DIGITAL PERDISTORTION TECHNIQUE FOR COMPENSATING MEMORY EFFECTS OF POWER AMPLIFIERS IN WIDEBAND APPLICATIONS
Pooria Varahram - Somayeh Mohammady - Mohd Nizar Hamidon - Roslina M. Sidek - Sabira Khatun
The application of digital predistortion in base band signal is an extended method of amplifier linearization to reduce
the Adjacent Channel Interference (ACI) in those systems in which a varying envelope modulation scheme like OFDM and
MQAM is used. Digital baseband predistortion is a highly cost-effective way to linearize Power amplifiers (PAs), but
most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as
wideband code-division multiple access (WCDMA), wideband orthogonal frequency-division multiplexing (W-OFDM) and
worldwide interoperability for microwave access (WiMAX), PA memory effects can no longer be ignored. In this paper a
novel technique for compensating such effects is proposed. This technique is a combination of two techniques, memory
polynomial predistortion and the gain based predistorter method. This method is compared with the other technique,
memory polynomial method and validated using a Mini-Circuit power amplifier and QPSK signal with 1 MHz bandwidth.
Simulations and results show improvement in ACLR reduction and EVM with applying this method.
Keywords: digital predistortion, memory effects, ACLR, power amplifier, WCDMA