U.S. patent application number 16/256928 was filed with the patent office on 2019-06-06 for systems and methods for backwards-compatible preamble formats for multiple access wireless communication.
The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Simone Merlin, Hemanth Sampath, Rahul Tandra, Sameer Vermani.
Application Number | 20190173637 16/256928 |
Document ID | / |
Family ID | 51686746 |
Filed Date | 2019-06-06 |
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United States Patent
Application |
20190173637 |
Kind Code |
A1 |
Vermani; Sameer ; et
al. |
June 6, 2019 |
SYSTEMS AND METHODS FOR BACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR
MULTIPLE ACCESS WIRELESS COMMUNICATION
Abstract
Systems, methods, and devices for wireless communication are
disclosed herein. One aspect of the disclosure provides a method of
transmitting to two or more wireless communication devices. The
method includes transmitting a first section of a preamble
according to a first format, the first section of the preamble
containing information informing devices compatible with the first
format to defer to the transmission, transmitting a second section
of the preamble according to a second format, the second section of
the preamble containing tone allocation information, the tone
allocation information identifying two or more wireless
communication devices; and transmitting data to the two or more
wireless communication devices simultaneously, the data contained
on two or more sub-bands.
Inventors: |
Vermani; Sameer; (San Diego,
CA) ; Tandra; Rahul; (San Diego, CA) ; Merlin;
Simone; (Solana Beach, CA) ; Sampath; Hemanth;
(San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
51686746 |
Appl. No.: |
16/256928 |
Filed: |
January 24, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14250276 |
Apr 10, 2014 |
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16256928 |
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61898809 |
Nov 1, 2013 |
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61871267 |
Aug 28, 2013 |
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61847525 |
Jul 17, 2013 |
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61819028 |
May 3, 2013 |
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61812136 |
Apr 15, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 27/2613 20130101;
H04L 5/0044 20130101; H04L 27/261 20130101; H04L 5/0094 20130101;
H04W 56/0035 20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04L 27/26 20060101 H04L027/26; H04W 56/00 20060101
H04W056/00 |
Claims
1. A method of wireless communication with two or more wireless
communication devices, the method comprising: transmitting a first
section of a preamble using a first phase shift keying modulation
on at least a first symbol of the first section; transmitting a
second section of the preamble using a second phase shift keying
modulation on at least a second symbol of the second section,
wherein the first phase shift keying modulation is different than
the second phase shift keying modulation, and wherein the second
section includes tone allocation information identifying the two or
more wireless communication devices; and transmitting data after
the preamble to the two or more wireless communication devices.
2. The method of claim 1, wherein the second section indicates a
bandwidth for each of a number of sub-bands spanning a
communication bandwidth.
3. The method of claim 2, wherein the second section includes
information assigning one or more of the sub-bands to each of the
two or more wireless communication devices for receiving the data
associated with the respective wireless communication device.
4. The method of claim 3, wherein the assignment of the one or more
sub-bands to each of the two or more wireless communication devices
is based, at least in part, on the tone allocation information.
5. The method of claim 1, wherein the first section comprises a
signal field decodable by devices compatible with an IEEE 802.11a
standard.
6. The method of claim 1, wherein the second section comprises a
high-efficiency (HE) signal field.
7. The method of claim 1, wherein the first section comprises a
first high-efficiency (HE) signal field and the second section
comprises a second high-efficiency (HE) signal field.
8. The method of claim 7, wherein the first HE signal field
includes information indicating the second phase shift keying
modulation used on the second section.
9. An apparatus, comprising: at least one processor; and at least
one memory communicatively coupled with the at least one processor
and storing processor-readable code that, when executed by the at
least one processor, causes the apparatus to wirelessly communicate
with two or more wireless communication devices by performing
operations comprising: transmitting a first section of a preamble
using a first phase shift keying modulation on at least a first
symbol of the first section; transmitting a second section of the
preamble using a second phase shift keying modulation on at least a
second symbol of the second section, wherein the first phase shift
keying modulation is different than the second phase shift keying
modulation, and wherein the second section includes tone allocation
information identifying the two or more wireless communication
devices; and transmitting data after the preamble to the two or
more wireless communication devices.
10. The apparatus of claim 9, wherein the second section indicates
a bandwidth for each of a number of sub-bands spanning a
communication bandwidth.
11. The apparatus of claim 10, wherein the second section includes
information assigning one or more of the sub-bands to each of the
two or more wireless communication devices for receiving the data
associated with the respective wireless communication device.
12. The apparatus of claim 11, wherein the assignment of the one or
more sub-bands to each of the two or more wireless communication
devices is based, at least in part, on the tone allocation
information.
13. The apparatus of claim 9, wherein the first section comprises a
signal field decodable by devices compatible with an IEEE 802.11a
standard.
14. The apparatus of claim 9, wherein the second section comprises
a high-efficiency (HE) signal field.
15. The apparatus of claim 9, wherein the first section comprises a
first high-efficiency (HE) signal field and the second section
comprises a second high-efficiency (HE) signal field.
16. The apparatus of claim 15, wherein the first HE signal field
includes information indicating the second phase shift keying
modulation used on the second section.
17. An access point, comprising: means for transmitting, to two or
more wireless communication devices, a first section of a preamble
using a first phase shift keying modulation on at least a first
symbol of the first section; means for transmitting, to the two or
more wireless communication devices, a second section of the
preamble using a second phase shift keying modulation on at least a
second symbol of the second section, wherein the first phase shift
keying modulation is different than the second phase shift keying
modulation, and wherein the second section includes tone allocation
information identifying the two or more wireless communication
devices; and means for transmitting, to the two or more wireless
communication devices, data after the preamble.
18. The access point of claim 17, wherein the second section
indicates a bandwidth for each of a number of sub-bands spanning a
communication bandwidth.
19. The access point of claim 18, wherein the second section
includes information assigning one or more of the sub-bands to each
of the two or more wireless communication devices for receiving the
data associated with the respective wireless communication
device.
20. The access point of claim 19, wherein the assignment of the one
or more sub-bands to each of the two or more wireless communication
devices is based, at least in part, on the tone allocation
information.
21. The access point of claim 17, wherein the first section
comprises a signal field decodable by devices compatible with an
IEEE 802.11a standard.
22. The access point of claim 17, wherein the first section
comprises a first high-efficiency (HE) signal field and the second
section comprises a second high-efficiency (HE) signal field.
23. The access point of claim 22, wherein the first HE signal field
includes information indicating the second phase shift keying
modulation used on the second section.
24. A non-transitory computer-readable storage medium comprising
instructions that, when executed by one or more processors of an
apparatus, cause the apparatus to wirelessly communicate with two
or more wireless communication devices by performing operations
comprising: transmitting a first section of a preamble using a
first phase shift keying modulation on at least a first symbol of
the first section; transmitting a second section of the preamble
using a second phase shift keying modulation on at least a second
symbol of the second section, wherein the first phase shift keying
modulation is different than the second phase shift keying
modulation, and wherein the second section includes tone allocation
information identifying the two or more wireless communication
devices; and transmitting data after the preamble to the two or
more wireless communication devices.
25. The non-transitory computer-readable storage medium of claim
24, wherein the second section indicates a bandwidth for each of a
number of sub-bands spanning a communication bandwidth for
receiving the data associated with the respective wireless
communication device.
26. The non-transitory computer-readable storage medium of claim
25, wherein the second section includes information assigning one
or more of the sub-bands to each of the two or more wireless
communication devices for receiving the data associated with the
respective wireless communication device.
27. The non-transitory computer-readable storage medium of claim
26, wherein the assignment of one or more sub-bands to each of the
two or more wireless communication devices is based, at least in
part, on the tone allocation information.
28. The non-transitory computer-readable storage medium of claim
24, wherein the first section comprises a signal field decodable by
devices compatible with an IEEE 802.11a standard.
29. The non-transitory computer-readable storage medium of claim
24, wherein the first section comprises a first high-efficiency
(HE) signal field and the second section comprises a second
high-efficiency (HE) signal field.
30. The non-transitory computer-readable storage medium of claim
29, wherein the first HE signal field includes information
indicating the second phase shift keying modulation used on the
second section.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present Application for Patent is a continuation of U.S.
application Ser. No. 14/250,276 entitled "SYSTEMS AND METHODS FOR
BACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESS
COMMUNICATION" filed Apr. 10, 2014, which claims priority to U.S.
Provisional Application No. 61/812,136 entitled "SYSTEMS AND
METHODS FOR BACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE
ACCESS WIRELESS COMMUNICATION" filed Apr. 15, 2013, to U.S.
Provisional Application No. 61/819,028 entitled "SYSTEMS AND
METHODS FOR BACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE
ACCESS WIRELESS COMMUNICATION" filed May 3, 2013, to Provisional
Application No. 61/847,525 entitled "SYSTEMS AND METHODS FOR
BACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESS
COMMUNICATION" filed Jul. 17, 2013, to Provisional Application No.
61/871,267 entitled "SYSTEMS AND METHODS FOR BACKWARDS-COMPATIBLE
PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESS COMMUNICATION" filed
Aug. 28, 2013, and to Provisional Application No. 61/898,809
entitled "SYSTEMS AND METHODS FOR BACKWARDS-COMPATIBLE PREAMBLE
FORMATS FOR MULTIPLE ACCESS WIRELESS COMMUNICATION" filed Nov. 1,
2013. The disclosures of all of these prior applications are
considered part of, and are incorporated by reference in, this
patent application.
TECHNICAL FIELD
[0002] The present application relates generally to wireless
communications, and more specifically to systems, methods, and
devices to enable backward-compatible multiple access wireless
communication.
DESCRIPTION OF THE RELATED TECHNOLOGY
[0003] In many telecommunication systems, communications networks
are used to exchange messages among several interacting
spatially-separated devices. Networks may be classified according
to geographic scope, which could be, for example, a metropolitan
area, a local area, or a personal area. Such networks may be
designated respectively as a wide area network (WAN), metropolitan
area network (MAN), local area network (LAN), or personal area
network (PAN). Networks also differ according to the
switching/routing technique used to interconnect the various
network nodes and devices (e.g., circuit switching vs. packet
switching), the type of physical media employed for transmission
(e.g., wired vs. wireless), and the set of communication protocols
used (e.g., Internet protocol suite, SONET (Synchronous Optical
Networking), Ethernet, etc.).
[0004] Wireless networks are often preferred when the network
elements are mobile and thus have dynamic connectivity needs, or if
the network architecture is formed in an ad hoc, rather than fixed,
topology. Wireless networks employ intangible physical media in an
unguided propagation mode using electromagnetic waves in the radio,
microwave, infra-red, optical, etc. frequency bands. Wireless
networks advantageously facilitate user mobility and rapid field
deployment when compared to fixed wired networks.
SUMMARY
[0005] The systems, methods, and devices of the invention each have
several aspects, no single one of which is solely responsible for
its 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 that include efficient use of the wireless
medium.
[0006] One innovative aspect of the subject matter described in
this disclosure can be implemented as a method of transmitting a
preamble to two or more wireless communication devices. The method
may include transmitting a first section of the preamble using a
first phase shift keying format on at least a first symbol of the
first section, and transmitting a second section of the preamble
using a second phase shift keying format on at least a second
symbol of the second section, wherein the first phase shift keying
format is different than the second phase shift keying format, and
wherein the second section includes tone allocation information
identifying the two or more wireless communication devices. The
method may also include simultaneously transmitting data to each of
the two or more wireless communication devices using one or more
assigned sub-bands.
[0007] In some implementations, the first section may include a
signal field decodable by devices compatible with an IEEE 802.11a
standard. In other implementations, the first section may include a
high-efficiency (HE) signal field. In some implementations, the
second section may indicate a bandwidth for each of a number of
sub-bands spanning a communication bandwidth, may include
information assigning one or more of the sub-bands to each of the
two or more wireless communication devices, or both. In some
aspects, the assignment of one or more sub-bands to each of the two
or more wireless communication devices may be based, at least in
part, on the tone allocation information. In addition, or in the
alternative, the second section may be a high-efficiency (HE)
signal field.
[0008] Another innovative aspect of the subject matter described in
this disclosure can be implemented in an apparatus to transmit a
preamble to two or more wireless communication devices. The
apparatus may include at least one processor and at least one
memory communicatively coupled with the at least one processor. The
at least one memory may store processor-readable code that, when
executed by the at least one processor, causes the apparatus to
perform operations including transmitting a first section of the
preamble using a first phase shift keying format on at least a
first symbol of the first section, and transmitting a second
section of the preamble using a second phase shift keying format on
at least a second symbol of the second section, wherein the first
phase shift keying format is different than the second phase shift
keying format, and wherein the second section includes tone
allocation information identifying the two or more wireless
communication devices. Execution of the processor-readable code may
also cause the apparatus to perform operations further including
simultaneously transmitting data to each of the two or more
wireless communication devices using the assigned one or more
sub-bands.
[0009] In some implementations, the first section may include a
signal field decodable by devices compatible with an IEEE 802.11a
standard. In other implementations, the first section may include a
high-efficiency (HE) signal field. In some implementations, the
second section may indicate a bandwidth for each of a number of
sub-bands spanning a communication bandwidth, may include
information assigning one or more of the sub-bands to each of the
two or more wireless communication devices, or both. In some
aspects, the assignment of one or more sub-bands to each of the two
or more wireless communication devices may be based, at least in
part, on the tone allocation information. In addition, or in the
alternative, the second section may be a high-efficiency (HE)
signal field.
[0010] Another innovative aspect of the subject matter described in
this disclosure can be implemented in an apparatus to transmit a
preamble to two or more wireless communication devices. The
apparatus may include means for transmitting a first section of the
preamble using a first phase shift keying format on at least a
first symbol of the first section, and means for transmitting a
second section of the preamble using a second phase shift keying
format on at least a second symbol of the second section, wherein
the first phase shift keying format is different than the second
phase shift keying format, and wherein the second section includes
tone allocation information identifying the two or more wireless
communication devices. The apparatus may also include means for
simultaneously transmitting data to each of the two or more
wireless communication devices using one or more assigned
sub-bands.
[0011] In some implementations, the first section may include a
signal field decodable by devices compatible with an IEEE 802.11a
standard. In other implementations, the first section may include a
high-efficiency (HE) signal field. In some implementations, the
second section may indicate a bandwidth for each of a number of
sub-bands spanning a communication bandwidth, may include
information assigning one or more of the sub-bands to each of the
two or more wireless communication devices, or both. In some
aspects, the assignment of one or more sub-bands to each of the two
or more wireless communication devices may be based, at least in
part, on the tone allocation information. In addition, or in the
alternative, the second section may be a high-efficiency (HE)
signal field.
[0012] Another innovative aspect of the subject matter described in
this disclosure can be implemented in a non-transitory
computer-readable storage medium. The non-transitory
computer-readable storage medium may include instructions that,
when executed by one or more processors of an apparatus, cause the
apparatus to transmit a preamble to two or more wireless
communication by performing a number of operations. In some
implementations, the number of operations may include transmitting
a first section of the preamble using a first phase shift keying
format on at least a first symbol of the first section, and
transmitting a second section of the preamble using a second phase
shift keying format on at least a second symbol of the second
section, wherein the first phase shift keying format is different
than the second phase shift keying format, and wherein the second
section includes tone allocation information identifying the two or
more wireless communication devices. The number of operations may
also include simultaneously transmitting data to each of the two or
more wireless communication devices using the assigned one or more
sub-bands.
[0013] In some implementations, the first section may include a
signal field decodable by devices compatible with an IEEE 802.11a
standard. In other implementations, the first section may include a
high-efficiency (HE) signal field. In some implementations, the
second section may indicate a bandwidth for each of a number of
sub-bands spanning a communication bandwidth, may include
information assigning one or more of the sub-bands to each of the
two or more wireless communication devices, or both. In some
aspects, the assignment of one or more sub-bands to each of the two
or more wireless communication devices may be based, at least in
part, on the tone allocation information. In addition, or in the
alternative, the second section may be a high-efficiency (HE)
signal field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a channel allocation for channels
available for IEEE 802.11 systems.
