Multi-mode quadrature amplitude modulation receiver for high rate wireless personal area networks
View Patent ↗A wireless transceiver includes a Radio Frequency (RF) transceiver, a baseband transmitter section, and a baseband receiver section. The baseband receiver section receives a baseband signal from the RF transceiver, extracts data therefrom, and provides the data to a host system. The baseband receiver section includes a programmable gain amplifier, an Analog-to-Digital Converter (ADC), a symbol timing compensation section, an RF carrier compensation section, a decision feedback equalizer section, and a preamble processor. The symbol timing compensation section modifies the samples of the baseband signal to compensate for symbol timing variations between a symbol clock of the wireless device and a symbol clock of a transmitting wireless device. The RF carrier compensation section modifies the samples of the baseband signal to compensate for RF carrier variations between an RF carrier of the wireless device and an RF carrier of the transmitting wireless device. The preamble processor determines a PGA gain factor, initial settings for the RF carrier compensation section, and equalizer coefficients.
1. A baseband receiver section of a wireless device that couples to a Radio Frequency (RF) transceiver of the wireless device and that extracts data from a baseband signal received from the RF transceiver of the wireless device, the baseband receiver section comprising:
a programmable gain amplifier that receives the baseband signal and adjusts the gain of the baseband signal;
an Analog-to-Digital Converter (ADC) that receives the baseband signal from the programmable gain amplifier and that samples the baseband signal to produce samples of the baseband signal;
a symbol timing compensation section that modifies the samples of the baseband signal to compensate for symbol timing variations between a symbol clock of the wireless device and a symbol clock of a transmitting wireless device;
an RF carrier compensation section that modifies the samples of the baseband signal to compensate for RF carrier variations between an RF carrier of the wireless device and an RF carrier of the transmitting wireless device, wherein the RF carrier compensation section comprises:
a tentative decision block that determines an error in a tentative decision according to:
Im
{
z
n
b
n
*
}
b
n
2
where:
z n is the input to the tentative decision block; and
b n is the output of the tentative decision block; and
a carrier tracking block that uses the error in the tentative decision to determine an adjustment operator e −jΨ(n) is used to modify the samples of the baseband signal;
a decision feedback equalizer that filters the modified samples of the baseband signal and extracts the data from the modified samples of the baseband signal; and
a preamble processor that receives samples of the baseband signal corresponding to a preamble of a frame that carries the data and, based upon the samples of the preamble:
estimates a gain to be applied by the programmable gain amplifier;
estimates initial settings for the RF carrier compensation section; and
estimates equalizer coefficients for the decision feedback equalizer.
2. The baseband receiver section of claim 1 , wherein the preamble comprises a plurality of periods of a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence.
3. The baseband receiver section of claim 1 , wherein:
the preamble processor characterizes a channel between the wireless device and the transmitting wireless device based upon the preamble; and
the preamble processor determines the equalizer coefficients based upon an estimate of the wireless channel.
4. The baseband receiver section of claim 1 , wherein the baseband signal is coded in one of Binary Phase Shift Keying, Quadrature Phase Shift Keying, 16 Quadrature Amplitude Modulation, 32 Quadrature Amplitude Modulation, and 64 Quadrature Amplitude Modulation.
5. The baseband receiver section of claim 4 , wherein the baseband signal is also coded using Trellis Code Modulation.
6. The baseband receiver section of claim 1 , wherein the adjustment operator
ⅇ
-
jΨ
(
n
)
is determined according to:
Ψ
(
n
+
1
)
=
Ψ
(
n
)
-
y
·
Im
{
z
n
b
n
*
}
b
n
2
+
2
π
f
c
·
Δ
^
f
(
n
)
where
:
Δ
^
f
(
n
)
=
Δ
^
f
(
n
-
1
)
-
α
·
Im
{
z
n
b
n
*
}
b
n
2
;
γ is a constant;
α is a constant; and
f c is the RF carrier frequency.
7. The baseband receiver section of claim 1 , wherein the symbol timing compensation section comprises:
a tentative decision block that determines an error in a tentative decision;
a timing update section that generates a timing update based upon the error in the tentative decision; and
a cubic interpolator/resampler coupled to the output of the ADC that resamples the baseband signal based upon the timing update.
