Abstract:
An apparatus includes a transmitter to transmit a first orthogonal frequency-division multiplexing signal including a first signal burst with a plurality of first fields of a first type. Each of a plurality of pair fields includes a second field of a second type and a third field of a third type. The second type is different than the first type and the third type is different than the first type and the second type. Each first field in the first signal burst is transmittable prior to a corresponding pair field of the plurality of pair fields. Each second field of a given pair field comprises an indicator to indicate whether a first field is transmitted subsequent to the given pair field. A controller selects a number of pair fields to be transmitted in the first signal burst of the first orthogonal frequency-division multiplexing signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/143,049, filed Jun. 2, 2005, which claims the benefit of U.S. Provisional Patent Application No. 60/653,220, filed Feb. 14, 2005, and claims the benefit of U.S. Provisional Patent Application No. 60/685,522, filed May 27, 2005, the disclosures thereof incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     The present invention relates generally to data communications. More particularly, the present invention relates to automatic gain control for orthogonal frequency-division multiplexing (OFDM) receivers in local area network (LAN) systems. 
     In OFDM wireless LANs (WLANs) such as those specified by IEEE Standard 802.11a, 802.11g, and 802.11n, data is transmitted in bursts of variable duration that are separated by inter-burst gaps of fixed duration.  FIG. 1  shows a conventional OFDM WLAN signal  100  comprising a plurality of bursts  102 A-K separated by inter-burst gaps (ISG)  103 . Each burst  102  comprises a plurality of preamble fields  106 A,B-N, each followed by a respective signal field  108 A,B-N and a respective payload field  110 A,B-N each comprising a packet of data  112 A,B-N. 
     Payload fields  110  comprise packets  112  of variable length, and so are of variable duration, generally on the order of ten or 100 microseconds. In contrast, preamble fields  106  are used by the receiver of signal  100  to acquire signal  100 , and so must have a predetermined minimum duration on the order of tens of microseconds. Therefore, in many cases, preambles  106  constitute the majority of the bandwidth of signal  100 . 
     SUMMARY 
     In general, in one aspect, the invention features an apparatus to communicate data, comprising: a transmitter to transmit an orthogonal frequency-division multiplexing (OFDM) signal comprising a plurality of signal bursts each comprising m preamble fields, n payload fields, and n signal fields; wherein m&lt;n; wherein each of the m preamble fields comprises a plurality of training sequences; wherein each of the n payload fields is preceded by one of the n signal fields; wherein each one of the n signal fields comprises information describing the following one of the n payload fields, and preamble data, wherein the preamble data in one of the n payload fields is set to a predetermined value only when one of the m preambles occurs between the one of the n signal fields and the next one of the n signal fields; wherein each of the n payload fields comprises a packet of the data; and a controller to select a value of n for each of the signal bursts of the OFDM signal. 
     Particular implementations can include one or more of the following features. In some embodiments, the controller selects a value of m for each of the signal bursts of the OFDM signal. Some embodiments comprise a receiver to receive a second OFDM signal responsive to the OFDM signal, wherein the second OFDM signal comprises a description of a quality of reception of the OFDM signal; and wherein the controller selects the value of n for each of the signal bursts of the OFDM signal based on the description of the quality of reception of the OFDM signal. In some embodiments, the description of the quality of reception of the OFDM signal comprises at least one of the group consisting of: a number of the packets of the data received; a number of the packets of the data not received; a signal level of the OFDM signal; and a link margin of the OFDM signal. In some embodiments, at least one of the n payload fields is followed by an inter-frame gap; and wherein the one of the n signal fields preceding the at least one of the n payload fields comprises an inter-frame gap value that indicates the duration of the one of the inter-frame gaps following the at least one of the n payload fields. In some embodiments, a second receiver receives the OFDM signal and controls a gain of the OFDM signal based on a signal level of the OFDM signal during each one of the m preambles when the preamble data is set to the predetermined value in the one of the n signal fields preceding the one of the m preambles. In some embodiments, the apparatus is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11a, 802.11g, and 802.11n. 
