Abstract:
The present invention relates to a method and apparatus of radio link selection based on delay spread, the user equipment according to the present invention receives radio signals from neighboring multiple base stations, measures delay spread of the signals received from the multiple neighboring base stations, selects at least one base station among the neighboring base stations based on the delay spread measured, and connects a radio link with the selected at least one base station. According to the present invention, the inter-symbol interference due to delay spread can be decreased, thereby it is available to implement the maximum transmission speed in a given propagation environment.

Description:
[0001]    Priority to Korean patent application number 10-2014-0006895 filed on Jan. 20, 2014, the entire disclosure of which is incorporated by reference herein, is claimed. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to wireless communications and more particularly to a method and apparatus of radio link selection based on delay spread. 
         [0004]    2. Discussion of the Related Art 
         [0005]    In the common wireless communication system, in the situation that 1:N radio link is available such as the case that a user equipment is located in the region where the coverage of multiple base stations (or access points; APs) is overlapped, in case that a radio link is selected among the N candidate radio links, the radio link whose signal attenuation is the smallest, that is, whose strength of the received signal is the biggest is selected so as to receive the best signal. However, in case of digital communication systems, there is a problem that the speed of data transmission decreases due to inter-symbol interference generated by delay spread that occurs owing to multiple paths. Although the technique enables more data to be transmitted rapidly in digital communication, the limitation in the data transmission speed is still problematic since the delay spread is generated due to propagation environment such as obstacles or geographic features around the radio link. For example, in the situation that a user equipment is connected to one of the multiple base stations or a user equipment is connected to one of the multiple APs which are spread in space, if the radio link is connected to a base station or AP whose signal strength is simply big, a high speed wireless data transmission technique may not be used due to the inter-symbol interference caused by the delay spread. 
       SUMMARY OF THE INVENTION 
       [0006]    It is a principal object of the present invention is to provide a method and apparatus of radio link selection based on delay spread. 
         [0007]    It is another object of the present invention is to guarantee high transmission speed between a user equipment and a base station considering the delay spread. 
         [0008]    It is further object of the present invention is to provide a method and apparatus for configuring a radio link considering the delay spread and signal strength. 
         [0009]    According to an aspect of the present invention, a user equipment performing a radio link selection is provided. The user equipment includes a communicating unit configured to receive signals from neighboring base stations, a measuring unit configured to measure delay spread of the signals received from the neighboring base stations, and generates information of the delay spread, and a selecting unit configured to select at least one base station among the neighboring base stations based on the information of the delay spread, and generates request information for radio link connection with the at least one base station, wherein the communicating unit transmits the request information to the selected at least one base station. 
         [0010]    According to another aspect of the present invention, a method of radio link selection performed by a user equipment is provided. The method includes receiving signals from neighboring base stations, measuring delay spread of the signals received from the neighboring base stations, and generating information of the delay spread, selecting at least one base station among the neighboring base stations based on the information of the delay spread, generating a request information for radio link connection with the at least one base station, and transmitting the request information to the selected at least one base station. 
         [0011]    According to yet another aspect of the present invention, a radio link selection system is provided. The radio link selection system includes a plurality of base stations configured to transmit radio signals, and a user equipment configured to measure delay spread of the signals received from the multiple neighboring base stations, select at least one base station among the neighboring base stations based on the delay spread measured, and connect a radio link with the selected at least one base station. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1A and 1B  illustrate an example of a network where multiple base stations or multiple APs exist around a user equipment (UE). 
           [0013]      FIG. 2  is a flowchart schematically illustrating a conventional method for selecting a radio link based on signal strength. 
           [0014]      FIG. 3  is a flowchart illustrating an example of a method for selecting a radio link based on delay spread according to the present invention. 
           [0015]      FIG. 4  is an example of block diagram illustrating a UE that performs radio link selection based on delay spread according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The preferred embodiment of the present invention now will be described in detail by reference to the accompanying exemplary drawings in this specification. In attaching reference numerals to elements in each drawing it should be understood that the same reference numeral is used for the same element even if the element is shown in different drawings. In addition, in case that the detailed description for the related known elements and functions is determined to obscure the inventive concept in this specification, the redundant description for the same element will be omitted. 
         [0017]      FIGS. 1A and 1B  illustrate an example of a network where multiple base stations or multiple APs exist around a user equipment (UE). The UE may be fixed or have mobility, and also referred to as another terms such as a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device and so on. 
         [0018]    Referring to  FIG. 1A  illustrates the case in which multiple base stations  110  are disposed around a UE  100 . For example, the UE  100  may be connected to at least one base station among the neighboring base stations  110  using millimeter wave, and perform a wireless communication. Previously, in this situation, the UE  100  constructed a radio link by selecting the base station whose signal strength received is the biggest among the multiple base stations  110 . For example, if the signal strength received from the base station B  110 - 2  is greater than the signal strength received from the base station A  110 - 1  and the signal strength received from the base station C  110 - 3 , the UE  100  may be connected to the base station B  110 - 2  and perform a wireless communication. 
