U.S. patent number RE48,629 [Application Number 16/686,468] was granted by the patent office on 2021-07-06 for backward-compatible long training sequences for wireless communication networks.
This patent grant is currently assigned to Bell Northern Research, LLC. The grantee listed for this patent is Bell Northern Research, LLC. Invention is credited to Rajendra T. Moorti, Jason Alexander Trachewsky.
United States Patent |
RE48,629 |
Trachewsky , et al. |
July 6, 2021 |
Backward-compatible long training sequences for wireless
communication networks
Abstract
A network device for generating an expanded long training
sequence with a minimal peak-to-average ratio. The network device
includes a signal generating circuit for generating the expanded
long training sequence. The network device also includes an Inverse
Fourier Transform for processing the expanded long training
sequence from the signal generating circuit and producing an
optimal expanded long training sequence with a minimal
peak-to-average ratio. The expanded long training sequence and the
optimal expanded long training sequence are stored on more than 52
sub-carriers.
Inventors: |
Trachewsky; Jason Alexander
(Menlo Park, CA), Moorti; Rajendra T. (Mountain View,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bell Northern Research, LLC |
Chicago |
IL |
US |
|
|
Assignee: |
Bell Northern Research, LLC
(Chicago, IL)
|
Family
ID: |
36574175 |
Appl.
No.: |
16/686,468 |
Filed: |
November 18, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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11188771 |
Jan 12, 2010 |
7646703 |
|
|
|
60634102 |
Dec 8, 2004 |
|
|
|
|
60591104 |
Jul 27, 2004 |
|
|
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Reissue of: |
12684650 |
Jan 8, 2010 |
7990842 |
Aug 2, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
27/262 (20130101); H04L 27/2613 (20130101); H04B
2201/70706 (20130101); H04B 2201/70701 (20130101); H04L
5/0048 (20130101); H04L 25/0226 (20130101) |
Current International
Class: |
H04L
27/26 (20060101); H04L 5/00 (20060101); H04L
25/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
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Layer (PHY) specifications: High-speed Physical Layer in the 5 GHZ
Band," IEEE Std 802. 11a-1999 (Supplement to IEEE Std 802.11-1999),
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.
Ogawa, Yasutaka et al. "A MIMO-OFDM System for High-Speed
Transmission," 2003 IEEE 58th Vehicular Technology Conference, Oct.
9, 2003, pp. 493-497, IEEE, Orland, United States. cited by
applicant .
Abhayawardhana, V. S. et al., "Frequency Scaled Time Domain
Equalization for OFDM in Broadband Fixed Wireless Access Channels,"
2002 IEEE Wireless Communications and Networking Conference Record,
Mar. 21, 2002, pp. 67-72, IEEE, Orland, United States. cited by
applicant .
Liebetreu, John et al., "Modifications to OFDM FFT-256 mode for
supporting mobile operation," IEEE C802.16e-03/12, Mar. 3, 2003,
pp. 0-8, IEEE. cited by applicant .
Decision: Settlement Prior to Institution of Trial; IPR 2019-01174;
dated Dec. 11, 2019. cited by applicant .
Decision: Settlement Prior to Institution of Trial; IPR 2019-01345;
dated Dec. 11, 2019. cited by applicant .
Decision: Settlement Prior to Institution of Trial; IPR 2019-01437;
dated Dec. 11, 2019. cited by applicant .
Order Granting Joint Motion for Dismissal as to Counts III and IV
of BNR's Complaint and Partial Dismissal of Counts I and II of
Coolpad's Counterclaims; C.A. No. 3:18-cv-1783-CAB-BLM; dated Oct.
7, 2019. cited by applicant .
Order Granting Joint Morion to Dismiss; Case No.
18-CV-1785-CAB-BLM; dated Aug. 5, 2019. cited by applicant .
