Patent Publication Number: US-2013244585-A1

Title: Transmission Power Control Negotiation Method and Wireless Communication System Using the Same

Description:
BACKGROUND 
     The present invention relates to a transmission power control negotiation method and wireless communication system using the same, and more particularly, to a transmission power control negotiation method and wireless communication system using the same capable of negotiating with a transceiver in a receiving end, to determine an adequate transmission power which reduces unnecessary power consumption as most in a short cable case and avoids an interoperability issue in a long cable case. 
     In Ethernet, the transmission amplitude is defined to fixed value, i.e. a default transmission power, with small variance. In such a situation, when a local device transmits signals to a remote device via a cable, the transmission amplitude is usually overqualified in a short cable case and is unqualified in a long cable case. As a result, unnecessary transmission power consumption might occur in the short cable case and an interoperability issue might happen in the long cable case, e.g. power of transmitted signal is too low after a long cable and thus signal quality is too bad for the remote device. 
     Therefore, a conventional guess method is applied in the local device to reduce power consumption in the short cable case. In detail, the local device adopts cable estimator to detect a cable length first, and then adjusts transmission amplitude based on a cable length index and predefined lookup tables. In such a situation, excellent cable length estimator and lookup tables are necessary for properly adjusting transmission amplitude to reduce power consumption. 
     However, since the local device estimates the cable length by itself, the estimated cable length may not be reliable due to unideal factors. Besides, since the adjusted transmission amplitude is not confirmed by the remote device, there is still an interoperability issue. Therefore, the conventional guess method is conservative in reducing transmission power level to ensure the remote device receives signals with enough signal quality, and thus the conventional guess method can not reduce unnecessary power consumption at most. Therefore, there is a need for improvement. 
     SUMMARY 
     It is therefore an objective of the present invention to provide a transmission power control negotiation method and wireless communication system using the same capable of negotiating with a transceiver in a receiving end, to determine an adequate transmission power which reduces unnecessary power consumption as most in a short cable case and avoids interoperability issue in a long cable case. 
     The present invention discloses a transmission power control negotiation method for a communication system. The communication system includes a first transceiver and a second transceiver. The transmission power control negotiation method includes the first transceiver transmitting first adjustment signal to the second transceiver with a first transmission power; the second transceiver analyzing the first adjustment signal and sending negotiation messages for the first transceiver to adjust the first transmission power; and the first transceiver transmitting following signals with the first transmission power. 
     The present invention further discloses a wireless communication system. The wireless communication system includes a first transceiver including a first transmission power control circuit, including a first request circuit and a first response circuit; and a second transceiver including a second transmission power control circuit, including a second request circuit and a second response circuit; wherein the first transceiver and the second transceiver perform the above transmission power control negotiation method. 
     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. 1A  is a schematic diagram of a communication system according to an embodiment of the present invention. 
         FIG. 1B  is a schematic diagram of a transmission power control negotiation process for the communication system shown in  FIG. 1A  according to an embodiment of the present invention. 
         FIG. 2A  is a schematic diagram of operations of one transceiver indicating another transceiver shown in  FIG. 1A  to start adjusting transmission power according to an embodiment of the present invention. 
         FIG. 2B  is a schematic diagram of operations of one transceiver indicating another transceiver that the one transceiver shown in  FIG. 1A  starts to adjust itself transmission power according to an embodiment of the present invention. 
