Abstract:
A method for controlling transmission power of a wireless device is provided. A WiFi link is established to a communication device. A data rate of data packets transmitted to the communication device is monitored. Information from the communication device is obtained in response to the transmitted data packets. A transmission power of the wireless device is decreased when the data rate of the data packets reaches a highest data rate and the first information satisfies a specific condition.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of U.S. Provisional Application No. 61/521,151, filed on Aug. 8, 2011, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a wireless device, and more particularly to a method for controlling transmission power of a wireless device. 
     2. Description of the Related Art 
     In recent years, mobile phones have become more popular and have various powerful applications, such as “Hot Spot” wireless fidelity (WiFi) wireless Internet connection, which provides Internet access over a wireless local area network (WLAN) for users nearby a mobile phone. However, the mobile phone functioning as a Hot Spot will consume lots of power due to the mobile phone operating in a transmission mode. 
     Therefore, it is desired to save power for mobile devices in a transmission mode. 
     BRIEF SUMMARY OF THE INVENTION 
     Methods for controlling transmission power of a wireless device and a wireless device are provided. An embodiment of a method for controlling transmission power of a wireless device is provided. The method comprises: establishing a WiFi link to a communication device; monitoring a data rate of data packets transmitted to the communication device; obtaining first information from the communication device in response to the transmitted data packets; decreasing a transmission power of the wireless device when the data rate of the data packets reaches a highest data rate and the first information satisfies a specific condition. 
     Furthermore, an embodiment of a method for controlling transmission power of a wireless device is provided. The method comprises: establishing a WiFi link to a communication device; transmitting data packets to the communication device according to a first transmission power; adjusting a data rate of the data packets according to a packet error rate (PER); transmitting data packets to the communication device according to a second transmission power smaller than the first transmission power when the data rate of the data packets reaches a highest data rate and the PER satisfies a specific condition; and transmitting data packets to the communication device according to the first transmission power when the data rate of the data packets reaches the highest data rate and the PER does not satisfy the specific condition. 
     Moreover, a wireless device is provided. The wireless device comprises a processor, an antenna and a radio frequency (RF) module coupled between the antenna and the processor. The RF module comprises a power amplifier which transmits data packets from the processor to a communication device with a first transmission power. The processor establishes a WiFi link to the communication device via the RF module and the antenna, and obtains first information from the communication device in response to the transmitted data packets. The processor controls the power amplifier to transmit the data packets with a second transmission power smaller than the first transmission power when a data rate of the data packets reaches a highest data rate and the first information satisfies a specific condition. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows a schematic diagram illustrating IEEE 802.11 wireless fidelity (WiFi) network communications between two electrical devices; 
         FIG. 2  shows a block diagram illustrating a WLAN module equipped in a wireless device according to an embodiment of the invention; 
         FIG. 3  shows a method for controlling transmission power of a wireless device with the WLAN module of  FIG. 2  according to an embodiment of the invention; 
         FIG. 4  shows a method for controlling transmission power of a wireless device with the WLAN module of  FIG. 2  according to another embodiment of the invention; 
         FIG. 5  shows an exemplary diagram illustrating the relationships between a data rate and input power (RSSI). 
         FIG. 6  shows a method for controlling transmission power of a wireless device with the WLAN module of  FIG. 2  according to another embodiment of the invention; 
         FIGS. 7A and 7B  show a method for controlling transmission power of a wireless device with the WLAN module of  FIG. 2  according to another embodiment of the invention; 
         FIG. 8  shows a schematic diagram illustrating a mobile network communication system according to an embodiment of the invention; and 
         FIG. 9  shows a schematic diagram illustrating an internet network communication system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 1  shows a schematic diagram illustrating IEEE 802.11 wireless fidelity (WiFi) network communications between two electrical devices  10  and  20 , wherein the electrical devices  10  and  20  may be computers, portable devices (such as mobile phone, tablet computer) and so on. In  FIG. 1 , the devices  10  and  20  are equipped with wireless local area network (WLAN) modules (e.g. 802.11b, 802.11g or 802.11n) to perform peer to peer communications. When one of the electrical devices  10  and  20  uses a highest data rate to transmit data packets to the other electrical device, e.g. 11 Mbps for the 802.11b specification, 54 Mbps for the 802.11g specification or MCS7 for the 802.11n specification, the one of the electrical devices  10  and  20  will perform a method to control transmission power of the WLAN module thereof according to an embodiment of the invention, so as to achieve lower power consumption. 
