@article {1047, title = {Link Adaptation for Rate Splitting Systems with Partial CSIT}, journal = {IEEE Journal on Selected Areas in Communications}, year = {2023}, doi = {10.1109/JSAC.2023.3240787}, author = {Carlos Mosquera and Felipe G{\'o}mez-Cuba} } @article {985, title = {Link Adaptation and SINR errors in Practical Multicast Multibeam Satellite Systems with Linear Precoding}, journal = {International Journal of Satellite Communications and Networking}, year = {2020}, keywords = {link adaptation, multi-beam satellite, precoding, satellite communications}, author = {Anxo Tato and Stefano Andrenacci and Eva Lagunas and Symeon Chatzinotas and Carlos Mosquera} } @mastersthesis {979, title = {Link Adaptation Techniques for Future Terrestrial and Satellite Communications}, year = {2019}, month = {2019}, pages = {1-247}, abstract = {
The increasing demand of access to data from the users and the enormous number of connected devices requires to enhance the capacity of the wireless networks. They must provide a higher throughput to serve all the requested traffic and they must accommodate the vast number of the Internet of the Things (IoT) devices. In this context, this thesis focus its attention on three different scenarios which have in common that they are a future evolution of current terrestrial and satellite communications systems. These scenarios are Mobile Satellite Systems (MSS), Fixed Satellite Systems (FSS) and next generation 5G networks.
The adoption of Dual Polarization (DP) in MSS along with Multiple Input Multiple Output (MIMO) signal processing techniques allows to double the capacity of previous systems with the same bandwidth and transmit power. On the other hand, the shift to more aggressive frequency reuse patterns in FSS can also provide remarkable gains in the capacity of High Throughput Satellites (HTS) for offering BroadBand Satellite Services (BBS). Linear precoding stands out as a technique to cope with the high level of interference which arises in this scenario. Lastly, energy efficient modulation schemes, like Spatial Modulation (SM) and its many variants, are being proposed for increasing the capacity of future 5G networks since they represent a good trade-off between spectral efficiency, energy efficiency and transmitter complexity.\ \ \
Adaptive Coding and Modulation (ACM) technology is omnipresent in most of the communication standards since it enables a better exploitation of the system capacity by means of the adaptation of the Modulation and Coding Scheme (MCS). The link adaptation algorithm is responsible for selecting the optimum MCS, as well as other physical layer parameters in some cases, to adapt the transmission bit rate according to the instantaneous channel capacity of the time variant channel. Thus, link adaptation algorithms permit to increase the spectrum efficiency and guarantee a robust communication, adapting the level of redundancy of the coded information bits and the ruggedness of the modulation scheme.
In this thesis, several link adaptation algorithms are proposed for the three considered scenarios and its effectiveness is supported with simulations. Furthermore, an experimental validation of some algorithms is provided using a real satellite link, implemented with Software Defined Radio (SDR) technology. It is also studied how the carrier detection errors in the Channel State Information (CSI) affect linear precoding in FSS. The errors in the users Signal to Interference and Noise Ratio (SINR) that the gateway calculates to allocate MCS to the users is analyzed statistically and geographically. Moreover, a link adaptation algorithm with an adaptive margin per user is shown to allow a robust communication in the presence of SINR errors whereas the throughput of the system is barely compromised. In addition, a new method for making capacity calculations in SM and Generalized SM systems based on a neural network is proposed, which improves both accuracy and computational complexity with regard to the existing analytical approximations in the literature. With regard to MSS using DP, an adaptation mechanism is proposed in order to select the optimum MIMO mode and MCS which offer the highest throughput. Simulation results in a maritime mobile satellite channel show the dependence of the optimum MIMO mode with the average Signal to Noise Ratio (SNR), and how the spectral efficiency can be maximized whereas a target outage probability can be guaranteed. Lastly, the adaptation in SM systems is also addressed and several methods for deciding the coding rate in SM are given. These include the computation of the capacity prior to\ the adaptation, and also the use of a deep neural network. The latter offers very good results, with a spectral efficiency very close to the maximum achievable value.