         FIG. 3-6  are schematic diagrams of operations of request circuits, and response circuits shown in  FIG. 1A  under different scenarios. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1A  and  FIG. 1B .  FIG. 1A  is a schematic diagram of a communication system  10  according to an embodiment of the present invention, and  FIG. 1B  is a schematic diagram of a transmission power control negotiation process  15  for the communication system  10  according to an embodiment of the present invention. As shown in  FIG. 1A , the communication system  10  is preferably an Ethernet communication system, and includes transceivers  102 ,  104 . The transceivers  102 ,  104  are linked by a wire or cable, and include transmission power control circuits  106 ,  108 , transmitters (TXs)  110 ,  112 , receivers (RXs)  114 ,  116 , other circuits  118 ,  120 , respectively, wherein the transmission power control circuits  106 ,  108  include request circuits  122 ,  124 , and response circuits  126 ,  128 . Operations of the transmitters  110 ,  112 , the receivers  114 ,  116 , and the other circuits  118 ,  120  for realizing other functions of the transceivers  102 ,  104  are similar to those of conventional transceivers, and are known by those skilled in the art. The transceivers  102 ,  104  further include the transmission power control circuits  106 ,  108 , and thus can perform the transmission power control negotiation process  15  shown in  FIG. 1B . The transmission power control negotiation process  15  includes the following steps: 
     Step  152 : The transceiver  102  transmits adjustment signals AS 1  to the transceiver  104  with an adjusted transmission power ATP 1 . 
     Step  154 : The transceiver  104  analyzes the adjustment signals AS 1  and sends negotiation messages for the transceiver  102  to adjust the adjusted transmission power ATP 1 . 
     Step  156 : The transceiver  102  transmits following signals with the adjusted transmission power ATP 1 . 
     According to the transmission power control negotiation process  15 , when the transceiver  102  starts to adjust its transmission power (e.g. passively requested by the transceiver  104 , or actively), the transceiver  102  (a transmitting end) transmits adjustment signals AS 1  to the transceiver  104  (a receiving end) with an adjusted transmission power ATP 1  which is different from a default transmission power. Then, after analyzing the adjustment signals AS 1 , the transceiver  104  sends negotiation messages for the transceiver  102  to adjust the adjusted transmission power ATP 1 , wherein the negotiation messages can be request messages which indicate the transceiver  102  to increase or decrease the adjusted transmission power ATP 1 , acknowledgements for the adjustment signals AS 1  which the transceiver  102  can adjust the adjusted transmission power ATP 1  accordingly, or end messages which indicate the adjusted transmission power ATP 1  is adequate. Afterwards, after adjusting transmission power according to the negotiation messages, the transceiver  102  can transmit following signals with the adjusted transmission power ATP 1 . Under such a situation, since the transceiver  102  derives the final adjusted transmission power ATP 1  by negotiating with the transceiver  104 , the final adjusted transmission power ATP 1  is acceptable to the transceiver  104 . As a result, the present invention can determine the adequate adjusted transmission power ATP 1  which reduces unnecessary power consumption as most in a short cable case and avoids an interoperability issue in a long cable case. 
     In detail, please refer to  FIG. 2A  and  FIG. 2B .  FIG. 2A  is a schematic diagram of operations of the transceiver  104  indicating the transceiver  102  to start adjusting transmission power according to an embodiment of the present invention, and  FIG. 2B  is a schematic diagram of operations of the transceiver  102  indicating the transceiver  104  that the transceiver  102  starts to adjust its transmission power according to an embodiment of the present invention. In other words, there are two forms of initiating the transmission power control negotiation process  15 . One is passively initiated by one transceiver to adjust transmission power of another transceiver as shown in  FIG. 2A , i.e. the transceiver  104  adjust the transceiver  102 , and another is actively initiated by one transceiver to adjust itself transmission power as shown in  FIG. 2B , i.e. the transceiver  102  adjust itself. 
     As shown in  FIG. 2A , when the transceiver  104  intends to adjust transmission power of the transceiver  102 , the transceiver  104  sends a request message REQ 1  to indicate the transceiver  102  to start adjusting transmission power. After receiving the request message REQ 1 , the transceiver  102  can optionally replies an acknowledgement ACK 1  for the request message REQ 1  and adopts the adjusted transmission power ATP 1  to transmit the adjustment signals AS 1 , wherein the adjusted transmission power ATP 1  is different from the default transmission power and can be indicated by the request message REQ 1  or chosen by the transceiver  102 . Then, after receiving and analyzing the adjustment signals AS 1 , the transceiver  104  sends a request message REQ 2  to indicate the transceiver  102  to increase the adjusted transmission power ATP 1  if the adjustment signals AS 1  are unqualified (i.e. signal quality is not enough) or to decrease the adjusted transmission power ATP 1  if the adjustment signals AS 1  are overqualified (i.e. unnecessary power consumption). 
