Wireless communication systems and methods for long-code communications for regenerative multiple user detection involving implicit waveform subtraction
View Patent ↗The invention provides improved CDMA, WCDMA (UTMS) or other spread spectrum communication systems of the type that processes one or more spread-spectrum waveforms, each representative of a waveform received from a respective user (or other transmitting device). The improvement is characterized by a first logic element that generates a residual composite spread-spectrum waveform as a function of an arithmetic difference between a composite spread-spectrum waveform for all users (or other transmitters) and an estimated spread-spectrum waveform for each user. It is further characterized by one or more second logic elements that generate, for at least a selected user (or other transmitter), a refined spread-spectrum waveform as a function of a sum of the residual composite spread-spectrum waveform and the estimated spreads-spectrum waveform for that user.
1. A spread spectrum communication system of the type that processes one or more spread-spectrum waveforms (“user spread-spectrum waveforms”), each representative of a waveform associated with a respective user, comprising:
a first logic element that generates a residual composite spread-spectrum waveform as a function of an arithmetic difference between a composite spread-spectrum waveform and an estimated composite spread-spectrum waveform,
one or more second logic elements each coupled to the first logic element, each second logic element generating a refined matched-filter detection statistic for at least a selected user as a function of
(i) the residual composite spread-spectrum waveform and
(ii) a characteristic of an estimate of the selected user's spread-spectrum waveform
wherein each second logic element comprises rake logic and summation logic which generates the refined matched-filter detection statistics based on the relation
y k (n+1) [m]=A k (n) 2 ·{circumflex over (b)} k (n) [m]+y res,k (n) [m]
wherein
A k (n) 2 represents an amplitude statistic,
{circumflex over (b)} k (n) [m] represents a soft symbol estimate for the k th user for the m th symbol period,
y res,k (n) [m] represents a residual matched-filter detection statistic for the A th user, and
n is an iteration count.
2. The system of claim 1 , wherein the characteristic is at least one of an estimated amplitude and an estimated symbol associated with the estimate of the selected user's spread-spectrum waveform.
3. The system of claim 1 , wherein the spread-spectrum communications system comprises a code division multiple access (CDMA) base station.
4. The system of claim 1 , wherein the CDMA base station comprises one or more long-code receivers, and each long-code receiver generating one or more respective matched-filter detection statistics, from which the estimated composite spread-spectrum waveform is, in part, generated.
5. The system of claim 1 , wherein the first logic element comprises summation logic which generates the residual composite spread-spectrum waveform based on the relation
r res (n) [t]≡r[t]−{circumflex over (r)} (n) [t],
wherein
r res (n) [t] is the residual composite spread-spectrum waveform,
r[t] represents the composite spread-spectrum waveform,
{circumflex over (r)} (n) [t] represents the estimated composite spread-spectrum waveform,
t is a sample time period, and
n is an iteration count.
6. The system of claim 5 , wherein the estimated composite spread-spectrum waveform is pulse-shaped and is based on estimated complex amplitudes, estimated delay lags, estimated symbols, and codes of the one or more user spread-spectrum waveforms.
7. The system of claim 1 , wherein the refined matched-filter detection statistic for each user is iteratively generated.
8. The system of claim 1 , wherein the refined matched-filter detection statistic for at least a selected user is generated by a long-code receiver.
9. The system of claim 1 , wherein the first and second logic elements are implemented on any of processors, field programmable gate arrays, array processors and co-processors, or any combination thereof.
10. A spread spectrum communication system of the type that processes one or more user spread-spectrum waveforms, each representative of a waveform associated with a respective user, comprising:
a first logic element which generates an estimated composite spread-spectrum waveform that is a function of estimated user complex channel amplitudes, time lags, and user codes,
a second logic element coupled to the first logic element, the second logic element generating a residual composite spread-spectrum waveform as a function of an arithmetic difference between a composite user spread-spectrum waveform and the estimated composite spread-spectrum waveform,
one or more third logic elements each coupled to the second logic element, the third logic element generating a refined matched filer detection statistic for at least a selected user as a function of
(i) the residual composite spread-spectrum waveform and
(ii) a characteristic of an estimate of the selected user's spread-spectrum waveform
wherein the first logic element further comprises arithmetic logic which generates the estimated composite spread-spectrum waveform based on the relation
r
^
(
n
)
[
t
]
=
∑
r
g
[
r
]
ρ
(
n
)
[
t
-
r
]
,
wherein
{circumflex over (r)} (n) [t] represents the estimated composite spread-spectrum waveform,
p (n) [t-r] represents an estimated composite re-spaced waveform,
g[r] represents a raised-cosine pulse shape.
