METHODS FOR CODEBOOK SUB-SAMPLING
Disclosed are methods for codebook sub-sampling. In various implementations, a wireless terminal receives a reference signal, determines, based on the reference signal, a first precoding index i 2 for a first subband and a second precoding index i′ 2 for a second subband. The wireless terminal transmits a representation of i 2 and a representation of 4 to a base station. In various implementations, i′ 2 belongs to the set S i 2 which, in one implementation, equals {mod(i 2 −K 1 k,K), k=0, 1, . . . , K 2 }, where K 1 >1, and where K 2 >1 and K>1 are integers. According to an implementation, the wireless terminal receives the reference signal from a first base station and transmits the representations of i 2 and i′ 2 to a second base station.
1 . A method in a wireless terminal, the method comprising:
receiving a reference signal from a first base station;
determining a first precoding index i 1 based on the reference signal, wherein i 1 is an index of a first codebook;
if a last reported Rank Indicator (RI) corresponds to rank 1, then transmitting, to a second base station, a report that includes an M bit representation of i 1 ; and
if the last reported RI corresponds to rank 2, then transmitting, to the second base station, a report that includes a K-bit representation of i 1 , wherein M<K.
2 . The method of claim 1 , further comprising:
determining a second precoding index i 2 based on the reference signal, wherein the second precoding index i 2 is an index of a second codebook, and wherein the first precoding index and second precoding index jointly determine a precoding matrix of a third codebook with a product structure.
3 . The method of claim 2 , wherein the third codebook comprises:
i 2
i 1
0
1
2
3
4
5
6
7
0-15
W i 1 ,0,0 (1)
W i 1 ,1,0 (1)
W i 1 ,2,0 (1)
W i 1 ,3,0 (1)
W i 1 +8,0,1 (1)
W i 1 +8,1,1 (1)
W i 1 +8,2,1 (1)
W i 1 +8,3,1 (1)
i 2
i 1
8
9
10
11
12
13
14
15
0-15
W i 1 +16,0,2 (1)
W i 1 +16,1,2 (1)
W i 1 +16,2,2 (1)
W i 1 +16,3,2 (1)
W i 1 +24,0,3 (1)
W i 1 +24,1,3 (1)
W i 1 +24,2,3 (1)
W i 1 +24,3,3 (1)
where
W
m
,
n
,
r
(
1
)
=
1
2
[
v
m
β
n
α
(
r
)
v
m
]
β
n
=
e
j
2
π
n
/
4
α
(
r
)
=
e
j
2
π
·
2
r
/
32
4 . The method of claim 2 , further comprising:
transmitting, to the second base station, a first report with a first periodicity, the first report including an RI; and
transmitting, to the second base station, a second report with a second periodicity, the second report including a representation of i 1 and i 2 .
5 . The method of claim 2 , further comprising:
transmitting, to the second base station, a first report with a first periodicity, the first report including an RI and a representation i 1 ; and
transmitting, to the second base station, a second report with a second periodicity, the second report including a representation of i 2 .
6 . The method of claim 2 , further comprising:
transmitting, to the second base station, a first report with a first periodicity, the first report including an RI and a precoder-type indication (PTI);
if a most recently transmitted PTI is set to 0, then transmitting, to the second base station, a second report with a periodicity based on a second periodicity, the second report including a representation of i 1 ; and
if the most recently transmitted PTI is set to 1, then transmitting, to the second base station, a second report with another periodicity based on the second periodicity, the second report including a representation of i 2 .
7 . A wireless terminal comprising:
at least one transceiver operative to receive a reference signal from a first base station; and
a controller, operatively coupled to the at least one transceiver operative to:
determine a first precoding index i 1 based on the reference signal, wherein i 1 is an index of a first codebook;
if a last reported Rank Indicator (RI) corresponds to rank 1, then transmitting, to a second base station, a report that includes an M bit representation of i 1 ; and
if the last reported RI corresponds to rank 2, then causing at least one transceiver to transmit, to the second base station, a report that includes a K-bit representation of i 1 , wherein M<K.
8 . The wireless terminal of claim 7 , wherein the controller further operates to:
determine a second precoding index i 2 based on the reference signal, wherein the second precoding index i 2 is an index of a second codebook, and wherein the first precoding index and second precoding index jointly determine a precoding matrix of a third codebook with a product structure.
9 . The wireless terminal of claim 8 , wherein the third codebook comprises:
i 2
i 1
0
1
2
3
4
5
6
7
0-15
W i 1 ,0,0 (1)
W i 1 ,1,0 (1)
W i 1 ,2,0 (1)
W i 1 ,3,0 (1)
W i 1 +8,0,1 (1)
W i 1 +8,1,1 (1)
W i 1 +8,2,1 (1)
W i 1 +8,3,1 (1)
i 2
i 1
8
9
10
11
12
13
14
15
0-15
W i 1 +16,0,2 (1)
W i 1 +16,1,2 (1)
W i 1 +16,2,2 (1)
W i 1 +16,3,2 (1)
W i 1 +24,0,3 (1)
W i 1 +24,1,3 (1)
W i 1 +24,2,3 (1)
W i 1 +24,3,3 (1)
where
W
m
,
n
,
r
(
1
)
=
1
2
[
v
m
β
n
α
(
r
)
v
m
]
β
n
=
e
j
2
π
n
/
4
α
(
r
)
=
e
j
2
π
·
2
r
/
32
10 . The wireless terminal of claim 8 , wherein the controller further operates to:
transmit, to the second base station, a first report with a first periodicity, the first report including an RI; and
transmit, to the second base station, a second report with a second periodicity, the second report including a representation of i 1 and i 2 .
11 . The wireless terminal of claim 8 , wherein the controller further operates to:
transmit, to the second base station, a first report with a first periodicity, the first report including an RI and a representation i 1 ; and
transmit, to the second base station, a second report with a second periodicity, the second report including a representation of i 2 .
12 . The wireless terminal of claim 8 , wherein the controller further operates to:
transmit, to the second base station, a first report with a first periodicity, the first report including an RI and a precoder-type indication (PTI);
if a most recently transmitted PTI is set to 0, then transmit, to the second base station, a second report with a periodicity based on a second periodicity, the second report including a representation of i 1 ; and
if the most recently transmitted PTI is set to 1, then transmit, to the second base station, a second report with another periodicity based on the second periodicity, the second report including a representation of i 2 .