Transmitter warm-up using dummy frame generation

An electronic device includes a medium access controller (MAC) to generate frames and transmitter circuitry to convert the frames to radio-frequency (RF) analog signals for transmission. The MAC is to initiate frame generation at a time that precedes initiation of RF analog signal transmission by a specified time period. In a first mode, the MAC is to generate a dummy frame during a first portion of the specified time period and to initiate generation of a transmit frame during a subsequent second portion of the specified time period. Also in the first mode, the transmitter circuitry is to convert the dummy frame into a first analog signal, discard the first analog signal, convert the transmit frame into a second analog signal, and transmit the second analog signal.

TECHNICAL FIELD

The present embodiments relate generally to communication systems, and more specifically to noise mitigation when transmitting signals.

BACKGROUND OF RELATED ART

Designing communication devices (e.g., wireless communication devices) to have a low error rate (e.g., a low error-vector magnitude or EVM) presents significant engineering challenges. For example, switching between receive and transmit modes results in transient noise that manifests as an increased EVM. In some instances, this noise affects the frequency of a reference oscillating signal provided by an RF frequency synthesizer, which takes time to settle after switching. As a result, frequency estimation performed using packet header training fields may be inaccurate, such that it differs from frequency estimation performed using entire packets. Inaccurate frequency estimation results in increased EVM.

DETAILED DESCRIPTION

Embodiments are disclosed in which a warm-up time is provided in a transmitter before generating a transmit frame and corresponding analog signal. A dummy frame and corresponding analog signal may be generated during the warm-up time.

In some embodiments, an electronic device includes a medium access controller (MAC) to generate frames and transmitter circuitry to convert the frames to radio-frequency (RF) analog signals for transmission. The MAC is to initiate frame generation at a time that precedes initiation of RF analog signal transmission by a specified time period. In a first mode, the MAC is to generate a dummy frame during a first portion of the specified time period and to initiate generation of a transmit frame during a subsequent second portion of the specified time period. Also in the first mode, the transmitter circuitry is to convert the dummy frame into a first analog signal, discard the first analog signal, convert the transmit frame into a second analog signal, and transmit the second analog signal.

In some embodiments, a method of signal generation includes successively generating a dummy frame and a transmit frame. The dummy frame is converted into a first analog signal and the first analog signal is discarded. The transmit frame is converted into a second analog signal and the second analog signal is transmitted on a channel.

In the following description, numerous specific details are set forth such as examples of specific components, circuits, and processes to provide a thorough understanding of the present disclosure. Also, in the following description and for purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present embodiments. However, it will be apparent to one skilled in the art that these specific details may not be required to practice the present embodiments. In other instances, well-known circuits and devices are shown in block diagram form to avoid obscuring the present disclosure. The term “coupled” as used herein means connected directly to or connected through one or more intervening components or circuits. Any of the signals provided over various buses described herein may be time-multiplexed with other signals and provided over one or more common buses. Additionally, the interconnection between circuit elements or software blocks may be shown as buses or as single signal lines. Each of the buses may alternatively be a single signal line, and each of the single signal lines may alternatively be buses, and a single line or bus might represent any one or more of a myriad of physical or logical mechanisms for communication between components. The present embodiments are not to be construed as limited to specific examples described herein but rather to include within their scope all embodiments defined by the appended claims.

FIG. 1is a block diagram of a system100that includes wireless devices (WD)110and access points (AP)120in accordance with some embodiments. The wireless devices110and access points120compose a wireless local area network (WLAN)130. A respective wireless device110in the WLAN130may communicate wirelessly with one or more access points130and/or with other wireless devices110. In some embodiments, a respective wireless device110is a mobile device (e.g., a cell phone, personal digital assistant, tablet computer, laptop computer, or the like). In some embodiments, the WLAN130is implemented in accordance with one or more protocols in the IEEE 802.11 family of protocols and thus is a WiFi network. Each of the wireless devices110and access points120thus may be WiFi-enabled.

