Abstract:
A method of recognizing states and locations of user equipment in a network by using a random access (RA) channel at a base station without alteration of the conventional network environment or configurations of user equipment. A mobile communication system of an embodiment includes a first base station; and one or more second base stations having service regions smaller than a service region of the first base station. The first base station is operable to broadcast configuration information to the user equipment for connecting to at least one of the one or more second base stations. The user equipment is operable to transmit an uplink signal to at least one of the one or more second base stations in accordance with the configuration information received from the first base station, and at least one of the one or more second base stations is operable to transmit information on the user equipment that transmitted the uplink signal to the first base station after receiving the uplink signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Korean Patent Application No. 10-2008-0137394 filed on Dec. 30, 2008, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention may generally relate to a communication method in a mobile communication environment. More particularly, the present invention may relate to a method of identifying user equipment by a base station based on states of wireless channels between the user equipment and the base station. 
     BACKGROUND 
     In a mobile communication environment, it is widely known to adopt a random access (RA) channel for communication between user equipment and the base station. The RA channel is a common channel which can be used by all user equipment. In using the RA channel instead of a dedicated channel, additional channel recognition processes are not necessary between the base station and user equipment since parameters, resources, etc., required to use the RA channel, are already set up by the base station. 
     Generally, usage of the RA channel for the communication is as follows. Through the RA channel, the first uplink signal is transferred when a user equipment initially accesses the base station. The RA channel may be used in uplink measurement for synchronization of physical layers. The RA channel is also used to transmit signals relating to a specific request from the user equipment to the base station. During a handover process, the RA channel is used to control the synchronization between a destination base station of the user equipment and the physical layers. 
     According to the conventional communication between the base station and the user equipment by using the RA channel, the base station broadcasts configuration information on the RA channel to the user equipment in cells of a service area covered by the base station. The configuration information includes RA codes and information on uplink RA channels available to the user equipment. The user equipment selects the uplink RA channel and transmits the RA codes to the base station in accordance with the configuration information on the RA channel set by the base station. Upon receiving the RA codes transmitted from the user equipment, the base station broadcasts a RA response corresponding to the received RA codes. In the RA response, the received RA codes and RA channel information are included. After receiving the RA response, the user equipment decides whether the RA codes and the RA channel information included in the RA response are respectively identical to the RA codes and the RA channel information having been transmitted from the user equipment itself. If the codes and the information are the same, the user equipment transmits an RA message for requesting a specific service. Upon receiving the RA message, the base station identifies the user equipment which transmitted the RA message and provides the requested service. 
     The user equipments can start communication with the base station with the RA channel mentioned above. However, there is the problem that locations or states of the user equipment which communicate with the base station through the RA channel cannot be reported to the base station. 
     SUMMARY 
     The present invention provides a method of recognizing states and locations of user equipment in a network by using a random access (RA) channel at a base station without alteration of the conventional network environment or configurations of user equipment. 
     In one embodiment, a method of identifying a user equipment by a base station, in a mobile communication system is provided. The method includes broadcasting configuration information to a user equipment so that the user equipment transmits an uplink signal to one or more base stations; and determining a location of the user equipment based on a service region of one or more base stations having received the uplink signal from the user equipment. 
     In another embodiment, the uplink signal includes random access (RA) codes. 
     In other embodiments, at least one of the one or more base stations includes any one of a femto base station, a macro base station and a micro base station. 
     In another embodiment, the method further includes measuring intensity of the uplink signal received from the user equipment at at least one of the one or more base stations. The step of determining the location of the user equipment includes determining the location in consideration of only the service region of at least one of the base stations that received the uplink signal with a higher intensity than a predetermined threshold value. 
     In other embodiments, a mobile communication system is provided. The system includes a first base station; and one or more second base stations having service regions smaller than a service region of the first base station, wherein the first base station is operable to broadcast configuration information to the user equipment for connecting to at least one of the one or more second base stations. The user equipment is operable to transmit an uplink signal to at least one of the one or more the second base stations in accordance with the configuration information received from the first base station, and at least one of the one or more second base stations is operable to transmit information on the user equipment having transmitted the uplink signal to the first base station after receiving the uplink signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a network environment for communication with random access channels in accordance with the present invention; 
         FIG. 2  is a schematic diagram showing a communication method between a user equipment and a base station with the random access channels in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic diagram showing a communication method between a user equipment and a base station with the random access channels in accordance with another embodiment of the present invention; and 
         FIG. 4  is a schematic diagram showing a communication method between a user equipment and a base station with the random access channels in accordance with a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, various embodiments of the present invention are described in detail with reference to the attached drawings. In the drawings, well-known elements, in the relevant art, have been omitted in order not to obscure the present invention in unnecessary detail. 
