Patent Publication Number: US-2010113035-A1

Title: Location-based handovers from a macrocell to a femtocell using event-triggered measurement reporting

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. ______, filed on Nov. 5, 2008, entitled “LOCATION-BASED HANDOVERS FROM A MACROCELL TO A FEMTOCELL USING PERIODIC MEASUREMENT REPORTING” inventors CRISTIAN DEMETRESCU and SUAT ESKICIOGLU. (2100.043100). 
     This application is related to U.S. patent application Ser. No. ______, filed on Nov. 5, 2008, entitled “METHOD FOR ASSOCIATING A CLUSTER OF PREMIER FEMTOCELLS WITH USER EQUIPMENT” inventors CRISTIAN DEMETRESCU and SUAT ESKICIOGLU. (2100.043300). 
     This application is related to U.S. patent application Ser. No. ______, filed on Nov. 5, 2008, entitled “METHOD FOR ASSOCIATING A PREMIER FEMTOCELL WITH USER EQUIPMENT” inventors CRISTIAN DEMETRESCU and SUAT ESKICIOGLU. (2100.043400). 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to communication systems, and, more particularly, to wireless communication systems. 
     2. Description of the Related Art 
     Conventional wireless communication systems use a network of base stations to provide wireless connectivity to one or more mobile units. In some cases, the mobile units may initiate wireless communication with one or more base stations in the network, e.g., when the user of the mobile unit would like to initiate a voice or data call. Alternatively, the network may initiate the wireless communication link with the mobile unit. For example, in conventional hierarchical wireless communications, a server transmits voice and/or data destined for a target mobile unit to a central element such as a Radio Network Controller (RNC). The RNC may then transmit paging messages to the target mobile unit via one or more base stations or node-Bs. The target mobile unit may establish a wireless link to one or more of the base stations in response to receiving the page from the wireless communication system. A radio resource management function within the RNC receives the voice and/or data and coordinates the radio and time resources used by the set of base stations to transmit the information to the target mobile unit. The radio resource management function can perform fine grain control to allocate and release resources for broadcast transmission over a set of base stations. 
     A conventional base station provides wireless connectivity within a geographical region that is referred to as a cell, a macrocell, and/or a sector. Conventional base stations can transmit signals using a predetermined amount of available transmission power, which in some cases is approximately 35 W for a base station. The range of the macrocell is determined by numerous factors including the available transmission power, angular distribution of the available power, obstructions within the macrocell, environmental conditions, and the like. For example, the range of a macrocell can vary from as little as 300 m in a densely populated urban environment to as much as 10 km in a sparsely populated rural environment. The coverage area can also vary in time if any of these parameters changes. 
     One alternative to the conventional hierarchical network architecture is a distributed architecture including a network of access points, such as base station routers, that implement distributed communication network functionality. For example, each base station router may combine RNC and/or PDSN functions in a single entity that manages radio links between one or more mobile units and an outside network, such as the Internet. Base station routers wholly encapsulate the cellular access technology and may proxy functionality that utilizes core network element support to equivalent IP functions. For example, IP anchoring in a UMTS base station router may be offered through a Mobile IP Home Agent (HA) and the GGSN anchoring functions that the base station router proxies through equivalent Mobile IP signaling. Compared to hierarchical networks, distributed architectures have the potential to reduce the cost and/or complexity of deploying the network, as well as the cost and/or complexity of adding additional wireless access points, e.g. base station routers, to expand the coverage of an existing network. Distributed networks may also reduce (relative to hierarchical networks) the delays experienced by users because packet queuing delays at the separate RNC and PDSN entities in hierarchical networks may be reduced or removed. 
     At least in part because of the reduced cost and complexity of deploying a base station router, base station routers may be deployed in locations that are impractical for conventional base stations. For example, a base station router may be deployed in a residence or building to provide wireless connectivity to the occupants of the residents of the building. Base station routers deployed in a residence are typically referred to as home base station routers or femtocells because they are intended to provide wireless connectivity to a much smaller area (e.g., a femtocell) that encompasses a residence. Femtocells have a much smaller power output than conventional base stations that are used to provide coverage to macrocells. For example, a typical femtocell has a transmission power on the order of 10 mW. Consequently, the range of a typical femtocell is much smaller than the range of a macrocell. For example, a typical range of a femtocell is about 100 m. Clusters of femtocells may also be deployed to provide coverage to larger areas and/or to more users. 
