Power Amplifiers are the most critical components in a communication system and are inherently nonlinear. The nonlinearity generates spectral regrowth, which leads to adjacent channel interference and violations of the out-of-band emission requirements. The nonlinearity also causes in-band distortion degrading the performance of the bit error rate (BER). It is possible to reduce the nonlinearity by backing off the power amplifier to work in the linear region. Still, this method is not viable because of the low efficiency of the power amplifier in this regime.
Power amplifiers must be linearized using different techniques to enhance efficiency without compromising the linearity. IQSTAR 1.2 introduced several DPD techniques and algorithms to verify that the Power amplifier under test can be linearized with more or less complexity.
When different DPD techniques must be tested on the Power amplifier, the software must make more than one algorithm available. Starting version 1.2 of IQSTAR, a dedicated DPD module was released to respond to this request:
- This technique is an iterative measurement-based method that allows achieving quasi-ideal linearization results for reference purposes. Indeed, this method is used during the verification and development phase of the PA and cannot be implemented as a real-time DPD algorithm in a transmitter.
- Memoryless (M)
- Memoryless models focus on the power amplifier with a memoryless nonlinearity: the current output depends only on the current input through a nonlinear mechanism. This instantaneous nonlinearity is usually characterized by the power amplifier’s AM/AM and AM/PM responses. The output signal amplitude and phase deviation of the power amplifier output are given as functions of the amplitude of its current input.
- Memory Polynomial (MP)
- The memory model is commonly used as the signal bandwidth gets wider and the power amplifiers exhibit memory effects, especially for high-power amplifiers used in wireless base stations. Consequently, the current output of the power amplifier depends on the current input and the past input values.
- Generalized Memory Polynomial (GMP)
- This model is built by augmenting the memory polynomial model taking into account the cross-term order. The user can set this order.
- Nanosemi Single-band Algorithm (DLL to be acquired by the customer)
- This option controls the Nanosemi single-band algorithm through a DLL and applies it externally to the measurements using instruments from different vendors. The Nanosemi DLL must be acquired separately.
- Nanosemi Dual-Band Algorithm (DLL to be acquired by the customer)
- This option controls the Nanosemi dual-band algorithm through a DLL and applies it externally to the measurements using instruments from different vendors. The Nanosemi DLL must be acquired separately.
- Matlab-based customer-developed DPD algorithm
- This option is a gateway to run a Matlab-based DPD algorithm developed by the user. This option also offers an Open-source MP algorithm that the user can adjust and optimize to his power amplifier under test. Matlab license must be acquired separately.