Abstract:
An exemplary method of communicating includes storing a locating neighbor list that corresponds to a mobile station being in a communication range of a selected picocell. Upon receiving a current neighbor list, a determination is made whether the current neighbor list corresponds to the stored, locating neighbor list. If there is sufficient correspondence, that indicates that the mobile station is in a communication range of the picocell.

Description:
1. FIELD OF THE INVENTION 
       [0001]    This invention generally relates to communication. More particularly, this invention relates to wireless communication. 
       2. DESCRIPTION OF THE RELATED ART 
       [0002]    Wireless communication systems are well known and in widespread use. Many systems are referred to as cellular systems because of the way that wireless communication coverage is designed. Base station transceivers are arranged to provide wireless communication coverage over geographic areas surrounding the base station. The geographic area is typically referred to as a cell. Traditional base station transceivers provide relatively large geographic coverage and the corresponding cells can be referred to as macrocells. 
         [0003]    It is possible to establish smaller-sized cells within a macrocell. These are sometimes referred to as picocells. One proposed way for establishing a picocell is to provide a picocell base station unit that operates within a relatively limited range within the coverage area of a macrocell. One example use of a picocell base station unit is to provide wireless communication coverage within a building, for example. 
         [0004]    Various challenges are introduced by the possibility of having multiple picocells within a macrocell. It is necessary to be able to identify the picocells to facilitate accurate handovers between the macrocell and a desired picocell, for example. With the likely proliferation of many picocells, the task of identifying each of them uniquely becomes daunting. Further, there must be some mechanism for locating them for a possible handover. 
         [0005]    It is necessary to generate a user-specific neighbor list that includes candidate cells that a mobile station can consider. In addition to the existing macrocells, it will become necessary to include a user&#39;s home or work picocell, for example, within the neighbor list. While creating a unique neighbor list for each user that includes such a picocell is one possibility, there are additional costs, complexity and signaling overheads on the network side, which render such an approach undesirable. For example, one radio network controller can control over 100 macrocell base stations and there could be thousands of picocells within the corresponding area. Providing unique neighbor lists for individual mobiles places too high a burden on the network. 
         [0006]    Additionally, it is not desirable for a mobile station to continuously search for a home or work picocell because that wastes energy and reduces mobile battery life. Further, the possibility of scrambling code or PN offset re-use will result in incorrect picocell identifications. 
         [0007]    There is a need for an efficient arrangement for identifying picocells in a manner that facilitates accurate handovers between a macrocell and a desired picocell. 
       SUMMARY 
       [0008]    An exemplary method of communicating includes storing a locating neighbor list that corresponds to a mobile station being in a communication range of a selected picocell. Upon receiving a current neighbor list, a determination is made whether the current neighbor list corresponds to the stored, locating neighbor list. If there is sufficient correspondence, that indicates that the mobile station is in a communication range of the picocell. 
         [0009]    An exemplary wireless communication mobile station device includes a storage having a locating neighbor list corresponding to the mobile station being in a communication range of a selected picocell. The mobile station device includes a transceiver for receiving a current neighbor list. A detection module is configured to determine whether the current neighbor list corresponds to the locating neighbor list. When there is sufficient correspondence, that indicates that the mobile station is in a communication range of the picocell. 
         [0010]    The various features and advantages of a disclosed example will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  schematically shows selected portions of a wireless communication system that is useful with an embodiment of this invention. 
           [0012]      FIG. 2  schematically shows selected portions of an example mobile station and schematically illustrates one example approach. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  schematically illustrates selected portions of a communication system  20 . A base station  22  includes a base station transceiver unit and appropriate radio communication equipment for conducting wireless communications in a generally known manner. The base station  22  establishes a wireless communication coverage area  24  that is referred to as a macrocell for purposes of discussion. The geographic region of the macrocell  24  will depend on, in part, the capabilities of the base station  22  and the surrounding geography. There are known techniques for establishing a desired macrocell coverage area. 