     In general, in one aspect, the invention features an apparatus to communicate data, comprising: a transmitter to transmit a signal comprising a plurality of signal bursts each comprising m preamble fields, n payload fields, and n signal fields; wherein m&lt;n; wherein each of the m preamble fields comprises a plurality of training sequences; wherein each of the n payload fields is preceded by one of the n signal fields; wherein each one of the n signal fields comprises information describing the following one of the n payload fields, and preamble data, wherein the preamble data in one of the n payload fields is set to a predetermined value only when one of the m preambles occurs between the one of the n signal fields and the next one of the n signal fields; wherein each of the n payload fields comprises a packet of the data; and a controller to select a value of n for each of the signal bursts of the signal. 
     In general, in one aspect, the invention features a method to communicate data, comprising: transmitting a orthogonal frequency-division multiplexing (OFDM) signal comprising a plurality of signal bursts each comprising m preamble fields, n payload fields, and n signal fields; wherein m&lt;n; wherein each of the m preamble fields comprises a plurality of training sequences; wherein each of the n payload fields is preceded by one of the n signal fields; wherein each one of the n signal fields comprises information describing the following one of the n payload fields, and preamble data, wherein the preamble data in one of the n payload fields is set to a predetermined value only when one of the m preambles occurs between the one of the n signal fields and the next one of the n signal fields; wherein each of the n payload fields comprises a packet of the data; and selecting a values of n for each of the signal bursts of the OFDM signal. 
     Particular implementations can include one or more of the following features. Some embodiments comprise selecting a value of m for each of the signal bursts of the OFDM signal. Some embodiments comprise receiving a second OFDM signal responsive to the OFDM signal, wherein the second OFDM signal comprises a description of a quality of reception of the OFDM signal; and selecting the value of n for each of the signal bursts of the OFDM signal based on the description of the quality of reception of the OFDM signal. In some embodiments, the description of the quality of reception of the OFDM signal comprises at least one of the group consisting of: a number of the packets of the data received; a number of the packets of the data not received; a signal level of the OFDM signal; and a link margin of the OFDM signal. In some embodiments, at least one of the n payload fields is followed by an inter-frame gap; and wherein the one of the n signal fields preceding the at least one of the n payload fields comprises an inter-frame gap value that indicates the duration of the one of the inter-frame gaps following the at least one of the n payload fields. In some embodiments, a receiver of the OFDM signal controls a gain of the OFDM signal based on a signal level of the OFDM signal during each one of the m preambles when the preamble data is set to the predetermined value in the one of the n signal fields preceding the one of the m preambles. In some embodiments, the method is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11a, 802.11g, and 802.11n. 
     In general, in one aspect, the invention features an apparatus to communicate data, comprising: a receiver to receive a orthogonal frequency-division multiplexing (OFDM) signal comprising a plurality of signal bursts each comprising m preamble fields, n payload fields, and n signal fields; wherein m&lt;n; wherein each of the m preamble fields comprises a plurality of training sequences; wherein each of the n payload fields is preceded by one of the n signal fields; wherein each one of the n signal fields comprises information describing the following one of the n payload fields, and preamble data, wherein the preamble data in one of the n payload fields is set to a predetermined value only when one of the m preambles occurs between the one of the n signal fields and the next one of the n signal fields; wherein each of the n payload fields comprises a packet of the data; and an automatic gain control circuit to control a receiver gain of the OFDM signal based on a signal level of the OFDM signal during each one of the m preambles when the preamble data is set to the predetermined value in the one of the n signal fields preceding the one of the m preambles. 
