Patent Publication Number: US-10778472-B2

Title: Opportunistic measurement and feedback in a wireless local area network

Description:
PRIORITY APPLICATION 
     This application claims benefit of U.S. Provisional Patent Application No. 62/264,719 filed on Dec. 8, 2015 and entitled “OPPORTUNISTIC MEASUREMENT AND FEEDBACK IN A WIRELESS LOCAL AREA NETWORK,” which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The described embodiments relate generally to multiple access wireless communications using electronic devices, including systems and techniques for opportunistically estimating wireless channel characteristics between an access point and a first wireless station, and between the access point and a second wireless station. 
     BACKGROUND 
     Institute of Electronic and Electrical Engineers (IEEE) standard 802.11ac provides an arrangement for channel estimation of uplink and downlink channels between an access point (AP) and multiple wireless stations (STAs). The channel estimation involves a process called sounding. To perform downlink sounding, an AP transmits a Null Data Packet-Announcement (NDP-A). The NDP-A contains the addresses of particular STAs to which the AP wishes to transmit data. The NDP-A is followed by a Null Data Packet (NDP). The NDP represents pilot energy; that is, a pre-defined pattern. Each STA addressed by the NDP-A measures the downlink wireless channel from the AP to itself. The channel measurement is possible because the given STA knows the pre-defined pattern and can estimate the effects of the channel on that pattern (for example, amplitude attenuation, carrier phase rotation, and time delay). Uplink sounding can be performed by instructing one or more STAs to send NDPs, which the AP then observes. 
     IEEE 802.11n specifies a high throughput (HT) physical layer and medium access control layer. IEEE 802.11ac specifies a very high throughput (VHT) physical layer and medium access control layer. More information can be found in IEEE P802.11 Wireless LANS,  Specification Framework for TGax , Nov. 25, 2015, doc.: IEEE 802.11-15/0132r10. 
     For downlink channel measurements, various STAs feedback their channel measurements to an AP and an AP with multiple antennas can transmit multiple streams to the multiple STAs (each with multiple antennas) based on the received channel information. 
     Wireless Local Area Networks (WLANs) supporting uplink and downlink transmission between multiple STAs and APs rely on accurate channel information. An AP may have many STAs desiring service, with different radio channels to each STA due to unique scattering geometries between the AP and each STA. A conventional AP can allocate bandwidth of an uplink transmission to a STA that has a weak uplink channel to the AP. Other STAs will not be scheduled to transmit, and the overall system throughput is low. 
     SUMMARY 
     Representative embodiments set forth herein disclose various systems and techniques for opportunistically estimating wireless channel characteristics between an access point and a first wireless station, and between the access point and a second wireless station. Embodiments can be implemented to provide various advantages, including improving determination of uplink channel information from multiple STAs, which can provide for improved allocation of uplink radio resources by the AP. 
     WLAN systems include APs and STAs. The embodiments provided herein include providing observed downlink channel information from STAs to an AP. In configurations in which the AP can estimate the uplink channel based on the downlink channel (e.g., when a channel reciprocity property applies) the AP can improve uplink channel allocation based on the received observations of downlink channel transmission. 
     In order to efficiently allocate uplink resources to multiple STAs, an estimate of a joint uplink channel matrix H with submatrix components H 1  and H 2  is provided by embodiments of this disclosure. The AP can solicit observations from STAs or receive unsolicited channel information from STAs. The AP then applies an algorithm based on the channel information to determine which STAs should be allocated uplink resources in a given time interval. The STAs can provide different representations of channel information and the information can be sent flexibly in a number of different message types. 
     This Summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the subject matter described herein. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described will become apparent from the following Detailed Description, Figures, and Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The included drawings are for illustrative purposes and serve to provide examples of possible structures and arrangements for the disclosed systems and techniques, e.g., for intelligently and efficiently managing calls and other communications between multiple associated user devices. These drawings in no way limit any changes in form and/or detail that may be made to the embodiments by one skilled in the art without departing from the spirit and scope of the embodiments. The embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIG. 1  illustrates an exemplary WLAN system including an AP and multiple STAs, according to some embodiments. 
