Abstract:
Methods for coordinating power usage and link adaptation in wireless communications are described. Terminals and/or access points (APs) may attempt to modify terminals&#39; transmit power in relation to a desired communication data transfer rate. Link adoption may also be used in conjunction with the described methods.

Description:
TECHNICAL FIELD  
       [0001]     Aspects of the present invention relate to wireless communications. More particularly, aspects of the present invention relate to controlling power used to transmit wireless signals.  
       RELATED ART  
       [0002]     The growth of wireless communications and integration with the internet continues to influence the growth of local area networks. Since the expansion of IEEE 802.11-based communication protocols and related devices, wireless local area networks (WLANs) are appearing with regular frequency. WLANs provide high speed wireless connectivity between PCs, PDAs and other equipment in corporate, public and home environments. WLAN users have come to expect access to WLANs and wanting larger coverage areas and higher throughputs. For portable users power consumption concerns are also an issue.  
         [0003]     Currently, IEEE 802.11 -series protocols are the leading WLAN standards. Some standards (ex: IEEE 802.11 a/b/g) have finished standardization. Some of these standards include the ability to modify power on a link to a unit.  
         [0004]     At the same time, wireless providers are experimenting with adaptive antenna arrays (also referred to as smart array antennas). Current approaches to adaptive antenna arrays do not address power control issues. Rather, adaptive arrays concentrate on beam steering techniques.  
       SUMMARY  
       [0005]     Aspects of the present invention address one or more of the issues identified above, thereby providing an improved power control system for use with wireless communications.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0006]     Aspects of the present invention are described in relation to the following drawings.  
         [0007]      FIG. 1  shows transmit power control in accordance with aspects of the present invention.  
         [0008]      FIGS. 2A and 2B  show changing array patterns based on load equalization in accordance with aspects of the present invention.  
         [0009]      FIGS. 3A and 3B  show changing array patterns based on packet steering in accordance with aspects of the present invention.  
         [0010]      FIG. 4  shows a process for reducing power in accordance with aspects of the present invention.  
         [0011]      FIG. 5  shows a conventional link adaptation method.  
         [0012]      FIGS. 6 and 7  show link adaptation in accordance with aspects of the present invention.  
         [0013]      FIGS. 8A and 8B  show modifications of antenna parameters in accordance with aspects of the present invention.  
         [0014]      FIGS. 9-18  show link adaptation in accordance with aspects of the present invention.  
         [0015]      FIG. 19  shows an illustrative example of a base station in accordance with aspects of the present invention.  
         [0016]      FIGS. 20-21  show additional illustrative examples of access points in accordance with aspects of the present invention.  
         [0017]      FIG. 22  shows a process for determining premium gain in accordance with aspects of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0018]     Aspects of the present invention relate to controlling power in access points for us with wireless local area networks. The following has been divided into sections to assist the reader: power control; transmit power control in IEEE 802.11 h; transmit power control in IEEE 802.11b, 802.11e, and other standards; link adaptation methods; and transmit power control with link adaptation.  
         [0019]     It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect.  
         [0000]     Power Control  
         [0020]     Aspects of the present invention may be used with non-reciprocal uplink and downlink systems in terms of link gain. For instance, aspects of the present invention may be used with WLAN systems using access points (APs) with smart antennas. Here, aspects of the present invention address at least one of the stations transmit rate but also the stations power consumption. Transmit power control (TPC) capabilities and link adaptation may be used with various environments or expectations. For example, aspects of the present invention may be used in systems where stations transmit with their highest data rate or where stations transmit with their lowest power.  
         [0021]     To realize the reduction in power consumption while maintaining usefulness of the system, methods and systems that function with TPC and compliant wireless LAN APs and stations may be used.  
         [0022]     Power reduction does not mean that all devices will always be connected to an access point. Rather, hidden terminals exist where every station&#39;s transmit power isn&#39;t enough to reach every other station or back to an access point. In the 802.11b or 802.11e specification, stations transmit with a constant power and have no TPC functionality. The following describes various approaches to allow TPC in 802.11 protocols.  
         [0000]     Transmit Power Control In IEEE 802.11h  
         [0023]     IEEE 802.11h is a specification for Europe in 5-GHz band. This specification mainly deals with TPC and Dynamic Frequency Selection (DFS). The primary reason for TPC in 802.11h is that TPC (which means maximum regulatory transmit power setting in 802.11h) is required for operation on a 5 GHz band in Europe. Concerning TPC, 802.11h defines only the frame structure. It describes no method to achieve TPC.  
         [0024]     Aspects of the present invention relate to using IEEE 802.11h specification&#39;s Probe Request/Response or Action commands to send some TPC information. These features may help other IEEE 802.11 specifications use TPC. These commands may or may not be used to transmit control signals to help avoid any hidden terminals. If control signals are used, they may be set to transmit with normal power to avoid the hidden terminal problem. This may include some modification of both AP and stations. However, aspects of the present invention may use any slot or frame that is reserved in 802.11b/e specification to allow for TPC based on a technique similar to that used with 802.11h.  
         [0025]     While both 802.11 1 h and 802.11b have frame structures, they are not identical. The following describes various observations in 802.111h and how to achieve TPC in non-802.11h protocols. 
        a. For a TPC report, 802.11h changes the Probe response for this operation. While the response is changed, no change is made with the Probe Request to initiate TPC. Rather, 802.11h uses an Action frame for a TPC request. 
            i. The same changes in Probe response in 802.11b/e are possible, because an order number that is used for TPC in 802.11h is currently reserved in 802.11b/e.     ii. In 802.11b, there is no regulation for an Action frame. Thus, it is easier to modify Probe request in this protocol.     iii. In 802.11 e, both an Action frame and a Probe request are defined.    
            b. In 802.11h, a station knows that an AP does TPC if a Spectrum Management slot (inside Beacon or Probe response) is set by 1. 
            i. The same slot of a Spectrum Management slot is reserved in 802.11b/11e. Aspects of the present invention may use this slot to achieve TPC.    
               