FIG. 2Aillustrates circuitry200for transmitting data in accordance with some embodiments. The circuitry200may be found, for example, in each of the wireless devices110and access points120of the WLAN130(FIG. 1). In the circuitry200, a media access controller (MAC)202generates frames and provides the frames to transmitter circuitry204, which converts the frames into radio-frequency (RF) analog signals for transmission. The transmitter circuitry204includes digital baseband (BB) processing circuitry206, a digital-to-analog converter (DAC)208, an analog baseband low-pass filter (BB LPF)210, and a mixer212. In some embodiments, the BB processing circuitry206includes an encoder to encode data in the frames, a modulator to modulate the encoded data into symbols, and an inverse fast Fourier transform (IFFT) implementation to generate digital samples based on the symbols. The BB processing circuitry206provides the digital samples to the DAC208, which converts the digital samples into baseband analog signals. The analog BB LPF210filters the baseband analog signals and provides the filtered baseband analog signals to the mixer212, which up-converts the filtered baseband analog signals to radio frequency. To perform this up-conversion, a frequency synthesizer214generates an RF oscillating signal and provides the RF oscillating signal to the mixer212, which mixes the filtered baseband analog signals with the RF oscillating signal to produce RF analog signals. The mixer212thus functions as an up-converter. An RF power amplifier (PA)216amplifies the RF analog signals, which are transmitted through an antenna218onto a channel (e.g., a wireless channel).

The circuitry200also includes a control register220that stores a value that specifies a mode of operation. For example, the control register220includes a bit field that stores a value specifying the duration of a delay between the time when the MAC202begins frame generation and the time when the PA216begins to output a signal. This value is propagated to the MAC202and to the transmitter circuitry204. For example, a control register222in the MAC202may duplicate the control register220, as may registers (not shown) in the BB processing circuitry206, DAC208, analog BB LPF210, and/or mixer212. Storing a first value in the control register220(e.g., setting a bit field in the register to ‘1’) programs the circuitry200to operate in a first mode (e.g., the mode illustrated below inFIG. 4B, or alternativelyFIG. 4C) and storing a second value in the control register (e.g., setting a bit field in the register to ‘0’) programs the circuitry200to operate in a second mode (e.g., the mode illustrated below inFIG. 4A).

The MAC202may include a counter224corresponding to the time period between initiation of frame generation by the MAC202and initiation of signal transmission. In some embodiments, the counter224is programmable. For example, the value to which it counts may be specified in or determined based on a field of the registers220and/or222.

The wireless devices110and access points120(FIG. 1) each include receiver circuitry as well as the circuitry200for transmitting data. For example, the wireless devices110and access points120each include transceiver circuitry230as shown inFIG. 2Bin accordance with some embodiments. The transceiver circuitry230includes the MAC202, transmitter circuitry204, frequency synthesizer214, power amplifier216, and antenna218ofFIG. 2A. In addition, the transceiver circuitry230includes receiver circuitry234and a switch232to couple either the transmitter circuitry204and power amplifier216, or the receiver circuitry234, to the antenna218at a given time. The switch232thus selectively couples the transmitter circuitry204and power amplifier216to the antenna218for signal transmission and selectively couples the receiver circuitry234to the antenna218for signal reception. The transceiver circuitry230thus may perform time-division duplexing (TDD), such that signals are either transmitted or received, but not both, during respective specified time slots.

The receiver circuitry234includes an amplifier236to amplify RF analog signals received through the antenna218. The amplifier236provides the amplified RF analog signals to a mixer238, which down-converts the amplified RF analog signals to baseband by mixing them with an RF oscillating signal from the frequency synthesizer214. The down-converted analog signals are filtered by an analog BB LPF240and then converted into digital samples by an analog-to-digital converter (ADC)242. The ADC242is coupled to BB processing circuitry244, which generates frames based on the digital samples from the ADC242and provides the frames to the MAC202.

Frames that are generated and transmitted (and/or received) using the circuitry200(FIG. 2A) or230(FIG. 2B) include data fields (e.g., of one or more OFDM symbols) as well as preamble fields.FIGS. 3A-3Cillustrate examples of frame formats in accordance with different IEEE 802.11 (i.e., WiFi) protocols.FIG. 3Ashows the format of a frame300as defined in the IEEE 802.11a/g protocols. The frame300has a data field308preceded by a preamble that includes legacy short training fields (L-STF)302, two legacy long training fields (L-LTF 1 & 2)304, and a legacy signal field (L-SIG)306. The device receiving the frame300uses the L-STF302for coarse frequency estimation, as well as for automatic gain control and timing recovery, and uses the L-LTF 1 & 2304for fine frequency estimation as well as channel estimation and fine timing recovery. The L-SIG306may be used to convey modulation and coding information.