     Femtocells are expected to be deployed in conjunction with a macro-cellular network in an overlay configuration. For example, a macro-cellular network may be used to provide wireless connectivity to a neighborhood that includes numerous residences. Any mobile unit traveling through the neighborhood or located in one of the residences can access the wireless communication system using the macro-cellular network. Individual femtocells can be deployed in one or more of the residences to provide overlay coverage within (or near) the residence. Clusters of femtocells can also be deployed in one or more of the buildings to provide overlay coverage within (or near) the building. In either case, there will be a one-to-many relationship between the macrocells and the femtocells within the coverage area. However, user equipment will typically only be authorized to camp on selected femtocells. For example, user equipment operated by an individual user can be authorized to camp on femtocells that were installed by the user in their residence. For another example, user equipment operated by employees can be authorized to camp on femtocells in a femtocell cluster installed by a business. 
     As the user moves throughout the geographic areas served by the macrocells and the femtocells, the user equipment can be handed off between the macrocells and/or the femtocells. Conventional communication systems use radio conditions and/or the availability of radio resources to determine when to hand off user equipment. For example, channel qualities and/or signal strengths can be measured using signals transmitted between the user equipment and the macrocells and/or the femtocells. The conventional system hands off the user equipment from a macrocell to a femtocell when the channel qualities and/or signal strengths for signals transmitted by the macrocell are poor relative to the measured channel qualities and/or signal strengths for the femtocell. However, the conventional handoff criteria do not discriminate between generic femtocells, femtocells associated with particular user equipment, and macrocells. Consequently, user equipment may not be handed off to authorized home and/or business femtocells as long as the radio conditions in the macro-cellular network are sufficiently high quality, even if the user is inside the home or business covered by the associated femtocell. For example, when the femtocells are on a different frequency than the macrocells, radio conditions in the macro-cellular network may remain sufficiently high quality to prevent substantially all handovers to the femtocell, e.g., when the femtocell is deployed at the center of a macrocell&#39;s coverage area. 
     SUMMARY OF THE INVENTION 
     The disclosed subject matter is directed to addressing the effects of one or more of the problems set forth above. The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an exhaustive overview of the disclosed subject matter. It is not intended to identify key or critical elements of the disclosed subject matter or to delineate the scope of the disclosed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
     In one embodiment, a method is provided for implementation in user equipment that is configured to communicate with a wireless communication system that includes one or more macro-cells and one or more femtocells. The method includes comparing, at the user equipment, a location of the user equipment and a location of one or more femtocells. The method also includes transmitting, from the user equipment to the macrocell(s), a first measurement report, with a location-based event, when the comparison indicates that the user equipment is within a selected range of the femtocell(s). 
     In another embodiment, a method is provided for implementation in a radio network controller that is configured to for deployment in a wireless communication system that includes one or more macrocells and one or more femtocells. The method includes receiving, from the macrocell(s), a first measurement report that is transmitted by the user equipment when a comparison of a location associated with the user equipment and a location associated with the femtocell(s) indicates that the user equipment is within a selected range of the femtocell(s). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
         FIG. 1  conceptually illustrates a first exemplary embodiment of a wireless communication system; 
         FIG. 2  conceptually illustrates a second exemplary embodiment of a wireless communication system; 
         FIG. 3  conceptually illustrates a first exemplary embodiment of a method of handing off user equipment between a macrocell and a femtocell that operate on the same frequency; and 
         FIG. 4  conceptually illustrates a second exemplary embodiment of a method of handing off user equipment between a macrocell and a femtocell that operate on different frequencies. 
     