 
         [0032]     Considering this overview, in 802.11h, TPC may be accomplished as shown in  FIG. 1 .  FIG. 1  shows an access point  101  and a mobile station  102 . Transmit power is included in TPC Report from mobile station  102  to access point  101 . The TPC Report may be included as part of an Action Frame or part of a Probe Response. This figure shows the situation where the access point  101  wants to adjust a transmit power of mobile station  102 . The TPC report is generated in response to a TPC Request from access point  101  to mobile station  102  using an access frame. If mobile station  102  wants to adjust access point  101 &#39;s transmit power, it may by having reciprocal requests and reports.  
         [0033]     However, there is no availability for mobile station  102  to adjust its own transmit power. The current transmit power information for TPC is contained in the Probe response frame. This means that any calculation must be done at a receiver.  
         [0034]     Aspects of the present invention include the ability of a mobile station  102  to adjust its own transmit power. The access point  101  may calculate the difference between a current mobile station  102 &#39;s transmit power, update this information, and forward this information to the mobile station  102 .  
         [0000]     Transmit Power Control in IEEE 802.11b, 802.11e, and other Standards  
         [0035]     To achieve TPC in 802.11 b/e, a minor modification of the slot structure of 802.11h may be used. Various TPC approaches may be constrained by the ability to modify 802.11 b/e protocol&#39;s frame structure. The access point  101  and mobile station  102  may also need to be modified to allow for TPC. TPC may be realized as a method of using Probe Request and Probe Response signals. Both types of situations (fixed array and changing array) may be used with TPC. This is shown with respect to  FIGS. 2A, 2B ,  3 A, and  3 B.  
         [0036]     Referring to  FIGS. 2A and 2B , TPC is described. Here, station mobile stations know whether the access point  201  changes the various array patterns. 
        a. A station  207  sends an RTS (Request to Send) signal  208  to access point  201 . A Probe request/response time may be added to a NAV setting timer in the Duration field of the frame. The access point  201  receives the RTS  208  and replies with a CTS (Clear to Send) signal  209  to the mobile station.     b. The station  207  sends a Probe Request  210  and requests access point  201  to use TPC (for instance, by setting a TPC flag).     c. The access point  201  detects the received power from the station and determines the value difference between a received power and a power needed to communicate with the access point  201 .     d. The access point  201  sends a Probe Response  211  to the mobile station and informs the mobile station of the value difference.     e. The mobile station then reduces a transmit power and continues operation as normal.        
 
