Abstract:
Communication circuitry that employs persistent scheduling conventionally uses one initiation command to establish the modulation and coding scheme (“MCS”) that will be used for transmission of subsequent payload bursts, at least until it is time to send another initiation command. Inefficiency can result if transmission channel conditions change between initiation commands. To avoid such inefficiency, the disclosed circuitry maintains a count of unsuccessful transmission attempts. When the count deviates from a predetermined reference standard, the circuitry automatically and autonomously makes an appropriate change in the MCS selection without waiting for the next initiation command. Both transmitter and receiver circuits independently operate in the same way at the same time so that both ends of a communication link remain coordinated with one another.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of commonly-assigned U.S. patent application Ser. No. 12/573,473, filed Oct. 5, 2009, now U.S. Pat. No. 8,705,460, which claims the benefit of U.S. Provisional Patent Application No. 61/105,266, filed Oct. 14, 2008 and copending therewith, each of which is hereby incorporated by reference herein in its respective entirety. 
    
    
     BACKGROUND 
     This disclosure relates to electronic communication. More particularly, the disclosure relates to electronic communication of the type that employs what is known as persistent scheduling. 
     Certain types of electronic communication can make use of any one of two or more (i.e., a plurality of) different modulation and coding schemes (“MCSs”) for communication at different times, depending on the condition of the communication or transmission link at such different times. Examples of different types of modulation that may be used are quadrature phase shift keying (“QPSK”), 16-quadrature amplitude modulation (“16-QAM”), 64-quadrature amplitude modulation (“64-QAM”), etc. Examples of different types of coding that may be used are tail-biting convolutional codes (“TBCC”) or convolutional turbo codes (“CTC”) with various specific code rates of 1/4, 1/2, 3/4, and the like. Thus MCS in this disclosure means the combination of modulation and coding rate, such as QPSK 1/4, QPSK 1/2, 16-QAM 1/2, 64-QAM 1/2, 64-QAM 3/4, and the like. The different MCSs provide trade-offs between bandwidth efficiency and transmission reliability. For example, one such MCS may have greater transmission reliability than a second such MCS. The first MCS may therefore need to be used to achieve satisfactory communication while the condition of the transmission link is relatively poor. However, such a greater-reliability MCS may be relatively slow and/or may consume greater bandwidth. Therefore, when communication link conditions improve, it may be advantageous to switch to use of another MCS with lesser but still adequate transmission reliability. 
     The type of communication known as persistent scheduling employs one burst of initiation command signals followed by a specified number of successive bursts of “payload” data signals. Among other parameters, the initiation command burst establishes what MCS will be used for all subsequent payload bursts (at least until the next full initiation command burst). Persistent scheduling can be efficient because persistent scheduling confines all set-up instructions to the initiation burst, and then allows several payload bursts to be transmitted free of such set-up information. This makes the payload bursts more efficient. A problem or inefficiency can arise, however, if transmission link conditions change significantly subsequent to transmission of an initiation burst and during transmission of the following payload bursts. For example, if the transmission link deteriorates, some payload bursts may need to be transmitted more than once until the payload bursts are properly received. On the other hand, if transmission link conditions improve, it is not possible to take advantage of that improvement by switching to a more efficient MCS until after completion of the full persistent scheduling sequence, when another full initiation burst can be sent to change the MCS. 
     SUMMARY 
     In accordance with certain possible aspects of the disclosure, a method of operating transceiver circuitry for electronic communication that can employ any one of a plurality of modulation and coding schemes (“MCSs”) may include selecting a first MCS of the plurality of MCSs; using the first MCS to receive successive bursts of electronic data, at least some of the bursts requiring the transceiver circuitry to transmit an acknowledge (“ACK”) or non-acknowledge (“NAK”) signal respectively indicative of whether or not the transceiver circuitry correctly received the burst; maintaining an electronic record indicative of occurrences of the NAK signal; comparing the record to an electronically stored reference standard; causing the transceiver circuitry to select a second MCS of the plurality of MCSs in response to the record deviating from the reference standard; and using the second MCS to receive further successive bursts of electronic data. 