Order Granting Joint Motion for Dismissal as to Counts 3 and 6 of
BNR's Amended Complaint and Counts VI, VII, X, and XI of ZTE
Corporation, ZTE (TX), Inc., and ZTE (USA) Inc.'s Counterclaims;
C.A. No. 3:18-cv-1786-CAB-BLM; dated Oct. 4, 2019. cited by
applicant .
Order Granting Joint Motion for Dismissal as to Counts III and VI
of BNR's Second Amended Complaint; C.A. No. 3:18-cv-1784-CAB-BLM;
dated Oct. 21, 2019. cited by applicant.
|
Primary Examiner: Sager; Mark
Attorney, Agent or Firm: Mendelsohn Dunleavy, P.C.
Mendelsohn; Steve
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is .Iadd.a reissue application for U.S.
Pat. No. 7,990,842, which was .Iaddend.a CONTINUATION of U.S.
application Ser. No. 11/188,771, filed Jul. 26, 2005 .Iadd.and
issued as U.S. Pat. No. 7,646,703.Iaddend.. Said U.S. application
Ser. No. 11/188,771 makes reference to, claims priority to and
claims benefit from U.S. Application No. 60/591,104, filed Jul. 27,
2004; and U.S. Application No. 60/634,102, filed Dec. 8, 2004. The
above-identified applications are hereby incorporated herein by
reference in their entirety.
Claims
What is claimed:
1. A wireless communications device, comprising: a signal generator
that generates an extended long training sequence; and an Inverse
Fourier Transformer operatively coupled to the signal generator,
wherein the Inverse Fourier Transformer processes the extended long
training sequence from the signal generator and provides an optimal
extended long training sequence with a minimal peak-to-average
ratio, and wherein at least the optimal extended long training
sequence is carried by a greater number of subcarriers than a
standard wireless networking configuration for an Orthogonal
Frequency Division Multiplexing scheme.Iadd., wherein the optimal
extended long training sequence is carried by exactly 56 active
sub-carriers, and wherein the optimal extended long training
sequence is represented by encodings for indexed sub-carriers -28
to +28, excluding indexed sub-carrier 0 which is set to zero, as
follows: TABLE-US-00001 Sub-carrier -28 -27 -26 -25 -24 -23 -22
Encoding +1 +1 +1 +1 -1 -1 +1 Sub-carrier -14 -13 -12 -11 -10 -9 -8
Encoding +1 +1 +1 -1 -1 +1 +1 Sub-carrier 1 2 3 4 5 6 7 Encoding +1
-1 -1 +1 +1 -1 +1 Sub-carrier 15 16 17 18 19 20 21 Encoding +1 +1
-1 -1 +1 -1 +1 Sub-carrier -21 -20 -19 -18 -17 -16 -15 Encoding +1
-1 +1 -1 +1 +1 +1 Sub-carrier -7 -6 -5 -4 -3 -2 -1 Encoding -1 +1
-1 +1 +1 +1 +1 Sub-carrier 8 9 10 11 12 13 14 Encoding -1 +1 -1 -1
-1 -1 -1 Sub-carrier 22 23 24 25 26 27 28 Encoding -1 +1 +1 +1 +1
-1 -1.
.Iaddend.
.[.2. The wireless communications device according to claim 1,
wherein at least the optimal extended long training sequence is
carried by at least 56 active sub-carriers..].
.[.3. The wireless communications device according to claim 2,
wherein the at least 56 active sub-carriers correspond to at least
indexed sub-carriers -28 to +28. .].
4. The wireless communications device according to claim .[.2.].
.Iadd.1.Iaddend., wherein the optimal extended long training
sequence has a minimum peak-to-average power ratio of 3.6 dB.
.[.5. The wireless communications device according to claim 1,
wherein at least the optimal extended long training sequence is
carried by at least 63 active sub-carriers..].
.[.6. The wireless communications device according to claim 5,
wherein the at least 63 active sub-carriers correspond to at least
indexed sub-carriers -32 to +31..].
.[.7. The wireless communications device according to claim 5,
wherein the optimal extended long training sequence has a minimum
peak-to-average power ratio of 3.6 dB..].