         FIG. 2  illustrates an exemplary message sequence in which two STAs opportunistically provide feedback channel estimation, according to some embodiments. 
         FIG. 3  illustrates an exemplary message sequence in which an AP requests a channel estimate from a STA, according to some embodiments. 
         FIG. 4  illustrates an exemplary message sequence in which a STA opportunistically provides a channel estimate in a medium access control (MAC) header, according to some embodiments. 
         FIG. 5  illustrates an exemplary message sequence in which a STA opportunistically provides a channel estimate in a management frame, according to some embodiments. 
         FIG. 6  illustrates an exemplary message sequence in which a STA opportunistically provides a channel estimate in a control frame, according to some embodiments. 
         FIG. 7  illustrates an exemplary message sequence in which the AP stimulates transmission of null data packets by STAs in order to initiate explicit uplink channel measurement, according to some embodiments. 
         FIG. 8  illustrates an exemplary message sequence in which an AP sends a null data packet and then a trigger frame to collect feedback from STAs, according to some embodiments. 
         FIG. 9  illustrates exemplary measurements of channel responses at OFDM tone positions corresponding to particular resource units (RUs) in a frequency spectrum, according to some embodiments. 
         FIG. 10  illustrates an exemplary logic flow for a first STA, according to some embodiments. 
         FIG. 11  illustrates an exemplary logic flow for an AP, according to some embodiments. 
         FIG. 12  illustrates an exemplary apparatus for implementation of embodiments disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Representative applications of apparatuses, systems, and methods according to the presently described embodiments are provided in this section. These examples are being provided solely to add context and to aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the presently described embodiments can be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the presently described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
     In order to implement Multi-User, Multiple Input, Multiple Output (MU-MIMO) on an uplink, it is useful to determine channel information between a set of STAs that will transmit together (e.g., in the same time interval) to the AP. In some embodiments, to obtain multiple received streams with good signal to noise ratio at the receiver, the AP will compute transmission parameters based on a decomposition of a joint channel matrix H, where H represents uplink channel information from each STA scheduled to transmit in a same time interval. H can be estimated at the AP. 
     Particular aspects of the embodiments are now discussed with reference to the figures. 
     Communication System 
       FIG. 1  illustrates an exemplary WLAN system including STA  102 , STA  104 , AP  110 , and Internet  120 . The wireless connection between STA  102  and AP  110  is indicated as link  106  and the connection between STA  104  and AP  110  is indicated as link  108 . The direction or sense of these connections is described as follows. Transmission from AP  110  to the STAs is downlink transmission. Transmission from either STA to AP  110  is uplink transmission. In some embodiments, uplink and downlink transmissions use different frequency bands. In that case, the channel response on the downlink from AP  110  to STA  102 , for example, may differ from the channel response on the uplink from STA  102  to AP  110 , e.g., because of the different path lengths and/or signal characteristics. A channel response is based on the phenomenon of radio waveforms at the downlink or uplink frequency interacting with scatterers. When uplink and downlink frequencies differ, a given waveform at the uplink frequency can experience a different total carrier phase rotation accumulated in interacting with a set of scatterers than a waveform at the downlink frequency interacting with the same set of scatterers. Attenuation generally also is a function of frequency. In some embodiments, uplink and downlink transmissions use the same frequency band. When uplink and downlink transmissions are on the same band(s), the principle of channel reciprocity implies that the channel response on the downlink from AP  110  to STA  102 , for example, should be the same as the channel response on the uplink from STA  102  to AP  110 . 
