Patent Publication Number: US-2018042022-A1

Title: Wireless communication system and associated method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/369,786 filed on Aug. 2, 2016, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     In the IEEE 802.11ax standard, multiple transmitters are allowed to transmit at different sub-carriers simultaneously in a multi-user system, where said multi-user system may be, but not limited to, an Orthogonal Frequency-Division Multiple Access (OFDMA) system, a Multi-input Multi-output (MIMO) system, etc. Therefore, the receiver needs to demodulate signals that are transmitted from multiple transmitters using different transmission powers and experience different attenuations, which may introduce some challenges for the receiver&#39;s design. For instance, higher power transmitters may leak energy to adjacent sub-bands which causes the incorrect receiving of the packets for the receiver. For another instance, the difficulty of the implementations of the automatic gain control (AGC) and the demodulator of the receiver increases due to the limited dynamic range and the limited sensitivity of the receiver. Therefore, a novel design for the receiver in a multi-user system is desired. 
     SUMMARY 
     One of the objectives of the present invention is to provide a wireless communication system and an associated method to solve the abovementioned problems. 
     According to an embodiment of the present invention, an exemplary wireless communicating method employed by an access point is disclosed. The exemplary wireless communicating method comprises: sending a trigger frame to at least one station, wherein the trigger frame comprises power information indicating a targeted receive power of data sent from the at least one station to the access point and an output power of the trigger frame; and receiving the data sent from the at least one station. 
     According to an embodiment of the present invention, an exemplary wireless communicating method employed by a station is disclosed. The exemplary wireless communicating method comprises: receiving a trigger frame from an access point, wherein the trigger frame comprises power information indicating a targeted receive power and an output power of the trigger frame; and sending data to the access point by referring to at least the targeted power. 
     According to an embodiment of the present invention, an exemplary wireless communication system is disclosed. The exemplary wireless communication system comprises: an access point; and at least one station; wherein the access point sends a trigger frame comprising power information for indicating a targeted receive power of data sent from the at least one station to the access point and an output power of the target frame, and the at least one station sends data to the access point by referring to the targeted power. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a wireless communication system according to an embodiment of the present invention. 
         FIG. 2  is a diagram illustrating a format of a trigger frame according to an embodiment of the present invention. 
         FIG. 3  is a diagram illustrating the communication between an access point and stations comprised in a wireless communication system according to an embodiment of the present invention. 
         FIG. 4  is a diagram illustrating the communication between an access point and stations comprised in a wireless communication system before transmitting a trigger frame according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should not be interpreted as a close-ended term such as “consist of”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
       FIG. 1  is a diagram illustrating a wireless communication system  100  according to an embodiment of the present invention. The wireless communication system  100  may include at least one access point (AP) and at least one station (STA). As shown in  FIG. 1 , the wireless communication system  100  comprises one access point (AP)  110  and a plurality of stations (STAs)  121 ,  122 ,  123 ,  124 . The number of APs comprised in the wireless communication system  100  and the number of STAs comprised in the wireless communication system  100  are not meant to be limitations of the present invention. For example, in other embodiments, the wireless communication system  100  can comprise multiple APs each communicating with one or more STAs. The AP  110  is arranged to transmit a trigger frame TRI to STAs  121 - 124 , wherein the trigger frame TRI comprises power information PI indicating a targeted power P tar  which implies the desired received power for the AP  110  receiving data from the STAs  121 - 124 , and further indicating a power P 1  which implies the transmitting power for the AP  110  transmitting the trigger frame TRI to the STAs  121 - 124 . The STA  121  determines a power P 21  implying the received power when the trigger frame TRI is received by the STA  121 . The power P 21  can be determined according to, for example, a Received Signal Strength Indicator (RSSI) of the trigger frame TRI . After determining the power P 21 , the STA  121  calculates a transmission attenuation P att1  between the STA  121  and the access point  110  by the equation: P att1 =P 1 −P 21 . The STA  121  then calculates a power P 31  by the equation: P 31 =P att1 +P tar , and transmits data to the AP  110  by referring to the power P 31 . It should be noted that the STA  121  may not be able to transmit data with the power P 31  exactly due to the limitation of hardware or other factors. In one embodiment, the STA  121  transmits data with the transmitting power as close to the power P 31  as possible. For example, if the calculated power P 31  is −10 dBm and the lowest power of the STA  121 , however, is 0 dBm, the STA  121  transmits data to the AP  110  with the lowest power 0 dBm therefore. 
