Method and arrangement in a cellular communication system
The basic idea of the present invention is to not only design a frequency-selective precoder with respect to the channel properties but also to ensure that the time-domain spread is limited. Hence the energy of the time-domain impulse response of the frequency-selective precoder is concentrated. According to a first embodiment, the time-domain spread is limited by designing a precoder such that it allows smooth transitions in the frequency domain between the values of the precoder when the precoder provides a staircase function. The smooth transitions can either be achieved by lowpass filtering the frequency-domain representation, the staircase function, of the precoder or by designing the precoder such that the sharp jumps are replaced by slopes. According to a second embodiment, the time-domain spread is controlled. The control may be achieved by employing a time-domain parameterization to precisely control the introduced additional time-domain spread.
1. A method in a communication device in a cellular network to select characteristics of a frequency-selective precoder for a transmitter of the communication device, wherein the frequency selective precoder is frequency selective and is configured to take any value which is unknown by a receiver of a node in the cellular network, the method comprising:
concentrating energy of a time-domain impulse response of the frequency-selective precoder by controlling time-domain spread of the frequency-selective precoder,
wherein controlling time-domain spread comprises employing a time-domain model parameterization of the time-domain impulse response of the frequency-selective precoder to control additional time dispersion introduced by the frequency-selective precoder.
2. The method according to claim 1 , wherein parameters of the time domain model parameterization are selected to increase and/or maximize received power.
3. A communication device in a cellular network, the communication device comprising:
a transmitter;
a frequency-selective precoder for the transmitter, wherein the frequency-selective precoder is frequency selective and is configured to take any value which is unknown by a receiver of a node in the cellular network; and
a concentrator configured to select characteristics of the frequency selective precoder, wherein the concentrator is further configured to concentrate energy of a time-domain impulse response of the frequency-selective precoder, wherein the concentrator is configured to concentrate the energy of the time-domain impulse response of the frequency-selective precoder by controlling a time-domain spread of the frequency-selective precoder,
wherein the concentrator is configured to control the time-domain spread by employing a time-domain model parameterization of the impulse response of the frequency-selective precoder to control additional time dispersion introduced by the frequency-selective precoder.
4. The communication device according to claim 3 , wherein the concentrator is configured to select parameters of the time-domain model parameterization to increase and/or maximize received power.
5. The communication device according to claim 3 , wherein the communication device comprises a User Equipment, wherein the transmitter is located in the User Equipment, and wherein the receiver is located in a base station and/or a relay of the cellular network.
6. The communication device according to claim 3 , wherein the communication device comprises a first relay, wherein the transmitter is located in the first relay, and wherein the receiver is located in a second relay or a base station.