Method of correcting gain and phase imbalance of a multi-carrier transmission signal, transmitter and base station
Method of correcting a gain and phase imbalance of an analogue modulator ( 32 ) for multiple channels (CHi) of a multi-carrier transmission signal, the method comprising the steps of determining a gain imbalance correction factor (GCFi) and phase imbalance correction factor (PCFi) for each channel individually and applying said correction factors (GCFi, PCFi) to the corresponding channel (CHi) individually, before the multi-carrier synthesis of the channels is done, whereas step a) for each one of the multiple channels (CHi) is performed in a time-multiplexed manner with step a) for the other ones of the multiple channels (CHi).
1. A method of correcting a gain and phase imbalance of an analogue modulator for multiple digital channels of a multi-carrier transmission signal, wherein the different channels are to be transmitted on different carrier frequencies, the method comprising the steps of
a) determining a gain imbalance correction factor and phase imbalance correction factor for each channel individually and
b) applying said correction factors to the corresponding channel individually, before a multi-carrier synthesis of the channels is done,
wherein step a) for each one of the multiple channels is performed in a time-multiplexed manner with step a) for the other ones of the multiple channels, whereby said correction factors being applied in a continuous manner, using new correction factors as soon as new correction factors have been determined; and
wherein step a) further comprises the steps of:
ai) channel-separating a RF signal output by said modulator,
aii) comparing the channel-separated modulator output signal with the corresponding input channel signal for each channel individually.
2. The method according to claim 1 , wherein aL,H) said step a) is performed first for the channels corresponding to the lowest-band and highest-band carriers by comparing the channel-separated modulator output signal with the corresponding input channel signal of the lowest-band carrier and of the highest-band carrier and
said step a) is then performed for the other ones of the multiple channels by linear approximation from said gain and phase imbalance correction factors determined in step aL,H).
3. The method according to claim 1 , wherein said channel separation step comprises the steps of
digitizing the RF signal output by said modulator
separating the channels in said digitized version of the RF signal output by said modulator.
4. The method according to claim 1 , wherein said channel separation step comprises the steps of
separating the channels in the analogue RF signal output by said modulator to obtain an analogue signal for each channel
digitizing said analogue signal for each channel individually.
5. A transmitter for performing the method of claim 1 , comprising a digital part and an analogue part, the digital part comprising a multi-carrier synthesis module, a determination module for determining gain and phase imbalance at one channel and a correction module for each channel for applying gain and phase correction factors determined by said determination module to each corresponding channel individually, whereby the correction factors are applied to the respective correction modules, using new correction factors as soon as new correction factors have been determined,
the analogue part comprising an analogue modulator,
the transmitter further comprising a feedback path from an output of said analogue modulator to said determination module, wherein said determination module channel-seperates an RF signal output by said modulator and compares the channel-seperated modulator output signal with the corresponding input channel signal for each channel individually.
6. A base station comprising the transmitter of claim 5 .