8. The wireless communications device according to claim 1, wherein
a binary phase shift key encoding is used for each sub-carrier
above the +26 indexed sub-carrier and below the -26 indexed
sub-carrier.
9. The wireless communications device according to claim 1, wherein
the Inverse Fourier Transformer comprises .[.at least one of the
following:.]. an Inverse Fast Fourier Transformer .[.and.].
.Iadd.or .Iaddend.an Inverse Discrete Fourier Transformer.
10. The wireless communications device according to claim 1,
wherein the wireless communications device comprises one or more of
the following: a personal digital assistant, a laptop computer, a
personal computer.Iadd., a processor, .Iaddend.and a cellular
phone.
11. The wireless communications device according to claim 1,
wherein the wireless communications device comprises a wireless
mobile communications device.
12. The wireless communications device according to claim 1,
wherein the wireless communications device comprises one or more of
the following: an access point and a base station.
13. The wireless communications device according to claim 1,
wherein the wireless communications device is backwards compatible
with legacy wireless local area network devices.
14. The wireless communications device according to claim 1,
wherein the optimal extended long training sequence is longer than
a long training sequence used by a legacy wireless local area
network device in accordance with a legacy wireless networking
protocol standard.
15. The wireless communications device according to claim 14,
wherein the legacy wireless local area network device uses the
optimal extended long training sequence to estimate a carrier
frequency offset even though the optimal extended long training
sequence is longer than the long training sequence that is
specified by the legacy wireless networking protocol standard.
16. The wireless communications device according to claim 15,
wherein the long training sequence that is specified by the legacy
wireless networking protocol standard is maintained in the extended
long training sequence or the optimal extended long training
sequence.
17. The wireless communications device according to claim 1,
wherein the wireless communications device decreases power
back-off.
18. The wireless communications device according to claim 1,
wherein the wireless communications device registers with one or
more of the following: an access point and a base station.
19. The wireless communications device according to claim 1,
wherein the extended long training sequence or the optimal extended
long training sequence is encoded using binary phase shift key
encoding on each of the .Iadd.56 active .Iaddend.subcarriers.
20. The wireless communications device according to claim 1,
comprising: a symbol mapper operatively coupled to the signal
generator, wherein the symbol mapper receives coded bits and
generates symbols for each of 64 subcarriers of an Orthogonal
Frequency Division Multiplexing sequence.
.Iadd.21. The wireless communications device according to claim 14,
wherein the legacy wireless networking protocol standard for the
Orthogonal Frequency Division Multiplexing scheme corresponds to
exactly 52 active subcarriers..Iaddend.
.Iadd.22. The wireless communications device according to claim 21,
wherein, for a long training sequence of the legacy wireless
networking protocol standard, the indexed sub-carrier 0 is set to
zero and encodings for the indexed sub-carriers -26 to +26
excluding the indexed sub-carrier 0 are: TABLE-US-00002 Sub-carrier
-26 -25 -24 -23 -22 -21 -20 Encoding +1 +1 -1 -1 +1 +1 -1
Sub-carrier -13 -12 -11 -10 -9 -8 -7 Encoding +1 +1 -1 -1 +1 +1 -1
Sub-carrier 1 2 3 4 5 6 7 Encoding +1 -1 -1 +1 +1 -1 +1 Sub-carrier
14 15 16 17 18 19 20 Encoding -1 +1 +1 -1 -1 +1 -1 Sub-carrier -19
-18 -17 -16 -15 -14 Encoding +1 -1 +1 +1 +1 +1 Sub-carrier -6 -5 -4
-3 -2 -1 Encoding +1 -1 +1 +1 +1 +1 Sub-carrier 8 9 10 11 12 13
Encoding -1 +1 -1 -1 -1 -1 Sub-carrier 21 22 23 24 25 26 Encoding
+1 -1 +1 +1 +1 +1.
.Iaddend.
