Abstract:
A first wireless device including a control module and a transmitter. The control module is configured to estimate a first path loss between the first wireless device and a second wireless device, estimate a second path loss between the first wireless device and the second wireless device, generate an absolute value of a difference between the first path loss and the second path loss, and compare the absolute value of the difference between the first path loss and the second path loss to a predetermined threshold. The transmitter is configured to transmit a radio frequency signal at the first minimum transmit power in response to the absolute value of the difference being less than or equal to the predetermined threshold, and transmit the radio frequency signal at a second minimum transmit power in response to the absolute value being greater than the predetermined threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This present disclosure is a continuation of U.S. application Ser. No. 12/836,183, filed on Jul. 14, 2010, which is a continuation of U.S. application Ser. No. 11/400,982, filed Apr. 10, 2006 (now U.S. Pat. No. 7,760,681), which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/738,693, filed Nov. 21, 2005. This present disclosure is related to U.S. application Ser. No. 11/401,392 (now U.S. Pat. No. 7,672,282), filed Apr. 10, 2006, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to wireless network devices. 
     BACKGROUND 
     A wireless local area network (WLAN) provides a wireless station (STA), such as a laptop computer and/or networked appliance, with a wireless connection to a computer network. The STA includes a WLAN transceiver that sends and receives packets. An access point (AP) also includes a WLAN transceiver that sends and receives the packets and provides a communication bridge between the STA and the computer network. 
     In some instances more than one AP is available for providing the STA with access to the computer network. The STA must then decide which AP to associate with. Since many STAs are portable and powered by batteries, it is prudent for the STA to consider battery life when choosing between the available APs. In some systems the STA monitors a received signal strength indicator (RSSI) associated with signals received from each of the APs. The STA then associates with the AP having the strongest RSSI. This approach assumes that the RSSI provides an indication of the distance and/or proximity of the STA to the AP. The STA then assumes it can have a better quality communication path (e.g. lower signal loss and/or higher signal-to-noise ratio) with the AP having the highest RSSI. Under this assumption the STA would conserve battery power by not having to resend packets that are dropped. 
     Referring now to  FIG. 1 , a functional block diagram is shown of a WLAN  10 . WLAN  10  includes a STA  12  that employs the RSSI approach described above. STA  12  can connect to a distributed communications system (DCS)  14  such as the Internet through one of a first AP  16 - 1  and a second AP  16 - 2 . The first AP  16 - 1  may be located 100 meters from STA  12  and have a radiated power of 10 decibels over 1 milliwatt (10 dB m ). The second AP  16 - 2  may be located 200 meters from STA  12  and have a radiated power of 18 dB m . 
     Assuming free space propagation, the relation between RSSI in dB m  (Rx) and transmitted power in dB m  (Tx) at 5 Ghz, can be expressed as:
 
 Rx ( D )= Tx− 46.42−20 log  D,   (Eq.1)
 
where D represents the distance in meters between the transmitter and the receiver. The number 46.42 is a correction factor on the free-space path loss and is based on known equations and factors such as the frequency of interest, conductor losses, and anticipated antenna gains.
 
     As is shown below, Eq. 1 can be used to determine Rx values between STA  12  and each of first AP  16 - 1  and second AP  16 - 2 .
 
 Rx   AP1 =10 dB m −46.42−20 log 100 m=−76.42 dB m , and
 
 Rx   AP2 =18 dB m −46.42−20 log 200 m=−74.44 dB m .
 
Since Rx AP2 &gt;Rx AP1 , STA  12  will generate a stronger RSSI for second AP  16 - 2 . STA  12  will therefore associate with second AP  16 - 2  even though second AP  16 - 2  is further from STA  12  than first AP  16 - 1 . This means that STA  12  will consume more power transmitting to second AP  16 - 2  than it would have consumed transmitting to first AP  16 - 1 .
 
