Allocation of uplink reference signals in a mobile communication system

An apparatus for controlling a network node that serves a plurality of user equipments in a mobile communication system, the apparatus comprising:

• logic configured to provide the network node with a number, NRS, of orthogonal reference signals, wherein NRS is less than a maximum number, NMAX—AP, of user equipment antenna ports that can be served by the network node;
• and
• logic configured to ascertain, for each of the antenna ports, a channel quality of a channel between the antenna port and the network node;
• logic configured to allocate all NRS orthogonal reference signals to a subset of all of the antenna ports by means of an allocation process such that, whenever a number of antenna ports of user equipments being served by the network node exceeds the number, NRS, of orthogonal reference signals:
• each orthogonal reference signal is allocated to only one of the antenna ports;
• each antenna port has no more than one orthogonal reference signal allocated to it;
• and
• allocation decisions made by the allocation process are a function of the channel qualities of the respective antenna ports such that the higher the channel quality, the higher priority the corresponding antenna port is given as a candidate for receiving an orthogonal reference signal allocation.