       FIG. 2  shows a block diagram illustrating a WLAN module  100  equipped in a wireless device (e.g.  10  or  20  of  FIG. 1 ) according to an embodiment of the invention. The WLAN module  100  comprises a Baseband chip  110  and a radio frequency (RF) module  120 . The RF module  120  is coupled between the Baseband chip  110  and an antenna  170 , which comprises a low noise amplifier (LNA)  130 , a power amplifier (PA)  140  and a TX/RX processing unit  150 . The TX/RX processing unit  150  receives and modulates the data DAT out  from a processor  160  of the Baseband chip  110 , so as to provide the RF signal RF out  to the antenna  170  via the PA  140  for transmitting data packets to another wireless device. Simultaneously, the processor  160  of the Baseband chip  110  further provides a control signal Ctrl to the PA  140  for controlling transmission power of the wireless device. In general, the receiving wireless device will send back acknowledge (ACK) messages in response to the data packets transmitted by the transmitting wireless device. Therefore, the TX/RX processing unit  150  of the transmitting wireless device will receive and demodulate the RF signal RF in  corresponding to the ACK message via the LNA  130  and the antenna  170 , so as to provide the data DAT in  to the processor  160  of the Baseband chip  110 , and then the processor  160  of the Baseband chip  110  obtains a packet error rate (PER) according to the data DAT in . The PER is the number of incorrectly received data packets divided by the total number of received packets, wherein a packet is declared incorrect if at least one bit is erroneous. Therefore, the smaller the PER, the better the communication quality. When the receiving wireless device and the transmitting wireless device approach each other, the processor  160  of the Baseband chip  110  will obtain a better PER. 
       FIG. 3  shows a method for controlling transmission power of a wireless device with the WLAN module  100  of  FIG. 2  according to an embodiment of the invention. Referring to  FIG. 2  and  FIG. 3  together, first, the WLAN module  100  of the wireless device operates in a normal mode and establishes a WiFi link to a communication device (step S 210 ). In step S 220 , the WLAN module  100  continues to monitor/detect a data rate of data packets transmitted to the communication device and obtains a PER corresponding to the ACK messages from the communication device in response to the transmitted data packets. In the WLAN module  100 , the processor  160  obtains the data rate of data packets transmitted to the communication device according to the modulation operations of the TX/RX processing unit  150 . Once it is detected that the PER is good (i.e. the PER does not exceed a threshold PER th ) and the data rate reaches a highest data rate that can be supported by the WLAN module  100  (step S 230 ), such as 11 Mbps for the 802.11b specification, 54 Mbps for the 802.11g specification or MCS7 for the 802.11n specification, the WLAN module  100  enters a power conservation mode (step S 240 ), and then the processor  160  provides the control signal Ctrl to the PA  140 , to decrease transmission power. Next, the WLAN module  100  checks whether the PER is still good (i.e. the PER does not exceed the threshold PER th ) (step S 250 ). If no (i.e. the PER exceeds the threshold PER th ), the WLAN module  100  returns back to the normal mode, and the processor  160  provides the control signal Ctrl to the PA  140 , to recover the transmission power (i.e. increase transmission power) (step S 270 ), and then step S 220  is performed to continue monitoring the data rate and the PER. On the contrary, if the PER is good (i.e. the PER does not exceed the threshold PER th ), the WLAN module  100  continues to operate in the power conservation mode, so as to transmit the data packets with lower transmission power to the communication device (step S 260 ). Thus, power consumption of the WLAN module  100  is decreased. In addition, the WLAN module  100  periodically checks the PER in the power conservation mode (step S 250 ), so as to determine whether to return to the normal mode. In the power conservation mode, the wireless device of the invention may decrease the current transmission power according a predefined scale, such as 1 dB, 3 dB (i.e. a half of the current transmission power) and so on, so as to obtain an optimal transmission power without affecting the PER. Furthermore, the wireless device performs the method of  FIG. 3  without additional circuits and complex operations due to the data rate and the PER being given. In other words, it is easy to implement the method for controlling transmission power of a wireless device according to the embodiment. In the embodiment, the threshold PER th  is determined according to actual applications. 
     TABLE 1 shows an example illustrating the relationships between the data rate, transmission power and power consumption of various WiFi modes according to the method of  FIG. 3 . Taking the 802.11b specification as an example, when a wireless device uses a highest data rate 11 Mbps to transmit data packets to a communication device in a normal mode and obtains a good PER in response to the transmitted data packets, the wireless device will enter a power conservation mode, to decrease the transmission power from 18 dBm to 13 dBm. Thus, power consumption of the wireless device is decreased from 260 mA to 170 mA. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Transmission Power 
                 power consumption 
               
