Abstract:
A wireless network apparatus includes a receive circuit, a transmit circuit, and a processor. The receive circuit receives a first signal over a wireless link. The first signal represents packets of first data. The transmit circuit transmits a second signal over the wireless link at a power level indicated by a transmit power control signal. The second signal represents packets of second data. The processor determines a link quality of the wireless link based on the first signal. The processor selects one of a plurality of link quality thresholds based on the power level. The processor compares the link quality to the selected one of the plurality of link quality thresholds. The processor generates the transmit power control signal based on the comparison.

Description:
BACKGROUND 
   The present invention relates generally to wireless data communications. More particularly, the present invention relates to a self-adaptive method for transmit power control in a wireless network. 
   Many wireless network devices such as laptop computers are battery-powered to provide the mobility permitted by wireless networks such as those specified by IEEE 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16 and 802.20. For this reason, such portable wireless network devices must use power efficiently to permit long operation times. With respect to the wireless link, this involves controlling the transmit power of the wireless network device to maintain throughput levels with distance, maintain the quality and integrity of the signal, mitigate interference effects to other users, and maximize the signal-to-noise ratio of the signal. 
   SUMMARY 
   In general, in one aspect, the invention features a wireless network apparatus and corresponding method and computer program. It comprises a receive circuit to receive a first signal over a wireless link, the first signal representing packets of first data; a transmit circuit to transmit a second signal over the wireless link at a power level indicated by a transmit power control signal, the second signal representing packets of second data; and a processor to determine a link quality of the wireless link based on the first signal, and to generate the transmit power control signal based on the link quality. 
   Particular implementations can include one or more of the following features. The processor determines the link quality of the wireless link based on at least one of the group consisting of a signal strength of the first signal; a signal quality of the first signal; a packet error rate of the packets of first data; and a current transmit power level of the second signal. The transmit circuit transmits the second signal over the wireless link at a data rate indicated by a transmit data rate control signal; and wherein the processor generates the transmit data rate control signal based on the link quality. The processor determines the link quality of the wireless link based on at least one of the group consisting of a signal strength of the first signal; a signal quality of the first signal; a packet error rate of the packets of first data; a current transmit power level of the second signal; and a current transmit data rate of the second signal. The wireless network apparatus further comprises an antenna in communication with the receive circuit and the transmit circuit. The processor asserts a decrease power state of the transmit power control signal when the link quality of the wireless link exceeds a predetermined link quality, and a current transmit power level of the second signal is greater than a maximum transmit power level for a next higher transmit data rate of the first data; and the transmit circuit decreases a power of the second signal in response to the decrease power state of the transmit power control signal. The processor increases a rate of transmission of the first data when the link quality of the wireless link exceeds a predetermined link quality, and a current transmit power level of the second signal is not greater than a maximum transmit power level for a next higher transmit data rate of the first data. The processor asserts an increase power state of the transmit power control signal when the link quality of the wireless link does not exceed a predetermined link quality, and a current transmit power level of the second signal is less than a maximum transmit power level for the current transmit data rate of the first data; and the transmit circuit increases the power of the second signal in response to the increase power state of the transmit power control signal. The processor decreases a rate of transmission of the first data when the link quality of the wireless link does not exceed a predetermined link quality, and a current transmit power level of the second signal is not less than a maximum transmit power level for the current transmit data rate of the first data. The processor asserts a decrease power state of the transmit power control signal when a packet error rate of the first packets of data does not exceed a predetermined packet error rate threshold, the signal strength of the first signal exceeds a predetermined signal strength threshold, and a current transmit power level of the second signal is greater than a maximum transmit power level for a next higher transmit data rate of the first data; and the transmit circuit decreases a power of the second signal in response to the decrease power state of the transmit power control signal. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. The processor increases a rate of transmission of the first data when a packet error rate of the first packets of data does not exceed a predetermined packet error rate threshold, a signal strength of the first signal exceeds a predetermined signal strength threshold, and a current transmit power level of the second signal is not greater than a maximum transmit power level for a next higher transmit data rate of the first data. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. The processor asserts an increase power state of the transmit power control signal when a packet error rate of the first packets of data exceeds a predetermined packet error rate threshold, the signal strength of the first signal does not exceed a predetermined signal strength threshold, and a current transmit power level of the second signal is less than a maximum transmit power level for the current transmit data rate of the first data; and the transmit circuit increases the power of the second signal in response to the increase power state of the transmit power control signal. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. The processor decreases a rate of transmission of the first data when a packet error rate of the first packets of data exceeds a predetermined packet error rate threshold, a signal strength of the first signal does not exceed a predetermined signal strength threshold, and a current transmit power level of the second signal is not less than a maximum transmit power level for the current transmit data rate of the first data. The predetermined packet error rate threshold and the predetermined signal strength threshold are selected based on a current transmit power level of the second signal. An integrated circuit comprises the wireless network apparatus. A wireless network device comprises the wireless network apparatus. A wireless client comprises the wireless network device. A wireless access point comprises the wireless network device. The wireless network device is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16, and 802.20. The receive circuit comprises a media access controller receive circuit; and a physical-layer device receive circuit. The transmit circuit comprises a media access controller transmit circuit; and a physical-layer device transmit circuit. 
   In general, in one aspect, the invention features a wireless network apparatus and corresponding method and computer program. It comprises a receive circuit to receive a first signal over a wireless link, the first signal representing packets of first data; a processor to determine a link quality of the wireless link based on the first signal; and a transmit circuit to transmit a second signal over the wireless link at a data rate based on the link quality of the wireless link, the second signal representing packets of second data. 
   Particular implementations can include one or more of the following features. The processor determines the link quality of the wireless link based on at least one of the group consisting of a signal strength of the first signal; a signal quality of the first signal; a packet error rate of the packets of first data; and a current transmit power level of the second signal. The wireless network apparatus further comprises an antenna in communication with the receive circuit and the transmit circuit. An integrated circuit comprises the wireless network apparatus. A wireless network device comprises the wireless network apparatus. A wireless client comprises the wireless network device. A wireless access point comprises the wireless network device. The wireless network device is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16, and 802.20. 
   The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  shows a wireless network device in communication with another wireless network device according to a preferred embodiment of the present invention. 
       FIG. 2  shows a transmit power control process for the wireless network device of  FIG. 1  according to a preferred embodiment. 
       FIG. 3  shows a process for determining a link quality according to a preferred embodiment. 
       FIG. 4  shows a table of the power levels for each data rate according to a preferred embodiment. 
       FIG. 5  shows a flow diagram for embodiments in which the only the power level of the transmitted signal is adjusted. 
       FIG. 6  shows a process for decreasing the power level of a transmitted signal for a wireless network device having three transmit power levels P 0 , P 1 , and P 2  where P 0 &lt;P 1 &lt;P 2  according to a preferred embodiment. 
       FIG. 7  shows a process for increasing the power level of a transmitted signal for a wireless network device having three transmit power levels P 0 , P 1 , and P 2  where P 0 &lt;P 1 &lt;P 2  according to a preferred embodiment. 
   