     Particular implementations can include one or more of the following features. Some embodiments comprise a transmitter to transmit a second OFDM signal, wherein the second OFDM signal comprises a description of a quality of reception of the OFDM signal. Some embodiments comprise wherein a second transmitter transmits the OFDM signal, receives the second OFDM signal and selects the value of n for each of the signal bursts of the OFDM signal based on the description of the quality of reception of the OFDM signal. In some embodiments, the description of the quality of reception of the OFDM signal comprises at least one of the group consisting of: a number of the packets of the data received; a number of the packets of the data not received; a signal level of the OFDM signal; and a link margin of the OFDM signal. In some embodiments, at least one of the n payload fields is followed by an inter-frame gap; and wherein the one of the n signal fields preceding the at least one of the n payload fields comprises an inter-frame gap value that indicates the duration of the one of the inter-frame gaps following the at least one of the n payload fields. In some embodiments, the apparatus is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11a, 802.11g, and 802.11n. 
     In general, in one aspect, the invention features an apparatus to communicate data, comprising: a receiver to receive a signal comprising a plurality of signal bursts each comprising m preamble fields, n payload fields, and n signal fields; wherein m&lt;n; wherein each of the m preamble fields comprises a plurality of training sequences; wherein each of the n payload fields is preceded by one of the n signal fields; wherein each one of the n signal fields comprises information describing the following one of the n payload fields, and preamble data, wherein the preamble data in one of the n payload fields is set to a predetermined value only when one of the m preambles occurs between the one of the n signal fields and the next one of the n signal fields; wherein each of the n payload fields comprises a packet of the data; and an automatic gain control circuit to control a receiver gain of the signal based on a signal level of the signal during each one of the m preambles when the preamble data is set to the predetermined value in the one of the n signal fields preceding the one of the m preambles. 
     In general, in one aspect, the invention features a method to communicate data, comprising: receiving a orthogonal frequency-division multiplexing (OFDM) signal comprising a plurality of signal bursts each comprising m preamble fields, n payload fields, and n signal fields; wherein m&lt;n; wherein each of the m preamble fields comprises a plurality of training sequences; wherein each of the n payload fields is preceded by one of the n signal fields; wherein each one of the n signal fields comprises information describing the following one of the n payload fields, and preamble data, wherein the preamble data in one of the n payload fields is set to a predetermined value only when one of the m preambles occurs between the one of the n signal fields and the next one of the n signal fields; wherein each of the n payload fields comprises a packet of the data; and controlling a receiver gain of the OFDM signal based on a signal level of the OFDM signal during each one of the m preambles when the preamble data is set to the predetermined value in the one of the n signal fields preceding the one of the m preambles. 
     Particular implementations can include one or more of the following features. Some embodiments comprise transmitting a second OFDM signal, wherein the second OFDM signal comprises a description of a quality of reception of the OFDM signal. In some embodiments, a transmitter of the OFDM signal receives the second OFDM signal and selects the value of n for each of the signal bursts of the OFDM signal based on the description of the quality of reception of the OFDM signal. In some embodiments, the description of the quality of reception of the OFDM signal comprises at least one of the group consisting of: a number of the packets of the data received; a number of the packets of the data not received; a signal level of the OFDM signal; and a link margin of the OFDM signal. In some embodiments, at least one of the n payload fields is followed by an inter-frame gap; and wherein the one of the n signal fields preceding the at least one of the n payload fields comprises an inter-frame gap value that indicates the duration of the one of the inter-frame gaps following the at least one of the n payload fields. In some embodiments, the method is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11a, 802.11g, and 802.11n. 
     In general, in one aspect, the invention features a signal comprising: a plurality of signal bursts each comprising m preamble fields, n payload fields, and n signal fields; wherein m&lt;n; wherein each of the m preamble fields comprises a plurality of training sequences; wherein each of the n payload fields is preceded by one of the n signal fields; wherein each one of the n signal fields comprises information describing the following one of the n payload fields, and preamble data, wherein the preamble data in one of the n payload fields is set to a predetermined value only when one of the m preambles occurs between the one of the n signal fields and the next one of the n signal fields. 