    
    
     While the disclosed subject matter is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims. 
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Illustrative embodiments are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions should be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     The disclosed subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
       FIG. 1  conceptually illustrates a first exemplary embodiment of a wireless communication system  100 . In the illustrated embodiment, a base station  105  provides wireless connectivity to a plurality of macro-cells  110 ( 1 - 3 ). Although the indices ( 1 - 3 ) can be used to identify individual macro cells  110 ( 1 ) or subsets thereof, these indices may be dropped when referring collectively to the macro-cells  110 . This convention may be applied to other elements depicted in the drawings and referred to using an identifying numeral and one or more distinguishing indices. The macro-cells  110  shown in  FIG. 1  correspond to different sectors associated with the base station  105 . For example, the base station  105  may include three antennas (or three groups of antennas) that provide wireless connectivity to three sectors associated with the three macro-cells  110 . However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that alternative embodiments may use a different base station  105  to provide wireless connectivity to each macro-cell  110 . Moreover, the wireless communication system  100  may include any number of macro-cells  110  and/or base stations  105 . In alternative embodiments, the base stations  105  may be a part of a hierarchical network or a distributed network. 
     The wireless communication system  100  also includes an overlay network of femtocells  115 . For example, the femtocells  115  may be installed in businesses and/or residences by individual users, companies, or other entities. In the interest of clarity, only four femtocells  115  are depicted in  FIG. 1 . However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the wireless communication system  100  may include any number of femtocells  115  distributed throughout the wireless communication system  100 . User equipment, such as the mobile unit  120  shown in  FIG. 1 , can be associated with one or more of the femtocells  115 . For example, a user that has installed the femtocell  115 ( 1 ) in a residence can configure the user equipment  120  so that the user equipment  120  recognizes the femtocell  115 ( 1 ) as its premier femtocell. The user equipment  120  may therefore preferentially handoff to the premier femtocell  115 ( 1 ) when the user equipment  120  approaches the premier femtocell  115 ( 1 ). In one embodiment, the femtocell  115 ( 1 ) may be part of a femtocell cluster (not shown in  FIG. 1 ). 
     The femtocell  115 ( 1 ) is a premier femtocell for the user equipment  120 . As used herein, the term “premier femtocell” refers to a femtocell that has been associated with the user equipment  120  so that the user equipment  120  is authorized to preferentially access the premier femtocell. Exemplary situations in which a premier femtocell can be defined include femtocell installed by users in their homes, femtocells (or clusters of femtocells) installed in a place of business, and the like. Mobility information related to the premier femtocell  115 ( 1 ) may be stored in the user equipment  120  and network entities such as the base station  105  and/or a radio network controller (not shown in  FIG. 1 ) that is communicatively coupled to the base station  105 . Exemplary mobility information includes, but is not limited to, information identifying the premier femtocell  115 ( 1 ), information indicating a location of the premier femtocell  115 ( 1 ), information indicating a frequency (or frequencies) used by the premier femtocell  115 ( 1 ) for communication over the air interface, and the like. 
     In the illustrated embodiment, the user equipment  120  has an existing wireless communication link  125  with the base station  105 , i.e., the user equipment  120  is in communication with the macrocell  110 ( 3 ) via one or more antennas supported by the base station  105 . The user equipment  120  may then determine a distance  130  between the user equipment  120  and its premier femtocell  115 ( 1 ). For example, the user equipment  120  may compare its location to the location of the premier femtocell  115 ( 1 ) to determine the distance  130 . If the distance  130  is less than a selected distance threshold value and, in some cases, if one or more measures of the quality of the wireless communication link  135  are better than a selected quality threshold, the user equipment  120  can send a message with a specific location-based event to the base station  105  indicating that the location-based and quality-based thresholds for a handoff to the femtocell  115 ( 1 ) have been reached. The wireless communication system  100  then initiates a handoff of the user equipment  120  from the base station  105  and corresponding macrocell  110 ( 3 ) to the femtocell  115 ( 1 ). 