[0015] FIG. 2 illustrates a structure of a physical-layer packet
(PPDU frame) which may be used in an IEEE 802.11a/b/g/j/p
communication.
[0016] FIG. 3 illustrates a structure of a physical-layer packet
(PPDU frame) which may be used in an IEEE 802.11n
communication.
[0017] FIG. 4 illustrates a structure of a physical-layer packet
(PPDU frame) which may be used in an IEEE 802.11ac
communication.
[0018] FIG. 5 illustrates an exemplary structure of a downlink
physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0019] FIG. 6 illustrates an exemplary illustration of a signal
which may be used to identify STAs and to allocate sub-bands to
those STAs.
[0020] FIG. 7 illustrates a 2.sup.nd exemplary structure of a
downlink physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0021] FIG. 8 illustrates a 3.sup.rd exemplary structure of a
downlink physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0022] FIG. 9 illustrates a 4.sup.th exemplary structure of a
downlink physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0023] FIG. 10 illustrates an example of a wireless communication
system in which aspects of the present disclosure may be
employed.
[0024] FIG. 11 shows a functional block diagram of an exemplary
wireless device that may be employed within the wireless
communication system of FIG. 1.
[0025] FIG. 12 illustrates an exemplary structure of an uplink
physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0026] FIG. 13 illustrates a process flow diagram for an example
method of a transmitting a high-efficiency packet to two or more
wireless communication devices.
[0027] FIG. 14 illustrates an exemplary structure of a hybrid
downlink physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0028] FIG. 15 illustrates an exemplary method of transmitting a
hybrid packet.
[0029] FIG. 16 illustrates an exemplary method of receiving a
hybrid packet.
[0030] FIG. 17 illustrates a packet with one example HE preamble
format.
[0031] FIG. 18 illustrates a packet with another example HE
preamble format.
[0032] FIG. 19 illustrates a packet with another example HE
preamble format.
[0033] FIG. 20 illustrates example bit allocation for an HE-SIG 1
field.
[0034] FIG. 21 illustrates an exemplary structure of an uplink
physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0035] FIG. 22 illustrates another exemplary structure of an uplink
physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications.
[0036] FIG. 23 illustrates an exemplary method of receiving a
packet.
[0037] FIG. 24 is an exemplary uplink packet structure for an
uplink HE packet.
[0038] FIG. 25 is exemplary uplink packet structure for an uplink
HE packet.
[0039] FIG. 26 is an exemplary downlink message from the AP which
includes information on how many spatial streams each transmitting
device may use.
[0040] FIG. 27 is an illustration of a tone-interleaved LTF which
may be used in an UL OFDMA packet.
[0041] FIG. 28 is an illustration of a sub-band interleaved LTF
which may be used in an UL OFDMA packet.
[0042] FIG. 29 is an exemplary LTF portion of a packet which may be
transmitted in an UL OFDMA packet.
[0043] FIG. 30 is an illustration of a packet with a common SIG
field prior to the HE-STF and per-user SIG field after all of the
HE-LTFs.
[0044] FIG. 31 illustrates an exemplary method of transmitting to
one or more devices in a single transmission.
[0045] FIG. 32 illustrates an exemplary method of transmitting to
one or more first devices with a first set of capabilities and
simultaneously transmitting to one or more second devices with a
second set of capabilities.
[0046] FIG. 33 illustrates an exemplary method of receiving a
transmission compatible with both devices with a first set of
capabilities and devices with a second set of capabilities.
[0047] FIG. 34 illustrates an exemplary method of receiving a
transmission, where portions of the transmission are transmitted by
different wireless devices.
[0048] FIG. 35 illustrates various components that may be utilized
in a wireless device that may be employed within the wireless
communication system.
DETAILED DESCRIPTION
[0049] Various aspects of the novel systems, apparatuses, and
methods are described more fully hereinafter with reference to the
accompanying drawings. The teachings disclosed may, however, be
embodied in many different forms and should not be construed as
limited to any specific structure or function presented throughout
this disclosure. Rather, these aspects are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the disclosure to those skilled in the art. Based on the
teachings herein one skilled in the art should appreciate that the
scope of the disclosure is intended to cover any aspect of the
novel systems, apparatuses, and methods disclosed herein, whether
implemented independently of or combined with any other aspect of
the invention. For example, an apparatus may be implemented or a
method may be practiced using any number of the aspects set forth
herein. In addition, the scope of the invention is intended to
cover such an apparatus or method which is practiced using other
structure, functionality, or structure and functionality in
addition to or other than the various aspects of the invention set
forth herein. It should be understood that any aspect disclosed
herein may be embodied by one or more elements of a claim.
[0050] Although particular aspects are described herein, many
variations and permutations of these aspects fall within the scope
of the disclosure. Although some benefits and advantages of the
preferred aspects are mentioned, the scope of the disclosure is not
intended to be limited to particular benefits, uses, or objectives.
Rather, aspects of the disclosure are intended to be broadly
applicable to different wireless technologies, system
configurations, networks, and transmission protocols, some of which
are illustrated by way of example in the figures and in the
following description of the preferred aspects. The detailed
description and drawings are merely illustrative of the disclosure
rather than limiting, the scope of the disclosure being defined by
the appended claims and equivalents thereof.
[0051] Wireless network technologies may include various types of
wireless local area networks (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 WiFi or, more
generally, any member of the IEEE 802.11 family of wireless
protocols. For example, the various aspects described herein may be
used as part of a IEEE 802.11 protocol, such as an 802.11 protocol
which supports orthogonal frequency-division multiple access
(OFDMA) communications.
[0052] It may be beneficial to allow multiple devices, such as
STAs, to communicate with an AP at the same time. For example, this
may allow multiple STAs to receive a response from the AP in less
time, and to be able to transmit and receive data from the AP with
less delay. This may also allow an AP to communicate with a larger
number of devices overall, and may also make bandwidth usage more
efficient. By using multiple access communications, the AP may be
able to multiplex OFDM symbols to, for example, four devices at
once over an 80 MHz bandwidth, where each device utilizes 20 MHz
bandwidth. Thus, multiple access may be beneficial in some aspects,
as it may allow the AP to make more efficient use of the spectrum
available to it.
[0053] It has been proposed to implement such multiple access
protocols in an OFDM system such as the 802.11 family by assigning
different subcarriers (or tones) of symbols transmitted between the
AP and the STAs to different STAs. In this way, an AP could
communicate with multiple STA's with a single transmitted OFDM
symbol, where different tones of the symbol were decoded and
processed by different STA's, thus allowing simultaneous data
transfer to multiple STA's. These systems are sometimes referred to
as OFDMA systems.
[0054] Such a tone allocation scheme is referred to herein as a
"high-efficiency" (HE) system, and data packets transmitted in such
a multiple tone allocation system may referred to as
high-efficiency (HE) packets. Various structures of such packets,
including backward compatible preamble fields are described in
detail below.
[0055] Various aspects of the novel systems, apparatuses, and
methods are described more fully hereinafter with reference to the
accompanying drawings. This disclosure may, however, be embodied in
many different forms and should not be construed as limited to any
specific structure or function presented throughout this
disclosure. Rather, these aspects are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the disclosure to those skilled in the art. Based on the
teachings herein one skilled in the art should appreciate that the
scope of the disclosure is intended to cover any aspect of the
novel systems, apparatuses, and methods disclosed herein, whether
implemented independently of, or combined with, any other aspect of
the invention. For example, an apparatus may be implemented or a
method may be practiced using any number of the aspects set forth
herein. In addition, the scope of the invention is intended to
cover such an apparatus or method which is practiced using other
structure, functionality, or structure and functionality in
addition to or other than the various aspects of the invention set
forth herein. It should be understood that any aspect disclosed
herein may be embodied by one or more elements of a claim.
[0056] Although particular aspects are described herein, many
variations and permutations of these aspects fall within the scope
of the disclosure. Although some benefits and advantages of the
preferred aspects are mentioned, the scope of the disclosure is not
intended to be limited to particular benefits, uses, or objectives.
Rather, aspects of the disclosure are intended to be broadly
applicable to different wireless technologies, system
configurations, networks, and transmission protocols, some of which
are illustrated by way of example in the figures and in the
following description of the preferred aspects. The detailed
description and drawings are merely illustrative of the disclosure
rather than limiting, the scope of the disclosure being defined by
the appended claims and equivalents thereof.
[0057] Popular wireless network technologies may include various
types of wireless local area networks (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.
[0058] In some aspects, wireless signals may be transmitted
according to an 802.11 protocol. 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 an STA serves as a user of the WLAN. For example, an STA
may be a laptop computer, a personal digital assistant (PDA), a
mobile phone, etc. In an example, an STA connects to an AP via a
WiFi compliant wireless link to obtain general connectivity to the
Internet or to other wide area networks. In some implementations an
STA may also be used as an AP.
[0059] An access point (AP) may also comprise, be implemented as,
or known as a base station, wireless access point, access node or
similar terminology.
[0060] A station "STA" 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, user
equipment, or some other terminology. 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 for network communication via a
wireless medium.
[0061] As discussed above, certain of the devices described herein
may implement an 802.11 standard, for example. Such devices,
whether used as an 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.
[0062] FIG. 1 illustrates a channel allocation for channels
available for 802.11 systems. Various IEEE 802.11 systems support a
number of different sizes of channels, such as 5, 10, 20, 40, 80,
and 160 MHz channels. For example, and 802.11ac device may support
20, 40, and 80 MHz channel bandwidth reception and transmission. A
larger channel may comprise two adjacent smaller channels. For
example, an 80 MHz channel may comprise two adjacent 40 MHz
channels. In the currently implemented IEEE 802.11 systems, a 20
MHz channel contains 64 subcarriers, separated from each other by
312.5 kHz. Of these subcarriers, a smaller number may be used for
carrying data. For example, a 20 MHz channel may contain
transmitting subcarriers numbered -1 to -28 and 1 to 28, or 56
subcarriers. Some of these carriers may also be used to transmit
pilot signals. Over the years, the IEEE 802.11 standard has evolved
through several versions. Older versions include the 11a/g and 11n
versions. The most recently released is the 802.11ac version.
[0063] FIGS. 2, 3, and 4 illustrate data packet formats for several
currently existing IEEE 802.11 standards. Turning first to FIG. 2,
a packet format for IEEE 802.11a, 11b, and 11g is illustrated. This
frame includes a short training field 22, a long training field 24,
and a signal field 26. The training fields do not transmit data,
but they allow synchronization between the AP and the receiving
STAs for decoding the data in the data field 28.
[0064] The signal field 26 delivers information from the AP to the
STA's about the nature of the packet being delivered. In IEEE
802.11a/b/g devices, this signal field has a length of 24 bits, and
is transmitted as a single OFDM symbol at a 6 Mb/s rate using BPSK
modulation and a code rate of 1/2. The information in the SIG field
26 includes 4 bits describing the modulation scheme of the data in
the packet (e.g. BPSK, 16QAM, 64QAM, etc.), and 12 bits for the
packet length. This information is used by a STA to decode the data
in the packet when the packet is intended for the STA. When a
packet is not intended for a particular STA, the STA will defer any
communication attempts during the time period defined in the length
field of the SIG symbol 26, and may, to save power, enter a sleep
mode during the packet period of up to about 5.5 msec.
[0065] As features have been added to IEEE 802.11, changes to the
format of the SIG fields in data packets were developed to provide
additional information to STAs. FIG. 3 shows the packet structure
for the IEEE 802.11n packet. The 11n addition to the IEEE.802.11
standard added MIMO functionality to IEEE.802.11 compatible
devices. To provide backward compatibility for systems containing
both IEEE 802.11a/b/g devices and IEEE 802.11n devices, the data
packet for IEEE 802.11n systems also includes the STF, LTF, and SIG
fields of these earlier systems, noted as L-STF 22, L-LTF 24, and
L-SIG 26 with a prefix L to denote that they are "legacy" fields.
To provide the needed information to STA's in an IEEE 802.11n
environment, two additional signal symbols 140 and 142 were added
to the IEEE 802.11n data packet. In contrast with the SIG field and
L-SIG field 26, however, these signal fields used rotated BPSK
modulation (also referred to as QBPSK modulation). When a legacy
device configured to operate with IEEE 802.11a/b/g receives such a
packet, it will receive and decode the L-SIG field 26 as a normal
11a/b/g packet. However, as the device continued decoding
additional bits, they will not be decoded successfully because the
format of the data packet after the L-SIG field 26 is different
from the format of an 11a/b/g packet, and the CRC check performed
by the device during this process will fail. This causes these
legacy devices to stop processing the packet, but still defer any
further operations until a time period has passed defined by the
length field in the initially decoded L-SIG. In contrast, new
devices compatible with IEEE 802.11n would sense the rotated
modulation in the HT-SIG fields, and process the packet as an
802.11n packet. Furthermore, an 11n device can tell that a packet
is intended for an 11a/b/g device because if it senses any
modulation other than QBPSK in the symbol following the L-SIG 26,
it will ignore it as an 11a/b/g packet. After the HT-SIG1 and SIG2
symbols, additional training fields suitable for MIMO communication
are provided, followed by the data 28.
[0066] FIG. 4 illustrates a frame format for the currently existing
IEEE 802.11ac standard, which added multi-user MIMO functionality
to the IEEE 802.11 family. Similar to IEEE 802.11n, an 802.11ac
frame contains the same legacy short training field (L-STF) 22 and
long training field (L-LTF) 24. An 802.11ac frame also contains a
legacy signal field L-SIG 26 as described above.
[0067] Next, an 802.11ac frame includes a Very High Throughput
Signal (VHT-SIG-A1 150 and A2 152) field two symbols in length.
This signal field provides additional configuration information
related to 11ac features that are not present in 11a/b/g and 11n
devices. The first OFDM symbol 150 of the VHT-SIG-A may be
modulated using BPSK, so that any 802.11n device listening to the
packet will believe the packet to be an 802.11a packet, and will
defer to the packet for the duration of the packet length as
defined in the length field of the L-SIG 126. Devices configured
according to 11a/g will be expecting a service field and MAC header
following the L-SIG 26 field. When they attempt to decode this, a
CRC failure will occur in a manner similar to the procedure when an
11n packet is received by an 11a/b/g device, and the 11a/b/g
devices will also defer for the period defined in the L-SIG field
26. The second symbol 152 of the VHT-SIG-A is modulated with a
90-degree rotated BPSK. This rotated second symbol allows an
802.11ac device to identify the packet as an 802.11ac packet. The
VHT-SIG-A1 150 and A2 152 fields contain information on a bandwidth
mode, modulation and coding scheme (MCS) for the single user case,
number of space time streams (NSTS), and other information. The
VHT-SIG-A1 150 and A2 152 may also contain a number of reserved
bits that are set to "1." The legacy fields and the VHT-SIG-A1 and
A2 fields may be duplicated over each 20 MHz of the available
bandwidth.
[0068] After the VHT-SIG-A, an 802.11ac packet may contain a
VHT-STF, which is configured to improve automatic gain control
estimation in a multiple-input and multiple-output (MIMO)
transmission. The next 1 to 8 fields of an 802.11ac packet may be
VHT-LTFs. These may be used for estimating the MIMO channel and
then equalizing the received signal. The number of VHT-LTFs sent
may be greater than or equal to the number of spatial streams per
user. Finally, the last field in the preamble before the data field
is the VHT-SIG-B 154. This field is BPSK modulated, and provides
information on the length of the useful data in the packet and, in
the case of a multiple user (MU) MIMO packet, provides the MCS. In
a single user (SU) case, this MCS information is instead contained
in the VHT-SIG-A2. Following the VHT-SIG-B, the data symbols are
transmitted. Although 802.11ac introduced a variety of new features
to the 802.11 family, and included a data packet with preamble
design that was backward compatible with 11a/g/n devices and also
provided information necessary for implementing the new features of
11ac, configuration information for OFDMA tone allocation for
multiple access is not provided by the 11ac data packet design. New
preamble configurations are necessary to implement such features in
any future version of IEEE 802.11 or any other wireless network
protocol using OFDM subcarriers. Advantageous preamble designs a
represented below, especially with reference to FIGS. 3-9.
