based on monitoring its vehicle&#39;s direction and speed, or based on a parameter versus distance or versus time function on that path communicated to the WTRU  20  from base station  22 /RNC  23 .  
      For a handoff, the base station  22  or RNC  23  provides the WTRU  20  with data related to the change in signal strength (step  55 ) and other parameters, including Doppler frequency adjustment (step  59 ) and hands off the WTRU  20  (step  62 ). Optionally, the base station  22  or RNC  23  also provides the WTRU  20  with cell synchronization information of the new cell, such as a scrambling code and frequency of a broadcast channel for 3GPP W-CDMA systems.  
       FIG. 3  is a schematic block diagram showing a WTRU  81  and base station  83  The WTRU  81  includes transmit receive circuitry  85 , and a location determining device, such as GPS receiver  86 . The WTRU  86  also includes signal analysis circuitry, such as path loss calculation circuit  87 , frequency estimator  88  and voice processing circuitry  89 . These components may be integrated into a common circuit, and may use a common processor to implement some or all of these components. The WTRU  81  provides the base station  83  with data relating to signal measurements as well as the GPS data (via GPS receiver  86 ), and receives signal parameters from the base station  83 . The base station  83  has transmit/receive circuitry  91 , a processor  92  and has access to a database  93 . In some configurations, the base station  83  may have a locating device  94  for determining locations of the WTRU  81 . The base station  83  uses data concerning the location from the WTRU  81  and from the locating device  94  to determine a location of the WTRU  81 . In addition, the database  93  can be used to estimate the location of the WTRU  81 . The WTRU  81  provides signal parameter data and signal strength estimations based on the actual signal measurements as combined with data obtained from the database  93 .  
      For certain measurements, other factors may affect the measurement. To illustrate, an interference measurement, such as interference signal code power (ISCP), made during peak hours may have little correlation to off peak hours, such as at night. Accordingly, a time of the day of the measurements may be stored so that only measurements reflecting similar channel conditions are combined. Another factor may be the weather. Measurements taken during a thunderstorm may vary significantly from measurements taken during a sunny day. As a result, a factor representing the weather conditions may be stored along with the measurements. Other factors include cell loading, speed of the WTRU  20  and the type of WTRU  20  taking the measurement.  
      In one embodiment, the system uses WTRUs  20  capable of location determination. The WTRU  20  allows their location information to be transmitted to the serving cell. In return for providing location information, the users receive better quality of service, avoidance of dropouts, superior emergency and convenience services, and an extension of battery life. The WTRU  20  periodically transmits its location information to the serving cell (and the RNC  23 ) on a control channel, which is typically available on the communication link between the WTRU  20  and the base station  22 . In some instances an accurate location determination may not be possible. As a result, the network or WTRU may estimate the WTRU&#39;s location by past measurements and a movement vector.  
      According to one embodiment, a WTRU  20  sends its coordinates to the base station while in motion and the RNC  23  identifies not only where the WTRU  20  is, but where it is going (direction and velocity can be calculated either in the WTRU  20  or RNC  23 ). The RNC  23  has access to a database which provides information concerning where predictable fades and Doppler shifts occur in the cell because of the detailed survey, such as performed by a roving monitor during site acceptance tests and annual surveys thereafter. The cell fixed monitors (which have an established mathematical relationship with the survey baseline) provide current state information to the RNC  23 .  
      Based on this information, the RNC  23  warns the WTRU  20  of approaching fades and Doppler shifts, and indicates how to correct them, such as by a signal or message. Since the RNC  23  is aware of when a WTRU  20  is entering a section of road where the power changes precipitously, it can unilaterally change the downlink power to an approximately correct value to avoid the typical slow 1 dB step changes commanded by the WTRU  20  in the standard closed loop transmit power control process. This procedure avoids a possible call dropout due to an overpowering fade.  
      Similar advantages apply to other link controls, such as adaptive modulation and coding, in which coding and modulation are adjusted to reduce the information data rate in the presence of adverse environmental conditions. The invention forewarns the WTRU  20  that it is approaching an adverse condition and provides guidance to the WTRU  20  to adjust its coding and modulation, and by how much. Likewise when conditions improve, the invention guides the WTRU  20  to adjust its coding and modulation to take quick advantage of improved conditions thus increasing cell capacity.  
      As the RNC  23  collects information, it can determine heavily and lightly traveled routes, such as highways. This type of mapping can also be done on a site survey. Once the RNC  23  is aware of the routes, it can take fewer samples in areas with little parameter changes. For areas with high parameter changes, the RNC  23  may take more samples to fully characterize the transient. For example, a road perpendicular to a base station  22  that suddenly makes a turn toward or away from the base station  22  produces a Doppler transient in a traveling WTRU  20 . A road that suddenly moves close to a busy interstate highway creates an interference transient. A road that moves behind a group of high rise buildings generates a power transient (fade).  
      The RNC&#39;s knowledge is preferably kept current. In one embodiment, stationary monitors are provided at key locations in the cell whose output is used to provide real time updates to the baseline data. On a long term basis, such updates acknowledge new roads, new tall buildings, etc. On a short term basis, updates report real time changes in the air interface conditions due to weather, temperature, interference, etc.  