     Under such a situation, the transceiver  104  can repeat sending several request messages REQ 2  to indicate the transceiver  102  to adjust the adjusted transmission power ATP 1  until the adjustment signals AS 1  are not overqualified or unqualified, and then the transceiver  104  optionally sends an end message END 1  to indicate the adjusted transmission power ATP 1  is adequate if the adjustment signals AS 1  are not overqualified or unqualified and the transceiver  104  finished transmission power adjustment of its part. Then, when the transceiver  102  receives the end message END 1  or does not receive the request message REQ 2  for a long time (i.e. the transceiver  104  does not optionally send the end message END 1 ), the transceiver  102  finishes transmission power adjustment of its part and transmits following signals with the adjusted transmission power ATP 1 . Under such a situation, the transceiver  104  can ask the transceiver  102  to adjust transmission power of the transceiver  102  to an adequate level, and the transceiver  102  can operate accordingly. As a result, the transceiver  102  can reduce unnecessary power consumption as most in a short cable case and avoids an interoperability issue in a long cable case when transmitting signals to the transceiver  104 . 
     Noticeably, other than indicating the transceiver  102  to increase or decrease the adjusted transmission power ATP 1 , the request message REQ 2  can further indicate the transceiver  102  to increase or decrease the adjusted transmission power ATP 1  by a desired power level. Besides, when the transceiver  102  receives the request message REQ 2  and then increases or decreases the adjusted transmission power ATP 1  to a largest available power or a smallest available power, the transceiver  102  can optionally send a MAX LEVEL DONE message or a MIN LEVEL DONE message to inform the transceiver  104 , such that the transceiver  104  can finish adjusting transmission power of the transceiver  102  accordingly. 
     On the other hand, as shown in  FIG. 2B , when the transceiver  102  intends to adjust itself transmission power, the transceiver  102  sends a request message REQ 3  to indicate the transceiver  104  that the transceiver  102  starts to adjust itself transmission power. After receiving the request message REQ 3 , the transceiver  104  can optionally reply an acknowledgement ACK 2  for the request message REQ 3 . After optionally receiving the acknowledgement ACK 2 , the transceiver  102  adopts the adjusted transmission power ATP 1  to transmit the adjustment signals AS 1 , wherein the adjusted transmission power ATP 1  is different from the default transmission power and is chosen by the transceiver  102 . Then, after receiving and analyzing the adjustment signals AS 1 , the transceiver  104  sends an acknowledgement ACK 3  for the adjustment signals AS 1  if the adjustment signals AS 1  are not unqualified (i.e. signal quality is good enough, but may be overqualified) 
     Under such a situation, when the transceiver  102  receives the acknowledgement ACK 3  for the previous adjustment signals AS 1 , in order to reduce power consumption at most, the transceiver  102  can further lower the adjusted transmission power ATP 1  to transmit the adjustment signals AS 1 , and the transceiver  104  can keep sending the acknowledgement ACK 3  for the adjustment signals AS 1  until the adjustment signals AS 1  are unqualified. During the above operations, the transceiver  104  can optionally send an end message END 2  to indicate the adjusted transmission power ATP 1  is adequate if the adjustment signals AS 1  are not overqualified or unqualified. Therefore, when the transceiver  102  receives the end message END 2 , the transceiver  102  finishes transmission power adjustment of its part and transmits following signals with the adjusted transmission power ATP 1 ; otherwise, when the transceiver  102  does not receive the acknowledgement ACK 3  for a long time (i.e. the transceiver  104  does not optionally send the end message END 2 ), the transceiver  102  adjusts the adjusted transmission power ATP 1  as a default transmission power (e.g. not receiving any the acknowledgement ACK 3 ) or a adjusted transmission power ATP 2  with which the transceiver  102  transmits adjustment signals AS 2  and receives an acknowledgement ACK 4  for the adjustment signals AS 2 , e.g. the lowest adjusted transmission power ATP 1  corresponding to the last received acknowledgement ACK 3 . Then, the transceiver  102  finishes transmission power adjustment of its part and transmits following signals with the adjusted transmission power ATP 1 , i.e. the default transmission power or the adjusted transmission power ATP 2 . 
