802.11 VERY HIGH THROUGHPUT PREAMBLE SIGNALING FIELD
WITH LEGACY COMPATIBILITY
BACKGROUND
This disclosure relates generally to the field of wireless network communication,
and in particular to a method and apparatus configured to provide a 802. 11 very high
throughput (VHT) preamble signaling field with legacy compatibility.
Wireless communication systems may operate in accordance with one or more
protocol standards including, but not limited to, IEEE 802.1 1, Bluetooth, advanced mobile
phone services (AMPS), digital AMPS, global system for mobile communications (GSM),
code division multiple access (CDMA), local multi-point distribution systems(LMDS),
multi-channel-multi-point distribution systems (MMDS), and the like. The applicable
protocol for wireless communications standard may vary. As the IEEE 802. 11
specification has evolved from IEEE 802.1 1 to IEEE 802.1 lb (standard 1lb) to
IEEE802.1 l a (standard 11a) and to IEEE 802.1 l g (standard 1lg), wireless communication
devices that are compliant with standard 1lb may exist in the same wireless local area
network (WLAN) as standard 1l g compliant wireless communication devices.
When legacy devices such as those compliant with an earlier version of a standard
reside in the same WLAN as devices compliant with later versions of the standard,
mechanisms or processes may be employed for the legacy devices to know when the
newer version devices are utilizing the wireless channel to avoid interference or a
collision. A legacy system may be an existing system that is in place and available for use
in wireless local area networks. The issue of legacy systems may be important because
these systems may remain in place after new standards, methods or networks for future
wire local area networks are implemented.
The different protocols or standards may operate within different frequency ranges,
such as 5 to 6 gigahertz (GHz) or, alternatively, 2.4 GHz. For example, standard 11a may
operate within the higher frequency range. An aspect of standard 1l a is that portions of
the spectrum, between 5 to 6 GHz, are allocated to a channel for wireless communications.
The channel may be 20 megahertz (MHz) wide within the frequency band. Standard 11a
also may use orthogonal frequency division multiplexing (OFDM). OFDM may be
implemented over subcarriers that represent lines, or values, within the frequency domain
of the 20 MHz channels. A signal may be transmitted over different subcarriers within
the channel. The subcarriers may be orthogonal to each other so that information or data
is extracted off each subcarrier about the signal.
Backward compatibility with legacy devices may be enabled at the physical (PHY)
layer. At the PHY layer, backward compatibility is achieved by re-using the PHY
preamble from a previous standard. Legacy devices may decode the preamble portion of
all signals, which provides sufficient information for determining that the wireless channel
is in use for a specific period of time, to avoid interference and collisions even though the
legacy devices cannot fully demodulate or decode the transmitted frame(s).
As new standards or protocols are implemented, backward compatibility of
receiving and transmitting signals may become more of a concern. New signaling formats
may desire more robustness than legacy formats. Further, frames exchanged within a
wireless system may include immediate acknowledgement capabilities, bursting
information and exchanging more bits of information than frames used by legacy devices.
It is desired to provide a very high throughput preamble signaling field that is compatible
with legacy STAs.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows an example diagram of a WLAN which includes wireless
communication stations such as an access point (AP) and n STAs in accordance with
various aspects of the present disclosure.
Figure 2 shows an example protocol architecture for both the access point and the
STAs in Figure 1.
Figure 3a shows a conventional 802.1 l a frame format.
Figure 3b shows a conventional 802,1 In HT MF frame format.
Figure 3c shows a 802.1 1 TGac VHT MF frame format according to an aspect of
the present disclosure.
Figure 3d shows a conventional 802.1 In HT GF frame format.
Figure 3e show a 802.1 1 TGac VHT GF frame format according to an aspect of
the present disclosure.
Figure 4a, 4b and 4c shows a PLCP receive procedure according to an aspect of the
present disclosure.