FIG. 3Bshows the format of a frame320as defined in the IEEE 802.11n protocol. In addition to the fields302,304, and306(FIG. 3A), the frame320includes in its preamble two high-throughput signal fields (HT-SIG 1 & 2)322, a high-throughput short training field (HT-STF)324, and four high-throughput long training fields (HT-LTFs)326.FIG. 3Cshows the format of a frame340as defined in the IEEE 802.11ac protocol. In addition to the fields302,304, and306(FIGS. 3A-3B), the frame340includes in its preamble a first very high-throughput signal field (VHT-SIG A)342, a very high-throughput short training field (VHT-STF)344, and four very high-throughput long training fields (VHT-LTFs)346. Also, the data field348may include a second very high-throughput signal field (VHT-SIG B) as well as a data payload.

The HT-SIG 1 & 2322, VHT-SIG A342, and VHT-SIG B may be used to convey modulation and coding information. The HT-STF324and VHT-STF344may be used for automatic gain control. The HT-LTFs326and VHT-LTFs346may be used for multiple-input-multiple-output (MIMO) channel estimation.

Frames with formats such as those shown inFIGS. 3A-3Cthus include preamble fields (e.g., L-STF302and L-LTF 1 & 2304) that can be used for frequency estimation: a receiving device performs frequency estimation for a signal received from a transmitting device and compensates accordingly, thereby reducing the error rate (e.g., the EVM) of the receiving device. Use of a preamble field in a frame to perform frequency estimation, assumes, however, that the frequency of a local oscillating signal in the transmitting device (e.g., the frequency of the RF oscillating signal generated by the frequency synthesizer214,FIGS. 2A-2B) is constant throughout generation and transmission of an analog signal corresponding to the frame. This assumption is not necessarily justified. For example, when an electronic device (e.g., a wireless device110or access point120,FIG. 1) switches from receiving a signal to transmitting a signal, the switching may generate noise that is coupled into the frequency synthesizer214(FIGS. 2A-2B). Until this noise settles out and the frequency synthesizer214achieves steady state, the frequency of the RF oscillating signal produced by the frequency synthesizer214may vary from the desired value. The frequency used to up-convert the portion of a signal corresponding to a particular preamble field (e.g., L-STF302or L-LTF 1 & 2304,FIGS. 3A-3C) thus may very from the frequency used to up-convert the portion of the signal corresponding to the data payload (e.g., corresponding to the data field308or348,FIGS. 3A-3C). Frequency estimation based on the preamble thus may be inaccurate, resulting in an increased EVM.

FIG. 4Ais a timing diagram400illustrating timing for operation of the circuitry200(FIG. 2A) and/or230(FIG. 2B) during a mode of operation that is susceptible to inaccurate preamble-based frequency estimation. The mode of operation ofFIG. 4Amay be referred to as a normal mode of operation in accordance with some embodiments. In some embodiments, the circuitry200and/or230operates in the mode of operation ofFIG. 4Awhen a particular value (e.g., ‘0’) is stored in a specified bit field in the register220and/or222(FIGS. 2A-2B).

A carrier-sense multiple access (CSMA) time slot408, which is also referred to as a contention-based time slot408, extends from a time t1to a time t5. In one example, the time slot408is approximately 9 us in duration. During a first portion410of the time slot408, receiver circuitry (e.g., including the receiver circuitry234,FIG. 2B) in a device with data to transmit listens to the channel to determine if the channel is idle or if another device is transmitting. The first portion410extends from t1to a time t4that precedes t5. In one example, the first portion410is approximately 7 us in duration. If the channel is idle, such that no transmissions by other devices are detected, the MAC202(FIGS. 2A-2B) begins to generate a transmit frame starting at t4, as indicated by assertion of the transmit frame (“Tx frame”) control signal402. In some embodiments, the transmit frame is generated in accordance with an IEEE 802.11 protocol and includes the preamble fields ofFIG. 3A,3B, or3C. In some embodiments, the MAC202sets a bit in the header of the transmit frame to specify the normal mode of operation.

