Per stream and per antenna cyclic shift delay in uplink multi-user MIMO

A method, an apparatus, and a computer-readable medium for wireless communication are provided. In one aspect, an apparatus includes a processor configured to determine a first set of CSD values for transmitting a first set of information on a plurality of antennas, determine a second set of CSD values for transmitting a second set of information on the plurality of antennas, and transmit the first set of information based on the first set of CSD values and the second set of information based on the second set of CSD values.

BACKGROUND

Field

The present disclosure relates generally to communication systems, and more particularly, to per stream and per antenna cyclic shift delay (CSD) in uplink multi-user (MU) multiple-input-multiple-output (MIMO) transmissions.

Background

SUMMARY

The systems, methods, computer-readable medium, and devices of the invention each have several aspects, no single one of which is solely responsible for the invention's desirable attributes. Without limiting the scope of this invention as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description,” one will understand how the features of this invention provide advantages for devices in a wireless network.

One aspect of this disclosure provides an apparatus (e.g., a station) for wireless communication. The apparatus is configured to determine a first set of CSD values for transmitting a first set of information on a plurality of antennas. The apparatus is configured to determine a second set of CSD values for transmitting a second set of information on the plurality of antennas. The apparatus is configured to transmit the first set of information based on the first set of CSD values and transmit the second set of information based on the second set of CSD values.

DETAILED DESCRIPTION

Popular wireless network technologies may include various types of WLANs. A WLAN may be used to interconnect nearby devices together, employing widely used networking protocols. The various aspects described herein may apply to any communication standard, such as a wireless protocol.

In some aspects, wireless signals may be transmitted according to an 802.11 protocol using orthogonal frequency-division multiplexing (OFDM), direct-sequence spread spectrum (DSSS) communications, a combination of OFDM and DSSS communications, or other schemes. Implementations of the 802.11 protocol may be used for sensors, metering, and smart grid networks. Advantageously, aspects of certain devices implementing the 802.11 protocol may consume less power than devices implementing other wireless protocols, and/or may be used to transmit wireless signals across a relatively long range, for example about one kilometer or longer.

In some implementations, a WLAN includes various devices which are the components that access the wireless network. For example, there may be two types of devices: access points (APs) and clients (also referred to as stations or “STAs”). In general, an AP may serve as a hub or base station for the WLAN and a STA serves as a user of the WLAN. For example, a STA may be a laptop computer, a personal digital assistant (PDA), a mobile phone, etc. In an example, a STA connects to an AP via a Wi-Fi (e.g., IEEE 802.11 protocol) compliant wireless link to obtain general connectivity to the Internet or to other wide area networks. In some implementations a STA may also be used as an AP.

An access point may also comprise, be implemented as, or known as a NodeB, Radio Network Controller (RNC), eNodeB, Base Station Controller (BSC), Base Transceiver Station (BTS), Base Station (BS), Transceiver Function (TF), Radio Router, Radio Transceiver, connection point, or some other terminology.

A station may also comprise, be implemented as, or known as an access terminal (AT), a subscriber station, a subscriber unit, a mobile station, a remote station, a remote terminal, a user terminal, a user agent, a user device, a user equipment, or some other terminology. In some implementations, a station may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, a headset, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a gaming device or system, a global positioning system device, or any other suitable device that is configured to communicate via a wireless medium.

In an aspect, MIMO schemes may be used for wide area WLAN (e.g., Wi-Fi) connectivity. MIMO exploits a radio-wave characteristic called multipath. In multipath, transmitted data may bounce off objects (e.g., walls, doors, furniture), reaching the receiving antenna multiple times through different routes and at different times. A WLAN device that employs MIMO will split a data stream into multiple parts, called spatial streams (or multi-streams), and transmit each spatial stream through separate antennas to corresponding antennas on a receiving WLAN device.

The term “associate,” or “association,” or any variant thereof should be given the broadest meaning possible within the context of the present disclosure. By way of example, when a first apparatus associates with a second apparatus, it should be understood that the two apparatuses may be directly associated or intermediate apparatuses may be present. For purposes of brevity, the process for establishing an association between two apparatuses will be described using a handshake protocol that requires an “association request” by one of the apparatus followed by an “association response” by the other apparatus. It will be understood by those skilled in the art that the handshake protocol may require other signaling, such as by way of example, signaling to provide authentication.

Any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations are used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must precede the second element. In addition, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: A, B, or C” is intended to cover: A, or B, or C, or any combination thereof (e.g., A-B, A-C, B-C, and A-B-C).

As discussed above, certain devices described herein may implement the 802.11 standard, for example. Such devices, whether used as a STA or AP or other device, may be used for smart metering or in a smart grid network. Such devices may provide sensor applications or be used in home automation. The devices may instead or in addition be used in a healthcare context, for example for personal healthcare. They may also be used for surveillance, to enable extended-range Internet connectivity (e.g. for use with hotspots), or to implement machine-to-machine communications.

