Wireless communication systems and methods for long-code communications for regenerative multiple user detection involving matched-filter outputs
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 spread-spectrum waveform for that user.
1. In a spread spectrum communication system that processes one or more spread-spectrum waveforms (“user spread-spectrum waveforms”), each representative of a waveform associated with a respective user, the improvement comprising:
a first logic element which generates an estimated composite spread-spectrum waveform that is a function of one or more of estimated complex amplitudes, estimated time lags, estimated symbols, and codes of the one or more user spread-spectrum waveforms,
one or more second logic elements each coupled to the first logic element, the one or more second logic elements generating a second matched-filter detection statistic for at least a selected user as a function of a difference between a first matched-filter detection statistic for that user and an estimated matched-filter detection statistic for that user as a function of the estimated composite spread-spectrum waveform.
2. The system of claim 1 , wherein the one or more second logic elements generate the second matched-filter detection statistic for at least the selected user as a function of a difference between (i) a sum of the first matched-filter detection statistic for that user and a characteristic of an estimate of the selected user's spread-spectrum waveform and (ii) the estimated matched-filter detection statistic for that user.
3. The system of claim 2 , 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.
4. The system of claim 1 , wherein the spread-spectrum communications system is a code division multiple access (CDMA) base station.
5. The system of claim 4 , wherein the CDMA base station comprises long-code receivers.
6. The system of claim 1 , wherein the first logic element comprises arithmetic logic which generates an estimated composite 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 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 c is a number of samples per chip, and
n is an iteration count.
7. The system of claim 6 , wherein the arithmetic logic further 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, and
g[t] represents a pulse shape.
8. The system of claim 1 , wherein the estimated composite spread-spectrum waveform is pulse-shaped and is based on the user spread-spectrum waveform.
9. The system of claim 1 , wherein each second logic element comprises rake logic and summation logic which generates the second matched-filter detection statistic based on the relation
y k (n+1) [m]=A k (n) 2 ·{circumflex over (b)} k (n) [m]+y k (n) [m]−y est,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 mth symbol period,
y k (n) [m] represents the first matched-filter detection statistic for the selected user,
y est,k (n) [m] represents the estimated matched-filter detection statistic for the selected user, and
n is an iteration count.
10. The system of claim 9 , wherein the system generates the second matched-filter detection statistic for the selected user and zero, one or more further second matched-filter detection statistics for that user iteratively.
11. The system of claim 1 , wherein the first matched-filter detection statistic for at least the selected user is generated by a long-code receiver.
12. The system of claim 1 , wherein the logic elements are implemented on any of processors, field programmable gate arrays, array processors and co-processors, or any combination thereof.
13. A method for multiple user detection in a spread-spectrum communication system that processes long-code spread-spectrum user waveforms, the improvement comprising a method of generating user matched-filter detection statistics for at least a selected user comprising:
generating a composite spread-spectrum waveform as a function of a pulsed-shaped composite re-spread waveform,
generating a refined user matched-filter detection statistic for at least the selected user that is a function of a difference between a first matched-filter detection statistic for that user and an estimated matched-filter detection statistic for that user
further comprising generating the refined matched-filter detection statistic for at least the selected user as a function of a difference between (i) the sum of the first matched-filter detection statistic for that user and a characteristic of an estimate of the selected user's spread-spectrum waveform and (ii) the estimated matched-filter detection statistic for that user.
14. The method of claim 13 , the further improvement wherein the characteristic is at least one of an estimated amplitude, and an estimated symbol associated with an estimate of the selected user's spread-spectrum waveform.
15. A method for multiple user detection in a spread-spectrum communication system that processes long-code spread-spectrum user waveforms, the improvement comprising a method of generating user matched-filter detection statistics for at least a selected user comprising:
generating a composite spread-spectrum waveform as a function of a pulsed-shaped commposite re-spread waveform,
generating a refined user matched-filter detection statistic for at least the selected user that is a function of a difference between a first matched-filter detection statistic for that user and an estimated matched-filter detection statistic for that user
wherein the step of generating the second 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 ·{circumflex over (b)} k (n) [m]+y k (n) [m]−y est,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 mth symbol period,
y k (n) [m] represents the first matched-filter detection statistic,
y est,k (n) [m] represents the estimated matched-filter detection statistic, and
n is an iteration count.
16. The method of claim 15 , wherein second matched-filter detection statistic is derived from the estimated composite spread-spectrum waveform based on the relation
y
est
,
k
(
n
)
[
m
]
≡
Re
{
∑
p
=
1
L
a
^
kp
(
n
)
H
·
1
2
N
k
∑
r
=
0
N
k
-
1
r
^
(
n
)
[
rN
c
+
τ
^
kp
(
n
)
+
mT
k
]
·
c
km
*
[
r
]
}
,
wherein
L is a number of multi-path components,
â kp (n) is an estimated complex channel amplitude for the p th multipath component for the k th user,
N k is a spreading factor for the k th user,
{circumflex over (r)} (n) [t] represents the estimated composite spread-spectrum waveform,
N c is a number of samples per chip, and
{circumflex over (τ)} kp (n) is an estimated time lag for the p th multipath component for the k th user,
m is a symbol period,
T k is a data bit duration,
n is an iteration count and
c km [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.