         [0014]    Within the macrocell  24 , a picocell base station unit (PCBSU)  30  provides wireless communication coverage within a picocell  32 . As can be appreciated from the illustration, the size of the coverage area of the picocell  32  is much smaller than that of the macrocell  24 . The illustration is not to scale but the point is that the picocell coverage area of the picocell  32  is much smaller than that of the macrocell  24 . In one example, the picocell  32  corresponds to the user&#39;s home. 
         [0015]    Another PCBSU  34  provides wireless coverage within a picocell  36 . Still another PCBSU  38  provides a picocell coverage area  40 . 
         [0016]    It is possible for a mobile station  44  within the macrocell  24  to communicate with the macrocell by communicating with the base station  22  in a known manner. When the mobile station  44  enters into a picocell area where that mobile station is authorized for communications within the picocell, it will be desirable to handover from the macrocell  24  to the corresponding picocell. In the illustrated example, the user of the mobile station  44  has rights for using the communication capabilities of the PCBSU  30  for communicating within the picocell  32 . 
         [0017]    The example mobile station  44  has a capability of detecting and reporting the picocell  32  when it comes into a communication range where the mobile station  44  can communicate with the PCBSU  30 .  FIG. 2  schematically shows selected portions of the mobile station  44 . A memory or storage  50  includes a locating neighbor list  52  corresponding to at least one time when the mobile station  44  is in a communication range of the picocell  32 . In one example, the mobile station  44  stores the neighbor list from a time when registering the mobile station  44  with the PCBSU  30 . This may occur during installation of the PCBSU or an initial use of the mobile station  44  within the picocell  32 , for example. In one example, when the mobile station  44  has an active communication link with the PCBSU  30 , it stores the neighbor list available to it at that time as the locating neighbor list  52 . 
         [0018]    The illustrated example storage  50  also includes a plurality of measurements  54  that are made by the mobile station  44  at a time associated with the stored locating neighbor list  52 . For example, the mobile station  44  makes a plurality of measurements from at least some of the macrocell base stations or PCBSUs within the locating neighbor list  52 . 
         [0019]    The locating neighbor list  52  will include at least a plurality of macrocell base station identifiers. In some examples, the locating neighbor list  52  will include PCBSUs associated with nearby picocells, if appropriate. The mobile station  44  uses the stored locating neighbor list  52  for purposes of determining when it is nearby or within the picocell  32 . The illustrated example includes a PCBSU detection module  60  that utilizes the stored locating neighbor list  52  for determining when the mobile station  44  is in a communication range of the picocell  32 . 
         [0020]    The mobile station  44  includes a transceiver portion  62  that communicates with the serving macrocell base station  22 . The transceiver portion  62  receives a current neighbor list  64  provided by a macrocell radio network controller, for example, as schematically shown at  66 . The PCBSU detection module  60  determines whether the current neighbor list  64  corresponds to the stored locating neighbor list  52 . In one example, the PCBSU detection module  60  determines whether there is an identical match between the current neighbor list  64  and the locating neighbor list  52 . In another example, the PCBSU detection module  60  is capable of determining a level of correspondence between the current neighbor list  64  and the locating neighbor list  52 . If the amount of correspondence exceeds a threshold, the PCBSU detection module  60  determines that there is sufficient correspondence between the current neighbor list  64  and the locating neighbor list  52  to indicate that the mobile station  44  is likely within a communication range of the picocell  32 . 
