Method for precoding using a block diagonal matrix
An objective problem of the invention is to provide a mechanism for improving the performance of a radio access network. According to a first aspect of the present invention, the object is achieved by a method in a first node for adapting a multi-antenna transmission to a second node over an effective channel. The first node and the second node are comprised in a wireless communication system. The method comprises the steps of obtaining at least one symbol stream and determining a precoding matrix having a block diagonal structure. The method comprises the further steps of precoding the at least one symbol stream with the determined precoding matrix, and transmitting the at least one precoded symbol stream over the effective channel to the second node.
1. A method in a first node for adapting a multi-antenna transmission to a second node over an effective channel, the effective channel having multiple inputs and at least one output, the first node and the second node being included in a wireless communication system, the method comprising the steps of:
obtaining at least one symbol stream;
determining a precoding matrix, wherein the precoding matrix matches the effective channel which is block diagonal and the precoding matrix has a corresponding block diagonal structure, and wherein the effective channel is intentionally set up to be block-diagonal by arranging a first antenna setup in the first multi-antenna system or a second antenna setup in the second multi-antenna system to obtain the block diagonal effective channel without tracking instantaneous channel conditions of a physical channel;
precoding the at least one symbol stream with the determined precoding matrix to improve radio link performance of the effective channel; and
transmitting the precoded at least one symbol stream over the effective channel to the second node.
2. The method according to claim 1 , wherein the effective channel comprises more than two inputs.
3. The method according to claim 2 , wherein the step of obtaining at least one symbol stream involves performing transmission rank adaptation by selecting the number of symbol streams to match the characteristics of the effective channel.
4. The method according to claim 1 , wherein the precoded at least one symbol stream from the first node is transmitted using the first multi-antenna system with a cross-polarized antenna set-up and the precoded at least one symbol stream is received in the second node by the second multi-antenna system, wherein the first and second multi-antenna systems result in an intentionally block diagonal effective channel matrix.
5. The method according to claim 1 , wherein the first and the second antenna setup are arranged to obtain the block diagonal effective channel without any processing in spatial domain at the first node after encoding and without any processing in spatial domain at the second node before decoding, and wherein said processing in spatial domain depends on the instantaneous channel conditions determined by the fast fading introduced by the physical channel.
6. The method according claim 1 , wherein the precoding matrix is determined to match the effective channel by adopting a similar block diagonal structure as the effective channel.
7. The method according to claim 6 , wherein the precoding matrix has a block diagonal structure similar to the block diagonal structure of the effective channel when each on-diagonal block in the precoding matrix has the same number of rows as its corresponding block in the block diagonal structure of the effective channel.
8. The method according to claim 7 , wherein one or more on-diagonal blocks in the precoding matrix have a different number of columns than the corresponding blocks in the block diagonal structure of the effective channel.
9. The method of claim 1 , wherein the effective channel is considered to be block diagonal when an effective channel matrix modeling the effective channel can be rearranged via row or column permutations to have a form in which the average powers of the channel coefficients in off-diagonal blocks are significantly lower than the average powers of the channel coefficients in on-diagonal blocks.
10. A method in a second node for assisting a first node in the adaptation of a multi-antenna transmission from the first node to the second node over an effective channel, the effective channel having multiple inputs and at least one output, the first node and the second node being included in a wireless communication system, the method comprising the steps of:
selecting a precoding matrix to match the effective channel, wherein the effective channel is block diagonal and the selected precoding matrix has a corresponding block diagonal structure, and wherein the effective channel is intentionally set up to be block-diagonal by arranging a first antenna setup in the first multi-antenna system or a second antenna setup in the second multi-antenna system to obtain the block diagonal effective channel without tracking instantaneous channel conditions of a physical channel;
conveying information regarding the selected precoding matrix to the first node; and
receiving at least one precoded symbol stream over the effective channel transmitted from the first node, wherein the received at least one symbol stream is precoded with the selected precoding matrix in the first node.