11. The system of claim 10 , wherein the characteristic is at least one of an estimated amplitude, an estimated delay lag and an estimated symbol associated with the estimate of the selected user's spread-spectrum waveform.
12. The system of claim 10 , wherein the spread-spectrum communications system is a code division multiple access (CDMA) base station.
13. The system of claim 12 , wherein the CDMA base station comprises long-code receivers.
14. The system of claim 10 , wherein the first logic element comprises arithmetic logic which generates an estimated composite re-spread waveform based on the relation
ρ
(
n
)
[
t
]
=
∑
k
=
1
K
v
∑
p
=
1
L
∑
r
δ
[
t
-
τ
^
kp
(
n
)
-
rN
c
]
·
a
^
kp
(
n
)
·
c
k
[
r
]
·
b
^
k
(
n
)
[
⌊
r
/
N
k
⌋
]
,
wherein
K v is a number of simultaneous dedicated physical channels for all users,
δ[t] is a discrete-time delta function,
{circumflex over (α)} kp (n) is an estimated complex channel amplitude for the p th multipath component for the k th user,
c k [r] represents a user code comprising at least a scrambling code, an orthogonal variable spreading factor code, and a j factor associated with even numbered dedicated physical channels,
{circumflex over (b)} k (n) [m] represents a soft symbol estimate for the k th user for the m th symbol period,
{circumflex over (τ)} kp (n) is an estimated time lag for the p th th multipath component for the k th user,
N k is a spreading factor for the k th user,
t is a sample time index,
L is a number of multi-path components,
N o is a number of samples per chip, and
n is an iteration count.
15. The system of claim 10 , wherein the second logic element comprises summation logic which generates the residual composite spread-spectrum waveform that based on the relation
r res (n) [t]≡r[t]−{circumflex over (r)} (n) [t],
wherein
r res (n) [t] is the residual composite spread-spectrum waveform,
r[t] represents the composite spread-spectrum waveform,
{circumflex over (r)} (n) [t] represents the estimated composite spread-spectrum waveform,
t is a sample time period, and
n is an iteration count.
16. The system of claim 15 , wherein the estimated composite spread-spectrum waveform is pulse-shaped and is based on the user spread-spectrum waveform.
17. A spread spectrum communication system of the type that processes one or more user spread-spectrum waveforms, each representative of a waveform associated with a respective user, comprising:
a first logic element which generates an estimated composite spread-spectrum waveform that is a function of estimated user complex channel amplitudes, time lags, and user codes,
a second logic element coupled to the first logic element, the second logic element generating a residual composite spread-spectrum waveform as a function of an arithmetic difference between a composite user spread-spectrum waveform and the estimated composite spread-spectrum waveform,
one or more third logic elements each coupled to the second logic element, the third logic element generating a refined matched-filter detection statistic for at least a selected user as a function of
(i) the residual composite spread-spectrum waveform and
(ii) a characteristic of an estimate of the selected user's spread-spectrum waveform
wherein the second logic element comprises summation logic which generates the residual composite spread-spectrum waveform that based on the relation
r res (n) [t]≡r[t]−{circumflex over (r)} (n) [t],
wherein
r res (n) [t] is the residual composite spread-spectrum waveform,
r[t] represents the composite spread-spectrum waveform,
{circumflex over (r)} (n) [t] represents the estimated composite spread-spectrum waveform,
t is a sample time period, and
n is an iteration count
wherein the estimated composite spread-spectrum waveform is pulse-shaped and is based on the user spread-spectrum waveform
wherein each third logic element comprises rake logic and summation logic which generates the second user matched-filter detection statistic based on the relation
y k (n+1) [m]=A k (n) 2 ·{circumflex over (b)} k (n) [m]+y res,k (n) [m],
wherein
A k (n) 2 represents an amplitude statistic,
{circumflex over (b)} k (n) [m] represents a soft symbol estimate for the k th user for the m th symbol period,
y res,k (n) [m] represents the user residual matched-filter detection statistic for the m th symbol period, and
n is an iteration count.