     In accordance with certain other possible aspects of the disclosure, electronic circuitry for electronic communication using any one of a plurality of MCSs may include receiver circuitry to receive successive bursts of data signals using any one of the plurality of MCSs; decision circuitry to determine whether a burst of data has been properly received, and if not, to cause transmitter circuitry of the electronic circuitry to transmit a NAK signal; record circuitry to maintain a record of occurrences of the NAK signal; and selection control circuitry to select which of the plurality of MCSs is used by the receiver circuitry based on comparison of the record to a reference standard. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified diagram showing an example of known persistent scheduling in electronic communication. 
         FIG. 2  is a simplified transmission sequence diagram showing an example of communication like that illustrated by  FIG. 1 . 
         FIG. 3  is a simplified schematic block diagram showing an illustrative embodiment of apparatus in accordance with the disclosure. 
         FIG. 4  is a simplified schematic block diagram showing another illustrative embodiment of apparatus in accordance with the disclosure. 
         FIG. 5  is a simplified schematic block diagram of an illustrative embodiment of a component that can be used in the  FIG. 3  and/or  FIG. 4  apparatus. 
         FIG. 6  is a table showing correspondence between components that are the same or similar in  FIGS. 3 and 4 . 
         FIGS. 7A and 7B  (sometimes referred to collectively as  FIG. 7 ) are a simplified flow chart of an illustrative embodiment of methods in accordance with certain possible aspects of the disclosure. 
         FIG. 8  is a simplified flow chart of an illustrative embodiment of a modification of a portion of the  FIG. 7  method in accordance with certain other possible aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an example of known wireless electronic communication that is primarily from a base station (“BS”)  10  to a mobile station (“MS”)  20 . An alternative term for base station  10  is eNodeB or the like. Alternative terms for mobile station  20  are mobile unit, user equipment (“UE”), or the like. The communication depicted in  FIG. 1  employs persistent scheduling. Although this example shows primarily “downlink” communication (from base station  10  to mobile station  20 ), it will be understood that the communication can alternatively be “uplink” communication (i.e., from mobile station  20  to base station  10 ), or both downlink and uplink communication. 
     As shown in  FIG. 1 , a persistent scheduling communication sequence begins with initiation command signal burst  12 , which establishes most or all parameters for the subsequent persistent scheduling or payload signal bursts  14   a ,  14   b , etc. For example, initiation command  12  establishes the MCS that will be used for all payload bursts  14  that follow the initiation burst. 
       FIG. 2  shows an example of persistent scheduling communication in the type of communication known as WiMAX. Such communication employs a succession of “frames,” illustratively numbered 1-14 in  FIG. 2 . Each frame reserves times for (1) “MAP” signalling, which can be used for transmitting an initiation command like  12  in  FIG. 1 ; (2) downlink (“DL”) signalling, which can be used for payload data communication from base station  10  to mobile station  20 ; and (3) uplink (“UL”) signalling, which can be used for payload data communication from mobile station  20  to base station  10 . 
     The particular persistent scheduling protocol that has been set up (by the initiation command  12   a  in frame  1 ) intends to send three subsequent downlink payload bursts  14   a ,  14   b , and  14   c  in frames  1 ,  5 , and  9 , respectively. Thus, later in frame  1 , base station  10  sends payload burst  14   a  to mobile station  20 . During the UL phase of subsequent frame  2 , mobile station  20  sends back to base station  10  signals  16   a  that indicate whether or not mobile station  20  successfully received payload burst  14   a . A signal burst (like  16   a ) indicating successful receipt of a payload burst (like  14   a ) is called an “acknowledge” or “ACK” signal. A signal burst (like  16   a ) indicating that a payload burst (like  14   a ) was not successfully received is called a “non-acknowledge” or “NAK” signal. In the particular example shown in  FIG. 2 , signal  16   a  is an ACK signal. This allows the persistent scheduling communication to proceed as originally specified in initiation command  12   a.    