     An OFDM system uses a plurality of subcarriers; let the number of subcarriers in an OFDM symbol be L. Generally the uplink channel from STA  102 , H 1 , is an L-vector formed of L complex scalars, each scalar representing a channel gain at the corresponding subcarrier. For some delay spread and subcarrier spacings of interest, H 1  changes slowly in response to frequency differences from element to element of H 1 , and it is not necessary to perform a measurement at each subcarrier. For example, measurements can be made at subcarriers indexed with an even index value, and the values of H 1  corresponding to the odd indices can be estimated by interpolating between the values of H 1  at the even indices. AP  110  can also learn the uplink channel response, H 2 , associated with link  108 , e.g., by asking STA  104  to send an NDP data packet as described below. The joint matrix H may be written as H=[H 1  H 2 ] and an observation at one antenna of the AP may be written as y=H′[x 1 ′ x 2 ′]′ (neglecting noise) where x is a transmit vector and z′ is the Hermitian transpose of z. Many symbolic representations are possible. Let two antennas at the AP be labelled A and B. The two observations may be written y A =H A ′[x 1 ′ x 2 ′]′ and y B =H B ′[x 1 ′ x 2 ′]′. In the two antenna-AP case, H 1 , the uplink channel from STA  102  to AP  110 , generalizes to H 1A  and H 1B . Expressions in terms of more than two antennas at the AP are straightforward. Particular details of OFDM modulation, such as subcarriers, will be touched on as needed in the explanations of the channel sounding techniques provided herein. 
     Dynamic Resource Allocation for Uplink 
     In some embodiments, AP  110  executes a dynamic resource allocation algorithm in order to maximize the total transfer of information on the uplink for multiple devices attempting to access a shared resource (the bandwidth available for transmission). In a bandwidth distribution solution of information theory known as water-filling, the multiple access channel reaches a high throughput when the channel users with the best channels devote the most energy to the channel. To identify which STAs have the best channels and thus should transmit the most bits in a given time, AP  110  needs to learn (or assess) the channel. When AP  110  has adequate information from STAs of interest, it can run its dynamic channel allocation algorithm and allocate multiple access resources, such as OFDM RUs to various STAs according to a configuration determined by the algorithm. 
     Uplink Channel Estimate, Opportunistic STA Feedback 
       FIG. 2  illustrates an exemplary message sequence that results in the AP  110  obtaining an estimate of the uplink channels H 1  and H 2 . Three timelines ( 203 ,  213 , and  223 ) are shown in  FIG. 2 , one for each of AP  110 , STA  102  and STA  104  (indicated in parentheses in  FIG. 2 ). The three timelines illustrate transmitted signals (for example, the variables x 1  and/or x 2  as explained with respect to  FIG. 1 ); corresponding received versions of the transmitted signals (for example, the variable y as explained with respect to  FIG. 1 ) are shown as data  202 -R 1  and data  202 -R 2 . Generally, the received versions of signals are not shown in these figures. In  FIG. 2 , uplink channel information is collected in a time sequence. The first event occurs on timeline  203 . AP  110  sends data  202  addressed to STA  102 . STA  102  receives data  202  (indicated with dashed box data  202 -R 1 ) and responds by transmitting block acknowledgement BA  210 . STA  102  also sends an estimate of downlink channel H 1  as feedback information FB  212 . FB  212  can be a frame with a MAC header and MAC payload, or it can be, for example, a management frame. STA  102  creates FB  212  based on its observation of data  202 . The channel information sent by STA  102  in FB  212  is encoded in some fashion. The channel information may be signal to noise ratio (SNR) information per subcarrier, received signal strength indication (RSSI) information for an entire modulated bandwidth, or, for example, a ranking of strongest subcarriers or RUs observed in data  202  by STAs  102  and/or  104 . 
     The channel information may be extensive, such as per subcarrier or per RU. The value of each SNR value, for example, may be precise such as 8 bits, or may be quantized using a lower number of bits, such as 1, 2, 3, or 4 bits. The number of subcarriers or number of RUs represented may be extensive, such as approximately 256 subcarriers in 20 MHz or 9 RUs. Alternatively, the number of subcarriers (or RUs) represented may be a sampling, such as 10, 20 or 50 subcarriers in 20 MHz. In some embodiments, the channel information may include a ranking without intensity or power or signal to noise ratio information. For example, STA  102  may provide an indication of the strongest observed subcarrier or RU. In some embodiments, this indication is an index or address of the indicated subcarrier or RU. In some embodiments, STA  102  provides indications of a strongest N subcarriers or strongest M RUs. For example, M can be 3 indicating the strongest 3 RUs. N can be 4 indicating the strongest 4 subcarriers. In some embodiments, STA  102  provides a single global power measurement, such as an amount of power observed over a time interval in a certain bandwidth, for example, 20 MHz. This power measurement can be an RSSI value encoded with high resolution (for example 8 bits) or roughly quantized (for example: 1, 2, 3, or 4 bits). 