[0069] FIG. 5 illustrates an exemplary structure of a
physical-layer packet which may be used to enable
backward-compatible multiple access wireless communications in this
environment.
[0070] In this example physical-layer packet, a legacy preamble
including L-STF 22, L-LTF 26, and L-SIG 26 are included. Each of
these may be transmitted using 20 MHz, and multiple copies may be
transmitted for each 20 MHz of spectrum that the AP uses.
[0071] This packet also contains an HE-SIG1 symbol 455, an HE-SIG2
symbol 457, and one or more HE-SIG3 symbols 459. The structure of
these symbols should be backward compatible with IEEE
802.11a/b/g/n/ac devices, and should also signal OFDMA HE devices
that the packet is an HE packet. To be backward compatible with
IEEE 802.11a/b/g/n/ac devices, appropriate modulation may be used
on each of these symbols. In some implementations, the first
symbol, HE-SIG1 455 may be modulated with BPSK modulation. This
will cause the same effect on 11a/b/g/n device as is currently the
case with 11ac packets that also have their first SIG symbol BPSK
modulated. For these devices, it does not matter what the
modulation is on the subsequent HE-SIG symbols 457, 459. The second
symbol 457 may be BPSK or QPSK modulated. If BPSK modulated, an
11ac device will assume the packet is an 11a/b/g packet, and will
stop processing the packet, and will defer for the time defined by
the length field of L-SIG 26. If QBPSK modulated, an 11ac device
will produce a CRC error during preamble processing, and will also
stop processing the packet, and will defer for the time defined by
the length field of L-SIG. To signal HE devices that this is an HE
packet, at least the first symbol of HE-SIG3 459 may be QBPSK
modulated.
[0072] The information necessary to establish an OFDMA multiple
access communication may be placed in the HE-SIG fields 455, 457,
and 459 in a variety of positions. In the example of FIG. 5,
HE-SIG1 455 contains the tone allocation information for OFDMA
operation. HE-SIG3 459 contains bits defining user specific
modulation type for each multiplexed user. In addition, HE-SIG2 457
contains bits defining user specific MIMO spatial streams, such as
is provided in the 11ac format of FIG. 4. The example of FIG. 5 may
allow four different users to be each assigned a specific sub-band
of tones and a specific number of MIMO space time streams. 12 bits
of space time stream information allows three bits for each of four
users such that 1-8 streams can be assigned to each one. 16 bits of
modulation type data allows four bits for each of four users,
allowing assignment of any one of 16 different modulation schemes
(16QAM, 64QAM, etc.) to each of four users. 12 bits of tone
allocation data allows specific sub-bands to be assigned to each of
four users.
[0073] One example SIG field scheme for subband allocation is
illustrated in FIG. 6. This example includes a 6 bit Group ID field
similar to that currently used in IEEE 802.11ac as well as 10 bits
of information to allocate sub-band tones to each of four users.
The bandwidth used to deliver the packet 130 may be allocated to
STAs in multiples of some number of MHz. For example, the bandwidth
may be allocated to STAs in multiples of B MHz. The value of B may
be a value such as 1, 2, 5, 10, 15, or 20 MHz. The values of B may
be provided by the two bit allocation granularity field of FIG. 6.
For example, the HE-SIG 155 may contain one two-bit field, which
allows for four possible values of B. For example, the values of B
may be 5, 10, 15, or 20 MHz, corresponding to values of 0-3 in the
allocation granularity field. In some aspects, a field of k bits
may be used to signal the value of B, defining a number from 0 to
N, where 0 represents the least flexible option (largest
granularity), and a high value of N represents the most flexible
option (smallest granularity). Each B MHz portion may be referred
to as a sub-band.
[0074] The HE-SIG1 may further use 2 bits per user to indicate the
number of sub-bands allocated to each STA. This may allow 0-3
sub-bands to be allocated to each user. The group-id (G_ID) concept
from 802.11ac may be used in order to identify the STAs which will
receive data in an OFDMA packet. This 6-bit G_ID may identify up to
four STAs, in a particular order, in this example.
[0075] In this example, the allocation granularity field is set to
"00." In this example, the allocation granularity field is a
two-bit field, the values of which may correspond to 5, 10, 15 or
20 MHz, in order. For example, a "00" may correspond to an
allocation granularity of 5 MHz.
[0076] In this example, the first two bits give the number of
sub-bands for the first user identified by the G_ID. Here, user-1
is given "11" sub-bands. This may correspond to user-1 receiving 3
sub-bands. If each sub-band is 5 MHz, this may mean the user-1 is
allocated 15 MHz of spectrum. Similarly, user-2 also receives 3
sub-bands, while user-3 receives zero sub-bands, and user-4
receives 2 sub-bands. Thus, this allocation may correspond to a 40
MHz signal, in which 15 MHz is used for both user-1 and user-2,
while user-4 receives 10 MHz, and user-3 does not receive any
sub-bands.
[0077] The training fields and data which is sent after the HE-SIG
symbols is delivered by the AP according to the allocated tones to
each STA. This information may potentially be beamformed.
Beamforming this information may have certain advantages, such as
allowing for more accurate decoding and/or providing more range
than non-beamformed transmissions.
[0078] Depending on the space time streams assigned to each user,
different users may require a different number of HE-LTFs 165. Each
STA may require a number of HE-LTFs 165 that allows channel
estimation for each spatial stream associated with that STA, which
is generally equal to or more than the number of spatial streams.
LTFs may also be used for frequency offset estimation and time
synchronization. Because different STA's may receive a different
number of HE-LTFs, symbols may be transmitted from the AP that
contain HE-LTF information on some tones and data on other
tones.
[0079] In some aspects, sending both HE-LTF information and data on
the same OFDM symbol may be problematic. For example, this may
increase the peak-to-average power ratio (PAPR) to too high a
level. Thus, it may be beneficial to instead to transmit HE-LTFs
165 on all tones of the transmitted symbols until each STA has
received at least the required number of HE-LTFs 165. For example,
each STA may need to receive one HE-LTF 165 per spatial stream
associated with the STA. Thus, the AP may be configured to transmit
a number of HE-LTFs 165 to each STA equal to the largest number of
spatial streams assigned to any STA. For example, if three STAs are
assigned a single spatial stream, but the fourth STA is assigned
three spatial streams, in this aspect, the AP may be configured to
transmit four symbols of HE-LTF information to each of the four
STAs before transmitting symbols containing payload data.
[0080] It is not necessary that the tones assigned to any given STA
be adjacent. For example, in some implementations, the sub-bands of
the different receiving STAs may be interleaved. For example, if
each of user-1 and user-2 receive three sub-bands, while user-4
receives two sub-bands, these sub-bands may be interleaved across
the entire AP bandwidth. For example, these sub-bands may be
interleaved in an order such as 1,2,4,1,2,4,1,2. In some aspects,
other methods of interleaving the sub-bands may also be used. In
some aspects, interleaving the sub-bands may reduce the negative
effects of interferences or the effect of poor reception from a
particular device on a particular sub-band. In some aspects, the AP
may transmit to STAs on the sub-bands that the STA prefers. For
example, certain STAs may have better reception in some sub-bands
than in others. The AP may thus transmit to the STAs based at least
in part on which sub-bands the STA may have better reception. In
some aspects, the sub-bands may also not be interleaved. For
example, the sub-bands may instead be transmitted as
1,1,1,2,2,2,4,4. In some aspects, it may be pre-defined whether or
not the sub-bands are interleaved.
[0081] In the example of FIG. 5, HE-SIG3 symbol modulation is used
to signal HE devices that the packet is an HE packet. Other methods
of signaling HE devices that the packet is an HE packet may also be
used. In the example of FIG. 7, the L-SIG 126 may contain
information that instructs HE devices that an HE preamble will
follow the legacy preamble. For example, the L-SIG 26 may contain a
low-energy, 1-bit code on the Q-rail which indicates the presence
of a subsequent HE preamble to HE devices sensitive to the Q signal
during the L-SIG 26. A very low amplitude Q signal can be used
because the single bit signal can be spread across all the tones
used by the AP to transmit the packet. This code may be used by
high-efficiency devices to detect the presence of an
HE-preamble/packet. The L-SIG 26 detection sensitivity of legacy
devices need not be significantly impacted by this low-energy code
on the Q-rail. Thus, these devices will be able to read the L-SIG
26, and not notice the presence of the code, while HE devices will
be able to detect the presence of the code. In this implementation,
all of the HE-SIG fields can be BPSK modulated if desired, and any
of the techniques described herein related to legacy compatibility
can be used in conjunction with this L-SIG signaling.
[0082] FIG. 8 illustrates another method to implement backward
compatibility with 11ac devices as well. In this example, the
HE-SIG-A1 455 may contain a bit that is set to a value flipped from
the value that an 11ac device requires when decoding a VHT-SIG
field. For example, an 802.11ac VHT-SIG-A field contains bits 2 and
23 which are reserved and set to 1 in a correctly assembled
VHT-SIG-A field. In the high-efficiency preamble HE-SIG-A 455, one
or both of these bits may be set to zero. If an 802.11ac device
receives a packet which contains a reserved bit with such a flipped
value, an 11ac device stop processing the packet, treating it as
undecodable, while still deferring to the packet for the duration
specified in the L-SIG 26. In this implementation, backward
compatibility with 11a/b/g/n devices can be achieved by using BPSK
modulation on the HE-SIG1 symbol 455, and signaling HE devices can
be achieved by using QBPSK modulation on one or more symbols of
HE-SIG2 457 or HE-SIG3 459.
[0083] As shown by the example illustrated in FIG. 9, the structure
of an HE packet may be based upon the packet structure utilized in
802.11ac. In this example, after the legacy preamble 22, 24, 26,
two symbols are provided, termed HE-SIG-A1 and HE-SIG-A2 in FIG. 9.
This is the same structure as the VHT-SIG-A1 and VHT-SIG-A2 of FIG.
4. To fit both space time stream allocation and tone allocation
into these two 24 bit symbols, less freedom is provided for space
time stream options.
[0084] The example of FIG. 9 also places an HE-SIG-B symbol 459
after the HE training fields, which is also analogous to the
VHT-SIG-B field 154 of FIG. 4.
[0085] However, one potential problem with this 11ac-based preamble
is that this design may run into space limitations in the HE-SIG-B
470. For example, the HE-SIG-B 470 may need to contain at least the
MCS (4 bits) and the tail bits (6 bits). Thus, the HE-SIG-B 470 may
need to contain at least 10 bits of information. In the 802.11ac
specification, the VHT-SIG-B is one OFDM symbol. However, there may
not be a sufficient number of bits in a single OFDM symbol,
depending upon the bandwidth of each sub-band. For example, Table 1
below illustrates this potential issue.
TABLE-US-00001 TABLE 1 BW per user # of bits per # of bits
remaining (in MHz) user/OFDM symbol # of tail bits for MCS field 10
13 6 7 6 8 6 2 5 6 6 0
[0086] As illustrated in Table 1, if each sub-band is 10 MHz, a
single OFDM symbol provides 13 bits. Six of these bits are
necessary as tail bits, and thus, 7 bits remain for the MCS field.
The MCS field, as noted above, requires four bits. Thus, if each
sub-band is at least 10 MHz, a single OFDM symbol may be used for
the HE-SIG-B 470, and this may be sufficient to include the 4 bit
MCS field. However, if each sub-band is instead 5 or 6 MHz, this
may only allow 6 or 8 bits per OFDM symbol. Of these bits, 6 bits
are tail bits. Thus, only 0 or 2 bits are available for the MCS
field. This is insufficient to provide the MCS field. In those
cases where the sub-band granularity is too small to provide the
required information in the SIG-B fields, more than one OFDM symbol
may be used for the HE-SIG-B 470. The number of symbols needed will
be related to the smallest sub-band the system will allow. If this
is 5 MHz, corresponding to 13 tones in the IEEE 802.11 family OFDM
system, two symbols for the HE-SIG-B would allow BPSK modulation
and a 1/2 forward error correction code rate to provide 12 bits,
which is a sufficient length for the HE-SIG-B information MCS and
tail bits.
[0087] FIG. 10 illustrates an example of a wireless communication
system 100 in which aspects of the present disclosure may be
employed. The wireless communication system 100 may operate
pursuant to a wireless standard, for example the IEEE 802.11
standards. The wireless communication system 100 may include an AP
104, which communicates with STAs 106a, 106b, 106c, and 106d
(collectively STAs 106). The network may include both legacy STAs
106b and high-efficiency (HE) STAs 106a, 106c, 106d.
[0088] A variety of processes and methods may be used for
transmissions in the wireless communication system 100 between the
AP 104 and the STAs 106. For example, signals may be sent and
received between the AP 104 and the STAs 106 in accordance with
OFDM/OFDMA techniques. If this is the case, the wireless
communication system 100 may be referred to as an OFDM/OFDMA
system.
[0089] A communication link that facilitates transmission from the
AP 104 to one or more of the STAs 106 may be referred to as a
downlink (DL) 108, and a communication link that facilitates
transmission from one or more of the STAs 106 to the AP 104 may be
referred to as an uplink (UL) 110. Alternatively, a downlink 108
may be referred to as a forward link or a forward channel, and an
uplink 110 may be referred to as a reverse link or a reverse
channel. In some aspects, some DL 108 communications may be HE
packets, such as HE packet 130. Such HE packets may contain legacy
preamble information, such as preamble information in according
with specifications such as 802.11a and 802.11n, which contains
information sufficient to cause legacy STA 106b to recognize the HE
packet 130 and to defer to the transmission of the HE packet 130
for the duration of the transmission. Similarly, the DL 108
communications which are HE packets 130 may contain information
sufficient to inform HE STAs 160a, 106c, 106d which devices may
receive information in the HE packet 130, as discussed above.
[0090] The AP 104 may act as a base station and provide wireless
communication coverage in a basic service area (BSA) 102. The AP
104 along with the STAs 106 associated with the AP 104 and that use
the AP 104 for communication may be referred to as a basic service
set (BSS). It should be noted that the wireless communication
system 100 may not have a central AP 104, but rather may function
as a peer-to-peer network between the STAs 106. Accordingly, the
functions of the AP 104 described herein may alternatively be
performed by one or more of the STAs 106.
[0091] FIG. 11 illustrates various components that may be utilized
in a wireless device 202 that may be employed within the wireless
communication system 100. The wireless device 202 is an example of
a device that may be configured to implement the various methods
described herein. For example, the wireless device 202 may comprise
the AP 104 or one of the STAs 106 of FIG. 10. In some aspects, the
wireless device 202 may comprise an AP that is configured to
transmit HE packets, such as HE packet 130.
[0092] The wireless device 202 may include a processor 204 which
controls operation of the wireless device 202. The processor 204
may also be referred to as a central processing unit (CPU). Memory
206, which may include both read-only memory (ROM) and random
access memory (RAM), provides instructions and data to the
processor 204. A portion of the memory 206 may also include
non-volatile random access memory (NVRAM). The processor 204
typically performs logical and arithmetic operations based on
program instructions stored within the memory 206. The instructions
in the memory 206 may be executable to implement the methods
described herein. For example if the wireless device 202 is an AP
104, the memory 206 may contain instructions sufficient to allow
the wireless device 202 to transmit HE packets, such as HE packet
130. For example, the memory 206 may contain instructions
sufficient to allow the wireless device 202 to transmit a legacy
preamble, followed by an HE preamble, including an HE-SIG or an
HE-SIG-A. In some aspects, the wireless device 202 may include a
frame formatting circuit 221, which may contain instructions
sufficient to allow the wireless device 202 to transmit a frame
according to embodiments disclosed herein. For example, the frame
formatting circuit 221 may contain instructions sufficient to allow
the wireless device 202 to transmit a packet which includes both a
legacy preamble and a high-efficiency preamble.
[0093] The processor 204 may comprise or be a component of a
processing system implemented with one or more processors. The one
or more processors may be implemented with any combination of
general-purpose microprocessors, microcontrollers, digital signal
processors (DSPs), field programmable gate array (FPGAs),
programmable logic devices (PLDs), controllers, state machines,
gated logic, discrete hardware components, dedicated hardware
finite state machines, or any other suitable entities that can
perform calculations or other manipulations of information.
