HARQ indicator determination
In order to determine whether a hybrid automatic repeat request (HARQ) indicator received by user equipment (UE) from a base station is an acknowledgment (ACK) or negative acknowledgement (NACK), when a signal representing the HARQ indicator is received by the UE, a plurality of symbols encoded in the received signal are determined to obtain a softbit for each of the symbols by summing an in-phase component and a quadrature component of each symbol. Thereafter, the softbits are summed up to be compared with the amplitude of the symbols to determine whether the HARQ indicator is an ACK or NACK.
1. A method for determining whether a hybrid automatic repeat request (HARQ) indicator received by user equipment (UE) from a base station is an acknowledgment (ACK) or negative acknowledgement (NACK), the method including the steps of:
receiving a signal representing the HARQ indicator transmitted from the base station to the UE,
determining the amplitude of a plurality of symbols encoded in the received signal,
determining a softbit for each of these symbols, each softbit being the sum of an in phase and quadrature component of the symbol,
summing the softbits, and
comparing the amplitude of the symbols to the sum of the softbits in order to determine whether the HARQ indicator is an ACK or NACK.
2. The method as claimed in claim 1 , wherein the amplitude of the symbols is multiplied by a fixed threshold before being compared to the sum of the softbits.
3. The method as claimed in claim 2 , wherein an ACK is indicated by the sum of the softbits being less than the amplitude of the symbols multiplied by a fixed threshold and a NACK is indicated by the sum of the softbits being equal to or greater than the amplitude of the symbols multiplied by a fixed threshold.
4. The method as claimed in claim 2 , wherein the fixed threshold is determined by simulations.
5. The method as claimed in claim 1 , wherein the amplitude of the symbols is calculated according to the formula:
Amp
=
∑
i
=
0
N
-
1
(
I
i
2
+
Q
i
2
)
where
Amp is the amplitude
N is the number of symbols
I is the in phase component of the de-scrambled signal
Q is the quadrature component of the de-scrambled signal.
6. The method as claimed in claim 1 , wherein the amplitude of the symbols is calculated according to the formula:
Amp
=
∑
i
=
0
N
-
1
[
max
(
I
i
,
Q
i
)
+
0.5
min
(
I
i
,
Q
i
)
]
where
Amp is the amplitude
N is the number of symbols
I is the in phase component of the de-scrambled signal
Q is the quadrature component of the de-scrambled signal.
7. The method as claimed in claim 1 , wherein the signal is transmitted on the physical hybrid automatic repeat request indicator channel (PHICH).
8. User equipment comprising:
a receiver which receives a signal representing a hybrid automatic repeat request (HARQ) indicator; and
a processor which determines whether the HARQ indicator is an acknowledgement (ACK) or negative acknowledgment (NACK);
wherein:
the processor comprises:
a portion which determines the amplitude of a plurality of symbols encoded in the received signal;
a portion which determines a softbit for each of these symbols, each softbit being the sum of an in phase and quadrature component of the symbol,
a portion which sums the softbits, and
a portion which compares the amplitude of the symbols to the sum of the softbits in order to determine whether the HARQ indicator is an ACK or NACK.
9. The user equipment as claimed in claim 8 , wherein the amplitude of the symbols is calculated according to the formula:
Amp
=
∑
i
=
0
N
-
1
(
I
i
2
+
Q
i
2
)
where
Amp is the amplitude
N is the number of symbols
I is the in phase component of the de-scrambled signal
Q is the quadrature component of the de-scrambled signal.
10. The user equipment as claimed in claim 8 , wherein the amplitude of the symbols is calculated according to the formula:
Amp
=
∑
i
=
0
N
-
1
[
max
(
I
i
,
Q
i
)
+
0.5
min
(
I
i
,
Q
i
)
]
where
Amp is the amplitude
N is the number of symbols
I is the in phase component of the de-scrambled signal
Q is the quadrature component of the de-scrambled signal.