Patent ID: 7747250

Claim:
A method of calibrating a transmitting part of a node in a wireless communication network, which communication network comprises at least a first radio node and a second radio node which can be arranged to be in radio communication with each other, and wherein at least one radio node receives radio signals from multiple antennas, said calibration method comprises the steps of transmitting first pilots signals both from the first radio node to the second radio node and from the second radio node to the first radio node; determining in the second radio node a first estimate of the channel characteristics from the first radio node to the second radio node, and in the first radio node determining a second estimate of the channel characteristics from the second radio node to the first radio node, said determining based on respective received first pilot signals; calculating at least one channel correction factor in the first radio node based on the first and second channel estimates, transmitting a modified second pilot signal from the first radio node to the second radio node, said modification based on the second channel estimate; estimating transmission errors in the second radio node, said estimation based on the first channel estimate and the received second pilot signal and calculating a correction vector with correction terms for each of the multiple antennas based on the transmission errors; exchanging the correction vector from the second radio node to the first radio node; and in that the step of calculating correction factors comprises calculating one correction factor for each antenna, the correction factors are based at least partly on the respective correction terms in the correction vector, said correction factors adapted for use in transmissions from the first radio node to the second radio node.