   The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
   DETAILED DESCRIPTION 
   Conventional wireless devices, on detecting a wireless link of insufficient quality, for example by detecting a failed transmission of a packet, simply repeat the transmission of the packet until the packet is successfully transmitted. This method wastes considerable power and time. In contrast, embodiments of the present invention, on detecting a wireless link of insufficient quality, adjust the power level and/or data rate of the transmitted signal to obtain successful transmissions. The techniques employed, described in detail below, can result in a reduction of power consumption of 30%-40% compared to conventional methods. In addition, these techniques provide reduced interference and enhanced security. 
   Embodiments of the present invention provide power and/or data rate control for a transmitted signal in a wireless network such as an IEEE 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16 or 802.20 wireless local-area network, a personal-area network such as a Bluetooth network, and other sorts of wireless networks and communication links. In particular, the power level and/or data rate of the transmitted signal are controlled based on a link quality of the wireless link. In a preferred embodiment, the link quality is determined based on the packet error rate of packets in the transmitted signal and the signal strength of received signals, as described in detail below. In some embodiments the power level of the transmitted signal is controlled based on the packet error rate of packets in the transmitted signal, the signal strength of received signals, and a current transmit power level of the transmitted signal, also as described in detail below. 
     FIG. 1  shows a wireless network device  100  in communication with another wireless network device  108  according to a preferred embodiment of the present invention. Wireless network devices  100  and  108  can be wireless clients, wireless access points, or other sorts of wireless network devices. Wireless network device  100  is preferably otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16, and 802.20. 
   Wireless network device  100  comprises a host  102  such as a laptop computer, personal digital assistant, and the like, a media access controller (MAC)  104 , a physical-layer device (PHY)  106 , and an antenna  122 . MAC  104  comprises a processor  110 , a memory  112 , a MAC receive circuit  114 , and a MAC transmit circuit  116 . PHY  106  comprises a PHY receive circuit  118  and a PHY transmit circuit  120 . MAC receive circuit  114  and PHY receive circuit  118  together define a receive circuit  134 . MAC transmit circuit  116  and PHY transmit circuit  120  together define a transmit circuit  136 . 
     FIG. 2  shows a transmit power control process  200  for wireless network device  100  according to a preferred embodiment. Processor  110  initializes wireless network device  100  by setting the power level of the signal transmitted by wireless network device  100  to its minimum power level, and by setting the data rate of the data transmitted by wireless network device  100  to its maximum rate (step  202 ). Processor  110  preferably sets the power level of the transmitted signal by asserting a predetermined state of a transmit power control (TPC) signal  124 , although other methods can be used. PHY transmit circuit  120  sets the power level according to TPC signal  124 . Processor  110  preferably sets the data rate of the transmitted signal by asserting a predetermined state of a data rate control (DRC) signal  134 , although other methods can be used. PHY transmit circuit  120  sets the data rate according to DRC signal  134 . 
   Processor  110  then determines the link quality of the link  128  between wireless network device  100  and wireless network device  108  (step  204 ). In preferred embodiments the determination of link quality is based on a packet error rate (PER) of the signal  130  transmitted by wireless network device  100  to wireless network device  108  and a received signal strength indication (RSSI)  126  of the signal  132  received by wireless network device  100  from wireless network device  108 . 
   Processor  110  compares the link quality to one or more predetermined link qualities. In a preferred embodiment the link quality threshold comprises a packet error rate threshold and a signal strength threshold. In some embodiments multiple such thresholds can be used to provide hysteresis. Preferably the thresholds are selected based on the current power level of the transmitted signal  130 . 
     FIG. 3  shows a process  300  for determining a link quality according to a preferred embodiment. Of course, other processes can be used. For example, assume that physical-layer transmit circuit  120  is capable of transmitting at three different power levels P 0 , P 1 , and P 2 , where P 0 &lt;P 1 &lt;P 2  and otherwise complies with at least one of IEEE 802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.16 and 802.20.  FIG. 4  shows a table of the power levels for each data rate according to a preferred embodiment. Note that some of the data rates have only one or two possible power levels. Thus there is only one possible path through the table, as shown by the arrows in  FIG. 4 . This path reflects the fact that, when increasing the data rate, it is necessary to first decrease the transmitted power to avoid distortion in the transmitted waveform. 
   Process  300  first determines the transmit power level P of the transmitted signal  130  and the link quality LQ of wireless link  128  (step  302 ). The link quality LQ can be determined based on a signal strength of received signal  132 , a signal quality of received signal  132 , a packet error rate of the packets of data in received signal  132 , a current transmit power level of transmitted signal  130 , a current transmit data rate of transmitted signal  130 , other such criteria, or any combination thereof. If P=P 0 , then the link quality LQ is compared to a predetermined link quality LQ 01  (step  304 ). The link quality LQ is determined to be below threshold when LQ&lt;LQ 01  (step  306 ) and above threshold otherwise (step  308 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 01  and a PER threshold PER 01 . In particular, the link quality is determined to be below threshold when RSSI≦RSSI 01  or PER≧PER 01 , and above threshold otherwise. 
   But if at step  302  P=P 1 , then the link quality LQ is compared to a predetermined link quality LQ 12  (step  310 ). The link quality LQ is determined to be below threshold when LQ&lt;LQ 12  (step  306 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 12  and a PER threshold PER 12 . In particular, the link quality is determined to be below threshold when RSSI&lt;RSSI 12  or PER≧PER 12 . But if at step  306  LQ≧LQ 12 , then the link quality LQ is compared to a predetermined link quality LQ 10  (step  312 ). The link quality LQ is determined to be below threshold when LQ&gt;LQ 10  (step  314 ) and neither above nor below threshold otherwise (step  316 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 10  and a PER threshold PER 10 . In particular, the link quality is determined to be above threshold when RSSI≧RSSI 10  and PER≦PER 10 , and neither above nor below threshold otherwise. 
   But if at step  302  P=P 2 , then the link quality LQ is compared to a predetermined link quality LQ 21  (step  318 ). The link quality LQ is determined to be above threshold when LQ&gt;LQ 21  (step  320 ) and below threshold otherwise (step  322 ). In a preferred embodiment, the threshold determination is made based on a RSSI threshold RSSI 2 , and a PER threshold PER 21 . In particular, the link quality is determined to be above threshold when RSSI≧RSSI 21  and PER≦PER 21 , and below threshold otherwise. 
   Example numbers for thresholds RSSI 01 , RSSI 12 , RSSI 21 , RSSI 10 , PER 01 , PER 12 , PER 21  and PER 10  are given below in Table 1 for an IEEE 802.11a link and a IEEE 802.11g link. Of course these numbers are given for example only, and should not be considered limiting. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
               IEEE 802.11a 
               IEEE 802.11g 
             