FIG. 1shows an example wireless communication system100in which aspects of the present disclosure may be employed. The wireless communication system100may operate pursuant to a wireless standard, for example the IEEE 802.11 standard. The wireless communication system100may include an AP104, which communicates with STAs (e.g., STAs112,114,116, and118).

A variety of processes and methods may be used for transmissions in the wireless communication system100between the AP104and the STAs. For example, signals may be sent and received between the AP104and the STAs in accordance with OFDM/OFDMA techniques. If this is the case, the wireless communication system100may be referred to as an OFDM/OFDMA system. Alternatively, signals may be sent and received between the AP104and the STAs in accordance with CDMA techniques. If this is the case, the wireless communication system100may be referred to as a CDMA system.

A communication link that facilitates transmission from the AP104to one or more of the STAs may be referred to as a downlink (DL)108, and a communication link that facilitates transmission from one or more of the STAs to the AP104may be referred to as an uplink (UL)110. Alternatively, a downlink108may be referred to as a forward link or a forward channel, and an uplink110may be referred to as a reverse link or a reverse channel. In some aspects, DL communications may include unicast or multicast traffic indications.

The AP104may suppress adjacent channel interference (ACI) in some aspects so that the AP104may receive UL communications on more than one channel simultaneously without causing significant analog-to-digital conversion (ADC) clipping noise. The AP104may improve suppression of ACI, for example, by having separate finite impulse response (FIR) filters for each channel or having a longer ADC backoff period with increased bit widths.

The AP104may act as a base station and provide wireless communication coverage in a basic service area (BSA)102. A BSA (e.g., the BSA102) is the coverage area of an AP (e.g., the AP104). The AP104along with the STAs associated with the AP104and that use the AP104for communication may be referred to as a basic service set (BSS). It should be noted that the wireless communication system100may not have a central AP (e.g., AP104), but rather may function as a peer-to-peer network between the STAs. Accordingly, the functions of the AP104described herein may alternatively be performed by one or more of the STAs.

The AP104may transmit on one or more channels (e.g., multiple narrowband channels, each channel including a frequency bandwidth) a beacon signal (or simply a “beacon”), via a communication link such as the downlink108, to other nodes (STAs) of the wireless communication system100, which may help the other nodes (STAs) to synchronize their timing with the AP104, or which may provide other information or functionality. Such beacons may be transmitted periodically. In one aspect, the period between successive transmissions may be referred to as a superframe. Transmission of a beacon may be divided into a number of groups or intervals. In one aspect, the beacon may include, but is not limited to, such information as timestamp information to set a common clock, a peer-to-peer network identifier, a device identifier, capability information, a superframe duration, transmission direction information, reception direction information, a neighbor list, and/or an extended neighbor list, some of which are described in additional detail below. Thus, a beacon may include information that is both common (e.g., shared) amongst several devices and specific to a given device.

In some aspects, a STA (e.g., STA114) may be required to associate with the AP104in order to send communications to and/or to receive communications from the AP104. In one aspect, information for associating is included in a beacon broadcast by the AP104. To receive such a beacon, the STA114may, for example, perform a broad coverage search over a coverage region. A search may also be performed by the STA114by sweeping a coverage region in a lighthouse fashion, for example. After receiving the information for associating, the STA114may transmit a reference signal, such as an association probe or request, to the AP104. In some aspects, the AP104may use backhaul services, for example, to communicate with a larger network, such as the Internet or a public switched telephone network (PSTN).

In an aspect, the STA114may include one or more components for performing various functions. For example, the STA114may include a CSD component124configured to determine a first set of CSD values for transmitting a first set of information on a set of antennas associated with the STA114. The CSD component124may be configured to determine a second set of CSD values for transmitting a second set of information on the set of antennas. The CSD component124may be configured to transmit the first set of information based on the first set of CSD values and the second set of information based on the second set of CSD values.

FIG. 2is a diagram200of a wireless network (e.g., a Wi-Fi network employing the IEEE 802.11 standard). The diagram200illustrates an AP202broadcasting/transmitting within a service area214. STAs206,208,210,212are within the service area214of the AP202(although only four STAs are shown inFIG. 2, more or less STAs may be within the service area214). The AP202may transmit a trigger message216to the STA212(and to the STAs206,208,210). The trigger message216may include configuration information related to each of the STAs206,208,210,212.

