Digital Signal Processing Group

The EmRG Digital Signal Processing Group investigates novel algorithms and their hardware implementations for enhancing the performance of RF front-ends and beamforming systems in terrestrial and non-terrestrial communications. Our work focuses on device and behavioural modelling, linearization, pre-coding and calibration techniques.

16-element phased array under test in the EmRG anechoic chamber

Ongoing research projects

MIMO transmitter emulation

Prediction of MIMO transmitter performance using a single transmit chain, without the need to build the entire system.

MIMO transmitter emulation setup using Keysight signal generation, downconverter and digitizer

MIMO transmitter emulation setup: signal generation, downconversion and digitizing

FR3 MIMO front-end

Design and fabrication of an integrated, scalable MIMO system — circuitry and antennas for 8–9 GHz — as a testbed for the FR3 band. The current system forms a 4×4 digital beamforming system and serves as a demonstrator for investigating new DSP algorithms critical to mitigating hardware non-idealities.

Rendering of the FR3 MIMO front-end rack with stacked circuit boards and antennas

FR3 MIMO front-end: stacked circuit boards and antennas

FR3 phased-array front end on a tripod in the anechoic chamber, cabled to a 16-channel signal analyser and bench power supply

16-channel MIMO measurement setup in an anechoic chamber

Wideband active load-pull system

Using VNA frequency extenders to conduct comprehensive load-pull measurements with wideband OFDM modulated signals at millimetre waves.

Wideband active load-pull system built from VNA frequency extenders and IF vector signal generation and analysis

Wideband active load-pull system built from VNA frequency extenders and IF vector signal generation and analysis

Experimental demonstrations

Algorithms are validated on the group’s own hardware. The figures below come from linearization of frequency-multiplier-based sources, from wideband active load-pull characterization, and from the FR1 fully digital MIMO testbed.

Power spectral density before and after digital pre-distortion, showing the shoulders falling by about twenty decibels

Output spectrum before and after digital pre-distortion of an RF multiplier based source

Scatter plot of gain distortion against output power, before and after digital pre-distortion

Gain distortion before and after digital pre-distortion, for RF multipliers at 58 GHz

Smith chart showing measured reflection coefficient trajectories synthesised by the wideband active load-pull system

Measured reflection coefficient using the wideband active load-pull system

16-element phased array under test in the anechoic chamber, with an oscilloscope on the rack above

FR1 fully digital MIMO test and measurement setup

Power spectral density before and after digital pre-distortion, showing the shoulders falling by about twenty decibels
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Output spectrum before and after digital pre-distortion of an RF multiplier based source
Scatter plot of gain distortion against output power, before and after digital pre-distortion
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Gain distortion before and after digital pre-distortion, for RF multipliers at 58 GHz

Recent publications

Journal articles

  1. M. A. Chalaki, E. Gu, A. B. Ayed, P. Mitran, S. Boumaiza, “Robust Digital Predistortion of Load-Modulated Power Amplifiers Under Varying Signal Conditions,” IEEE Microwave Magazine, vol. 27, no. 6, June 2026.
  2. A. B. Ayed, S. Boumaiza, “Millimeter-Wave Wideband Active Load—Pull System Using Vector Network Analyzer Frequency Extenders,” IEEE Microwave and Wireless Technology Letters, vol. 35, no. 6, June 2025.
  3. A. B. Ayed, P. Mitran, S. Boumaiza, “Recent Advances in Linearization Techniques for Frequency Multiplier-Based Transmitters Driven With Vector-Modulated Signals,” IEEE Microwave Magazine, vol. 26, no. 1, Jan. 2025.
  4. Z. J. Su, A. B. Ayed, N. Messaoudi, P. Mitran, S. Boumaiza, “Frequency-Stitching-Based Ultrawideband Signal Generation for 6G Component/System Testing: Achieving 12-GHz Instantaneous Bandwidth and 96-Gbps Data Rate at D Band,” IEEE Transactions on Microwave Theory and Techniques, vol. 73, no. 5, May 2025.
  5. A. B. Ayed, I. Jaffri, A. M. Darwish, P. Mitran, S. Boumaiza, “Digital Predistortion of Frequency Multiplier-Based Vector Signal Sources With Constrained Transmitter and Observation Receiver Bandwidth,” IEEE Transactions on Microwave Theory and Techniques, vol. 72, no. 11, Nov. 2024.
  6. A. B. Ayed, P. Mitran, S. Boumaiza, “Millimeter-Wave Device Characterization Under Wideband Modulated Signals Using Vector Network Analyzer Frequency Extenders,” IEEE Microwave and Wireless Technology Letters, vol. 34, no. 6, June 2024.
  7. J. G. Lim, H. Barkhordar-Pour, A. B. Ayed, P. Mitran, S. Boumaiza, “On the Viability of Using a Subset of Transmitter- Observation Receivers for Training a Common DPD in Fully Digital MIMO Transmitters,” IEEE Microwave and Wireless Technology Letters, vol. 33, no. 6, June 2023.
  8. M. Almoneer, P. Mitran, S. Boumaiza, “Load and Power Indexed Predistortion for Improved Robustness to MIMO Channel Conditions,” IEEE Microwave and Wireless Technology Letters, vol. 33, no. 4, Apr. 2023.
  9. M. Almoneer, P. Mitran, S. Boumaiza, “Wideband Digital Predistortion for Frequency Multipliers Driven by Nonideal Upconverters,” IEEE Microwave and Wireless Technology Letters, vol. 33, no. 1, Jan. 2023.
  10. A. Amini, S. Boumaiza, “A Time-Domain Multi-Tone Distortion Model for Effective Design of High Power Amplifiers,” IEEE Access, vol. 10, 2022.