               
                 Mode 
                 Data rate 
                 (dBm) 
                 (mA) 
               
               
                   
               
             
             
               
                 802.11b 
                   1 Mbps 
                 18 
                 260 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                   2 Mbps 
                 18 
                 260 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 5.5 Mbps 
                 18 
                 260 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  11 Mbps 
                 18 
                 260 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  11 Mbps 
                 13 
                 170 
               
               
                   
                 (power conservation 
                   
                   
               
               
                   
                 mode) 
                   
                   
               
               
                 802.11g 
                   6 Mbps 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                   9 Mbps 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  12 Mbps 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  18 Mbps 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  24 Mbps 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  36 Mbps 
                 13 
                 160 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  48 Mbps 
                 13 
                 140 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  54 Mbps 
                 13 
                 140 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                  54 Mbps 
                 10 
                 100 
               
               
                   
                 (power conservation 
                   
                   
               
               
                   
                 mode) 
                   
                   
               
               
                 802.11n 
                 MCS0 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 MCS1 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 MCS2 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 MCS4 
                 13 
                 170 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 MCS5 
                 13 
                 160 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 MCS6 
                 13 
                 140 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 MCS7 
                 13 
                 140 
               
               
                   
                 (Normal mode) 
                   
                   
               
               
                   
                 MCS7 
                 10 
                 100 
               
               
                   
                 (power conservation 
                   
                   
               
               
                   
                 mode) 
               
               
                   
               
             
          
         
       
     