In practice, data gathered by wireless sensor networks often belongs in a low-dimensional subspace, but it can present missing as well as corrupted values due to sensor malfunctioning and/or malicious attacks. We study the problem of Maximum Likelihood estimation of the low-rank factors of the underlying structure in such situation, and develop an Expectation-Maximization algorithm to this purpose, together with an effective initialization scheme. The proposed method outperforms previous schemes based on an initial faulty sensor identification stage, and is competitive in terms of complexity and performance with convex optimization-based matrix completion approaches.
}, keywords = {winter, wsn}, author = {R. L{\'o}pez-Valcarce and Josep Sala} } @conference {944, title = {Link Adaptation and Carriers Detection Errors in Multibeam Satellite Systems with Linear Precoding}, booktitle = {9th Advanced Satellite Multimedia Systems Conference (ASMS) and 15th Signal Processing for Space Communications Workshop (SPSC)}, year = {2018}, address = {Berlin, Germany}, abstract = {The application of linear precoding at the gateway side enables broadband multibeam satellite systems to use more aggressive frequency reuse patterns increasing the overall capacity of future High Throughput Satellites (HTS). However, although some previous works about precoding consider imperfect CSIT (Chanel State Information at the Transmitter) adding some CSI estimation errors, that is not the main cause of CSI degradation. In practice, receivers can only detect and estimate a few coefficients of the CSI vector being the other nullified, replaced by zeros. This introduces errors in the SINR calculation by the gateway that lead to the assignment of Modulation and Coding Schemes (MCS) over the decoding possibilities of the users, increasing the rate of erroneous frames. In this work, the errors in the SINR calculation caused by the nullification of the CSI are analyzing statistically and geographically using a radiation diagram of 245 beams over Europe. Furthermore, a solution based on a link adaptation algorithm with a per user adaptive margin is proposed, helping to achieve the QEF (Quasi-error Free) target of DVB-S2X systems.
\
The use of dual polarization in mobile satellite systems is
very promising as a means for increasing the transmission capacity. In this paper a system which uses simultaneously two orthogonal polarizations in order to communicate with the users is studied. The application of MIMO signal processing techniques along with Adaptive Coding and Modulation in the forward link can provide remarkable throughput gains up to 100 \% when compared with the single polarization system. The gateway is allowed to vary the MIMO and Modulation\ and Coding Schemes for each frame. The selection is done by means of a link adaptation algorithm which uses a tunable margin to achieve a predefined target Frame Error Rate.
Millimeter communication systems use large antenna arrays to provide good average received power and to take advantage of multi-stream MIMO communication. Unfortunately, due to power consumption in the analog front-end, it is impractical to perform beamforming and fully digital precoding at baseband. Hybrid precoding/combining architectures have been proposed to overcome this limitation. The hybrid structure splits the MIMO processing between the digital and analog domains, while keeping the performance close to that of the fully digital solution. In this paper, we introduce and analyze several algorithms that efficiently design hybrid precoders and combiners starting from the known optimum digital precoder/combiner, which can be computed when perfect channel state information is available. We propose several low complexity solutions which provide different trade-offs between performance and complexity. We show that the proposed iterative solutions perform better in terms of spectral efficiency and/or are faster than previous methods in the literature. All of them provide designs which perform close to the known optimal digital solution. Finally, we study the effects of quantizing the analog component of the hybrid design and show that even with coarse quantization, the average rate performance is good.
