Method of generating a codebook
A precoding codebook matrix/vector of length 2L is generated by the selection of two matrices/vectors, each from one of a predetermined set of L×L matrices and multiplying each column of one of the matrices/vectors by a complex coefficient.
1. A method for operating a primary station, the primary station comprising means for carrying out precoded MIMO transmissions to at least one secondary station, the method comprising:
generating a first precoding codebook comprising a plurality of matrices of length 2L with at least one entry of the form:
W
new
m
v
=
G
v
[
W
n
1
{
s
1
}
ϕ
3
{
s
3
}
W
n
3
{
s
3
}
ϕ
2
{
s
2
}
W
n
2
{
s
2
}
ϕ
4
{
s
4
}
W
n
4
{
s
4
}
]
wherein W new m ν is the precoding codebook entry for the first precoding codebook with index m and number of layers ν, being derived from a selection of four entries from a second codebook comprising a plurality of L×L matrices, the selected entries for a given value m being denoted by W n1 {s1} , W n2 {s2} , W n3 {s3} and W n4 {s4} respectively and defined by indices n1, n2, n3 and n4 to matrices in the second codebook and respective sets of one or more columns {s1}, {s2}, {s3} and {s4} thereof, where φ 2 {s2} , φ 3 {s3} and φ 4 {s4} are sets of one or more complex coefficients, which could be different per column and G, is a scaling factor.
2. The method of claim 1 , wherein L=4.
3. The method of claim 1 , wherein the complex coefficients are {0,1,−1,j,−j}.
4. The method of claim 1 , wherein the first precoding codebook is used regardless of the number of secondary stations communicating with the primary station in a MIMO mode.
5. The method of claim 1 , wherein {s1}={s2}, and {s3}={s4}.
6. The method of claim 5 , wherein A is an element of a Discrete Fourier Transform based codebook.
7. The method of claim 5 , wherein the set of phase differences consists of values φ m ε{1, j,−1,−j}.
8. The method of claim 1 , wherein the effective size of the first codebook is not the same for all values of transmission rank.
9. A primary station comprising:
one or more antennas; and
a circuit configured to:
generate a first precoding codebook comprising a plurality of matrices of length 2L with at least one entry of the form:
W
new
m
v
=
G
v
[
W
n
1
{
s
1
}
ϕ
3
{
s
3
}
W
n
3
{
s
3
}
ϕ
2
{
s
2
}
W
n
2
{
s
2
}
ϕ
4
{
s
4
}
W
n
4
{
s
4
}
]
wherein W new m ν is the precoding codebook entry for the first precoding codebook with index m and number of layers ν, being derived from a selection of four entries from a second codebook comprising a plurality of L×L matrices, the selected entries for a given value denoted by W n1 {s1} , W n2 {s2} , W n3 {s3} and W n4 {s4} respectively and defined by indices n1, n2, n3 and n4 to matrices in the second codebook and respective sets of one or more columns {s1}, {s2}, {s3}and {s4} thereof, where φ 2 {s2} , φ 3 {s3} and φ 4 {s4} are sets of one or more complex coefficients, which could be different per column and G ν is a scaling factor; and
transmit a precoded Multiple-Input Multiple-Output signal from a transmitter using the one or more antennas, based on the first precoding codebook.
10. The primary station of claim 9 , wherein the complex coefficients are {0,1,−1,j,−j}.
11. A secondary station comprising:
one or more antennas; and
a circuit configured to:
generate a first precoding codebook comprising a plurality of matrices of length 2L with at least one entry of the form:
W
new
m
v
=
G
v
[
W
n
1
{
s
1
}
ϕ
3
{
s
3
}
W
n
3
{
s
3
}
ϕ
2
{
s
2
}
W
n
2
{
s
2
}
ϕ
4
{
s
4
}
W
n
4
{
s
4
}
]
wherein W new m ν is the precoding codebook entry for the first precoding codebook with index m and number of layers ν, being derived from a selection of four entries from a second codebook comprising a plurality of L×L matrices, the selected entries for a given value denoted by W n1 {s1} , W n2 {s2} , W n3 {s3} and W n4 {s4} respectively and defined by indices n1, n2, n3 and n4 to matrices in the second codebook and respective sets of one or more columns {s1}, {s2}, {s3}and {s4} thereof, where φ 2 {s2} , φ 3 {s3} and φ 4 {s4} are sets of one or more complex coefficients, which could be different per column and G ν is a scaling factor; and
receive a transmission based on the first precoding codebook from a primary station using the one or more antennas.
12. A secondary station according to claim 11 , additionally comprising a circuit to transmit to a primary station an indication of an entry in the first precoding codebook that could be used by said primary station to transmit to the secondary station.