     Under such a situation, the transceiver  102  can notify the transceiver  104  that the transceiver  102  will adjust itself transmission power, and thus the transceiver  104  can know transmission power adjustment occurs and analyze the adjustment signals AS 1  without accidentally discarding the adjustment signals AS 1  with less good signal quality. Then, the transceiver  102  can adjust itself transmission power to an adequate level according to receiving status of the acknowledgement ACK 3 . As a result, the transceiver  102  can reduce unnecessary power consumption as most in a short cable case and avoids an interoperability issue in a long cable case when transmitting signals to the transceiver  104 . 
     Noticeably, the spirit of the present invention is that one transceiver can analyze adjustment signals with adjusted transmission power and send messages for another transceiver to adjust the adjusted transmission power, to reduce unnecessary power consumption as most in a short cable case and avoid an interoperability issue in a long cable case. Those skilled in the art should make modifications or alterations accordingly. For example, the above messages can be implemented by Fast Link Pulse (FLP) in auto-negotiation flow, undefined Physical Coding Sublayer (PCS) coding or Medium Access Control (MAC) protocol, and the communication system  10  can be other communication systems other than an Ethernet communication system. 
     Besides, the above embodiment illustrates an asynchronous transmission power adjustment, i.e. only one transceiver adjusts transmission power at a time. However, in the asynchronous transmission power adjustment, after one transceiver finishes adjusting transmission power, another transceiver can start adjusting transmission power, which requires long adjustment time. 
     Therefore, in other embodiments, in order to reduce adjustment time, synchronous transmission power adjustment is performed as well, i.e. two transceivers simultaneously adjust transmission power. In other words, during the transmission power control negotiation process  15 , the transceiver  104  (a transmitting end) can also transmit adjustment signals AS 3  to the transceiver  102  (a receiving end) with an adjusted transmission power ATP 3  which is different from the default transmission power. Then, after analyzing the adjustment signals AS 3 , the transceiver  102  sends negotiation messages for the transceiver  104  to adjust the adjusted transmission power ATP 3 , wherein the negotiation messages can be request messages which indicate the transceiver  104  to increase or decrease the adjusted transmission power ATP 3 , acknowledgements for the adjustment signals AS 3  which the transceiver  104  can adjust the adjusted transmission power ATP 1  accordingly, or end messages which indicate the adjusted transmission power ATP 3  is adequate. Afterwards, after adjusting transmission power according to the negotiation messages, the transceiver  104  can transmit following signals with the adjusted transmission power ATP 3 . As a result, the transceivers  102 ,  104  can simultaneously adjust transmission power, to reduce adjustment time. 
     Moreover, please refer to  FIG. 3-6 , which are schematic diagrams of operations of the request circuits  122 ,  124 , and the response circuits  126 ,  128  under different scenarios. As shown in  FIG. 3 , when the transceiver  104  intends to adjust transmission power of the transceiver  102  in an asynchronous transmission power adjustment, operations of the request circuit  124  of the transceiver  104  and the response circuit  126  of the transceiver  102  can be summarized into processes  30 ,  35  (operations of the request circuit  122  and the response circuits  128  are similar when the transceiver  102  intends to adjust transmission power of the transceiver  104 ). The process  30  includes the following steps: 
     Step  300 : ASK: check if both the transceivers  102 ,  104  support asynchronous transmission power control negotiation. If yes, go to step  302 ; otherwise, go to step  308 . 
