Robust detection of packet types
First Claim
1. A method for determining a modulation of an orthogonal frequency-division multiplexing (OFDM) symbol, the method comprising:
- receiving the symbol;
multiplying the received symbol by the conjugate transpose of an overall channel response for the symbol;
applying a decision function to the result of the multiplication for a set of sub-carriers, wherein the decision function is to sum the result of the multiplication and the determination is made based on a location of a result of the sum in a real-imaginary plane, wherein the location is determined relative to boundary lines in the real-imaginary plane, where the boundary lines are set in accordance with one of;
arctangent of Im(s)/Re(s),|Im(s)|n−
|Re(s)|n, or|Re(s)|n−
|Im(s)|n,
wherein s is the result of the sum, and n is a variable;
determining the modulation of the symbol in accordance with the result of the decision function; and
processing a packet in accordance with the determination of the modulation.
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Accused Products
Abstract
Disclosed herein is a system and method for determining the presence of rotated-BPSK modulation. In addition, disclosed herein is a system and method for determining if a received packet is a Legacy, Mixed-Mode, or Green-Field packet in accordance with the determination of the presence of rotated-BPSK modulation. The presence of a Green-Field packet may be determined by detecting if additional tones are being excited in an LTF symbol of the received packet and/or if a SIG field symbol following the LTF symbol is modulated by rotated-BPSK. The presence of a Mixed-Mode packet may be determined by detecting if the first four bits of the SIG field symbol following the LTF symbol are [1 1 0 1] and/or detecting if a symbol following an L-SIG symbol is modulated by rotated-BPSK. The presence of a Legacy packet may be determined by detecting if the symbol following the L-SIG symbol is modulated by BPSK.
49 Citations
17 Claims
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1. A method for determining a modulation of an orthogonal frequency-division multiplexing (OFDM) symbol, the method comprising:
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receiving the symbol; multiplying the received symbol by the conjugate transpose of an overall channel response for the symbol; applying a decision function to the result of the multiplication for a set of sub-carriers, wherein the decision function is to sum the result of the multiplication and the determination is made based on a location of a result of the sum in a real-imaginary plane, wherein the location is determined relative to boundary lines in the real-imaginary plane, where the boundary lines are set in accordance with one of; arctangent of Im(s)/Re(s), |Im(s)|n−
|Re(s)|n, or|Re(s)|n−
|Im(s)|n,
wherein s is the result of the sum, and n is a variable;determining the modulation of the symbol in accordance with the result of the decision function; and processing a packet in accordance with the determination of the modulation. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for determining a modulation of an orthogonal frequency-division multiplexing (OFDM) symbol, the method comprising:
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receiving the OFDM symbol; multiplying the received OFDM symbol by the conjugate transpose of an overall channel response for the OFDM symbol; applying a decision function to the result of the multiplication for a set of sub-carriers, wherein the decision function is;
Σ
kε
Sx(yk,l),
where yk,l is the result of the multiplication for an l-th symbol that is received on a k-th sub-carrier, S is a subset of sub-carriers, and x(yk,l) is one of;arctangent of Im(yk,l)/Re(yk,l), |Im(yk,l)|n−
|Re(yk,l)|n, or|Re(yk,l)|n−
|Im(yk,l)|n,where n is a variable; determining the modulation of the OFDM symbol in accordance with the result of the decision function; and processing a packet in accordance with the determination of the modulation, wherein the type of modulation for the OFDM symbol is rotated-binary phase shift keying (BPSK) if the result of the decision function is greater than β
, and wherein the type of modulation for the OFDM symbol is BPSK if the result of the decision function is less than β
, where β
is any of |S|/2, −
|S|/2, (Σ
kε
Shk*Akhk)/2, −
(Σ
kε
Shk*Akhk)/2, or zero and where hk is the overall channel response, and Ak is a diagonal matrix for scaling the OFDM symbol in accordance with different noise variances on the set of sub-carriers.