     As a result of the ACK in frame  2 , the persistent scheduling proceeds with the DL of another payload burst  14   b  in frame  5 . This time, however, the payload burst is not successfully received, which causes mobile station  20  to upload a NAK  16   b  in frame  6 . Such a NAK causes the persistent scheduling routine to modify itself as follows. In frame  7  a supplementary initiation command  12   a ′ is sent by base station  10  to tell mobile station  20  to expect a repeat of payload burst  14   b  (now referenced  14   b ′) later in frame  7 . Although other possibilities exist for supplementary initiation burst  12   a ′, one possibility (generally contemplated here) is for burst  12   a ′ to be less than a full initiation burst like  12   a . Instead, burst  12   a ′ can be greatly abbreviated, primarily for the purpose of telling mobile station  20  that a repeat of payload burst  14   b  is coming later in frame  7 , but not otherwise altering the persistent scheduling previously set up in initiation burst  12   a . For example, burst  12   a ′ does not alter the MCS choice or selection made in burst  12   a . The above-mentioned repetition of payload burst  14   b  (now referenced  14   b ′) is then sent.  FIG. 2  shows that this repetition is successfully received, as indicated by the ACK  16   b ′ sent in frame  8 . This allows the original persistent scheduling routine to continue with the transmission of payload burst  14   c  in frame  9 . This payload burst is successfully received, as acknowledged by the ACK  16   c  in frame  10 . Another persistent scheduling routine can begin with another full initiation burst  12   b  in frame  13 . 
     From the foregoing, it will be seen that the typical persistent scheduling scheme does not include the ability to change the MCS that is initially selected, even though the quality of the transmission link may become inappropriate during the persistent scheduling communication. Such inappropriateness may be due to either under-adequacy or over-adequacy of the transmission link for communication using the MCS initially selected. 
     An illustrative embodiment of modifications that can be made to base station and mobile station circuitry in accordance with this disclosure to allow such system components to autonomously change MCS when desirable (and with or without otherwise affecting persistent scheduling) is shown in  FIG. 3 .  FIG. 3  shows a modified base station  100  and a modified mobile unit  200  for communication that is basically DL communication (i.e., like the communication shown in  FIGS. 1 and 2 ). However,  FIG. 4  shows an illustrative embodiment of generally similar circuitry  300  that can be used in either a base station or a mobile unit in order to implement the present disclosure in systems that employ full two-way communication (i.e., both full DL and full UL communication).  FIG. 3  will be described first;  FIG. 4  will be described later. 
     As shown in  FIG. 3 , an illustrative embodiment of base station circuitry  100  in accordance with the disclosure includes transmitter circuitry  110  and receiver circuitry  120 , each of which can be per se conventional. Circuitry  100  may thus sometimes be referred to as transceiver circuitry. Basically, transmitter circuitry  110  transmits data (embodied in electrical, electronic, electro-magnetic, optical, or the like form) from upstream circuitry (not shown, but per se conventional) to mobile unit  200 . For convenience herein, all of the various possible forms of communication between a base station and a mobile unit will sometimes be referred to generically as “electronic communication” of “electronic data” or the like. Similarly, all suitable forms of base stations and mobile units will sometimes be referred to generically as “electronic communication devices” or the like. 
     “Data signal in” lead  108  is the route by which transmitter  110  receives the above-mentioned data signal information from the upstream circuitry. The data on lead  108  may include any MAP or DL data that needs to be sent to mobile unit  200 . The transmission link  112   a  from transmitter  110  to mobile unit  200  may be any form of communication link (typically electrical, electronic, electro-magnetic, optical, or the like, and also typically at least partly wireless). Although a separate return transmission link  112   b  is shown in  FIG. 3 , it will be understood that links  112   a  and  112   b  may be partly or wholly combined into one two-way communication link. 
     In one implementation, transmitter circuitry  110  operates, at least partly, under the control of persistent scheduling control signals  106  that may (like data-in signal  108 ) also come from the above-mentioned upstream circuitry in base station  100 . As just one example of such persistent scheduling control signals  106 , these signals may tell transmitter  110  which one of two or more MCSs the transmitter should use for sending data to mobile  200 . In accordance with the present disclosure, however, such an MCS instruction in signals  106  can be over-ridden or superceded by a different MCS instruction applied to transmitter  110  via lead or leads  192  (the use of which will be described in detail later in this specification). 
     Receiver circuitry  120  receives UL data/information signals from mobile unit  200  via transmission link  112   b . For example, this data may include ACK (e.g.,  16   a  in  FIG. 2 ) or NAK (e.g.,  16   b  in  FIG. 2 ) signals from the mobile unit. Receiver  120  outputs the data the receiver  120  receives via “data signal out” lead  122 . This data output from receiver  120  can go to the above-mentioned upstream circuitry in base station  100  for processing and use in various ways that can be per se conventional. For example, the upstream circuitry can recognize ACK and respond thereto by allowing a persistent scheduling communication sequence to continue without repetition of any already-transmitted data (e.g., as shown in frame  5  in  FIG. 2 ). Alternatively, the upstream circuitry may recognize a NAK and respond thereto by causing transmitter  110  to send a supplementary MAP command or burst  12   a ′ and a repeated payload data burst  14   b ′ as shown in frame  7  in  FIG. 2 . The data output  122  of receiver  120  is also applied to ACK/NAK recognition circuitry  130 . 