DETAILED DESCRIPTION
In the description that follows, like components have been given the same
reference numerals, regardless of whether they are shown in different embodiments. To
illustrate an embodiment(s) of the present disclosure in a clear and concise manner, the
drawings may not necessarily be to scale and certain features may be shown in somewhat
schematic form. Features that are described and/or illustrated with respect to one
embodiment may be used in the same way or in a similar way in one or more other
embodiments and/or in combination with or instead of the features of the other
embodiments.
DEFINITIONS
Access Point (AP): Any entity that has a station (STA) functionality and provides
access to the distribution services, via the wireless medium (WM) for associated STAs.
Greenfield format (GF): A frame format that is more efficient than mixed format
but lacks features that would make it compatible with legacy devices.
High Throughput (HT): A station (STA) that conforms to the IEEE 802.1 In
standard.
Media Access Control (MAC): A Media Access Control (MAC) is a data
communication protocol sub-layer, also known as the Medium Access Control, is a
sublayer of the Data Link Layer specified in the seven-layer OSI model (layer 2).
Mixed format (MF): A frame format that is compatible with legacy devices, i.e., is
useable in mixed environments where legacy devices are present.
Station (STA): Any device that contains an IEEE 802.1 1-conformant medium
access control (MAC) and physical layer (PHY) interface to the wireless medium (WM).
Very High Throughput Station (VHT STA): A station (STA) that conforms to the
expected IEEE 802.1 lac standard.
Very High Throughput Mixed Format (VHT MF): A mixed format frame that is
compatible with both HT STAs and legacy STAs.
Very High Throughput Greenfield Format (VHT GF): A Greenfield format that is
not necessarily compatible with either HT STAs or legacy STAs.
Wireless medium (WM): The medium used to implement the transfer of protocol
data units (PDUs) between peer physical layer (PHY) entities of a wireless local area
network (LAN).
DESCRIPTION
In accordance with various embodiments of this disclosure, a method is disclosed
that comprises creating a VHT frame that includes information relating to a modulation
and a coding scheme with which a data portion of the VHT frame is modulated and
encoded; and transmitting the VHT frame to one or more STAs. Moreover, an apparatus
is disclosed that is arranged to perform the method, the apparatus including a controller
that is configured to create the VHT frame and a transmitter that is configured to transmit
the VHT frame to the one or more STAs. The apparatus can be configured to operate in a
wireless environment including legacy STAs, HT STAs and TGac STAs.
In accordance with various embodiments of this disclosure, the VHT frame can be
a mixed-format frame (MF) or a Greenfield format (GF) frame. The transmitted VHT
frame can be a MF frame and includes a legacy compatible portion, wherein the legacy
compatible portion includes information relating to a length of time for which a legacy
STA or a HT STA will defer transmission on detecting the frame. The transmitted VHT
MF frame can be configured to be detected as a VHT MF frame by a VHT STA and to be
detected as a legacy frame by legacy STAs or HT STAs. The transmitted VHT MF frame
can includes a VHT-SIG field that appears in the same place as the HT-SIG field of a HT
MF frame, but for which a constellation rotation that would be applied to the HT-SIG field
of an HT MF frame is not applied to the VHT-SIG field of the VHT frame. The
transmitted VHT frame can be received at an HT STA as a legacy frame because the
constellation rotation on the portion of the frame where the HT-SIG field would appear is
not present, and wherein, as a result, the HT STA defers transmission based on a frame
length indicated in the legacy compatible portion of the frame. In addition, the cyclic
redundancy check (CRC) of the VHT-SIG field can be configured to appear invalid to HT
STAs. The transmitted VHT MF frame would be detected by an HT STA as a legacy
frame because of the invalid CRC and, as a result, the HT STA will defer transmission
based on the frame length indicated in the legacy compatible portion of the frame.
