Fast training on multi-antenna systems

Certain aspects of the present disclosure relate to methods and apparatus for performing beamforming training in multi-antenna wireless devices. For example, an apparatus for wireless communication may include a first interface configured to obtain, from each of a plurality of radio frequency (RF) modules, a first information regarding detection of one or more pilot signals via at least one antenna element at a respective one of the plurality of RF modules. The apparatus may also include a processing system configured to process the first information obtained from the plurality of RF modules to generate second information to synchronize the plurality of RF modules, and a second interface configured to provide the second information to the plurality of RF modules.

BACKGROUND

Field of the Disclosure

The present disclosure relates generally to wireless communication, and more particularly, to methods and apparatus to reduce time of beamforming training for multi-antenna systems.

Description of Related Art

The 60 GHz band is an unlicensed band which features a large amount of bandwidth and a large worldwide overlap. The large bandwidth means that a very high volume of information can be transmitted wirelessly. As a result, multiple applications, that use transmission of a large amount of data, can be developed to allow wireless communication around the 60 GHz band. Examples for such applications include, but are not limited to, wireless high definition TV (HDTV), wireless docking stations, wireless Gigabit Ethernet, and many others.

SUMMARY

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a first interface configured to obtain, from each of a plurality of radio frequency (RF) modules, first information regarding detection of one or more pilot signals via at least one antenna element at a respective one of the RF modules, a processing system configured to process the first information obtained from the plurality of RF modules to generate second information to synchronize the RF modules, and a second interface configured to provide the second information to the RF modules.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a detector configured to detect one or more pilot signals via at least one activated antenna element, a first interface configured to provide, to a processing module, first information regarding the detection of the one or more pilot signals via the at least one activated antenna element, a second interface configured to obtain, from the processing module, second information generated at least based on the first information, and a processing system configured to make adjustments to components of the RF module based on the second information.

Aspects generally include methods, apparatus, systems, computer readable mediums, and processing systems, as substantially described herein with reference to and as illustrated by the accompanying drawings. Numerous other aspects are provided.

DETAILED DESCRIPTION

Certain aspects of the present disclosure provide improved techniques for beamforming training of multi-antenna systems. The techniques may help substantially reduce the time needed for beamforming training by simultaneously training multiple antennas.

FIG. 1illustrates an example laptop computer100that includes an RF system110for transmission and reception of signals. The form factor of the RF system110is spread between the base102and lid planes105of the laptop computer100.

The RF system110includes a baseband module120and a radio frequency (RF) module130respectively connected to the base plane102and lid plane105. The RF module130is coupled to active transmit (TX) and receive (RX) antennas. The TX and RX antennas may be one or more active antennas in an antenna array (e.g., a phased antenna array). When transmitting signals, the baseband module120may provide the RF module130with a control signal, and one or more other signals such as a local oscillator (LO), intermediate frequency (IF). The control signal may be used for functions, such as gain control, RX/TX switching, power level control, sensors, and detectors readouts. Specifically, beam-forming based RF systems may use high frequency beam steering operations which are performed under the control of the baseband module120. The control typically originates at the baseband120of the system, and transfers between the baseband module120and RF module130.

The RF module130may perform up-conversion, using a mixer (not shown) on the IF signal(s) to RF signals and then transmits the RF signals through the TX antenna according to the control of the control signals. A power signal such as a DC voltage signal may be used to power the various components of the RF module130.

In the receive direction, the RF module130receives RF signals (e.g., at the frequency band of 60 GHz), through the active RX antenna and performs down-conversion, using a mixer, to IF signals using the LO signals, and sends the IF signals to baseband module120. The operation of the RF module130is controlled by the control signal, but certain control information (e.g., feedback signal) is sent back to the baseband module120.

In some cases, at least two cables (transmission lines) may be used to transfer the IF, LO, and control signals between the baseband and RF modules120and130.

The drawback to this approach is especially critical in millimeter-wave RF systems, e.g., systems that operate in the 60 GHz frequency bands, as the RF module130may be located close to the active antennas to perform the functions described above in order to reduce the power loss of the received and transmit signals. Thus, the baseband module120is located apart from the RF module130. Further, because transferring high frequency signals over the cables significantly attenuates the signals, cables that provide low attenuation characteristics may be used. However, such cables are relativity expensive, thus increasing the bill of material (BoM) of consumer electronics devices.

While the example provided inFIG. 1include a laptop computer to facilitate understanding, aspects of the present disclosure may be used by any wireless device for wireless communication. For example, aspects of the present disclosure may be used for wireless communication by a tablet, a base station, an access point, a user-equipment or a station.