     SUMMARY 
     In general, in one aspect, this specification discloses a first wireless device including a control module and a transmitter. The control module is configured to estimate a first path loss between the first wireless device and a second wireless device, estimate a second path loss between the first wireless device and the second wireless device, generate an absolute value of a difference between the first path loss and the second path loss, and compare the absolute value of the difference between the first path loss and the second path loss to a predetermined threshold. The transmitter is configured to transmit a radio frequency signal at the first minimum transmit power in response to the absolute value of the difference being less than or equal to the predetermined threshold, and transmit the radio frequency signal at a second minimum transmit power in response to the absolute value being greater than the predetermined threshold. 
     In other features the wireless client station includes a transmitter that generates a radio frequency signal having a power determined by the transmit power control signal. The transmitter control module estimates the path loss further based on a link margin included in the signal. The transmitter control module updates the transmit power control signal when the path loss changes by a predetermined amount. The transmitter control module generates the transmit power control signal further based on a predetermined transmit power delta. The wireless device includes an access point (AP). The wireless device includes a wireless client station. The signal is otherwise compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11H. 
     A wireless client station includes a received signal strength module that estimates N signal strengths of N packets received from N wireless stations (STAs). The N packets include N corresponding transmit power values. A transmitter control module estimates N corresponding path losses to the N STAs based on the N signal strengths and N transmit power values and generates a transmit power control signal based on the N path losses. 
     In other features the wireless client station includes a transmitter that generates a radio frequency signal having a power determined by the transmit power control signal. The transmitter control module estimates the N path losses further based on N link margins transmitted by corresponding ones of the N STAs. The transmit power control signal includes N magnitudes corresponding to the N path losses and the transmitter control module updates one of the N magnitudes when a corresponding one of the N path losses changes by a predetermined amount. The transmitter control module generates the transmit power control signal further based on a predetermined transmit power delta. The N STAs are configured as an ad-hoc network. A magnitude of the transmit power control signal is constant for all of the N path losses and is based on one of the N path losses. The one of the N path losses corresponds to a greatest one of the N path losses. The N packets are otherwise compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11H. 
     A method of operating a wireless client station includes receiving a signal that includes transmit power data from a wireless device, estimating a signal strength of the signal, estimating a path loss to the wireless device based on the signal strength and the transmit power data, and generating a transmit power control signal based on the path loss. 
     In other features the method includes generating a radio frequency signal having a power based on the transmit power control signal. The method includes estimating the path loss further based on a link margin included in the signal. The method includes updating the transmit power control signal when the path loss changes by a predetermined amount. The method includes generating the transmit power control signal further based on a predetermined transmit power delta. The signal is otherwise compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11H. 
     A method of operating a wireless client station includes estimating N signal strengths of N packets received from N wireless stations (STAs). The N packets include N corresponding transmit power values. The method also includes estimating N corresponding path losses to the N STAs based on the N signal strengths and N transmit power values and generating a transmit power control signal based on the N path losses. 
     In other features the method includes generating a radio frequency signal having a power determined by the transmit power control signal. The method includes estimating the N path losses further based on N link margins transmitted by corresponding ones of the N STAs. The transmit power control signal includes N magnitudes corresponding to the N path losses. The method includes updating one of the N magnitudes when a corresponding one of the N path losses changes by a predetermined amount. The method includes generating the transmit power control signal further based on a predetermined transmit power delta. The N STAs are configured as an ad-hoc network. A magnitude of the transmit power control signal is constant for all of the N path losses and is based on one of the N path losses. The one of the N path losses corresponds to a greatest one of the N path losses. The N packets are otherwise compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11. 
     A method of operating a wireless client station includes estimating N signal strengths of N packets received from N wireless stations (STAs). The N packets include N corresponding transmit power values. The method also includes estimating N corresponding path losses to the N STAs based on the N signal strengths and N transmit power values and generating a transmit power control signal based on the N path losses. 
     In other features the method includes generating a radio frequency signal having a power determined by the transmit power control signal. The method includes estimating the N path losses further based on N link margins transmitted by corresponding ones of the N STAs. The transmit power control signal includes N magnitudes corresponding to the N path losses. The method includes updating one of the N magnitudes when a corresponding one of the N path losses changes by a predetermined amount. The method includes generating the transmit power control signal further based on a predetermined transmit power delta. The N STAs are configured as an ad-hoc network. A magnitude of the transmit power control signal is constant for all of the N path losses and is based on one of the N path losses. The one of the N path losses corresponds to a greatest one of the N path losses. The N packets are otherwise compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11H. 
     A computer program stored on a tangible computer medium for operating a wireless client station includes estimating N signal strengths of N packets received from N wireless stations (STAs). The N packets include N corresponding transmit power values. The computer program also includes estimating N corresponding path losses to the N STAs based on the N signal strengths and N transmit power values and generating a transmit power control signal based on the N path losses. 
     In other features, the computer program includes generating a radio frequency signal having a power determined by the transmit power control signal. The computer program includes estimating the N path losses further based on N link margins transmitted by corresponding ones of the N STAs. The transmit power control signal includes N magnitudes corresponding to the N path losses. The computer program includes updating one of the N magnitudes when a corresponding one of the N path losses changes by a predetermined amount. The computer program includes generating the transmit power control signal further based on a predetermined transmit power delta. The N STAs are configured as an ad-hoc network. A magnitude of the transmit power control signal is constant for all of the N path losses and is based on one of the N path losses. The one of the N path losses corresponds to a greatest one of the N path losses. 
     A wireless client station includes received signal strength means for receiving a signal from a wireless device and estimating a signal strength of the signal. The signal includes transmit power data. The wireless clients station also includes transmitter control means for estimating a path loss to the wireless device based on the signal strength and the transmit power data and generating a transmit power control signal based on the path loss. 
     In other features the wireless client station includes transmitter means for generating a radio frequency signal having a power determined by the transmit power control signal. The transmitter control means estimates the path loss further based on a link margin included in the signal. The transmitter control means updates the transmit power control signal when the path loss changes by a predetermined amount. The transmitter control means generates the transmit power control signal further based on a predetermined transmit power delta. The wireless device includes access point (AP) means for providing a wireless connection to a distributed communications network. The wireless device includes client station means for generating the signal. The signal is otherwise compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11H. 
     A wireless client station includes received signal strength means for estimating N signal strengths of N packets received from N wireless stations (STAs). The N packets include N corresponding transmit power values. The wireless client station also includes transmitter control means for estimating N corresponding path losses to the N STAs based on the N signal strengths and N transmit power values and generating a transmit power control signal based on the N path losses. 
     In other features the wireless client station includes transmitter means for generating a radio frequency signal having a power determined by the transmit power control signal. The transmitter control means estimates the N path losses further based on N link margins transmitted by corresponding ones of the N STAs. The transmit power control signal includes N magnitudes corresponding to the N path losses and the transmitter control means updates one of the N magnitudes when a corresponding one of the N path losses changes by a predetermined amount. The transmitter control means generates the transmit power control signal further based on a predetermined transmit power delta. The N STAs are configured as an ad-hoc network. A magnitude of the transmit power control signal is constant for all of the N path losses and is based on one of the N path losses. The one of the N path losses corresponds to a greatest one of the N path losses. N packets are otherwise compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11H. 
     In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a computer readable medium such as but not limited to memory, non-volatile data storage and/or other suitable tangible storage mediums. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of a WLAN of the prior art; 
         FIG. 2  is a functional block diagram of a WLAN STA; 
         FIG. 3  is functional block diagram of a WLAN that includes the STA of  FIG. 2 ; 
         FIG. 4  is a protocol diagram of messages related to transmit power; 
         FIG. 5  is a flowchart of a method for choosing an AP to associate with; 
         FIG. 6  is a flowchart of a method for determining a minimum transmit power; 
         FIG. 7  is a memory map of an array of minimum transmit power values; 
         FIG. 8  is a functional block diagram of a STA that includes an application program interface (API); 
         FIG. 9A  is a table of API message fields in a transmit power control configuration message; 
         FIG. 9B  is a table of API message fields in a transmit power control configuration response; 
         FIG. 10A  is a functional block diagram of a high definition television; 
         FIG. 10B  is a functional block diagram of a vehicle control system; 
         FIG. 10C  is a functional block diagram of a cellular phone; 
         FIG. 10D  is a functional block diagram of a set top box; and 
         FIG. 10E  is a functional block diagram of a media player. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module, circuit and/or device refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     Referring now to  FIG. 2 , a STA  20  communicates with a host  22 . By way of non-limiting example, host  22  can be implemented in a laptop computer, personal digital assistant, voice-over-internet protocol (VoIP) telephone, and/or other devices that communicate in a WLAN. 
     An interface  28  provides a communication bridge between host  22  and a media access controller (MAC)  30 . MAC  30  forms data from host  22  into packets and communicates the packets to a modulator  32 . MAC  30  also extracts data from packets that it receives from a demodulator  34 . MAC  30  communicates the extracted data to host  22  via interface  28 . 
     MAC  30  includes a central processing unit (CPU)  36  and associated memory  38 . In addition to performing the data and packet operations described above, CPU  36  executes computer instructions that associate STA  20  with one of several access points (APs)  102  (shown in  FIG. 3 ). CPU  36  also executes computer instructions that control a transmit power signal  40 . 
     A transmit portion of STA  20  includes modulator  32  which digitally modulates the packets and communicates them to a digital-to-analog converter (D/A)  46 . D/A  46  generates an analog modulating signal that is communicated to an RF transmitter  48 . RF transmitter  48  generates one or more modulated RF carriers based on the analog signal and applies the modulated RF carrier(s) to one pole of a digitally-controlled switch  51 . A common terminal of switch  51  communicates with a feed line  50  that connects to an antenna (not shown). The RF transmitter and RF receiver form part of a physical layer (PHY) module  49  of the STA  20 . 
     A receive portion of STA  20  receives modulated RF carrier(s) from the antenna through a second pole of switch  51 . These modulated RF carrier(s) are transmitted by APs  102  (see  FIG. 3 ) and/or other STAs. The other STAs can be configured differently than STA  20 . The modulated RF carrier(s) are communicated to a receiver  62 . Receiver  62  generates a modulated signal based on data included in the received modulated RF carrier(s). An amplitude of the modulated signal is based on a gain control signal  65  that is generated by a gain controller  81 . The modulated signal is communicated to an analog-to-digital converter (A/D)  66  that generates modulated digital data based on the modulated signal. The modulated digital data is filtered by a low-pass filter  68  before being communicated to an input of demodulator  34 . Demodulator  34  generates packets based on the filtered and modulated digital data and communicates the packets to MAC  30 . 
     Demodulator  34  also generates a gain signal  70  based on the output of low-pass filter  68 . An error amplifier  72  generates an error signal  74  based on a difference between gain signal  70  and a desired gain signal  76  that is generated by MAC  30 . An amplifier  78  amplifies the error signal  74  and communicates an amplified error signal to an accumulator  80 . Accumulator  80  integrates and/or differentiates the amplified error signal and generates an accumulated error signal that is communicated to an input of gain controller  81 . Gain controller  81  then generates the gain control signal  65  and an RSSI signal  82  based on the accumulated error signal. 
     Referring now to  FIG. 3 , a functional block diagram is shown of a WLAN  100  that includes improved STA  20 . STA  20  can connect to DCS  14  through one of a first AP  102 - 1  and a second AP  102 - 2 , collectively referred to as APs  102 . Each of APs  102  are compliant with a transmit power control (TPC) protocol. The TPC protocol includes data regarding the RF power being dissipated by the transmitting station. The data can be included in a beacon signal and/or a response to a TPC request from another STA  20 . 
     Referring briefly to  FIG. 4 , a protocol diagram shows two methods that STA  20  and APs  102  use to implement the TPC protocol. The second of the two methods also allows APs  102  to transmit respective link margin data to STA  20 . The link margins correspond to the communication paths between the APs  102  and STA  20 . 
     In the first method, AP  102  broadcasts a beacon message that includes a transmit power control (TPC) report  130 . TPC report  130  includes the transmitter RF power data of the transmitting AP  102 . 
     In the second method, STA  20  sends a TPC request  132  to one of the APs  102 . The TPC request  132  includes the transmitter RF power data of STA  20 . Each AP  102  responds to TPC request  132  by sending a TPC reply  134 . TPC reply  134  includes the transmitter RF power data of the sending AP  102  and also a link margin between STA  20  and the sending AP  102 . In some embodiments TPC report  130 , TPC request  132 , and TPC reply  134 , collectively referred to as TPC messages, are compliant with the Institute of Electrical and Electronics Engineers (IEEE) 802.11h specification, which is hereby incorporated by reference in its entirety. 
     Returning now to  FIG. 3 , STA  20  uses the RF power data in the TPC report  130  and/or TPC reply  134  to determine respective path losses in the communication paths between STA  20  and APs  102 . STA  20  then associates with the AP  102  that has the lowest path loss. 
     Path loss (PL) in dBm can be determined from the equation:
 
 PL=Tx−Rx,   (Eq. 2)
 
where Tx is the RF power in dBm at the transmitter and Rx is based on the received power as indicated by RSSI signal  82 . Eq. 2 can be implemented as Computer instructions in memory  38  and executed by CPU  36 .
 
     Example path loss calculations will now be provided that include the values shown in  FIG. 3 . Assuming APs  102 - 1  and  102 - 2  are transmitting 10 dB m  and 18 dB m  of RF power respectively, then Eq. 1 shows that RSSI signal  82  indicates Rx=−76.42 dB m  for first AP  102 - 1  and Rx=−74.44 dBm for second AP  102 - 2 . The path losses between STA  20  and APs  62  can then be determined from Eq. 2 as follows:
 
 P   LAP1 =10 dB m −(−76.42 dB m )=86.42 dB m  and
 
 P   LAP2 =18 dB m −(−74.44 dB m )=92.44 dB m .
 
For simplicity, small scale effects and multi-path fading are not taken into account in the analysis above. The affect of distance becomes more pronounced when fading is taken into account. A similar conclusion can be reached at in presence of multipath fading.
 
     Referring now to  FIG. 5 , a method  120  is shown for determining which of several APs  102  that STA  20  should associate with. Method  120  can be implemented as computer instructions stored in memory  38  and executed by CPU  36 . Method  120  can be executed each time STA  20  receives a TPC report  130  and/or TPC reply  134 . 
     Method  120  enters through block  122  and proceeds to block  124 . In block  124 , control determines respective path losses between STA  20  and APs  102  that transmit TPC reports  130  and/or TPC replies  134 . Control then proceeds to block  126  and associates STA  20  with the available AP  102  corresponding to the lowest path loss. Control then proceeds to block  127  and transmits a TPC request  132  (shown in  FIG. 4 ). In response to TPC request  132 , the associated AP  102  sends a TPC reply  134  that includes a Link Margin. Link Margin is described below. Control then proceeds to block  128  and uses transmit power signal  40  to adjust transmitter RF power to at least a minimum value Tx min  based on the calculated path loss. Control then returns to other tasks via return block  129 . 
     In block  128  control can determine Tx min  according to the following properties and equations. RF power losses in the communication path can be described by:
 
 PL=TxPwr−RSSI   (Eq. 3)
 
where PL is the path loss, in dBm, that corresponds with TPC reply  134 , TxPwr is the transmitter RF power indicated in TPC reply  134 , and RSSI is indicated the receive signal strength indication corresponding to the message.
 
     The link margin in the communication path can be described by:
 
Link Margin= RSSI   TPCReq   −Rx  Sensitivity,  (Eq. 4)
 
where Link Margin is expressed in dBm, RSSI TPCReq  is a received signal strength indication at AP  102  (or another STA in an ad-hoc network) that corresponds to TPC request  132 , and Rx Sensitivity is a minimum signal strength that receiver  62  is able to detect and demodulate with a desired degree of reliability.
 
     Assuming a symmetric link, control can determine Rx Sensitivity based on:
 
 Rx  Sensitivity= TxREQ −Path Loss−Link Margin,  (Eq. 5)
 
where TxREQ is the transmitter RF power of STA  20 . Control can then determine the minimum transmit power based on
 
 Tx   min   =PL+Rx  Sensitivity  (Eq. 6)
 
Control use the transmit power signal  40  to control the transmit power based on Tx min . In some embodiments the actual transmit power is determined based on a sum of Tx min  and a predetermined transmit power delta that is described below in more detail.
 
     For a time varying channel or in a mobile environment, Path Loss will be a function of time. STA  20  can therefore execute a method, which is described below, to adapt Tx min  according to changes in Path Loss. 
     Referring now to  FIG. 6 , a method  150  is shown for adjusting the minimum transmitter power Tx min  of STA  20 . Method  150  allows STA  20  to periodically adapt Tx min  to changes in the path loss between STA  20  and the associated AP  102 . Changes in path loss are commonly caused by STA  20  moving about within a coverage area of the associated AP  102 . As the distance between the associated AP  102  and STA  20  reduces STA  20  can conserve energy by reducing Tx min . As the distance between the associated AP  102  and STA  20  increases STA  20  can increase Tx min  as little as possible to maintain reliable communication with the associated AP  102 . Method  150  can be implemented as computer instructions in memory  38  and executed by CPU  36 . Method  150  can be executed each time STA  20  receives a TPC reply  134  and/or beacon  130 . 
     Method  150  enters through block  152  and proceeds to decision block  154 . In decision block  154 , control determines an absolute value of the difference between the present path loss (PathLoss t ) and the path loss associated with the present value of Tx min  (PathLoss t0 ). Control compares the absolute value to a predetermined path loss delta Δ PathLoss . If the absolute value is larger than Δ PathLoss  then control branches to block  156  and determines a new value of Tx min  based on the present path loss. On the other hand, if the absolute value is less than Δ PathLoss  in decision block  154  then control branches to block  158  and continues using the present value of Tx min . Control returns to other processes through return block  160  after completing the steps of blocks  156  and  158 . 
     Referring now to  FIG. 7  a memory map  170  is shown of an array of Tx min  values. Such an array can be used when STA  20  is part of an ad-hoc network. An ad-hoc network consists of a plurality of STAs and does not include an AP  102 . The plurality of STAs communicate only with each other and do not have access to DCS  14 . 
     CPU  36  maintains memory map  170  in memory  38 . Memory map  170  allocates memory for an identifier associated with each STA in the ad-hoc network. An example of an identifier includes a unique MAC address  172 . Memory map  170  also allocates memory for a Tx min  value associated with each identifier. In order for STA  20  calculate Tx min  the other STA must use the TPC protocol. STA  20  can use a default value of TX min  for each STA that does not transmit the RF power data. STA  20  can adjust its transmit power each time it transmits a data frame to a recipient STA. The transmit power is based on the Tx min  value associated with the recipient STA. 
     If STA  20  is not configured to modify transmit power on a per-frame basis then STA  20  can repeatedly use the transmit power corresponding to the maximum of the Tx min  values computed for each of the STAs. Stated mathematically,
 
 Tx   min =max{ Tx   min1   ,Tx   min2   , . . . , Tx   minN }  (Eq. 7)
 