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9. A method for determining a modulation of an orthogonal frequency-division multiplexing (OFDM) symbol, the method comprising:
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receiving the OFDM symbol; multiplying the received OFDM symbol by the conjugate transpose of an overall channel response for the OFDM symbol; applying a decision function to the result of the multiplication for a set of sub-carriers, wherein the decision function is;
P−
N,
where P is the number of elements in the set{k|kε
S and |xk|>
β
}, N is the number of elements in the set {k|kε
S and |xk|<
β
}, β
is any of |S|/2, −
|S|/2,(Σ
kε
Shk*Akhk)/2, −
(Σ
kε
Shk*Akhk)/2, or zero, where hk is the overall channel response, Ak is a diagonal matrix for scaling the OFDM symbol in accordance with different noise variances on the set of sub-carriers, S is a subset of sub-carriers, and xk is one of;arctangent of Im(yk,l)/Re(yk,l), |Im(yk,l)|n−
|Re(yk,l)|n, or|Re(yk,l)|n−
|Im(yk,l)|n,where yk,l is a result of the multiplication for an /-th symbol that is received on a k-th sub-carrier, and were n is a variable; determining the modulation of the OFDM symbol in accordance with the result of the decision function; and processing a packet in accordance with the determination of the modulation, wherein the type of modulation for the OFDM symbol is determined to be rotated-binary phase shift keying (rotated-BPSK) if the result of the decision function is greater than β
, and wherein the type of modulation for the OFDM symbol is determined to be binary phase shift keying (BPSK) if the result of the decision function is less than β
.
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10. An apparatus comprising:
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a plurality of antennas; at least one receiver, coupled to the plurality of antennas, configured to receive a packet of data; and a central processor for determining whether the packet is a Legacy, Mixed-Mode, or Green-Field packet and for processing the packet in accordance with the determined type of packet, wherein the central processor determines whether the packet is the Legacy, Mixed-Mode, or Green-Field packet in accordance with a type of modulation by applying a decision function to a symbol on a subset of sub-carriers in a channel, the decision function is;
Σ
kε
Sx(yk,l),where yk,l is a result of multiplying an l-th symbol that is received on a k-th sub-carrier by a conjugate transpose of the k-th sub-carrier'"'"'s channel response, S is the subset of sub-carriers, and x(yk,l) is one of; arctangent of Im(yk,l)/Re(yk,l), |Im(yk,l)|n−
|Re(yk,l)|n, or|Re(yk,l)|n−
|Im(yk,l)|n,
where n is a variable,wherein the type of modulation for the symbol is rotated-binary phase shift keying (rotated-BPSK) if the result of the decision function is greater than β
, and wherein the type of modulation for the symbol is BPSK if the result of the decision function is less than β
, where β
is any of |S|/2, −
|S|/2, (Σ
kε
Shk*Akhk)/2, −
(Σ
kε
Shk*Akhk)/2, or zero and where hk is the overall channel response, and Ak is a diagonal matrix for scaling the symbol in accordance with different noise variances on the set of sub-carriers. - View Dependent Claims (11, 12, 13)
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14. A central processor comprising:
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a radio frequency RF and signal conditioning portion for receiving a packet; a synchronizer for detecting a preamble of the received packet; a fast Fourier transform (FFT) coupled to the synchronizer for performing a FFT transformation; a channel estimator for receiving results of the FFT transformation; a packet type detector coupled to FFT and the channel estimator for determining whether the received packet is a Legacy, Mixed-Mode, or Green-Field packet; and a packet processor configured to process the packet in accordance with the determination, the determination comprising; applying a decision function to a signal (SIG) field symbol following a legacy long training field (L-LTF) symbol of the packet for a subset of all of sub-carriers in a channel to determine a type of modulation for the SIG field symbol following the L-LTF symbol; determining that the packet is the Green-Field packet if the type of modulation for the SIG field symbol is a high throughput signal (HT-SIG) field symbol following the L-LTF symbol is a high throughput long training field (HT-LTF) symbol and is rotated-binary phase shift keying (rotated-BPSK); if the packet is not the Green-Field packet, applying the decision function to a symbol following a legacy signal (L-SIG) field symbol of the packet for the subset of all of the sub-carriers in the channel to determine a type of modulation for the symbol following the L-SIG field symbol; determining that the packet is the Mixed-Mode packet if the type of modulation for the symbol following the L-SIG field symbol is rotated-BPSK; and determining that the packet is the Legacy packet if the type of modulation for the symbol following the L-SIG field symbol is binary phase shift keying (BPSK), wherein the subset of sub-carriers includes sub-carriers from a predefined set of sub-carriers that are equally spaced in frequency or any of the sub-carriers in the channel that meet a criteria |a−