     Particular implementations can include one or more of the following features. In some embodiments, at least one of the n payload fields is followed by an inter-frame gap; and wherein the one of the n signal fields preceding the at least one of the n payload fields comprises an inter-frame gap value that indicates the duration of the one of the inter-frame gaps following the at least one of the n payload fields. In some embodiments, the signal is an orthogonal frequency-division multiplexing (OFDM) signal. In some embodiments, the signal is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11a, 802.11g, and 802.11n. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a conventional OFDM WLAN signal comprising a plurality of bursts separated by inter-burst gaps (IBG). 
         FIG. 2  shows a OFDM WLAN signal comprising a plurality of bursts each comprising only one preamble and multiple data packets according to a preferred embodiment of the present invention. 
         FIG. 3  shows a OFDM WLAN signal comprising multiple bursts each comprising multiple preambles and multiple data packets according to a preferred embodiment of the present invention. 
         FIG. 4  shows a transmitter according to a preferred embodiment of the present invention. 
         FIG. 5  shows a process for the transmitter of  FIG. 4  according to a preferred embodiment. 
         FIG. 6  shows a receiver according to a preferred embodiment of the present invention. 
         FIG. 7  shows a process for the receiver of  FIG. 6  according to a preferred embodiment. 
         FIG. 8  shows eight plots of throughput (Mbps) vs. packet size (Bytes). 
     
    
    
     The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention produce and utilize a signal comprising one or more signal bursts each comprising fewer preamble fields than data fields. While embodiments of the present invention are discussed in terms of OFDM WLAN signals such as those specified by IEEE Standard 802.11a, 802.11g, and 802.11n, other embodiments employ other signals, including point-to-point signals as well as network signals. In addition, embodiments of the present invention are not limited to wireless communications. 
       FIG. 2  shows a OFDM WLAN signal  200  comprising a plurality of bursts  202 A-K each comprising only one preamble  206  and multiple data packets  212  according to a preferred embodiment of the present invention. Bursts  202  are separated by inter-burst gaps (IBG)  203 . Each burst  202  comprises one preamble field  206  and N payload fields  210 A,B-N where N&gt;1, each preceded by a respective signal field  208 A,B-N. Each payload field  210  (except the last in a burst  202 ) is followed by a respective inter-frame gap (IFG)  204 A,B-N-1. 
     Preamble fields  206  contain training sequences that allow receivers of signal  200  to acquire signal  200 , and to set a receiver gain for signal  200 , as is well-known in the relevant arts. Each signal field  208  comprises information describing the following payload field  210  such as data rate, the number of antennas used for multiple-input multiple-output (MIMO) systems, and the like, as is also well-known in the relevant arts. Each payload field  210 A-N comprises a respective packet of data  212 A-N. 
     The value of N can be fixed or can be selected dynamically by a transmitter of signal  200 , for example based on feedback describing the quality of reception of signal  200  by a receiver of signal  200 . One advantage of signal  200  over prior art signal  100  is that, by using fewer preambles, the effective data bandwidth of signal  200  is greater. 
     In order for a receiver of signal  200  to properly utilize preamble fields  206 , the receiver must predict when a preamble field  206  is due to arrive at the receiver. In conventional signals such as signal  100  of  FIG. 1 , each inter-frame gap  104  has a known, fixed duration, and is followed by a preamble  106  having a known, fixed duration. Therefore a receiver can easily predict the arrival of each preamble  106 . 
     But in signal  200  not every inter-frame gap  204  is followed by a preamble  206 . Therefore, according to a preferred embodiment, each signal field  208  comprises preamble data such as a preamble flag (PF) that is set to a predetermined value only when a preamble  206  occurs between that signal field  208  and the next one of the signal fields  208 . For example, referring to  FIG. 2 , preamble flag PF is clear in each of the signal fields  208 A through  208 N-1, but is set in signal field  208 N. 