     In some embodiments, STA  102  provides channel information concerning, e.g., approximately one half of the RUs in a given bandwidth. For example, STA  102  can provide information about four or five RUs of nine RUs in a 20 MHz bandwidth. In some embodiments, STA  102  provides 3 or 4 bit SNR values for the highest quality observed RUs observed. The location or identity of the RUs for which information is provided by the STA can be identified using indices. 
     In some embodiments, STA  102  ranks 9 RUs observed in 20 MHz and sends the ordered list determined by the ranking to AP  110 . Such a transmission could be realized using four bits per RU index for nine RUs, thus a maximum number of bits needed would be four times nine or 36 bits. Other encoding schemes could be used by STA  102  to indicate the ordered list to AP  110 . The ranking and/or the RSSI information, in some embodiments, can be sent by STA  102  to AP  110 . 
     After receiving the channel information, AP  110  can use it to decide which STA to schedule for a next uplink physical layer convergence protocol (PLCP) protocol data unit (PPDU) transmission opportunity and which RU or RUs should be allocated to that STA. 
     AP  110 , in some embodiments, estimates uplink channel H 1  from STA  102  as being equal to the downlink channel from AP  110  to STA  102 . This assumption is strong when AP  110  and STA  102  operate, for example, in a time division duplex (TDD) manner of some kind on a common frequency band; this may be referred to as the TDD assumption (see discussion of reciprocity above). In some embodiments, TDD does not impose a strict time slot structure. STA  104  may also observe data  202  and decide to opportunistically transmit a channel estimate to AP  110 ; STA  104 &#39;s observation is indicated in  FIG. 2  as a dashed box marked data  202 -R 2 . STA  104  may obtain a downlink channel estimate based on known components (e.g., pre-determined bit or symbol values) of a header or preamble in the frame indicated as data  202  in  FIG. 2 . A channel estimate may also be referred to as a channel quality herein. In some embodiments, STA  104  produces channel information based on power observations and not intensity. In that case, STA  104  does not need knowledge of components of data  202 . An example of such a data-value-insensitive measurement is RSSI. Thus, in  FIG. 2 , an exemplary transmission FB  220  from STA  104  provides AP  110  with information about the downlink channel from AP  110  to STA  104 . AP  110  can estimate (e.g., under the TDD assumption) uplink channel H 2  from STA  104  as being equal to the downlink channel from AP  110  to STA  104 . In  FIG. 2 , STAs  102  and  104  provided feedback information opportunistically. This information is useful and can also be used by AP  110  in its dynamic resource allocation algorithm to select which STAs should be granted uplink resources for a given time interval and the number of RUs to be granted to each selected STA. 
     Uplink Channel Estimate, Solicited STA Feedback 
     Alternatively or additionally, in some embodiments, AP  110  can solicit STA feedback.  FIG. 3  illustrates an exemplary implementation in which AP  110  sends channel estimate request (FB request)  302  after receiving the block acknowledgement BA  210 . FB request  302  can be implemented with any desired fields, such as a feedback control field and an address field. Alternatively, STA options can be implied by a standard specification set of policies or rules; thus, an explicit feedback control field, in some embodiments, is not included in FB request  302 . The feedback control field can be asserted (for example, set to “11” as an example feedback control field value) to indicate the feedback is required. The address field can be used to indicate a specific STA or a group of STAs, or can be omitted or unused for some values of the control field. In some embodiments, the feedback control field has a soft aspect, that is, the control field indicates that feedback is permitted, but not required (an exemplary value may be “10”). If the feedback control field is not asserted, this can indicate that feedback is discouraged (an exemplary value “01”) or not permitted (an exemplary value “00”). AP  110  may send such a request under several scenarios. In some embodiments AP  110  can determine that more channel information about the uplink channel from STA  102  would improve its dynamic resource allocation algorithm. To obtain this information, it can request feedback from STA  102 . STA  102 , in some embodiments, evaluates the feedback control field to arrive at a reporting decision. When STA  102  arrives at a positive reporting decision and responds with an estimate of the downlink channel (this estimate is included in message FB  312 ), AP  110  can approximate the uplink channel as being equal to the downlink channel. STA  102 , in some embodiments retains recent reporting decision outcomes in a reporting record. 