[0094] The processing system may also include machine-readable
media for storing software. Software shall be construed broadly to
mean any type of instructions, whether referred to as software,
firmware, middleware, microcode, hardware description language, or
otherwise. Instructions may include code (e.g., in source code
format, binary code format, executable code format, or any other
suitable format of code). The instructions, when executed by the
one or more processors, cause the processing system to perform the
various functions described herein.
[0095] The wireless device 202 may also include a housing 208 that
may include a transmitter 210 and a receiver 212 to allow
transmission and reception of data between the wireless device 202
and a remote location. The transmitter 210 and receiver 212 may be
combined into a transceiver 214. An antenna 216 may be attached to
the housing 208 and electrically coupled to the transceiver 214.
The wireless device 202 may also include (not shown) multiple
transmitters, multiple receivers, multiple transceivers, and/or
multiple antennas.
[0096] The wireless device 202 may also include a signal detector
218 that may be used in an effort to detect and quantify the level
of signals received by the transceiver 214. The signal detector 218
may detect such signals as total energy, energy per subcarrier per
symbol, power spectral density and other signals. The wireless
device 202 may also include a digital signal processor (DSP) 220
for use in processing signals. The DSP 220 may be configured to
generate a data unit for transmission. In some aspects, the data
unit may comprise a physical layer data unit (PPDU). In some
aspects, the PPDU is referred to as a packet.
[0097] The wireless device 202 may further comprise a user
interface 222 in some aspects. The user interface 222 may comprise
a keypad, a microphone, a speaker, and/or a display. The user
interface 222 may include any element or component that conveys
information to a user of the wireless device 202 and/or receives
input from the user.
[0098] The various components of the wireless device 202 may be
coupled together by a bus system 226. The bus system 226 may
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.
Those of skill in the art will appreciate the components of the
wireless device 202 may be coupled together or accept or provide
inputs to each other using some other mechanism.
[0099] Although a number of separate components are illustrated in
FIG. 11, one or more of the components may be combined or commonly
implemented. For example, the processor 204 may be used to
implement not only the functionality described above with respect
to the processor 204, but also to implement the functionality
described above with respect to the signal detector 218 and/or the
DSP 220. Further, each of the components illustrated in FIG. 11 may
be implemented using a plurality of separate elements. Furthermore,
the processor 204 may be used to implement any of the components,
modules, circuits, or the like described below, or each may be
implemented using a plurality of separate elements.
[0100] FIG. 12 illustrates an exemplary structure of an uplink
physical-layer packet 830 which may be used to enable
backward-compatible multiple access wireless communications. In
such an uplink message, no legacy preamble is needed, as the NAV is
set by the AP's initial downlink message. Thus, the uplink packet
830 does not contain a legacy preamble. The uplink packet 830 may
be sent in response to a UL-OFDMA-announce message that is sent by
the AP.
[0101] The uplink packet 830 may be sent by a number of different
STAs. For example, each STA that is identified in the downlink
packet may transmit a portion of the uplink packet 830. Each of the
STAs may transmit in its assigned bandwidth or bandwidths
simultaneously, and the transmissions may be received by the AP as
a single packet.
[0102] In the packet 830, each STA uses only the channels, or
sub-bands, assigned to it during the tone assignment in the initial
downlink message, as discussed above. This allows for completely
orthogonal receive processing on the AP. In order to receive
messages on each of these sub-bands, the AP must receive pilot
tones. These pilot tones are used in 802.11 packets for phase
tracking, in order to estimate a phase offset per symbol to correct
for phase changes across data symbols due to residual frequency
offset or due to phase noise. This phase offset may also feed into
time and frequency tracking loops.
[0103] In order to transmit pilot tones, at least two different
options may be used. First, each user may transmit the pilot tones
that fall into its assigned sub-bands. However, for low bandwidth
OFDMA allocations, this may not allow a sufficient number of pilot
tones for some users. For example, there are 4 pilot tones in a 20
MHz transmission in 802.11a/n/ac. However, if a user only has 5 MHz
assigned to it, the user may have only one pilot tone in its
sub-band. If some problem, such as a deep fade, occurs with that
pilot tone, it may be very difficult to obtain a good phase
estimate.
[0104] Another possible method of transmitting pilot tones may
involve each user transmitting on all the pilot tones, not just
those which fall in its sub-band. This may result in a larger
number of pilot tones being transmitted per user. But, this may
result in the AP receiving each pilot tone from multiple users
simultaneously, which may be more difficult for the AP to process.
The AP would need to estimate channels for all users. In order to
accomplish this, more LTFs may be needed, such as one that
corresponds to the sum of all users' spatial streams. For example,
if each of four users were associated with two spatial streams, in
this approach, eight LTFs may be used.
[0105] Thus, each STA may transmit an HE-STF 835. As shown in
packet 830, the HE-STF 835 may be transmitted in 8 us, and contain
two OFDMA symbols. Each STA may also transmit one or more HE-LTF
840. As shown in packet 830, the HE-LTF 840 may be transmitted in 8
us, and contain two OFDMA symbols. For example, as before, each STA
may transmit a HE-LTF 840 for each sub-band assigned to the STA.
Each STA may also transmit a HE-SIG 845. The length of the HE-SIG
845 may be one ODFMA symbol long (4 us) for each of U, where U is
the number of STAs multiplexed in the transmission. For example, if
four STAs are sending the uplink packet 830, the HE-SIG 845 may be
16 us. After the HE-SIG 845, additional HE-LTFs 840 may be
transmitted. Finally, each STA may transmit data 855.
[0106] In order to send a combined uplink packet 830, each of the
STAs may be synchronized with each other in time, frequency, and in
power with the other STAs. The timing synchronization required for
such a packet may be on the order of approximately 100 ns. This
timing may be coordinated by responding to the AP's
UL-OFDMA-announce message. This timing accuracy may be obtained
using several solutions which are known to those of skill in the
art. For example, techniques used by 802.11ac and 802.11n devices
in order to time short interframe space (SIFS) may be sufficient to
provide the timing accuracy needed in order to obtain a combined
uplink packet 830. This timing accuracy may also be maintained by
using an 800 ns long guard interval only for the uplink OFDMA to
get 400 ns guard time, in order to absorb timing errors and round
trip delay differences between uplink clients.
[0107] Another technical issue that must be addressed by the uplink
packet 830 is that the frequencies of the sending devices must be
synchronized. There are multiple options to deal with
frequency-offset synchronization among STAs in an UL-OFDMA system,
such as that of uplink packet 830. First, each STA may calculate
and correct for its frequency differences. For example, the STAs
may calculate a frequency offset with respect to the AP, based upon
the UL-OFDMA-announce message sent to the STAs. Based upon this
message, the STAs may apply a phase ramp on the time-domain uplink
signal. The AP may also estimate the common phase offset for each
STA, using the LTFs. For example, the LTFs which are transmitted by
the STAs may be orthogonal in frequency. Hence, the AP can use a
windowed inverse fast Fourier transform (IFFT) function to separate
the STA impulse responses. The variation of these impulse responses
across two identical LTF symbols may give us a frequency offset
estimate for every user. For example, frequency offset in a STA may
lead to phase ramp, over time. Thus, if two identical LTF symbols
are transmitted, the AP may be able to use the differences between
the two symbols to calculate a slope of the phase across the two
impulse responses in order to get an estimate of the frequency
offset. This approach may be similar to the tone-interleaved
approach that has been proposed in UL-MU-MIMO message, which may be
known to persons of skill in the art.
[0108] FIG. 13 illustrates a process flow diagram for an example
method of a transmitting a high-efficiency packet to two or more
wireless communication devices. This method may be done by a
device, such as an AP.
[0109] At block 905, the AP transmits a legacy preamble, the legacy
preamble containing information sufficient to inform legacy devices
to defer to the packet. For example, the legacy preamble may be
used to alert legacy devices to defer to the packet. The legacy
packet may contain a reserved bit or a combination of reserved
bits. These reserved bits may alert high-efficiency devices to
continue listening to the packet for a high-efficient preamble,
while also causing legacy devices to defer to the packet. In some
aspects, the means for transmitting a legacy preamble, the legacy
preamble containing information sufficient to inform legacy devices
to defer to the packet, may comprise a transmitter.
[0110] At block 910, the AP transmits a high-efficiency signal, the
high-efficiency signal containing tone allocation information, the
tone allocation information identifying two or more wireless
communication devices. In some aspects, the high-efficiency signal
may contain tone allocation information, which may include
information that identifies the STAs that will receive information
in the packet, and may alert those STAs which sub-bands are
intended for them. In some aspects, the high-efficiency packet may
also include information sufficient to cause 802.11ac devices to
defer to the packet. In some aspects, the means for transmitting a
high-efficiency signal, the high-efficiency signal containing tone
allocation information, the tone allocation information identifying
two or more wireless communication devices may comprise a
transmitter. In some aspects, the high-efficiency signal may
further comprise an indication of a number of spatial streams may
be assigned to each of the two or more wireless communications
devices. For example, each of the two or more wireless
communications devices may be assigned one or more spatial streams.
In some aspects, the means for assigning one or more spatial
streams to each of the two or more wireless communications devices
may comprise a transmitter or a processor.
[0111] At block 915, the AP transmits data to the two or more
wireless communication devices simultaneously, the data contained
on two or more sub-bands. For example, the AP may transmit data to
up to four STAs. In some aspects, the means for transmitting data
to the two or more wireless communication devices simultaneously,
the data contained on two or more sub-bands may comprise a
transmitter.
[0112] In some aspects, an AP may transmit a hybrid packet, which
includes data for both for a legacy device, such as an IEEE
802.11a/n/ac device, and data for one or more high-efficiency
devices. Such a hybrid packet may allow more efficient uses of
bandwidth in mixed environments containing both legacy and
high-efficiency devices. For example, in a legacy system if an AP
is configured to use 80 MHz, a portion of the bandwidth assigned to
the AP may go unused if the AP is transmitting a packet to a device
that is not capable of using the full 80 MHz. This is one problem
that is addressed by the use of high-efficiency packets. However,
in an environment in which some of the STAs are high-efficiency and
some of the STAs are legacy devices, bandwidth may still go unused
when transmitting to legacy devices that are not capable of using
the full bandwidth that the AP is configured to use. For example,
while the high-efficiency packets in such a system may use the full
bandwidth, as discussed above, legacy packets may not. Thus, it may
be beneficial to provide a hybrid packet, in which a legacy device
may receive information in one portion of the bandwidth of a
packet, while high-efficiency devices may receive information in
another portion of the packet. Such a packet may be referred to as
a hybrid packet, as a portion of the packet may transmit data in a
legacy-compatible format, such as IEEE 802.11a/n/ac, and a portion
of the packet may transmit data to high-efficiency devices.
[0113] An exemplary hybrid packet 1400 is illustrated in FIG. 14.
Such a hybrid packet may be transmitted by a wireless device, such
as an AP. A hybrid packet may include a legacy portion, in which
data is transmitted to a legacy device, and a high-efficiency
portion, in which data is transmitted to a high-efficiency
device.
[0114] A hybrid packet 1400 may include a number of legacy
preambles, each duplicated over some portion of the bandwidth of
the packet. For example, the exemplary hybrid packet 1400 is
illustrated as an 80 MHz packet, which contains four 20 MHz legacy
preambles duplicated over the 80 MHz of bandwidth of the packet
1400. Such duplication may be used in legacy formats, in order to
ensure that other devices, which may operate on only a portion of
the 80 MHz bandwidth, defer to the packet. In some aspects each of
the devices in the network may, by default, monitor only the
primary channel.
[0115] A hybrid packet 1400 may include an L-STF 1405 and an L-LTF
1410 which are the same as those specified in legacy formats, such
as IEEE 802.11a/n/ac. These fields may be the same as those
discussed above. However, the L-SIG 1415 of a hybrid packet 1400
may differ from that of a legacy packet. The L-SIG 1415 may contain
information which is used to signal to high-efficiency devices that
the packet is a hybrid packet. In order for legacy devices to be
able to also receive information in the packet, this information
must be hidden from the legacy devices, such that it does not
disrupt their reception of the L-SIG 1415.
[0116] The L-SIG 1415 may signal to high-efficiency devices that
the packet is a hybrid packet by placing a one-bit code orthogonal
to the information in the L-SIG 1415. For example, as discussed
above, a one-bit code may be placed on the Q-rail of the L-SIG
1415. Legacy devices may not notice the one-bit code, and may be
able to read the L-SIG 1415 as normal, while high-efficiency
devices may look specifically for this one-bit code, and be able to
determine whether or not it is present. This one-bit code may be
used to signal to high-efficiency devices that a hybrid packet is
being sent. In some aspects, the one-bit code may be hidden from or
invisible to legacy devices, which may not be configured to look
for the code. In some aspects, legacy devices may be able to
understand the L-SIG 1415 without observing any irregularities due
to the presence of the one-bit code. In some aspects, only the
L-SIG 1415 in the primary channel may contain the one-bit code to
instruct high-efficiency devices to look at other channels for an
HE-SIG 1425. In some aspects, a number of L-SIGs 1415 may have this
one-bit indicator, where the number of L-SIGs 1415 with the
indicator is equal to the number of channels which are to be used
for the legacy packet. For example, if the legacy packet will
include both the first and second channels, but not a third
channel, then the L-SIG in the first and second channels may
contain the one-bit indicator, while the L-SIG in the third channel
may not contain this indicator. High-efficiency devices may be
configured to look for the first channel with an L-SIG that does
not contain a one-bit code, and to monitor that channel for the
presence of an HE-SIG 1425. In some aspects, the bandwidth
information in a VHT-SIG-A 1420 may contain information regarding
how much bandwidth the legacy packet 1430 will use, and thus, at
which bandwidth the HE packet 1435 may begin. In some aspects, the
one-bit code may only be included in L-SIGs 1415 which are being
transmitted in channels which will be used for transmitting data to
HE devices. For example, if the first channel is used to transmit
to a legacy device, and three other channels are used to transmit
to HE devices in a particular packet, each of the L-SIGs 1415
transmitted in the three other channels may include the one-bit
code. In some aspects, in an HE packet, each L-SIG 1415 may include
the one-bit code to indicate that each channel may be used to
transmit data to HE devices. In some aspects, this may allow the
bandwidth used for the HE portion of an HE packet or a hybrid
packet to be signaled using the L-SIG 1415 of the packet. If the
bandwidth used for the HE portion of the packet is signaled in the
L-SIG 1415, this may allow the HE-SIG 1425 in a HE packet or a
hybrid packet to span a larger portion of the bandwidth assigned to
the HE portion of the packet. For example, the HE-SIG 1425 may be
configured to span the bandwidth assigned to the HE packet. In some
aspects, using more bandwidth for the HE-SIG 1425, rather than only
using 20 MHz for the HE-SIG 1425, may allow more information to be
transmitted in the HE-SIG 1425. In some aspects, the first symbol
of the HE-SIG 1425 may be transmitted in duplicate on each 20 MHz
of the bandwidth assigned to the HE portion of the packet, while
the remaining symbols of the HE-SIG 1425 may be transmitted using
the full bandwidth assigned to the HE portion of the packet. For
example, the first symbol of the HE-SIG 1425 may be used to
transmit the bandwidth allocated to the HE portion of the HE or
hybrid packet, and thus, subsequent symbols may be transmitted on
the entire bandwidth assigned to the HE portion of the packet.
[0117] Upon receiving the one-bit code in the L-SIG 1415,
high-efficiency devices may be configured to look in
higher-bandwidth portions of the bandwidth allocated to the AP,
such as higher-bandwidth channels, to find an HE-SIG 1425. For
example, in the hybrid packet 1400, upon receiving the L-SIG 1415
with the one-bit code in an orthogonal direction, high-efficiency
devices may be configured to look in the 20 MHz channels apart from
the channel carrying data to legacy devices for HE-SIGs, such as
HE-SIG 1425, which may be transmitted in other frequency bands,
alongside a legacy packet. For example, in exemplary hybrid packet
1400, HE-SIG 1425 is illustrated as being transmitted
simultaneously with VHT-SIG-A 1420. In this example, the hybrid
packet 1400 may include an IEEE 802.11ac-compatible packet on the
lower portion of the bandwidth, and a high-efficiency packet on the
higher portion of the bandwidth. The hybrid packet 1400 may also
contain an IEEE 802.11a or IEEE 802.11n-compatible packet in the
lower portion. Importantly, regardless of which type of packet the
lower portion is, the L-SIG 1415 may be configured to contain
signaling information, sufficient to signal to high-efficiency
devices that the packet is a hybrid packet, and thus, to look for
an HE-SIG 1425 in another frequency.