         [0019]      FIG. 1B  illustrates the case in which a user equipment  150  uses a wireless communication based on WiFi, and multiple APs  160  are disposed therearound. Previously, in this situation, the UE  150  was connected to the AP B  160 - 2  whose signal strength is the biggest from the point of view of the UE  150 , and able to perform a wireless communication. 
         [0020]    Meanwhile, although the base station  110  and the AP  160  are separately depicted in  FIGS. 1A and 1B , this is just an example for description. Hereinafter, the base station  110  is a concept including the AP  160 , and also referred to as another term such as an evolved-NodeB (eNB), a base transceiver system (BTS), a femto nodeB, a home nodeB, a relay and so on. 
         [0021]      FIG. 2  is a flowchart schematically illustrating a conventional method for selecting a radio link based on signal strength. 
         [0022]    Referring to  FIG. 2 , a UE searches neighboring base stations (step, S 200 ), and measures the signal strength received from the base stations (step, S 210 ). 
         [0023]    The UE detects a base station whose signal strength received is the biggest among the base stations (step, S 220 ), and connects a radio link to the detected base station (step S 230 ). Later, the UE may perform a wireless communication with the base station to which the radio link is connected. Even in the situation in which a radio link is connected to a certain base station already, the UE continuously measures the signal strength received from the neighboring base stations, and if a base station that provide the biggest signal strength is changed, the UE may change the radio link to the base station that currently provides the biggest signal strength. 
         [0024]    However, the conventional method described above has a problem that the received signal strength is only considered, but the interference occurred by propagation environment is not considered. In order to implement high speed data communication based on the recent digital way, it is required that the radio link selection in which the inter-symbol interference due to delay spread as well as the received signal strength is considered. 
         [0025]      FIG. 3  is a flowchart illustrating an example of a method for selecting a radio link based on delay spread according to the present invention. 
         [0026]    Referring to  FIG. 3 , a UE searches neighboring base stations (step, S 300 ), and measures the delay spread of the signal received from the neighboring base stations (step, S 310 ). It goes without saying that the UE is able to measure the signal strength received from the base stations. 
         [0027]    The UE updates the list of base station information in small order of the delay spread based on the information of the delay spread measured (step, S 320 ), and selects at least one base station based on the information of the delay spread and connects a radio link (step, S 330 ). The UE may select the base station whose delay spread is the smallest based on the information of the delay spread and connect the radio link to it. In addition, the UE may select the base station whose delay spread is under a predetermined threshold value and connect the radio link to it. In this case, if there are multiple the base stations whose delay spread are under a predetermined threshold value, the UE may select a base station by further considering the received signal strength, and connect the radio link to the corresponding base station. 
         [0028]    Meanwhile, a UE may determine whether a wireless communication is terminated (step, S 340 ). In case that the wireless communication is not terminated, that is, in the situation that a radio link is already connected to a base station, the UE may continuously measure the delay spread of the signal received from neighboring base stations by going back to step, S 310 , and select a base station again based on the information of the newly measured delay spread and change the radio link. If the delay spread of a base station which is connected to the existing radio link is still the smallest based on the information of the newly measured delay spread, the UE may maintain the radio link with the base station. 
         [0029]      FIG. 4  is an example of block diagram illustrating a UE that performs radio link selection based on delay spread according to the present invention. 
         [0030]    Referring to  FIG. 4 , the UE according to the present invention includes a communicating unit  410 , a measuring unit  420  and a selecting unit  430 . 
         [0031]    The measuring unit  420  measures the delay spread of the signal received from neighboring base stations through the communicating unit  410 . That is, the measuring unit  420  measures the delay spread for each of the neighboring base stations, and generates the information of the delay spread. The measuring unit  420  may further measure the signal strength received from the neighboring base stations. 
         [0032]    The selecting unit  430  selects at least one base station based on the information of the delay spread. As an example, the selecting unit  430  may select the base station whose delay spread is the smallest based on the information of the delay spread. As another example, the selecting unit  430  may select at least one base station whose delay spread is under a predetermined threshold value and connects a radio link to it. In this case, if there are multiple base stations whose delay spread are under a predetermined threshold value, the UE may select at least one base station by further considering the received signal strength. 
         [0033]    The selecting unit  430  transmits request information for connecting a radio link with the at least one base station to the selected at least one base station through the communicating unit  410 . 
         [0034]    So far, the present invention has been described by reference to the drawings and the embodiments as an example, and it should be understood by those skilled in the art, however, that the present invention can be modified or changed in various ways without departing from the technical principles and scope. Accordingly, the embodiment disclosed in the present invention is not intended to limit the scope of the inventive concept of the present invention, but to describe, and the scope of the inventive concept of the present invention is not, limited to the embodiment. The scope of the present invention should be interpreted by the claims below, and it should be interpreted that all inventive concept within the equivalent scope is included in the scope of the present invention.