The AP202may transmit symbols (e.g., data symbols or long training field (LTF) symbols)204to one or more STAs (e.g., STAs206,208,210,212) in one or more frames, and vice versa. A frame250may include a preamble260and data symbols298. The preamble260may be considered a header of the frame250with information identifying a modulation and coding scheme, a transmission rate, and a length of time to transmit the frame250, among other information. For example, the preamble260may include a legacy preamble270and a high-efficiency (HE) preamble280(e.g., the HE preamble280may be used in future IEEE 802.11 standards). The legacy preamble270may contain header information for older Wi-Fi standards to enable products incompatible with newer Wi-Fi standards to decode the frame250. The legacy preamble270may include a legacy short training field (L-STF) symbol272, a legacy long training field (L-LTF) symbol274, a legacy signal field (L-SIG) symbol276, a very high throughput signal field A (VHT-SIG-A) symbol278, and/or other fields. Each of the various fields in the legacy preamble270may include one or more OFDM symbols and may have a 1× symbol time duration (e.g., symbol duration of 3.2 μs or some multiple of 3.2 μs). The L-STF symbol272may be used to improve automatic gain control (AGC) in a multi-transmit and multi-receive system. The L-LTF symbol274may be used to provide the information needed for a receiver (e.g., the STA206or the AP202) to perform channel estimation. The L-SIG symbol276and the VHT-SIG-A symbol278may be used to provide transfer rate and length information. The symbols in the legacy preamble270may have a 1× symbol time duration (e.g., 4 μs of which 0.8 μs may be the cyclic prefix (CP))

In addition to the legacy preamble270, the preamble260may include an HE preamble280. The HE preamble280may contain header information related to a future Wi-Fi standard. The HE preamble280may include an HE signal field (HE-SIG) symbol292, an HE short training field (HE-STF) symbol294, one or more HE long training field (HE-LTF) symbols296, and/or other fields. The HE-STF symbols294may be used to improve AGC. The HE-SIG symbol292may be used to provide transfer rate and length information. And the HE-LTF symbols296may be used for channel estimation. The number of HE-LTF symbols296may be equal to or greater than the number of space-time streams from different STAs. For example, if there are 4 STAs, there may be 4 LTF symbols (i.e. HE-LTF1, HE-LTF2, HE-LTF3, HE-LTF4). The frame250may also include a set of data symbols298that contain the user data to be communicated between the STA206, for example, and the AP202. The HE preamble280together with the data symbols298may make up an HE portion290. The symbols in the HE preamble280and the data symbols298may have a 4× symbol time duration (e.g., 16 μs of which 3.2 μs may be the CP).

In uplink multi-user MIMO transmissions within a Wi-Fi network, such as the Wi-Fi network inFIG. 2, each STA may have multiple transmission antennas for MIMO. For example, the STA206may have 4 transmission antennas, the STA208may have 2 transmission antennas, and the STAs210,212may each have 4 transmission antennas. If the STAs206,208,210,212simultaneously transmit to the AP202, each STA may not know how many transmission antennas from the other STAs will be participating in an uplink transmission. Unless the timing of the various transmissions is offset from each other, unintentional beamforming may result. As such, a need exists to determine how to apply a per antenna and/or per stream CSD for each STA (and to each antenna within each respective STA) to avoid unintentional beamforming, to ease the AGC settings, and to provide diversity for users/STAs especially in a flat fading scenario.

FIG. 3illustrates diagrams300,330,360of different LTF designs for uplink multi-user MIMO. Diagram300illustrates 5 tone interleaved LTFs (e.g., HE-LTF). Each LTF symbol has a set of tones. In diagram300, there are 4 streams, each denoted by a respective indicator (e.g., square, circle, triangle, x). Every stream visits (or is transmitted on) every tone by the end of the LTFs, which enables per-LTF phase tracking. In another design, a p-matrix-based LTF may be used with a 4× symbol duration. Diagram330illustrates a delay-based LTF (e.g., HE-LTF) with a 4× symbol duration. As shown in diagram330, assuming there are 4 users, each having 1 stream, the stream for each respective user is offset by [0, 3.2, 6.4, 9.6] μs delays in an OFDM symbol which may have a 16 μs symbol duration with a 3.2 μs CP. In yet another design, diagram360illustrates a delay-based LTF (e.g., HE-LTF) with a 4× symbol duration. As shown in diagram360, assuming there are 2 users, each having 1 stream, the stream for each respective user is offset by [0, 6.4] μs delays in an OFDM symbol which has a 16 μs symbol duration with a 3.2 μs CP.

FIG. 4illustrates diagrams400,450of stations determining per antenna and/or per stream CSD values for transmitting information (e.g., the legacy preamble270and the HE portion290). Diagram400illustrates 3 STAs410,420,430(which may correspond to STAs208,210,212) associated with/served by an AP (e.g., the AP202). Each of the STAs410,420,430may have 4 antennas. For example, the STA410may have antennas412,414,416,418. The STA420may have antennas422,424,426,428. The STA430may have antennas432,434,436,438. Similarly, diagram450illustrates 2 STAs460,470(which may correspond to STAs210,212) associated with an AP (e.g., the AP202). Each of the STAs460,470has 2 antennas. For example, the STA460has antennas462,464. The STA470has antennas472,474. Referring to diagram400, during uplink transmission, for example, the antennas for the STAs410,420,430may transmit information to an AP (e.g., the AP202), and the information may include the legacy preamble270, the HE preamble280, and the data symbols298. As previously discussed, however, the STA410, for example, may not know how many transmission antennas from the STAs420,430will be participating in uplink transmissions. To avoid unintentional beamforming, among other issues previously mentioned, CSD may be used for transmitting the legacy preamble270, the HE preamble280, and/or the data symbols298.