     Referring back to  FIG. 2 , the RF module  120  may further use a measure circuit to obtain a received signal strength indicator (RSSI) according to the RF signal RF in  that comprises the ACK messages from the communication device in response to the data packets transmitted by the wireless device, and provide the RSSI to the processor  160  of the Baseband chip  110 . The measure circuit may be an independent circuit or may be integrated into the LNA  130  or the TX/RX processing unit  150 .  FIG. 4  shows a method for controlling transmission power of a wireless device with the WLAN module  100  of  FIG. 2  according to another embodiment of the invention. Referring to  FIG. 2  and  FIG. 4  together, first, the WLAN module  100  of the wireless device operates in a normal mode and establishes a WiFi link to a communication device (step S 310 ). In step S 320 , the WLAN module  100  continues to monitor/detect a data rate of data packets transmitted to the communication device and obtains an RSSI corresponding to the ACK messages from the communication device in response to the transmitted data packets. Once it is detected that the RSSI is good (i.e. the RSSI exceeds a threshold RSSI th ) and the data rate reaches a highest data rate that can be supported by the WLAN module  100  (step S 330 ), such as 11 Mbps for the 802.11b specification, 54 Mbps for the 802.11g specification or MCS7 for the 802.11n specification, the WLAN module  100  enters a power conservation mode (step S 340 ), and then the processor  160  provides the control signal Ctrl to the PA  140 , to decrease transmission power. Next, the WLAN module  100  checks whether the PER is good (step S 350 ). If no (i.e. the PER exceeds the threshold PER th ), the WLAN module  100  returns back to the normal mode, and the processor  160  provides the control signal Ctrl to the PA  140 , to recover the transmission power (i.e. increase transmission power) (step S 370 ), and then step S 320  is performed to continue monitoring the data rate and the RSSI. On the contrary, if the PER is good (i.e. the PER does not exceed the threshold PER th , the WLAN module continues to operate in the power conservation mode, so as to transmit the data packets with lower transmission power to the communication device (step S 360 ). Thus, power consumption of the WLAN module  100  is decreased. In addition, the WLAN module  100  periodically checks the PER in the power conservation mode (step S 350 ), so as to determine whether to return to the normal mode. In the embodiment, the threshold PER th  and RSSI th  are determined according to actual applications. 
       FIG. 5  shows an exemplary diagram illustrating the relationships between a data rate and input power (RSSI). In  FIG. 5 , the wireless device will switch to a power conservation mode from a normal mode when the data rate reaches a highest value such as 54 Mbps and the input power is sustained at a good quality such as a value larger than −60 dBm, thus the transmission power drops to 10 dBm from 13 dBm. 
       FIG. 6  shows a method for controlling transmission power of a wireless device with the WLAN module  100  of  FIG. 2  according to another embodiment of the invention. Referring to  FIG. 2  and  FIG. 6  together, first, the WLAN module  100  of the wireless device operates in a normal mode and establishes a WiFi link to a communication device (step S 602 ). In step S 604 , the WLAN module  100  continues to monitor a data rate of data packets transmitted to the communication device and obtains a PER in response to the transmitted data packets. Next, it is determined whether the PER is good (step S 606 ). If no (i.e. the PER exceeds the threshold PER th ), the WLAN module  100  decreases the data rate of data packets (step S 610 ). Otherwise, if the PER has not exceeded the threshold PER th ), the WLAN module  100  continues to monitor the data rate (step S 608 ), to detect whether the data rate has reached a highest data rate that can be supported by the WLAN module  100  (step S 612 ), such as 11 Mbps for the 802.11b specification, 54 Mbps for the 802.11g specification or MCS7 for the 802.11n specification. If the data rate has not reached the highest data rate, the WLAN module  100  increases the data rate of data packets (step S 614 ), and then step S 606  is performed to continue monitoring the PER. Otherwise, the WLAN module  100  enters a power conservation mode (step S 616 ), and then the processor  160  provides the control signal Ctrl to the PA  140 , to decrease transmission power. Next, the WLAN module  100  checks whether the PER is still good (step S 618 ). If no (i.e. the PER exceeds the threshold PER th ), the WLAN module  100  returns back to the normal mode, and the processor  160  provides the control signal Ctrl to the PA  140 , to recover the transmission power (i.e. increase transmission power) (step S 620 ), and then step S 604  is performed to continue monitoring the data rate. On the contrary, if the PER is good (i.e. the PER does not exceed the threshold PER th ), the WLAN module  100  continues to operate in the power conservation mode, so as to transmit the data packets with the decreased transmission power (step S 622 ). Thus, power consumption of the WLAN module  100  is decreased. In addition, the WLAN module  100  periodically checks the PER in the power conservation mode (step S 618 ), so as to determine whether to return to the normal mode. In the embodiment, the threshold PER th  is determined according to actual applications. 