       FIG. 1  shows a network environment for communication with random access channels in accordance with the present invention. Network environment  100  may include user equipment  110 , macro base station  120 , femto base stations  130  and  132  and backbone network  150 . While the coverage of macro base station  120  may be above a few kilometers, the coverage femto basestations  130  and  132  may be within a few tens of meters. Macro base station  120  and femto base stations  130  and  132  may be connected through an additional backbone network. 
       FIG. 1  shows one macro base station  120  and two femto base stations  130  and  132 . However, the numbers of the macro base stations and the femto base stations are not limited thereto. Further, macro base station  120  and femto base stations  130  and  132  can be replaced with a pico base station or a micro base station. In another embodiment, all the base stations may be configured with the same type of base station selected among the macro base station, micro base station and femto base station. 
     The present invention provides a multiple destination random access (MDRA) scheme with which the user equipment may transmit RA codes to a plurality of femto base stations. According to a conventional communication scheme adopting an RA channel, the user equipment transmits the RA codes to only a single base station after receiving broadcasted information on setting up the RA channel. Unlike the conventional communication scheme, in accordance with the MDRA scheme of the present invention, user equipment  110  may transmit RA codes to one or more femto base stations  130  and  132 . In one embodiment, user equipment  110  can transmit the RA codes at low power or a predetermined power since femto base stations  130  and  132  are located in a nearby region compared with macro base station  120 . After receiving the RA codes, femto base stations  130  and  132  may report information on user equipment  110  to macro base station  120  through a network, for instance, backbone network  150 . The information on user equipment  110  may include the received RA codes and the intensity of a received signal. Further, the femto-base-stations  130  and  132  may also be a relay or a proxy during the communication between user equipment  110  and macro base station  120  through the RA channel. 
     In one embodiment, femto base stations  130  and  132  may select signals from the signals transmitted from the user equipment that have intensities that are not less than a threshold intensity and may report the selected signals to macro base station  120 . The threshold intensity may vary dynamically as according to the circumstances. 
     In another embodiment, user equipment  110  may transmit a signal including an RA code at a predetermined transmitting power. Upon receiving the RA code, femto base stations  130  and  132  may compare a real receiving power of the signal with the predetermined transmitting power. Femto base stations  130  and  132  may calculate a path loss with a difference between the real receiving power and the predetermined transmitting power. Information on the path loss may be included in the information on user equipment which is reported to macro base station  120 . 
     In other embodiments, macro base station  120  may determine where user equipment  110  is currently located between two service regions of femto base stations  130  and  132  based on which of base stations  130  and  132  reported information on the user equipment. If only femto-base-station  130  reported information on user equipment  110  to macro base station  120 , macro base station  120  can determine that user equipment  110  is located in the service region of femto base station  130 . If femto base stations  130  and  132  both reported information on user equipment  110  to macro base station  120 , macro base station  120  can determine that user equipment  110  is located in an overlap region of the service regions of both femto base stations  130  and  132 . Further, it can be estimated how far it is from user equipment  110  to femto base station  130  or  132 , based on the path loss. 
     Since it is possible to estimate how close it is from the user equipment to the femto base station, the location of the user equipment can be accurately figured out even though the user equipment does not have a global positioning system (GPS) receiver. Thus, this can be utilized in a location-based service. 
     Hereinafter, detailed descriptions of communication methods in accordance with embodiments of the present invention may be provided with reference to the accompanying drawings  FIGS. 2 to 4 . 