Different CSD options may apply with respect to the legacy preambles compared to the HE preambles and the data symbols because cyclic shifts for legacy preambles are limited to 200 ns. As such, the discussion below presents CSD options for legacy preambles and CSD options for non-legacy preambles and data symbols.

CSD Options for Legacy Preambles

With respect to legacy preambles, two per antenna CSD options may be used.

Per Antenna CSD Option1

In per antenna CSD option1, uplink transmissions may be offset by assigning each STA a user CSD offset. Referring to diagram400, each of the 4 antennas for the STAs410,420,430may have information to transmit to an AP (e.g., the AP202), and the information may include the legacy preamble270, for example. The STAs410,420,430may have an initial set of per antenna CSD values, which may be preconfigured within each of the STAs based on the antenna configuration (e.g., based a number of antennas). For example, the STA410may apply an initial set of CSD values [0 −50 −100 −150] ns to each of the 4 antennas412,414,416,418, respectively. Each of the other STAs420,430may use the same initial set of CSD values [0 −50 −100 −150] ns for each of the 4 respective antennas. To avoid having the same delay from different users, a different CSD offset for each STA may be applied. In one configuration, the STAs410,420,430may receive user CSD offsets of 0 ns, −25 ns, and −50 ns, respectively via a trigger message (e.g., the trigger message216). The STA410may modify the initial set of CSD values [0 −50 −100 −150] ns based on the user CSD offset. In an aspect, the STA410may modify the initial set of CSD values [0 −50 −100 −150] for the antennas412,414,416,418based on a 0 ns user CSD offset and have the same set of CSD values. The STA420may modify the initial set of CSD values based on a −25 ns user CSD offset and have a set of CSD values [−25 −75 −125 −175] ns for the antennas422,424,426,428. The STA430modify the initial set of CSD values based on a −50 ns user CSD offset and have a set of CSD values [−50 −100 −150 −200] ns for the antennas432,434,436,438. In an aspect, the initial set of CSD values [0 −50 −100 −150] may be preconfigured into each of the STAs410,420,430based on the antenna configuration. In one aspect, the user CSD offset may be determined by the STAs410,420,430based on a user index which may be indicated in scheduling signaling from the AP202. For example, when the AP202transmits a user index of 0 in scheduling signaling to the STA410, the user index of 0 may correspond to a user CSD value of 0 ns. A user index of 1 may correspond to a user CSD value of −25 ns, etc. In an aspect, the STA410may have a table that indicates which user index corresponds to which CSD value, and the STA410may determine which CSD value to use upon receiving a user index based on the table. In another aspect, the user CSD value may be transmitted in a trigger message216from the AP202. By adding time diversity to the CSD delay based on a per user CSD offset, the likelihood of unintentional beamforming for the uplink transmissions may be reduced. Although this example shows 4 antennas, more or less antennas may be used, and a different initial set of CSD values may also be used.

In an aspect, the per user CSD offset/value for each of the STAs410,420,430may be zero. In this aspect, each of the STAs410,420,430may apply the same per antenna CSD (e.g., [0 −50 −100 −150] ns if the number of transmission antennas is 4 for all STAs). Because different users may transmit using different transmission powers, in some instances, having the same delays among users may not cause beamforming (or excessive beamforming), especially when a service area has more than two users. With a greater number of STAs/users, there may be linear shifts due to the different inter-arrival times of transmissions among different STAs, which may offset the STA/user transmissions so that the probability of an unintentional beamforming may be reduced.

Per Antenna CSD Option2

In per antenna CSD option2, uplink transmissions may be offset by assigning/allocating one or more CSD values to each of the STAs according to the number of space-time streams each STA has been allocated. For example, referring to diagram450inFIG. 4, assume that the STAs460,470are being served by the AP202and that the AP202has 4 antennas that support the STAs460,470. Each of the STAs460,470has 2 antennas. In this example, the STA460may be assigned 2 streams for transmitting the legacy preamble270associated with the STA460, and the STA470may be assigned 1 stream for transmitting the legacy preamble270associated with the STA470. The STA460may be assigned two CSD values from the initial set of CSD values, which may be 0 ns and −50 ns. The STA460may apply these CSD values on the antennas462,464, respectively. The STA470, which may have 1 space-time stream (Nsts=1) corresponding to the third stream of the multi-user MIMO streams, may be assigned the third CSD value from the initial set of CSD values, which may be −100 ns. Because the STA470has two antennas472,474, the STA470may map the −100 ns CSD value to the two antennas472,474via a spatial mapping matrix [1;1], which corresponds to −100 ns for both the antennas472,474for the STA470. In this aspect, antennas may have the same CSD value when the number of spatial streams is less than a number of antennas for a given STA/user. Further, in this option, the assigned/allocated CSD value may be determined in part by the order in which each STA is allocated CSD values. For example, if the STA460is assigned CSD values first and the STA470is assigned CSD values second, then the STA460may be assigned CSD values of 0 ns and −50 ns, and the STA470may be assigned the CSD value −100 ns. By contrast, if the STA470is assigned CSD values first and the STA460is assigned CSD values second, then the STA470may be assigned the CSD value 0 ns and the STA460may be assigned the CSD values of −50 ns and −100 ns. In this option, each of the STAs460,470may derive the assigned CSD value from a received spatial stream allocation information from the AP202. The received spatial stream allocation information may be received in a trigger message216or in another message/packet from the AP202, for example. Although this example uses an AP with 4 antennas and STAs with 2 antennas, other configurations may be used.