         [0042]      FIGS. 2A and 2B  show transition of coverage areas of an array  201  changing automatically to load equalize each beam.  
         [0043]      FIGS. 3A and 3B  show transition of coverage areas of an array  301  changing automatically by packet steering.  
         [0044]      FIG. 4  shows a signal flow chart between a mobile station  401 , an access point  402 , and other mobile stations 403. An access point  402  sends a beacon or probe response  404  to announce, for instance, that the antenna beam array associated with access point 402 is going to change. Next, mobile station  401  sends an RTS  405  at high power to access point  402 . This may be picked up by other mobile stations  403  as signal  406 . Of course, the other mobile stations  403  may or may not be in range to be able to pick up signal  406 . Next, access point  402  transmits a CTS signal  407  to mobile station  401 . The CTS signal  407  may or may not be received by other mobile stations  403 .  
         [0045]     Access point  402  may then send a Probe Request or Action signal  408  to access point  402 . The same signal may or may not be received by other mobile stations  403  (shown here as broken signal  409 . The access point  402  next determines in step  410  the power to be reduced with respect to mobile station  401 .  
         [0046]     Access point  402  then sends a Probe Response  411  to mobile station  401  that includes the new power setting or the amount by which mobile station  401  may reduce power. Using the new low power setting, mobile station  401  transmits data at signal  412  to access point  402 . The access point  402  then acknowledges (ACK signal  413 ) the receipt of the data. The transmission of signal  413  may be performed at high power to ensure that mobile station  401  knows that the access point  402  has received the data signal  412 . Alternatively, ACK signal  413  may be transmitted at low power to save energy at access point  402 .  
         [0047]     One benefit of transmitting ACK signal  413  at high power is that other stations  403  may then recognize that mobile station  401  has completed transmitting data and now other mobile stations  403  may start the process of transmitting data with access point  402 .  
         [0048]     Two navigation setting intervals may occur. A first  414  may occur from RTS signal  405  through acknowledgement signal  413 . A second  415  may occur from CTS signal  406 . through acknowledgement signal  413 .  
         [0000]     Link Adaptation Methods  
         [0049]     The following describes various link adaptation methods in accordance with aspects of the present invention. Here, each station may check a received power and change a data rate according to a received power from an access point. These methods may minimize or eliminate the need to send any control information from/to AP.  
         [0050]     A practical method for link adaptation is not defined in current IEEE 802.11 specifications. Nonetheless, most of the current IEEE 802.11 chipsets or relate equipment perform a type of link adaptation with traditional approaches. Considerations include setting a transfer rate at a highest rate first then decrease it according to channel condition, setting a transfer rate at a lowest rate then increasing it, how often should link adaptation be performed, should a received power and an error detection result be used for link adaptation, and the like.  FIG. 5  illustrates a conventional link adaptation method. Each station  502  receives a beacon or control signal  503  from access point  501 . The stations  502  may use the beacon or other control signal to determine whether changing power according to the power of the received signal as shown in step  504 .  
         [0051]     As shown in  FIG. 5 , these link adaptation methods assume that uplinks and downlinks between access point  501  and stations  502  are reciprocal in terms of link gain. This suggests current approaches to not use smart antennas. This is because, when a system uses an access point with a smart antenna, uplinks and downlinks are not always reciprocal. This is because antenna patterns for receiving is not always the same as that for transmission, especially in packet steering systems as shown in  FIG. 3 . In addition, link adaptation is currently performed on the supposition that all access points  501  have a constant transmit power in current wireless LAN. However, in the future, access points may not be able to change transmit power using an adaptive array or similar devices to reduce interference. While the link adaptation methods of  FIG. 5  may be used with a smart antenna, they will likely be error prone and not provide quality service to users.  
         [0052]      FIGS. 6 and 7  show various link adaptation methods that may be used with a smart antenna in accordance with aspects of the present invention. Referring to  FIG. 6 , access point  601  determines if it antenna parameters are going to be changed in step  603 . If yes from step  603 , then the parameters of the new antenna pattern and/or the access point  601 &#39;s transmit power are inserted into a beacon (or other control signal)  605 . If no from step  603 , then step  604  is skipped.  
         [0053]     Next, the beacon or other control signal  605  is sent to station  602 . The station  602  then changes in step  606  its transmission rate up or down according to the information in the beacon (or other signal)  605 . The modifications may occur once per beacon or once per multiple beacons. The access point  601  and station  602  then wait (paths  607  and  608 , respectively) for a next transmission of the beacon or other signal  605 . Also link adaptation may be performed with the transmission of every beacon signal, may be done periodically, or may only be performed when the antenna parameters change.  
         [0054]     Antenna parameters may be, for example, the gain difference between transmit beam and receive beam. This may be applicable in a system that uses packet steering as the transmit beams are wide to cover a larger area.  
         [0055]      FIG. 7  shows an approach in which an access point  601  only sends only sends change antenna parameter information or change AP&#39;s transmit power information (inserted in step  604 ) in the beacon  605 . The station may then change the rate up or down per information in the beacon (occurring once per beacon or once per multiple beacons). Each station  602 , which receives beacon  605  with any change information, sends a Probe request or Action frame  701  to request power control information from access point  601 . The access point  601  then calculates in step  702  the margin or gain difference between a transmit beam and a received beam. Next, access point  601  sends the gain difference or margin in a Probe Response or Action frame  703  to station  602 . Alternatively or additionally, access point  601  may send its transmit power using the Probe Response or Action Frame  703  to station  602 .  
         [0056]      FIGS. 8A and 8B  show examples of antenna parameters used in packet steering. In general, for both wide beam  802  (G A , G B , G C ) and sharp beams  803 - 805  (G A ′, G B ′, G C ′) from access point  801 , antenna parameters are different according to the azimuth (G A ≠G B ≠G C , G A ′≠G B ≠G C ′) for stations A-C. However, access point  801  may be limited as not being able to accommodate all these differences when it sends antenna parameters to all stations (as represented in  FIGS. 6 and 7 . Two approaches are described that address the situation where less than all antenna parameters are forwarded (including but not limited to no antenna parameters) to all stations with Beacon  605 .  
         [0057]     In a first approach, access point  801  calculates and informs the minimum gain difference ((δG) min ) as antenna parameters. Access point  801  next sends control information with the wide beam (G A , G B , G C )  802  and receives each station&#39;s signal with the sharp beam (G A ′, G B ′, G C ′)  803 - 805 . (δG) min  may be represented by the following equations: 
 
(δ G ) min =Min[( G   A   ′−G   A ),( G   B   ′−G   B ),( G   C   ′−G   C )]  Eq. (1) 
 
 or 
 
(δ G ) min =Min[ G   A ′, G B ′, G C ′]−Max [G A , G B , G C ]Eq.   (2) 
 
         [0058]     This method is easy to implement. However, not every station may achieve an individual optimum gain with this approach. The process for the equations is shown in  FIG. 22 .  
         [0059]     In a second approach, access point  801  knows a direction of each station and sends this information to each station in advance. Each station A-C memorizes or stores the direction information. Next, when access point  801  changes its antenna radiation pattern, access point  801  calculates the relationship between antenna directivity and a radiation characteristic, and send this information to stations as an estimated radiation characteristic of antenna beam (or beam pattern). Stations A-C receive this information and calculate a premium gain by using the new beam using current condition and an estimated radiation characteristic of antenna beam.  
         [0060]     For example, as shown in  FIGS. 8A and 8B , access point  801  decides a center direction G ct . Station B, for instance, received information from access point  801  that an angular direction between the center G ct  and station B is +⅛π. Next, access point  801  changes the antenna radiation pattern and sends the stations A-C information relating to the current center gain is G ct ′ dB. Transmitted with this information or transmitted separately is an indication that a gain of direction +⅛π it is a dB smaller than that of the center direction. Station B receives and adjusts its antenna parameter as (G ct ′−α) dB.  
         [0061]     Generally, each station has some information about the relationship between received power and affordable transmit rate to be used for link adaptation. If a station complies with one of the above link adaptation methods, it may modify a received power using the following equation: 
 
Received power=actual received power+antenna parameter Eq.   (3) 
 
