ACK/NACK detection in LTE PUSCH
View Patent ↗The present invention relates to ACK-NACK detection in an LTE wireless communication system. To determine a threshold value for an ACK-NACK transmission, an SC-FDMA signal is received from user equipment. Then, a power estimate of soft data bits is used to establish a threshold value for determining the presence of an ACK-NACK signal. Using this threshold value, a signal from the user equipment is analyzed to determine if it contains an ACK or NACK transmission.
1. In a LTE wireless communication system, a method for determining the presence of an ACK or NACK transmission comprising:
receiving an SC-FDMA signal transmitted from user equipment;
using a power estimate of received random data bits that do not include a reference signal to establish, without involving an estimate of noise in the received random data bits, a threshold value for determining an ACK-NACK signal, wherein the received random data bits being received via a physical uplink shared channel and the power estimate being computed according to soft bits corresponding to the received random data bits; and
using the threshold value to determine if the transmitted signal from the user equipment contains an ACK or NACK transmission.
2. A method of determining the presence of an ACK or NACK transmission according to claim 1 wherein for an input, X n (i), of the i-th soft bit of the n-th data symbol, for i=0 to Q m −1 where Q m is a modulation level, the power estimate is calculated using the following equation:
P
RD
(
i
)
=
1
2
M
Data
∑
n
=
0
M
Data
-
1
(
X
n
(
2
i
)
2
+
X
n
(
2
i
+
1
)
2
)
,
for
i
=
0
,
…
,
Q
m
2
-
1
where M data is the number of data symbols to be used for the power estimation.
3. A method of determining the presence of an ACK or NACK transmission according to claim 1 wherein if the threshold value is not met, the transmission is determined to be DTX.
4. A method of determining the presence of an ACK or NACK transmission according to claim 3 wherein, based on the determination of an ACK or NACK or DTX transmission, the LTE system decides whether or not to retransmit a relevant downlink transport block.
5. A LTE wireless communication system comprising:
a base station for receiving SC-FDMA transmissions from user equipment; the base station including a receiver which includes:
a threshold computation module for calculating an ACK-NACK threshold value based on a power estimate of data bits received from the user equipment that do not contain a reference signal, without involving an estimate of noise in the data bits in the calculating of the threshold value, wherein the data bits being received via a physical uplink shared channel and the power estimate being computed according to soft bits corresponding to the data bits; and
an ACK-NACK detector that uses the threshold value to determine if the SC-FDMA signal received from the user equipment includes an ACK or NACK transmission.
6. A LTE wireless communication system according to claim 5 further comprising a data-control demultiplexer that separates data bits from bits which may contain ACK or NACK data.
7. A LTE wireless communication system according to claim 6 further comprising a modulation demapper.
8. A LTE wireless communication system according to claim 7 wherein the modulation demapper outputs the soft bits.
9. A LTE wireless communication system according to claim 8 further comprising a data descrambler and a HARQ descrambler.
10. A LTE wireless communication system according to claim 8 wherein the ACK-NACK detector comprises a soft decoder receiving the soft bits from the modulation demapper and a determination module for determining whether output from the soft decoder meets the threshold value computed in the threshold computation module.
11. A LTE wireless communication system according to claim 10 in which the soft decoder performs a calculation which, for an input, X n (i), of the i-th soft bit of the n-th data symbol, for i=0 to Q m −1 where Q m is a modulation level, the power estimate is calculated using the following equation:
P
RD
(
i
)
=
1
2
M
Data
∑
n
=
0
M
Data
-
1
(
X
n
(
2
i
)
2
+
X
n
(
2
i
+
1
)
2
)
,
for
i
=
0
,
…
,
Q
m
2
-
1
where M data is the number of data symbols to be used for the power estimate.
12. A LTE wireless communication system according to claim 5 wherein the base station is an evolved Node B.
13. In a LTE wireless communication system, a method for determining the presence of an ACK or NACK transmission comprising:
receiving an SC-FDMA signal transmitted from user equipment;
using a power estimate of received random data bits that do not include a reference signal to establish, without involving an estimate of noise in the received random data bits, a threshold value for determining an ACK-NACK signal; and
using the threshold value to determine if the transmitted signal from the user equipment contains an ACK or NACK transmission;
wherein for an input, X n (i), of the i-th soft bit of the n-th data symbol, for i=0 to Q m −1 where Q m is a modulation level, the power estimate is calculated using the following equation:
P
RD
(
i
)
=
1
2
M
Data
∑
n
=
0
M
Data
-
1
(
X
n
(
2
i
)
2
+
X
n
(
2
i
+
1
)
2
)
,
for
i
=
0
,
…
,
Q
m
2
-
1
where M data is the number of data symbols to be used for the power estimation.