     In some scenarios, AP  110  serves many STAs and at some times has channel information with high confidence (low error variance on the channel estimates) for the STAs with active links. In this case, AP  110  may refrain from soliciting feedback, since the feedback event occupies a finite portion of the available channel bandwidth. In such a case, the feedback control field of FB request  302  may have value “00”, and STA  102  would send BA  210  but not FB  312 . In some embodiments, the feedback control field and address field can be sent in a header of data  202 . In that case, in some embodiments, FB request  302  need not be sent and STA  102  will still receive the feedback control field and can act accordingly. STA  102 , in some embodiments, can behave as follows: i) transmit FB  312  based on a corresponding request for feedback (e.g., feedback control field of data  202  having value “11”), ii) transmit FB  312  based on a field encouraging feedback (e.g., feedback control field “10”), iii) transmit FB  312  despite a field discouraging feedback (e.g., feedback control field “01”), iv) not transmit FB  312  based on a field prohibiting feedback (e.g., feedback control field “00”) v) optionally not transmitting FB  312  based on the feedback control field value “10”, or vi) optionally not transmitting FB  312  based on the feedback control field value “01.” 
       FIGS. 4-6  illustrate flexible approaches by which a STA, e.g., STA  102 , can provide an encoding of downlink channel information to AP  110 . 
     PPDU, Management Frames and Control Frames 
       FIG. 4  includes an illustration of an exemplary MAC header embodiment. A transmission by an AP or by a STA can include a PPDU. A MAC PPDU can have a header and a payload. The header can be a MAC header. The payload can be a MAC payload.  FIG. 4  illustrates a control field  414  in a MAC header  412 . MAC header  412  is followed by MAC payload  416 . Control field  414  can include a compressed version of a downlink channel estimate. STA  102  performs a channel estimate based on its observation of data  202 . The encoding can be done in a fashion similar to that in FB  212  or FB  220  of  FIG. 2 . For example, SNR and/or RSSI may be encoded with various levels of quantization. A ranking of RUs may be sent. In some embodiments, opportunistic feedback FB  212  (or FB  220 ) of  FIG. 2  can be or can include a MAC header  412  with a control field  414 . 
       FIG. 5  illustrates an exemplary management frame in which opportunistic feedback FB  212  (or FB  220 ) of  FIG. 2  comprises a management frame  502 . A management frame sent by STA  102  (or STA  104 ), in some embodiments, is not scheduled by AP  110 . AP  110  may not know when management frame  502  will be transmitted by STA  102 . The time axis  213  in  FIG. 5  is shown broken with an indication that STA  102  may perform other activities and some time can pass before transmission of management frame  502 . Consequently, the channel may be busy when management frame  502  is sent, and a collision can occur with a transmission from AP  110  or STA  104 , for example. The management frame  502  can be sent with an immediate ACK policy. If AP  110  successfully decodes management frame  502  and an immediate ACK policy is indicated in management frame  502 , AP  110 , in some embodiments, responds with ACK  510 . STA  102  receives ACK  510  and then does not re-transmit the encoded channel information of management frame  502 . When STA  102  does not receive an ACK after transmission of the management frame, it can retransmit the information of management frame  502 . In some embodiments, management frame  502  is sent with a no ACK policy. In that case, AP  110  need not send ACK  510  and STA  102  need not wait for an ACK before continuing with other uplink data to be sent. In some embodiments, AP  110  sends a FB request in a management frame and expects STA  102  to respond with channel information in a management frame. 
       FIG. 6  illustrates an exemplary channel feedback embodiment in which solicited feedback FB  312  of  FIG. 3  comprises a control frame  612 . A control frame to be sent by STA  102  is scheduled by AP  110  using FB request  602 ; that is, FB request  602  can include a control frame sent by AP  110 . In some embodiments, FB request  602  polls OFDMA RU quality information from STA  102 . AP  110  expects control frame  612  to be transmitted by STA  102  in a limited forthcoming time interval as shown in  FIG. 6 . In some embodiments, the time interval is a short interframe space (SIFS). 
     NDP-A Examples 
       FIG. 7  illustrates an exemplary AP-initiated uplink (UL) measurement using a null data packet-announce (NDP-A) message  702 . In some embodiments described herein, AP  110  learns the uplink channel response, H 1 , associated with link  106  by asking STA  102  to send a pilot or sounding or null data packet (NDP) signal on the uplink. AP  110  then samples the NDP arriving from STA  102 . Because AP  110  knows the NDP waveform sent by STA  102 , it can estimate the channel H 1 , for example, using a correlation function. With regard to the discussion of  FIG. 1 , x 1  in the  FIG. 7  case of pilot transmission is the NDP waveform, and so x 1  is known to AP  110  before it is sent by STA  102 . In some embodiments, NDP-A  702  instructs STA  102  to energize particular ones of the RUs of the uplink channel frequency band with pilot energy. The location of the energized pilots can be referred to as a map. The instruction of NDP-A  702  includes an OFDMA RU allocation. NDP-A indicates a different OFDMA RU allocation to be used by STA  104 . In embodiments, the intersection of pilot energy locations of the resulting NDP  710  map and the resulting NDP  720  map shows no common subcarriers in use at a given OFDM symbol time. Thus NDP  710  and NDP  720  are frequency division multiplexed (see  FIGS. 7 and 9 ) at the RU level in some embodiments.  