         [0062]     Then, if the case that an access point  801  changes its power, stations may need received power and transmit rates and the transmit power of access point  801  to perform link adaptation as described above.  
         [0063]     Tables 1 and  2  show various relationships between transmit power, received power, and data rates tables. Using information similar to that shown in table 1, stations may adjust their power to achieve a useful transfer rate.  
                       TABLE (1)                       Transmit power   Receive power   Rate                   −15   −84   11 Mb/s       −15   −87    7 Mb/s       :   :   :       :   :   :                  
 
         [0064]                                TABLE (2)                                   Power loss               (= Transmit power − Receive power)   Rate                           :   11 Mb/s           :    7 Mb/s           :           :                        
 Transmit Power Control with Link Adaptation 
 
         [0065]     TPC and link adaptation may be used together as a systematic control, because both of them use a received power level of station. Both methods may be combined based on different priorities or adopted policies for TPC.  
         [0066]     The following lists various possible policies for TPC methods with combined link adaptation: 
        a. A first policy emphasizes data throughput 
            i. Each station transmits with as high rate as link adaptation permits.     ii. Stations transmit with a constant rate. For example, if an access point restricts an acceptable rate as 11 Mb/s and station&#39;s current rate is not 11 Mb/s, then that station does not transmit or it changes its rate into 11 Mb/s.    
            b. A second policy emphasizes power conservation 
            i. If all stations emphasize only power, sometimes some stations may transmit at a much lower data rate than link adaptation permits. This may adversely affect other stations. In this policy assumes that all stations are able to handle a lowest data rate.    
            c. A third policy emphasizes data rates based on a networks condition 
            i. When a network is not crowded, each station emphasizes TPC.     ii. When the network is crowded, each station emphasizes throughput. 
                1. Each station transmits with the maximum rate or     2. The access point sets the minimum rate and prohibits any station from transmitting with lower rate than the minimum rate.    
               
               
 
         [0077]     Next, a TPC interval performed by a station is related to system throughput as well as control complexity. The following three situations are considered: 
        a. TPC is performed at every station&#39;s signal sending opportunity     b. TPC messaging is reduced using the following two considerations: 
            i. TPC level from access point is calculated with sufficient fading margin to maintain a link during the TPC message interval. Alternatively, TPC level is calculated with sufficient margin to maintain the link even if the access point changes its array pattern.     ii. Access point informs a station that access point&#39;s antenna directivity or other radiation characteristics are changed whenever it is required by a station. When the change does not occur, TPC is not required.    
            c. TPC messaging is reduced using only the following: 
            i. TPC level from access point is calculated with sufficient fading margin to maintain a link during the TPC message interval. Alternatively, TPC level is calculated with sufficient margin to maintain the link even if the access point changes its array pattern.    
               
 
         [0084]     The combinations of control policies and message frequency for TPC are shown in the following table 3. Various examples are shown in the following figures as well. The examples described herein include examples 1-9. The number in the following table shows the example number to which it corresponds.  
                                                                   TABLE (3)                                           Reduce               Frequency of           TPC on   TPC Message            Method/   Required Rate is   Every Sending   Using i.   Using       Policy   calculated at . . .   Opportunity   and ii.   only i.               Emphasis on       1   2   3       Throughput            Emphasis on   Station       4       Transmit   Access Point       5       Power       Reduction       Emphasis   Station   6       on WLAN   Access Point   7 and 9*   8       Resource       Management                 *where the access point restricts the minimum required rate             
 
       EXAMPLE 1  
       [0085]      FIG. 4  shows this first example. Here, each station  401  or  403  performs link adaptation using one of the methods described above. Then, when station  401  wants to send its data, station  401  performs TPC as shown in  FIG. 4 .  
         [0086]      FIG. 4  shows the case which satisfies the Distributed Coordination Function (DCF) operation of the IEEE 802.11 specification. However, it may also be used with a modification of the Point Coordination Function (PCF) operation of IEEE 802.11, Enhanced Distributed Channel Access (EDCA) operation and Hybrid Coordination Function (HCF) operation of IEEE 802.11 e specification.  
         [0087]     In the case of EDCA, the method is similar to that of DCF. One difference for TPC between DCF and EDCA is that Block ACK mode exists in EDCA. In the Block ACK mode, ADDBA request/ADDBA response commands are used instead of RTS/CTS and they can replace RTS/CTS in  FIG. 4 . Additionally, ADDBA request/ADDBA response have several reserve bits, so one may enclose TPC request and response signals to the reserve bits. In this alternative approach, one does not need to use the Probe request/ response or Action frame to transmit the power to be reduced.  
         [0088]     In cases of PCF or HCF, a Point Coordinator (PC) (Hybrid Coordinator (HC) in 802.11e) controls these signals. The PC (HC) may be located in an access point. The PCF scheme may be initiated by stations requesting that the PC (HC) registers them on a polling list, and the PC (HC) then regularly polls the stations for traffic while also delivering traffic to the stations. Stations may be controlled by the PC (HC) and allows transmitting one (or several) frame(s) for each polling signal from PC (HC). (See IEEE 802.11 specification.)  
         [0089]     Thus, in PCF (HCF), a station should enclose TPC requests in DATA+CF ACK frames and PC (HC) should enclose TPC responses in DATA+CF Poll frames. Currently, slots for address 4 are N/A in 802.11/802.11e (according the specification, this is for the case of transmit between an access point and another access point). It can be used for the TPC signals as described herein. Alternatively, any other reserved slots can be used. One may also use RTS/CTS.  
         [0090]     In future specifications, some or all of the modes will generally be backwards compatible and interoperable with IEEE 802.11 a/b/g. Thus, the TPC and link adaptation described herein may likely suit every standard in the 802.11 family.  
         [0091]     To enable TPC, the access point may use tables showing transmission rate and required received power levels to maintain a link with specified rate. Most stations have such tables to perform link adaptation. Table 4-1 and 4-2 are the sample tables. “b” is a variable that represents the required power for 11 Mb/s. Here for example, a station sending a signal with 11 Mb/s and its received power is (b+4) dBm. The access point checks and knows from the table that the required rate 11 Mb/s needs b dBm power. Thus, the access point tells the mobile station to reduce power by 4 dB. In response, the station reduces its transmit power by 4 dB.  
                             TABLE (4-1)                           Required Received       Rate   Power (dBm)                                11   b       5   b − 3       2   b − 6       1   b − 9                  
 