11. The method according to claim 10 , wherein the effective channel comprises more than two inputs.
12. The method according to claim 10 , wherein the effective channel comprises at least two outputs.
13. The method according to claim 10 , wherein the precoded at least one symbol stream from the first node is transmitted using the first multi-antenna system with a cross-polarized antenna set-up and the precoded at least one symbol stream is received in the second node by the second multi-antenna system, wherein the first and second multi-antenna systems result in an intentionally block diagonal effective channel matrix.
14. The method according to claim 10 , wherein the first and the second antenna setup are arranged to obtain the block diagonal effective channel without any processing in spatial domain at the first node after encoding and without any processing in spatial domain at the second node before decoding, and wherein said processing in spatial domain depends on the instantaneous channel conditions determined by the fast fading introduced by the physical channel.
15. The method according claim 10 , wherein the precoding matrix is selected to match the effective channel by adopting a similar block diagonal structure as the effective channel.
16. The method according to claim 15 , wherein the precoding matrix has a block diagonal structure similar to the block diagonal structure of the effective channel when each on-diagonal block in the precoding matrix has the same number of rows as its corresponding block in the block diagonal structure of the effective channel.
17. The method according to claim 16 , wherein one or more on-diagonal blocks in the precoding matrix have a different number of columns than the corresponding blocks in the block diagonal structure of the effective channel.
18. The method according to claim 10 , wherein the precoding matrix is selected to maximize a predicted throughput at reception of the transmission of the at least one precoded symbol stream from the first node.
19. The method according to claim 10 , wherein the precoding matrix is selected to maximize the Signal to Noise Ratio at reception of the transmission of the at least one precoded symbol stream from the first node.
20. The method of claim 10 , wherein the effective channel is considered to be block diagonal when an effective channel matrix modeling the effective channel can be rearranged via row or column permutations to have a form in which the average powers of the channel coefficients in off-diagonal blocks are significantly lower than the average powers of the channel coefficients in on-diagonal blocks.
21. A first node, the first node being arranged to adapt a multi-antenna transmission to a second node over an effective channel, the effective channel having multiple inputs and at least one output, the first node and the second node being comprised in a wireless communication system, the first node comprising:
an obtaining circuit configured to obtain at least one symbol stream;
a determination circuit configured to determine a precoding matrix, wherein the precoding matrix matches the effective channel which is block diagonal and the precoding matrix has a corresponding block diagonal structure, and wherein the effective channel is intentionally set up to be block-diagonal by arranging a first antenna setup in the first multi-antenna system or a second antenna setup in the second multi-antenna system to obtain the block diagonal effective channel without tracking instantaneous channel conditions of a physical channel;
a precoding circuit configured to precode the at least one symbol stream with the determined precoding matrix; and
a transmission circuit configured to transmit the precoded at least one symbol stream over the effective channel to the second node.
22. The first node according to claim 21 , wherein the effective channel comprises more than two inputs.
23. The first node according to claim 22 , wherein the obtaining circuit is further configured to involve performing transmission rank adaptation in the sense of selecting the number of symbol streams to match the characteristics of the effective channel.
24. A second node, the second node being arranged to receive a multi-antenna transmission from a first node over an effective channel, the effective channel having multiple inputs and at least one output, the first node and the second node being included in a wireless communication system, the second node comprising:
a selecting circuit configured to select a precoding matrix having a block diagonal structure, wherein the effective channel is block diagonal and the selected precoding matrix has a corresponding block diagonal structure, and wherein the effective channel is intentionally set up to be block-diagonal by arranging a first antenna setup in the first multi-antenna system or a second antenna setup in the second multi-antenna system to obtain the block diagonal effective channel without tracking instantaneous channel conditions of a physical channel;
a conveying circuit configured to convey information regarding the selected precoding matrix to the first node; and
a receiving circuit configured to receive at least one precoded symbol stream over the effective channel transmitted from the first node, wherein the received at least one symbol stream is precoded with the selected precoding matrix in the first node.
25. The second node according to claim 24 , wherein the effective channel comprises more than two inputs.
26. The second node according to claim 24 , wherein the effective channel comprises at least two outputs.