     We turn now to more possible aspects of the receiver portion of circuitry  100 . Some of these aspects (such as control  104  and the branch of control  192  that is shown going to receiver  120 ) may not be needed in the base station for DL operation (in which receiver  120  only needs to check the ACK/NAK from transmission link  112   b ). However, these aspects are needed for UL operation, and so they are described here to make the base station transceiver discussion complete for more generalized operation. 
     Like transmitter  110 , receiver  120  may be at least partly controlled by persistent scheduling control signals  104  (similar to or the same as above-described signals  106 ). For example, signals  104  may tell receiver  120  what MCS to use in its operation; although, again, this MCS selection may be over-ridden by a different MCS selection supplied via lead or leads  192  in accordance with this invention. 
     ACK/NAK recognition circuitry  130  can be per se conventional circuitry that can recognize when UL data received from mobile unit  200  is (or includes) an ACK or NAK signal. In addition, circuitry  130  can distinguish ACK from NAK, and can output signals  132  indicative of whether an ACK or a NAK has been received. The output signals  132  of circuitry  130  are applied to ACK and/or NAK record circuitry  140 . 
     Although  FIG. 3  shows circuitry  130  as a separate element, it will be appreciated that the above-mentioned upstream circuitry in base station  100  may also need to perform a similar ACK/NAK recognition function. Thus an alternative way to get the ACK-indicating and NAK-indicating signals  132  needed by circuitry  140  may be to obtain them from the above-mentioned upstream circuitry. 
     ACK and/or NAK record circuitry  140  is circuitry for maintaining a record of recent occurrences of at least NAK signals. An illustrative embodiment of how circuitry  140  may be constructed is shown in  FIG. 5 . In this embodiment, circuitry  140  basically includes a shift register circuit  142  and a summation circuit  146 . Shift register  142  includes a plurality of register stages  144   a  through  144   n . All of stages  144  are clocked by the same “clock” signal, which can be asserted whenever circuitry  130  detects the occurrence of either an ACK signal or a NAK signal. The “data” applied to register  142  for shifting through that register in response to (and in synchronization with) the clock signal is a “NAK” signal (e.g., logic 1 whenever a NAK has occurred, and logic 0 otherwise (e.g., when an ACK has occurred)). Accordingly, at any given time, the ones and zeros stored in registers  144   a  through  144   n  are a record of the n most-recent ACK and NAK signals. For example, register  144   n  will contain the oldest of that ACK/NAK historical data or information, and register  144   a  will contain the newest of that data. The parameter n may have any desired integer value. 
     In addition to passing its data content on to the next register or stage  144  in shift register  142  in response to each assertion of the “clock” signal, each register  144  also applies its current data content to a respective one of the inputs of summation (adder) circuitry  146 . Circuitry  146  adds all the ones and zeros applied to it, and produces output signals  148  indicative of that sum. As an example, if within the n ACK/NAK data samples stored in shift register  142  there have been 4 NAK occurrences, then the output  148  of summation circuitry  146  may be 4 (or any other output proportional to or indicative of 4). 
     Because shift register  142  only retains the n most recent ACK-indicating and NAK-indicating signals (e.g., from circuitry  130 ), the “record” of this data maintained by circuitry  140  is a “moving record.” This means that shift register  142  is always discarding its oldest data (from register stage  144   n ) in order to take in each successive new data item (into register stage  144   a ). The outputs  148  of circuit  146  will therefore tend to move up (increase in numerical value) and down (decrease in numerical value) over time as the number of recent NAKs increases or decreases. Outputs  148  therefore provide a measure of how good a match for current transmission link conditions the current MCS selection is. If outputs  148  are relatively high (e.g., as a fraction or percentage of n), then a lot of NAKs have recently occurred, and the currently selected MCS may not be providing high enough transmission reliability relative to what may be relatively poor transmission link performance. This may call for selection of a different MCS having greater transmission reliability. On the other hand, if outputs  148  are relatively low (e.g., as a fraction or percentage of n), then relatively few NAKs have recently occurred. This may warrant selection of a different MCS having less transmission reliability so that transmission link  112  can be used more efficiently. 