         [0092]    
       
         
               
               
             
               
               
             
           
               
                 TABLE (4-2) 
               
               
                   
               
               
                   
               
               
                   
                 Required Received 
               
               
                 Rate (Mb/s) 
                 Power (dBm) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 11 
                 b 
               
               
                 5.5 
                 b − 3 
               
               
                 2 
                 b − 4 
               
               
                 1 
                 b − 7 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 2  
       [0093]     Example 2 shows a example where the system attempts to reduce the frequency of TPC message exchange. Two approaches are described with respect.  
         [0094]     In a first approach with an access point  601  and a station  602 , the station  602  examines whether access point  601  has changed its antenna radiation pattern or other characteristic at every transit opportunity. When the access point  601  uses a smart antenna (adaptive antenna) and changes its array width, for instance, reception conditions of station  602  are also changed. Thus, station  602  inquires whether a change has occurred. If a change has occurred, the station invokes TPC.  
         [0095]     This approach also applies where access point  601  changes its transmit power for other reasons. Stations  602  with antenna parameter signals can respond where an access point  601  changes its condition more precisely. If an access point  601  changes an array width or transmits power on a large scale and, if link adaptation is done only at every several control signals, for instance, the rate which is changed by link adaptation may not be updated as well as it should be. Thus, under this condition, having an antenna parameter is useful.  
         [0096]     In a second approach, TPC is described with an additional control margin to reduce its frequency. This margin is set so that a usual fading depth by typical multi-path and shadowing are impacted by a little change of an antenna parameter. Here, when the antenna parameters do not exceed the margin, the station does not need TPC at every transmission time.  
         [0097]     This second approach has two advantages. First, this approach may reduce the transmission of additional signals being transmitted only for TPC between a station and an access point. One reason why decreasing the frequency of transmission of signals only for TPC is because redundant signals waste bandwidth. This may also be referred to as throughput degradation. This is noticeable in the situations that use RTS/CTS. (See Table 5.) One may use reserved slots in RTS/CTS for TPC. However, the maximum reserved slots are 3 bits only in RTS/CTS slots in the current 802.11 standard. These 3 bits may not be enough to inform the power value to be reduced with a sufficient range and accuracy.  
         [0098]     Second, this approach provides advantages for channel conditions between access points and stations that are not changed and where the station (or access point) wants to send signals almost constantly (like voice etc). The reduction of unnecessary processing for TPC can avoid dissipating signal processing resources as well as consuming power.  
         [0099]      FIG. 9  shows the flow chart of the latter example. When a station  602  wants to send data, the station changes a rate in step  901  and checks to see if antenna parameters have changed in step  902 . If an antenna parameter signal changes, then the station  602  determines if a TPC change is required. Here, the TPC change includes RTS signals  904 , CTS signals  905 , a probe request  906 , and a determination if TPC is required (step  907 ). Here, the access point  601  checks the received rate and power of the signal and determines if TPC is needed.  
         [0100]     If TPC is required then it is performed in step  908  and the information transmitted between the station  602  and access point  601  using a probe response  909 , data signals  910 , and ACK  911 . If no TPC is required, then the process steps to probe response, data and ACK signals  909 - 911 . Finally the new rate is stored in step  912 .  
         [0101]     If there was no change in antenna parameters from step  902 , then the stations  602  determines if the difference of rate or/and power between a current rate (rate c ) and a previous rate (rates) is greater than 2 times the rate level in step  903 . It is noted that power information may be used in conjunction or in place of the rate information.  
         [0102]     If yes from step  903 , then the system proceeds as above. If no, the system begins a new cycle.  
         [0103]     In step  907 , the access point  601  calculates the value of a difference based on the signal data and a margin information which may be taken from the tables shown for instance as Tables 4-1 and 4-2. For example, using Table 4-1, when the received rate is 2 Mb/s (required power is (b−6)), access point  601  calculates the difference between received power and required power for transmission at rate 5.5 Mb/s, which is one-level higher than current rate, and required power at this rate is (b−m3). In this case, the value of difference is “received power—(b−3)”. This 3 dB is the margin. The margin level in this example is 1 level, but it can be changed according to a control policy. Also, if Table 4-2 is used, the power difference between rates 2 Mb/s and 5.5 Mb/s is little and it is possible to group them together in such a case.  
                   TABLE (5)                       Signal   Total Length (MAC header length)                   RTS           CTS/ACK   14 octets (10 octets)       DATA   34 + 0˜2312 octets           (30 octets)       Management frame   28 + 0˜2312 octets       (Beacon, Probe Request/response)   (24 octets)                  
 