[0118] In some aspects, the HE-SIG 1425 may be similar to any of
the previous high-efficiency signal fields previously discussed. In
some aspects, an AP which transmits both high-efficiency packets
and hybrid packets may use a symbol with a rotated BPSK
constellation (QBPSK) symbol in an HE-SIG 1425 to indicate that a
packet is a high-efficiency packet, rather than using a one-bit
signal in the Q-rail, as using a one-bit signal on the Q-rail may
instead be used to signal that a packet is a hybrid packet, such as
hybrid packet 1400. For example, the HE-SIG 1425 may be used to
indicate to high-efficiency devices which device or devices may
receiving information in the packet, such as by using a group ID,
as discussed earlier. Thus, high-efficiency devices may be
configured to receive and decode the L-STF 1405, L-LTF 1410, and
L-SIG 1415. If the L-SIG 1415 includes a one-bit code,
high-efficiency devices may be configured to locate and decode the
HE-SIG 1425 which is at a higher frequency band, in order to
determine whether the high-efficiency portion of the hybrid packet
contains information for that particular device.
[0119] In some aspects, the legacy packet may, as illustrated, take
up only 20 MHz of bandwidth. However, the legacy portion of the
packet 1400 may also take up a different amount of bandwidth as
well. For example, the legacy portion of the hybrid packet may
comprise a 40 MHz, 60 MHz, 80 MHz or other size legacy packet,
while the high-efficiency portion of the hybrid packet 1400 may use
the remainder of the available bandwidth. In some aspects, channels
of sizes other than 20 MHz may also be used. For example, channels
may be 5, 10, 15, 40 MHz, or other sizes. In some aspects,
following the legacy VHT-SIG-A 1420, a legacy packet 1430 may be
transmitted in a primary channel to a legacy device. In some
aspects, the legacy packet 1430 may include at least the primary
channel, and may also include additional channels. For example,
this legacy packet 1430 may be compatible with IEEE 802.11a,
802.11n, or 802.11ac devices. In some aspects, following the one or
more HE-SIGs 1425, a high-efficiency packet 1435 may be transmitted
to one or more high-efficiency devices, using at least a portion of
the bandwidth available to the AP. In some aspects, the legacy
packet may be sent to multiple legacy devices. For example, the
hybrid packet may comprise a MU-MIMO 802.11ac packet, which is sent
to two or more 802.11ac-compatible STAs.
[0120] FIG. 15 illustrates an exemplary method 1500 of transmitting
a hybrid packet. This method may be done by a wireless device, such
as an AP.
[0121] At block 1505, the AP transmits to one or more first devices
in a first portion of a bandwidth, the one or more first devices
having a first set of capabilities. In some aspects, the one or
more first devices may be legacy devices. In some aspects, the
first portion of the bandwidth may be a primary channel. In some
aspects, the means for transmitting to a first device may be a
transmitter.
[0122] At block 1510, the AP simultaneously transmits to one or
more second devices in a second portion of the bandwidth, the one
or more second devices having a second set of capabilities wherein
the transmission comprises a preamble which includes an indication
for devices with the second set of capabilities to locate a
frequency band where symbols containing a set of transmission
parameters for devices with the second set of capabilities are
sent, and where the indication is sent so as to have no substantial
impact on a preamble decoding of devices with the first set of
capabilities. In some aspects, the means for transmitting to one or
more second devices may be a transmitter. In some aspects, the
preamble may be a legacy preamble, and the indication may be a
one-bit code in an L-SIG in the legacy preamble. In some aspects,
the indication may be contained in the L-SIG in the primary
channel, in the primary channel and one or more other channels, or
in other channels.
[0123] FIG. 16 illustrates an exemplary method of receiving a
hybrid packet. In some aspects, this method may be used by a STA,
such as a high-efficiency wireless communication device.
[0124] At block 1605, the STA receives a legacy preamble in a
primary channel. In some aspects, the means for receiving a legacy
preamble may be a receiver.
[0125] At block 1610, the STA determines whether the legacy
preamble contains information sufficient to inform high-efficiency
devices to locate a high-efficiency signal field in one or more
non-primary channels. In some aspects, the means for determining
may be a processor or a receiver.
[0126] At block 1615, the STA receives the high-efficiency signal
field in at least one of the one or more non-primary channels. In
some aspects, the means for receiving the high-efficiency signal
field may be a receiver. In some aspects, the STA may further
receive data on at least one of the one or more non-primary
channels. In some aspects, the means for receiving data may be a
receiver.
[0127] Delay Spread Protection and Potential Structures of a
High-Efficiency Signal Field
[0128] In some aspects, outdoor or other wireless networks may have
channels with relatively high delay spreads, such as those in
excess of 1 .mu.s. For example, an access point at a high
elevation, such as a pico/macro cell tower access point, may have
high delay spreads. Various wireless systems, such as those in
accordance with 802.11a/g/n/ac, use a Cyclic Prefix (CP) length of
only 800 ns. Nearly half of this length may be consumed by transmit
and receive filters. Because of this relatively short CP length and
the overhead from the transmit and receive filters, such
802.11a/g/n/ac networks may be unsuitable for an outdoor deployment
with a high delay spread.
[0129] According to aspects of the present disclosure, a packet
format (PHY waveform) that is backwards compatible with such legacy
systems and supports cyclic prefixes longer than 800 ns is provided
that may allow the use of 2.4 and 5 GHz WiFi systems in outdoor
deployments.
[0130] For example, one or more bits of information may be embedded
in one or more of an L-STF, an L-LTF, an L-SIG, or in another
portion of a packet preamble, such as an HE-SIG. These one or more
bits of information may be included for devices configured to
decode them, as above, but may not impact decoding by legacy (e.g.,
802 11a/g/n/ac) receivers. These bits may include an indication of
a packet which includes delay spread protection, in order to allow
the use of such a packet in an outdoor setting, or another setting
with potentially high delay spread.
[0131] In some aspects, a number of methods may be used to provide
delay spread protection or tolerance. For example, different
transmission parameters may be used to increase symbol duration
(e.g., downclocking to decrease sample rate or increasing FFT
length while maintaining the same sample rate). Increasing the
symbol duration, such as by 2.times. or 4.times., may increase
tolerance to higher delay spreads.
[0132] In some aspects, an increased symbol duration may be
signaled in a field of an L-SIG or an HE-SIG. In some aspects,
other packets on the network may not contain the signaling for
increased symbol duration, but rather be packets with a
conventional or "normal" symbol duration. Preserving a "normal"
symbol duration may be desirable in some instances because
increased symbol duration typically means increased FFT size and
thus increased sensitivity to frequency error and increased PAPR.
Further, not every device in a network will need this increased
delay spread tolerance. Thus, in some cases, an increased FFT size
may hurt performance, and so it may be desirable for some packets
to use conventional symbol duration.
[0133] Thus, in some aspects, all packets may contain an increased
symbol duration after an L-SIG or HE-SIG field. In other aspects,
only packets which include information signaling an increased
symbol duration in an L-SIG or an HE-SIG may include an increased
symbol duration. In some aspects, the signaling for an increased
symbol duration may be contained within an HE-SIG, and L-SIG, a
VHT-SIG-A, or another field in a packet. In some aspects, this
signaling may be conveyed by, for example, a Q-BPSK rotation in a
symbol of a SIG field, such as an L-SIG or an HE-SIG. In some
aspects, this signaling may be conveyed by hiding information in an
orthogonal rail, such as an imaginary axis, of a field of a
packet.
[0134] In some aspects, increase symbol duration may be used for
either or both of uplink or downlink packets. For an uplink packet,
an AP may signal in preceding downlink packet that the uplink
packet may be transmitted using an increased symbol duration. For
example, in an uplink OFDMA packet, the AP may send a tone
allocation message which tells users to use longer symbol
durations. In that case, the uplink packet itself may not need to
carry an indication indicating a particular symbol duration. In
some aspects, a signal from the AP to a STA may inform the STA to
use a particular symbol duration in all future uplink packets,
unless told otherwise.
[0135] In some aspects, such delay spread protection may be
incorporated into high-efficiency packets such as those described
above. The preamble formats presented herein provide a scheme in
which delay spread protection may be included in packets, while
allowing legacy devices to detect whether a packet is an 802.11n,
802.11a or 802.ac packet.
[0136] The preamble formats presented herein may preserve the
L-SIG-based deferral as in an IEEE 802.11ac (mixed mode preamble)
packet. Having a legacy section of a preamble decodable by 802.11
a/an/ac stations may facilitate mixing legacy and HE devices in the
same transmission. Preamble formats provided herein may help
provide protection on the HE-SIG, which may help achieve robust
performance. For example, these preamble formats may help to reduce
a SIG error rate to 1% or less in relatively stringent standard
test scenarios.
[0137] FIG. 17 illustrates a packet with one example HE preamble
format, in accordance with aspects of the present disclosure. The
example HE preamble format is compared with a VHT preamble format.
As illustrated, the HE preamble format may include one or more
signal (SIG) fields decodable by a first type of device (e.g.,
802.11a/ac/n devices) and one or more SIG fields (HE-SIG1)
decodable by a second type of devices (e.g., HE devices). As
illustrated, 802.11a/ac/n devices may defer based on a duration
field in the L-SIG. The L-SIG may be followed by a repeated
high-efficiency SIG (HE-SIG) field. As illustrated, after the
repeated HE-SIG field, a device may already know if the packet it
is a VHT packet, so there may be no problem with VHT-STF gain
setting.
[0138] In the example format shown in FIG. 17, HE-SIG1 fields may
be repeated and preceded with a normal guard interval (GI), which
gives protection to HE-SIG1 for HE devices. Because of the repeated
HE-SIG1, this packet may have a lower signal-to-noise ratio
operating point, and thus provide more robust protections from
inter-symbol-interference (ISI). In some aspects, the L-SIG may
transmit at 6 Mbps, as packet type detection based on Q-BPSK checks
on 2 symbols after L-SIG may not be impacted.
[0139] Various techniques may be used to signal the HE packet to HE
devices, as discussed above. For example, the HE packet may be
signaled by placing an orthogonal rail indication in L-SIG, based
on a CRC check in HE-SIG1, or based on the repetition of the
HE-SIG1.
[0140] The delay spread protection on HE-SIG2 may take various
forms. For example, HE-SIG2 may be transmitted over 128 tones (in
20 MHz) to provide additional delay spread protection. This may
result in a guard interval of 1.6 us, but may require interpolation
of channel estimates calculated based on L-LTF, which would contain
the traditional number of tones. As another example, HE-SIG2 may
have the same symbol duration, but may be sent with a 1.6 us cyclic
prefix. This may lead to more cyclic prefix overhead than the
traditional value of 25%, but may not require interpolation. In one
aspect, HE-SIG2 may also be sent over the full bandwidth, rather
than repeating every 20 MHz. This may require that bandwidth bits
be placed in HE-SIG1, in order to indicate the full bandwidth.
[0141] FIG. 18 illustrates a packet with another example HE
preamble format, in accordance with aspects of the present
disclosure. As with FIG. 17, the example HE preamble format is
compared with a VHT preamble format. As before, IEEE 802.11 a/ac/n
devices may defer to the packet based on the duration field in the
L-SIG. The L-SIG may be followed by a repeated high-efficiency SIG
(HE-SIG) field. In the example format shown in FIG. 18, the HE-SIG1
fields may be repeated but with the first HE-SIG1 field preceded
with a normal guard interval, while the second HE-SIG1 precedes a
normal guard interval.
[0142] This repetition of HE-SIG1, with a guard interval placed
before the first HE-SIG1 and after the second HE-SIG1 may provide
protection for HE devices. It may be noted that the middle portion
of HE-SIG1 section may appear as an HE-SIG1 symbol with a
relatively large CP. In this aspect, a Q-BPSK check on the first
symbol after L-SIG may be unaffected. However, a Q-BPSK check on
the second symbol may give random results due to the guard interval
after the second HE-SIG1. However, these random results may not
have an adverse impact on VHT devices. For example, VHT devices may
classify the packet as an 802.11ac packet, but at this point the
devices may attempt to perform a VHT-SIG CRC check, and this will
fail. Accordingly, VHT devices will still defer to this packet,
despite the random results of the Q-BPSK check on the second symbol
after the L-SIG.
[0143] Because the auto-detection process for legacy devices, such
as VHT devices (those compatible with IEEE 802.11ac), will cause
those devices to defer to the packet in FIG. 18, these packets may
still carry 6 Mbps. As with the packet in FIG. 17, a number of
techniques discussed above may be used to signal to HE devices that
the packet is an HE packet. Similarly, HE devices may be provided
information about the delay spread protection of the packet in a
number of ways, such as a field contained in HE-SIG2.
[0144] FIG. 19 illustrates a packet with another example HE
preamble format, in accordance with aspects of the present
disclosure. As before, the example HE preamble format is similar to
an 802.11ac VHT preamble format. As illustrated, 802.11a/ac/n
devices may defer to the packet based on the duration field in the
L-SIG. The L-SIG may be followed by a repeated high-efficiency SIG
(HE-SIG) field.
[0145] In the example format shown in FIG. 19, repeated HE-SIG1
fields may be preceded by a double guard interval (DGI). The use of
such a double guard interval may result in a random result of a
Q-BPSK check on the first symbol after the L-SIG. Thus, some legacy
devices may not defer to this packet if the L-SIG signals a rate of
6 Mbps. Accordingly, the L-SIG in such a packet may need to signal
a rate other than 6 Mbps, in order to ensure that all IEEE
802.11a/ac/n devices defer to the packet. For example, the L-SIG
may signal a rate of 9 Mbps. Techniques similar to those discussed
above may be used to signal that the packet is an HE packet, and
may be used to signal whether the packet contains delay spread
protection.
[0146] Various optimization may be provided for preamble formats,
such as those shown in FIGS. 17-19. For example, for the example
formats shown in FIGS. 18 and 19, it may be possible to truncate
the second HE-SIG1 symbol and start the next symbol earlier, to
save overhead. In addition, there may be some benefit to having a
SIG-B after the HE-LTFs, which may provide per-user bits for
MU-MIMO.
[0147] FIG. 20 illustrates example bit allocation for an HE-SIG 1
field. As illustrated, there may be 2-3 bits for BW indication, an
8-bit Length indication, a bit to indicate longer symbols are used,
2-3 reserved bits, 4 bits for a CRC, and 6 tail bits. If a Longer
Symbols ON bit is provided in HE-SIG1, this may be used to signal
either of the following: that HE-SIG2 has delay spread protection
or everything after HE-SIG2 uses an increased FFT size. The above
HE-SIG formats, where HE-SIG is made up of HE-SIG1 and HE-SIG2 may
allow for delay spread protection, and may be used in packets which
allow multiple access, such as OFDMA packets.
[0148] Uplink Packet with Legacy Preamble
[0149] FIG. 21 illustrates an exemplary structure of an uplink
physical-layer packet 2100 which may be used to enable
backward-compatible multiple access wireless communications.
Typically, in an uplink packet, a legacy preamble may not be
needed, as the NAV is set by the AP's initial downlink message. The
AP's initial downlink message may cause legacy devices on the
network to defer to the uplink packet. However, some wireless
devices may be outside the range of the AP, but within the range of
STAs that are transmitting to the AP. Accordingly, these devices,
if they are legacy devices, may not defer to the AP as they did not
receive the AP's initial downlink message. These devices may also
not defer to an uplink packet like those in FIG. 12, because those
packets do not have a legacy preamble that legacy devices can
recognize. Accordingly, the transmission of such a device may
interfere with an uplink packet, and so it may be desirable to
transmit an uplink packet which contains a legacy preamble
sufficient to cause legacy devices to defer to the packet. These
uplink packets may take a number of possible forms. Uplink packet
2100 is an exemplary uplink packet which contains a legacy
preamble. Note that while packet 2100 includes times for each
portion of the packet, these times are merely exemplary. Each
portion of the packet 2100 may be longer or shorter than indicated.