     In the illustrated embodiment, the location-based handoff is only applied to premier femtocells  115 ( 1 ) associated with the user equipment  120 . Accordingly, the user equipment  120  may be preferentially handed off to its premier femtocell  115 ( 1 ) even though the air interface  125  to the macrocell  110 ( 3 ) may be providing sufficiently high quality channel conditions or even channel conditions that are superior to the channel conditions supported by the air interface  135 . 
       FIG. 2  conceptually illustrates a second exemplary embodiment of a wireless communication system  200 . In the illustrated embodiment, the wireless communication system  200  includes a femtocell  205 , user equipment  210 , a base station  215 , and a radio network controller (RNC)  220 . Persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the wireless communication system  200  may include other elements that are not depicted in  FIG. 2  to avoid unnecessarily obscuring the discussion. The femtocell  205  is a premier femtocell for the user equipment  210 . In the illustrated embodiment, the femtocell  205  stores information  225  including an identifier and information indicating the location of the femtocell  205 . The location information may be determined using numerous different techniques, including Global Positioning System (GPS) functionality incorporated into the femtocell  205  or manual configuration of the femtocell  205  by a user or a service provider. 
     Neighboring cell lists are typically maintained at the radio network controller  220  so that it knows which cells reported by the user equipment  210  should be considered for potential handovers. The radio network controller  220  may therefore ignore measurement reports associated with cells that are not listed in the neighboring cell list. Including the femtocell  205  in a neighboring cell list may be too cumbersome and unmanageable for the service operators due in part to the high volume of femtocells that may be deployed in a network. Therefore, in the illustrated embodiment, the femtocell  205  is not included in a neighboring cell list associated with the macrocell corresponding to the base station  215 . However, user equipment  210  can still measure distance and radio qualities of femtocell  205  by including the femtocell  205  in its detected cell set  237 . Then, the femtocell  205  that is included in detected cell  237  can be considered for handoff by the radio network controller  220 . Measurement reports transmitted by the user equipment include the femtocells  205  in the detected set that are then considered when determining whether to handoff the user equipment  210 . 
     The user equipment  210  has been configured so that it recognizes the femtocell  205  as its premier femtocell. In the illustrated embodiment, the user equipment  210  stores the identity of the premier femtocell  205 , the location of the premier femtocell  205 , and any other mobility parameters associated with the premier femtocell  205 . Exemplary mobility parameters include, but are not limited to, primary scrambling codes (PSC), an international mobile subscriber identity, a UTRAN Radio Network Temporary Identifier (U-RNTI), and the like. In the illustrated embodiment, the user equipment  210  defines a local variable, e.g. a data structure  230 , to store the femtocell information relevant to mobility. In the illustrated embodiment, the user equipment  210  stores the current cell information (relevant to mobility) and the location information (which may be provided by the femtocell  205  in a RRC Connection Setup message) into the PremierFemtoCell local data structure  230  when a PremierFemtoCellAvailable Boolean value in the setup message from the femtocell  205  is set to TRUE. 
     The radio network controller  220  maintains a context database  235  that stores contact information associated with the user equipment  210 , as well as other user equipment served by macro-cells that are connected to the radio network controller  220 . In the illustrated embodiment, the radio network controller  220  stores the information associated with the user equipment  210  and information indicating that the user equipment  210  is associated with a premier femtocell in the RRC context  235  for the user equipment  210 . For example, the context  235  for the user equipment  210  may include an identifier, a Boolean variable indicating that a premier femtocell is available, a parameter indicating the frequency used by the premier femtocell  205 , and the location of the femtocell  205 . Once the context  235  for the user equipment  215  has been configured, the radio network controller  220  knows that the user equipment  210  is associated with a premier femtocell. Although the user equipment  210  has been depicted as being associated with a single premier femtocell, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that in alternative embodiments the user equipment  210  may be associated with more than one premier femtocell. 