       EXAMPLE 3  
       [0104]      FIG. 10 a  signal flow chart for example 3. The approach of Example 3 is similar to that of Example 2. However, step  903  is performed as step  1001  in place of step  902 . Here, station  602  does not check a change in antenna parameters. This is because, if access point  601  array changes, the influence is reflected in the received power and transmission rate using link adaptation. In this example, the station  602  does not need to check for a change in antenna parameters of access point  601  prior to performing TPC. One advantage of the system of Example 3 is that is may be easier to implement than that of Example 2.  
         [0105]     Example 3 may be useful under one or more of the following conditions:  
         [0106]     Where access point  601  rarely changes its antenna radiation pattern or other characteristics, or where these changes are too small to effect stations  602 .  
         [0107]     Station  602  performs link adaptation by comparing its frequency of TPC with the frequency of access point&#39;s  601  frequency of the changing its antenna parameters, or station  602  performs link adaptation as soon as it receives a new antenna parameter of access point  601 .  
         [0108]     The following examples are described with respect to one of the above approaches. For the following examples, one may substitute steps  902 - 903  with step  1001  as well as step  1001  with steps  902 - 903  for the reasons specified above.  
       EXAMPLE 4  
       [0109]      FIG. 11  shows an approach used by Example 4. Example 4 represents an approach where a policy provides an emphasis on power restriction. Here, each station  602  calculates a required rate before transmission.  
         [0110]     When station  602  wants to send a payload, it checks a transmit payload category according to traffic or content and its required rate using table like that shown in Table 6 below, for instance. A margin may be set at an access point  601  as shown in  FIG. 11 .  FIG. 11  is similar to that of  FIG. 9 . However, if no from step  902 , then the process steps to point B  1101 . Point B continues at  FIG. 12 .  
         [0111]     In step  1201 , the station  602  checks the data transmit category and its required rate. Various rates are shown in Table 6. In step  1202 , the station  602  checks to see if the required rate is less than the current rate. If yes, then in step  1203 , the system sets the required rate as the current rate. If no from step  1202 , then the process continues with step  903  where station  602  checks to see if TPC is needed with or without a margin.  
         [0112]     For example, using Table 6, if the transmit data category is “voice” (the required rate being 2 Mb/s according to this table) and current rate is 7 Mb/s, station updates the rate to 2 Mb/s. The advantage of this case is that each station can transmit with sufficiently high rate for desired traffic or content and lower power.  
         [0113]     The values used shown in Table 6 are for example purposes only. They may be altered based on system preferences.  
         [0114]     Station  602  can use antenna parameter change information for examination as shown in Example 2. The process at the access point  601  is the same as that of Examples 2 and 3.  
                                         TABLE (6)                                   Traffic Category   Rate (Mb/s)                                        Video   11           Photo   5.5           Voice   2           Best Effort   1                      
 
       EXAMPLE 5  
       [0115]     Example 5 is shown with respect to  FIGS. 10 and 13 . Example 5 is similar to that of Example 4 but where the required by the access point  601 . The calculation begins at point A  1002  in  FIG. 10  and continues with  FIG. 13 . At step  1301 , the system checks the required rate and the current rate at access point  601 . In step  1302 , the access point  601  determines if the current rate is larger than the required rate. If yes, then the process steps to  1303  where the current rate is set to the required rate. Next, the access point  601  determines if TPC is required in step  907 . If no from step  1302 , then the process continues with step  907 .  
         [0116]     One advantage is that station  602  does not need to have Table 6. Also, station  602  is not required to set the appropriate rate. This example may be beneficial where station  602  is desired to have less processing functions so as to minimize power consumption for the station  602 . However, in this example, the access point  601  needs to send not only a value difference but also rate information. Current Probe response or similar signals can be used to send both power and rate with a little modification.  
         [0117]     Table 7 shows a sample of a table that may be used with Example 6. “b” shows the required power for 2 Mb/s. In this case, access point  601  has both traffic category-rate and rate-required power information. Station  602  may or may not use an antenna parameter for examination like that shown in Example 2. Because this process is shown in  FIG. 9 , it is not shown in  FIG. 11  (but is considered within the scope of this example).  
                                                 TABLE (7)                                           Required Terminal           Traffic Category   Rate   Transmit Power (dB)                                        Video   11   b + 8           Photo   5.5   b + 4           Voice   2   b           Best Effort   1   b − 3                      
 