       FIG. 2  is a diagram illustrating a format of the trigger frame TRI according to an embodiment of the present invention. The trigger frame TRI comprises a plurality of fields C 1 -Cn, wherein the field C 5 , such as a common information field, is arranged to store the power information PI. However, this is only for illustrative purpose. In other embodiments, the power information PI can be stored in a different place in the trigger frame TRI. In addition, the targeted power P tar  and the power PI can be recorded in the power information PI in any form. For example, 4 bits of the power information PI are arranged to interpret the power P 1  in units of 2 dBm, and 4 bits of the power information PI are arranged to interpret the target power P tar  in units of −10 dBm. However, this is only for illustrative purpose as well, not a limitation of the present invention. 
     Referring to  FIG. 1  again, the STA  122  determines a power P 22  implying the received power when the trigger frame TRI is received by the STA  122 . The power P 22  can be determined according to, for example, a Received Signal Strength Indicator (RSSI) of the trigger frame TRI. After determining the power P 22 , the STA  122  calculates a transmission attenuation P att2  between the STA  122  and the access point  110  by the equation: P att2 =P 1 −P 22 .The STA  122  then calculates a power P 32  by the equation: P 32 =P att2 +P tar , and transmits data to the AP  110  by referring to the power P 32 . It should be noted that the STA  122  may not be able to transmit data with the power P 32  exactly due to the limitation of hardware or other factors. In one embodiment, the STA  122  transmits data with the transmitting power as close to the power P 32  as possible. For example, if the calculated power P 32  is −10 dBm and the lowest power of the STA  122 , however, is 0 dBm, the STA  122  transmits data to the AP  110  with the lowest power 0dBm thereby. 
     Likewise, the STA  123  determines a power P 23  implying the received power when the trigger frame TRI is received by the STA  123 . The power P 23  can be determined according to, for example, a Received Signal Strength Indicator (RSSI) of the trigger frame TRI. After determining the power P 23 , the STA  123  calculates a transmission attenuation P att3  between the STA  123  and the access point  110  by the equation: P att1 =P 1 −P 23  . The STA  123  then calculates a power P 33  by the equation: P 33  =P att3 +P tar , and transmits data to the AP  110  by referring to the power P 33 . It should be noted that the STA  123  may not be able to transmit data with the power P 33  exactly due to the limitation of hardware or other factors. In one embodiment, the STA  123  transmits data with the transmitting power as close to the power P 33  as possible. For example, if the calculated power P 33  is −10 dBm and the lowest power of the STA  123 , however, is 0 dBm, the STA  123  transmits data to the AP  110  with the lowest power 0 dBm thereby. 
     In addition, the STA  124  determines a power P 24  implying the received power when the trigger frame TRI is received by the STA  124 . The power P 24  can be determined according to, for example, a Received Signal Strength Indicator (RSSI) of the trigger frame TRI. After determining the power P 24 , the STA  124  calculates a transmission attenuation P att4  between the STA  124  and the access point  110  by the equation: P att4 =P 1 −P 24 . The STA  124  then calculates a power P 34  by the equation: P 34 =P att4 +P tar , and transmits data to the AP  110  by referring to the power P 34 . It should be noted that the STA  124  may not be able to transmit data with the power P 34  exactly due to the limitation of hardware or other factors. In one embodiment, the STA  124  transmits data with the power as close to the power P 34  as possible. For example, if the calculated power P 34  is −5 dBm and the lowest power of the STA  124  is −15 dBm, the STA  124  transmits data to the AP  110  with the lowest power −5 dBm thereby. 
     It should be noted that the trigger frame TRI can be further arranged to allocate a subcarrier (or a resource unit) to each STA for transmitting data to the AP  110 . The skilled in the art should easily understand the implementation of assigning a resource unit to each STA, and the detailed description is omitted here for brevity. 
