Patent Publication Number: US-2015063226-A1

Title: Method of transmitting a downlink radio signal from a distributed antenna system to a mobile device and distributed antenna system

Description:
CROSS-REFERENCE  TO RELATED  APPLICATION 
     This application claims priority to Taiwanese Application. No. 102131524, filed on Sep. 2, 2013. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention, relates to a method for communicating a signal, more particularly to a method of transmitting a downlink radio signal from a distributed antenna system to a mobile device. 
     2. Description of the Related Art 
       FIG. 1  illustrates a conventional method of transmitting a signal from a distributed antenna system  5  to a mobile device  7 . The mobile device  7  is moved along a path  6 . The distributed antenna system  5  includes a plurality of transceivers  51 - 54  arranged along the path  6 , and a control module  50 . 
     The control module  50  provides a downlink radio signal to each of the transceivers  51 - 54 , which subsequently transmit the downlink radio signal to the mobile device  7 . 
     However, the downlink radio signals transmitted respectively by the transceivers  51 - 54  are all received from the control module  50  and have the same frequency, and the transceivers  51 - 54  are generally not far apart from each other, resulting in co-channel interference among the downlink radio signals received by the mobile device  7  from respective transceivers  51 - 54 . As a result, data throughput from the distributed antenna system  5  to the mobile device  7  may be adversely affected. For example, when, the mobile device  7  is moved to a position between the transceivers  51 ,  52 , it may also receive the downlink radio signals from the transceivers  52 - 54 , which may interfere with the downlink radio signal from the transceiver  51 . 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a method of transmitting a downlink radio signal from a distributed antenna system to a mobile device, which is capable of providing relatively large data throughput for the mobile device. 
     According to the present invention, there is provided a method of transmitting a downlink radio signal from a distributed antenna system to a mobile device. The distributed antenna system includes a plurality of transceivers and a control module. The method comprises the following steps of: a) receiving, by each of the transceivers, an uplink radio signal from the mobile device as a respective received signal; b) transmitting, by each of the transceivers, the received signal to the control module; c) providing to each of the transceivers, by the control module, the downlink radio signal with a respective intensity, which is determined by the control module according to an intensity of the received signal from the transceiver; and d) transmitting, by each of the transceivers, the downlink radio signal. 
     According to another aspect of this invention, there is provided a distributed antenna system for transmitting a downlink radio signal to a mobile device. The distributed antenna system comprises a plurality of transceivers and a control module. Each of the transceivers is configured to receive an uplink radio signal from the mobile device as a respective received signal. The control module is configured to receive the received signal from each of the transceivers, and is operable to provide to each of the transceivers the downlink radio signal with a respective intensity, which is determined by the control module according to an intensity of the received signal from the transceiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic diagram of a conventional method of transmitting a signal from a distributed antenna system to a mobile device; 
         FIG. 2  is a flow chart illustrating a method of transmitting a radio signal from a distributed antenna system to a mobile device according to a first preferred embodiment of the present invention; 
         FIGS. 3 and 4  are schematic diagrams for illustrating the mobile device moving along a path and receiving the radio signal from the distributed antenna system according to the first preferred embodiment; and 
         FIGS. 5 and 6  are schematic diagrams for illustrating the mobile device moving along the path and receiving the radio signal from the distributed antenna system according to a second preferred embodiment of the method of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
     Referring to  FIGS. 2 to 4 , the first preferred embodiment of the method of transmitting a downlink radio signal to a mobile device  3  is implemented by a distributed antenna system  1 . The distributed antenna system  1  includes a plurality of transceivers  11 - 14  and a control module  10 . The transceivers  11 - 14  are arranged along a path  2 . 
     In this embodiment, the path  2  may be a high speed railway, a train railway or the like, and the mobile device  3  may be a mobile communication device (such as a mobile phone or a tablet computer) disposed in a vehicle travelling along the path  2 . 
     To reduce interference among radio signals transmitted from the transceivers  11 - 14 , each of the transceivers  11 - 14  receives an uplink radio signal from the mobile device  3  as a respective received signal in step S 11 . 
     Each of the transceivers  11 - 14  is operable to transmit the received signal to the control module  10  in step S 12 , and the control module  15  is operable to determine a distance between the mobile device  3  and each of the transceivers  11 - 14  according to the intensity of the received signal from the transceiver  11 - 14  in step S 13 . In step S 14 , the control module  10  is operable to provide a downlink radio signal to each of the transceivers  11 - 14  with a respective intensity that negatively correlates with the distance between the respective one of the transceivers  11 - 14  and the mobile device  3 . That is to say, the respective intensity of the downlink radio signal, provided to each of the transceivers  11 - 14  is determined by the control module  10  according to the intensity of the received signal from the transceiver  11 - 14 . Then, in step S 15 , each of the transceivers  11 - 14  is operable to transmit the downlink radio signal to the mobile device  3 . 