         [0021]    The amount of correspondence may be based upon various factors such as a percentage of matching cell codes within the neighbor lists  64  and  52 . Another example technique for determining an amount of correspondence between the neighbor lists  64  and  52  when they are not identical is to use measurements obtained by the mobile station  44  associated with each list. The stored measurements  54  may be compared to a set of current measurements  68  obtained by the mobile station  44  at the time of trying to determine whether the current neighbor list  64  sufficiently corresponds to the locating neighbor list  52 . One example includes determining whether at least a minimum percentage of the current power measurements correspond to the stored measurements  54 . If there is sufficient correspondence between at least some of the measurements and there is sufficient correspondence between the members of the neighbor list  64  and the locating neighbor list  52 , the PCBSU detection module  60  in one example determines that the mobile station  44  is within a communication range of the picocell  32 . Another example technique includes using signal timing information as a metric for determining correspondence or similarity between the neighbor lists. Given this description, those skilled in the art will be able to determine an appropriate correlation technique and appropriate thresholds to meet the needs of their particular situation. 
         [0022]    An example that includes requiring some amount of correlation between a current neighbor list and a stored locating neighbor list provides an advantage over an arrangement where an exact match between the neighbor lists is required. For example, if there is a change in the macrocellular configuration over time, that could cause a change in a current neighbor list such that it would not match an out-dated, previously stored locating neighbor list. 
         [0023]    Once the mobile station  44  determines that there is sufficient correspondence between the current neighbor list  64  and the locating neighbor list  52 , the mobile station  44  begins to perform measurements for the PCBSU  30  cell code (e.g., UMTS scrambling code or CDMA PN offset or an equivalent). In one example, the mobile station  44  also begins to perform measurements for neighboring PCBSUs to assist in identifying whether the mobile station  44  is, in fact, in the vicinity of the picocell  32 . 
         [0024]    When the mobile station  44  detects the PCBSU  30  signal, it reports the cell code of the PCBSU  30  back to the macrocell base station  22  as schematically shown at  70 . The PCBSU  30  is, therefore, reported as part of the mobile station&#39;s detected set. The radio network controller associated with the macrocell base station  22  responsively includes the PCBSU  30  in the measured set and requests measurements from the mobile station  44  regarding the picocell  32 . 
         [0025]    Once measurements from the picocell  32  indicate that the mobile station  44  obtains a sufficient signal from the PCBSU  30 , the radio network controller initiates a handover from the macrocell  24  to the picocell  32 . After successful handover, the mobile station  44  in one example updates the stored locating neighbor list  52  and measurements  54  while the mobile station  44  is in the picocell  32 . Periodically updating the locating list  52  and the measurements  54  allows for accommodating changes that may have occurred in the macrocellular configuration or the picocellular configuration of the surrounding area in the vicinity of the picocell  32 . This example technique allows for adapting to network changes such as the addition of a new base station in the area. 
         [0026]    The disclosed example provides a technique for a mobile station to determine when it enters a communication range of a selected picocell. The task of identifying when that occurs, which corresponds to the mobile station requiring a modified neighbor list that includes the PCBSU of a selected picocell, is assigned to the mobile station. This de-centralized approach relieves any burden from the network side such that specialized neighbor lists need not be handled by the radio network controller of the macrocell network. Instead, the mobile station  44  attempts to correlate a currently received neighbor list with the locating neighbor list. The mobile station  44  only needs to search for the PCBSU of a selected picocell when the probability of success for locating that picocell is high. This is based upon a sufficient correspondence between the current neighbor list  64  and the stored locating neighbor list  52 . Searching for a particular PCBSU only when there is a likelihood of finding it saves battery power for the mobile station. 
         [0027]    One advantage to the disclosed example is that it allows for mobile stations to use a stored locating neighbor list and measurement results to identify when the mobile station is in proximity to a selected picocell. The disclosed example provides a robust picocell area detection even when an overall network configuration changes. Because the disclosed example delegates the task of identifying proximity to a selected picocell to a mobile station, it provides cost savings by reducing complexity and signaling overhead on the network side. Additionally, by limiting the amount of time a mobile station spends searching for a particular picocell, power consumption is reduced and battery life is increased. Another advantage to the disclosed example is that it reduces the likelihood of incorrect picocell identifications, which may otherwise occur because of cell code re-use, for example. 
         [0028]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.