In some aspects, it may be beneficial for the legacy portions of
the preamble, such as L-STF, L-LTF, and L-SIG to be the listed
times, in order to allow legacy devices to decode the legacy
portion of the preamble and defer to the packet 2100.
[0150] Accordingly, the packet 2100 may be used to inform such
legacy devices to defer to the uplink packet, by providing a legacy
preamble which such legacy devices may recognize. This legacy
preamble may include an L-STF, an L-LTF, and an L-SIG. Each of the
transmitting devices, as in the packet 830, may be configured to
transmit their own preamble on their assigned bandwidth. These
legacy preambles may protect the uplink communications from nodes
which did not hear the AP's initial downlink message.
[0151] As in packet 830, each of a number of devices, here N
devices, may transmit in their assigned bandwidth simultaneously.
Following the legacy preamble, each device may transmit a
high-efficiency preamble on its assigned tones. For example, each
device may transmit an HE-SIG on its own assigned tones. Following
this HE-SIG, each device may then transmit an HE-STF, and may
transmit one or more HE-LTFs. For example, each device may transmit
a single HE-STF, but may transmit a number of HE-LTFs which
correspond to the number of spatial streams assigned to that
device. In some aspects, each device may transmit a number of
HE-LTFs corresponding to the number of spatial streams assigned to
the device with the highest number of spatial streams. This
assignment of spatial streams may be done, for example, in the AP's
initial downlink message. If each device sends the same number of
HE-LTFs, this may reduce a peak-to-average-power ratio (PAPR). Such
a reduction of PAPR may be desirable. Further, if each device
transmits the same number of HE-LTFs, this may make processing the
received uplink packet easier for the AP. For example, if a
different number of HE-LTFs are sent by each device, the AP may
receive the preamble for one device while receiving data from
another device. This may make decoding the packet more complex for
the AP. Accordingly, it may be preferable to use the same number of
HE-LTFs for each devices. For example, each of the transmitting
devices may be configured to determine the maximum number of
spatial streams any device is receiving, and to transmit a number
of HE-LTFs corresponding to that number.
[0152] In some aspects, the L-STF in such a packet may include
small cyclic shifts, on the order of approximately up to 200 ns.
Large cyclic shifts may cause issues in such L-STFs with legacy
devices which might use a detection algorithm based upon
cross-correlation. The HE-STF in such a packet 2100 may include
larger cyclic shifts, on the order of approximately 800 ns. This
may allow for more accurate gain settings in the AP which is
receiving the uplink packet 2100.
[0153] FIG. 22 illustrates another exemplary structure of an uplink
physical-layer packet 2200 which may be used to enable
backward-compatible multiple access wireless communications. This
packet 2200 may be similar to the packet 2100, however, in this
packet 2200, each of the transmitting devices may not transmit an
HE-STF. Instead, each of the transmitting devices may transmit an
L-STF with larger cyclic shifts, such as on the order of
approximately 800 ns. While this may impact legacy devices with
cross-correlation packet detectors, this may allow a packet to be
shorter, as this may allow the transmitting devices to not transmit
an HE-STF. While packet 2200 includes times for each portion of the
packet, these times are merely exemplary, and each portion of the
packet may be longer or shorter than indicated. In some aspects, it
may be beneficial for the legacy portions of the preamble, such as
L-STF, L-LTF, and L-SIG to be the listed times, in order to allow
legacy devices to decode the legacy portion of the preamble and
defer to the packet 2200.
[0154] In packet 2200, each device may transmit a number of HE-LTFs
corresponding to the number of spatial streams assigned to that
device. In some aspects, each device may instead transmit a number
of HE-LTFs corresponding to the number of spatial streams assigned
to the device which is assigned the highest number of spatial
streams. As discussed above, such an approach may reduce PAPR.
[0155] In some aspects, longer symbol duration can provide delay
spread protection and protection from timing offsets. For example,
the devices transmitting an uplink packet may not begin to transmit
the packet at the same time, but instead begin at slightly
different times. A longer symbol duration may also aid the AP in
interpreting the packet in such instances. In some aspects, devices
may be configured to transmit with a longer symbol duration based
on a signal in the AP's downlink trigger message. In some aspects,
for a green-field packet such as packet 830, the entire waveform
may be transmitted at a longer symbol duration, as there is no need
for legacy compatibility. In an uplink packet which includes a
legacy preamble, such as packet 2100 or 2200, the legacy preamble
may be transmitted with a conventional symbol duration. In some
aspects, the portion after the legacy preamble may be transmitted
with a longer symbol duration. In some aspects, longer symbol
duration may be achieved by using an existing IEEE 802.11 tone plan
in a smaller bandwidth. For example, smaller subcarrier spacing may
be used, which may be referred to as down-clocking. For example, a
5 MHz portion of bandwidth may use a 64-bit FFT 802.11a/n/ac tone
plan, whereas 20 MHz may be conventionally used. Thus, each tone
may be 4.times. longer in such a configuration than in a typical
IEEE 802.11 a/n/ac packet. Other durations may also be used. For
example, it may be desirable to use tones which are twice as long
as in a typical IEEE 802.11 a/n/ac packet.
[0156] FIG. 23 illustrates an exemplary method 2300 of receiving a
packet. This method may be done by a wireless device, such as an
AP.
[0157] At block 2305, the AP receives a first portion in a first
section of a bandwidth, the first portion transmitted by a first
wireless device, the first portion comprising a legacy section of a
first preamble containing information sufficient to inform legacy
devices to defer to the packet and a high-efficiency section of the
first preamble. In some aspects, the means for receiving may be a
receiver.
[0158] At block 2310, the AP simultaneously receives a second
portion in a second section of the bandwidth, the second portion
transmitted by a second wireless device, the second portion
comprising a legacy section of a second preamble containing
information sufficient to inform legacy devices to defer to the
packet and a second high-efficiency section of the second preamble.
In some aspects, the means for simultaneously receiving may be a
receiver. In some aspects, the first wireless device and/or the
second wireless device may transmit on a number of spatial streams.
In some aspects, the high-efficiency portion of the preamble
transmitted by the first and second wireless devices may contain a
number of long training fields. In some aspects, the number of long
training fields can be based on the number of spatial streams
assigned to that particular device or the highest number of spatial
streams assigned to any wireless device.
[0159] In some aspects, it may be desirable for an uplink OFDMA
packet to have a structure which more closely mimics that of an
uplink multi-user multiple input and multiple-output (MU-MIMO)
packet. For example, a number of the preceding packets, such as
packet 2100 in FIG. 21, may include an HE-SIG prior to one or more
HE-LTFs. Similarly, in packet 830 in FIG. 12, each of the
transmitting devices transmits a single HE-LTF, followed by an
HE-SIG, followed by the remaining number of HE-LTFs. However, in
order to have an uplink packet with a structure more similar to the
of an uplink MU-MIMO packet, it may be desirable to have a packet
in which the HE-SIG follows after all of the HE-LTFs in the
packet.
[0160] Accordingly, in any of the packets described, it may be
possible to transmit the HE-SIG following all of the HE-LTFs. In
some aspects, it may be desirable to find another method of
signaling the number of spatial streams being used by each
transmitting device in the uplink packet when the HE-SIG follows
after all of the HE-LTFs. For example, in some of the
previously-described packets, the first HE-LTF from a transmitting
device may include information sufficient to allow the AP to decode
the HE-SIG from that transmitting device. In some of the
previously-described packets, the HE-SIG from a transmitting device
may include information regarding the number of spatial streams
which are being used by that device in the packet, and thus, in
some aspects, the HE-SIG may indicate the number of HE-LTFs which
will be transmitted by that transmitting device. However, if an
HE-SIG is transmitted following each HE-LTF, it may be desirable to
indicate the number of spatial streams used by a transmitting
device in a different manner than this. For example, the number of
spatial streams used by a transmitting device may be indicated in a
downlink message from the AP. For example, the uplink OFDMA packet
may be sent in response to a downlink packet from the AP, which
indicates which devices may transmit on the uplink OFDMA packet.
Accordingly, this downlink packet may also assign a number of
spatial streams to each device.
[0161] FIG. 24 is an exemplary uplink packet structure in which the
HE-SIG is transmitted after each HE-LTF. In uplink OFDMA packet
2400, each of the transmitting devices may transmit an HE-STF 2410,
as in other packets described above. Following the HE-STF 2410,
each of the transmitting devices may transmit a number of HE-LTFs
2420. Each of the transmitting devices may transmit a number of
HE-LTFs 2420 which corresponds to the number of spatial streams
which are being used by that transmitting device. For example, if a
transmitting device is transmitting using two spatial streams, that
device may transmit two HE-LTFs 2420. Following transmitting all of
its HE-LTFs 2420, each transmitting device then transmit an HE-SIG
2430. This HE-SIG 2430 may contain information similar to that
described above.
[0162] As illustrated, in packet 2400, each transmitting device
transmits a number of HE-LTFs 2420 which corresponds to the number
of spatial streams being used by that device. As discussed above,
in some other aspects, the number of spatial streams being used by
a device may be indicated in the HE-SIG sent by that device.
However, in packet 2400, the number of spatial streams may not be
included in the HE-SIG 2430, as this indication may arrive too late
for an AP to anticipate the number of HE-LTFs 2420 that the
transmitting device may transmit. Accordingly, other methods for
the AP to determine the number of spatial streams from a given
event may be used. For example, a downlink message from the AP,
such as the message triggering the uplink OFDMA packet 2400, may
assign a number of spatial streams to each transmitting device. An
exemplary downlink message from the AP is illustrated in FIG. 26
which includes information on how many spatial streams each
transmitting device may use. In some aspects, the number of spatial
streams used by each transmitting device may be determined in other
ways as well. For example, the number of spatial streams to each
transmitting device may be conveyed in a periodic downlink message,
such as in a beacon. In some aspects, the AP may be configured to
determine the number of spatial streams based upon the received
packet 2400. For example, the AP may be configured to determine the
number of HE-LTFs 2420 being transmitted by each transmitting
device without prior knowledge of how many spatial streams may be
transmitted such as by analyzing the incoming packet 2400 and
detecting the end of the HE-LTFs 2420 and the beginning of the
HE-SIG 2430. Other methods may also be used to enable the AP to
determine the number of spatial streams, and thus the number of
HE-LTFs 2420 being transmitted by each device in packet 2400.
Following the HE-SIG 2430 from each transmitting device, that
device may transmit the data 2440 which it wishes to transmit in
packet 2400. In some aspects, each device may transmit the same
number of HE-LTFs 2420 in packet 2400. For example, each
transmitting device may transmit a number of HE-LTFs 2420 which
corresponds to the number of spatial streams assigned to the device
which is assigned the highest number of spatial streams.
[0163] FIG. 25 is another exemplary uplink packet structure in
which the HE-SIG is transmitted after each HE-LTF. Packet 2500 may
correspond to a mixed-mode packet, in which each transmitting
device transmits a legacy preamble prior to transmitting a
high-efficiency portion of the packet. In packet 2500, each device
first transmits a legacy preamble, which includes an L-STF 2502,
and L-LTF 2504, and an L-SIG 2506. These portions of the packet
2500 may be transmitted as described above.
[0164] Following the legacy preamble, packet 2500 is similar to
packet 2400. Each of the transmitting devices may transmit an
HE-STF 2510, followed by a number of HE-LTFs 2520, followed by an
HE-SIG 2530, followed by the data 2540 which the transmitting
device wishes to transmit to the AP. Each of these portions of the
packet may be transmitted in methods similar to those disclosed
above. The number of HE-LTFs 2520 transmitted by each device may be
based, at least in part, on the number of spatial streams that each
device is transmitting on. For example, a device which is
transmitting on two spatial streams may transmit two HE-LTFs
2520.
[0165] In some aspects, each device in packet 2500 may transmit an
equal number of HE-LTFs 2520. For example, each of the transmitting
devices may transmit a number of HE-LTFs 2520 which corresponds to
the highest number of spatial streams being transmitted by any of
the transmitting devices. Accordingly, in packet 2500, each of the
transmitting devices must have knowledge of how many HE-LTFs 2520
to transmit in the packet. As before, having each of the
transmitting devices transmit the same number of HE-LTFs 2520 may
be beneficial, as this may reduce the PAPR of the packet. Such a
reduction in PAPR may result in benefits for the AP receiving the
packet 2500, as described above. If each transmitting device in
packet 2500 transmits the same number of HE-LTFs 2520, each of
these devices should be aware of how many HE-LTFs 2520 to transmit.
This may be accomplished in a number of ways. For example, the AP
may send a downlink trigger message to the transmitting devices.
This trigger message may include information such as which devices
may transmit in the uplink packet, the bandwidth assigned to each
device, and the number of spatial streams assigned to each device.
This trigger message may also indicate to the transmitting devices
how many HE-LTFs 2520 to include in the uplink packet 2500. For
example, the downlink message may indicate to the transmitting
devices how many spatial streams each device may use. An exemplary
downlink trigger message from the AP is illustrated in FIG. 26
which includes information on how many spatial streams each
transmitting device may use. Similarly, the number of spatial
streams assigned to each device may be fixed. For example, a
network may be constructed in which each device may use only two
spatial streams. Similarly, the number of spatial streams assigned
to each device may be conveyed in a message such as in a beacon
message which is periodically transmitted from the AP. Accordingly,
the transmitting devices may transmit a number of HE-LTFs 2520
which corresponds to the number of spatial streams assigned to the
device which is assigned the most spatial streams. In some aspects,
other methods may also be used to coordinate the number of HE-LTFs
2520 transmitted by each transmitting device.
[0166] An exemplary downlink message 2600 from the AP is
illustrated in FIG. 26 which includes information on how many
spatial streams each transmitting device may use. This message 2600
may include trigger message information 2605. For example, this
information 2605 may include timing information on when an uplink
message may be sent. This information 2605 may further include
information regarding whether the transmitting devices should
confirm receipt of the trigger message. Following this information
2605, the downlink message 2600 may include an identification 2610
of device 1. This identification 2610 may be, for example, a unique
number or value which is assigned to device 1, and which identifies
device 1. The downlink message 2600 may also include a number of
streams 2615 which are assigned to device 1. For example, device 1
may be assigned two spatial streams. The downlink message may also
include an identification 2620 of device 2, a number of spatial
streams 2625 for device 2, an identification 2630 of device 3, and
a number of spatial streams 2635 for device 3. In some aspects,
other numbers of devices may also be identified in a downlink
message 2600. For example, two, three, four, five, six or more
devices may be identified in the downlink message 2600. Note that
this downlink message 2600 is merely exemplary. Other information
may also be contained in a downlink trigger message, and may be
contained in a different order or number than illustrated in
downlink message 2600.
[0167] In some aspects, it may be beneficial to harmonize the LTFs
which are transmitted in an uplink OFDMA packet with those
transmitted in an UL MU-MIMO packet. For example, in an UL MU-MIMO
packet, each transmitting device may transmit messages across all
tones. Accordingly, the LTFs in an UL MU-MIMO packet may need to
contain sufficient information to allow a receiving STA, such as an
AP, to recognize the transmissions from each transmitting STA on
each tone. Such LTF formats may be used both in an UL MU-MIMO
packet, and in an UL OFDMA packet.
[0168] For example, one format that may be used for LTFs, in either
an UL MU-MIMO packet or an UL OFDMA packet, is to transmit P-matrix
based LTFs. In this approach, LTFs may be transmitted by each of
the transmitting STAs on each tone. The LTFs from each device may
be transmitted in such a way that they are orthogonal to each
other. The number of LTFs transmitted may correspond to the number
of spatial streams assigned to all devices. For example, if two
devices transmit on one stream each, two LTFs may be sent. In some
aspects, in the first LTF, the value at a given tone may be equal
to H1+H2, where H1 is the signal from the first device and H2 is
the signal from the second device. In a next LTF, the value at a
given tone may be equal to H1-H2. Accordingly, because of this
orthogonality, the receiving device may be able to identify the
transmission of each of the two transmitting devices on each tone.
