Methods and apparatus using precoding matrices in a MIMO telecommunications system
The present invention provides methods and apparatus for transmitting and receiving over a MIMO radio link. In particular, a preceding matrix is applied to transmitted signals and constrained in such a way so as to limit the additional peak to average power ratio (PAPR) caused by applying the precoding matrix. For example, each row of the precoding matrix may have at least one zero element and one non-zero element, and each column may have at least one non-zero element.
1. A communication device adapted for single-carrier transmission over a MIMO radio link, the communication device comprising:
a transmitter comprising a plurality of antennas; and
processing circuitry,
said processing circuitry being adapted for single-carrier transmission and to apply a precoding matrix to a symbol vector to generate a precoded vector,
said precoding matrix having four rows and two or three columns,
said transmitter being adapted to transmit said precoded vector over a MIMO radio link using only a single carrier, wherein
said precoding matrix is constrained such that each row comprises at least one zero element, such that the number of non-zero elements in each row is less than the number of columns in said precoding matrix, and
said precoding matrix is further constrained in that each of said columns has at least one non-zero element and each of said rows has at least one non-zero element.
2. The communication device as claimed in claim 1 , wherein said precoding matrix is constrained such that each row has a single non-zero element.
3. The communication device as claimed in claim 2 , wherein the precoding matrix has two columns, and wherein said precoding matrix is constrained such that each column has the same number of non-zero elements.
4. The communication device as claimed in claim 1 , wherein said precoding matrix is constrained such that each column has the same number of non-zero elements.
5. The communication device as claimed in claim 1 , wherein each non-zero element has the same absolute value.
6. The communication device as claimed in claim 1 , wherein said precoding matrix is selected from a codebook comprising a plurality of predetermined precoding matrices.
7. The communication device as claimed in claim 6 , wherein a subset of said plurality of predetermined precoding matrices are constrained.
8. The communication device as claimed in claim 1 , wherein said processing circuitry is adapted for discrete Fourier transform spread orthogonal frequency division multiplexed (DFTS-OFDM) transmissions.
9. The communication device as claimed in claim 1 , wherein said communication device is a user equipment.
10. The communication device as claimed in claim 1 , wherein said communication device is a radio base station.
11. A method in a communication device of single-carrier transmission over a MIMO radio link for limiting increase in peak to average power ratio (PAPR), comprising:
applying a precoding matrix to a symbol vector, generating a precoded vector; and
transmitting the precoded vector over the MIMO radio link using only a single carrier, wherein
said precoding matrix has four rows and two or three columns,
said precoding matrix is constrained such that each row comprises at least one zero element, such that the number of non-zero elements in each row is less than the number of columns in said precoding matrix, and
said precoding matrix is further constrained in that each of said columns has at least one non-zero element and each of said rows has at least one non-zero element.
12. The method as claimed in claim 11 , wherein said precoding matrix is further constrained such that each row has a single non-zero element.
13. The method as claimed in claim 12 , wherein the precoding matrix has two columns, and wherein said precoding matrix is constrained such that each column has the same number of non-zero elements.
14. The method as claimed in claim 11 , wherein said precoding matrix is constrained such that each column has the same number of non-zero elements.
15. The method as claimed in claim 11 , wherein each non-zero element has the same absolute value.
16. The method as claimed in claim 11 , wherein said precoding matrix is selected from a codebook comprising a plurality of predetermined precoding matrices.
17. The method as claimed in claim 16 , wherein a subset of said plurality of predetermined precoding matrices are constrained.