Method for channel estimation in a wireless communication system, communication unit, terminal and communication system

1. A method for channel estimation in a wireless communication system comprising a communication unit and one or more terminals, wherein the communication unit comprises a plurality of antennas, the method comprising:

transmitting pilot signals from at least one antenna of the plurality of antennas towards the one or more terminals;

performing correlative coding with respect to the transmitted pilot signals at the one or more terminals to form correlatively coded pilot signals, the correlatively coded pilot signals being provided with a terminal-specific correlation signature or an antenna-specific correlation signature if the one or more terminals comprise more than one antenna;

retransmitting the correlatively coded pilot signals from the one or more terminals to the plurality of antennas;

estimating uplink channels between the one or more terminals and the plurality of antennas based on the correlatively coded pilot signals; and

obtaining estimates of the downlink channels between the plurality of antennas and the one or more terminals based on the estimated uplink channels, wherein the method further comprises:

transmitting signals from the one or more terminals to the plurality of antennas, at least one signal comprising information related to an identity of the transmission source from which the signal originates; and

linking uplink and downlink channels to corresponding terminals using the transmission source identity information.

2. The method according to claim 1 , wherein the transmission source identity information is terminal-specific information if the one or more terminals are provided with a single antenna or antenna-specific information if the one or more terminals are provided with more than one antenna.

3. The method according to claim 1 , wherein correlative coding comprises filtering received pilot signals by an auto-regressive model, preferably an auto-regressive model of order 1.

4. The method according to claim 1 , wherein correlative coding comprises executing a circular convolution operation onto the pilot signals.

5. The method according to claim 1 , wherein estimating uplink channels between the one or more user terminals and the plurality of antennas utilizes a second-order blind identification algorithm.

6. An apparatus comprising:

a plurality of antennas;

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:

transmitting pilot signals from at least one antenna of the plurality of antennas towards one or more terminals in a communication system;

receiving correlatively coded pilot signals from the one or more terminals at the plurality of antennas, the correlatively coded pilot signals being provided with a terminal-specific correlation signature or an antenna-specific correlation signature if the one or more terminals comprise more than one antenna;

estimating uplink channels between the one or more terminals and the plurality of antennas based at least on the coded pilot signals; and

obtaining estimates of the downlink channels between the plurality of antennas and the one or more user terminals based at least on the estimated uplink channels, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform:

receiving signals from the one or more terminals via the plurality of antennas, the signals comprising information related to an identity of the transmission source from which the signal originates; and

linking uplink and downlink channels to corresponding terminals using the transmission source identity information as received.

7. The apparatus according to claim 6 , wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform estimating the uplink channels by utilizing a second-order blind identification algorithm.

8. An apparatus comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:

receiving pilot signals transmitted from at least one antenna of a plurality of antennas;

performing correlative coding with respect to the received pilot signals to form correlatively coded pilot signals, the correlatively coded pilot signals being provided with a terminal-specific correlation signature or an antenna-specific correlation signature if one or more terminals comprise more than one antenna; and

retransmitting the coded pilot signals to the plurality of antennas and estimating uplink channels based at least on the coded pilot signals and to obtain an estimate of downlink channels based on the estimated uplink channels, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform:

transmitting signals from the one or more terminals via the plurality of antennas, the signals comprising information related to an identity of the transmission source from which the signal originates; and

linking uplink and downlink channels to corresponding terminals using the transmission source identity information as received.

9. The apparatus according to claim 8 , wherein correlative coding as performed by the coding unit comprises filtering received pilot signals by an autoregressive model.

10. The apparatus according to claim 8 , wherein the terminal is a user terminal.

11. The apparatus according to claim 8 , wherein the terminal is a relay station.

12. A system comprising the apparatus according to claim 6 and the apparatus according to claim 8 .