Such a format for LTFs has been used, for example, in previous IEEE
802.11 formats. However, one potential problem with P matrix based
LTFs is that they may not be as effective if two or more of the
transmitting devices have a high frequency offset with respect to
one another. In that circumstance, the orthogonally of the LTFs may
be lost, and accordingly, the ability of the receiving device to
properly decode the packet may be impaired. Accordingly, in some
aspects, it may be desirable to use a different LTF format for UL
MU-MIMO and UL OFDMA packets.
[0169] Another possible different LTF format for UL MU-MIMO and UL
OFDMA packets is to use a tone-interleaved or sub-band interleaved
LTF. As before, the number of LTFs which is transmitted may
correspond to the total number of spatial streams sent by all
transmitting devices. Such LTF formats may be especially useful
when there is a big frequency offset among the various devices
transmitting the uplink packet. These LTF formats could be used in
an UL MU-MIMO packet. In order to harmonize an UL OFDMA packet with
an UL MU-MIMO packet, these LTF formats may also be used in an UL
OFDMA packet.
[0170] FIG. 27 is an illustration 2700 of a tone-interleaved LTF
which may be used in an UL OFDMA packet. For example, these LTFs
may be used in any of the previously described UL OFDMA packets.
For example, in this packet, there are four spatial streams. These
spatial streams may be numbered, for example, as spatial stream
1-4. Each spatial stream may be transmitted by a separate device,
or one device may transmit two or more of the spatial streams.
Accordingly, four spatial streams may correspond to an UL OFDMA
packet which is being transmitted by two, three, or four devices.
Because four spatial streams are present, four LTFs may be sent,
labeled LTF1 2705, LTF2 2710, LTF3 2715, and LTF4 2720. Each LTF
may include a number of tones, here numbered from 1 to 8. Any
number of tones may be included in the LTF, corresponding to the
number of tones which are included in the data portion of the UL
OFDMA packet. In this tone-interleaved LTF, during LTF1 2705, the
first stream may transmit on tones 1, 5, 9, and so on. In some
aspects, the spacing between these tones (that is, the spacing
between 1 and 5) is based on the number of spatial streams. For
example, in the illustration 2700 there are four spatial streams
and so the spacing between tones which each stream transmits on is
also four. During LTF1 2705, the second stream may transmit on
tones 2, 6, 10, and so on, while the third spatial stream may
transmit on tones 3, 7, 11 and so one, and the fourth spatial
stream may transmit on tones 4, 8, 12, and so on. In a next LTF,
LTF2 2710, each spatial stream may transmit on tones which are 1
tone higher than the previous LTF. For example, in LTF1 2705,
stream 1 transmitted on tones 1 and 5, while in LTF2 2710, stream 1
transmits on tones 2 and 5. Accordingly, after a number of LTFs
equal to the number of spatial streams, each spatial stream may
have transmitted on each tone. Using this tone-interleaved LTF,
since spatial streams do not transmit at the same frequency at the
same time, cross-stream leakage may not be an issue because of the
offset. For example, the offset may be a few kHz. In some aspects,
it may be advantageous to repeat LTF1 2725 again after the last
LTF, in order to estimate per-stream frequency offset. For example,
LTF1 2705 may be identical to LTF1 2725. However, these two LTFs
may be compared to FIG. 28 is an illustration 2800 of a sub-band
interleaved LTF which may be used in an UL OFDMA packet. For
example, these LTFs may be used in any of the previously described
UL OFDMA packets. The UL OFDMA packet may include a number of
spatial streams, and may be transmitted on a number of tones. For
example, illustration 2800 includes four spatial streams. Because
there are four spatial streams, the tones, from 1 to N.sub.SC,
where N.sub.SC is the total number of subcarriers excluding guard
tones and DC tones, are divided into four sub-bands. For example,
if there were 64 tones, tones 1-16 could be sub-band 1, tones 17-32
could be sub-band 2, tones 33-48 could be sub-band 3 and tones
49-64 could be sub-band 4. In some aspects, the number of tones in
each sub-band may be equal or may be approximately equal. In each
of the four LTFs, each of the four spatial streams may transmit on
the tones of its assigned sub-band. For example, in LTF1 2805,
sub-band 1 may be assigned to spatial stream 1, sub-band 2 may be
assigned to spatial stream 2, and so one. In the subsequent LTF2
2810, each of the sub-bands may be assigned to a different one of
the spatial streams. Accordingly, after four LTFs, each of the four
spatial streams may have transmitted once on each of the four
sub-bands.
[0171] The LTF structures illustrated in illustration 2700 and
illustration 2800 may have a number of advantages. For example,
this structure may offer better performance when there is a large
frequency offset between uplink clients. Further, these LTF
structures will allow the AP to receive transmissions in each of
the spatial streams on each of the tones. This may allow, for
example, a spatial stream to switch from certain tones to certain
other tones if such a switch was desired. Further, this may allow
the AP to determine the signal strength of a given spatial stream
of a given device on each tone. This may allow the AP, in a future
packet, to assign tones to a device based on which tones that
device has the best signal. For example, if the AP assigns tones to
various devices, the AP may observe that a certain device has a
lower signal-to-noise ratio and a stronger signal on some tones
over other tones. Accordingly, the AP may assign that device those
stronger tones in a future packet. FIG. 29 is an exemplary LTF
portion 2900 of a packet which may be transmitted in an UL OFDMA
packet. For example, as described above, in certain UL OFDMA
packets, rather than allocating tones in a SIG portion of the
packet, tones may be allocated elsewhere. For example, as described
above, certain UL OFDMA packets may allocate tones in a signaling
message from the AP to the transmitting devices, which may allocate
certain tones to certain devices. Thus, while in previous UL
packets, the SIG may include MCS, coding bits, and tone allocation
information, in some aspects, the tone allocation information need
not be included in a SIG field. Thus, it may be that a SIG field
could include only MCS and coding bits, which together comprise 6-7
bits of information, and binary convolutional coding (BCC) tail
bits, which may be six bits. Accordingly, it may be inefficient to
transmit a SIG field which includes only 6-7 bits of information,
when transmitting such a SIG field also includes 6 bits of CRC
information as overhead. Further, it is not clear whether including
such CRC information has sufficient benefits in this case at all.
Thus, it may be desired to send an LTF portion 2900 of a packet
which includes the MCS information 2910 and coding bits 2915. By
including this information in an LTF portion of the packet, the
packet may not need to include a SIG field at all.
[0172] This information may be included in the LTF portion 2900 of
the packet in a number of ways. For example, signaling mechanisms
which can use non-coherent demodulation may be used. In some
aspects, the MCS information 2910 and coding bits 2915 may be
includes in a low-strength code across some or all of the tones of
the LTF. In some aspects, the MCS information 2910 and coding bits
2915 may be transmitted in a single LTF, such as in LTF1 2825 or
another LTF. In some aspects, the MCS information 2910 and coding
bits 2915 may be split across each of the multiple LTFs. For
example, one or more bits of the MCS information 2910 and coding
bits 2915 may be includes in two or more of the LTFs. Accordingly,
in some aspects, an explicit SIG field may be needed in an UL OFDMA
packet, as this information may be contained within the LTFs of the
packet.
[0173] Typically, in an UL MU-MIMO packet, a per-user SIG field may
be included after each of the LTFs for that packet have been
transmitted. For example, this format may be similar to that of
packet 2400. However, in an UL OFDMA packet, the HE-SIG may be
included prior to the STFs or LTFs of a packet, as illustrated in
packet 2100. In some aspects, in order to harmonize an UL MU-MIMO
packet with an UL OFDMA packet, it may be desirable to transmit a
packet with a SIG field in both locations. For example, a packet
may be transmitted which includes a common SIG field, prior to the
HE-STF, and also includes a per-user SIG field after all of the
RE-LTFs.
[0174] FIG. 30 is an illustration of a packet 3000 with a common
SIG field prior to the HE-STF and per-user SIG field after all of
the HE-LTFs. In packet 3000, the packet is shown to include a
legacy preamble, include a legacy short training field 3005, a
legacy long training field 3010, and a legacy SIG field 3015.
However, this packet may also be transmitted without such a legacy
preamble. Following the legacy preamble, if such a preamble is
include, the packet 3000 includes a common SIG 3020. In some
aspects, this common SIG 3020 may include information similar to
that included in such a SIG field in previous UL OFDMA packets. For
example, the common SIG may carry the number of spatial streams
included in the OFDMA packet. For example, each transmitting device
in an UL OFDMA packet may popular a portion of the tones of the
Common SIG 3020. Following the Common SIG 3020, an HE-STF 3025 and
HE-LTFs 3030 are transmitted. These fields may be transmitted
according to the above disclosures. For example, the HE-LTFs 3030
may be based upon the LFT formats illustrated in FIGS. 27 and 28.
Any number of HE-LTFs 3030 may be transmitted. For example, the
number of HE-LTFs 303 which are transmitted may be based at least
in part, on the sum of the number of spatial streams which are a
part of the packet 3000. Following the HE-LTFs 303, a second SIG
field may be transmitted. This per-user SIG 3035 may be transmitted
by each of the devices transmitting the UL OFDMA packet. The format
of the per-user SIG field 3035 may be based upon the format of the
SIG field in a UL MU-MIMO packet. Following the per-user SIG field
3035, data 3040 may be transmitted. Accordingly, packet 3000 may
include both the Common SIG 3020, as in other UL OFDMA packets, and
a per-user SIG field 3035, as in other UL MU-MIMO packets. Because
both SIG fields are included in packet 3000, this packet format may
be reused in both UL OFDMA and UL MU-MIMO.
[0175] FIG. 31 illustrates an exemplary method 3100 of transmitting
to one or more devices in a single transmission. This method may be
done by a wireless device, such as an AP.
[0176] At block 3105, the AP transmits a first section of a
preamble according to a first format, the first section of the
preamble containing information sufficient to inform devices
compatible with the first format to defer to the transmission. For
example, the first format may be a pre-existing format, such as a
format defined by one or more of the existing IEEE 802.11
standards. In some aspects, the first format may be referred to as
a legacy format. In some aspects, the first section of the preamble
may contain information sufficient to alert devices with a second
set of capabilities and/or compatible with a second format that
another section of the preamble may be transmitted to those
devices. In some aspects, the means for transmitting the first
section may include a transmitter.
[0177] At block 3110, the AP transmits a second section of the
preamble according to a second format, the second section of the
preamble containing tone allocation information, the tone
allocation information identifying two or more wireless
communication devices. For example, the second section of the
preamble may comprise a high-efficiency preamble, and the second
format may include an IEEE 802.11 format which is newer than the
first format. In some aspects, the second section of the AP may
identify two or more wireless communication devices and may assign
each of those devices one or more sub-bands of the bandwidth of the
transmission. In some aspects, the means for transmitting the
second section may include a transmitter.
[0178] At block 3115, the AP transmits data to the two or more
wireless communication devices simultaneously, the data contained
on two or more sub-bands. In some aspects, each of the sub-bands
may be transmitted on separate and distinct non-overlapping
portions of the bandwidth of the transmission. For example, each
sub-band may correspond to a certain portion of the bandwidth of
the transmission, and each wireless communication device may be
assigned to receive data on one or more of the sub-bands.
Accordingly, the AP may transmit different data to two or more
different wireless communication devices at the same time, in
different sub-bands of the bandwidth of the transmission. In some
aspects, the means for transmitting data may include a
transmitter.
[0179] FIG. 32 illustrates an exemplary method 3200 of transmitting
to one or more first devices with a first set of capabilities and
simultaneously transmitting to one or more second devices with a
second set of capabilities. This method may be done by a wireless
device, such as an AP.
[0180] At block 3205, the AP transmits to one or more first devices
in a first portion of a bandwidth, the one or more first devices
having a first set of capabilities. In some aspects, this
transmission may occur on a primary channel and may also occur on
one or more secondary channels of a given bandwidth. In some
aspects, the devices with the first set of capabilities may include
devices which are compatible with certain IEEE 802.11
standards.
[0181] A block 3210, the AP simultaneously transmits to one or more
second devices in a second portion of the bandwidth, the one or
more second devices having a second set of capabilities wherein the
transmission comprises a preamble which includes an indication for
devices with the second set of capabilities to locate a frequency
band in the bandwidth for symbols containing a set of transmission
parameters for devices with the second set of capabilities, and
where the indication is sent so as to have no substantial impact on
a preamble decoding of devices with the first set of capabilities.
For example, the indication may be a one-bit code which is on an
imaginary axis of a portion of the preamble. This indication may be
sent with low power, such that it may not interfere with the
reception of the preamble by devices with the first set of
capabilities. In some aspects, the second set of capabilities may
be newer and more advanced than the first set of capabilities. For
example, the first set of capabilities may correspond to a "legacy"
format, while the second set of capabilities may correspond to a
"high-efficiency" format. In some aspects, the devices with the
second set of capabilities may be configured to look for the
indication in a transmission, and if the indication is found, may
be configured to locate and receive the portion of the transmission
contained in the second portion of the bandwidth. In some aspects,
the transmission in the second portion of the bandwidth may
correspond to various types of high-efficiency packets described
above.
[0182] In some aspects, the indication may be included as a one-bit
code in the preamble. In some aspects, the preamble may be
transmitted, in duplicate, across a bandwidth of the transmission.
In some aspects, the indication may be included in certain portions
of this preamble. For example, the indication may be included in
the copies of the preamble which are transmitted in portions of the
bandwidth which will contain transmissions to devices having the
second set of capabilities. In some aspects, the means for
transmitting to one or more first devices and the means for
simultaneously transmitting to one or more second devices may
include a transmitter.
[0183] FIG. 33 illustrates an exemplary method 3300 of receiving a
transmission compatible with both devices with a first set of
capabilities and devices with a second set of capabilities. This
method may be done by a wireless device, such as a STA with the
second set of capabilities.
[0184] At block 3305, the STA receives a preamble in a first
portion of a bandwidth, the preamble transmitted in a format
compatible with devices having a first set of capabilities. In some
aspects, the first portion of the bandwidth may include a primary
channel and may optionally include one or more secondary channels.
In some aspects, the first set of capabilities may include an IEEE
802.11 standard, such as IEEE 802.11a or 802.11ac. In some aspects,
the means for receiving the preamble may include a receiver.
[0185] At block 3310, the STA determines whether the preamble
contains information sufficient to inform devices having a second
set of capabilities to locate a signal field in a second portion of
the bandwidth, the second portion of the bandwidth not overlapping
with the first portion of the bandwidth. For example, as indicated
above, the preamble may contain an indication such as a one-bit
code on an imaginary axis in at least a portion of the preamble.
Accordingly, the STA may be configured to determine whether or not
this information is present in a given preamble. In some aspects,
the second portion of the bandwidth may include one or more
secondary channels. In some aspects, the means for determining
whether the preamble contains the information may include a
processor or a receiver.
[0186] At block 3315, the STA receives the signal field in the
second portion of the bandwidth. For example, the indication may
provide the STA with enough information to locate the second
portion of the bandwidth, and to be aware that a signal field will
be transmitted in the second portion of the bandwidth. Thus, the
STA may be configured to receive the signal field in this portion
of the bandwidth. In some aspects, the signal field may be all or
part of a preamble, such as a "high-efficiency" preamble which is
transmitted to devices with the second set of capabilities in the
second portion of the bandwidth. In some aspects, this may allow
devices with the second set of capabilities to receive information
from an AP or another device on portions of the bandwidth without
interrupting the reception of devices with the first set of
capabilities on the first portion of the bandwidth. Accordingly, as
discussed above, this may allow for more efficient use of the
bandwidth that is available to an AP or another device, as this may
allow for fuller use of the bandwidth more of the time. In some
aspects, the means for receiving the signal field may include a
receiver.
[0187] FIG. 34 illustrates an exemplary method 3300 of receiving a
transmission, where portions of the transmission are transmitted by
different wireless devices. The method may be done by a wireless
device, such as an AP.
