Fast power back-off adjustment by efficient cubic metric determination

In order to support higher data rates of up to 5.76 Mbps in the uplink the UMTS specification is enhanced by HSUPA. These higher data rates are achieved by multiplexing more code channels on the same transmit bandwidth. For certain configurations the adjacent channel leakage is however also increased due to the power amplifier nonlinearities. Thus the standard requires a power back-off for these cases. It has been shown that the required power back-off can be reliably estimated by the cubic metric. In order to determine the cubic metric a large number of computations however has to be performed which results in a delayed adjustment for the PA. Hence in this contribution a method is introduced which considerably reduces the computational load for the determination of the cubic metric and thus enabling a fast power back-off. This is achieved by applying a versatile polynomial interpolation method.