In accordance with various embodiments of this disclosure, an apparatus is
disclosed that comprises a receiver configured to receive a VHT MF frame which is
arranged to be compatible with HT STAs and legacy STAs and include information
relating to a modulation and an encoding scheme with which the data portion of the VHT
MF frame is modulated and encoded; and a controller configured to process the received
VHT MF frame. The VHT frame can be detected as not being an HT frame by virtue of
the constellation rotation not being present on a VHT-SIG field of the received frame.
The received frame can be detected as a VHT MF frame and not a legacy frame by
detecting a valid CRC on a VHT-SIG field of the received frame.
In accordance with various embodiments of this disclosure, a method is disclosed
that comprises receiving a VHT frame at a VHT STA; and determining if the received
VHT frame is a mixed format frame or a Greenfield frame.
The method can include detecting if the received VHT frame includes a HT-GFSTF
field; and demodulating and checking a CRC validity of a HT-SIG field if the
received VHT frame included the HT-GF-STF field.
In accordance with various embodiments of this disclosure, a method is disclosed
that comprises receiving a wireless frame at a VHT STA; and determining whether
received wireless frame is a VHT frame, an HT frame or a legacy frame. Moreover, the
method can include detecting if the received wireless frame includes a HT-GF-STF field;
demodulating and checking a CRC validity of a VHT-SIG field if the received wireless
frame included the HT-GF-STF field; and processing the received wireless frame as a
VHT GF frame if the CRC is valid. Furthermore, the method can include detecting if the
received wireless frame includes a L-SIG field; demodulating and checking a parity of the
L-SIG field if the received wireless frame included the L-SIG field; and detecting a HTSIG
field by detecting a constellation rotation of the HT-SIG field; demodulating and
checking a CRC validity of the HT-SIG; and processing the received wireless frame as a
802.1 In HT MF frame if the CRC is valid. Further, the method can include detecting if
the received wireless frame includes a VHT-SIG field by demodulating and checking the
CRC validity of a VHT-SIG field; processing the received wireless frame as a TGac
VHT MF frame if the CRC is valid; and processing the received wireless frame as a
legacy frame if the CRC is invalid.
These and other features and characteristics, as well as the methods of operation
and functions of the related elements of structure and the combination of parts and
economies of manufacture, will become more apparent upon consideration of the
following description and the appended claims with reference to the accompanying
drawings, all of which form a part of this specification, wherein like reference numerals
designate corresponding parts in the various Figures. It is to be expressly understood,
however, that the drawings are for the purpose of illustration and description only and are
not intended as a definition of the limits of claims. As used in the specification and in the
claims, the singular form of "a", "an", and "the" include plural referents unless the context
clearly dictates otherwise.
In many wireless communication systems, a frame structure is used for data
transmission between a transmitter and a receiver. For example, the IEEE 802. 11 standard
uses frame aggregation in a Media Access Control (MAC) layer and a physical (PHY)
layer. In a typical wireless station such as a transmitter, a MAC layer inputs a MAC
Service Data Unit (MSDU) from upper layers and attaches a MAC header thereto, in order
to construct a MAC Protocol Data Unit (MPDU). The MAC header includes information
such as a source address (SA) and a destination address (DA). The MPDU is a part of a
PHY Service Data Unit (PSDU) and is transferred to a PHY layer in the transmitter to
attach a PHY header thereto to construct a PHY Protocol Data Unit (PPDU) for
transmission to another wireless station such as a receiver. The PHY header includes
parameters for determining a transmission scheme including a coding/modulation scheme.
Figure 1 shows an example diagram of an example WLAN system 300 which
includes communication stations such as an AP 102 and n STAs 104 (STA1, . . . , STAn),
according to an embodiment of the present invention. The STAs 104 can include TGac
STAs, HT STAs and legacy STAs. The AP 102 provides central coordination.
A legacy frame and a legacy STA are a frame or a STA respectively that conform
to 802. 1la/g standard. An HT frame or HT STA are a frame or a STA respectively that
conforms to the 802. 1In standard. An HT STA is backwardly compatible with a legacy
STA. A VHT frame and a VHT STA, in accordance to various aspects of the present
disclosure, are a frame or a STA respectively that conforms to 802. 11 standard being
developed by the TGac task group within 802. 11 working group. The VHT STA would be
backward compatible with an HT STA and a legacy STA.