FIG. 2illustrates an example RF system200utilized to describe various aspects of the present disclosure. The RF system200includes a baseband module210coupled to a chip-to-line interface module220. In addition, the RF system200includes an RF module230coupled to a line-to-chip interface unit240. The RF module230comprises a RF circuitry231to perform up and down conversions of radio signals and to control the TX and RX active antennas232and233. In certain aspects, each of the antennas232and233is a phase array antenna. The RF system200enables the efficient transmission and reception of signals in at least the 60 GHz band.

The baseband module210and RF module230are apart from each other and may be connected using a single transmission line250(e.g., a coax cable) through the interfaces220and240. In certain aspects, the baseband and RF modules210and230are respectively located at the base and lid planes of a laptop computer.

At least four different signals may be simultaneously transferred over the transmission line250including, but not limited to, control, intermediate frequency (IF), and local oscillator source (LO). In some cases, a power signal may be transferred over the transmission line250as well. It should be noted that the IF and control signals are transferred over the line250in both directions. The control signal controls, at least, the switching of the TX and RX active antennas, the direction of the antenna (beam forming), and gain control. The LO signals may be used to synchronize the two modules and to perform up and down conversions of high frequency signals.

Each signal transferred over the transmission line250may have a different frequency band. In certain aspects, a frequency plan is described that enables the efficient transfer of the five signals over the transmission line250. In accordance with an embodiment, the transmission line250is a standard micro coaxial cable. According to certain aspects, the transmission line250may be formed by fabricating a metal line on a multilayer substructure.

During the simultaneous transfer of the LO, IF, and control signals over the transmission line250, the interface units220and240are used. The interface units220and240multiplex the various signals and impedance matches between the transmission line250and the PCBs to which the modules210and230are connected to.

As shown inFIG. 2, the chip-to-line interface unit220includes a multiplexer222and a Bias-T unit224and the line-to-chip interface unit240includes a demultiplexer242and a Bias-T unit244. The multiplexer222multiplexes the IF signal, LO signal, and control signal to be output on a single output provided to the input of the Bias-T unit224. In some cases, the Bias-T unit224also adds a DC voltage signal from a power source and outputs the signal to the transmission line250. The multiplexer222also performs a demultiplexing operation to produce the IF signal(s) and control signal transferred from the RF module230.

The demultiplexer242de-multiplexes the input received on the transmission line250, to generate the control signal, IF signal, and LO signal. Prior to that, the Bias-T unit244may extract the DC voltage signal to power the RF module230if the input received on the transmission line includes a power signal. In some cases, the Bias-T244may extract the control signal from the input received on the transmission line250, as will be described in more detail herein. The demultiplexer242also performs a multiplexing operation on the IF signal (results of a down conversion of the received RF signals) and control signal to be transferred to the baseband module210.

In certain aspects, the multiplexer222and Bias-T unit224are integrated in the baseband module210which are embedded in an RFIC. In the same fashion, the demultiplexer242and Bias-T unit244may be integrated in the RF module230, which is fabricated as an RFIC, as will be described in more detail herein. In certain aspects, the multiplexer222and demultiplexer242may be part of the baseband and RF modules respectively, thus are part of the RFICs. The Bias-T units224and244may be part of a mainboard201and an antenna board202, respectively.

In certain aspects, the baseband module210and RF module230are fabricated on different substrates and connected using a transmission line (e.g., a cable). According to another embodiment, the RF and baseband modules are fabricated on the same substrate and are connected using a coaxial cable. In this embodiment, the techniques described herein for multiplexing the signals may also be applied.

FIG. 3shows a non-limiting block diagram of the multiplexer222constructed in accordance with one embodiment. The multiplexer222separates the frequency spectrum to three different frequency bands: fIF, fLO, and fCTRLto multiplex the LO signal, IF signal, and control signal in these bands respectively. Specifically, the multiplexer222includes a high-pass filter (HPF)310, a base-pass filter (BPF)320, and a low-pass filter (LPF)330; each passes signals in the fIF, fLO, and fCTRLrespectively.

While the description above refers to the laptop computer100as a reference example of a type of device that may implement the techniques presented herein, those of ordinary skill in the art will recognize that the techniques presented herein may also be implemented in a variety of other types of devices (e.g., such as mobile phones, desktop computer, household devices, etc.). Further, those of ordinary skill in the art will recognize that the form factor of the RF system110described above is provided merely as a reference example, and that the techniques presented herein may be applied to other configurations of the RF system110.

