Technique for precoding a radio transmission

A device for transmitting on a multiple-input channel from a transmitting device to at least one receiving device, the device comprising at least one processor and a memory, said memory comprising instructions executable by said at least one processor, whereby the device is operative to:

• determine a quality of a channel estimate of the multiple-input channel from the transmitting device to the at least one receiving device;
• and
• transmit on the multiple-input channel from the transmitting device to the at least one receiving device, wherein the transmission is spatially precoded using at least one precoder determined out of a set of precoders, wherein a size of the set of precoders is an increasing or non-decreasing function of the determined quality of the channel estimate;
• wherein the set is a first set if the determined quality is less than a first quality threshold value, and the set is a second set if the determined quality is greater than the first quality threshold value, and wherein the first set is a proper subset of the second set, and wherein the second set is the superset and the first set is the proper subset of the second set resulting from restricting the second set according to a constraint depending on the determined quality of the channel estimate.

A method of transmitting on a multiple-input channel from a transmitting device to at least one receiving device, the method comprising or initiating the steps of:

• determining a quality of a channel estimate of the multiple-input channel from the transmitting device to the at least one receiving device;
• and
• transmitting on the multiple-input channel from the transmitting device to the at least one receiving device, wherein the transmission is spatially precoded using at least one precoder determined out of a set of precoders, wherein a size of the set of precoders is an increasing or non-decreasing function of the determined quality of the channel estimate;
• wherein the set results from selectively restricting a superset of precoders according to a constraint depending on the determined quality of the channel estimate, wherein each of the precoders in the set defines complex gains for respective multiple inputs of the multiple-input channel, and wherein the constraint restricts the complex gains to an equal amplitude.