To the authors'best knowledge, the concept of post-distorted receivers appeared in the early 1990s [1,2]. Initially, post-distortion was thought as a solution for compensating intermodulation distortions resulting from the AM-AM and AM-PM non-linear behaviour of a mobile terminal power amplifier at the base-station receiver side. It was then considered as an alternative to pre-distortion that aimed to relax out-of-band emission specifications of portable transmitters while improving their power efficiency.

Chapter Contents:

• 4.1 Motivations for post-distortion of radio receivers and ADCs
• 4.1.1 Ideal vs. practical radio receiver
• 4.1.2 Dynamic range issues of modern radio receivers
• 4.1.3 Principle of post-distortion
• 4.1.4 Figures of merit
• 4.2 Review of distortions issues met in radio receivers
• 4.2.1 Distortion issue of IF-digitising superheterodyne receivers
• 4.2.2 Distortion issue of low-IF receivers
• 4.2.3 Distortion issue of full-digital receivers
• 4.3 Model-based post-distortion: modelling
• 4.3.1 The passband Volterra model
• 4.3.2 The baseband Volterra model
• 4.3.3 Physical interpretation and dimensioning of Volterra model non-linearity order and memory depth
• 4.3.4 Derivatives of Volterra model
• 4.3.5 Modelling ADCs
• 4.3.6 Modelling IF-digitising superheterodyne and full-digital receivers
• 4.3.7 Modelling low-IF receivers
• 4.3.8 On the usage of baseband Volterra model for reducing computational burden of passband Volterra model
• 4.3.9 On sampling frequency required for non-linear system modelling
• 4.4 Model-based post-distortion: identification and inversion
• 4.4.1 Statements of the model identification problem
• 4.4.2 Dealing with the need of both distorted and undistorted signal samples
• 4.4.3 Solution of direct Wiener filter problem
• 4.4.4 Inversion of a model determined by a direct identification scheme
• 4.4.5 On the numerical instability issue
• 4.4.5.1 About persistence of a system excitation
• 4.4.5.2 Numerical analysis of the persistence of an excitation
• 4.4.5.3 Physical interpretation of the persistence of an excitation
• 4.4.6 Effects of numerical instability on the least square solution
• 4.4.7 Effects of numerical instability on stochastic least mean square and recursive least square solutions
• 4.4.7.1 Simple and normalised stochastic least mean square algorithms
• 4.4.7.2 Recursive least square algorithm
• 4.5 Study of an example of ADC and receiver model-based post-distortion solution
• 4.5.1 Targeted system features
• 4.5.2 Block diagram of the post-distortion solution
• 4.5.3 Modelling features
• 4.5.4 Identification features
• 4.5.5 Inversion features
• 4.5.6 Results of post-distortion operated on a simulated full-digital receiver
• 4.5.7 Results of post-distortion operated on the targeted system
• 4.6 Look-up-table-based post-distortion of ADCs
• 4.6.1 LUT-based post-distortion strategies
• 4.6.2 Determination of LUT values
• 4.6.3 INL sequence modelling
• 4.7 Conclusion
• References

Inspec keywords: radio transmitters; analogue-digital conversion; intermodulation distortion; mobile radio; power amplifiers; radio receivers

Other keywords: out-of-band emission; AM-AM nonlinear behaviour; post-distorted receivers; base-station receiver side; digital post-distortion; intermodulation distortions; portable transmitters; analog-to-digital converters; mobile terminal power amplifier; AM-PM nonlinear behaviour; radio receivers

Subjects: Signal processing and conditioning equipment and techniques; Mobile radio systems; Amplifiers; Modulation and coding methods