     Step  302 : MONITOR: analyze signal quality of the adjustment signals AS 1 . If the adjustment signals AS 1  are unqualified or overqualified, go to step  304 ; if the adjustment signals AS 1  are adequate, optionally go to step  306  or go to step  308 . 
     Step  304 : SEND REQUEST: send the request message REQ 2  to ask the transceiver  102  to adjust transmission power. 
     Step  306 : SEND OK: tell the transceiver  102  that the negotiation in the transceiver  104  will be finished via the end message END 1 . 
     Step  308 : END. 
     The process  35  includes the following steps: 
     Step  350 : CHK REQUEST: check if the request message REQ 2  is received. If yes, go to step  352 . 
     Step  352 : ADJUST TX AMP: ask the TX  110  to adjust transmission power level according to the request message REQ 2 . 
     According to the processes  30 ,  35 , when the transceiver  104  intends to adjust transmission power of the transceiver  102  in an asynchronous transmission power adjustment, the request circuit  124  first checks if both the transceivers  102 ,  104  support asynchronous transmission power control negotiation. If one of the transceivers  102 ,  104  does not support asynchronous transmission power control negotiation, asynchronous transmission power control negotiation is not performed. If both the transceivers  102 ,  104  support asynchronous transmission power control negotiation, the request circuit  124  analyzes signal quality of the adjustment signals AS 1 . If the adjustment signals AS 1  are unqualified or overqualified, the request circuit  124  sends the request message REQ 2  to ask the transceiver  102  to increase or decrease transmission power and thus the response circuit  126  can ask the TX  110  to increase or decrease transmission power according to the request message REQ 2 . The request circuit  124  and the response circuit  126  repeat the above adjustment operations until the adjustment signals AS 1  are adequate. Then, the request circuit  124  can optionally tell the transceiver  102  that the negotiation in its part will be finished via the end message END 1  and then finish, or directly finish the negotiation in its part without telling the transceiver  102 . Details of the processes  30 ,  35  can be derived by referring to  FIG. 2A  and related descriptions. 
     As shown in  FIG. 4 , when the transceivers  102 ,  104  intend to adjust transmission power of the transceivers  102 ,  104  in a synchronous transmission power adjustment, operations of the request circuit  124  and the response circuit  128  of the transceiver  104  can be summarized into processes  40 . The process  40  includes the following steps: 
     Step  400 : ASK: check if both the transceivers  102 ,  104  support synchronous transmission power control negotiation. If yes, go to step  402 ; otherwise, go to step  412 . 
     Step  402 : MONITOR: analyze signal quality of the adjustment signals AS 1 . If the adjustment signals AS 1  are unqualified or overqualified, go to step  404 ; if the adjustment signals AS 1  are adequate, go to step  406 . 
     Step  404 : SEND REQUEST: send the request message REQ 2  to ask the transceiver  102  to adjust transmission power. 
     Step  406 : SEND OK: tell the transceiver  102  that the negotiation in the transceiver  104  will be finished via the end message END 1 . 
     Step  408 : CHECK REQUEST/ACK: check if a request message for adjusting transmission power of the transceiver  104  is received and if an acknowledgement for the request message REQ 2  or an acknowledgement for the end message END 1  is received. If the request message is received or the acknowledgement for the request message REQ 2  is not received for a long time, go to step  410 ; if no request message is received, go to step  402 ; if the acknowledgement for the end message END 1  is received and an end message from the transceiver  102  is received, go to step  412 . 
     Step  410 : ADJUST TX AMP: ask the TX  112  to adjust transmission power level. 
     Step  412 : END. 
     Noticeably, main differences between the process  40  and the processes  30 ,  35  are that the process  40  is applied in the transceiver  104  wherein the transceiver  104  adjusts transmission power of the transceiver  102  while being adjusted by the transceiver  102  which performs operations similar to the process  40  in a synchronous transmission power adjustment while the processes  30 ,  35  are applied in the transceivers,  102 ,  104  wherein the transceiver  104  adjusts transmission power of the transceiver  102  in a asynchronous transmission power adjustment. Under such a situation, when a transceiver receives a request message or an end message, the transceiver needs to reply an acknowledgement message, such that another transceiver can know the request message or the end message is actually received (signal quality of the request message or the end message may be too low for the transceiver). Besides, end messages are required for the transceivers  102 ,  104  to realize when to finish synchronous transmission power adjustment. 