Example Fast Beamforming Training

Certain aspects of the present disclosure provide improved techniques for beamforming training of multi-antenna systems. The techniques may help to substantially reduce the time used for beamforming training by simultaneously training multiple antennas.

In certain multi-antenna systems (e.g., mmWave systems), beamforming training typically involves the transmitter sending fixed pilots as the receiver trains its elements on the received signal. In some cases, the training may involve receiving many elements using a Hadamard matrix. In case of multiple antennas, but a single RF chain, then the training may take a substantial amount of time as each antenna is trained in sequence.

Aspects of the present disclosure, however, may take advantage of the presence, in many multi-array systems, of a detector per RF antenna. For example, aspects of the present disclosure propose using the detectors in the RF antenna to simultaneously train the multiple antennas, thus significantly improving efficiency and simplifying the training flow.

The techniques provided herein may reduce the amount of time by reducing the amount of time required for a beam refinement phase (BRP) in 802.11ad/ay/aj devices. Each BRP IE typically has substantial data (e.g., 38 bytes) which are sent using MCS0 or MCS1. The techniques provided herein may result in an advantage (e.g., of 4-5×) in time savings for the BRP-RX phase of massive-array with 8 antennas.

FIG. 4is a flow diagram of example operations400for wireless communications, in accordance with certain aspects of the present disclosure. The operations400may be performed, for example, by a baseband module to simultaneously train multiple antenna elements of multiple RF modules.

The operations400begin, at402, by obtain, from each of a plurality of radio frequency (RF) modules, first information regarding detection of one or more pilot signals via at least one antenna element at a respective one of the plurality of RF modules. At404, the apparatus process the first information obtained from the plurality of RF modules to generate second information to synchronize the plurality of RF modules. At406, the second information is provided to the plurality of RF modules.

FIG. 5is a flow diagram of example operations500for wireless communications, in accordance with certain aspects of the present disclosure. The operations500may be performed, for example, by an RF module being trained by a baseband module performing operations400described above.

The operations500begin, at502, by detect one or more pilot signals via at least one activated antenna element. At504, the apparatus provides, to a processing module, first information regarding the detection of the one or more pilot signals via the at least one activated antenna element. At506, the apparatus obtains, from the processing module, second information generated at least based on the first information. At508, the apparatus makes adjustments to components of the RF module based on the second information.

As will be described in greater detail below, in some cases, training operations may initiated, by a triggering message sent from the base band chip to the one or more RF modules. The triggering message may be sent using a broadcast to all RF modules at the same time, to start off at the same time. The triggering message may comprise additional information, for example, regarding the carrier frequency offset associated with (e.g., between) the transmitter and the receiver (e.g., in PPM), as estimated in the base band chip during frame decoding. The triggering message may also comprise an index to a sector for use as pilots in the RF processing and toggling.

FIG. 6illustrates an example of simultaneous training of multiple RF modules (labeled RF chips), by a baseband module (labeled as a modem or “M-chip”). In one or more cases, operations that make up the training of the multiple RF modules may be performed by the baseband module. In some cases, another processor or a second baseband module may be provided that communicates with the baseband module and the RF modules and performs one or more of the operations. As illustrated inFIG. 6, the training consists of performing Golay cross-correlation using at least one Golay cross-correlator (at each of the RF modules), based on directional pilot signals sent as training (TRN) fields from a transmitter, and picking the right tap for the training. These detected peaks may be sent from each RF module to base band chip for joint processing of the results.

According to certain aspects, this joint processing may involve, among other things, tracking which corrects the frequency offset and the phase noise difference between the transmitter and receiver. In some cases, the joint processing may involve leveling the antenna gains between the RF antennas. In some cases, the joint processing may involve deciding on the best array pattern (e.g., an omnidirectional or directed pattern) setting for tracking pilots. The results of this joint processing may be included in the second information. Accordingly, in some cases, the second information may include information allowing at least one of the RF modules or a baseband module to correct for at least one of frequency offset or timing offset between each of the RF modules or the baseband module and a transmitter of the pilot signals. In some cases, the second information may include information allowing at least one of the RF modules or a baseband module to correct for phase noise difference between each of the RF modules or the baseband module and a transmitter of the pilot signals.

In some cases, time synchronization between RF modules may be performed in the BB module, but tracking may also track in RF modules. In some cases, the BB module may control toggling of antennas. In some cases, the toggling may involve selective activation. In some cases, selective activation may include a processing system that generates third information to trigger each RF module to activate or deactivate one or more antenna elements for pilot signal detection. In some cases, the antennas may be antennas to be trained.

The baseband module may perform initial frequency offset and timing correction, which may be sent from the baseband module to each RF module. The RF module may then use this information for phase estimation. The BB module and/or RF modules may also perform an additional phase of synchronization among all antennas.

In general, the BB module may measure all RF antennas, each at a time. For example, the BB module may measure a single activated antenna element from each antenna activated at a time with the remaining antenna deactivated. From this measurement, the BB module may synchronize the entire training between antennas of each RF module.

As illustrated inFIGS. 7A and 7B, a BB module700may control (via a trigger message) all antennas to start toggling at the same time. As noted above, such a trigger message may be broadcast to all RF modules and may comprise additional information (e.g., carrier frequency offset and/or a sector index) The RF modules may then send a BRP report or one or more BRP reports (e.g., with detected peaks) to the BB module, allowing the BB module to perform synchronization between the RF modules. In one or more cases, each BRP report may include first information regarding detection of a pilot signal from a single antenna element or sector. In some cases, the BRP report may include information regarding one or more taps of a Golay cross-correlator of the RF module with detection peaks of the pilot signals. The information regarding one or more taps of a Golay cross-correlator may include an estimate of a phase of one or more of the detection peaks. By controlling training of multiple RF modules in this manner, the techniques described herein may speed training significantly relative to conventional techniques that train a single RF chain at a time.

FIG. 8illustrates another implementation800with components allowing for the performing of tracking in the RF module. As illustrated, an additional phasor810and time-buffer820may be used. As noted above, a triggering message (e.g. with PPM and OMNI sector) may be provided to all RF modules.

As illustrated inFIG. 9, during a detection stage, different arrays may be activated and set to different omni directions, which may speed detection. After detection of a certain omni setting, different RF modules may be set to the same certain omni setting that was detected. For example, as shown inFIG. 9, during the detection stage the arrays 1, 2, and 3 may start with different omni directions 1, 2, and 3, respectively. As shown the detection of a certain omni setting occurs in this example at array 1. Accordingly, as shown during the training stage, all three arrays may then be set to Omni1as illustrated. In some cases one or antennas may be deactivated for pilot signal detection.

As illustrated inFIG. 10, each RF module may send Golay cross-correlation peaks for each tap per element for each TRN frame to the baseband module. Phases and gains may be determined at the baseband module. In some cases, as illustrated inFIG. 11, however, tracking may be implemented in the RF module and the RF modules may just send information for the best taps. In such cases, the baseband module may determine phases and gains for the reported taps. In any case, multiple taps may be processed in parallel, for the same TRN frames. This processing may be useful for first arrival correction interference alignment.

As illustrated inFIG. 12, depending on a particular implementation, the amount of processing performed at each RF module, and amount of information provided may vary. For example, according to one option shown in the first column of the table ofFIG. 12, all (IQ) measurements (for each tap) may be provided to the BB module, while tracking is performed at the BB module only. According to a second option shown in the second column of the table ofFIG. 12, all (IQ) measurements (for each tap) may be provided to the BB module, but tracking is performed at the RF modules, while phases are determined at the BB module. According to a third option shown in the third column of the table ofFIG. 12, only gain measurements for a limited number of taps (e.g., 16) may be provided to the BB module, and tracking may be performed and phases are determined at the RF modules.

Synchronization for the multi-array antenna system may be performed as follows in accordance with one or more cases. For all RF modules, same TRN is received by the baseband module (M-chip) and the RF modules (R chip) for the Omni element. Track and cross-correlation may be performed on both receptions. In implementation option 1, described above, track is done twice in the M-chip. In implementation options 2 and 3, track is done once in the M-chip and once in the RF-chip. Cross-correlation may be done both in the M-chip and RF-chip. Peak indices [7 bit index inside the CES] for both receptions may be taken for the pi/2+Phasor compensation. The reception may be synchronized by using the strongest peak from M and RF. For example, this strongest peak may be obtained by summing the 16 taps from all RF antennas or up to 128 taps when each array receives different reception. In some cases, the strongest tap may be obtained as the following sum:

The phase correction and gain correction may be used to adjust components to align the phase and gain in the RF modules. In one or more cases, adjustments of one or more antenna weights of the RF module may be provided to enable the antenna array pattern.

Synchronization for the multi-array antenna system may be performed as follows. For all RF modules, same TRN is received by the baseband module for the Omni element for each RF antenna sequentially. Track and cross-correlation may be performed on both receptions. The reception may be synchronized by using the strongest peak as selected by the M from the receptions in the synchronization stage or by combining receptions done in all RFs. For example, this strongest peak may be obtained by summing the 16 taps from all RF antennas or up to 128 taps when each array receive different reception. In some cases, the strongest tap may be obtained as the following sum:

In another embodiment the strongest peak may be chosen from the strongest peak of the cross correlation output during the omni reception at the base band chip.

The phase correction and gain correction may be used to adjust components to align the phase and gain in the RF modules.

Generally, a mainboard may comprise, for example, a circuit board that includes a baseband module, and an antenna board may comprise, for example, a circuit board that includes an RF module. An RF module may comprise, for example, a module that includes RF front end circuitry for generating RF signals. A baseband module may comprise, for example, circuitry configured to generate baseband signals. A regulator may comprise, for example, a circuit used to regulate a voltage (e.g., a linear regular or a switch mode regulator). A DC-to-DC regulator may comprise, for example, a regulator that receives an input DC signal and generates a regulated DC output signal. Bias-T circuit may comprise, for example, a circuit configured to combine (or split) high-frequency and low-frequency signals. A low-pass filter (LPF) may comprise, for example, a circuit for passing low-frequency signals and blocking high-frequency signals.

In some cases, rather than actually transmitting a frame, a device may have an interface to output a frame for transmission. For example, a processor may output a frame, via a bus interface, to an RF front end for transmission. Similarly, rather than actually receiving a frame, a device may have an interface to obtain a frame received from another device. For example, a processor may obtain (or receive) a frame, via a bus interface, from an RF front end for transmission.

The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. For example, operations400illustrated inFIG. 4, and operations500illustrated inFIG. 5, correspond to means400A illustrated inFIG. 4A, means500A illustrated inFIG. 5A, respectively.

For example, means for obtaining, means for providing, or means for detecting may include an RF module130or an IF module120as illustrated inFIG. 1, an RF module or baseband module210as illustrated inFIG. 2, and/or an RF chip or M-chip as illustrated inFIG. 6, 10, or11. Means for processing, means for estimating, means for adjusting, means for including, means for activating, or means for making may comprise a processing system, which may include one or more processors, such as the RF module130or IF module120illustrated inFIG. 1, the baseband module210or the RF module230illustrated inFIG. 2, the RF chip or M-chip illustrated inFIG. 6, 10, or11, and/or the BB module700or implementation800as illustrated inFIGS. 7A, 7B, and 8, respectively.

According to certain aspects, such means may be implemented by processing systems configured to perform the corresponding functions by implementing various algorithms (e.g., in hardware or by executing software instructions) described above for providing an immediate response indication in a PHY header. For example, an algorithm for outputting a first frame for transmission to another apparatus at a first time, an algorithm for obtaining, at a second time, a second frame transmitted by the other apparatus in response to the first frame, and an algorithm for generating a third frame for transmission to the other apparatus via the transmit interface, the third frame including information indicating a difference between the first time and the second time and an indication of at least one of an angle of departure of the first frame or an angle of arrival of the second frame. In another example, an algorithm for outputting a second frame for transmission to another apparatus in response to a first frame received from the other apparatus, an algorithm for obtaining a third frame transmitted by the other apparatus in response to the second frame, the third frame including information indicating a difference between the first time and the second time and an indication of at least one of an angle of departure of the first frame or an angle of arrival of the second frame, and an algorithm for estimating a location of the apparatus relative to the other apparatus based, at least in part, on the difference between the first time and the second time and at least one of the angle of departure of the first frame or the angle of arrival of the second frame.

Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer-readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For example, instructions for outputting a first frame for transmission to another apparatus at a first time, instructions for obtaining, at a second time, a second frame transmitted by the other apparatus in response to the first frame, and instructions for generating a third frame for transmission to the other apparatus via the transmit interface, the third frame including information indicating a difference between the first time and the second time and an indication of at least one of an angle of departure of the first frame or an angle of arrival of the second frame. In another example, instructions for outputting a second frame for transmission to another apparatus in response to a first frame received from the other apparatus, instructions for obtaining a third frame transmitted by the other apparatus in response to the second frame, the third frame including information indicating a difference between the first time and the second time and an indication of at least one of an angle of departure of the first frame or an angle of arrival of the second frame, and instructions for estimating a location of the apparatus relative to the other apparatus based, at least in part, on the difference between the first time and the second time and at least one of the angle of departure of the first frame or the angle of arrival of the second frame.