Method and apparatus for controlling equivalent isotropic radiated power

An access point for a wireless communication network, the access point comprising:

• an array of antenna elements;
• a digital beamforming weights matrix for applying a weightset to one or more signals streams;
• a respective transmit chain for each antenna element;
• and
• a processor configured to control an Equivalent Isotropic Radiated Power (EIRP) emitted from the antenna array in one or more beams by:
• calibrating transmission phase and gain of a respective transmit chain for each antenna element;
• providing a polar radiation model for an antenna element of the array;
• determining a first weightset for the beamforming weights matrix for a first mode of operation subject to a constraint that a maximum total EIRP for the one or more beams in combination in any azimuth direction is maintained within a predetermined EIRP limit;
• and
• switching from the first mode of operation to a second mode of operation,
• wherein the first mode is a sector mode in which signals from the respective transmit chains are combined to form a beam sufficiently broad to provide coverage of a sector of a cellular radio network, and
• the second mode is a combining mode, in which signals from the respective transmit chains are combined to form at least one beam which is narrower in azimuth than that formed in the sector mode, the at least one beam being steered to an individual subscriber mode within the sector of the cellular radio network;
• in the second mode of operation, configuring one or more beams by applying a second weightset for the beamforming weights matrix to the one or more signal streams,
• wherein the second weightset is determined subject to a constraint that a maximum total EIRP for the one or more beams in combination in any azimuth direction is maintained within the same predetermined EIRP limit as for the first mode,
• wherein said determining, in each mode of operation, is based at least on a spatial separation of the antenna elements, the polar radiation model and the calibrated transmission phase and gain of each respective transmit chain.