     According to the process  40 , when the transceiver  104  intends to adjust transmission power of the transceiver  102  in a synchronous transmission power adjustment, the request circuit  124  first checks if both the transceivers  102 ,  104  support synchronous transmission power control negotiation. If one of the transceivers  102 ,  104  does not support synchronous transmission power control negotiation, synchronous transmission power control negotiation is not performed. If both the transceivers  102 ,  104  support synchronous transmission power control negotiation, the request circuit  124  analyzes signal quality of the adjustment signals AS 1 . If the adjustment signals AS 1  are unqualified or overqualified, the request circuit  124  sends the request message REQ 2  to ask the transceiver  102  to increase or decrease transmission power. 
     Meanwhile, if the request message sent by the transceiver  102  for adjusting transmission power of the transceiver  104  is received, the response circuit  128  asks the TX  112  to adjust transmission power level according to the request message. If no request message sent by the transceiver  102  for adjusting transmission power of the transceiver  104  is received, i.e. transmission power of the transceiver  104  may be adequate, the response circuit  128  keeps analyzes signal quality of the adjustment signals AS 1  to adjust transmission power of the transceiver  102 . During adjusting transmission power of the transceiver  102 , if the request circuit  124  sends the request message REQ 2  and an acknowledgement for the request message REQ 2  is not received for a long time, i.e. transmission power for sending the request message REQ 2  is too low, the response circuit  128  asks the TX  112  to increase transmission power level. 
     Then, by repeat the above operations, when the adjustment signals AS 1  are adequate, the request circuit  124  sends the end message END 1  to indicate the adjusted transmission power ATP 1  is adequate, and the response circuit  126  of the transceiver  102  replies an acknowledgement for the end message END 1 . Under such a situation, if the acknowledgement for the end message END 1  is received and an end message sent by the transceiver  102  is received, i.e. transmission power of both the transceivers  102 ,  104  is adequate, the transceiver  104  finishes the synchronous transmission power adjustment of its part, i.e. transmitting following signals with adjusted transmission power, and finishing to indicate the transceiver  102  to adjust transmission power. Details of the process  40  can be derived by referring to  FIG. 2A  and related descriptions, and operations of the request circuit  122  and the response circuit  126  of the transceiver  102  are similar. 
     On the other hand, as shown in  FIG. 5 , when the transceiver  102  intends to adjust itself transmission power in an asynchronous transmission power adjustment, operations of the request circuit  122  and the response circuit  126  of the transceiver  102  can be summarized into process  50  (operations of the request circuit  124  and the response circuits  128  of the transceiver  104  are similar when the transceiver  102  intends to adjust itself transmission power). The process  50  includes the following steps: 
     Step  500 : ASK: check if both the transceivers  102 ,  104  support asynchronous transmission power control negotiation. If yes, go to step  502 ; otherwise, go to step  508 . 
     Step  502 : SEND REQUEST: send the request message REQ 3  to indicate the transceiver  104  that the transceiver  102  starts to adjust itself transmission power. The acknowledgement ACK 2  for the request message REQ 3  is optional. With the implementation of ACK 2 , go to step  504  if the acknowledgement ACK 2  for the request message REQ 3  is received. However, go to step  508  if the acknowledgement ACK 2  for the request message REQ 3  is not received for a long time; without the implementation of ACK 2 , go the step  504  after sending request message REQ 3 . 
     Step  504 : ADJUST TX AMP: ask the TX  110  to adjust transmission power level. If the optional end message END 2  is received or the acknowledgement ACK 3  for the adjustment signals AS 1  is not received for a long time, go to step  508 . 