8. A baseband receiver section of a wireless device that couples to a Radio Frequency (RF) transceiver of the wireless device and that extracts data from a baseband signal received from the RF transceiver of the wireless device, the baseband receiver section comprising:
a programmable gain amplifier that receives the baseband signal and adjusts the gain of the baseband signal;
an Analog-to-Digital Converter (ADC) that receives the baseband signal from the programmable gain amplifier and that samples the baseband signal to produce samples of the baseband signal;
a symbol timing compensation section that modifies the samples of the baseband signal to compensate for symbol timing variations between a symbol clock of the wireless device and a symbol clock of a transmitting wireless device, the symbol timing compensation section comprising:
a tentative decision block that determines an error in a tentative decision;
a timing update section that generates a timing update based upon the error in the tentative decision, wherein the timing update is determined according to:
Re {( z n −z n−2 )·e n−1 *}
where:
z n is the input to the tentative decision block; and
e n is the error in the tentative decision; and
a cubic interpolator/resampler coupled to the output of the ADC that resamples the baseband signal based upon the timing update;
an RF carrier compensation section that modifies the samples of the baseband signal to compensate for RF carrier variations between an RF carrier of the wireless device and an RE carrier of the transmitting wireless device;
a decision feedback equalizer that filters the modified samples of the baseband signal and extracts the data from the modified samples of the baseband signal; and
a preamble processor that receives samples of the baseband signal corresponding to a preamble of a frame that carries the data and, based upon the samples of the preamble:
estimates a gain to be applied by the programmable gain amplifier;
estimates initial settings for the RE carrier compensation section; and
estimates equalizer coefficients for the decision feedback equalizer.
9. The baseband receiver section of claim 8 , wherein the samples of the baseband signal output by the ADC are resampled by the cubic interpolator/resampler according to:
mod
1
2
f
s
′
(
T
(
n
)
)
where
:
T
(
n
+
1
)
=
T
(
n
)
+
1
2
f
s
′
-
Υ
·
Re
{
(
z
n
-
z
n
-
2
)
·
e
n
-
1
*
}
+
Δ
T
(
n
)
;
Δ
T
(
n
)
=
Δ
T
(
n
-
1
)
-
α
·
Re
{
(
z
n
-
z
n
-
2
)
·
e
n
-
1
*
)
;
γ is a constant;
α is a constant; and
f′ s is the symbol clock frequency.
10. The baseband receiver section of claim 9 , wherein the cubic interpolator/resampler resamples the baseband signal further according to:
h
-
2
(
μ
n
)
=
(
μ
n
+
1
)
·
μ
n
·
(
μ
n
-
1
)
6
;
h
-
1
(
μ
n
)
=
(
μ
n
+
1
)
·
μ
n
·
(
μ
n
-
2
)
-
2
;
h
0
(
μ
n
)
=
(
μ
n
+
1
)
·
(
μ
n
-
1
)
·
(
μ
n
-
2
)
2
;
and
h
1
(
μ
n
)
=
μ
n
·
(
μ
n
-
1
)
·
(
μ
n
-
2
)
-
6
.
11. A method for extracting data from a received baseband signal, the method comprising:
based upon a preamble of a frame that carries the data:
estimating a gain factor;
estimating initial RF carrier compensation section settings; and
estimating equalizer coefficients;
adjusting the gain of the baseband signal by the gain factor;
sampling the baseband signal to produce samples of the baseband signal;
modifying the samples of the baseband signal to compensate for symbol timing variations between a symbol clock of a receiving wireless device and a symbol clock of a transmitting wireless device;
modifying the samples of the baseband signal to compensate for RF carrier variations between an RF carrier of the receiving wireless device and an RF carrier of the transmitting wireless device, wherein the samples of the baseband signal are modified to compensate for RF carrier variations by:
determining an error in a tentative decision according to:
Im
{
z
n
b
n
*
}
b
n
2
where:
z n is the input to the tentative decision block; and
b n is the output of the tentative decision block; and
modifying the samples of the baseband signal by an adjustment operator e −jΨ(n) ;
filtering the modified samples of the baseband signal using the equalizer coefficients; and
extracting the data from the modified samples of the baseband signal.