.Iadd.23. The wireless communications device according to claim 22,
wherein: the Inverse Fourier Transformer comprises an Inverse Fast
Fourier Transformer or an Inverse Discrete Fourier Transformer; the
wireless communications device comprises one or more of the
following: a personal digital assistant, a laptop computer, a
personal computer, a cellular phone, an access point, a processor,
and a base station; the wireless communications device is backwards
compatible with the legacy wireless local area network device; the
legacy wireless local area network device uses the optimal extended
long training sequence to estimate a carrier frequency offset even
though the optimal extended long training sequence is longer than
the long training sequence that is specified by the legacy wireless
networking protocol standard; the wireless communications device
decreases power back-off; the extended long training sequence or
the optimal extended long training sequence is encoded using binary
phase shift key encoding on each of the 56 active subcarriers; and
the wireless communications device further comprises a symbol
mapper operatively coupled to the signal generator, wherein the
symbol mapper receives coded bits and generates symbols for each of
64 subcarriers of an Orthogonal Frequency Division Multiplexing
sequence..Iaddend.
.Iadd.24. The wireless communications device according to claim 1,
wherein at least one output of the Inverse Fourier Transformer is
operatively coupled to at least one digital-to-analog
converter..Iaddend.
.Iadd.25. The wireless communications device according to claim 1,
wherein at least one output of the Inverse Fourier Transformer is
operatively coupled to multiple digital-to-analog
converters..Iaddend.
.Iadd.26. The wireless communications device according to claim 1,
wherein an input of the signal generator is operatively coupled to
a frequency-domain windower..Iaddend.
.Iadd.27. The wireless communications device according to claim 1,
wherein an output of the Inverse Fourier Transformer is operatively
coupled to a time-domain windower..Iaddend.
.Iadd.28. The wireless communications device according to claim 27,
wherein an output of the time-domain windower is operatively
coupled to at least one digital-to-analog converter..Iaddend.
.Iadd.29. The wireless communication device according to claim 1,
wherein an output of the Inverse Fourier Transformer is operatively
coupled to a digital transmit filter..Iaddend.
.Iadd.30. The wireless communications device according to claim 1,
wherein an output of the Inverse Fourier Transformer is operatively
coupled to a parallel-to-serial convertor..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to wireless communication
systems and more particularly to long training sequences of minimum
peak-to-average power ratio which may be used by legacy
systems.
2. Description of the Related Art
Each wireless communication device participating in wireless
communications includes a built-in radio transceiver (i.e.,
receiver and transmitter) or is coupled to an associated radio
transceiver. As is known to those skilled in the art, the
transmitter typically includes a data modulation stage, one or more
intermediate frequency stages, and a power amplifier. The data
modulation stage converts raw data into baseband signals in
accordance with a particular wireless communication standard. The
intermediate frequency stages mix the baseband signals with one or
more local oscillations to produce RF signals. The power amplifier
amplifies the RF signals prior to transmission via an antenna.
The receiver is typically coupled to the antenna and includes a low
noise amplifier, one or more intermediate frequency stages, a
filtering stage, and a data recovery stage. The low noise amplifier
receives, via the antenna, inbound RF signals and amplifies the
inbound RF signals. The intermediate frequency stages mix the
amplified RF signals with one or more local oscillations to convert
the amplified RF signal into baseband signals or intermediate
frequency (IF) signals. The filtering stage filters the baseband
signals or the IF signals to attenuate unwanted out of band signals
to produce filtered signals. The data recovery stage recovers raw
data from the filtered signals in accordance with a particular
wireless communication standard.