FIG. 7  indicates the transmissions from STA  102  and STA  104  are Multi-User (MU) multiplexed. This MU multiplexing is from the point of view of AP  110 . AP  110  estimates the uplink channels H 1  and H 2  based on a composite received signal (the variable y discussed with respect to  FIG. 1 ). The composite received signal is based on H 1 , H 2 , NDP  710  and NDP  720 . Subsequently, AP  110  can send a trigger message (not shown), which can include multi-user transmit parameters, and thus AP  110  will schedule the transmission of data by STA  102  and STA  104 . 
       FIG. 8  illustrates an exemplary AP-initiated DL-measurement-based UL estimate using an NDP-A  702 , NDP  802  and trigger message  804 . In particular,  FIG. 8  illustrates an exemplary embodiment to estimate the uplink channels from STA  102  and STA  104  based on first obtaining downlink channel information from STA  102  and STA  104 . The uplink channels can be approximated by AP  110  based on the downlink channel estimates using the TDD assumption/reciprocity as described above. STAs  102  and  104  receive NDP-A  702  and then await NDP  802 . STA  102  estimates its downlink channel based on sampling NDP  802  as received at STA  102 . STA  104  estimates its downlink channel based on sampling NDP  802  as received at STA  104 . AP  110  then transmits trigger  804  addressed to STAs  102  and STA  104 . STAs  102  and  104  respond with channel estimate messages FB  812  and FB  822  respectively. AP  110  estimates uplink channels H 1  and H 2  based on information in FB  812  and FB  822 , respectively. The waveform versions of FB  812  and FB  822  received at AP  110  are also generally a function of the uplink channels H 1  and H 2  since FB  812  travels through at least some subcarriers of H 1  and FB  822  travels through at least some subcarriers of H 2 , in some embodiments. 
     RU Description and Quality Measures 
     Further description of RUs and channel information is provided in  FIG. 9 .  FIG. 9  illustrates an available system bandwidth of 20 MHz (although other bandwidths can be used in other implementations). Each STA that is provided with an uplink transmission grant is assigned one or more RUs on which to transmit. The duration of the subsequent data transmission from a STA, in some instances, will be for one PPDU, that is, one packet interval. An example downlink PPDU is data  202 . An RU, in some embodiments, represents  26  contiguous tones or subcarriers (although other arrangements of tones or subcarriers can be used). For example, STA  102  of  FIG. 1  may be provided with an allocation representing each of RU  921 ,  922 , . . . ,  929 , that is, the entire 20 MHz band. In some embodiments, STA  102  is provided RU  921 , a STA  103  (not shown) is provided RU  922  and STA  104  of  FIG. 1  is provided RU  929 . In some embodiments, STA  102  is provided with RU  921  and STA  104  is provided with RU  922  and RU  924 . The allocations of one or more RUs to a particular STA need not be contiguous in frequency. 
       FIG. 9  illustrates allocations  921  . . .  929  representing nine twenty-six-tone RUs in a 20 MHz system bandwidth. In order to learn which RUs to assign to which STAs, the AP can collect information using one or more of the implementations described above with regard to  FIGS. 2-8 .  FIG. 9  illustrates that STA  102  may observe tones  912 , . . . ,  914 , . . . , and  992  and produce exemplary quality measures indicated as SNR 1 , . . . , SNR 9  or rank 1 , . . . , rank 9 . These quality measures are reported, for example, as encodings described with regard to feedback message FB  212 , FB  220 , FB  312 , FB  812  or, for example, FB  822  described above. The transmission of the encoded information can be performed according to the frame types discussed with respect to one or more of  FIGS. 4-6  and  FIG. 8 . In some embodiments, one report contains quality values for multiple RUs and these RUs can be based on certain criteria, for example the top three RUs that have the best SNR values. In some embodiments, the RU allocations  921  . . .  929  (shown in  FIG. 9 ) have values assigned to the variables rank 1 , . . . , rank 9 . For example (see Table 1), these 9 rank values (rank 1 , . . . , rank 9 ) may have example ranks of {5, 2, 9, 6, 4, 8, 1, 3, 7} where 1 indicates the highest SNR out of the set SNR 1 , . . . , SNR 9  and 9 represents the lowest (noisiest) SNR out of the set. If the top 3 SNR values are to be sent, then, in this example, SNR 7  (strongest), SNR 2  (second strongest), and SNR 8  (third strongest) will be sent in the report. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Rank Example 
               