CSD Options for Non-Legacy Information

For non-legacy information (e.g., the HE preamble280and the data symbols298) per antenna and per stream CSD options are available.

Per Stream CSD

Non-legacy information, which may include the HE preamble280and the data symbols298, may be transmitted in spatial streams with a per stream CSD. For example, referring diagram450ofFIG. 4, the STA460may determine/identify two spatial streams—stream A and stream B—for transmitting the HE preamble280. The STA460may determine a per stream CSD value for each of stream A and stream B. For example, stream A may be given a 0 ns CSD value and stream B may be given a −400 ns CSD value. Accordingly, stream A may be transmitted at time0and stream B may transmitted with a 400 ns cyclic delay compared to stream A. Per stream CSD may be used with respect to HE-LTFs, for example, such as P-matrix based LTFs and those discussed with respect to diagrams300,330, and360. However, for the delay based LTF in diagram330, which uses a delay (equal to a multiple of the CP length) to separate users, further applying a per stream CSD could make different user channels collide with each other unless the users are separated by a delay of at least two times (2×) CP length. As such, for a symbol with a 4× symbol duration, an LTF design as shown in diagram360may be preferable to the LTF design as shown in diagram330.

In addition to per stream CSD, per antenna CSD may be applied to the symbols in the HE preamble280and the data symbols298.

Per Antenna CSD Option1

In per antenna CSD option1, uplink transmissions may be offset by assigning each STA a user CSD offset. Referring to diagram400, each of the 4 antennas for the STAs410,420,430may have information to transmit to an AP, and the information may include the HE preamble280and/or the data symbols298, for example. The STAs410,420,430may have an initial set of per antenna CSD values, which may be preconfigured within each of the STAs based on the antenna configuration (e.g., based a number of antennas). For example, the STA410may apply an initial set of CSD values [0 −400 −200 −600] ns to each of the 4 antennas412,414,416,418, respectively. Each of the other STAs420,430may use the same initial set of CSD values [0 −400 −200 −600] ns for each of the 4 respective antennas. To avoid having the same delay from different antennas, a different CSD offset for each STA may be applied. In one configuration, the STAs410,420,430may receiver user CSD offsets of 0 ns, −50 ns, and −100 ns, respectively via a trigger message (e.g., the trigger message216). The STA410may modify the initial set of CSD values [0 −400 −200 −600] ns based on the user CSD offset. In an aspect, the STA410may modify the initial set of CSD values [0 −400 −200 −600] for the antennas412,414,416,418based on a 0 ns user CSD offset and have the same set of CSD values. The STA420may modify the initial set of CSD values based on a −50 ns user CSD offset and have a set of CSD values [−50 −450 −250 −650] ns for the antennas422,424,426,428. The STA430modify the initial set of CSD values based on a −100 ns user CSD offset and have a set of CSD values [−100 −500 −300 −700] ns for the antennas432,434,436,438. In an aspect, the initial set of CSD values [0 −400 −200 −600] may be preconfigured into each of the STAs410,420,430based on the antenna configuration. In one aspect, the user CSD offset may be determined by the STAs410,420,430based on a user index which may be indicated in scheduling signaling from the AP202. For example, when the AP202transmits a user index of 0 in scheduling signaling to the STA410, the user index of 0 may correspond to a user CSD value of 0. A user index of 1 may correspond to a user CSD value of −50 ns, etc. In another aspect, the user CSD value may be transmitted in a trigger message216from the AP202. By adding time diversity to the CSD delay based on a per user CSD offset, the likelihood of unintentional beamforming for the uplink transmissions may be reduced. Although this example shows 4 antennas, more or less antennas may be used, and a different initial set of CSD values may also be used.

In an aspect, the per user CSD offset/value for each of the STAs410,420,430may be zero. In this aspect, each of the STAs410,420,430may apply the same per antenna CSD (e.g., [0 −400 −200 −600] ns if the number of transmission antennas is 4 for all STAs). Because different users may transmit using different transmission powers, in some instances, having the same delays among users may not cause beamforming (or excessive beamforming), especially when a service area has more than two users. With a greater number of STAs/users, there may be linear shifts due to the different inter-arrival times of transmissions among different STAs, which may offset the STA/user transmissions so that the probability of an unintentional beamforming may be reduced.