       EXAMPLE 6  
       [0118]     The policy for Example 6 is an emphasis on WLAN management. Here “WLAN resource” means how much wireless resource of access point  601  is occupied. It mainly depends on a number of stations which have payload to transmit/receive in each AP or in each array, a size of load from/to each station and so on. Note that AP sends a binary signal as “WLAN resource management signal” in this figure but any other signals can be also used. For example, “Station Count” and “Channel Utilization” signals are defined as a Beacon by IEEE 802.11e specification and we can use these signals as WLAN resource management signal. Here, “Station Count” indicates a total number of stations currently associated in each AP (or array), and “Channel Utilization” indicates a percentage of time AP (or array) senses the medium busy, as indicated by either physical or virtual carrier sense mechanism. In these cases, AP or stations sets a threshold. If the value of these signals becomes larger than the threshold, AP or stations consider the WLAN resource to be full. When stations examine whether the value becomes larger than the threshold, AP sends the value of threshold signal to station in advance. For example, if the maximum number of VoIP stations in each AP (or array) is x+2, AP sets the threshold x−1, and the current number of VoIP stations is x, AP or station consider the WLAN resource to be full.  
         [0119]      FIGS. 14 and 15  show the flow chart for example 6. Points C  1402 , E  1403 , and G  1404  are shown in parallel to reflect the various actions that may be taken with respect to Example 6 and other examples described below.  
         [0120]     When the process of  FIG. 14  steps to point C  1402 , the process continues in  FIG. 15 . In step  1501 , the system determines if the WLAN resource is full. If yes, then the process returns to  FIG. 14  and continues with the RTS/CTS signals. If no from step  1501 , the system checks the transmit traffic category and its required rate in step  1502 . Next, in step  1503 , if the required rate is less than the current rate then the process continues with step  1504 , where the required rate is set as the current rate. Otherwise, from step  1503  the process continues with the RTS/CTS signals of  FIG. 14 .  
         [0121]     Here, each array in an access point sends resource information to a master resource controller in the access point or in a backbone network. Next. A master resource controller examines the WLAN resource considering information from all arrays, and sends this result to each array. It is also possible that each array examines WLAN resource associated with itself. The same scheme can be used even if AP is not a smart antenna and only has one array.  
         [0122]     The AP may send WLAN resource information with control signals like the Beacon. Then, station considers modifying the rate considering WLAN resource. If this WLAN resource is full, each station sends signals at its maximum rate. However, if WLAN resource is not full, each station is not needed to send with its maximum power. In such case, station updates the rate into the required rate shown in Table 7 shown above to reduce the power consumption.  
       EXAMPLE 7  
       [0123]     Example 7 relates to where the AP calculates a transmit rate for each station considering the WLAN resource.  FIGS. 14 and 16  provide a flowchart for this example.  
         [0124]     The process of  FIG. 14  includes changing the rate in step  901  then processing the RTS/CTS signals. After probe request  906  and encountering point C  1406 , the process continues with  FIG. 16 . In  FIG. 16 , the AP determines if the WLAN resource is full. If no, then the system checks a transmit traffic category and its required rate in step  1602 . In step  1603  the AP determines if the required rate is less than the current rate. If yes from step  1603 , then the AP sets the required rate as the current rate in step  1604 . Next, the process continues with step  907 . If yes from step  1601  or no from step  1603 , then the process continues with step  907  as well.  
         [0125]     Here, a station requires TPC at every transmission in these figures but the station may function with only a sparser interval. When the station requires TPC, the AP calculates the value of difference. If WLAN resource is not full, it also calculates a transmit rate for each station. The advantages of this approach includes the station does not need to do WLAN load examination as well as to calculate the transmit rate.  
         [0126]     Here, the WLAN load information is used for control. Of course, other relevant information may also be available to achieve control with an emphasis on WLAN resource management.  
         [0127]     Optionally, it is possible to combine the flow charts of  FIGS. 14, 15  and  16 . In this optional combination, the WLAN resource is examined by the station and the AP. In this combinational approach, if a station misunderstands a WLAN and sends data at a low rate even though the resource is at full power, the AP also may examine the resource and modify the power accordingly.  
       EXAMPLE 8  
       [0128]     Example 8 shows a process where a station reduces the frequency of TPC using the margin shown in examples 2 and 3 above. Here,  FIGS. 14, 16 , and  17  show the process of example 8. Here, at point E  1403 , the process continues with  FIG. 17 . In step  1701 , a station checks whether a WLAN resource has changed from full to not full. If yes from step  1701 , then the process continues with exchanging the RTS/CTS signals of  FIG. 14 . If no from step  1701 , the system determines if there was a change in antenna parameters in step  1702 . If no, then in step  1703 , the system checks if the difference between a current rate and a previous rate is greater than or equal to two times a rate level. If no from step  1703 , the process continues to point F  1407 . If yes from any of steps  1702  or  1703 , then the process continues with exchanging the RTS/CTS signals of  FIG. 14 . The process may then continue with  FIG. 16  at point D  1406  as described above.  
         [0129]     Here, in  FIG. 17 , the station requires TPC, because WLAN resource management changes to full from not full and the AP asks every station to send with its maximum power. If no from the determination step, the station examines the necessity of TPC. Alternatively, “Change antenna parameter” information can be used either optionally or be a requirement.  
       EXAMPLE 9  
       [0130]     That process of example 9 is shown in  FIGS. 14 and 18 . From point G  1404 , a station then determines in step  1801  whether a WLAN resource is full. If yes, then the station determines if a current rate is greater than a minimum rate in step  1802 . If no, then the process returns to point H  1405  in  FIG. 14 . If yes, then the process continues with the exchange of the RTS/CTS signals in  FIG. 14 . If no from step  1801 , the transmit traffic category and its require rate are examined in step  1803 . Next, in step  1804 , the system determines if the required rate is less than a current rate. If no, then the process continues with the exchange of the RTS/CTS signals in  FIG. 14 . If yes, then the system sets the required rate as the current rate in step  1805 . Next, the process continues with the exchange of the RTS/CTS signals in  FIG. 14 .  