     Referring again to  FIG. 2 , the inventor has recognized that the duration of each inter-frame gap  204  that is not followed by a preamble can be reduced. Therefore, according to some embodiments, each signal field  208  includes an optional inter-frame gap duration value (IFGDV) that indicates the duration of the next inter-frame gap  204 . For example, the IFGDV can be a two-bit binary number indicating one of four durations ranging from two to eight microseconds. As another example, the IFGDV can be a gap flag GF indicating one of two predetermined durations: a “normal” duration for a inter-frame gap  204  that immediately precedes a preamble  206  and a “short” duration when no preamble  206  immediately follows the inter-frame gap  204 . In some embodiments, a single flag is used for both preamble and gap. That is, when the single flag is set, a preamble  206  immediately follows the next inter-frame gap  204  so a long gap duration is used, and when the single flag is clear, no preamble  206  immediately follows the next inter-frame gap  204  so a short gap duration is used. 
     In some embodiments, the signal bursts are so long that it is useful to change the receiver gain multiple times during a single burst. Therefore some embodiments of the present invention include two or more preambles in each burst. In particular, these bursts comprise m preambles, n signal fields, and n payload fields, where m&lt;n. 
       FIG. 3  shows a OFDM WLAN signal  300  comprising multiple bursts  302 A-K each comprising multiple preambles  306  and multiple data packets  312  according to a preferred embodiment of the present invention. Bursts  302  are separated by inter-burst gaps (IBG)  303 . Each burst  302  comprises M preamble fields  306 A-M and N payload fields  310 A-N each preceded by a signal field  308 A-N where M&gt;N. Each payload field  310  (except the last in a burst  302 ) is followed by a respective inter-frame gap (IFG)  304 A-N-1. 
     Preamble fields  306  contain training sequences that allow receivers of signal  300  to acquire signal  300 , and to set a receiver gain for signal  300 , as is well-known in the relevant arts. Each signal field  308  comprises information describing the following payload field  310  such as data rate, the number of antennas used for MIMO systems, and the like, as is also well-known in the relevant arts. Each payload field  310 A-N comprises a respective packet of data  312 A-N. 
     The values of N and M can be fixed or can be selected dynamically by a transmitter of signal  300 , for example based on feedback describing the quality of reception of signal  300  by a receiver of signal  300 . One advantage of signal  300  over prior art signal  100  is that, by using fewer preambles, the effective data bandwidth of signal  300  is greater. 
     To enable a receiver of signal  300  to predict when a preamble field  306  is due to arrive at the receiver, according to a preferred embodiment, each signal field  308  comprises a preamble flag (PF) that is set only when a preamble  306  occurs between that signal field  308  and the next one of the signal fields  308 . For example, referring to  FIG. 3  when M=2, preamble flag PF is set in burst  302  only in the signal field  308  immediately preceding the second preamble  306 B, and in the last signal field  308 N. 
     In some embodiments, signal field  308  includes an inter-frame gap duration value (IFGDV) or gap flag GF that functions as described above for  FIG. 2 . 
       FIG. 4  shows a transmitter  400  according to a preferred embodiment of the present invention. Transmitter  400  comprises an antenna  402  for transmitting signal  300 , a front end  404 , and a baseband processor  406 . Baseband processor  406  comprises a controller  408 , a buffer  410  to store packets  312  of data to be transmitted, and a switch  412  such as a multiplexer (MUX) to pass packets  312  of data from buffer  410  to front end  404 , and to pass control data including preambles  306  and signal fields  308  from controller  408  to front end  404 . While  FIG. 4  indicates one example of a configuration for transmitter  400 , embodiments of the present invention are not limited by that configuration. Some embodiment comprise an optional receiver  414  to receive feedback information from a receiver of signal  300 . In some embodiments, transmitter  400  is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11a, 802.11g, and 802.11n. 
       FIG. 5  shows a process  500  for transmitter  400  of  FIG. 4  according to a preferred embodiment. In the example of  FIG. 5 , the inter-frame gap duration value is represented by a gap flag GF that when clear indicates a “normal” duration for the next inter-frame gap  304  (for example, on the order of 2 microseconds), and when set indicates a “short” duration for the next inter-frame gap  304  (for example, on the order of a fraction of a microsecond). 