The IEEE 802. 1In builds on previous 802. 11 standards by adding multiple-input
multiple-output (MIMO) and 40 MHz channels to the PHY (physical layer), and frame
aggregation to the MAC layer. MIMO is a technology which uses multiple antennas to
coherently resolve more information than possible using a single antenna.
Figure 2 shows an example protocol architecture for each STA 104. Each STA
104 implements a WLAN PHY layer 210 and a MAC layer 212. The PHY layer 210
includes two sub-layers: a physical layer convergence procedure (PLCP) sub-layer and a
physical medium dependent (PMD) sub-layer. The MAC layer 212 constructs MAC
packets from frames of data, and provides them to the PHY layer 210 for transmission
over a shared wireless channel. Similarly, the AP 102 also includes a MAC layer and a
PHY layer, as described.
In general, TGac devices are devices that can operate in 5GHz frequency band.
TGac devices can utilize a mode of operation that supports a throughput of at least 500
Mbps at the top of the MAC data service access point (MAC SAP) utilizing no more than
80 MHz of channel bandwidth in 5GHz band or a mode of operation that supports an
aggregate throughput of at least 1 Gbps at the top of the MAC data service access points
(MAC SAPs) utilizing no more than 80 MHz of channel bandwidth in 5GHz band.
Typically, there is no restriction on the number of transmit or receive antennas being used
on any devices. TGac devices are backward compatible with IEEE 802.1 l a devices
operating in the 5 GHz frequency band and are backward compatible with IEEE 802.1 In
devices operating in the 5 GHz frequency band. TGac devices can be configured provide
mechanisms to enable coexistence and spectrum sharing with IEEE802.1 1a/n devices
operating in the same frequency band.
Figures 3a, 3b and 3d shows conventional 802.1 la, 802.1 In HT MF, and 802.1 In
HT GF frames, respectively. Figures 3c and 3e shows 802.1 1 TGac VHT MF and 802.1 1
TGac HT GF frames, respectively, in accordance with various aspects of the present
disclosure. As shown in Figure 3a, the conventional 802.1 l a frame consists of a preamble
followed by a data payload. The preamble includes the legacy short training field (LSTF),
legacy long training field (L-LTF) and legacy signal field (L-SIG). The data
payload includes the service field, user data (PSDU), pad bits and tail bits.
In IEEE 802. 1In WLAN communications, if legacy STAs and high-throughput
stations (HT-STAs) coexist in the same WLAN, then frames of the HT-stations use a
mixed mode PHY layer header which includes both a legacy PHY header part and a highthroughput
(HT) PHY header part followed by the data payload. Legacy format frames
can be successfully received by both the L-stations and the HT-stations. However, the
legacy STAs cannot receive HT frames successfully because the L-stations cannot
understand the HT PHY header part of the HT frames. As shown in Figure 3b, the
conventional 802.1 In HT MF frame includes legacy format frame in which a legacy PHY
header part includes legacy training fields (L-TFs) and a legacy signal field (L-SIG).
Further, an HT PHY header part includes an HT signal field (HT-SIG), HT short training
fields (HT-STF) and HT long training fields (HT-LTF1). The one or more data fields can
include service field, user data (PSDU), pad bits and tail bits.
In the Greenfield (GF) mode, high throughput (HT) packets are transmitted
without a legacy-compatible part. As shown in Figure 3d, the conventional 802.1 In
HT GF frame includes a high-throughput (HT) PHY header part including signaling
preamble fields followed by the data payload. The HT PHY header includes HT short
training field (HT-GF-STF), HT long training field (HT-LTF1) and HT signaling field
(HT-SIG). The data payload includes the service field, user data (PSDU), pad bits and tail
bits.
Figures 3c and 3e shows 802.1 1 TGac VHT MF and 802.1 1 TGac VHT GF
frames, respectively, in accordance with various aspects of the present disclosure. As
shown in Figure 3c, the 802. 11 TGac VHT MF frame includes a legacy PHY header part
includes legacy short training field (L-STF), legacy long training field (L-LTF) and legacy
signaling field (L-SIG) as shown and described in Figures 3a and 3b. A very high
throughput (VHT) signaling field (VHT-SIG) follows the L-SIG field and appears in the
same position as the HT-SIG field as shown and described in Figure 3b followed by the
data payload.
As shown in Figure 3e, the 802.1 1 TGac VHT GF frame includes a HT short
training field (HT-GF-STF) and HT long training field (HT-LTF1). A very high
throughput (VHT) signaling field (VHT-SIG) follows the HT-LTF1 field and appears in
the same position as the HT-SIG field as shown and described in Figure 3d followed by
the data payload which can include a service field, user data (PSDU), pad bits and tail bits.
Turning again to Figure 1, one of the STAs can be configured to create a VHT
frame as shown in Figures 3c or Figure 3e. The STAs can be equipped with one or more
antennas that are arranged to transmit the VHT frame to one or more other STAs. The
transmitting STA can be configured to operate in a wireless environment including legacy
STAs, HT STAs, and TGac STAs.
As discussed above, the VHT frame can be a mixed- format frame as shown in
Figure 3c or a Greenfield format frame as shown in Figure 3e. If the transmitted VHT
frame is the mixed-format frame, then it can include a legacy compatible portion, wherein
the legacy compatible portion includes information relating to a length of time for which a
legacy STA and a HT STA will defer transmission. The transmitted VHT frame can be
configured to be detected as a VHT frame by a VHT STA to be detected as a legacy frame
by legacy STAs or HT STAs. The transmitted VHT frame can includes a VHT-SIG field
that appears in the same place as the HT-SIG field of a HT frame, but for which a
constellation rotation that would be applied to the HT-SIG field of an HT frame is not
applied to the VHT-SIG field of the VHT frame.
The transmitted VHT frame can be received at an HT STA as a legacy frame
because the constellation rotation on the portion of the frame where the HT-SIG field
would appear is not present, and wherein, as a result, the HT STA defers transmission
based on a frame length indicated in the legacy compatible portion of the frame. In
addition, the cyclic redundancy check (CRC) of the VHT-SIG field can be configured to
appear invalid to the HT STAs. The transmitted VHT frame would be received at an HT
STA as a legacy frame because of the lack of constellation rotation and invalid CRC, and
wherein, as a result, the HT STA will defer transmission based on a frame length indicated
in the legacy compatible portion of the frame.
In some aspects, the VHT-SIG field can have the constellation rotation defined for
the VHT-SIG field, but not to be performed for TGac PHY formats. The VHT-SIG can be
modulated using the same binary phase shift keying (BPSK) rate ½ MCS (modulation and
coding scheme) used on the legacy SIG symbol and the VHT-SIG CRC definition can be
changed from that used for 802. 1In frames so that the CRC will appear invalid to an
802. 1In device. The VHT SIG CRC definition can be changed through one or more of the
following techniques: use a different polynomial, use a different initialization value,
perform a simple transform (such as inversion), include additional bits in the CRC
calculation (e.g., from the L-SIG field), use a different length CRC. This will allow that
an 802.1 In STA will treat the VHT frame as a legacy 802.1 l a frame and defer
transmission based on the frame length indicated in the legacy SIG field.
Figured 4a, 4b and 4c show a PLCP receive procedure for a VHT STA in
accordance with various aspects of the present disclosure. A frame is received at 405. At
410, a determination is made as to whether the received frame is a Greenfield format
frame by checking to see if an HT-GF-STF is received. If the result of the determination
at 410 is a yes, then the HT-SIG/VHT-SIG field is demodulated and the CRC validity
checked at 415. If the CRC is determined to be valid for an HT-SIG field at 420, then the
frame is determined to be an HT GF frame and treated as such at 425. If the CRC is
determined to be valid for an VHT-SIG field at 430, then the frame is determined to be an
TGac VHT GF frame and treated as such at 435. Otherwise, the received frame is treated
as an invalid frame at 440.
If the result of the determination at 410 is no, then the frame is detected for a LSIG
field at 445. The L-SIG field is demodulated and the parity of the L-SIG field is
validated at 450. The presence of a valid L-SIG field alone does not indicate that the
frame is a legacy 802.1 l a frame. At 455, a determination is made as to whether a HT-SIG
field is detected. If the constellation rotation is detected at 460, then the frame format is
treated as a 802. 1In HT MF frame 465. The HT-SIG field is then demodulated and
checked for validity of the CRC on the HT-SIG field.
If the constellation rotation is not detected at 460, then a VHT-SIG field is detected
at 470 by demodulating non-rotated BPSK constellation and validity CRC at 475. If the
CRC is determined to be valid at 480, then the frame format is determined from the
content of the VHT-SIG field at 485. If the CRC is determined not be valid at 480, then
the frame is treated as a legacy frame format at 490.
In some aspects, for a VHT format frame, a legacy 802. 11a device will fail the
Green field 802.1 In frame check (CRC). Moreover, a legacy 802.1 l a device will look for
and defer transmission based on the content of the L-SIG field. A legacy 802.1 In device
will look for an HT-SIG field. In some aspects, the legacy devices can look for the
constellation rotation only. In some aspects, the legacy devices can look for the
constellation rotation and valid CRC, and in some aspects, the legacy devices can just look
for a valid CRC. In these instances, since neither the constellation rotation nor the valid
CRC are present, these legacy devices will defer transmission based on the L-SIG content.
In some aspects, for the VHT-SIG CRC, there are various options that will ensure
that the CRC is determined to be invalid by a legacy 802.1 In device. The CRC may use a
different polynomial to the 802. 1In HT-SIG CRC. The CRC may use the same
polynomial, but a different initialization value to that used in the 802. 1In HT-SIG CRC.
The CRC may use the same polynomial and initialization value and perform a simple
transform (such as inversion) before insertion in the VHT-SIG. A simple transformation
(such as inversion) may be performed on other bits in the VHT-SIG after computation of
the CRC. The CRC may use the same polynomial and initialization value but cover
additional bits, such as the L-SIG field plus VHT-SIG field. The CRC may be a new CRC
of different length than the 802.1 In HT-SIG CRC with any polynomial.
Although the above disclosure discusses what is currently considered to be a
variety of useful embodiments, it is to be understood that such detail is solely for that
purpose, and that the appended claims are not limited to the disclosed embodiments, but,
on the contrary, are intended to cover modifications and equivalent arrangements that are
within the spirit and scope of the appended claims.

CLAIMS
What is being claimed is:
1. An apparatus comprising:
a controller configured to create a VHT frame that is arranged to include
information relating to a modulation and a coding scheme with which a data portion of the
VHT frame is modulated and encoded; and
a transmitter configured to transmit the VHT frame to one or more STAs.
2. The apparatus according to claim 1, wherein the VHT frame is a mixedformat
frame or a Greenfield frame.
3. The apparatus according to claim 1, wherein the apparatus is configured to
operate in a wireless environment including legacy STAs, HT STAs, and TGac STAs.
4. The apparatus according to claim 2, wherein the transmitted VHT frame is
a mixed-format frame and includes a legacy compatible portion.
5. The apparatus according to claim 4, wherein the legacy compatible portion
includes information relating to a length of time for which a legacy STA and a HT STA
will defer transmission.
6. The apparatus according to claim 4, wherein the transmitted VHT frame is
configured to be detected as a VHT frame by a VHT STA.
7. The apparatus according to claim 4, wherein the transmitted VHT frame is
configured to be detected as a legacy frame by legacy STAs or HT STAs.
8. The apparatus according to claim 6, wherein the transmitted VHT frame
includes a VHT-SIG field that appears in the same place as the HT-SIG field of a HT
frame, but for which a constellation rotation that would be applied to the HT-SIG field of
an HT frame is not applied to the VHT-SIG field of the VHT frame.
9. The apparatus according to claim 8, wherein the transmitted VHT frame is
received at an HT STA as a legacy frame because the constellation rotation on the portion
of the frame where the HT-SIG field would appear is not present, and wherein, as a result,
the HT STA defers transmission based on a frame length indicated in the legacy
compatible portion of the frame.
10. The apparatus according to claim 5, wherein a cyclic redundancy check
(CRC) of the VHT-SIG field is configured to appear invalid to the HT STAs.
11. The apparatus according to claim 6, wherein the transmitted VHT frame is
received at an HT STA as a legacy frame because of the invalid CRC on the expected HTSIG
field, and wherein, as a result, the HT STA will defer transmission based on a frame
length indicated in the legacy compatible portion of the frame.
12. An apparatus comprising
a VHT STA including a receiver configured to receive a wireless frame;
and
a controller configured to determine if the received wireless frame is a
mixed format frame or a Greenfield format frame by detecting if the received wireless
frame includes a HT-GF-STF field and process the received wireless frame as either a
mixed format frame or a Greenfield format frame based on the detected HT-GF-STF field.
13. The apparatus according to claim 12, wherein the controller is configured
to demodulate and check a CRC validity of a VHT-SIG field if the received wireless frame
included the HT-GF-STF field and processes the received wireless frame as a VHT
Greenfield format frame if the CRC is determined to be valid.
14. The apparatus according to claim 12, wherein the controller is configured
to detect if the received wireless frame includes a L-SIG field, demodulate and check a
parity of the L-SIG field if the received wireless frame included the L-SIG field, detect a
HT-SIG field, detect a constellation rotation of the HT-SIG; demodulate and check a CRC
validity of the HT-SIG, and process the received wireless frame as a 802.1 In HT MF
format frame if the CRC is valid.
15. The apparatus according to claim 14, wherein the controller is configured
to detect if the received wireless frame includes a VHT-SIG field, demodulate and check a
CRC validity of a VHT-SIG field if the received wireless frame included the VHT-SIG
field, process the received wireless frame as a TGac VHT MF frame if the CRC is valid,
and process the received wireless frame as a legacy frame if the CRC is invalid.
16. A method comprising:
receiving a wireless frame at a VHT STA;
determining if the received wireless frame is a mixed format frame or a
Greenfield format frame by detecting if the received wireless frame includes a HT-GFSTF
field; and
processing the received wireless frame as either a mixed format frame or a
Greenfield format frame based on the detected HT-GF-STF field.
17. The method according to claim 16, further comprising:
demodulating and checking a CRC validity of a VHT-SIG field if the
received wireless frame included the HT-GF-STF field; and
processing the received wireless frame as a VHT Greenfield format frame
if the CRC is determined to be valid.
18. The method according to claim 17, further comprising:
detecting if the received wireless frame includes a L-SIG field;
demodulating and checking a parity of the L-SIG field if the received
wireless frame included the L-SIG field; and
detecting a HT-SIG field;
detecting a constellation rotation of the HT-SIG;
demodulating and checking a CRC validity of the HT-SIG; and
processing the received wireless frame as a 802.1 In HT MF format frame
if the CRC is valid.
19. The method according to claim 18, further comprising:
detecting if the received wireless frame includes a VHT-SIG field;
demodulating and checking a CRC validity of a VHT-SIG field if the
received wireless frame included the VHT-SIG field;
processing the received wireless frame as a TGac VHT MF frame if the
CRC is valid; and
processing the received wireless frame as a legacy frame if the CRC is
invalid.