As the MAC202generates the transmit frame, it provides the transmit frame to the transmitter circuitry204(FIGS. 2A-2B). At t5, the transmitter circuitry204(FIGS. 2A-2B), or portions thereof, is enabled, as indicated by assertion of the transmitter-enable (TX On) control signal404. For example, the DAC208, analog BB LPF210, and mixer212are activated; the output of the BB processing circuitry206may also be activated. The power amplifier216is also activated at t5, as indicated by assertion of the PA-enable (PA On) control signal406. Activation of the power amplifier216initiates RF analog signal transmission. Initiation of frame generation by the MAC202thus precedes initiation of RF analog signal transmission by a specified time period412that extends from t4to t5. In one example, the specified time period412is approximately 2 us in duration. The specified time period412time may correspond to the latency between the MAC202and power amplifier216(FIGS. 2A-2B).

Noise that affects the frequency synthesizer214, such as noise resulting from activation of various components (including both digital components206and208and analog components210and212) in the transmitter circuitry204, may not have settled when RF analog signal transmission begins at t5. As a result, the frequency of the RF oscillating signal provided by the frequency synthesizer214may not yet have reached steady state, resulting in errors in the receiving device. To avoid this problem, the predefined period between the beginning of frame generation and the beginning of RF analog signal transmission may be increased.

FIG. 4Bis a timing diagram430illustrating timing for operation of the circuitry200(FIG. 2A) and/or230(FIG. 2B) during a mode of operation in which the predefined period between the beginning of frame generation and the beginning of RF analog signal transmission has been increased with respect to the timing diagram400(FIG. 4A). The mode of operation shown in the timing diagram430may be referred to as a transmitter warm-up mode in accordance with some embodiments. In some embodiments, the circuitry200and/or230operates in the warm-up mode ofFIG. 4Bwhen a particular value (e.g., ‘1’) is stored in a specified bit field in the register220and/or222(FIGS. 2A-2B).

In the timing diagram430, as in the timing diagram400(FIG. 4A), the CSMA time slot408extends from times t1to t5. During of first portion440of the time slot408, receiver circuitry (e.g., including the receiver circuitry234,FIG. 2B) listens to the channel to determine if the channel is idle or if another device is transmitting. The first portion440extends from t1to a time t2, and is thus shorter than the first portion410(FIG. 4A). In some examples, the first portion440is in the range of 1-2 us in duration. If the channel is idle, the MAC202(FIGS. 2A-2B) begins to generate a dummy frame starting at t2, as indicated by assertion of the transmit frame (“Tx frame”) control signal432. In some embodiments, the dummy frame is generated in accordance with an IEEE 802.11 protocol and include the preamble fields ofFIG. 3A,3B, or3C or a portion thereof (e.g., including L-STF302and L-LTF 1 & 2304,FIGS. 3A-3C). In some embodiments, the MAC202sets a bit in the header of the dummy frame to enable the warm-up mode of operation.

As the MAC202generates the dummy frame, it provides the dummy frame to the transmitter circuitry204(FIGS. 2A-2B). At a time t3, the transmitter circuitry204(FIGS. 2A-2B), or portions thereof, is enabled, as indicated by assertion of the TX On signal434. For example, the DAC208, analog BB LPF210, and mixer212are activated; the output of the BB processing circuitry206may also be activated. A specified time period444(e.g., of approximately 2 us) between t2and t3thus separates activation of transmitter circuitry204from initiation of frame generation by the MAC202. Upon activation of the DAC208at t3, the transmitter circuitry204begins to generate a baseband analog signal corresponding to the dummy frame. This baseband analog signal is filtered by the BB LPF210and up-converted to RF by the mixer212(FIGS. 2A-2B), resulting in an RF analog signal corresponding to the dummy frame. This RF analog signal is not transmitted, however, because the power amplifier216(FIGS. 2A-2B) has not yet been activated, as illustrated by de-assertion of the PA On control signal436during the period438.