     In the illustrated embodiment, the user equipment  210  is initially served by the base station  215  over a wireless communication link including an uplink  240  and a downlink  245 . The wireless communication system  200  defines two events that can be used to trigger a handoff from the base station  215  to the premier femtocell  205 . One event is a location-based intra-frequency measurement event that is used when the premier femtocell  205  and the base station  215  use the same frequencies for communication over the air interface and the second event is a location-based inter-frequency measurement event that is used when the premier femtocell  205  and the base station  215  use different frequencies. After a connection, such as a RRC connection is established using the uplink  240  and the downlink  245 , the radio network controller  220  configures the user equipment  210  to use either the intra-frequency event or the inter-frequency event, depending on the frequency used by the user equipment  210  and the base station  215 . 
     The user equipment  210  is aware of its location. In the illustrated embodiment, the user equipment  210  includes Global Positioning System (GPS) functionality  250  to determine its location using signals  255  provided by a network of GPS satellites  260  (only one shown in  FIG. 2 ). Alternatively, the user equipment  210  can be made aware of its location using information provided by the base station  215  over the downlink  245 . This approach can be referred to as an assisted-GPS technique. The user equipment  210  can therefore use the stored location of the premier femtocell  205  to determine how far away the premier femtocell  205  is from the user equipment  210 . If the intra-frequency event is configured, the user equipment  210  sends a measurement report to the macrocell (i.e., the base station  215 ) when the distance  265  falls below a threshold and, in some cases, when the channel quality of an air interface  270  to the femtocell  205  is better than the configured threshold indicating the need of a hand-off. The radio network controller  220  may then perform an intra-frequency handoff in response to the intra-frequency event. Alternatively, if the inter-frequency event is configured, the user equipment  210  sends a measurement reports to the macrocell when the distance  265  falls below the threshold indicating a hand-off. The radio network controller  220  then initiates inter-frequency mobility procedures by initiating compressed mode measurements. The user equipment  210  can perform channel quality measurements of the air interface  270  in the compressed mode. When the channel quality to the femtocell  205  reaches an appropriate level (e.g., as indicated by a selected threshold value) the user equipment  210  can notify the radio network controller  220 , which completes the inter-frequency handoff to the femtocell  205 . 
       FIG. 3  conceptually illustrates a first exemplary embodiment of a method  300  of handing off user equipment (UE) from a macrocell (MC/RNC) to a premier femtocell (PFC). In the first exemplary embodiment, the macrocell and the premier femtocell use the same frequencies for communications over the air interface. The first exemplary embodiment therefore depicts an intra-frequency handoff procedure. Initially, an RRC connection is established (at  305 ) between the user equipment and the macrocell. The macrocell then determines (at  310 ) whether the user equipment has an associated premier femtocell. For example, the macrocell may examine the context associated with the user equipment to determine (at  310 ) whether the variable PremierFemtoCellAvailable is set to TRUE. In the illustrated embodiment, the user equipment does have an associated premier femtocell, so the macrocell also determines ((at  310 ) the frequency used by the premier femtocell to communicate with the user equipment, which in the first exemplary embodiment is the same as the frequency of the macrocell. 
     The macrocell then transmits (at  315 ) a measurement control message that includes information that is used to configure the location-based intra-frequency event. The user equipment receives this information and configures (at  320 ) the location-based intra-frequency event. The user equipment may also store (at  320 ) parameters related to the location-based intra-frequency event including thresholds for the location-based handoff, thresholds for the channel quality needed for a handoff, and the like. A call and/or session may then be established (at  325 ) between the user equipment and the macrocell. At this point in the process (indicated by the dashed line  330 ), the call between the user equipment and the macrocell can proceed. However, the user equipment continues to compare its location to the location of its premier femtocell and, in some cases, to monitor the channel qualities associated with the air interface to the femtocell. 
     The user equipment determines (at  335 ) that the distance between the user equipment and the premier femtocell has fallen below a threshold value. For example, the user equipment can compare (at  335 ) its current location to a location of the premier femtocell stored in the user equipment&#39;s memory to determine the distance:
         UE_PremierFemto_distance=UE_coordinates−premierFemto_coordinates
 