Different wireless devices in a wireless communication system may
be compliant with different standards or different variations of
the same standard. For example, 802.11a an extension of the 802.11
standard, provides up to 54 Mbps in the 5 GHz band. 802.11b,
another extension of the 802.11 standard, provides 11 Mbps
transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz
band. 802.11g, another extension of the 802.11 standard, provides
20+ Mbps in the 2.4 GHz band. 802.11n, a new extension of 802.11,
is being developed to address, among other thins, higher throughput
and compatibility issues. An 802.11a compliant communications
device may reside in the same WLAN as a device that is compliant
with another 802.11 standard. When devices that are compliant with
multiple versions of the 802.11 standard are in the same WLAN, the
devices that are compliant with older versions are considered to be
legacy devices. To ensure backward compatibility with legacy
devices, specific mechanisms must be employed to insure that the
legacy devices know when a device that is compliant with a newer
version of the standard is using a wireless channel to avoid a
collision. New implementations of wireless communication protocol
enable higher speed throughput, while also enabling legacy devices
which might be only compliant with 802.11a or 802.11g to
communicate in systems which are operating at higher speeds.
Devices implementing both the 802.11a and 802.11g standards use an
orthogonal frequency division multiplexing (OFDM) encoding scheme.
OFDM is a frequency division multiplexing modulation technique for
transmitting large amounts of digital data over a radio wave. OFDM
works by spreading a single data stream over a band of
sub-carriers, each of which is transmitted in parallel. In 802.11a
and 802.11g compliant devices, only 52 of the 64 active
sub-carriers are used. Four of the active sub-carriers are pilot
sub-carriers that the system uses as a reference to disregard
frequency or phase shifts of the signal during transmission. The
remaining 48 sub-carriers provide separate wireless pathways for
sending information in a parallel fashion. The 52 sub-carriers are
modulated using binary or quadrature phase shift keying
(BPSK/QPSK), 16 Quadrature Amplitude Modulation (QAM), or 64 QAM.
Therefore, 802.11a and 802.11g compliant devices use sub-carriers
-26 to +26, with the 0-index sub-carrier set to 0 and 0-index
sub-carrier being the carrier frequency. As such, only part of the
20 Mhz bandwidth supported by 802.11a and 802.11g is use.
In 802.11a/802.11g, each data packet starts with a preamble which
includes a short training sequence followed by a long training
sequence. The short and long training sequences are used for
synchronization between the sender and the receiver. The long
training sequence of 802.11a and 802.11g is defined such that each
of sub-carriers -26 to +26.Iadd., except for the sub-carrier 0
which is set to 0, .Iaddend.has one BPSK .[.consellation.].
.Iadd.constellation .Iaddend.point, either +1 or -1.
There exists a need to create a long training sequence of minimum
peak-to-average ratio that uses more sub-carriers without
interfering with adjacent channels. The inventive long .[.trains.].
.Iadd.training .Iaddend.sequence with a minimum peak-to-average
power ratio should be usable by legacy devices in order to estimate
channel impulse response and to estimate carrier frequency offset
between a transmitter and a receiver.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a
network device for generating an expanded long training sequence
with a minimal peak-to-average ratio. The network device includes a
signal generating circuit for generating the expanded long training
sequence. The network device also includes an Inverse Fourier
Transform for processing the expanded long training sequence from
the signal generating circuit and producing an optimal expanded
long training sequence with a minimal peak-to-average ratio. The
expanded long training sequence and the optimal expanded long
training sequence are stored on more than 52 sub-carriers.
According to another aspect of the invention, there is provided a
network device for generating an expanded long training sequence
with a minimal peak-to-average ratio. The network device includes a
signal generating circuit for generating the expanded long training
sequence. The network device also includes an Inverse Fourier
Transform for processing the expanded long training sequence from
the signal generating circuit and producing an optimal expanded
long training sequence with a minimal peak-to-average ratio. The
expanded long training sequence and the optimal expanded long
training sequence are stored on more than 56 sub-carriers.
According to another aspect of the invention, there is provided a
network device for generating an expanded long training sequence
with a minimal peak-to-average ratio. The network device includes a
signal generating circuit for generating the expanded long training
sequence. The network device also includes an Inverse Fourier
Transform for processing the expanded long training sequence from
the signal generating circuit and producing an optimal expanded
long training sequence with a minimal peak-to-average ratio. The
expanded long training sequence and the optimal expanded long
training sequence are stored on more than 63 sub-carriers.