     The embodiment of circuitry  140  that is shown in  FIG. 5  is only an example of how such ACK and/or NAK record circuitry may be constructed. For example, instead of a shift register, one or more counters of various types may be used. As an illustration, a counter that counts up in response to each NAK occurrence and down in response to each ACK occurrence can be used to give an indication of whether there are too many or too few NAKs occurring. Still other variations will be apparent to those skilled in the art. 
     The output signals  148  of circuitry  140  are applied to one set of inputs to compare circuitry  160 . Signals  152  indicative of a reference standard  150  are applied to a second set of inputs to compare circuitry  160 . Reference standard element  150  may be circuitry (e.g., memory circuitry) for storing and outputting (on leads  152 ) signals indicative of what the outputs  148  of circuitry  140  should be if the MCS currently being used is reasonably appropriate (e.g., not causing too many or too few NAKs). Reference standard  150  may have more than one threshold. For example, it may output an upper limit threshold and a lower limit threshold, each of which is compared by compare circuitry  160  to the ACK/NAK record output signals  148  from circuitry  140 . To take a specific example of this, the upper limit may be 6 and the lower limit may be 0. When compare circuitry  160  detects that signals  148  have reached 6, circuitry  160  may output a signal  162  causing MCS selection control store circuitry  170  to increment (increase by 1) a value stored in (and output by) circuitry  170 . On the other hand, when compare circuitry  160  detects that signals  148  have reached 0, circuitry  160  may output a signal  162  causing circuitry  170  to decrement (decrease by 1) a value stored in (and output by) circuitry  170 . As long as outputs  148  are between 0 and 6, circuitry  160  outputs a “no change” signal  162 , which leaves the value stored in and output by circuitry  170  unchanged. 
     From the foregoing it will be appreciated that an illustrative embodiment of circuitry  170  may be a counter that counts up in response to an “increment” output signal  162 , that counts down in response to a “decrement” signal, and that does not change its count while output signal  162  indicates “no change.” Other constructions for circuitry  170  will be apparent to those skilled in the art. 
     The output signals  172  of circuitry  170  are applied to selection control inputs of multiplexer (“mux”) circuitry  190 . The selectable inputs  182  to mux circuitry  190  come from MCS protocols storage circuitry  180 . Each line  182  in  FIG. 3  typically represents several signal leads, sufficient in number to provide at least a unique signal code for each MCS that the  FIG. 3  circuitry can use. For simplicity (although this is not a requirement) it is assumed that these MCS codes (or other MCS signal information) are stored in (and output by) circuitry  180  in order of the transmission reliability that each MCS provides (so-called “hierarchical order”). Thus, for example, the MCS indicated by the information on the top-most line  182  may have the greatest transmission reliability measure. The MCS indicated by the information in the next-to-topmost line  182  may have the next-to-greatest transmission reliability measure. This hierarchical ordering may continue until the MCS indicated by the information on the bottom-most line  182  is reached, which MCS may have the least transmission reliability measure. (As some specific examples, transmission reliability decreases for illustrative MCSs QPSK 1/4, QPSK 1/2, 16-QAM 1/2, 64-QAM 1/2, and 64-QAM 3/4, in that order. (On the other hand, bandwidth efficiency increases.)) In such an example, a relatively high value  172  output by circuitry  170  causes mux  190  to select and output (on leads  192 ) MCS identifying or specifying signal information from a relatively high line  182 . This will be information for an MCS that gives relatively high transmission reliability. Conversely, a relatively low value  172  output by circuitry  170  causes mux  190  to select and output (on leads  192 ) MCS identifying or specifying signal information from a relatively low line  182 . This will be information for an MCS that gives relatively low transmission reliability. 