Per Antenna CSD Option2

In per antenna CSD option2, uplink transmissions may be offset by assigning/allocating one or more CSD values to each of the STAs according to the number of space-time streams each STA has been allocated. For example, referring to diagram450inFIG. 4, assume that the STAs460,470are being served by the AP202and that the AP202has 4 antennas that support the STAs460,470. Each of the STAs460,470has 2 antennas. In this example, the STA460may be assigned 2 streams for transmitting the HE preamble280and/or the data symbols298, and the STA470may be assigned 1 stream for transmitting the HE preamble280and/or the data symbols298. The STA460may be assigned two CSD values from the initial set of CSD values, which may be 0 ns and −400 ns. The STA460may apply these CSD values on the antennas462,464, respectively. The STA470, which may have 1 space-time stream (Nsts=1) corresponding to the third stream of the multi-user MIMO streams, may be assigned the third CSD value from the initial set of CSD values, which may be −200 ns. Because the STA470has two antennas472,474, the STA470may map the −200 ns CSD value to the two antennas472,474via a spatial mapping matrix [1;1], which corresponds to −200 ns for both the antennas472,474for the STA470. In this aspect, antennas may have the same CSD value when the number of spatial streams is less than a number of antennas for a given STA/user. Further, in this option, the assigned/allocated CSD value may be determined in part by the order in which each STA is allocated CSD values. In this option, each of the STAs460,470may derive the assigned CSD value from a received spatial stream allocation information from the AP202. The received spatial stream allocation information may be received in a trigger message216or in another message/packet from the AP202, for example. Although this example uses an AP with 4 antennas and STAs with 2 antennas, other configurations may be used.

In as aspect, non-legacy information may be transmitted in symbols with a 4× symbol duration (e.g., 16 μs), while legacy information may be transmitted in symbols with a 1× symbol duration (e.g., 4 μs). As such, the per stream CSD values or per antenna CSD values for the non-legacy information with a 4× symbol duration may be 4 times greater than the CSD values for the non-legacy information with a 1× symbol duration. For example, a CSD value for the non-legacy information with a 4× duration may be 1.6 μs and a CSD value for the non-legacy information with a 1× duration may be 0.4 μs. The criteria for determining the CSD value may depend on what CSD value minimizes quantization and saturation at the ADC and what CSD value minimizes the difference between the measured STF and the data power. For each multi-stream transmission case, a CSD combination that works best across the additional white Gaussian noise (e.g., flat fading with random phase), channel model D non-line-of-sight (D-NLOS), and urban micro (UMi) NLOS may be preferred.

FIG. 5is a functional block diagram of a wireless device502that may be employed within the wireless communication system100ofFIG. 1for transmitting information using per antenna and/or per stream CSD values. The wireless device502is an example of a device that may be configured to implement the various methods described herein. For example, the wireless device502may be the STAs112,114,116,118.

The wireless device502may include a processor504which controls operation of the wireless device502. The processor504may also be referred to as a central processing unit (CPU). Memory506, which may include both read-only memory (ROM) and random access memory (RAM), may provide instructions and data to the processor504. A portion of the memory506may also include non-volatile random access memory (NVRAM). The processor504typically performs logical and arithmetic operations based on program instructions stored within the memory506. The instructions in the memory506may be executable (by the processor504, for example) to implement the methods described herein.

The wireless device502may also include a housing508, and the wireless device502may include a transmitter510and/or a receiver512to allow transmission and reception of data between the wireless device502and a remote device. The transmitter510and the receiver512may be combined into a transceiver514. An antenna516may be attached to the housing508and electrically coupled to the transceiver514. The wireless device502may also include multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas.

The wireless device502may also include a signal detector518that may be used to detect and quantify the level of signals received by the transceiver514or the receiver512. The signal detector518may detect such signals as total energy, energy per subcarrier per symbol, power spectral density, and other signals. The wireless device502may also include a digital signal processor (DSP)520for use in processing signals. The DSP520may be configured to generate a packet for transmission. In some aspects, the packet may comprise a physical layer convergence procedure (PLCP) protocol data unit (PPDU).

The wireless device502may further comprise a user interface522in some aspects. The user interface522may comprise a keypad, a microphone, a speaker, and/or a display. The user interface522may include any element or component that conveys information to a user of the wireless device502and/or receives input from the user.

When the wireless device502is implemented as a STA (e.g., the STA114, the STA206), the wireless device502may also comprise a CSD component324. The CSD component324may be configured to determine a first set of CSD values for transmitting a first set of information on a plurality of antennas. The CSD component324may be configured to determine a second set of CSD values for transmitting a second set of information on the plurality of antennas. The CSD component324may be configured to transmit the first and second sets of information based on the first and second sets of CSD values. In one configuration, the CSD component324may determine the first set of CSD values by determining an antenna CSD value for each antenna of the plurality of antennas, by determining a user CSD offset, and by modifying the antenna CSD value for each antenna of the plurality of antennas based on the determined user CSD offset. In one configuration, the CSD component324may determine the first set of CSD values by determining at least one assigned CSD value and determining an antenna CSD value for each antenna of the plurality of antennas based on the determined at least one assigned antenna CSD value. In another configuration, the CSD component324may be further configured to determine a third set of CSD values for transmitting the second set of information on the plurality of antennas and transmit the second set of information based on the second and third sets of CSD values. In another configuration, the CSD component324may be configured to determine the third set of CSD values by determining an antenna CSD value for each antenna of the plurality of antennas, by determining a user CSD offset, and by modifying the antenna CSD value for each antenna of the plurality of antennas based on the determined user CSD offset. In another configuration, the CSD component324may be configured to determine at least one assigned CSD value and to determine an antenna CSD value for each antenna of the plurality of antennas based on the determined at least one assigned CSD value. In another configuration, the stream CSD value may be four times greater than a CSD value of a symbol with a 1× time duration. In another configuration, the antenna CSD value may be four times greater than a CSD value of a symbol with a 1× time duration.

The various components of the wireless device502may be coupled together by a bus system526. The bus system526may include a data bus, for example, as well as a power bus, a control signal bus, and a status signal bus in addition to the data bus. Components of the wireless device502may be coupled together or accept or provide inputs to each other using some other mechanism.

Although a number of separate components are illustrated inFIG. 5, one or more of the components may be combined or commonly implemented. For example, the processor504may be used to implement not only the functionality described above with respect to the processor504, but also to implement the functionality described above with respect to the signal detector518, the DSP520, the user interface522, and/or the CSD component524. Further, each of the components illustrated inFIG. 5may be implemented using a plurality of separate elements.

FIG. 6is a flowchart of an exemplary method600of wireless communication for transmitting information using per antenna and/or per stream CSD values. The method600may be performed using an apparatus (e.g., the STA114, the STA212, or the wireless device302, for example). Although the method600is described below with respect to the elements of wireless device502ofFIG. 5, other components may be used to implement one or more of the steps described herein. InFIG. 6, the blocks indicated with dotted lines represent optional operations.

At block605, the apparatus may determine a first set of CSD values for transmitting a first set of information on a plurality of antennas. For example, referring toFIGS. 2 and 4, the apparatus may be the STA410and the first set of information may be the legacy preamble270. In an aspect, the STA410may have the legacy preamble270for transmission. The STA410may receive a user CSD offset from the AP202in the trigger message216. The STA410may determine an initial set of CSD values [0 −50 −100 −150] ns for each of the 4 antennas412,414,416,418. The initial set of CSD values may be pre-configured at the STA410. Based on the trigger message216, the STA410may determine a user CSD offset of −25 ns (e.g., based on a user index set to 1). The STA410may modify the initial set of CSD values to determine a set of antenna CSD values [−25 −75 −125 −175] ns. In another example, the apparatus may be the STA460. The STA460may have the legacy preamble270(the first set of information) for transmission. In this example, the STA460may receive two assigned values [0 −50] ns and determine that the antenna462has a CSD value of 0 ns and the antenna464has a CSD value of −50 ns.

At block610, the apparatus may determine a second set of CSD values for transmitting a second set of information on the plurality of antennas. For example, referring toFIGS. 2 and 4, the apparatus may be the STA460and the second set of information may be the HE preamble280. In one example, the STA460may have the HE preamble280(e.g., HE-LTF symbols296) for transmission. The HE preamble280may be transmitted in two streams—stream A and stream B. The STA460may apply a per stream CSD by identifying the number of streams for transmitting the HE preamble280(e.g., 2 streams) and by determining a per stream CSD value for each of the streams, stream A and B, respectively. Stream A may have a stream CSD value of 0 ns, and stream B may have a stream CSD value of −400 ns. In another example, the STA460may apply a per antenna CSD.

At block615, the apparatus may determine a third set of CSD values for transmitting the second set of information on the plurality of antennas. For example, referring toFIGS. 2 and 4, the apparatus may be the STA460and the second set of information may be the HE preamble280. In an aspect, the STA460may apply a per antenna CSD for transmitting the HE preamble280. In this example, the STA460may receive a trigger message216from the AP202, and the trigger message216may indicate a user CSD offset of −50 ns. Based on the trigger message216, the STA460may determine a user CSD offset of −50 ns. The STA410may modify the set of CSD values, which may be [0 −400] ns based on block610, to determine a set of antenna CSD values [−50 −450] ns for transmitting the HE preamble280. In another aspect, the second set of CSD values may be a per antenna CSD and the third set of CSD values may be a per stream CSD.

At block620, the apparatus may transmit the first set of information based on the first set of CSD values and the second set of information based on the second set of CSD values. In one configuration, the apparatus may transmit the second set of information based on the second and third sets of CSD values. For example, referring toFIGS. 2 and 4, the STA460may transmit the legacy preamble270based on a set of per antennas CSD values [0 −50] ns and transmit the HE preamble280based on CSD values [−50 −450] ns, determined based on a set of per stream CSD values [0 −400] ns and a per antenna CSD value of −50 ns for the STA460.