Conference papers

  1. N. Messaoudi, S. Gao, M. W. Mansha, Y. Baeyens, S. Boumaiza, B. Hosein, S. Shahramian, “An Early Comparison of D-Band and G-Band On-Wafer Noise Figure Measurements,” 2025 105th ARFTG Microwave Measurement Conference (ARFTG), June 2025.
  2. Y. Chen, M. H. Sahlabadi, S. Boumaiza, “Calibration of Vector-Summing Type Variable-Gain Phase Shifters using Novel Rectangular Constellation Modeling,” 2025 IEEE/MTT-S International Microwave Symposium - IMS 2025, June 2025.
  3. N. Messaoudi, A. B. Ayed, S. Boumaiza, “A Piecewise Interpolation Based Digital Predistortion of Power Amplifiers Across Wide Power Ranges,” 2025 104th ARFTG Microwave Measurement Conference (ARFTG), Jan. 2025.
  4. Z. J. Su, A. B. Ayed, P. Mitran, S. Boumaiza, “Comparative Study of Two Architectures Suitable for the Generation of Wideband Signals at Sub-THz,” 2025 104th ARFTG Microwave Measurement Conference (ARFTG), Jan. 2025.
  5. Z. J. Su, N. Messaoudi, A. B. Ayed, J. Teyssier, S. Boumaiza, “Comparison of Signal Generation Approaches for Component Testing at D-Band,” 2024 103rd ARFTG Microwave Measurement Conference (ARFTG), June 2024.
  6. Z. J. Su, A. B. Ayed, S. Boumaiza, “Wideband Vector Signal Generation Using Multiple Narrowband Phase-Coherent Synchronous Signal Channels,” 2024 103rd ARFTG Microwave Measurement Conference (ARFTG), June 2024.
  7. H. Barkhordar-Pour, J. G. Lim, A. B. Ayed, P. Mitran, S. Boumaiza, “Linearizability Assessment of a 3.5 GHz 16-Chain Fully Digital MIMO Transmitter Under Wideband Modulated Signals,” 2024 103rd ARFTG Microwave Measurement Conference (ARFTG), June 2024.
  8. N. Messaoudi, S. Gao, M. W. Mansha, Y. Baeyens, M. Sayginer, S. Boumaiza, B. Hosein, S. Shahramian, “Enhanced Accuracy in On-Wafer Noise Figure Measurements at Sub-Terahertz Frequencies,” 2024 IEEE/MTT-S International Microwave Symposium - IMS 2024, June 2024.
  9. Y. Chen, S. Boumaiza, “Rapid Calibration of Variable Gain Phase Shifters: A Novel Characterization Approach with Sparse Measurements,” 2024 IEEE/MTT-S International Microwave Symposium - IMS 2024, June 2024.
  10. M. Eladwy, A. B. Ayed, S. Boumaiza, “VNA-Based Characterization of Frequency Multipliers Phase-Distortions Under Continuous-Wave and Modulated Signal Excitation,” 2023 101st ARFTG Microwave Measurement Conference (ARFTG), June 2023.