            
           
           
               
               
               
            
               
                 RU Index 
                 Rank 
                 SNR Value 
               
               
                   
               
               
                 921 
                 5 
                 SNR 1   
               
               
                 922 
                 2 
                 SNR 2   
               
               
                 923 
                 9 
                 SNR 3   
               
               
                 924 
                 6 
                 SNR 4   
               
               
                 925 
                 4 
                 SNR 5   
               
               
                 926 
                 8 
                 SNR 6   
               
               
                 927 
                 1 
                 SNR 7   
               
               
                 928 
                 3 
                 SNR 8   
               
               
                 929 
                 7 
                 SNR 9   
               
               
                   
               
            
           
         
       
     
     The reporting message, in some embodiments, includes indications of the top-ranked RU indices without sending indications of the corresponding SNR values. In the example of Table, in some embodiments, the reporting message would thus indicate indices  927 ,  922 , and  928  without reporting SNR 7 , SNR 2  or SNR 8 . 
     In other embodiments, a system bandwidth of 40 MHz is available for uplink transmission—corresponding to eighteen twenty-six-tone RUs. In a 40 MHz bandwidth, the AP can request that up to eighteen STAs respond with NDPs in order that the AP may determine up to 18 allocations. 
       FIG. 10  illustrates an exemplary logic flow realized in some embodiments by a wireless device. At  1002 , the wireless device receives a first message from a base station. At  1004 , the wireless device determines a reporting decision. The wireless device can favor a reporting decision if: i) a buffer status in the wireless device indicates a buffer has data to be sent or is about to overflow, ii) an estimate of a geographic mobility of the first device indicates that the uplink channel is changing rapidly and a base station should be updated, iii) in response to a feedback control field received from the base station, iv) a measure of overall network activity in uplink and downlink by the wireless device, and/or v) an estimate of arrival rate of received data at the wireless device. In some embodiments, the overall network activity is a cumulative value including a sum of the uplink activity (in terms of transmitted packet rate) and downlink activity (in terms of received packet rate). 
     When the reporting decision is negative, indicated by  1005 , the wireless device waits for a next message at  1007 . When the reporting decision is positive, indicated by  1006 , the wireless device obtains a channel estimate at  1008 ; in some embodiments this could be an SNR value, ranking value, RU index, and/or RSSI value. The channel estimate could be in memory, or it could be computed by the STA based on a message, such as the first message. At  1010 , the wireless device formats a second message with an encoding of the channel estimate. At  1012 , the wireless device sends the second message to the base station. A STA is an example of a wireless device and an AP is an example of a base station. 
       FIG. 11  illustrates an exemplary logic flow realized in some embodiments by a base station. At  1102 , the base station sends a message to a first wireless device. At  1104 , the base station receives a first channel estimate (e.g., an SNR value, ranking value, RU index, and/or RSSI value) based on the message. At  1106 , the base station receives a second channel estimate (e.g., an SNR value, ranking value, RU index, and/or RSSI value) based on the message. At  1108 , the base station allocates a multiple access resource, for example, an OFDMA RU, to the first wireless device or to the second wireless device.  1108  also indicates that transmissions of the first and second channel estimates by the first and second wireless devices, respectively, were not scheduled by the base station. A STA is an example of a wireless device and an AP is an example of a base station. 
     Wireless devices, and mobile devices in particular, can incorporate multiple different radio access technologies (RATs) to provide connections through different wireless networks that offer different services and/or capabilities. A wireless device can include hardware and software to support a wireless personal area network (“WPAN”) according to a WPAN communication protocol, such as those standardized by the Bluetooth® special interest group (“SIG”) and/or those developed by Apple referred to as an Apple Wireless Direct Link (AWDL). The wireless device can discover compatible peripheral wireless devices and can establish connections to these peripheral wireless devices located in order to provide specific communication services through a WPAN. In some situations, the wireless device can act as a communications hub that provides access to a wireless local area network (“WLAN”) and/or to a wireless wide area network (“WWAN”) to a wide variety of services that can be supported by various applications executing on the wireless device. Thus, communication capability for an accessory wireless device, e.g., without and/or not configured for WWAN communication, can be extended using a local WPAN (or WLAN) connection to a companion wireless device that provides a WWAN connection. Alternatively, the accessory wireless device can also include wireless circuitry for a WLAN connection and can originate and/or terminate connections via a WLAN connection. Whether to use a direct connection or a relayed connection can depend on performance characteristics of one or more links of an active communication session between the accessory wireless device and a remote device. Fewer links (or hops) can provide for lower latency, and thus a direct connection can be preferred; however, unlike a legacy circuit-switched connection that provides a dedicated link, the direct connection via a WLAN can share bandwidth with other wireless devices on the same WLAN and/or with the backhaul connection from the access point that manages the WLAN. When performance on the local WLAN connection link and/or on the backhaul connection degrades, a relayed connection via a companion wireless device can be preferred. By monitoring performance of an active communication session and availability and capabilities of associated wireless devices (such as proximity to a companion wireless device), an accessory wireless device can request transfer of an active communication session between a direction connection and a relayed connection or vice versa. 