     Referring now to  FIG. 8 , a functional block diagram is shown of STA  20  wherein host  22  includes a laptop computer. Host  22  includes a CPU (not shown) that communicates with CPU  36  via interface  28 . CPU  36  supports an application program interface (API) that is implemented in memory  38 . The API provides a standard communication format for the values used and/or determined in the methods described above. 
     Referring now to  FIG. 9A  various messages of the API are shown in table form. The table of  FIG. 9A  shows command messages that host  22  sends to CPU  36 . The table of  FIG. 9B  shows response messages that CPU  36  sends to host  22 . With the exception of a Result field at row  216 , the response messages of  FIG. 9B  are an echo of the command messages of  FIG. 9A . 
     First column  201  indicates the name of each message. A second column  202  indicates a data type for each message. Data type “UINT16” indicates an unsigned 16-bit integer and data type “UINT8” indicates an unsigned 8-bit integer. Other data types can also be used to encode the message data. A third column  203  provides a description of each message. 
     The messages will now be described beginning with the top row  213 . CmdCode is a fixed value that identifies the beginning of the API messages of  FIG. 9A . At row  214 , Size indicates a number of bytes in the API messages of  FIG. 9A . At row  215 , SeqNum provides a serial number for each transmitted group of API message. At row  216 , Result is not used when host  22  sends the API messages to CPU  36 . CPU  36  populates the Result field when CPU  36  sends the API results ( FIG. 9B ) to host  22 . 
     Examples of operations that have an effect on the Result field will now be described. At row  217 , Action indicates whether host  22  desires to enable or disable one or both of methods  120  and  150 . At row  218 , Transmit Power Delta indicates an additional amount of power that STA  20  desires to add to Tx min . The additional power provides a margin for error when determining the path loss and Tx min . At row  219 , Path Loss Trigger Threshold indicates Δ PathLoss  that is used in block  154  of method  150 . CPU  36  populates the Result field with an indication of whether it successfully executed the Action, Transmit Power Delta, and/or Path Loss Trigger Threshold commands from host  22 . 
     Referring now to  FIGS. 10A-10E , various exemplary implementations of the present invention are shown. 
     Referring now to  FIG. 10A , the present invention can be implemented in a high definition television (HDTV)  420 . The present invention may be implemented in a WLAN interface  429 . The HDTV  420  receives HDTV input signals in either a wired or wireless format and generates HDTV output signals for a display  426 . In some implementations, signal processing circuit and/or control circuit  422  and/or other circuits (not shown) of the HDTV  420  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other type of HDTV processing that may be required. 
     The HDTV  420  may communicate with mass data storage  427  that stores data in a nonvolatile manner such as optical and/or magnetic storage devices. Mass data storage  427  can include at least one hard disc drive (HDD) and/or at least one optical digital versatile disc (DVD). The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The HDTV  420  may be connected to memory  428  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The HDTV  420  also may support connections with a WLAN via WLAN network interface  429 . HDTV  420  can include a power supply  423 . 
     Referring now to  FIG. 10B , the present invention may be implemented in a WLAN interface  448  of a vehicle  430 . Vehicle  430  can include a powertrain control system  432  that receives inputs from one or more sensors  436  such as temperature sensors, pressure sensors, rotational sensors, airflow sensors and/or any other suitable sensors and/or that generates one or more output control signals  438  such as engine operating parameters, transmission operating parameters, and/or other control signals. 
     The present invention may also be implemented in other control systems  440  of the vehicle  430 . The control system  440  may likewise receive signals from input sensors  442  and/or output control signals to one or more output devices  444 . In some implementations, the control system  440  may be part of an anti-lock braking system (ABS), a navigation system, a telematics system, a vehicle telematics system, a lane departure system, an adaptive cruise control system, a vehicle entertainment system such as a stereo, DVD, compact disc and the like. Still other implementations are contemplated. 
     The powertrain control system  432  may communicate with mass data storage  446  that stores data in a nonvolatile manner. Mass data storage  446  can include at least one HDD and/or at least one DVD. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The powertrain control system  432  may be connected to memory  447  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The powertrain control system  432  also may support connections with a WLAN via WLAN network interface  448 . The control system  440  may also include mass data storage, memory and/or a WLAN interface (all not shown). The vehicle  420  can also include a power supply  433 . 
     Referring now to  FIG. 10C , the present invention can be implemented in a cellular phone  450  that may include a cellular antenna  451 . The present invention may be implemented in a WLAN interface  468 . In some implementations, the cellular phone  450  includes a microphone  456 , an audio output  458  such as a speaker and/or audio output jack, a display  460  and/or an input device  462  such as a keypad, pointing device, voice actuation and/or other input device. The signal processing and/or control circuits  452  and/or other circuits (not shown) in the cellular phone  450  may process data, perform coding and/or encryption, perform calculations, format data and/or perforin other cellular phone functions. 
     The cellular phone  450  may communicate with mass data storage  464  that stores data in a nonvolatile manner. Mass data storage  464  can include at least one HDD and/or at least one DVD. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The cellular phone  450  may be connected to memory  466  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The cellular phone  450  also may support connections with a WLAN via WLAN network interface  468 . The cellular phone  450  also may also include a power supply  453 . 
     Referring now to  FIG. 10D , the present invention can be implemented in a set top box  480 . The present invention may be implemented in a WLAN interface  496 . The set top box  480  receives signals from a source such as a broadband source and outputs standard and/or high definition audio/video signals suitable for a display  488  such as a television and/or monitor and/or other video and/or audio output devices. The signal processing and/or control circuits  484  and/or other circuits (not shown) of the set top box  480  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other set top box function. 
     The set top box  480  may communicate with mass data storage  490  that stores data in a nonvolatile manner. Mass data storage  490  can include at least one hard disc drive (HDD) and/or at least one optical digital versatile disc (DVD). The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The set top box  480  may be connected to memory  494  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The set top box  480  also may support connections with a WLAN via WLAN network interface  496 . Set top box  480  can include a power supply  483 . 
     Referring now to  FIG. 10E , the present invention can be implemented in a media player  500 . The present invention may be implemented in a WLAN interface  516 . In some implementations, the media player  500  includes a display  507  and/or a user input  508  such as a keypad, touchpad and the like. In some implementations, the media player  500  may employ a graphical user interface (GUI) that typically employs menus, drop down menus, icons and/or a point-and-click interface via the display  507  and/or user input  508 . The media player  500  further includes an audio output  509  such as a speaker and/or audio output jack. The signal processing and/or control circuits  504  and/or other circuits (not shown) of the media player  500  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other media player function. 
     The media player  500  may communicate with mass data storage  510  that stores data such as compressed audio and/or video content in a nonvolatile manner. In some implementations, the compressed audio files include files that are compliant with MP3 format or other suitable compressed audio and/or video formats. Mass data storage  510  can include at least one hard disc drive (HDD) and/or at least one optical digital versatile disc (DVD). The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The media player  500  may be connected to memory  514  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The media player  500  also may support connections with a WLAN via WLAN network interface  516 . Media player  500  can include a power supply  513 . Still other implementations in addition to those described above are contemplated.