       FIG. 3  is a diagram illustrating the communication between the AP  110  and STAs  121 - 124  comprised in the wireless communication system  100  according to an embodiment of the present invention. As shown in  FIG. 3 , the AP  110  transmits a trigger frame TRI comprising the power information PI to the STAs  121 - 124 , wherein the power information PI indicates the power P 1  implying the transmitting power for the AP  110  transmitting the trigger frame TRI to the STAs  121 - 124  is 20 dBm and the targeted power P tar  implying the desired received power for the AP  110  receiving data from the STAs  121 - 124  is −70 dBm. The STA  121  receives the trigger frame TRI and determines the power P 21  implying the received power when the trigger frame TRI is received by the STA  121  is −40 dBm, wherein the trigger frame TRI also allocates a resource unit RU 1  to the STA  121  for transmission. The transmission attenuation P att1  between the STA  121  and the AP  110  is 60 dBm decided by the equation: P att1 =P 1 −P 21 , and the power P 31  is −10 dBm decided by the equation: P 31 =P att1 +P tar  The lowest transmission power of the STA  121 , however, is 0 dBm. Hence, the STA  121  transmits a data DAT 1  at the resource unit RU 1  with the power 0 dBm. 
     The STA  122  receives the trigger frame TRI and determines the power P 22  implying the received power when the trigger frame TRI is received by the STA  122  is −65 dBm, wherein the trigger frame TRI also allocates a resource unit RU 2  to the STA  122  for transmission. The transmission attenuation P att2  between the STA  122  and the AP  110  is 85 dBm decided by the equation: P att2 =P 1 −P 22 , and the power P 32  is 15 dBm decided by the equation: P 32 =P att2 =P tar . The STA  122  thus transmits a data DAT 2  at the resource unit RU 2  with the power 15 dBm. 
     The STA  123  receives the trigger frame TRI and determines the power P 23  implying the received power when the trigger frame TRI is received by the STA  123  is −70 dBm, wherein the trigger frame TRI also allocates a resource unit RU 3  to the STA  123  for transmission. The transmission attenuation P att3  between the STA  123  and the AP  110  is 90 dBm decided by the equation: P att1 =P 1 −P 23 , and the power P 33  is 20 dBm decided by the equation: P 33 = P   att3 +P tar  However, the maximum transmission power of the STA  123  is limited to 15 dBm, the STA  123  thus transmits a data DAT 3  at the resource unit RU 3  with the power 15 dBm. 
     The STA  124  receives the trigger frame TRI and determines the power P 24  implying the received power when the trigger frame TRI is received by the STA  124  is −35 dBm, wherein the trigger frame TRI also allocates a resource unit RU 1  to the STA  124  for transmission. The transmission attenuation P att4  between the STA  124  and the AP  110  is 55 dBm decided by the equation: P att4 =P 1 −P 24 ,and the power P 34  is −15 dBm decided by the equation: P 34 =P att4 +P tar  . The transmission power of the STA  124  in this embodiment is not limited by hardware capability. Hence, the STA  124  transmits a data DAT 4  at the resource unit RU 4  with the power −15 dBm. 
     It should be noted that in the embodiment of  FIG. 3 , the transmission attenuations P att1 −P att4  mainly result from the distances between the AP  110  and the STAs  121 - 124 . For example, the transmission attenuation P att2  is greater than the transmission attenuation P att1  because the STA  122  is further than the STA  121  as shown in  FIG. 3 . However, in addition to the distance between the STA and the AP, the transmission attenuation may also depend upon other factors such as obstacles (e.g., buildings) between the STAs  121 - 124  and the AP  110 . Therefore, the relative location between the AP  110  and the STA  121 - 124  shown in  FIG. 1  and  FIG. 3  is only illustrative, not a limitation of the present invention. 
     By indicating the target power P tar  in the trigger frame TRI, the receiver (i.e. AP  110 ) can receive data (i.e. DAT 1 -DAT 4 ) transmitted with similar powers by multiple transmitters/users (i.e. STAs  121 - 124 ). In this way, the incorrect receiving issue mentioned in the prior art can be solved. 
     In order to prevent the higher power transmitters from leaking energy to adjacent sub-bands, the present invention further proposes an operation of categorizing the STAs  121 - 124  into groups based on the distance (or the transmission attenuation) by assigning a group ID to each STA before transmitting the trigger frame TRI. Referring to  FIG. 4  which is a diagram illustrating the communication between the AP  110  and the STAs  121 - 124  comprised in the wireless communication system  100  before transmitting the trigger frame TRI according to an embodiment of the present invention, STAs  121 - 124  initially transmit communication requests REQ 1 -REQ 4  to the AP  110  with max power for starting a communication, wherein the communication request REQ 1 -REQ 4  can be, but not limited to, association requests, probe requests, OFDMA requests, or data packets. When the communication requests REQ 1 -REQ 4  transmitted with max power of respective STAs  121 - 124  are received by the AP  110 , the AP  110  determines the relative distance between STAs  121 - 124  and the AP  110  based on the received power of each communication request, wherein the received power of each communication request can be determined by the RSSI of each communication request. For example, the AP  110  determines that the STAs  121  and  124  are relatively closer than the STAs  122  and  123  due to the received powers of the communication requests REQ 1  and REQ 4  are greater than that of the communication requests REQ  2  and REQ 3 . By this, the AP  110  categorizes STAs  121  and  124  into group  1  by assigning a group identity GID 1  in communication responses RES  1  and RES  4  generated in response to the communication requests REQ  1  and REQ 4 , respectively, and categorizes STAs  122  and  123  into group  2  by assigning a group identity GID 2  in communication responses RES  2  and RES  3  generated in response to the communication requests REQ 2  and REQ 3 , respectively. After assigning the group identities GID 1  and GID 2  to the STAs  121 - 124 , the AP  110  then can assign one of the group identities GID 1  and GID 2  in the trigger frame TRI shown in the embodiment of  FIG. 3  to ask the STAs corresponding to the assigned group identity to transmit data. For example, the AP  110  specifically indicates the group identity GID 1  in the trigger frame TRI. When the STAs  121 - 124  receive the trigger frame TRI, only the STAs corresponding to the group identity GID 1  (i.e. STAs  121  and  124 ) are allowed to transmit data. Next, the AP  110  specifically indicates the group identity GID 2  in the next trigger frame TRI. When the STAs  121 - 124  receive the trigger frame TRI, only the STAs corresponding to the group identity GID 2  (i.e. STAs  122  and  123 ) are allowed to transmit data. By assigning group identity to STAs  121 - 124 , the STAs closer to the AP  110  can transmit data corresponding to a trigger frame simultaneously while the STAs relatively further to the AP  110  can transmit data corresponding to another trigger frame simultaneously. In this way, during each communication period, the data packets from the STAs to the AP  110  are transmitted with similar/same powers, thus effectively avoiding the incorrect receiving of lower-power sub-band transmission interfered with adjacent higher-power sub-channel transmission. 
     In random access, any STA (e.g. the STAs  121 - 124 ) could try to contend using any RU for transmission. In this case, the present invention presents a solution by assigning the group identities to each STA. For example, the group identity GID 1  to the STAs  121  and  124  while the group ID GID 2  to the STAs  122  and  123 . The AP  110  sends the trigger frame TRI including one of the group identities GID 1  and GID 2  to let all the STAs (e.g. the STAs  121 - 124 ) know which STA could send data after the trigger frame TRI. 
     In another embodiment, the AP  110  may send the trigger frame TRI to those STAs with the same group identity (e.g. one of the group IDs GID 1  and GID 2 ) , wherein the trigger frame TRI specifies that which STA uses which RU for transmission without including the group identity therein. For example, the AP  110  sends the trigger frame TRI to those STAs with the group identity GID 1  (i.e. the STAs  121  and  124 ), wherein the trigger frame TRI specifies that the STA  121  uses the RU 1  for transmission while the STA  124  uses the RU 4  for transmission without including the group identity therein. Likewise, the AP  110  sends the trigger frame TRI to those STAs with the group identity GID 2  (i.e. the STAs  122  and  123 ) , wherein the trigger frame TRI specifies that the STA  122  uses the RU 2  for transmission while the STA  123  uses the RU 3  for transmission without including the group identity therein. 
     Referring to  FIG. 2 , the group identity may be assigned in any of the fields C 1 -Cn comprised in the trigger frame TRI. The location of the group identity recorded in the trigger frame TRI specified by the AP  110  is not a limitation of the present invention as long as the same goal can be achieved. 
     Briefly summarized, the present invention proposes a wireless communication system and associated method which can effectively solve the problems described in the prior art by indicating a targeted power in the trigger frame to achieve power control and categorizing the STAs into groups with group identities in communication responses. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.