     Specifically, in step S 13 , the control module  10  is operable to determine which one of the transceivers  11 - 14  is proximate to the mobile device  3  among the remaining transceivers  11 - 14  according to the intensity (power) of the received signal from each of the transceivers  11 - 14 . Then, in step S 14 , the control module  10  is operable to enhance the respective intensity of the downlink radio signal, which is provided to a proximate one of the transceivers  11 - 14 , and/or to reduce the respective intensity of the downlink radio signal, which is provided to each of the remaining transceivers except for the proximate one, so as to increase data throughput to the proximate one of the transceivers  11 - 14 . 
     For example, as shown in  FIG. 3 , when the mobile device  3  is proximate to the transceiver  11 , the control module  10  enhances the intensity of the downlink radio signal provided to the transceiver  11 . 
     As shown in  FIG. 4 , when the mobile device  3  is moved to a position proximate to the transceiver  12  and away from the transceiver  11 , e.g., a distance that the mobile device  3  is moved toward the transceiver  12  from the transceiver  11  is larger than half of a distance between the transceivers  11 ,  12 , the control module  10  enhances the intensity of the downlink, radio signal provided to the transceiver  12  and reduces the intensity of the downlink radio signal provided to the transceiver  11  at the same time. Similarly, when a distance that the mobile device  3  is moved toward the transceiver  13  from the transceiver  12  is more than half of a distance between the transceivers  12 ,  13 , the control module  15  enhances the intensity of the downlink radio signal provided to the transceiver  13  and reduces intensity of the downlink radio signal provided to the transceiver  12 , and so forth. 
     Alternatively, the control module  10  may enhance the intensity of the downlink radio signal provided to at least one of the transceivers  11 - 14  that are at a distance from the mobile device  3  smaller than a predetermined value. Taking  FIG. 4  as an example, when it is determined that the mobile device  3  is close to the transceivers  11  and  12 , the control module  10  is operable to enhance the respective intensity of the downlink radio signal, which is provided to each of the transceivers  11 ,  12 . It should he noted that, the control module  10  may reduce the intensity of the downlink, radio signal provided to at least one of the transceivers  11 - 14  that are at a distance from the mobile device  3  larger than a predetermined value in other embodiments of this invention. 
       FIGS. 5 and 6  illustrate a method of transmitting a downlink, radio signal, from the distributed antenna system  1  to the mobile device  3  according to a second preferred embodiment of the present invention. In this embodiment, the distributed antenna system  1  is shown to be similar to the first preferred embodiment, and the control module  10  is operable, in step S 13  (see  FIG. 2 ), to determine a distance between the mobile device  3  and each of the transceivers  11 - 14  according to the intensity of the received signal from the transceivers  11 - 14 . In step S 14  (see  FIG. 2 ), the control module  10  is operable to provide the downlink radio signal only to at least one of the transceivers  11 - 14  that is at a distance from the mobile device  3  smaller than a predetermined value. For example, the predetermined value is approximately equal to an average distance between any adjacent two of the transceivers  11 - 14 . 
     For example, as shown in  FIG. 5 , when it is determined that a distance from the mobile device  3  to each of the transceivers  11 ,  12  is smaller than the predetermined value, the control module  10  provides the downlink radio signal only to the transceivers  11 ,  12 . Further referring to  FIG. 6 , when the mobile device  3  is moved toward the transceiver  13  and away from the transceiver  11 , the control module  10  provides the downlink radio signal only to each of the transceivers  12 ,  13  rather than to the transceivers  11 ,  14 . Similarly, when the mobile device  3  is moved toward the transceiver  14  and away from the transceiver  12 , the control module  10  provides the downlink radio signal only to each of the transceivers  13 ,  14  rather than to the transceivers  11 ,  12 . 
     By this way, two of the transceivers  11 - 14  are always employed to transmit the downlink radio signals to the mobile device  3 , thus ensuring communication stability between the mobile device  3  and the transceivers  11 - 14 . Further, interference among the downlink radio signals received from transceivers  11 - 14  that are away from the mobile device  3  may be alleviated. 
     To sum up, in the present invention, each of the transceivers  11 - 14  first receives an uplink radio signal from the mobile device  3  as a respective received signal, and transmits the received signal to the control module  10 . Next, the control module  10  determines a distance between the mobile device  3  and each of the transceivers  11 - 14  according to the intensity of the received signal from the respective one of the transceivers  11 - 14 , and provides the downlink radio signal to each of the transceivers  11 - 14  with the respective intensity negatively correlating with the distance between the respective one of the transceivers  11 - 14  arid the mobile device  3 . Finally, each of the transceivers  11 - 14  transmits the downlink radio signal to the mobile device  3 . Therefore, the mobile device  3  may receive the downlink radio signal with relatively great intensity from the proximate one of the transceivers  11 - 14 . 
     While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.