18. The system of claim 10 , wherein the refined matched-filter detection statistic for each user is iteratively generated.
19. The system of claim 10 , wherein the logic elements are implemented on any of a processors, field programmable gate arrays, array processors and co-processors, or any combination thereof.
20. A method for multiple user detection in a spread-spectrum communication system the processes long-code spread-spectrum user transmitted waveforms comprising:
generating a residual composite spread-spectrum waveform as a function of an arithmetic difference between a composite spread-spectrum waveform and an estimated composite spread-spectrum waveform,
generating a refined matched-filter detection statistic that is a function of a sum of a rake-processed residual composite spread-spectrum waveform for a selected user and an amplitude statistic for that selected user, and
determining one or more symbols transmitted by at least one of the users based on the refined matched-filter detection statistic,
wherein the step of generating the refined matched-filter detection statistic representative of that user further comprises performing arithmetic logic based on the relation
y k (n+1) [m]=A k (n) 2 ·b k (n) [m]+y rex,k (n) [m]
wherein
A k (n) 2 represents an amplitude statistic,
{circumflex over (b)} k (n) [m] represents a soft symbol estimate for the k th user for the m th symbol period,
y res,k (n) [m] represents a residual matched-filter detection statistics, and
n is an iteration count.
21. The method of claim 20 , comprising generating a refined matched-filter detection statistic that is a function of a sum of a rake-processed residual composite spread-spectrum waveform for a selected user and an amplitude statistic for that selected user multiplied by a soft symbol estimate.
22. The method of claim 20 , further wherein the spread-spectrum communications system is a code division multiple access (CDMA) base station.
23. The method of claim 20 , wherein the step of generating the residual composite spread-spectrum waveform further comprises performing arithmetic logic that is based on the relation
r res (n) [t]≡r[t]−{circumflex over (r)} (n) [r],
wherein
r res (n) [t] is the residual composite spread-spectrum waveform,
r[t] represents the composite spread-spectrum waveform,
{circumflex over (r)} (n) [t] represents the estimated composite spread-spectrum waveform,
t is a sample time period, and
n is an iteration count.
24. The method of claim 20 , wherein the estimated composite spread-spectrum waveform is pulse-shaped and is based on a composite user re-spread waveform.
25. The method of claim 20 , the further improvement wherein the refined matched-filter detection statistic is generated by a long-code receiver.
26. A method for multiple user detection in a spread-spectrum communication system that processes long-code spread-spectrum user transmitted waveforms comprising:
generating a residual composite spread-spectrum waveform as a function of an arithmetic difference between a composite spread-spectrum waveform and an estimated composite spread-spectrum waveform,
generating a refined matched-filter detection statistic that is a function of a sum of a rake-processed residual composite spread-spectrum waveform for a selected user and an amplitude statistic for that selected user, and
determining one or more symbols transmitted by at least one of the users based on the refined matched-filter detection statistic,
wherein the step of generating the residual matched-filter detection statistic for an m th symbol period comprises performing arithmetic logic based on the relation
y
res
,
k
(
n
)
[
m
]
≡
Re
{
∑
p
=
1
L
a
^
kp
(
n
)
H
·
1
2
N
k
∑
r
=
0
N
λ
-
1
r
res
(
n
)
[
rN
c
+
τ
^
kp
(
n
)
+
mT
k
]
·
c
km
*
[
r
]
}
wherein
y res,k (n) [m] represents the user residual matched-filter detection statistic for the m th symbol period,
L is a number of multi-path components,
a ^(n)H kn is the estimated complex channel amplitude for the p th multipath component for the k th user,
N k is the spreading factor for the k th user,
r res (n) [t] is the residual composite spread-spectrum waveform,
N c is the number of samples per chip, and
{circumflex over (τ)} kp (n) is the time lag for the p th multipath component for the k th user,
m is a symbol period,
T k is a channel symbol duration for the k th user,
c* km [r] represents a complex conjugate of a user code comprising at least a scrambling code, an orthogonal variable spreading factor code, and a j factor associated with even numbered dedicated physical channels,
n is an iteration count.