     The signals  192  output by mux  190  are applied to transmitter  110 . If these signals  192  indicate a different MCS than transmitter  110  is currently using, then transmitter  110  switches to using that different MCS. Signals  192  may also be applied to receiver  120 , with similar effect on that circuitry. In other words, if signals  192  indicate a different MCS than receiver  120  is currently using, then receiver  120  switches to using that new MCS. In this way the circuitry of this invention can cause base station  100  to autonomously and automatically change the MCS the circuitry is using to better match the actual, current condition of transmission link  112 . If transmission link  112  is currently poor, leading to an undesirably high incidence or rate of NAKs, base station  100  automatically switches to an MCS that gives greater transmission reliability. On the other hand, if link  112  is performing well, resulting in a very low incidence or rate of NAKs, then the current MCS may be more reliable than is really needed for satisfactory communication, and base station  100  automatically switches to an MCS that has less transmission reliability. As noted above, these MCS changes are made autonomously by the circuitry shown in  FIG. 3  and (in one implementation) without otherwise changing or interrupting persistent scheduling communication that may be in progress. From the next section of this description it will be apparent that it is not necessary for base station  100  to communicate its autonomous MCS changes to mobile unit  200 , because mobile unit  200  is constructed and operated to independently, automatically, and autonomously mirror all MCS changes that base station  100  makes for itself. 
     Turning now to mobile unit  200 , that circuitry includes receiver circuitry  210  and transmitter circuitry  220 , both of which can be per se conventional. Circuitry  200  may thus sometimes be referred to as transceiver circuitry. Receiver  210  receives signals from link  112   a  and outputs those signals at  212 . Outputs  212  go to downstream circuitry (not shown, but per se conventional) in mobile unit  200  for whatever use is to be made of received signals. Outputs  212  are also applied to ACK/NAK decision circuitry  221 . The operation of receiver  210  may be at least partly controlled by persistent scheduling control signals  206 , which may come from the above-mentioned downstream circuitry in mobile unit  200 . Again, however, the MCS selection made by signals  206  may be over-ridden by signals  282  (described below). 
     ACK/NAK decision circuitry  221  examines received signals  212  to determine whether or not the received signals have been transmitted and received properly. If so, that is an ACK condition; if not, that is a NAK condition. If ACK/NAK decision circuitry  221  detects an ACK condition, ACK/NAK decision circuitry  221  generates ACK output signals on leads  222 , which transmitter circuitry  220  sends back to base station  100  via link  112   b . This is like the ACK UL  16   a  in frame  2  of  FIG. 2 . On the other hand, if ACK/NAK decision circuitry  221  detects a NAK condition, ACK/NAK decision circuitry  221  generates NAK output signals on leads  222 , which transmitter  220  sends back to base station  100  via link  112   b . This is like the NAK UL  16   b  in frame  6  of  FIG. 2 . 
     In addition to producing the ACK or NAK signals  222  that mobile unit  200  uplinks to base station  100 , ACK/NAK decision circuitry  221  outputs signals  224  indicative of whether ACK/NAK decision circuitry  221  has detected an ACK condition or a NAK condition. 
     Analogous to what was said about element  130  earlier, the above-mentioned downstream circuitry in mobile unit  200  may also need to (conventionally) perform functions like those performed by element  221 . Thus an alternative source for signals  222  and  224  may be the above-mentioned downstream circuitry, so that element  221  does not have to be separately (or duplicatively) provided. 
     It will be appreciated that the output signals  224  of circuitry  220  are not only similar to signals  132 , but that these signals  224  are also logically the same as the substantially concurrent signals  132 . In other words, signals  132  necessarily mirror signals  224  as a result of the conventional transmission of conventional ACKs and NAKs generated by mobile unit  200  to base station  100 . No additional signalling or communication between base station  100  and mobile unit  200  (beyond this conventional (prior art as in  FIG. 2 ) ACK and NAK signalling) is needed to cause signals  132  and  224  to thus synchronously mirror (duplicate) one another. 
     Signals  224  are applied to ACK and/or NAK record circuitry  230 , which can be the same as element  140  in base station  100 . Because these elements are the same, and because they receive signals that are logically the same at logically the same time, element  230  outputs signals  232  that approximately concurrently mirror output signals  148  of element  140 . 