     Step  506 : CHK RESPONSE: check if response messages from the transceiver  102  are received. 
     Step  508 : END. 
     According to the process  50 , when the transceiver  102  intends to adjust itself transmission power in an asynchronous transmission power adjustment, the request circuit  122  first checks if both the transceivers  102 ,  104  support asynchronous transmission power control negotiation. If one of the transceivers  102 ,  104  does not support asynchronous transmission power control negotiation, asynchronous transmission power control negotiation is not performed. If both the transceivers  102 ,  104  support asynchronous transmission power control negotiation, the request circuit  122  sends the request message REQ 3  to indicate the transceiver  104  that the transceiver  102  starts to adjust itself transmission power while the transceiver  104  optionally replies the acknowledgement ACK 2  for the request message REQ 3 . Under such a situation, if the transceiver  102  does not receive the acknowledgement ACK 2  for the request message REQ 3  for a long time, the request circuit  122  can optionally finish asynchronous transmission power adjustment. 
     On the other hand, if the transceiver  102  receives the acknowledgement ACK 2  for the request message REQ 3 , the request circuit  122  asks the TX  110  to adjust transmission power level and the transceiver  102  transmits the adjustment signals AS 1  accordingly. Then, transceiver  104  replies the acknowledgement ACK 3  for the adjustment signals AS 1  if the adjustment signals AS 1  is qualified, and optionally replies the end message END 2  for the adjustment signals AS 1  if the adjustment signals AS 1  is adequate. Therefore, if the transceiver  102  optionally receives the end message END 2  indicating the adjusted transmission power ATP 1  is adequate, the request circuit  122  finishes transmission power adjustment of its part and transmits following signals with the adjusted transmission power ATP 1 , or if the transceiver  102  does not receive the acknowledgement ACK 3  for the adjustment signals AS 1  for a long time, i.e. signal quality of the adjustment signals AS 1  is unqualified and thus the transceiver  104  does not respond the acknowledgement ACK 3  for the adjustment signals AS 1 , the transceiver  102  finishes transmission power adjustment of its part and transmits following signals with the default transmission power or the lowest adjusted transmission power ATP 1  corresponding to the last received acknowledgement ACK 3 . During the above operations, the response circuit  126  keeps checking if response messages (e.g. response for ASK, the acknowledgement ACK 2  for the request message REQ 3  or the acknowledgement ACK 3  for the adjustment signals AS 1 ) are received, and informs the request circuit  122  to operate correspondingly. Details of the process  50  can be derived by referring to  FIG. 2B  and related descriptions. 
     As shown in  FIG. 6 , when the transceivers  102 ,  104  intend to adjust themselves transmission power in a synchronous transmission power adjustment, operations of the request circuit  122  and the response circuit  126  of the transceiver  104  can be summarized into processes  60 . The process  60  includes the following steps: 
     Step  600 : ASK: check if both the transceivers  102 ,  104  support synchronous transmission power control negotiation. If yes, go to step  602 ; otherwise, go to step  610 . 
     Step  602 : SEND REQUEST: send the request message REQ 3  to indicate the transceiver  104  that the transceiver  102  starts to adjust itself transmission power. 
     Step  604 : CHK RESPONSE: check if response messages or adjustment signals from the transceiver  102  are received. If adjustment signals from the transceiver  102  are received, analyze the adjustment signals and go to step  606 ; if the acknowledgement ACK 3  for the adjustment signals AS 1  is not received for a long time or the acknowledgement ACK 3  for the adjustment signals AS 1  is optionally received, go to step  608 ; if the end message END 2  is received and an END message is transmitted to the transceiver  102 , go to step  610 . 
     Step  606 : SEND RESPONSE: send an acknowledgement for the adjustment signals to the transceiver  104  if the adjustment signals from the transceiver  104  are qualified and send an end message for the adjustment signals to the transceiver  104  if the adjustment signals from the transceiver  104  are adequate. go to step  604 . 