According to another aspect of the invention, there is provided a
method for generating an expanded long training sequence with a
minimal peak-to-average ratio. The method includes the steps of
generating the expanded long training sequence and producing an
optimal expanded long training sequence with a minimal
peak-to-average ratio. The method also includes the step of storing
the expanded long training sequence and the optimal expanded long
training sequence on more than 52 sub-carriers.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention that together with the description serve to explain
the principles of the invention, wherein:
FIG. 1 illustrates a communication system that includes a plurality
of base stations, a plurality of wireless communication devices and
a network hardware component;
FIG. 2 illustrates a schematic block diagram of a processor that is
configured to generate an expanded long training sequence;
FIG. 3 is a schematic block diagram of a processor that is
configured to process an expanded long training sequence;
FIG. 4 illustrates the long training sequence that is used in 56
active sub-carriers; and
FIG. 5 illustrates the long training sequence that is used in 63
active sub-carriers.
DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made to the preferred embodiments of the
present invention, examples of which are illustrated in the
accompanying drawings.
FIG. 1 illustrates a communication system 10 that includes a
plurality of base stations and/or access points 12-16, a plurality
of wireless communication devices 18-32 and a network hardware
component 34. Wireless communication devices 18-32 may be laptop
computers 18 and 26, personal digital assistant hosts 20 and 30,
personal computer 24 and 32 and/or cellular telephone 22 and 28.
Base stations or access points 12-16 are operably coupled to
network hardware 34 via local area network connections 36, 38 and
40. Network hardware 34, for example a router, a switch, a bridge,
a modem, or a system controller, provides a wide area network
connection for communication system 10. Each of base stations or
access points 12-16 has an associated antenna or antenna array to
communicate with the wireless communication devices in its area.
Typically, the wireless communication devices register with a
particular base station or access point 12-14 to receive services
from communication system 10. Each wireless communication device
includes a built-in radio or is coupled to an associated radio. The
radio includes at least one radio frequency (RF) transmitter and at
least one RF receiver.
The present invention provides an expanded long training sequence
of minimum peak-to-average power ratio and thereby decreases power
back-off. The inventive expanded long training sequence may be used
by 802.11a or 802.11g devices for estimating the channel impulse
response and by a receiver for estimating the carrier frequency
offset between the transmitter clock and receiver clock. The
inventive expanded long training sequence is usable by 802.11a or
802.11g systems only if the values at sub-carriers -26 to +26 are
identical to those of the current long training sequence used in
802.11a and 802.11g systems. As such, the invention .[.utilized.].
.Iadd.utilizes .Iaddend.the same +1 or -1 binary phase shift key
(BPSK) encoding for each new sub-carrier and the long training
sequence of 802.11a or 802.11g systems is maintained in the present
invention.
In a first embodiment of the invention, the expanded long training
sequence is implemented in 56 active sub-carriers including
sub-carriers -28 to +28 .Iadd.except the 0-index sub-carrier which
is set to 0.Iaddend.. In another embodiment, an expanded long
training sequence is implemented using 63 active sub-carriers,
i.e., all of the active sub-carriers (-32 to +31) except the
0-index sub-carrier which is set to 0. In both embodiments of the
invention, orthogonality is not affected, since a 64-point
orthogonal transform is used to generate the time-domain sequence.
Additionally, the output of an auto-correlator for computing the
carrier frequency offset is not affected by the extra
sub-carriers.
FIG. 2 illustrates a schematic block diagram of a processor that is
configured to generate an expanded long training sequence.
Processor 200 includes a symbol mapper 202, a frequency domain
window 204, a signal generating circuit 205, an inverse .[.fast.].