At the time t4, the MAC202ceases generation of the dummy frame and begins to generate a transmit frame. In some embodiments, the transmit frame is generated in accordance with an IEEE 802.11 protocol and includes the preamble fields ofFIG. 3A,3B, or3C. In some embodiments, the MAC202sets a bit in the header of the transmit frame to enable the warm-up mode of operation. The transmitter circuitry204(FIGS. 2A-2B) converts the transmit frame into an RF analog signal. For example, at or about the time t5, the BB processing circuitry206(FIGS. 2A-2B) re-starts generation of data samples corresponding to the L-STF302(FIGS. 3A-3C). In some embodiments, this L-STF302restart is performed in response to enablement of the transmitter warm-up mode by a value stored in the control registers220and/or222(FIGS. 2A-2B) and/or by the value of a bit in the header of the dummy and/or transmit frames.

Also at t5, the power amplifier216is activated, as illustrated by assertion of the PA On control signal436, and its output is provided to the antenna218. (If the timing diagram430is implemented using the circuitry230ofFIG. 2B, the switch232is closed to couple the power amplifier216to the antenna218at or before time t5.) The RF analog signal corresponding to the transmit frame thus is transmitted starting at time t5, beginning, for example, with a portion corresponding to the L-STF302(FIGS. 3A-3C). Initiation of frame generation by the MAC202in the timing diagram430therefore precedes initiation of RF analog signal transmission by a specified time period438that extends from times t2to t5. In one example, the specified time period438is approximately 7 us in duration.

In some embodiments, the specified time period438has a programmable duration (e.g., such that the time between initiation of frame generation and the L-STF restart at t5is programmable). For example, its duration may be programmed by adjusting the duration of a period442, which extends from times t2to t4and thus is part of the specified time period438. In some embodiments, the duration of the period442is determined using the counter224(FIGS. 2A-2B). The value to which the counter224will count is specified, for example, in a bit field of the control registers220and/or222(FIGS. 2A-2B). The duration of the period442equals this value of the counter224divided by the frequency of a system clock (e.g., an 80 or 88 MHz clock), which determines the rate at which the counter224counts. The maximum value of the counter224is constrained such that the time it specifies is less than the duration of the time slot408minus the duration of the period412. In some embodiments, the counter224is implemented and/or controlled in software.

In some embodiments, the analog signal corresponding to the dummy frame is discarded by decoupling the power amplifier216from the antenna218using the switch232(FIG. 2B), instead of (or in addition to) deactivating the power amplifier216.FIG. 4Cis a timing diagram460illustrating timing for operation of the circuitry230(FIG. 2B) in some such embodiments. The mode of operation shown in the timing diagram460, like the mode of operation for the timing diagram430(FIG. 4B), may be referred to as a transmitter warm-up mode. In some embodiments, the circuitry230(FIG. 2B) operates in the mode of operation ofFIG. 4Cwhen a particular value (e.g., ‘1’) is stored in a specified bit field in the register220and/or222(FIG. 2B).

At the time t1in the timing diagram460, the switch232is open between the power amplifier216and the antenna218, as indicated by de-assertion of the switch control signal464. The power amplifier216is thus decoupled from the antenna218. For example, the switch232couples the antenna218to the receiver circuitry234(FIG. 2B) at this time. The timing of the operation of the MAC202and DAC208is the same as in the timing diagram430(FIG. 4B), as illustrated by the transmit frame control signal432and TX On control signal434. The power amplifier216is activated at the time t3, however (e.g., along with the DAC208), which is earlier than the time t5when it is activated in the timing diagram430(FIG. 4B). Activation of the power amplifier216is illustrated by assertion of the PA On control signal462. Despite the activation of the power amplifier216, the RF analog signal corresponding to the dummy frame is not transmitted, because the switch232is open.

At the time t4, the MAC202ceases generation of the dummy frame and begins to generate a transmit frame. (The dummy frame and transmit frame may both be generated in accordance with an IEEE 802.11 protocol and include the preamble fields ofFIG. 3A,3B, or3C.) The transmitter circuitry204(FIGS. 2A-2B) converts the transmit frame into an RF analog signal. At the time t5, the switch232is closed, as illustrated by assertion of the switch control signal464, thus coupling the power amplifier216to the antenna218. The RF analog signal corresponding to the transmit frame therefore is transmitted starting at t5, beginning, for example, with a portion corresponding to the L-STF302(FIGS. 3A-3C). As in the timing diagram430(FIG. 4B), initiation of frame generation by the MAC202therefore precedes initiation of RF analog signal transmission by the specified time period438.

In some embodiments, a device selects between the normal mode ofFIG. 4Aand the warm-up mode ofFIG. 4Bor4C in accordance with one or more predefined criteria. For example, mode selection is based on the available timing for a particular transmission. The warm-up mode is selected if it will not result in a collision; otherwise the normal mode is selected. The time between the scheduled transmission of a packet and the reception of a previous packet is compared to the sum of a programmable warm-up time and baseband transmitter latency. If T1is the scheduled packet transmission time (e.g., t5at the end of the time slot408,FIGS. 4A-4C), T2is the arrival time of the previous packet (e.g., t1, if the arrival immediately precedes the time slot408,FIGS. 4A-4C), Twarm-upis the programmable warm-up time (e.g., the period442,FIGS. 4B-4C), and TBB-TXis the baseband transmitter latency (e.g., the period412,FIGS. 4A-4C), then the warm-up mode is selected if:
T1−T2>Twarm-up+TBB-TX(1)
Satisfaction of equation (1) ensures that the warm-up mode will not result in packet collision.

In some embodiments, mode selection is based at least in part on the type of transmission, and may further be based on whether the criterion of equation (1) is satisfied. Several examples with respect to IEEE 802.11 protocols are now described. If the transmission is of non-burst data without use of a Request to Send/Clear to Send (RTS/CTS) mechanism, then a warm-up mode (e.g., as shown inFIG. 4Bor4C) is used. If the transmission is in a short inter-frame spacing (SIFS) burst with no acknowledgment (no-ACK), then a warm-up mode is used. In these two examples, a receive frame is not immediately followed by a transmit frame; therefore, a warm-up mode may be used without risk of collision. If the transmission uses an RTS/CTS mechanism, then the mode is selected based on an analysis of available timing (e.g., using Equation (1)). Similarly, if the transmission is in a SIFS burst with acknowledgment (with ACK), the mode is selected based on an analysis of available timing (e.g., using Equation (1)). If the transmission is in a reduced inter-frame spacing (RIFS) burst, however, then the normal mode of operation is selected.

FIG. 5is a flowchart illustrating a method500of performing signal transmission in accordance with some embodiments. The method500is performed, for example, using the circuitry200and/or230(FIGS. 2A-2B) in an electronic device such as a wireless device110or access point120(FIG. 1).

A mode of operation is selected (502) for signal transmission. The selection is made, for example, between a first mode (e.g., the warm-up mode ofFIG. 4B, or alternatively the warm-up mode ofFIG. 4C) and a second mode (e.g., the normal mode ofFIG. 4A). In some embodiments, the selection is made based on an analysis of available timing (e.g., in accordance with Equation (1)) and/or based on the type of transmission.

If the first mode is selected, the device listens to the channel (e.g., during a period440in a CSMA time slot408,FIGS. 4B-4C) and determines (504) whether the channel is idle. In some embodiments, the listening is performed for a programmable duration. For example, the duration of the period440may be increased (or decreased) by decreasing (or increasing) the duration of the period442(e.g., by setting a value for the counter224,FIGS. 2A-2B).

If the channel is not idle (504—No), the operation504is repeated (e.g., during a subsequent time slot408,FIGS. 4B-4C). If the channel is idle (504—Yes), then a dummy frame and a first transmit frame are successively generated (506) (e.g., in accordance with the timing diagram430,FIG. 4B, or460,FIG. 4C).

The dummy frame is converted (508) into a first analog signal (e.g., an RF analog signal) and discarded (510). In some embodiments, the converting508includes transforming data in the dummy frame into digital samples (e.g., using the BB processing circuitry206,FIGS. 2A-2B), converting the digital samples into a first baseband analog signal (e.g., using the DAC208,FIGS. 2A-2B), and up-converting the first baseband analog signal to RF (e.g., using the mixer212,FIGS. 2A-2B). In some embodiments (e.g., in the example ofFIG. 4C), the converting further includes amplifying the up-converted signal (e.g., using the power amplifier216,FIG. 2B).