     In accordance with various embodiments described herein, the terms “wireless communication device,” “wireless device,” “mobile device,” “mobile station,” “wireless station”, “wireless access point”, “station”, “access point” and “user equipment” (UE) may be used herein to describe one or more common consumer electronic devices that may be capable of performing procedures associated with various embodiments of the disclosure. In accordance with various implementations, any one of these consumer electronic devices may relate to: a cellular phone or a smart phone, a tablet computer, a laptop computer, a notebook computer, a personal computer, a netbook computer, a media player device, an electronic book device, a MiFi® device, a wearable computing device, as well as any other type of electronic computing device having wireless communication capability that can include communication via one or more wireless communication protocols such as used for communication on: a wireless wide area network (WWAN), a wireless metro area network (WMAN) a wireless local area network (WLAN), a wireless personal area network (WPAN), a near field communication (NFC), a cellular wireless network, a fourth generation (4G) LTE, LTE Advanced (LTE-A), and/or 5G or other present or future developed advanced cellular wireless networks. 
     The wireless device, in some embodiments, can also operate as part of a wireless communication system, which can include a set of client devices, which can also be referred to as stations, client wireless devices, or client wireless devices, interconnected to an access point (AP), e.g., as part of a WLAN, and/or to each other, e.g., as part of a WPAN and/or an “ad hoc” wireless network, such as a Wi-Fi direct connection. In some embodiments, the client device can be any wireless device that is capable of communicating via a WLAN technology, e.g., in accordance with a wireless local area network communication protocol. In some embodiments, the WLAN technology can include a Wi-Fi (or more generically a WLAN) wireless communication subsystem or radio, the Wi-Fi radio can implement an Institute of Electrical and Electronics Engineers (IEEE) 802.11 technology, such as one or more of: IEEE 802.11a; IEEE 802.11b; IEEE 802.11g; IEEE 802.11-2007; IEEE 802.11n; IEEE 802.11-2012; IEEE 802.11ac; IEEE 802.11ax; or other present or future developed IEEE 802.11 technologies. 
     IEEE 802.11ac is an example of a system using Orthogonal Frequency Division Multiplexing (OFDM) to modulate data onto OFDM symbols. OFDM is a modulation scheme which uses many narrowband subcarriers to overcome delay spread yet provide high bandwidth. A modulation feature of an OFDM symbol known as a cyclic prefix reduces the need or complexity of equalization of multipath effects at a receiver in many scenarios. The distribution of subcarriers within a single OFDM symbol among more than one user is known as Orthogonal Frequency Division Multiple Access (OFDMA). A collection of subcarriers within an OFDM symbol can be referred to as a resource unit (RU). In an OFDMA frame structure, each subcarrier is modulated with a number of OFDM symbols. On a given subcarrier during a given frame, some RUs may be devoted to pilot energy and other RUs may be provided with no pilot energy. The collection of RUs over all the subcarriers is represented by a time/subcarrier map. A null data packet (NDP) comprises pilot tones useful for channel estimation. 
     Additionally, it should be understood that the wireless devices described herein may be configured as multi-mode wireless communication devices that are also capable of communicating via different third generation (3G) and/or second generation (2G) RATs. In these scenarios, a multi-mode wireless device or UE can be configured to prefer attachment to LTE networks offering faster data rate throughput, as compared to other 3G legacy networks offering lower data rate throughputs. For instance, in some implementations, a multi-mode wireless device or UE may be configured to fall back to a 3G legacy network, e.g., an Evolved High Speed Packet Access (HSPA+) network or a Code Division Multiple Access (CDMA) 2000 Evolution-Data Only (EV-DO) network, when LTE and LTE-A networks are otherwise unavailable. 
     Representative Exemplary Apparatus 
       FIG. 12  illustrates in block diagram format an exemplary computing device  1200  that can be used to implement the various components and techniques described herein, according to some embodiments. In particular, the detailed view of the exemplary computing device  800  illustrates various components that can be included in STA  102 , STA  104  or AP  110  illustrated in  FIG. 1 . As shown in  FIG. 12 , the computing device  1200  can include a processor  1202  that represents a microprocessor or controller for controlling the overall operation of computing device  1200 . The computing device  1200  can also include a user input device  1208  that allows a user of the computing device  1200  to interact with the computing device  1200 . For example, the user input device  1208  can take a variety of forms, such as a button, keypad, dial, touch screen, audio input interface, visual/image capture input interface, input in the form of sensor data, etc. Still further, the computing device  1200  can include a display  1210  (screen display) that can be controlled by the processor  1202  to display information to the user (for example, information relating to incoming, outgoing, or active communication session). A data bus  1216  can facilitate data transfer between at least a storage device  1240 , the processor  1202 , and a controller  1213 . The controller  1213  can be used to interface with and control different equipment through an equipment control bus  1214 . The computing device  1200  can also include a network/bus interface  1211  that couples to a data link  1212 . In the case of a wireless connection, the network/bus interface  1211  can include wireless circuitry, such as a wireless transceiver and/or baseband processor. 
     The computing device  1200  also includes a storage device  1240 , which can comprise a single storage or a plurality of storages (e.g., hard drives), and includes a storage management module that manages one or more partitions within the storage device  1240 . In some embodiments, storage device  1240  can include flash memory, semiconductor (solid state) memory or the like. The computing device  1200  can also include a Random Access Memory (“RAM”)  1220  and a Read-Only Memory (“ROM”)  1222 . The ROM  1222  can store programs, utilities or processes to be executed in a non-volatile manner. The RAM  1220  can provide volatile data storage, and stores instructions related to the operation of the computing device  1200 . 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, DVDs, magnetic tape, hard storage drives, solid state drives, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.