Fourier transform .[.(IFFT).]. module 206, a .[.serial to.].
parallel .Iadd.to serial .Iaddend.module 208, a digital transmit
filter and/or time domain window module 210, and digital to analog
converters (D/A) 212. For an expanded long training sequence,
symbol mapper 202 generates symbols from the coded bits for each of
the 64 subcarriers of an OFDM sequence. Frequency domain window 204
applies a weighting factor on each subcarrier. Signal generating
circuit 205 generates the expanded long training sequence and if 56
active sub-carriers are being used, signal generating circuit
generates the expanded long training sequence and stores the
expanded long training sequence in sub-carriers -28 to +28
.Iadd.except the 0-index sub-carrier which is set to 0.Iaddend.. If
63 active sub-carriers are being used, signal generating circuit
generates the expanded long training sequence and stores the
expanded long training sequence in sub-carriers -32 to +32 i.e.,
all of the active sub-carriers (-32 to +31) except the 0-index
sub-carrier which is set to 0. The inventive long training sequence
is inputted into an Inverse Fourier Transform 206. The invention
uses the same +1 or -1 BPSK encoding for each new sub-carrier.
Inverse Fourier Transform 206 may be an inverse Fast Fourier
Transform (IFFT) or Inverse Discrete Fourier Transform .[.(IFDT).].
.Iadd.(IDFT).Iaddend.. Inverse Fourier Transform 206 processes the
long training sequence from signal generating circuit 205 and
thereafter produces an optimal expanded long training sequence with
a minimal peak-to-average power ratio. The optimal expanded long
training sequence may be used in either 56 active sub-carriers or
63 active subscribers. .[.Serial to parallel.]. .Iadd.Parallel to
serial .Iaddend.module 208 converts the .[.serial.]. .Iadd.parallel
.Iaddend.time domain signals .Iadd.from the Inverse Fourier
Transform 206 .Iaddend.into .[.parallel.]. .Iadd.serial
.Iaddend.time domain signals that are subsequently filtered and
converted to analog signals via the D/A.
FIG. 3 is a schematic block diagram of a processor that is
configured to process an expanded long training sequence. Processor
300 includes a symbol demapper 302, a frequency domain window 304,
a fast Fourier transform (FFT) module 306, a .[.parallel to.].
serial .Iadd.to parallel .Iaddend.module 308, a digital receiver
filter and/or time domain window module 310, and analog to digital
converters (A/D) 312. A/D converters 312 convert the sequence into
digital signals that are filtered via digital receiver filter 310.
.[.Parallel to.]. .Iadd.Serial to parallel .Iaddend.serial module
308 converts the digital time domain signals into a plurality of
.[.serial.]. time domain signals. FFT module 306 converts the
.[.serial.]. time domain signals into frequency domain signals.
Frequency domain window 304 applies a weighting factor on each
frequency domain signal. Symbol demapper 302 generates the coded
bits from each of the 64 subcarriers of an OFDM sequence received
from the frequency domain window.
FIG. 4 illustrates the long training sequence with a minimum
peak-to-average power ratio that is used in 56 active sub-carriers.
Out of the 16 possibilities for the four new sub-carrier positions,
the sequence illustrated in FIG. 4 has the minimum peak-to-average
power ratio, i.e., a peak-to-average power ratio of 3.6 dB.
FIG. 5 illustrates the long training sequence with a minimum
peak-to-average power ratio that is used in 63 active sub-carriers.
Out of the 2048 possibilities for the eleven new sub-carrier
positions, the sequence illustrated in FIG. 5 has the minimum
peak-to-average power ratio, i.e., a peak-to-average power ratio of
3.6 dB.
It should be appreciated by one skilled in art, that the present
invention may be utilized in any device that implements the OFDM
encoding scheme. The foregoing description has been directed to
specific embodiments of this invention. It will be apparent,
however, that other variations and modifications may be made to the
described embodiments, with the attainment of some or all of their
advantages. Therefore, it is the object of the appended claims to
cover all such variations and modifications as come within the true
spirit and scope of the invention.
* * * * *