This distance can then be compared to the threshold and a handoff procedure can be triggered if:
   UE_PremierFemto_distance&lt;MacroToFemtoDistanceThreshold
 
The user equipment then determines (at  335 ) whether the quality of the channel between the user equipment and the femtocell is sufficiently high to support communication over the air interface. For example, the user equipment can use the pilot channel (CPICH) transmitted by the premier femtocell to assess the quality of the channel based on either signal-to-noise ratios or received signal channel powers (RSCP). Additional intra-frequency handover criteria from the macrocell to the femtocell are satisfied if:
   CPICH Ec/No&gt;event1kEcNoThreshold
 
and/or
   CPICH RSCP&gt;event1kRSCPThreshold.
 
When the handover conditions are satisfied, the user equipment sends (at  340 ) a measurement report that includes information indicating that the location-based intra-frequency handoff event has occurred. The measurement report may also include other mobility information including, but not limited to, primary scrambling codes, timing and/or offset information, CPICH Ec/No, CPICH RSCP, and the like. Thus, handover of the user equipment is triggered by proximity of the user equipment to the premier femtocell as long as the quality of the channel to the femtocell is sufficiently high. In this procedure, the channel quality associated with communication between user equipment and the macrocell does not need to be considered when deciding whether to handoff the user equipment to the premier femtocell.
       

     The radio network controller (RNC) uses the information included in the measurement report to execute (at  345 ) handover of the user equipment from the macrocell to the femtocell. In one embodiment, the radio network controller can send the primary scrambling code (PSC) and international mobile subscriber identity (IMSI) of the user equipment to a BSG femtocell gateway using an Iu Relocation Request. The gateway maps the femtocell primary scrambling code and the user equipment&#39;s IMSI to an identifier of the premier femtocell. The gateway can then send an Iu Relocation Command to the premier femtocell and the radio network controller sends (at  350 ) an Iu Reconfiguration Request to the user equipment. The reconfiguration request includes details identifying the premier femtocell so that the user equipment can establish communications with the premier femtocell. The user equipment then hands off (at  355 ) from the macrocell to the premier femtocell. 
       FIG. 4  conceptually illustrates a second exemplary embodiment of a method  400  of handing off user equipment (UE) from a macrocell (MC/RNC) to a premier femtocell (PFC). In the second exemplary embodiment, the macrocell and the premier femtocell use different frequencies for communications over the air interface. The second exemplary embodiment therefore depicts an inter-frequency handoff procedure. Initially, an RRC connection is established (at  405 ) between the user equipment and the macrocell. The macrocell then determines (at  410 ) whether the user equipment has an associated premier femtocell. For example, the macrocell may examine the context associated with the user equipment to determine (at  410 ) whether the variable PremierFemtoCellAvailable is set to TRUE. In the illustrated embodiment, the user equipment does have an associated premier femtocell, so the macrocell also determines (at  410 ) the frequency used by the premier femtocell to communicate with the user equipment, which in the second exemplary embodiment is different than the frequency of the macrocell. 
     The macrocell then transmits (at  415 ) a measurement control message that includes information that is used to configure the location-based inter-frequency event. The user equipment receives this information and configures (at  420 ) the location-based inter-frequency event. The user equipment may also store (at  420 ) parameters related to the location-based inter-frequency event including thresholds for the location-based handoff, thresholds for the channel quality needed for a handoff, the frequency used by the macrocell, and the like. A call and/or session may then be established (at  425 ) between the user equipment and the macrocell. At this point in the process (indicated by the dashed line  430 ), the call or session between the user equipment and the macrocell can proceed. However, the user equipment continues to compare its location to the location of its premier femtocell and, in some cases, to monitor the channel qualities associated with the air interface to the femtocell. 
     The user equipment determines (at  435 ) that the distance between the user equipment and the premier femtocell has fallen below a threshold value. For example, the user equipment can compare (at  435 ) its current location to a location of the premier femtocell stored in the user equipment&#39;s memory to determine the distance:
         UE_PremierFemto_distance=UE_coordinates−premierFemto_coordinates
 