FIG. 7is a functional block diagram of an exemplary wireless communication device700for transmitting information using per antenna and/or per stream CSD values. The wireless communication device700may include a receiver705, a processing system710, and a transmitter715. The processing system710may include a CSD component724and/or a frame generation component726. In an aspect, the frame generation component726may be configured to generate a frame to be transmitted. The frame generation component726may generate a legacy preamble, an HE preamble, and data associated with a frame to be transmitted. The frame generation component726may provide the frame to be transmitted to the CSD component724. 1. The processing system710and/or the CSD component724may be configured to determine a first set of CSD values for transmitting a first set of information on a plurality of antennas. The processing system710and/or the CSD component724may be configured to determine a second set of CSD values for transmitting a second set of information on the plurality of antennas. The processing system710, the CSD component724, and/or the transmitter715may be configured to transmit the first set of information based on the first set of CSD values and the second set of information based on the second set of CSD values. In one configuration, the processing system710and/or the CSD component724may be configured to determine the first set of CSD values by determining an antenna CSD value for each antenna of the plurality of antennas, by determining a user CSD offset, and by modifying the antenna CSD value for each antenna of the plurality of antennas based on the determined user CSD offset. In another configuration, the processing system710and/or the CSD component724may be configured to determine the first set of CSD values by determining at least one assigned CSD value and by determining an antenna CSD value for each antenna of the plurality of antennas based on the determined at least one assigned antenna CSD value. In another configuration, the processing system710and/or the CSD component724may be configured to determine the second set of CSD values by identifying a plurality of streams for transmitting the second set of information and by determining a stream CSD value for each stream of the plurality of streams. In an aspect, the stream CSD value for a symbol with a 4× time duration may be four times greater than a CSD value of a non-legacy symbol with a 1× time duration. In another configuration, the processing system710and/or the CSD component724may be configured to determine a third set of CSD values for transmitting the second set of information on the plurality of antennas. In this configuration, the second set of information may be transmitted based on the second and third sets of CSD values. In another configuration, the processing system710and/or the CSD component724may be configured to determining the third set of CSD values by determining an antenna CSD value for each antenna of the plurality of antennas, by determining a user CSD offset, and by modifying the antenna CSD value for each antenna of the plurality of antennas based on the determined user CSD offset. In an aspect, the antenna CSD value for a symbol with a 4× time duration may be four times greater than a CSD value of a non-legacy symbol with a 1× time duration. In another configuration, the processing system710and/or the CSD component724may be configured to determine the third set of CSD values by determining at least one assigned CSD value and by determining an antenna CSD value for each antenna of the plurality of antennas based on the determined at least one assigned CSD value.

The receiver705, the processing system710, the CSD component724, the frame generation component726, and/or the transmitter715may be configured to perform one or more functions discussed above with respect to blocks605,610,615, and620ofFIG. 6. The receiver705may correspond to the receiver512. The processing system710may correspond to the processor504. The transmitter715may correspond to the transmitter510. The CSD component724may correspond to the CSD component124and/or the CSD component524.

In one configuration, the wireless communication device700may include means for determining a first set of CSD values for transmitting a first set of information on a plurality of antennas. The wireless communication device700may include means for determining a second set of CSD values for transmitting a second set of information on the plurality of antennas. The wireless communication device700may include means for transmitting the first set of information based on the first set of CSD values and the second set of information based on the second set of CSD values. In one configuration, the means for determining the first set of CSD values may be configured to determine an antenna CSD value for each antenna of the plurality of antennas, to determine a user CSD offset, and to modifying the antenna CSD value for each antenna of the plurality of antennas based on the determined user CSD offset. In another configuration, the means for determining the first set of CSD values may be configured to determine at least one assigned CSD value and to determine an antenna CSD value for each antenna of the plurality of antennas based on the determined at least one assigned antenna CSD value. In another configuration, the means for determining the second set of CSD values may be configured to identify a plurality of streams for transmitting the second set of information and to determine a stream CSD value for each stream of the plurality of streams. In another configuration, the wireless communication device700may include means for determining a third set of CSD values for transmitting the second set of information on the plurality of antennas. In this configuration, the second set of information may be transmitted based on the second and third sets of CSD values. In another configuration, the means for determining the third set of CSD values may be configured to determine an antenna CSD value for each antenna of the plurality of antennas, to determine a user CSD offset, and to modifying the antenna CSD value for each antenna of the plurality of antennas based on the determined user CSD offset. In another configuration, the means for determining the third set of CSD values may be configured to determine at least one assigned CSD value and to determine an antenna CSD value for each antenna of the plurality of antennas based on the determined at least one assigned CSD value. In an aspect, the stream CSD value for a symbol with a 4× time duration may be four times greater than a CSD value of a non-legacy symbol with a 1× time duration. In another aspect, the antenna CSD value for a symbol with a 4× time duration may be four times greater than a CSD value of a non-legacy symbol with a 1× time duration.

For example, means for determining a first set of CSD values may comprise the CSD component724and/or the processing system710. The means for determining a second set of CSD values may comprise the CSD component724and/or the processing system710. The means for transmitting the first set of information and the second set of information may comprise the CSD component724, the processing system710, and/or the transmitter715. The means for determining a third set of CSD values may comprise the CSD component724and/or the processing system710.