b|/c≧
α
wherein the parameters a, b, c, and α
are chosen to balance performance and complexity of the decision function, wherein the parameters a, b, and c are specified to define one of three metrics for a sub-carrier from the predefined set of sub-carriers;reliability of a set of data based on log likelihood ratio, effective SNR, or distance to a mean metric across all sub-carriers, wherein the parameter α
is specified such that the K sub-carriers with either the largest or smallest metrics comprise the subset, wherein when the parameters use a discriminator, the discriminator is one of;arctangent of Im(yk,l)/Re(mk,l), |Im(yk,l)|n−
|Re(yk,l)|n, or|Re(yk,l)|n−
|Im(yk,l)|n,where yk,l is a result of multiplying an l-th symbol that is received on a k-th sub-carrier by a conjugate transpose of a channel response of the k-th sub-carrier, and where n is a variable. - View Dependent Claims (15)
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16. A central processor comprising:
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a radio frequency RF and signal conditioning portion for receiving a packet; a synchronizer for detecting a preamble of the received packet; a fast Fourier transform (FFT) coupled to the synchronizer for performing FFT transformation; a channel estimator for receiving results of the FFT transformation; a packet type detector coupled to the FFT and the channel estimator, said packet type detector for determining whether the received packet is a Legacy, Mixed-Mode, or Green-Field packet; and a packet processor configured to process the packet in accordance with the determination, the determination comprising; applying a decision function to a signal (SIG) field symbol following an legacy long training field (L-LTF) symbol of the packet for a subset of all of sub-carriers in a channel to determine a type of modulation for the SIG field symbol following the L-LTF symbol, wherein the decision function for the SIG field symbol following the L-LTF symbol or the symbol following a legacy signal (L-SIG) field symbol is;
P−
N,
where P is the number of elements in the set
{k|kε
S and |xk|>
β
}, N is the number of elements in the set {k|kε
S and |xk|<
β
}, β
is any of |S|/2, −
|S|/2,
(Σ
kε
Shk*Akhk)/2, −
(Σ
kε
Shk*Akhk)/2, or zero and where hk is an overall channel response, Ak is a diagonal matrix for scaling the symbol in accordance with different noise variances on the set of sub-carriers, S is the subset of sub-carriers, and xk is one of;arctangent of Im(yk,l)/Re(mk,l), |Im(yk,l)|n−
|Re(yk,l)|n, or|Re(yk,l)|n−
|Im(yk,l)|n,
where yk,l is a result of multiplying an l-th symbol that is received on a k-th sub-carrier by a conjugate transpose of a channel response of the k-th sub-carrier, and where n is a variable,
wherein the type of modulation for the SIG field symbol following the L-LTF symbol or the symbol following the L-SIG field symbol is determined to be rotated-binary phase shift keying (rotated-BPSK) if the result of the decision function is greater than β
, and wherein the type of modulation for the SIG field symbol following the L-LTF symbol or the symbol following the L-SIG field symbol is determined to be binary phase shift keying (BPSK) if the result of the decision function is less than β
;determining that the packet is the Green-Field packet if the type of modulation for the SIG field symbol is a high throughput signal (HT-SIG) field symbol following the L-LTF symbol is a high throughput long training field (HT-LTF) symbol and is rotated-BPSK; if the packet is not the Green-Field packet, applying the decision function to a symbol following a legacy signal (L-SIG) field symbol of the packet for the subset of all of the sub-carriers in the channel to determine a type of modulation for the symbol following the L-SIG field symbol; determining that the packet is the Mixed-Mode packet if the type of modulation for the symbol following the L-SIG field symbol is rotated-BPSK; and determining that the packet is the Legacy packet if the type of modulation for the symbol following the L-SIG field symbol is BPSK. - View Dependent Claims (17)
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Specification