     Baseband processor  406  receives packets  312  of data to be transmitted, and buffers the packets  312  in transmit buffer  410 . Controller  408  of baseband processor  406  optionally selects a number n of signal fields  308  and payload fields  310  to be transmitted in each of one or more subsequent signal bursts  302  to be transmitted (step  502 ). The number n can be fixed within transmitter  400 , can be communicated to transmitter  400 , or can be selected by controller  408  of transmitter  400 , for example based upon feedback from a receiver of the transmitted signal  300 . For example, receiver  414  can receive a description of a quality of reception of signal  300  that comprises a number of the packets  312  of the data received, a number of the packets  312  of the data not received, a signal level of wireless signal  300 , a link margin of the wireless signal  300 , and the like. 
     In embodiments where more that one preamble  306  can be transmitted in each signal burst  302 , controller  408  optionally selects a number m of preambles  306  to be transmitted in each of one or more subsequent signal bursts  302  to be transmitted (step  504 ), where m&lt;n, and selects the location of each preamble  306  within signal bursts  302 . The number m and location of preambles  306  can be fixed within transmitter  400 , can be communicated to transmitter  400 , or can be selected by controller  408  of transmitter  400 , for example based upon feedback from a receiver of the transmitted signal  300  such as the feedback described above. 
     Transmitter  400  then transmits a preamble  306  (step  506 ), followed by a signal field  308  (step  508 ). Transmitter  400  then transmits a payload field  310  comprising a packet  312  of data (step  510 ). If the last payload field  310  of burst  302  has been transmitted (step  512 ), then transmitter  400  waits until the next inter-burst gap  303  is done (step  514 ), and then resumes process  500  at step  502 . 
     But if at step  512  one or more further payload fields  310  remain to be transmitted in burst  302 , controller  408  determines whether a further preamble  306  should be transmitted first (step  516 ). If not, controller  408  clears preamble flag PF in signal field  308  (step  518 ) and optionally clears gap flag GF, if used, and sets a short duration for inter-frame gap  304  (step  520 ). Transmitter  400  then waits until the inter-frame gap is done (step  522 ), and then transmits signal field  308  (resuming process  500  at step  508 ). 
     But if at step  516  another preamble  306  is to be transmitted, controller  408  sets preamble flag PF in signal field  308  (step  524 ) and optionally sets gap flag GF, if used, and sets a long duration for inter-frame gap  304  (step  526 ). Transmitter  400  then waits until the inter-frame gap is done (step  528 ), and then transmits preamble field  306  (resuming process  500  at step  506 ). 
       FIG. 6  shows a receiver  600  according to a preferred embodiment of the present invention. Receiver  600  comprises an antenna  602  for receiving signal  300 , a front end  604 , and a baseband processor  606 . Front end  604  comprises a variable-gain amplifier (VGA)  608 . Preferably VGA  608  applies a receiver gain to signal  300  at a radio frequency (RF). However, other embodiments provide gain at intermediate frequency (IF) and/or at baseband instead of, or as well as, at RF. 
     Baseband processor  606  comprises an automatic gain control circuit (AGC)  610 , a preamble processor  612 , and a controller  614 . While  FIG. 6  indicates one example of a configuration for receiver  600 , embodiments of the present invention are not limited by that configuration. Some embodiments comprise an optional transmitter  618  to send feedback information to a transmitter of signal  300 . In some embodiments, receiver  600  is otherwise compliant with at least one standard selected from the group consisting of IEEE standards 802.11a, 802.11g, and 802.11n. 
       FIG. 7  shows a process  700  for receiver  600  of  FIG. 6  according to a preferred embodiment. In the example of  FIG. 7 , the inter-frame gap duration value is represented by a gap flag GF that when clear indicates a “normal” duration for the next inter-frame gap  304  (for example, on the order of 2 microseconds), and when set indicates a “short” duration for the next inter-frame gap  304  (for example, on the order of a fraction of a microsecond). 