         [0131]     Here, the AP instructs all stations the minimum required rate when WLAN resource is full or almost full. When a station wants to send a payload, but the WLAN resource is full or almost full, the AP sends a required rate. The station compares the current rate with this AP&#39;s required rate. If the current rate is higher than the required rate, this station can send. But if the current rate is lower than the required rate, this station cannot send any data.  
         [0132]     Optionally, the AP requires the minimum rate not only when the resource is full but also for other reasons. For example, even if the resource is not full, if one station transmits large scale of data with very low rate, it affects other stations and reduces the number of VoIP stations.  
         [0133]     Further, it is also possible in this case that AP does not send the minimum required rate and AP examines the station&#39;s transmit rate. In this way, station sends RTS at first, but when the AP determines that a station&#39;s transmit rate is lower than the required rate, the AP does not send the CTS.  
         [0134]     However, in this way, other stations in the same AP or in the same array must to set the NAV and may be prevented from sending any data for a while.  
       EXAMPLE 10  
       [0135]      FIG. 19  shows an illustrative example of block diagram of a station.  FIGS. 20-21  show block diagrams of illustrative AP to realize the above mentioned control schemes. These figures focus on blocks related to TPC and the link adaptation process. It is also possible the other configurations, for example, “TPC controller logic” may be included in a MAC or connected directly to a MAC. Further, the TPC controller logic may be included in a host CPU or other locations.  
         [0136]      FIG. 19  includes SW  1901  forwarding received signals to RF transceiver  1902 . In RF transceiver  1902 , receive radio  1903  forwards received data to the BB physical layer  1905 . The BB physical layer  1905  includes receive variable gain control and LNA GS  1906  and demodular  1908 , both of which receive data from receive radio  1903 . Demodulator  1908  transmits signals to MAC  1911  and clear channel assessment CCA  1907 . CCA  1907  provide signals to VGC and LNA GS  1906 , which then controls receive radio  1903 . CCA also transmits signals to CCA  1912  in MAC  1911 . Signals from CCA  1912  and demodulator  1908  are received by Rx MAC  1913  and transmitted to PCI bus  1915 . From PCI bus  1915 , the system may exchange data with any of host CPU  1916 , host memory  1917 , and TPC control logic  1918 . Tx MAC  1914  in MAC  1911  receives data from PCI bus  1915  CCA  1912 , and transmitted to modulator  1909  in BB physical layer  1905 . Information may be exchanged between modulator  1909  and CCA  1907 . Modulator  1909  that outputs data to transmit radio  1904  in RF transceiver  1902 . PA  1910  then receives control signals from TPC control logic  1918  and signals from transmit radio  1904  and sends them to SW  1901  for transmission.  
         [0137]     Link adaptation may generally be performed by done by “Tx MAC” using information from CCA (Clear Channel Assessment)  1917  or  1912 . At first when the station wants to send a payload and, if the TPC is required at every transmitting opportunity (see examples 1-3 above), Tx MAC  1914  sends a TPC request signal using a Probe request or Action or any other frame. If TPC is required at every several opportunities, Tx MAC  1914  or TPC controller logic  1918  examines the requirements for TPC using at least one of transmit rate and received power information, which may be derived from link adaptation unit in Tx MAC  1914  or CCA  1907  or  1912 .  
         [0138]     When a station receives a TPC response from an AP, the station picks up a value of difference information at Rx MAC  1913  and sends this information to TPC controller logic  1918 . TPC controller logic  1918  controls PA  1910  to change the transmit power. It is also possible that Rx MAC  1913  controls PA directly. In the cases where station checks a transmit data category and its required rate, the necessary tables are located in the memory, which is in MAC or host memory. Then TPC controller logic  1918  or Tx MAC  1914  accomplishes the control using information from both link adaptation unit and memory.  
         [0139]      FIGS. 20 and 21  show illustrative examples of access points. Components similar to those of  FIG. 19  are not described. The access point shown in  FIG. 20  includes a master resource controller  2001  that may include TPC logic controller  2002 . As connected to PCI bus  1915 . Each access point may include a combiner and divider  2003  with antenna elements  2004  providing access to various channels (channels  1 - 3  ( 2005 - 2007 ) shown here for example).  
         [0140]     When each channel  2005 - 2007  in AP receives a signal, that received power information may be noted and stored. When each channel receives a signal which includes a TPC required slot, receiver MAC  1913  sends a control signal to TPC controller logic unit  2002  indicating it that should initiate a TPC calculation. In  FIGS. 20 and 21 , PCI bus  1915  connects MAC  1911  and TPC controller logic  2002 , thereby allowing all channels use the same TPC controller logic  2002 . It is also possible that TPC controller logic  2002  may be located within each MAC  1911  for each channel.  
         [0141]     Next, a value of difference information may be sent to Tx MAC  1914  and conveyed in the transmit signal. Various tables may be stored in memory, which is located in MAC  1911  or host memory  1917 .  
         [0142]     When AP controls link adaptation and TPC considering the WLAN resource, Master resource controller  2001  controls the WLAN resource.  FIG. 20  shows the case that each AP has a master resource controller  2001  and  FIG. 19  shows the case that master resource controller  2108  is located in the backbone network and it controls resources for multiple APs.  
         [0143]      FIG. 21  shows access points with multiple channels  2101 - 2103  communicating with PCI bus  1915 . PCI bus may be connected with host CPU  2104 , host memory  2105 , and TPC controller logic  2106 . Host CPU  2104  and TPC controller logic  2106  may be connected to Ethernet  2109 , which may be connected to other access points  2107  and master resource controller  2108 . It is also possible that each channel has its own master resource controller  2108 .  
         [0144]     The following provides examples of various policies described above. 
        1. AP always emphasizes throughput.     2. AP always emphasizes transmit power.     3. AP always leaves it to each station which policy stations should select.     4. Basically AP leaves it to each station and only if a network becomes crowded, AP emphasizes throughput.        
 
         [0149]     If AP selects 3 or 4 mentioned above and each station decides how to select policy, the following examples may further be considered: 
        1. Station always emphasizes throughput.     2. As far as AP doesn&#39;t indicates to emphasize throughput, station always emphasizes transmit power.     3. If station is without power supply (and/or the rest of power is low), it emphasizes transmit power, if not it emphasizes throughput.     4. Station selects throughput or transmit power according to an application. (For example, station emphasizes throughput only if it sends/receives video application)        
 
         [0154]     The present invention has been described in terms of preferred and exemplary embodiments thereof. Numerous other embodiments, modifications and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure.