(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0233709 A1
`(43) Pub. Date:
`Oct. 20, 2005
`Gardner et al.
`
`US 2005O233709A1
`
`(54)
`
`(75)
`
`(73)
`(21)
`(22)
`
`(60)
`
`MODIFIED PREAMBLE STRUCTURE FOR
`IEEE 802.11A EXTENSIONS TO ALLOW FOR
`COEXISTENCE AND INTEROPERABILITY
`BETWEEN 802.11A DEVICES AND HIGHER
`DATA RATE, MIMO OR OTHERWISE
`EXTENDED DEVICES
`
`Inventors: James Gardner, San Ramon, CA (US);
`Vincent K. Jones IV, Redwood City,
`CA (US); D. J. Richard van Nee, De
`Meern (NL)
`Correspondence Address:
`TOWNSEND AND TOWNSEND AND CREW,
`LLP
`TWO EMBARCADERO CENTER
`EIGHTH FLOOR
`SAN FRANCISCO, CA 94111-3834 (US)
`Assignee: Airgo Networks, Inc., Palo Alto, CA
`Appl. No.:
`10/820,440
`Filed:
`Apr. 5, 2004
`Related U.S. Application Data
`Provisional application No. 60/461,999, filed on Apr.
`10, 2003.
`
`Publication Classification
`
`(51) Int. Cl." .............................. H04B 1/02; H03C 7/02;
`H04B 7/02; H04L 1/02; H01L 21/336
`(52) U.S. Cl. ............................................ 455/101; 375/267
`
`(57)
`
`ABSTRACT
`
`A modified preamble is used by extended devices that
`operate at higher rates, MIMO or other extensions relative to
`strict 802.11a-compliant devices. The extended devices
`might use multiple antenna techniques (MIMO), where
`multiple data Streams are multiplexed spatially and/or multi
`channel techniques, where an extended transmitter transmits
`using more than one 802.11a channel at a time. Such
`extensions to IEEE 802.11a can exist in extended devices.
`The modified preamble is usable for Signaling, to legacy
`devices as well as extended devices, to indicate capabilities
`and to cause legacy devices or extended devices to defer to
`other devices Such that the common communication channel
`is not Subject to unnecessary interference. The modified
`preamble. is also usable for obtaining MIMO channel esti
`mates and/or multi-channel estimates. The modified pre
`amble preferably includes properties that facilitate detection
`of conventional and/or extended modes (“mode detection”)
`and provides Some level of coexistence with legacy IEEE
`802.11a devices.
`
`Receive Signal
`
`Take 64-point FFT of
`Received Long Training
`Symbol Samples
`
`Multiply By Known Pilot
`Values
`
`Take 64-point IFFT of
`Result
`
`
`
`isolate the Impulse
`Responses for Each
`Mimo Transmitter
`
`
`
`
`
`
`
`
`
`
`
`S2
`
`S3
`
`S4
`
`Derive Channel
`Estimates
`
`S6
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 1 of 14
`
`

`

`Patent Application Publication Oct. 20, 2005 Sheet 1 of 5
`
`US 2005/0233709 A1
`
`0.8 (s
`(-)
`
`
`
`4 LS
`3.2 is
`1.6 us 3.2 us
`(--) (H------H)
`Sional Field
`
`FIG. 1 (PRIOR ART)
`
`L1 = ( 0
`
`O
`
`-1 -1
`1
`-1 - 1
`1
`O
`O
`O
`l
`l
`
`-
`O
`
`-1
`1
`1 -1
`O
`-1 -
`
`1
`- 1
`1
`1.
`1.
`1.
`1 -1 - 1
`l
`-1
`
`-1
`1.
`1.
`1
`
`-1 -1
`O
`O
`-1
`1.
`
`- 1
`
`-1 -1
`O
`O
`1 - 1
`1.
`1.
`
`O
`1.
`1 }
`
`FIG. 2 (PRIOR ART)
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 2 of 14
`
`

`

`Patent Application Publication Oct. 20, 2005 Sheet 2 of 5
`
`US 2005/0233709 A1
`
`106
`
`Wireless
`Device
`
`Wireless
`Device
`
`
`
`
`
`
`
`
`
`Legacy
`Wireless
`Device
`
`
`
`
`
`Wireless
`Space
`
`FIG 3
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 3 of 14
`
`

`

`Patent Application Publication Oct. 20, 2005 Sheet 3 of 5
`
`US 2005/0233709 A1
`
`l
`
`l
`-
`- 1
`
`-1
`-1
`1.
`1.
`-1
`- 1
`- 1
`- 1 -
`1
`1
`-1 - 1
`-
`1.
`1 -
`1
`1
`1 -1
`1.
`- 1 -
`- 1
`-1
`- 1
`1 -1 - 1 - 1
`
`O
`1.
`-1
`1.
`-
`1.
`-
`l
`
`1.
`- 1
`1.
`1
`-
`1
`-1, -1
`-
`1.
`l
`1
`1 -1
`as
`-
`
`- 1
`-
`1
`1.
`-1
`-1
`1
`
`-1
`1.
`-1.
`1.
`-
`1.
`-
`1.
`
`FG. 4
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 4 of 14
`
`

`

`Patent Application Publication Oct. 20, 2005 Sheet 4 of 5
`
`US 2005/0233709 A1
`
`out-of-band pilots
`
`Subcarrier
`Power
`
`t
`
`
`
`Subcarrier
`Power
`
`t
`
`
`
`
`
`Subcarrier
`Power
`
`t
`
`Channel 1
`
`Channel 2
`
`Channel 3
`
`Channel 4
`
`--> Frequency
`
`FIG. 5
`
`out-of-band pilots
`
`out-of-band pilots
`
`Channel 1
`
`Channel 2
`
`Channel 3
`
`Channel 4
`
`-> Frequency
`
`FIG. 6
`
`out-of-band pilots > is
`
`
`
`Channel 1
`
`Channel 2
`
`Channel 3
`
`Channel 4
`
`-> Frequency
`
`FG. 7
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 5 of 14
`
`

`

`Patent Application Publication Oct. 20, 2005 Sheet 5 of 5
`
`US 2005/0233709 A1
`
`Transmitter O
`0.8 is
`(-)
`
`1.6 us
`
`3.2 us
`
`3.2 us
`
`4 LS
`
`Receive Signal
`
`S1
`
`
`
`
`
`
`
`
`
`
`
`Take 64-point FFT of
`Received Long Training
`Symbol Samples
`
`Multiply By Known Pilot
`Values
`
`Take 64-point IFFT of
`Result
`
`S2
`
`S3
`
`S4
`
`Isolate the Impulse
`Responses for Each
`Mimo Transmitter
`
`
`
`
`
`S5
`
`Derive Channel
`Estimates
`
`S6
`
`FIG. 9
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 6 of 14
`
`

`

`US 2005/0233709 A1
`
`Oct. 20, 2005
`
`MODIFIED PREAMBLE STRUCTURE FOR IEEE
`802.11A EXTENSIONS TO ALLOW FOR
`COEXISTENCE AND INTEROPERABILITY
`BETWEEN 802.11A DEVICES AND HIGHER DATA
`RATE, MIMO OR OTHERWISE EXTENDED
`DEVICES
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`0001. This application claims priority from co-pending
`U.S. Provisional Patent Application No. 60/461,999, filed
`Apr. 9, 2003 entitled “MODIFIED PREAMBLE STRUC
`TURE FOR IEEE 802.11A EXTENSIONS,” which is
`hereby incorporated by reference, as if set forth in full in this
`document, for all purposes.
`
`BACKGROUND OF THE INVENTION
`0002 The IEEE 802.11a standard defines data rates of 6
`Mbps (megabits per second) up to 54 Mbps. For some
`applications, higher data rates for given modulations and
`data rates higher than 54 Mbps are desirable. Other exten
`sions, such as the use of MIMO (multiple-input, multiple
`output antenna Systems and other extensions might be
`desirable. In order to avoid conflicts with existing Standard
`ized communications and devices, extended devices that
`extend beyond the limits of the 802.11a standard and legacy
`devices that comply with the existing Standard and are not
`necessarily aware of extended Standards both need to coexist
`in a common communication Space and even interoperate at
`times.
`0003) Coexistence is where differing devices can operate
`in a common Space and Still perform most of their functions.
`For example, an extended transmitter transmitting to an
`extended receiver might coexist with a legacy transmitter
`transmitting to a legacy receiver and the extended devices
`can communicate while the legacy devices communicate, or
`at least where the two domains are Such that one defers to the
`other when the other is communicating. Coexistence is
`important So that the adoption and/or use of extended
`devices (i.e., devices that are outside, beyond or noncom
`pliant with one or more Standards with which legacy devices
`adhere and expect other devices to adhere) do not require
`replacement or disabling of existing infrastructures of legacy
`devices.
`0004 Interoperability is where an extended device and a
`legacy device can communicate. For example, an extended
`transmitter might initiate a transmission in Such a manner
`that a legacy device can receive the data Sent by the extended
`transmitter and/or indicate that it is a legacy device So that
`the extended transmitter can adjust its operations accord
`ingly. For example, the extended transmitter might revert to
`Standards compliant communications or Switch to a mode
`that, while not fully Standards compliant, is available to the
`legacy receiver. In another Situation, an extended receiver
`might Successfully receive data from a legacy transmitter.
`0005. The IEEE 802.11a standard defines a 20 microsec
`ond long preamble with a structure as shown in FIG. 1,
`having short training Symbols S (0.8 microSeconds each), a
`guard interval LG, long training Symbols L (3.2 microsec
`onds each) and a signal field (4 microSeconds). The pre
`amble is followed by data. The first eight microseconds
`comprises ten identical Short training Symbols that are used
`
`for packet detection, automatic gain control and coarse
`frequency estimation. The Second eight microSeconds com
`prise two identical long training Symbols, L, preceded by a
`guard interval LG that is the same pattern as the last half (1.6
`microSeconds) of the long training Symbol L. The long
`training Symbols can be used for channel estimation, timing,
`and fine frequency estimation.
`0006 FIG. 2 shows a long training sequence, L, that is
`used to generate the Signal representing the long training
`Symbol in a conventional 802.11a preamble. This sequence
`represents values used over a plurality of Subcarriers. AS
`specified in the standard, the Subcarriers span a 20 MHz
`channel and with 64 Subcarriers, they are Spaced apart by
`312.5 kHz. By convention, used here, the first value in the
`sequence is the value for the DC Subcarrier, followed by the
`value for the 1x312.5 kHz Subcarrier, then the value for the
`2x312.5=625 kHz Subcarrier, etc., up to the 32nd value for
`the 31x312.5 kHZ=9687.5 kHz Subcarrier. The 33rd value
`corresponds to the -10 MHz Subcarrier, followed by the
`-(10 MHz -312.5 kHz) subcarrier, and so on, with the 64
`value being for the -312.5 kHz Subcarrier.
`0007 As can be seen from FIG. 1, the DC value and the
`28th through 38th values, corresponding to the edges of the
`20 MHZ channel, are zero. The output of a transmitter is a
`training Symbol at a Sample rate of 64 SampleS/symbol. The
`samples are obtained by taking a 64-point IFFT (inverse
`fast-Fourier transform) of the long training sequence, L in
`this example. AS used herein, a Sequence in the frequency
`domain is expressed with uppercase letters (e.g., L(k)),
`while the corresponding time Sequence is expressed with
`lowercase letters (e.g., lck)).
`0008 One approach to obtaining higher data rates is the
`use of more bandwidth. Another approach, used by itself or
`as well as the use of more bandwidth, is MIMO (multiple
`input, multiple-output) channels, where a plurality of trans
`mitters transmit different data or the same data Separated by
`Space to result in possibly different multi-path reflection
`characteristics. In either case, care is needed for coexistence
`and interoperability between legacy devices and extended
`devices.
`
`BRIEF SUMMARY OF THE INVENTION
`0009. A modified preamble is used by extended devices
`that operate at higher rates, MIMO or other extensions
`relative to strict 802.11a-compliant devices. The extended
`devices might use one or more of multiple antenna tech
`niques (MIMO), where multiple data streams are multi
`plexed spatially and multi-channel techniques, where an
`extended transmitter transmits using more than one 802.11a
`channel at a time. Such extensions to IEEE 802.11a can exist
`in extended devices.
`0010. The modified preamble is usable for signaling, to
`legacy devices as well as extended devices, to indicate
`capabilities and to cause legacy devices or extended devices
`to defer to other devices Such that the common communi
`cation channel is not Subject to unnecessary interference.
`The modified preamble is also usable for obtaining MIMO
`channel estimates and/or multi-channel estimates.
`0011. The modified preamble preferably includes prop
`erties that facilitate detection of conventional and/or
`extended modes (“mode detection”) and provides some level
`of coexistence with legacy IEEE 802.11a devices.
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 7 of 14
`
`

`

`US 2005/0233709 A1
`
`Oct. 20, 2005
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0012 FIG. 1 illustrates the structure of a conventional
`802.11a preamble.
`0013 FIG. 2 shows a long training symbol sequence, L,
`used for a conventional 802.11a preamble.
`0.014
`FIG. 3 illustrates several devices coupled via a
`wireleSS network.
`0.015
`FIG. 4 illustrates other long training sequences,
`usable by extended devices.
`0016 FIG. 5 illustrates one possible layout for out-of
`band pilot tones for individual channels.
`0017 FIG. 6 illustrates one possible layout for out-of
`band pilot tones for commonly assigned adjacent individual
`channels, where the out-of-band Signals between adjacent
`bands are not attenuated.
`0018 FIG. 7 illustrates a layout for out-of-band pilot
`tones for four adjacent individual channels assigned to a
`Single device, where the out-of-band Signals between adja
`cent bands are not attenuated.
`0019 FIG. 8 illustrates a modified preamble usable for
`multi-channel packets with or without MIMO.
`0020 FIG. 9 is a flowchart illustrating one possible
`proceSS for obtaining channel estimates for each transmitter
`signal in a MIMO system.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`0021. The use of modified preambles is described herein.
`Such modified preambles can be used in packets Sent over a
`wireleSS network, Such as an 802.11a compliant wireleSS
`network. Such packets with modified preambles can be sent
`by transmitters according to embodiments of the present
`invention to be received by receivers according to embodi
`ments of the present invention, as well as being received by
`legacy receivers that are not configured to receive and
`interpret the modified preambles as would be done with
`receivers according to embodiments of the present inven
`tion.
`0022 FIG. 3 illustrates just one example of a wireless
`network being used for communications among transmitters
`and receivers as indicated. AS shown, two wireleSS devices
`102(1), 102(2) might use and interpret the modified pre
`ambles, while a legacy wireless device 104 might not be
`expecting the modified preambles, but might hear Signals
`representing Such preambles. Extended wireleSS devices 102
`might operate using multiple channels and/or multiple trans
`mit antennas and/or multiple receive antennas. Devices
`might have a single transmit antenna and a single receive
`antenna, or more than one transmit antenna and/or more than
`one receive antenna. While Separate transmit and receive
`antennas are shown, antennas might be used for both trans
`mitting and receiving in Some devices.
`0023 Border 106 is not a physical border, but is shown
`to represent a Space within which Signals can be received
`from devices within the Space. Thus, as one device transmits
`a signal representing a packet within border 106, other
`devices within border 106 pick up the signals and, as they
`are programmed, will attempt to determine if the Signals
`
`represent packets and if So, then demodulate/decode the
`packets to obtain the data represented therein.
`0024 Many variations of a modified preamble might be
`used. An example is the preamble shown in FIG. 1, where
`the long training Symbol is modified to use Sequences Such
`as one of the example Sequences shown in FIG. 4.
`0.025
`Preferably, a modified preamble will be such that 1)
`an extended receiver (e.g., one that can advantageously
`handle modified preambles) can distinguish between MIMO
`packets (or other extended mode packets) and conventional
`802.11a packets, 2) a legacy receiver (e.g., one that is not
`configured to receive and interpret the modified preambles
`and might not expect extended operations) can receive
`enough of a packet to determine either that the legacy
`receiver can understand the packet or can defer processing
`of incoming Signals for a time, thereby allowing a measure
`of coexistence, 3) the modified preamble is usable for
`MIMO synchronization and channel estimation, and 4) the
`modified preamble is useful in a process of detecting the use
`of multi-channel transmission. In Some embodiments of
`wireleSS devices according to the present invention, modi
`fied preambles are used that provide one, two, three or all of
`the preferable characteristics indicated above.
`0026 Combinations of Extensions
`0027 Multi-channel extended 802.11 systems might
`simultaneously transmit on several 20 MHZ channels,
`whereas a legacy 802.11 a system only transmits on a single
`20 MHZ channel using a single antenna, or if the legacy
`System does transmit with more than one antenna, each of
`the antennas transmits the same 802.11a signal, possibly
`with Some delay differences between Signals. As a result,
`data rates can be increased over 802.11a data rates using
`multiple transmit antennas or multiple channels or a com
`bination of both. Thus, in a communication channel, Such as
`the airspace of a wireleSS network cloud, Several types of
`packets might be present:
`0028. 1) Legacy SISO (single-input, single-output)
`802.11a, 802.11b, or 802.11g packets transmitted in a single
`20 MHZ channel;
`0029 2) Extended SISO in multiple 20 MHz channels
`(e.g., 40, 60, 80, or 100 MHz channels)
`0030) 3) Extended MIMO in a single 20 MHz channel;
`0.031) 4) Extended MIMO in multiple 20 MHz channels
`(e.g., 40, 60, 80, or 100 MHz channels)
`0032. Several satisfactory modified preamble structures
`can be derived by one of ordinary skill in the art after reading
`this disclosure. Some examples are described below. Pref
`erably, the unmodified preamble structure can provide
`interoperability and coexistence between SISO and MIMO
`Systems at various channel widths and coexistence between
`extended mode Systems and legacy Systems.
`0033) MIMO Single Channel (20 MHz)
`0034. A modified preamble can use the same structure as
`the 802.11a preamble, with a different long training symbol
`determined from a long training Symbol Sequence LD. By
`keeping the same Short Symbols S and using the same timing
`Structure as depicted in FIG. 1, a receiver using the extended
`mode can use the same hardware for detecting the repetitive
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 8 of 14
`
`

`

`US 2005/0233709 A1
`
`Oct. 20, 2005
`
`S and L Symbols, even though the actual contents of the L
`symbols may be different for the 802.11a extensions.
`0.035
`Various embodiments of wireless devices might
`use various long training Symbol Sequences. In one example
`of a modification, the long training Symbol Sequence LD has
`one or more of the following features: 1) it is formulated
`Such that channel estimation can be done for multiple
`transmitters, 2) it is Such that it has a low cross-correlation
`with the unmodified 802.11a long training Symbol Sequence,
`and/or 3) it is usable in a relatively simple process of
`detecting whether the preamble is an 802.11a packet or an
`extended mode packet, uSable in multipath channels. Suit
`able modified long training Symbol Sequences are shown as
`L and L, in FIG. 4, but other variations should be apparent
`upon reading this description.
`0036) Channel Estimation
`0037. By allowing for channel estimation for multiple
`transmitters, MIMO or space-time coding techniques can be
`supported to achieve 802.11a extensions. One way to do this
`is by Sending a different Set of Subcarriers from each
`transmitter. As an example, for the case of two transmitters,
`a device might modulate its OFDM subcarriers with the 64
`values of L, shown in FIG. 4, where one transmitter
`transmits the odd subcarriers {1, 3,..., 63} and the other
`transmitter transmits the even Subcarriers {0, 2, . . . , 62}.
`Thus, one transmitter would take an IFFT of the odd
`Subcarriers and transmit Samples of that time varying signal
`and the other transmitter would take an IFFT of the even
`Subcarriers and transmit Samples of that time varying Signal.
`0.038 L is a modified 802.11a long training symbol
`Sequence, wherein Some of the Subcarriers of the Standard
`802.11a sequence L (shown in FIG. 2) are inverted, and
`Some Subcarriers that are Zero in L are non-zero in L. The
`latter has Some advantages for channel estimation, but is not
`necessary for the purpose of discriminating 802.11a packets
`from extended mode packets.
`0039 Low Cross-Correlation
`0040. The second criterion is that the new training
`Sequence should have a low cross-correlation with the
`conventional IEEE 802.11a training Sequence. One way to
`achieve this is to invert every other group of four Subcarri
`ers, which is applied to Sequence L2 to get a new Sequence
`La that is nearly orthogonal to both L and L. Further, L is
`constructed Such that there is also a low cross-correlation
`between the even and odd elements of L and L. These
`Sequences L and L are shown in FIG. 4. The low croSS
`correlation is illustrated by Equation 1 and Equation 2 (note
`that in Equation 1, a high cross-correlation would have
`right-hand Side values closer to -32 or 32, Since the Sum is
`not normalized here).
`
`3.
`XL2(2k)L(2k) = -1
`ik=0
`
`3.
`X. L2(2k + 1)L(2k + 1) = 0
`ik=0
`
`(Equ. 1)
`
`(Equ. 2)
`
`0041) Mode Detection
`0042. The low cross-correlation between even and odd
`elements of L and La Supports the third criterion, as it
`makes it possible to detect extended mode packets by
`looking at the correlation of L and L with the odd and even
`Subcarriers of a received packet.
`0043. Various methods can be available for a receiver to
`detect from a received signal whether a transmitter trans
`mitted a conventional 802.11a packet or an extended mode
`packet. One method for detecting what type of packet was
`sent will now be described.
`0044) In this method, enough of the signal is received to
`identify what should be the two repeated long training
`Symbols, typically Sampled as two identical repetitions of 64
`samples for each receive antenna. An FFT (fast-Fourier
`transform) of the sum of the two identical repetitions of 64
`Samples is taken, generating an output Sequence S;(k), com
`prising 64 complex values per receive antenna, containing
`channel amplitudes and phases, as well as phase shifts
`caused by the long training Symbol Sequence that was
`actually used (e.g., Sequences Such as L., L2, La or L).
`0045. From the output sequence s(k), the receiver gen
`erates two other sequences, r(k) and r(k), by multiplying
`S;(k) by the Sequences L and La for each receive antennai,
`as illustrated by Equations 3a and 3b.
`
`0046) Next, the receiver calculates two metrics, m, and
`m, from r(k) and r(k) using a differential detection
`operation, Such as that illustrated by Equations 4a and 4b.
`
`is
`
`N-I. 26
`
`i=0 k=2
`
`iii.
`
`N- II
`
`r; (k)r (k - 1) + r(k+37), (k+36)
`
`(Equ. 4a)
`
`(Equ. 4b)
`
`Irni (2k+3)r (2k + 1) + ri (2k+41)r (2k+39) +
`i=0 k=0
`
`ri (2k+4)r (2k+2) + r(2k+42)r (2k+40)
`
`0047. If m>cm, then the receiver might assume that
`the received signal represents a conventional 802.11a
`packet, otherwise the receiver assumes the packet is an
`extended mode packet. The constant c is preferably equal to
`1, but may be different.
`0.048 SISO/MIMO Multiple Channel
`0049 Some modified preamble structures described
`herein provide interoperability and coexistence between
`SISO multi-channel packets/devices and MIMO multi-chan
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 9 of 14
`
`

`

`US 2005/0233709 A1
`
`Oct. 20, 2005
`
`nel packets/devices, as well as coexistence between multi
`channel packetS/devices and legacy packets/devices.
`0050 FIG. 5 illustrates the case where out-of-band pilots
`are attenuated for 20 MHZ channels used to transmit a
`MIMO signal. The preamble structure can be identical to a
`conventional 802.11a preamble, except that the long training
`Symbol Sequence may use what are otherwise considered
`out-of-band Subcarriers. Some or all of these out-of-band
`Subcarriers may also be used in the data Symbols to increase
`the data rate.
`0051). In the case of FIG. 5, different channels may be
`used by different devices, but it is also possible that the same
`device transmits on Several channels simultaneously. For
`instance, one device may transmit on channels 1 and 4
`Simultaneously, while channels 2 and 3 are used by other
`devices.
`0.052) If two adjacent channels are used simultaneously
`by one device, then there is no need to attenuate the
`“out-of-band Subcarriers' in the middle of this 40 MHz
`band. An example of this is shown in FIG. 6. The out-of
`band Subcarriers that are in between the two 20 MHz
`channels thus need not be attenuated. In FIG. 4, the
`Sequence L is the long training Symbol Sequence for a 40
`MHz preamble, which contains all 128 subcarrier values for
`a 40 MHZ channel long training symbol. The first 32 values
`are identical to the last 32 values of a 20 MHz preamble,
`corresponding to the Subcarriers in the left part of a 20 MHz
`channel. One difference between L and two separate 20
`MHZ long training Sequences is that the DC Subcarriers are
`at different locations, so at the position where a 20 MHz
`channel would normally have its DC Subcarrier, the 40 MHz
`Sequence can have a nonzero Subcarrier value. In L, these
`are subcarrier numbers 33 and 97, respectively.
`0.053 With unattenuated out-of-band Subcarriers, signal
`ing information can be carried on those Subcarriers during
`packet Setup, Such as Signaling operating and/or extension
`modes during a preamble, and additional data can be carried
`on those Subcarriers, to increase the datarate.
`0054 FIG. 7 shows the case of four 20 MHZ channels.
`0.055 One example of a modified preamble is the pre
`amble shown in FIG. 1 modified as shown in FIG. 8. The
`long training Symbol values for these out-of-band Subcarri
`ers can be the same as in the case of FIG. 1. The long
`training symbol is followed by a replica of the Signal field
`with identical Subcarrier values in each of the 20 MHz
`channels. This ensures that a receiver that operates on just
`one of the 20 MHZ channels will still be able to successfully
`decode at least the first part of the packet containing the
`Signal field and defer for the rest of the packet, as decoding
`the Signal field provides the receiver with information about
`the length of the packet and thus how long to defer. The
`Same technique can be extended to an arbitrary number of
`channels.
`0056 FIG. 8 shows a preamble for a two transmitter
`MIMO packet. The structure is the same as for 802.11a, but
`Some differences are that a) lo, 11, do di may contain
`out-of-band Subcarriers, b) S, l, d can be cyclically shifted
`relative to So, lo, do or c) lo and 1 can contain Subcarrier
`Sequences that have a low cross-correlation with the same
`Subcarrier Sequences of the 802.11a long training Symbol
`Sequence.
`
`Interoperability
`0057)
`Interoperability between the different extended
`0.058
`modes can be ensured by transmitting the same preamble
`and signal field in each 20 MHZ channel. The preamble time
`structure can be the same as that of IEEE 802.11a, as
`illustrated in FIG. 1. For a 20 MHZ MIMO transmitter, the
`long training symbol L can be modified to facilitate MIMO
`channel estimation and include out-of-band pilots. In one
`example of an extended transmitter using a plurality of
`channels, the transmitter transmits an identical copy of the
`preamble and signal field in each 20 MHZ channel used by
`that transmitter where the out-of-band pilots only have to be
`attenuated at the edges of a multi-channel and not between
`adjacent channels of the multi-channel. The out-of-band
`Subcarriers of the Signal field in might contain different data
`bits for different 20 MHZ channels, to signal information
`Such as the transmitter's multi-band mode, MIMO mode,
`channel number, data rate, and/or coding rate.
`0059 By transmitting the same preamble and signal field
`in any 20 MHZ channel, it is ensured that an extended device
`that only demodulates one 20 MHZ channel at least is able
`to decode the Signal field. From the information in the Signal
`field, the Single-channel extended device can either properly
`defer for the duration of the packet or find out what extended
`mode is used for this packet in the case that this information
`is encoded in the Signal field. For instance, the receiver could
`detect from the Signal field that the packet is transmitted over
`four adjacent channels, after which the extended receiver
`can decide to Switch to a four-channel receiving mode.
`0060) Notice that it typically does not matter for a single
`channel 20 MHz receiver whether the out-of-band Subcar
`riers depicted in FIGS. 5-7 are attenuated. For instance, if a
`Single-channel receiver demodulates channel 2 out of the 4
`transmitted channels shown in FIG. 7, the receive filter of
`that Single-channel receiver will partly attenuate the out-of
`band Subcarriers as well as Suppress the adjacent channels 1
`and 3 to the point where these adjacent channels do not
`cause interference to the desired Signal of channel 2.
`0061 Coexistence
`0062 One method of having coexistence between
`extended devices and legacy IEEE 802.11a and IEEE
`802.11g devices is by keeping the preamble Structure in each
`20 MHZ channel the same as for IEEE 802.11a. IEEE
`802.11a specifies an energy detect based defer behavior,
`which provides some level of coexistence. However, to
`guarantee that legacy devices properly defer for all extended
`mode packets down to received power levels of -82 dBm or
`other Suitable levels, the receivers have to be able to
`Successfully decode the Signal field, which contains the
`length information of the packet.
`0063 Some ways to do this are described by Bangerter,
`B., et al., “High-Throughput Wireless LAN Air Interface”,
`Intel Technology Journal, Vol. 7, Issue 3 (August 2003)
`(hereinafter “Bangerter”) and Boer, J., et al., “Backwards
`Compatibility”, IEEE 802.11 presentation, Document Num
`ber 802.11-03/714rO (September 2003) (hereinafter
`“Boer”).
`0064 Bangerter describes the use of multiple 802.11a
`preambles spread in frequency such that 20 MHZ channel
`legacy 802.11a devices will defer for multiple channel
`
`Exhibit 1016
`Panasonic v. UNM
`IPR2024-00364
`Page 10 of 14
`
`

`

`US 2005/0233709 A1
`
`Oct. 20, 2005
`
`devices, but additional advantages can be had through the
`use of out-of-band pilots or MIMO preambles, as described
`elsewhere herein.
`0065 Boer describes some possible MIMO preambles
`having some limited benefits. In one method described in
`Boer, each MIMO transmitter transmits an 802.11a pre
`amble while the other transmitters transmit nothing. While
`this makes distinguishing easier, training is significantly
`longer and that reduces throughput. In another method
`described in Boer, each MIMO transmitter transmits a part
`of the 802.11a subcarriers. For example, for two transmit
`ters, one transmitter transmits all odd Subcarriers and the
`other transmitter transmits all even Subcarriers. However,
`without more, mode detection based on the training Symbols
`might not be possible with that technique.
`0.066. A novel way of enabling coexistence or furthering
`coexistence for MIMO packets is to apply a cyclic delay
`shift on the long training symbol and Signal field IFFT
`outputs prior to applying the guard time extension. For
`example, assume L(k) and D(k) are the 64 Subcarrier values
`for the long training Symbol and Signal field Symbol, respec
`tively. For a conventional 802.11a single transmitter trans
`mission, the time Samples for the long training Symbol are
`derived by taking the 64-point IFFT of L(k) to obtainl(i) and
`transmitting the Samples of 10i). Thus, with the guard time,
`the long training Symbol and guard time are constructed as
`1(33:64) 1 (1:64) 1 (1:64)), i.e., the IFFT output is repeated
`twice and the last 32 Samples are prepended to form the long
`training guard interval. AS with the conventional timing, the
`long training guard interval (32 Samples) is twice as long as
`the guard interval for 802.11a data symbols (16 samples).
`The signal field is formed by d(49:64) d(1:64)), where
`d(1:64) are the 64 samples of the IFFT of D(k).
`0067. In the case of a two transmitter MIMO device, the
`first transmitter would transmit the long training Symbol and
`signal field like that of 802.11a. The second transmitter
`would apply a cyclic shift such that instead of the IFFT
`output 101:64), it uses the cyclically shifted Samples ls=
`1(33:64) l(1:32) to construct the long training symbol
`samples Ils(33:64) ls(1:64) ls(1:64)). For the signal field, it
`uses the shifted samples dS=d(33:64) d(1:32) to construct
`the signal field as ds(49:64) ds(1:64).
`0068. In a legacy 802.11a packet, one 3.2 microsecond
`repetition of the long training symbol L as shown in FIG. 1
`is expressed in the time domain as the IFFT of L(k), where
`L(k) contains 64 Subcarrier values, of which 52 are non
`Zero. The time samples 10i) are given as shown in Equation
`5, where the Subcarrier values of L(k):
`
`l(i) =X Lk exp(T)
`
`63
`
`ik=0
`
`27tik
`
`(Equ. 5)
`
`0069. In the extended modes described herein, some
`possible modifications will be described. First, L(k) can
`contain more than 52 non-Zero Subcarriers. Second, in the
`case of MIMO transmission, li) can have a cyclic shift that
`may be different for each transmitter. The shifted signall(i)
`can be derived from 1(i) as 1.(i)=l(i+64-dk1%64), where
`“%” denotes the modulo operator and dk is the cyclic delay
`
`of transmitter k in 20 MHz Samples. This expression
`assumes a 20 MHZ Sampling rate, Such