}, keywords = {compass, mmWave}, doi = {10.1109/TWC.2016.2614495}, author = {Cristian Rusu and Roi M{\'e}ndez-Rial and Nuria Gonz{\'a}lez-Prelcic and Robert W. Heath Jr.} } @conference {819, title = {Low Complexity Hybrid Sparse Precoding and Combining in Millimeter Wave MIMO Systems}, booktitle = {IEEE Int. Conference on Communications (ICC)}, year = {2015}, month = {06/2015}, publisher = {IEEE}, organization = {IEEE}, address = {London, UK}, keywords = {compass, mmWave}, author = {Cristian Rusu and Roi M{\'e}ndez-Rial and Nuria Gonz{\'a}lez-Prelcic and Robert W. Heath Jr.} } @conference {862, title = {Low Resolution Adaptive Compressed Sensing for mmWave MIMO receivers}, booktitle = {Asilomar Conf. on Signals, Systems, and Computers}, year = {2015}, month = {November, 2015}, keywords = {compass, mmWave}, author = {C. Rusu and Nuria Gonz{\'a}lez-Prelcic and R.W. Heath Jr.} } @article {739, title = {Learning-Based Adaptive Transmission for Limited Feedback Multiuser MIMO-OFDM}, journal = {IEEE Transactions on Wireless Communications}, year = {2014}, keywords = {adaptive signal processing, dynacs}, doi = {10.1109/TWC.2014.2314104}, author = {Alberto Rico-Alvari{\~n}o and Robert W. Heath Jr.} } @article {759, title = {A Least Squares Approach to the Static Traffic Analysis of High-Latency Anonymous Communication Systems}, journal = {IEEE Transactions on Information Forensics and Security}, year = {2014}, doi = {10.1109/TIFS.2014.2330696}, author = {Fernando P{\'e}rez-Gonz{\'a}lez and Carmela Troncoso and Simon Oya} } @conference {751, title = {Low-Power Active Interference Cancellation for OFDM Spectrum Sculpting}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2014}, month = {09/2014}, abstract = {Link adaptation in multiple user multiple-input multiple-output orthogonal frequency division multiplexing communication systems is challenging because of the coupling between user selection, mode selection, precoding, and equalization. In this paper, we present a methodology to perform link adaptation under this multiuser setting, focusing on the capabilities of IEEE 802.11ac. We propose to use a machine learning classifier to solve the problem of selecting a proper modulation and coding scheme, combined with a greedy algorithm that performs user and spatial mode selection. We observe that our solution offers good performance in the case of perfect channel state information or high feedback rate, while those scenarios with less feedback suffer some degradation due to inter-user interference.
}, keywords = {dynacs, link adaptation, Machine Learning, Multiuser MIMO-OFDM}, author = {Alberto Rico-Alvari{\~n}o and Robert W. Heath Jr.} } @article {675, title = {Least Squares Disclosure Attacks: User Profiling for Mix-based Anonymous Communication Systems}, year = {2013}, month = {01/2013}, institution = {University of Vigo}, address = {Vigo}, issn = {UV/TSC/FPG/30052012}, author = {Fernando P{\'e}rez-Gonz{\'a}lez and Carmela Troncoso} } @conference {709, title = {Link Adaptation in MIMO-OFDM with Practical Impairments}, booktitle = {Asilomar Conference on Signals Systems and Computers}, year = {2013}, keywords = {dynacs, link adaptation, MIMO-OFDM}, doi = {10.1109/ACSSC.2013.6810579}, author = {Alberto Rico-Alvari{\~n}o and Robert W. Heath Jr.} } @conference {688, title = {Localization of Forgeries in MPEG-2 Video through GOP Size and DQ analysis}, booktitle = {IEEE International Workshop on Multimedia Signal Processing (MMSP)}, year = {2013}, pages = {494-499}, address = {Pula (Sardinia), Italy}, abstract = {This work addresses forgery localization in MPEG-2 compressed videos. The proposed method is based on the analysis of Double Quantization (DQ) traces in frames that were encoded twice as intra (i.e., I-frames). \ Employing a state-of-the-art method, such frames are located in the video under analysis by estimating the size of the Group Of Pictures (GOP) that was used in the first compression; then, the DQ analysis is devised for the MPEG-2 encoding scheme and applied to frames that were intra-coded in both the first and second compression. In such a way, regions that were manipulated between the two encodings are detected. Compared to existing methods based on double quantization analysis, the proposed scheme makes forgery localization possible on a wider range of settings.