A first reference signal that complements a second reference signal

A first network node, the first network node being configured to:

• receive a first reference signal transmitted by a second network node using a first precoder;
• receive a second reference signal transmitted by the second network node using a second precoder that is complementary to the first precoder such that the second reference signal occupies a first part of a channel not occupied by the first reference signal;
• and
• use the first and second reference signals to generate a channel estimate, H, or
• use the first and second precoder to generate H.

A method performed by a network node, the method comprising:

• determining to transmit a first reference signal;
• determining whether a second reference signal should be transmitted;
• transmitting the first reference signal using a first precoder;
• and
• transmitting the second reference signal as a result of determining that the second reference signal should be transmitted, wherein
• the second reference signal is transmitted using a second precoder that is complementary to the first precoder such that the second reference signal occupies a first part of a channel not occupied by the first reference signal.

A method performed by a first network node, the method comprising:

• receiving a first reference signal transmitted by a second network node using a first precoder;
• receiving a second reference signal transmitted by the second network node using a second precoder that is complementary to the first precoder such that the second reference signal occupies a first part of a channel not occupied by the first reference signal;
• and
• using the first and second reference signals to generate a channel estimate, H, or
• using the first and second precoder to generate H.