Channel estimation in communications

An apparatus comprising

• at least one processor;
• and
• at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to
• obtain channel state information for antenna elements with a high-end radio frequency chain, wherein the antenna elements with the high-end radio frequency chain are placed in an antenna array intermittently with antenna elements with a low-cost radio frequency chain;
• estimate channel state information for the antenna elements with the low-cost radio frequency chain, by interpolating the channel state information obtained for the antenna elements with the high-end radio frequency chain.