     Step  608 : ADJUST TX AMP: ask the TX  110  to adjust transmission power level and go to step  604 . 
     Step  610 : END. 
     Noticeably, main differences between the process  60  and the process  50  are that the process  60  is applied in the transceiver  102  wherein the transceiver  102  adjusts itself transmission power while the transceiver  104  performs operations similar to the process  60  to adjust itself transmission power in a synchronous transmission power adjustment while the process  50  is applied in the transceiver  102  wherein the transceiver  103  adjusts itself transmission power in a asynchronous transmission power adjustment. Under such a situation, when a transceiver receives adjustment signals, the transceiver needs to reply an acknowledgement message or an end message, such that another transceiver can know the adjustment signals is actually received (signal quality of the adjustment signals may be too low for the transceiver). Besides, end messages are required for the transceivers  102 ,  104  to realize when to finish synchronous transmission power adjustment. 
     According to the process  60 , when the transceiver  102  intends to adjust itself transmission power in a synchronous transmission power adjustment, the request circuit  122  first checks if both the transceivers  102 ,  104  support synchronous transmission power control negotiation. If one of the transceivers  102 ,  104  does not support synchronous transmission power control negotiation, synchronous transmission power control negotiation is not performed. If both the transceivers  102 ,  104  support synchronous transmission power control negotiation, the request circuit  122  send the request message REQ 3  to indicate the transceiver  104  that the transceiver  102  starts to adjust itself transmission power and the transceiver  104  can optionally reply the acknowledgement ACK 2  for the request message REQ 3 . Then, the request circuit  122  asks the TX  110  to adjust transmission power level and the transceiver  102  transmits the adjustment signals AS 1  accordingly. Afterwards, transceiver  104  optionally replies the acknowledgement ACK 3  for the adjustment signals AS 1  if the adjustment signals AS 1  is qualified, and replies the end message END 2  for the adjustment signals AS 1  if the adjustment signals AS 1  is adequate. 
     Meanwhile, since the transceiver  104  can simultaneously send adjustment signals with adjusted transmission power, if adjustment signals from the transceiver  104  are received, the response circuit  126  analyzes the adjustment signals and sends an acknowledgement for the adjustment signals to the transceiver  104  if the adjustment signals from the transceiver  104  are qualified, and send an end message for the adjustment signals to the transceiver  104  if the adjustment signals from the transceiver  104  are adequate. 
     On the other hand, if the transceiver  102  optionally receives the acknowledgement ACK 3  for the previous adjustment signals AS 1 , in order to reduce power consumption at most, the transceiver  102  can further lower the adjusted transmission power ATP 1  to transmit the adjustment signals AS 1 ; if the transceiver  102  does not receive the acknowledgement ACK 3  for the adjustment signals AS 1  for a long time, i.e. signal quality of the adjustment signals AS 1  is unqualified and thus the transceiver  104  does not respond the acknowledgement ACK 3  for the adjustment signals AS 1 , the transceiver  102  could transmit following signals with the default transmission power or the lowest adjusted transmission power ATP 1  corresponding to the last received acknowledgement ACK 3 ; if the transceiver  102  has received the end message END 2  indicating the adjusted transmission power ATP 1  is adequate and has transmitted an end message for the adjustment signals of transceiver  104 , the request circuit  122  finishes transmission power adjustment of its part and transmits following signals with the adjusted transmission power ATP 1 . Details of the process  60  can be derived by referring to  FIG. 2B  and related descriptions. 
     In the prior art, since the local device estimates the cable length by itself, the estimated cable length may not be reliable due to unideal factors, and since the adjusted transmission amplitude is not confirmed by the remote device, there is still an interoperability issue. In comparison, in the present invention, one transceiver can analyze adjustment signals with adjusted transmission power and send messages for another transceiver to adjust the adjusted transmission power, to reduce unnecessary power consumption as most in a short cable case and avoid an interoperability issue in a long cable case. Besides, the present invention can perform synchronous transmission power adjustment, to reduce adjustment time. 
     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.