A linearization architecture from the Emerging Radio Systems Group, published in IEEE Microwave and Wireless Technology Letters, addresses the two things a fully digital MIMO transmitter has to get right at once — the distortion it radiates into neighbouring channels, and the signal quality each user actually receives — without making the precoder any more complex.
The problem is that the two targets pull in different directions. Suppressing out-of-band emission is a per-amplifier concern; the error vector magnitude seen at a user is a property of the beam formed across the whole array. Treating both with one predistorter usually means multi-input or high-order nonlinear models, and the cost grows with the number of transmit chains.
The proposed architecture splits the job in two. A single-input single-output digital predistorter sits on each channel, trained from a feedback signal passed through an in-band notch filter so that only out-of-band distortion drives it. A low-order linear MIMO pre-equalizer then sits ahead of the precoder and corrects the in-band distortion that reaches the user receivers. The two stages are trained jointly, so the pair converges on both objectives together rather than trading one against the other.
It was measured on a 16-channel fully digital transmitter at 3.5 GHz in a two-user line-of-sight scenario. The pre-equalizer brings user EVM down to 0.7%. A 13-coefficient per-antenna predistorter improves total radiated power ACPR from −33 to −43 dB, and ACPR at the two users from −36.5 to −49.6 dB and from −37 to −51.2 dB.
The work is by Jin Gyu Lim, Ahmed Ben Ayed and Slim Boumaiza.
Citation
J. G. Lim, A. Ben Ayed and S. Boumaiza, “A Two-Tier Low-Complexity Linearization Architecture for Fully Digital mMIMO Transmitters,” IEEE Microwave and Wireless Technology Letters, vol. 36, no. 6, pp. 946–949, June 2026, doi: 10.1109/LMWT.2026.3676260. Read it on IEEE Xplore →