     Compare circuitry  250  can be the same as base station element  160 . MCS selection control store circuitry  260  can be the same as base station element  170 . MCS protocols storage circuitry  270  can be the same as base station element  180 . And mux  280  can be the same as base station element  190 . The information stored in elements  240  and  150  can be the same. The information stored in elements  270  and  180  can also be the same. The above similarities mean that the outputs  282  of mobile unit mux  280  approximately concurrently (i.e., at logically the same time, but in reality after (small) transmission and propagation delay of the ACK/NAK signal from MS to BS in the DL operation) mirror the outputs  192  of base station mux  190 . Accordingly, whenever the base station circuitry shown in  FIG. 3  is making a change in the MCS used by transmitter  110 , the mobile station circuitry shown in  FIG. 3  automatically, autonomously, and independently makes the same change in the MCS used by receiver  210 . Elements  110  and  210  can thereby continue to “talk to” one another uninterruptedly, even though the MCS used on link  112   a  may have changed. Moreover, this communication can continue without disturbing, interrupting, or otherwise altering an on-going persistent scheduling communication sequence. No new, additional, or supplementary initiation or MAP data needs to be communicated to effect this MCS change. Elements  100  and  200  remain synchronized with one another with respect to what MCS is being used solely as a result of the conventional transmission of the conventional ACK and NAK signals or bursts (e.g., as at  16   a ,  16   b ,  16   b ′, and  16   c  in  FIG. 2 ). 
     If the MCS used by base station receiver  120  also changes with a transmitter  110  MCS change (e.g., in the more general case that the circuitry is intended to handle UL as well as DL communication), then the outputs  282  of mobile unit mux  280  should also be applied to mobile unit transmitter  220  to keep that element&#39;s MCS selection synchronized with the MCS of receiver  120 . On the other hand, the branch of output  282  to transmitter  220  may not be needed in the mobile unit for DL operation (in which transmitter  220  only needs to send the ACK/NAK over transmission link  112   b ). 
       FIG. 4  shows an illustrative embodiment of transceiver circuitry  300  in accordance with the disclosure that can be used in either a base station or a mobile unit. In one implementation, one instance of circuitry  300  can be used in a base station, and another instance of circuitry  300  can be used in a mobile unit. In such a system, base station transmission link terminals  312   a  and  312   b  are operatively coupled to mobile unit transmission link terminals  312   b  and  312   a , respectively. Such a system can be used for full, two-way (i.e., DL and UL) communication between the base station and the mobile unit. Thus either of these components can send data bursts to the other component, and either component can generate and send ACK and NAK signal bursts to the other component. On the other hand, it may still be the case that only the base station can send MAP bursts. 
       FIG. 6  shows that all of the circuit components in  FIG. 4  are either the same as or very similar to one or two components in  FIG. 3 . For example, element  310  in  FIG. 4  is the same as or similar to either of elements  110  and  220  in  FIG. 3 . It will therefore not be necessary to again describe most of the elements in  FIG. 4 , because they are already explained by the earlier description(s) of the corresponding element(s) in  FIG. 3 . 
     The only significant difference between  FIG. 4  and earlier-described  FIG. 3  is that in  FIG. 4  each instance of circuitry  300  can both generate an ACK or NAK signal (element  330   a ), and recognize an incoming ACK or NAK signal that has been received from the other instance of circuitry  300  (element  330   b ). ACK and/or NAK record circuitry  340  can maintain a record of both of these kinds of ACK and/or NAK occurrences. For example, circuitry  340  may maintain one combined record for all of these ACK and/or NAK occurrences (i.e., ACK/NAK signals originated locally by the same device  300 , and ACK/NAK signals originated remotely by the other device  300  in the pair of devices that is communicating via link  312 ). Each instance of circuitry  300  is therefore independently and automatically monitoring the success rate of communication in both directions between a base station and a mobile unit. Both of these base and mobile components monitor this success rate in the same way and apply the same reference standard  350  to the results of that monitoring. Thus both component  300  instances autonomously and concurrently (i.e., at logically the same time, but in reality after (small) transmission and propagation delay of the ACK/NAK signals between the MS and BS) reach the same conclusion about whether the MCS currently being used should continue to be used. If circuitries  300  determine that the current MCS should not continue to be used, then both of circuitries  300  autonomously and concurrently change to the same new MCS so that communication can continue uninterrupted. In particular, any persistent scheduling communication that is underway can proceed with only a change in MCS. (Note that if the  FIG. 4  circuitry is to be employed in a DL-only system, then some of the control connections shown in  FIG. 4  can be omitted as mentioned in the earlier discussion of  FIG. 3 . Which control connections are omitted will depend on whether a particular instance of the  FIG. 4  circuitry is in the BS or the MS.) 