      Using location adjustments allows the WTRU to take fewer measurements; work with more accurate information; and not be any less accurate in the case of discontinuous transmission (DTX) and sparse frame allocation where now it has to estimate the imprecise “virtual SIR”.  
      Faster outer loop power control, and improved downlink quality of service (QoS) is achieved by directly measuring the SIR BLER relationship. The initial downlink target SIR is largely based on relating BLER and initial target SIR, such as tables based on simulations.  
      The target SIR may be held constant for an extended period of time while the inner loop adjusts the downlink power to bring the SIR close to the target SIR. After this is done, the target SIR may be significantly off (in the sense that it is not producing the desired BLER). The location aided adjustment system may enter an algorithm that adaptively changes the target SIR step size. As a result, it may take a long time and numerous large and small steps to acquire the desired quality. The situation is worst for non real time data that may only last a few TTIs (transmission time intervals).  
      Location aided parameter adjustment directly relates the BLER to SIR. From its baseline survey, periodic updates, and statistics on WTRUs  20  traveling on certain roads in a particular direction (plus the interference and environment inputs from stationary monitors), the radio resource controller (RRC) can more accurately estimate the target SIR required to achieve the desired QoS, resulting in a dramatic improvement in speed and accuracy of corrections/adjustments.  
      In the downlink inner loop process, the WTRU commands the base station to increase or decrease power. With location aided adjustments, the RNC  23  looks up the correct power level based on the WTRU location. The power can be primarily adjusted by location updates rather than WTRU commands. The location based information can be occasionally verified, in a form of a confirmation check. The benefit is that both the signaling and WTRU internal calculations can be greatly reduced.  
      Instead of deploying monitors, the RNC  23  may learn the Doppler, power and other characteristics throughout the cell using measurements signaled by each WTRU  20 . Each passing WTRU  20  is a learning experience. For example, to determine the relation between the target SIR and BLER at some stretch of a road, the UTRAN assigns T 1  targetSIR to the first WTRU  20  and measures B 1  BLER as a result. The UTRAN assigns T 2  targetSIR to the next WTRU  20  and finds B 2  BLER. As a result, the database  93  can be updated by the individual WTRU measurements.  
      Also, by way of example, to determine the relation between the target SIR and BLER at some stretch of a road, the UTRAN assigns T 1  targetSIR to a first WTRU  20  and measures B 1  BLER as a result. The UTRAN assigns T 2  targetSIR to the next WTRU  20  and finds B 2  BLER. A database  93  is developed which is the electronic equivalent to a graph at each X,Y location in the cell. After completion, the RNC  23  has good data concerning parameters with respect to WTRU locations and air interface conditions in the cell. As a result, the RNC  23  is in a position to perform the following functions.  
      A long fade will tend to destabilize the target SIR. Consider the case of a WTRU  20  moving temporarily into the shadow of a large hill or apartment complex. As the BLER will tend to temporarily increase, the RRC will tend to increase the target SIR to compensate. Using location aided adjustments, the RNC  23  has access to data indicating that the situation is temporary and can (a) freeze the outer loop, and (b) guide the inner loop through the disturbance. The guide information may be power steps or may be a power level profile representing a power versus distance or time curve for the duration of the fade.  
      Automatic frequency control (AFC) can utilize the data concerning the WTRU&#39;s location and anticipated path. Based on the WTRU location and rate of motion, the RNC can inform the WTRU of an upcoming Doppler shift. The WTRU can therefore be handed the approximate frequency correction rather than wait, say, 40 frames for a reliable calculated value. Since the approximate frequency correction value is initially used, the measured value is more quickly obtained and is therefore more current than would be achievable by prior art techniques.  
      The location information provides an indication as to when a WTRU  20  is making a change in movement. This information provides the RNC with an indication when a WTRU  20  is making a major change in direction that radically changes the doppler offset. The RNC  23  can instruct the WTRU  20  to jump to the appropriate frequency correction, thus avoiding the normal, say, 40, frame correction period and the possibility of losing synchronization. Since the RNC  23  knows when a WTRU  20  is making a major change in direction that radically changes the doppler offset, it can instruct the WTRU  20  to jump to the appropriate frequency correction, thus avoiding the normal multi-frame correction period and the possibility of losing synchronization.  
      Additionally, emergency calling services are improved in their ability to locate the WTRU  20  used to make the call. In case of an emergency services call, the RNC  23  not only knows the location of the caller, but, if the caller is moving, the caller&#39;s path if the caller is moving. Caller movement is relevant, for example, if the caller is fleeing an attacker, en route to a hospital or other physical facility, or otherwise moving. The police will want to know not only where the person is but where he or she is headed. Furthermore, if an emergency vehicle is trying to find a caller in a poorly known location, the cell can provide mapping directions from area hospitals and fire and police stations.  
      The location capabilities can be used to provide road information. The RNC  23  can warn a WTRU user approaching a stop sign, entering a congested area, nearing an icy or foggy strip, approaching a dangerous intersection, and in general coming into a dangerous or backed up area. It can do this by signaling a buzzer or text message to the user, or interrupting a call with one of a set of pre recorded terse audio messages. Working with a tour or travel information service, the RNC  23  can alert WTRUs  20  about detours and general slowdowns. Working with a traffic service, the RNC  23  can alert a WTRU  20  to accidents and suggest alternate routes.