[0188] At block 3405, the AP receives a first portion of the
transmission in a first section of a bandwidth, the first portion
transmitted by a first wireless device and including a first
preamble and a first data section. In some aspects, the AP may have
previously sent a message to the first wireless device, informing
the first wireless device of a time and a bandwidth that it may
transmit to the AP.
[0189] At block 3410, the AP simultaneously receives a second
portion of the transmission in a second section of the bandwidth,
the second section of the bandwidth not overlapping with the first
section of the bandwidth, the second portion transmitted by a
second wireless device, the second portion including a second
preamble and a second data section. In some aspects, the first
preamble and the second preamble may each contain training fields.
In some aspects, the number of training fields that each preamble
contains may be based on the number of spatial streams assigned to
a particular device. For example, a device that is assigned three
spatial streams may transmit one short training field, and transmit
three long-training fields. Similarly, a device assigned one
spatial stream may transmit one short training field and one long
training field. In some aspects, each device may transmit a number
of training fields based on how many spatial streams were assigned
to that particular device. In some aspects, it may be advantageous
for each device to transmit the same number of spatial streams. For
example, if each device transmits the same number of spatial
streams, this may reduce peak-to-average power ratio of the
combined transmission, which may be advantageous. In some aspects,
the transmissions from the first and second wireless devices may be
triggered by a message from the AP. This message may also indicate
to each device how many spatial streams that device may transmit
on, and may indicate the number of training fields that each device
should transmit.
[0190] FIG. 35 illustrates various components that may be utilized
in a wireless device 3502 that may be employed within the wireless
communication system 100. The wireless device 3502 is an example of
a device that may be configured to implement the various methods
described herein. For example, the wireless device 3502 may
comprise the AP 104 or one of the STAs 106 of FIG. 10. In some
aspects, the wireless device 3502 may comprise a wireless device
that is configured to receive the packets described above.
[0191] The wireless device 3502 may include a processor 3504 which
controls operation of the wireless device 3502. The processor 3504
may also be referred to as a central processing unit (CPU). Memory
3506, which may include both read-only memory (ROM) and random
access memory (RAM), provides instructions and data to the
processor 3504. A portion of the memory 3506 may also include
non-volatile random access memory (NVRAM). The processor 3504
typically performs logical and arithmetic operations based on
program instructions stored within the memory 3506. The
instructions in the memory 3506 may be executable to implement the
methods described herein. For example, the memory 3506 may contain
instructions sufficient to allow the wireless device 3502 to
receive transmissions from high-efficiency devices. For example,
the memory 3506 may contain instructions sufficient to allow the
wireless device 3502 to receive packets which include a preamble
for device with a first set of capabilities, and a second preamble
for devices with a second set of capabilities. In some aspects, the
wireless device 3502 may include a frame receiving circuit 3521,
which may contain instructions sufficient to allow the wireless
device 3502 to receive packets as described in method 3300 and/or
method 3400. This frame receiving circuit 3521 may contain
instructions sufficient to allow a device to receive a preamble in
a first portion of the bandwidth, determine if an indication is
present, and receive a signal field in a second portion of the
bandwidth, as describe in method 3300. In some aspects, the frame
receiving circuit 3521 may contain instructions sufficient to allow
a device to receive a first portion of the transmission in a first
second of a bandwidth, and to simultaneously receive a second
portion of the transmission in a second section of the bandwidth,
as described in method 3400.
[0192] The processor 3504 may comprise or be a component of a
processing system implemented with one or more processors. The one
or more processors may be implemented with any combination of
general-purpose microprocessors, microcontrollers, digital signal
processors (DSPs), field programmable gate array (FPGAs),
programmable logic devices (PLDs), controllers, state machines,
gated logic, discrete hardware components, dedicated hardware
finite state machines, or any other suitable entities that can
perform calculations or other manipulations of information.
[0193] The processing system may also include machine-readable
media for storing software. Software shall be construed broadly to
mean any type of instructions, whether referred to as software,
firmware, middleware, microcode, hardware description language, or
otherwise. Instructions may include code (e.g., in source code
format, binary code format, executable code format, or any other
suitable format of code). The instructions, when executed by the
one or more processors, cause the processing system to perform the
various functions described herein.
[0194] The wireless device 3502 may also include a housing 3508
that may include a transmitter 3510 and a receiver 3512 to allow
transmission and reception of data between the wireless device 3502
and a remote location. The transmitter 3510 and receiver 3512 may
be combined into a transceiver 3514. An antenna 3516 may be
attached to the housing 3508 and electrically coupled to the
transceiver 3514. The wireless device 3502 may also include (not
shown) multiple transmitters, multiple receivers, multiple
transceivers, and/or multiple antennas.
[0195] The wireless device 3502 may also include a signal detector
3518 that may be used in an effort to detect and quantify the level
of signals received by the transceiver 3514. The signal detector
3518 may detect such signals as total energy, energy per subcarrier
per symbol, power spectral density and other signals. The wireless
device 3502 may also include a digital signal processor (DSP) 3520
for use in processing signals. The DSP 3520 may be configured to
generate a data unit for transmission. In some aspects, the data
unit may comprise a physical layer data unit (PPDU). In some
aspects, the PPDU is referred to as a packet.
[0196] The wireless device 3502 may further comprise a user
interface 3522 in some aspects. The user interface 3522 may
comprise a keypad, a microphone, a speaker, and/or a display. The
user interface 3522 may include any element or component that
conveys information to a user of the wireless device 3502 and/or
receives input from the user.
[0197] The various components of the wireless device 3502 may be
coupled together by a bus system 3526. The bus system 3526 may
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.
Those of skill in the art will appreciate the components of the
wireless device 3502 may be coupled together or accept or provide
inputs to each other using some other mechanism.
[0198] Although a number of separate components are illustrated in
FIG. 35, one or more of the components may be combined or commonly
implemented. For example, the processor 3504 may be used to
implement not only the functionality described above with respect
to the processor 3504, but also to implement the functionality
described above with respect to the signal detector 3518 and/or the
DSP 3520. Further, each of the components illustrated in FIG. 35
may be implemented using a plurality of separate elements.
Furthermore, the processor 3504 may be used to implement any of the
components, modules, circuits, or the like described below, or each
may be implemented using a plurality of separate elements. As used
herein, the term "determining" encompasses a wide variety of
actions. For example, "determining" may include calculating,
computing, processing, deriving, investigating, looking up (e.g.,
looking up in a table, a database or another data structure),
ascertaining and the like. Also, "determining" may include
receiving (e.g., receiving information), accessing (e.g., accessing
data in a memory) and the like. Also, "determining" may include
resolving, selecting, choosing, establishing and the like. Further,
a "channel width" as used herein may encompass or may also be
referred to as a bandwidth in certain aspects.
[0199] In some implementations, a method of transmitting to two or
more wireless communication devices is disclosed. In some aspects,
the method comprises transmitting a first section of a preamble
according to a first format, the first section of the preamble
containing information informing devices compatible with the first
format to defer to the transmission. In some aspects, the method
further comprises transmitting a second section of the preamble
according to a second format, the second section of the preamble
containing tone allocation information, the tone allocation
information identifying two or more wireless communication devices.
In some aspects, the method further comprises transmitting data to
the two or more wireless communication devices simultaneously, the
data contained on two or more sub-bands. In some aspects, the first
section of the preamble includes a one-bit code on a Q-rail which
indicates a presence of the second section of the preamble. In some
aspects, the second section of the preamble comprises a signal
field using the second format, the signal field comprised of at
least three orthogonal frequency-division multiplexing symbols, and
wherein a third symbol of the three symbols is a rotated signal
which indicates a presence of the second section of the preamble.
In some aspects, the transmitting the second section of the
preamble comprises transmitting one or more training fields
according to the second format to each of the two or more wireless
communication devices, the one or more training fields each
configured to be used for accurate frequency offset estimation,
time synchronization, and channel estimation. In some aspects, the
method further comprises assigning one or more spatial streams to
each of the two or more wireless communication devices, and wherein
transmitting one or more training fields comprises transmitting one
training field according to the second format to each of the two or
more wireless communication devices, the number of training fields
based on a number of spatial streams assigned to the respective
wireless communication device. In some aspects, the method further
comprises assigning one or more spatial streams to each of the two
or more wireless communication devices, and wherein transmitting
one or more training fields comprises transmitting a number of
training fields to each of the two or more wireless communication
devices, the number of training fields based on a number of spatial
streams assigned to the wireless communication device which is
assigned a highest number of spatial streams. In some aspects, the
second section of the preamble contains information sufficient to
inform devices of a tone allocation granularity of the
transmission. In some aspects, the information sufficient to inform
devices of a tone allocation granularity of the transmission
comprises a bandwidth of the transmission, from which devices
compatible with the second format may determine the tone allocation
granularity of the transmission. In some aspects, the information
sufficient to inform devices of a tone allocation granularity of
the transmission comprises a code of at least one bit in a signal
field indicating the tone allocation granularity of the
transmission. In some aspects, the tone allocation granularity
comprises an indication of the bandwidth size of each of a number
of sub-bands. In some aspects, the second section of the preamble
further includes an indication of a number of sub-bands assigned to
each of the identified two or more wireless communication devices.
In some aspects, the second section of the preamble comprises a
signal field according to the second format, and wherein a first
symbol of the signal field is transmitted in duplicate in each of a
plurality of channels and contains information identifying an
entire bandwidth, and wherein a subsequent symbol of the signal
field is transmitted using the entire bandwidth.
[0200] In some implementations, an apparatus for wireless
communication is disclosed. In some aspects, the apparatus
comprises a transmitter configured to transmit over a bandwidth. In
some aspects, the transmitting comprises transmitting a first
section of a preamble according to a first format, the first
section of the preamble containing information informing devices
compatible with the first format to defer to the transmission. In
some aspects, the transmitting further comprises transmitting a
second section of the preamble according to a second format, the
second section of the preamble containing tone allocation
information, the tone allocation information identifying two or
more wireless communication devices. In some aspects, the
transmitting further comprises transmitting data to the two or more
wireless communication devices simultaneously, the data contained
on two or more sub-bands. In some aspects, the first section of the
preamble includes a one-bit code on a Q-rail which indicates a
presence of the second section of the preamble to devices
compatible with the second format. In some aspects, the second
section of the preamble comprises a signal field using the second
format, the signal field comprising at least three orthogonal
frequency-division multiplexing symbols, and wherein a third symbol
of the three symbols is a rotated signal which indicates the
presence of the second format signal field. In some aspects, the
transmitter is further configured to transmit the second section of
the preamble, comprising transmitting one or more training fields
according to the second format to each of the two or more wireless
communication devices, the one or more training fields each
configured to be used for accurate frequency offset estimation,
time synchronization, and channel estimation. In some aspects, the
transmitter is further configured to transmit to each of the two or
more wireless communication devices on one or more spatial streams,
and wherein transmitting one or more training fields according to
the second format comprises transmitting a training field according
to the second format to each of the two or more wireless
communication devices, the number of training fields based on a
number of spatial streams assigned to the respective wireless
communication device. In some aspects, the transmitter is further
configured to transmit to each of the two or more wireless
communication devices on one or more spatial streams, and wherein
transmitting one or more training fields according to the second
format comprises transmitting a number of training fields to each
of the two or more wireless communication devices, the number of
training fields based on a number of spatial streams assigned to
the wireless communication device which is assigned a highest
number of spatial streams. In some aspects, the second section of
the preamble contains information sufficient to inform devices of a
tone allocation granularity of the transmission. In some aspects,
the second section of the preamble comprises a second format signal
field, and wherein a first symbol of the second format signal field
is transmitted in duplicate in each of a plurality of channels and
contains information identifying an entire bandwidth, and wherein a
subsequent symbol of the second format signal field is transmitted
using the entire bandwidth.
[0201] As used herein, 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, b, c, a-b, a-c, b-c, and a-b-c.
[0202] The various operations of methods described above may be
performed by any suitable means capable of performing the
operations, such as various hardware and/or software component(s),
circuits, and/or module(s). Generally, any operations illustrated
in the Figures may be performed by corresponding functional means
capable of performing the operations.
[0203] The various illustrative logical blocks, modules and
circuits described in connection with the present disclosure may be
implemented or performed with a general purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array signal (FPGA) or
other programmable logic device (PLD), discrete gate or transistor
logic, discrete hardware components or any combination thereof
designed to perform the functions described herein. A general
purpose processor may be a microprocessor, but in the alternative,
the processor may be any commercially available processor,
controller, microcontroller or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0204] In one or more aspects, the functions described may be
implemented in hardware, software, firmware, or any combination
thereof. If implemented in software, the functions may be stored on
or transmitted over as one or more instructions or code on a
computer-readable medium. Computer-readable media includes both
computer storage media and communication media including any medium
that facilitates transfer of a computer program from one place to
another. A storage media may be any available media that can be
accessed by a computer. By way of example, and not limitation, such
computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or
other optical disk storage, magnetic disk storage or other magnetic
storage devices, or any other medium that can be used to carry or
store desired program code in the form of instructions or data
structures and that can be accessed by a computer. Also, any
connection is properly termed a computer-readable medium. For
example, if the software is transmitted from a website, server, or
other remote source using a coaxial cable, fiber optic cable,
twisted pair, digital subscriber line (DSL), or wireless
technologies such as infrared, radio, and microwave, then the
coaxial cable, fiber optic cable, twisted pair, DSL, or wireless
technologies such as infrared, radio, and microwave are included in
the definition of medium. Disk and disc, as used herein, includes
compact disc (CD), laser disc, optical disc, digital versatile disc
(DVD), floppy disk and Blu-ray disc where disks usually reproduce
data magnetically, while discs reproduce data optically with
lasers. Thus, in some aspects computer readable medium may comprise
non-transitory computer readable medium (e.g., tangible media). In
addition, in some aspects computer readable medium may comprise
transitory computer readable medium (e.g., a signal). Combinations
of the above should also be included within the scope of
computer-readable media.
[0205] The methods disclosed herein comprise one or more steps or
actions for achieving the described method. The method steps and/or
actions may be interchanged with one another without departing from
the scope of the claims. In other words, unless a specific order of
steps or actions is specified, the order and/or use of specific
steps and/or actions may be modified without departing from the
scope of the claims.
[0206] The functions described may be implemented in hardware,
software, firmware or any combination thereof. If implemented in
software, the functions may be stored as one or more instructions
on a computer-readable medium. A storage media may be any available
media that can be accessed by a computer. By way of example, and
not limitation, such computer-readable media can comprise RAM, ROM,
EEPROM, CD-ROM or other optical disk storage, magnetic disk storage
or other magnetic storage devices, or any other medium that can be
used to carry or store desired program code in the form of
instructions or data structures and that can be accessed by a
computer. Disk and disc, as used herein, include compact disc (CD),
laser disc, optical disc, digital versatile disc (DVD), floppy
disk, and Blu-ray.RTM. disc where disks usually reproduce data
magnetically, while discs reproduce data optically with lasers.
[0207] 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 certain
aspects, the computer program product may include packaging
material.
[0208] Software or instructions may also be transmitted over a
transmission medium. For example, if the software is transmitted
from a website, server, or other remote source using a coaxial
cable, fiber optic cable, twisted pair, digital subscriber line
(DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of transmission
medium.
[0209] Further, it should be appreciated that modules and/or other
appropriate means for performing the methods and techniques
described herein can be downloaded and/or otherwise obtained by a
user terminal and/or base station as applicable. For example, such
a device can be coupled to a server to facilitate the transfer of
means for performing the methods described herein. Alternatively,
various methods described herein can be provided via storage means
(e.g., RAM, ROM, a physical storage medium such as a compact disc
(CD) or floppy disk, etc.), such that a user terminal and/or base
station can obtain the various methods upon coupling or providing
the storage means to the device. Moreover, any other suitable
technique for providing the methods and techniques described herein
to a device can be utilized.
[0210] It is to be understood that the claims are not limited to
the precise configuration and components illustrated above. Various
modifications, changes and variations may be made in the
arrangement, operation and details of the methods and apparatus
described above without departing from the scope of the claims.
[0211] While the foregoing is directed to aspects of the present
disclosure, other and further aspects of the disclosure may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
* * * * *