             
                 
                 
             
           
           
             
                 
               RSSI 01   
               19 dB 
               40 dB 
             
             
                 
               RSSI 12   
                9 dB 
               32 dB 
             
             
                 
               RSSI 21   
               11 dB 
               42 dB 
             
             
                 
               RSSI 10   
               21 dB 
               34 dB 
             
             
                 
               PER 01   
               25% 
               25% 
             
             
                 
               PER 12   
               25% 
               25% 
             
             
                 
               PER 21   
               16% 
               15% 
             
             
                 
               PER 10   
               16% 
               15% 
             
             
                 
                 
             
           
        
       
     
   
   Returning to  FIG. 2 , if in step  204  the link quality is determined to be above threshold ( 206 ), process  200  determines whether the current transmit power level P is greater than the maximum power level Pmh for the next higher data rate (step  208 ). If the current transmit power level is greater than the maximum power level for the next higher data rate, process  200  decreases the power level of transmitted signal  130  (step  210 ), and resumes at step  204 . 
   In other embodiments, processor  110  adjusts only the data rate of transmitted signal  130  based on the link quality. In still other embodiments, processor  110  adjusts only the power level of transmitted signal  130  based on the link quality, for example as illustrated by the flow diagram of  FIG. 5 . 
     FIG. 6  shows a process  600  for decreasing the power level of transmitted signal  130  for a wireless network device having three transmit power levels P 0 , P 1 , and P 2  where P 0 &lt;P 1 &lt;P 2  according to a preferred embodiment. Of course, other processes can be used. If the transmit power level P of the transmitted signal  130  is equal to P 0  (step  602 ), then process  600  ends because the power level is already at its minimum level. Otherwise if the transmit power level P of the transmitted signal  130  is greater than, or equal to, P 2  (step  604 ), then process  600  sets the transmit power level to P 1  and sets the data rate of the transmitted signal to its maximum rate (step  606 ). However if at step  604  the transmit power level P of the transmitted signal  130  is less than P 2 , process  600  sets the transmit power level to P 0  and sets the data rate of the transmitted signal to its maximum rate (step  610 ). 
   However, returning again to  FIG. 2 , if at step  208  process  200  determines that the current transmit power level is not greater than the maximum power level for the next higher data rate then process  200  increases the data rate (step  212 ) and resumes at step  204 . Any process can be used to increase the data rate. 
   Process  200  can use multiple link quality thresholds at step  204  to provide hysteresis, for example as described above with respect to  FIG. 5 . Therefore process  200  can determine that the link quality is neither above nor below the link quality thresholds ( 209 ). In that case, no action is taken, and process  200  repeats step  204 . 
   On the other hand, if at step  204  process  200  determines that the link quality is below the link quality threshold ( 207 ), process  200  compares the power level of transmitted signal  130  to respective predetermined values (step  214 ). In other embodiments, other criteria are used. If the current transmit power level P is less than the maximum power level Pmc for the current data rate then process  200  increases the power level of transmitted signal  130  (step  216 ), and returns to step  204 . 
     FIG. 7  shows a process  700  for increasing the power level of transmitted signal  130  for a wireless network device having three transmit power levels P 0 , P 1 , and P 2  where P 0 &lt;P 1 &lt;P 2  according to a preferred embodiment. Of course, other processes can be used. If the transmit power level P of the transmitted signal  130  is not less than P 2  (step  702 ), then process  700  ends because the power level is already at its maximum level. Otherwise if the transmit power level P of the transmitted signal  130  is less than P 1  (step  704 ), then process  700  sets the transmit power level to P 1  and sets the data rate of the transmitted signal to its maximum rate (step  706 ). However if at step  704  the transmit power level P of the transmitted signal  130  is greater than, or equal to, P 1 , process  700  sets the transmit power level to P 2  and sets the data rate of the transmitted signal to its maximum rate (step  710 ). 
   However, returning again to  FIG. 2 , if at step  214  process  200  determines that the current transmit power level P is not less than the maximum power level Pmc for the current data rate, then process  200  decreases the data rate (step  218 ) and resumes at step  204 . Any process can be used to decrease the data rate. 
   The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Apparatus of the invention can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the invention can be performed by a programmable processor executing a program of instructions to perform functions of the invention by operating on input data and generating output. The invention can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
   A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.