12. The method of claim 11 , wherein the preamble comprises a plurality of periods of a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence.
13. The method of claim 12 , wherein:
the preamble processor estimates a channel between the wireless device and the transmitting wireless device based upon the preamble; and
the preamble processor estimates the equalizer coefficients based upon an estimate of the wireless channel.
14. The method of claim 11 , wherein the baseband signal is coded in one of Binary Phase Shift Keying, Quadrature Phase Shift Keying, 16 Quadrature Amplitude Modulation, 32 Quadrature Amplitude Modulation, and 64 Quadrature Amplitude Modulation.
15. The method of claim 14 , wherein the baseband signal is also coded using Trellis Code Modulation.
16. The method of claim 11 , wherein the adjustment operator e −jΨ(n) is determined according to:
Ψ
(
n
+
1
)
=
Ψ
(
n
)
-
Υ
·
Im
{
z
n
b
n
*
}
b
n
2
+
2
π
f
c
·
Δ
^
f
(
n
)
where
:
Δ
^
f
(
n
)
=
Δ
^
f
(
n
-
1
)
-
α
·
Im
{
z
n
b
n
*
}
b
n
2
;
γ is a constant;
α is a constant; and
f c is the RF carrier frequency.
17. The method of claim 11 , wherein the samples of the baseband signal are modified to compensate for symbol timing variations by:
determining an error in a tentative decision;
generating a timing update based upon the error in the tentative decision; and
resampling the baseband signal based the timing update.
18. A method for extracting data from a received baseband signal, the method comprising:
based upon a preamble of a frame that carries the data:
estimating a gain factor;
estimating initial RF carrier compensation section settings; and
estimating equalizer coefficients;
adjusting the gain of the baseband signal by the gain factor;
sampling the baseband signal to produce samples of the baseband signal;
modifying the samples of the baseband signal to compensate for symbol timing variations between a symbol clock of a receiving wireless device and a symbol clock of a transmitting wireless device, wherein the samples of the baseband signal are modified to compensate for symbol timing variations by:
determining an error in a tentative decision;
generating a timing update based upon the error in the tentative decision,
wherein the timing update is determined according to:
Re {( z n −z n−2 )·e n−1 *}
where:
z n is the input to the tentative decision block; and
e n is the error in the tentative decision; and
resampling the baseband signal based upon the timing update;
modifying the samples of the baseband signal to compensate for RF carrier variations between an RF carrier of the receiving wireless device and an RF carrier of the transmitting wireless device;
filtering the modified samples of the baseband signal using the equalizer coefficients; and
extracting the data from the modified samples of the baseband signal.
19. The method of claim 18 , wherein the samples of the baseband signal are resampled according to:
mod
1
2
f
s
′
(
T
(
n
)
)
where
:
T
(
n
+
1
)
=
T
(
n
)
+
1
2
f
s
′
-
Υ
·
Re
{
(
z
n
-
z
n
-
2
)
·
e
n
-
1
*
}
+
Δ
T
(
n
)
;
Δ
T
(
n
)
=
Δ
T
(
n
-
1
)
-
α
·
Re
{
(
z
n
-
z
n
-
2
)
·
e
n
-
1
*
)
;
γ is a constant;
α is a constant; and
f′ s is the symbol clock frequency.
20. The method of claim 19 , wherein the samples of the baseband signal are resampled by cubically interpolating the baseband signal according to:
h
-
2
(
μ
n
)
=
(
μ
n
+
1
)
·
μ
n
·
(
μ
n
-
1
)
6
;
h
-
1
(
μ
n
)
=
(
μ
n
+
1
)
·
μ
n
·
(
μ
n
-
2
)
-
2
;
h
0
(
μ
n
)
=
(
μ
n
+
1
)
·
(
μ
n
-
1
)
·
(
μ
n
-
2
)
2
;
and
h
1
(
μ
n
)
=
μ
n
·
(
μ
n
-
1
)
·
(
μ
n
-
2
)
-
6
.