       FIG. 2  shows flow chart  200  of a communication method between a user equipment and a base station with use of RA channels in accordance with an embodiment of the present invention. In one embodiment, an MDRA communication method, performed by user equipment  110 , macro-base-station  120  and femto-base-station  130 , will be described. However, the present invention is not limited to this embodiment. For instance, a plurality of femto base stations may take part in the MDRA communication. Further, macro base station  120  may be replaced with a first base station selected from a pico base station, a micro base station and a femto base station. In this case, femto base station  130  may be replaced with a second base station that has a service region that is no larger than that of the first base station. 
     Macro base station  120  and femto base station  130  may share configuration information such as RA codes, channel resources and so on, for the MDRA communication through backbone network  150  or by a provisioning process (step  205 ). Macro base station  120  may broadcast the configuration information on MDRA channels to the user equipment (step  210 ). The configuration information may include RA codes and information on uplink RA channels available to the user equipment. User equipment  110  may select the RA codes and the uplink RA channel in accordance with the configuration information on the MDRA channel set by the base station (step  215 ). User equipment  110  may transmit the RA codes to a plurality of femto base stations at a predetermined power through the selected channel resource (step  220 ). In this step, it is noted that the RA codes are not transmitted to macro base station  120  but to the plurality of the femto base stations near the user equipment. 
     Femto base station  130  may analyze the RA code referring to the configuration information shared with the macro base station at step  205  (step  225 ). Femto base stations  130  may receive a message from the user equipment and report information (for instance, the RA codes) on user equipment to macro base station  120  based on the received message (step  230 ). In another embodiment, the information on user equipment may include the power received from the user equipment which transmits the message. In an alternate embodiment, femto base station  130  may report the information (for instance, the RA codes) to macro base station  120  only when the received power is not less than a threshold value. 
     Macro base station  120  may broadcast an RA response to user equipment  110  referring to the information on the user equipment reported by femto base station  130  (step  240 ). The RA response may include the RA codes and RA channel information, transmitted from femto base station  130 . After receiving the RA response, user equipment  110  may verify whether the RA codes and the RA channel information included in the RA response are respectively identical to those having been transmitted from the user equipment itself (step  245 ). If the codes and the information are the same, user equipment  110  may transmit an RA message for requesting a specific service to macro base station (step  250 ). After receiving the RA message, macro base station  120  may identify the user equipment which requested the service and provide the requested service (step  255 ). At step  255 , Macro base station  120  may determine a service region of a femto base station where user equipment  110  lies based on the RA message and information received from femto base station  130 . 
     As described above, femto base station  130  may perform an earlier communication with user equipment  110  based on the channel configuration information broadcasted by macro base station  120 . Macro base station  120  can determine the location of user equipment  110  with the information on user equipment  110  reported by the femto base station. 
       FIG. 3  shows flow chart  300  of a communication method between a user equipment and a base station with use of RA channels in accordance with another embodiment of the present invention. The method shown in  FIG. 3  is useful when time for transmitting and receiving messages between a macro base station and a femto-base-station at each step, is not enough. 
     Similar to the method described referring to  FIG. 2 , macro base station  120  and femto base station  130  may share configuration information such as RA codes, channel resources and so on, for the MDRA communication through backbone network  150  or through a provisioning process (step  305 ). Macro base station  120  may broadcast the configuration information on MDRA channels to the user equipment (step  310 ). The configuration information may include the RA codes and information on uplink RA channels available to the user equipment. User equipment  110  may select the RA codes and the uplink RA channel in accordance with the configuration information on the MDRA channel set by the base station (step  315 ). User equipment  110  may transmit the RA codes to a plurality of femto base stations at a predetermined power through the selected channel resource (step  320 ). 
     Femto base station  130  may analyze the RA codes referring to the configuration information shared with the macro base station at step  305  (step  325 ). Unlike the embodiment of  FIG. 2 , in this embodiment, femto base station  130  may broadcast the RA response to user equipment  110  (step  340 ). The RA response may include the RA codes and RA channel information received at femto base station  130 . 
     After receiving the RA response from femto base station  130 , user equipment  110  may verify whether the RA codes and the RA channel information included in the RA response are respectively identical to those having been transmitted from the user equipment itself (step  345 ). If the codes and the information are the same, user equipment  110  may transmit an RA message for requesting a specific service to the femto base station (step  350 ). 