In some embodiments, discarding (510) the first analog signal includes providing (512) the first analog signal to the power amplifier216(FIGS. 2A-2B) when the power amplifier216is deactivated (e.g., in accordance with the timing diagram430,FIG. 4B). In some embodiments, discarding the first analog signal includes opening (514) the switch232(FIG. 2B) to decouple the power amplifier from the antenna218(e.g., in accordance with the timing diagram460,FIG. 4C).

The transmit frame is converted (516) into a second analog signal (e.g., an RF analog signal) and transmitted (518) on a channel (e.g., a wireless channel in the WLAN130,FIG. 1). In some embodiments, the converting516includes transforming data in the transmit frame into digital samples (e.g., using the BB processing circuitry206,FIGS. 2A-2B), converting the digital samples into a second baseband analog signal (e.g., using the DAC208,FIGS. 2A-2B), and up-converting the second baseband analog signal to RF (e.g., using the mixer212,FIGS. 2A-2B). In some embodiments, transmitting the second analog signal includes activating (520) the power amplifier216(FIGS. 2A-2B) (e.g., at a time t5,FIG. 4B). In some embodiments, transmitting the second analog signal includes closing (522) the switch232(FIG. 2B) to couple the power amplifier216to the antenna218(e.g., at the time t5,FIG. 4C).

If the second mode is selected in operation502, the device listens to the channel (e.g., during a period410in a CSMA time slot408,FIG. 4A) and determines (524) whether the channel is idle. In some embodiments, the listening is performed for a programmable duration, which is longer in the second mode than in the first mode. If the channel is not idle (524—No), the operation524is repeated (e.g., during a subsequent time slot408,FIG. 4A).

If the channel is idle (524—Yes), then a second transmit frame is generated (526) (e.g., in accordance with the timing diagram400,FIG. 4A). The second transmit frame is converted (528) into a third analog signal. The third analog signal is transmitted (530) on the channel. In some embodiments, the converting528includes transforming data in the second transmit frame into digital samples (e.g., using the BB processing circuitry206,FIGS. 2A-2B), converting the digital samples into a third baseband analog signal (e.g., using the DAC208,FIGS. 2A-2B), and up-converting the third baseband analog signal to RE (e.g., using the mixer212,FIGS. 2A-2B). In some embodiments, the transmitting530includes amplifying the third analog signal using the power amplifier216(FIGS. 2A-2B) and providing the amplified signal to the antenna218(FIGS. 2A-2B).

The method500thus provides a first mode that includes time for the frequency of an RF oscillating signal output by the frequency synthesizer214(FIG. 2B) to settle to a steady-state value before signal transmission begins. The ability to select between modes in the method500, however, allows a second mode to be chosen when the first mode would result in a packet collision.

While the method500includes a number of operations that appear to occur in a specific order, it should be apparent that the method500can include more or fewer operations, which can be executed serially or in parallel. An order of two or more operations may be changed, performance of two or more operations may overlap, and two or more operations may be combined into a single operation. The method500may be repeated, such that the first mode is selected during one iteration and the second mode is selected during another iteration.

In some embodiments, the MAC202(FIGS. 2A-2B) is implemented in software, as illustrated inFIG. 6for an electronic device600(e.g., a wireless device110or access point120,FIG. 1). The electronic device600includes a physical layer device (PHY)602that includes, for example, the transmitter circuitry204, power amplifier216, frequency synthesizer214, and/or receiver circuitry234(FIGS. 2A-2B). The PHY602is coupled by a media-independent interface604to one or more processor cores606, which are coupled to memory608. In some embodiments, the memory608includes a non-transitory computer-readable medium (e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, and so on) that stores instructions for execution by the one or more processor cores606. In some embodiments, the instructions include instructions that, when executed by the processor core(s)606, cause the controller600to implement the functionality of the MAC202(FIGS. 2A-2C). In some embodiments, the instructions include instructions that, when executed by the processor core(s)606, cause the electronic device600to perform all or a portion of the method500(FIG. 5).

While the memory608is shown as being separate from the processor core(s)606, all or a portion of the memory608may be embedded in the processor core(s)606. In some embodiments, the memory608is implemented in the same integrated circuit as the processor core(s)606and/or PHY602.