     Methods of operating circuitry in accordance with this disclosure will be apparent to those skilled in the art from the information that has been provided thus far. As a further aid with regard to such operating methods, an example is provided in  FIGS. 7A and 7B  (which may sometimes be referred to collectively as  FIG. 7 ).  FIG. 7  shows an illustrative embodiment of operating transceiver circuitry (e.g., a mobile unit like  200  or  300  in the earlier disclosure).  FIG. 7  concentrates on the DL operations of mobile unit or MS transceiver circuitry, but it will be apparent from other disclosure herein how the transceiver can also include UL operations and/or be a BS transceiver (see also  FIG. 8 ). 
     At  710  in  FIG. 7A  the transceiver circuitry selects a first MCS. This may be done in response to a MAP initiation command received by the transceiver from a base station transmitter. At  712  the transceiver uses the first MCS to receive successive bursts of electronic data. Such bursts may be DL bursts from a base station transmitter. 
     At  720 , for any received burst that requires an ACK or NAK response indicating whether or not the burst was correctly received, the transceiver transmits the appropriate ACK or NAK signal. 
     Operation  730  shows that the transceiver maintains an electronic record (e.g., as in element  230  in  FIG. 3 ) of occurrences of the NAK signal. 
     At  740  the transceiver compares (e.g., as in element  250  in  FIG. 3 ) the record (e.g., from element  230 ) to an electronically stored reference standard (e.g., from element  240  in  FIG. 3 ). For example, as described earlier in this disclosure, the reference standard may indicate an acceptable range for the number of NAK signals that have occurred for a predetermined number of the most recent attempted data burst receptions. If the actual record of NAK signals is not within that range, then it has “deviated” from the reference standard. Operation  750  (related to operation  740 ) tests whether the record deviates from the reference standard. 
     If operation  750  produces a negative (“no”) result, then control passes to operation  760 , which allows the transceiver to continue to use the currently selected MCS. Control accordingly loops back from operation  760  to operation  720 . This is analogous, for example, to a “no change” output from element  250  in  FIG. 3 . 
     On the other hand, if operation  750  produces a positive (“yes”) result, then control passes to operation  770 , in which the transceiver selects another, different MCS. This is analogous to an “increment” or “decrement” output from element  250  in  FIG. 3 , for example; and it is further analogous to the operation of elements  260 ,  270 , and  280  in  FIG. 3 , for example, to cause a different MCS to be selected by the transceiver. As described earlier in this disclosure, the other, different MCS that is thus selected may have greater transmission reliability or less transmission reliability than the previously selected MCS, depending on how operation  750  found the record to deviate from the reference standard. 
     At  780  the transceiver begins to use the newly selected, different MCS to receive successive bursts of electronic data. From  780 , control loops back to  720  where operation of the transceiver continues using the newly selected, different MCS. 
     As mentioned earlier,  FIG. 8  shows an illustrative embodiment of modification of the transceiver (e.g., mobile unit) operating method of  FIG. 7  to include in the transceiver the ability to maintain a record of both the NAK signals it generates and any NAK signals it receives (e.g., from a base station transmitter). The  FIG. 8  modifications to the operating method of  FIG. 7  produce an operating method that can be implemented in transceiver circuitry constructed as shown, for example, in  FIG. 4 . Except for the added operations  822  and  824  shown in  FIG. 8 , this transceiver operating method can be as shown in  FIG. 7 . It will therefore not be necessary to again describe any operations with reference numbers in the  700  series. Only added operations  822  and  824  will be described below. 
     In operation  822 , the transceiver circuitry detects whether signals it has received are a NAK signal. This is analogous to what is done in element  330   b  in  FIG. 4 , for example. If the result of operation  822  is negative, control simply passes to previously described operation  740 . On the other hand, if the result of operation  822  is positive, then control passes to operation  824 . 
     In operation  824  the transceiver circuitry includes in the record it is maintaining (e.g., as in element  340  in  FIG. 4 ) the occurrence of the received NAK signal. The record of NAK signals is therefore a record of both NAK signals generated by the transceiver and NAK signals received by the transceiver. From operation  824  control passes to previously described operation  740 . 
     It will be understood that the foregoing is only illustrative of the principles of the disclosure, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the disclosure. For example, although some of the terms and illustrative examples employed herein are usually associated with WiMAX communication, it will be understood that the disclosure is equally applicable to many other forms of wireless communication employing persistent scheduling such as 3GPP LTE systems with semi-persistent scheduling (“SPS”). In addition, one or more steps of methods disclosed above may be performed in a different order (or concurrently) and still achieve desirable results. An exemplary use of the disclosure is for voice-over-internet protocol (“VoIP”) communication.