       FIGS. 7A and 7B  show a method for controlling transmission power of a wireless device with the WLAN module  100  of  FIG. 2  according to another embodiment of the invention. Referring to  FIG. 2  and  FIGS. 7A and 7B  together, first, the WLAN module  100  of the wireless device operates in a normal mode and establishes a WiFi link to a communication device (step S 702 ). In step S 704 , the WLAN module  100  continues to monitor a data rate of data packets transmitted to the communication device and obtains a PER in response to the transmitted data packets. Next, it is determined whether the PER is good (step S 706 ). If no (i.e. the PER exceeds a threshold PER th ), the WLAN module  100  decreases the data rate of data packets (step S 710 ). Otherwise, if the PER has not exceeded the threshold PER th , the WLAN module  100  continues to monitor the data rate (step S 708 ), to detect whether the data rate has reached a highest data rate that can be supported by the WLAN module  100  (step S 712 ), such as 11 Mbps for the 802.11b specification, 54 Mbps for the 802.11g specification or MCS7 for the 802.11n specification. If the data rate has not reached the highest data rate, the WLAN module  100  increases the data rate of data packets (step S 714 ), and then step S 706  is performed to continue monitoring the PER. Otherwise, the WLAN module  100  further monitors an RSSI (step S 716 ). Next, it is determined whether the RSSI exceeds a predetermined threshold RSSI th  (step S 718 ). If the RSSI has not exceeded the predetermined threshold RSSI th , step S 704  is performed to continue monitoring the data rate. Otherwise, the WLAN module  100  enters a power conservation mode (step S 720 ), and then the processor  160  provides the control signal Ctrl to the PA  140 , to decrease transmission power. Next, the WLAN module  100  checks whether the PER is good (step S 722 ). If no (i.e. the PER exceeds the threshold PER th ), the WLAN module  100  returns back to the normal mode and the processor  160  provides the control signal Ctrl to the PA  140  to recover the transmission power (step S 724 ), and then step S 704  is performed to continue monitoring the data rate. On the contrary, if the PER is good (i.e. the PER does not exceed the threshold PER th ), the WLAN module  100  continues to operate in the power conservation mode to transmit the data packets with the decreased transmission power (step S 726 ), thus power consumption of the WLAN module  100  is decreased. In addition, the WLAN module  100  periodically checks the PER in the power conservation mode (step S 722 ), so as to determine whether to switch back to the normal mode. In the embodiment, the threshold PER th  and RSSI th  are determined according to actual applications. 
       FIG. 8  shows a schematic diagram illustrating a mobile network communication system according to an embodiment of the invention. In  FIG. 8 , all electrical devices  10 ,  20 ,  30 ,  40  and  50  are equipped with WLAN modules (e.g. 802.11b, 802.11g or 802.11n specifications) to perform data communications, wherein the device  10  camps on a cellular station  60  of a service network. The wireless communications between the device  10  and the service network may be in compliance with various wireless technologies, such as the Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, Code Division Multiple Access 2000 (CDMA 2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, LTE Advanced (LTE-A) technology, and others. In  FIG. 8 , the device  10  functions as a hotspot in WiFi technology, which offers Internet access for the devices  20 ,  30 ,  40  and  50 , thus the devices  20 ,  30 ,  40  and  50  can access an Internet network through the device  10  and the cellular station  60  of the service network. In  FIG. 8 , the device  10  may use different or the same data rates to transmit packets to the devices  20 ,  30 ,  40  and  50 . Therefore, when the device  10  transmits packets to at least one of the devices  20 ,  30 ,  40  and  50  with a highest data rate (e.g. 11 Mbps for the 802.11b specification, 54 Mbps for the 802.11g specification or MCS7 for the 802.11n specification) and obtains a good PER (or RSSI) corresponding to the highest data rate, the device  10  may determine whether to decrease transmission power according the data rates of the devices other than the one with the highest data rate and the corresponding PERs or RSSIs. Specifically, according to the data rates of the packets transmitted to various devices  20 ,  30 ,  40  and  50  and the corresponding PERs or RSSIs, the device  10  will appropriately control its transmission power according to the methods of the invention without affecting packet transmissions, so as to decrease power consumption of the wireless device  10 . 
       FIG. 9  shows a schematic diagram illustrating an internet network communication system according to an embodiment of the invention. In  FIG. 9 , the electrical device  80  transmits data packets to an Internet network  90  through a wireless access point (AP) device  70 . As described above, when the electrical device  80  transmits data packets with a highest data rate (e.g. 11 Mbps for the 802.11b specification, 54 Mbps for the 802.11g specification or MCS7 for the 802.11n specification), the electrical device  80  may further determine whether to enter a power conservation mode according to the corresponding PER or RSSI. Specifically, if the electrical device  80  obtains a good PER (or RSSI) corresponding to the highest data rate, the wireless device  80  will appropriately control its transmission power without affecting packet transmissions, so as to decrease power consumption. 
     The embodiments of the innovation disclose the methods to control transmission power (i.e. output power) of a wireless device which uses IEEE 802.11 WiFi communication technologies to transmit data packets to other wireless devices. When the wireless device uses a highest data rate to transmit the data packets to the other wireless devices, the wireless device will enter a power conservation mode to decrease its transmission power without degrading communication quality. Therefore, power consumption is decreased for the wireless device; especially, for short-distances in a peer to peer mode or access mode. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.