     Receiver  600  receives a preamble  306  in a burst  302  of wireless signal  300  (step  702 ). Preamble processor  612  processes the preamble  306  to acquire and synchronize with signal burst  302 . Receiver  600  also sets a receiver signal gain while receiving preamble  306 . In particular, automatic gain control circuit (AGC)  610  controls the receiver gain of wireless signal  300  based on the signal level of wireless signal  300  during preamble  306  when preamble flag PF is set in the signal field  308  preceding the preamble  306 . Note that when preamble  306  is the first preamble  306  in signal burst  302 , it is assumed that preamble flag PF was set in the last signal field  308  of the previous signal burst  302 . In the embodiment of  FIG. 1 , AGC circuit  610  detects a level of signal  300  during preamble  306  and generates a gain control signal  616  that is provided to VGA  608 . VGA  608  applies a receiver gain to signal  300  in accordance with gain control signal  616 . At the end of preamble  306 , the receiver gain is held constant until the start of the next preamble  306  received. 
     Receiver  600  receives the signal field  308  that follows preamble  306  (step  704 ). Controller  614  of receiver  600  optionally checks the gap flag GF in the signal field  308  (step  706 ). If gap flag GF is set, controller  614  optionally configures baseband processor  606  in accordance with a short duration for the next inter-frame gap  304  (step  708 ). If gap flag GF is clear, controller  614  optionally configures baseband processor  606  in accordance with a long duration for the next inter-frame gap  304  (step  710 ). 
     Controller  614  checks the preamble flag PF in the signal field  308  (step  712 ). If the preamble flag PF is clear, no preamble  306  precedes the next signal field  308 , so after receiving and processing the payload field  310  following the signal field  308  (step  714 ), receiver  600  waits (step  716 ) for the inter-frame gap  304  duration established in steps  706 - 710  before receiving and processing the next signal field  308  (resuming at step  704 ). 
     But if at step  712  the preamble flag PF in the signal field  308  is set, a preamble  306  precedes the next signal field  308 . The preamble  306  could be part of the same burst as the previous preamble  306 , but if the signal field  308  having the preamble flag PF set is the last in a burst  302 , the preamble  306  is part of the next burst  302 . Therefore, after receiving and processing the payload field  310  following the signal field  308  (step  718 ), if that payload field  310  is not the last in the burst  302  (step  720 ), receiver  600  waits (step  722 ) for the inter-frame gap  304  duration established in steps  706 - 710  before receiving and processing the next preamble  306  (resuming at step  702 ). But if that payload field  310  is the last in the burst  302  (step  720 ), receiver  600  waits (step  724 ) for the inter-burst gap  303  duration before receiving and processing the next preamble  306 , which is the first in the next burst  302  (resuming at step  702 ). 
     Embodiments of the present invention produce significant improvements in data throughput, especially for small packets.  FIG. 8  shows eight plots of throughput (Mbps) vs. packet size (Bytes). For each of the plots, the physical data rate is 100 Mbps, the preamble duration is 50 microseconds, the inter-frame gap duration is 2 microseconds, and the inter-burst gap duration is 50 microseconds. As can be seen from  FIG. 8 , embodiments of the present invention are capable of increasing data throughput substantially. 
     Curve  802  represents a conventional system operating at a burst size (that is, the number of data packets in each burst) of 5, while curve  810  represents a system according to a preferred embodiment of the present invention, also operating at a burst size of 5. 
     Curve  804  represents a conventional system operating at a burst size of 10, while curve  812  represents a system according to a preferred embodiment of the present invention, also operating at a burst size of 10. 
     Curve  806  represents a conventional system operating at a burst size of 20, while curve  814  represents a system according to a preferred embodiment of the present invention, also operating at a burst size of 20. 
     Curve  808  represents a conventional system operating at a burst size of 50, while curve  816  represents a system according to a preferred embodiment of the present invention, also operating at a burst size of 50. 
     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.