This distance can then be compared to the threshold and a handoff procedure can be triggered if:
   UE_PremierFemto_distance&lt;MacroToFemtoDistanceThreshold
 
When the distance criterion is satisfied, the user equipment sends (at  440 ) a measurement report that includes information indicating that the location-based inter-frequency handoff event has occurred. The macrocell then responds (at  445 ) with a message indicating that the user equipment should operate in the inter-frequency compressed mode. In one embodiment, the Measurement Control message that activates the inter-frequency compressed mode is only used for the premier femtocells allowed by this user equipment.
       

     When the user equipment receives this message, the user equipment enters (at  450 ) the compressed mode and performs various channel quality measurements, e.g., using a pilot channel transmitted by the femtocell. The user equipment uses the inter-frequency compressed mode measurements to determine (at  450 ) whether the quality of the channel between the user equipment and the femtocell is sufficiently high to support communication over the air interface. For example, the user equipment can use the pilot channel (CPICH) transmitted by the premier femtocell to assess the quality of the channel based on signal-to-noise ratios and/or received signal channel powers (RSCP). The inter-frequency handover from the macrocell to the femtocell can then be triggered if:
         CPICH Ec/No&gt;event2gEcNoThreshold
 
and/or
   CPICH RSCP&gt;event2gRSCPThreshold.
 
When the handover condition(s) are satisfied, the user equipment sends (at  455 ) a measurement report that includes information indicating that the inter-frequency handoff event channel conditions have been satisfied. The measurement report may also include other mobility information including, but not limited to, primary scrambling codes, timing and/or offset information, CPICH Ec/No, CPICH RSCP, and the like. Thus, inter-frequency handover of the user equipment is triggered by proximity of the user equipment to the premier femtocell as long as the quality of the channel to the femtocell is sufficiently high. In this procedure, the channel quality associated with communication between user equipment and the macrocell does not need to be considered when deciding whether to handoff the user equipment to the premier femtocell.
       

     The radio network controller (RNC) uses the information included in the measurement report to execute (at  460 ) the inter-frequency handover of the user equipment from the macrocell to the femtocell. In one embodiment, the radio network controller can send the primary scrambling code and international mobile subscriber identity (IMSI) of the user equipment to a BSG femtocell gateway using an Iu Relocation Request. The gateway maps the femtocell primary scrambling code and the user equipment&#39;s IMSI to an identifier of the premier femtocell. The gateway can then send an Iu Relocation Command to the premier femtocell and the radio network controller sends (at  465 ) an Iu Reconfiguration Request to the user equipment. The reconfiguration request includes details identifying the premier femtocell so that the user equipment can establish communications with the premier femtocell. The user equipment then hands off (at  470 ) from the macrocell to the premier femtocell. 
     Portions of the disclosed subject matter and corresponding detailed description are presented in terms of software, or algorithms and symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     Note also that the software implemented aspects of the disclosed subject matter are typically encoded on some form of program storage medium or implemented over some type of transmission medium. The program storage medium may be magnetic (e.g., a floppy disk or a hard drive) or optical (e.g., a compact disk read only memory, or “CD ROM”), and may be read only or random access. Similarly, the transmission medium may be twisted wire pairs, coaxial cable, optical fiber, or some other suitable transmission medium known to the art. The disclosed subject matter is not limited by these aspects of any given implementation. 
     The particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.