     Thereafter, femto base station  130  may receive a message from the user equipment and report information (for instance, the RA codes, received power and so on) on the user equipment to macro base station  120  based on the received message (step  330 ). After receiving the RA message, macro base station  120  may identify the user equipment which requested the service and provide the requested service (step  355 ). 
       FIG. 4  shows flow chart  300  of a communication method between a user equipment and a base station with use of RA channels in accordance with a further embodiment of the present invention. The method shown in  FIG. 4  is useful when there is insufficient time during the step of reporting information on user equipment  110  from femto base station  130  to macro base station  120  due to the characteristics of backbone network  150 , for instance at step  230  or step  240 . 
     Similar to the method described referring to  FIG. 2 , macro base station  120  and femto base station  130  may share configuration information such as RA codes, channel resources and so on, for the MDRA communication through backbone network  150  or by a provisioning process (step  405 ). Macro base station  120  may broadcast the configuration information on MDRA channels to the user equipment  110  (step  410 ). The configuration information may include the RA codes and information on uplink RA channels, etc., available to the user equipment. User equipment  110  may select the RA codes and the uplink RA channels in accordance with the configuration information on the MDRA channel set by the base station (step  415 ). Unlike the methods described in relation to  FIGS. 2 and 3 , in this embodiment, user equipment  110  may transmit the RA codes to both macro base station  120  and femto base station  130  through a selected channel resource (steps  420  and  424 ). 
     Macro base station  120  and femto base station  130  may analyze, respectively, the RA codes referring to predetermined configuration information (steps  422  and  425 ). In this embodiment, macro base stations  120  may broadcast the RA response to user equipment  110  (step  440 ). The RA response may include the RA codes and RA channel information received at femto-base-station  130 . 
     After receiving the RA response from macro base station  120 , user equipment  110  may verify whether the RA codes and the RA channel information included in the RA response are respectively identical to those having been transmitted from the user equipment itself (step  445 ). If the codes and the information are the same, user equipment  110  may transmit an RA message for requesting a specific service to femto base station  130  (step  450 ). 
     Meanwhile, femto base station  130 , which analyzed the RA codes transmitted from user equipment  110  at step  425 , may report information (for instance, the RA codes, received power, etc.) on user equipment  110  to macro base station  120  (step  430 ). The reporting step (step  430 ) may be performed with the steps of transmitting the RA response and transmitting/receiving the RA message (steps  440  and  450 ) in parallel. Thus, even is the reporting step takes some time, there will not be any problems. After receiving the RA message, macro base station  120  may identify the user equipment which requested the service and can provide the requested service (step  455 ). 
     Since it is possible to determine which femto base station is close to the user equipment, the location of the user equipment can be accurately determined without having a GPS receiver on the user equipment. Thus, this can be effectively utilized in a location based service. Further, the location of the user equipment can be determined even if the user equipment lies inside where the GPS signal cannot be reached when the user equipment is located within the service regions of the femto-base-stations. 
     Further, at the start of a handover from the macro base station to the femto base station, the information (for instance, the intensities of signals received from the user equipment) obtained by the femto base station, may be utilized. When a handover is required, the base station broadcasts a list of neighboring base stations, and the user equipment retrieves a base station, which transmitted high-intensity signals, in the list. Then, the handover starts. If there are lots of femto base stations, there is a huge amount of data that is unnecessarily needed for the base station to broadcast the list regarding neighboring base stations. Also, many calculations are required to find a base station from which the high-intensity-signal is received. However, by adopting the MDRA scheme of the present invention, it is not necessary to broadcast the list of neighboring base stations or to find the base station which transmitted the highest-intensity-signal, since the macro base station recognizes the femto base station to which the user equipment belongs and intensities of the signals transmitted to the femto base stations from the user equipment. 
     Further, when adopting the MDRA scheme of the present invention, it is possible to determine which femto base station is closer to a user equipment. Thus, it is easy to estimate interference between the femto base stations and the user equipment and to control the interference. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof to facilitate an understanding of the present invention, it should be understood that the embodiments are only examples and numerous other modifications embodiments and equivalent replacements can be devised by those skilled in the art. For instance, the embodiments of the present invent have been described with the communication method adopting RA channels only. However, the present invention is not limited thereto. In other words, the present invention may be used in communication methods adopting any uplink channels. Therefore, the technical scope of the present invention should be determined by the appended claims.