Large size FFTs over time-varying channels

[EN] In orthogonal frequency division multiplexing (OFDM) signals, the usage of large size fast Fourier transforms (FFTs) reduces the guard interval percentage, and therefore increases the data throughput reducing the data overhead. In addition, for the same pilot pattern, the distance between adjacent pilots is smaller, which will improve the channel estimation. Nevertheless, up to now, they have not been considered for delivering mobile services as the inter-carrier interference (ICI) due to the Doppler effect is very critical. The main objective is to show that taking advantage of the latest improvements in error correction techniques, it is feasible to use large size FFTs for time-varying channels. Furthermore, there is also presented a theoretical estimation for quantifying the loss due to the ICI, and finally several simulation results that reinforce the idea that large OFDM symbols are suitable for mobile channels.This work has been financially supported in part by the University of the Basque Country UPV/EHU (UFI 11/30), by the Basque Government (IT-683–13 and SAIOTEK), by the Spanish Ministry of Science and Innovation under the project NG-RADIATE (TEC2009-14201), and by the Spanish Ministry of Economy and Competitiveness under the project HEDYT-GBB (TEC2012-33302)

Implementation Issues of Adaptive Energy Detection in Heterogeneous Wireless Networks

Abstract Spectrum sensing (SS) enables the coexistence of non-coordinated heterogeneous wireless systems operating in the same band. Due to its computational simplicity, energy detection (ED) technique has been widespread employed in SS applications; nonetheless, the conventional ED may be unreliable under environmental impairments, justifying the use of ED-based variants. Assessing ED algorithms from theoretical and simulation viewpoints relies on several assumptions and simplifications which, eventually, lead to conclusions that do not necessarily meet the requirements imposed by real propagation environments. This work addresses those problems by dealing with practical implementation issues of adaptive least mean square (LMS)-based ED algorithms. The paper proposes a new adaptive ED algorithm that uses a variable step-size guaranteeing the LMS convergence in time-varying environments. Several implementation guidelines are provided and, additionally, an empirical assessment and validation with a software defined radio-based hardware is carried out. Experimental results show good performance in terms of probabilities of detection (P-d > 0.9) and false alarm (P-f similar to 0.05) in a range of low signal-to-noise ratios around [4, 1] dB, in both single-node and cooperative modes. The proposed sensing methodology enables a seamless monitoring of the radio electromagnetic spectrum in order to provide band occupancy information for an efficient usage among several wireless communications systems.This work has been financially supported in part by the Spanish Ministry of Economy and Competitiveness under Project 5G-NewBROs (TEC2015-66153-P MINECO/FEDER, UE), and in part by the Basque Government (IT-683-13 and ELKARTEK program under BID3A3 and BID3ABI projects) and the European Regional Development Fund, ERDF

Performance Study of Layered Division Multiplexing Based on SDR Platform

[EN] Two of the main drawbacks of the current broadcasting services are, on the one hand, the lack of flexibility to adapt to the new generation systems requirements, and on the other hand, the incapability of taking a piece of the current mobile services market. In this paper, Layered Division Multiplexing (LDM), which grew out of the concept of Cloud Txn, is presented as a very promising technique for answering those challenges and enhancing the capacity of broadcasting systems. The major contribution of this work is to present the first comprehensive study of the LDM performance behavior. In particular, in this paper, the theoretical considerations of the LDM implementation are completed with the first computer based simulations and laboratory tests, covering a wide range of stationary channels and the mobile TU-6 channel. The results will support LDM as a strong candidate for multiplexing different services in the next generation broadcasting systems, increasing both flexibility and performance.This work has been financially supported in part by the University of the Basque Country UPV/EHU (UFI 11/30), by the Basque Government (IT-683-13 and SAIOTEK), by the Spanish Ministry of Science and Innovation under the project NG-RADIATE (TEC2009-14201), by the Spanish Ministry of Economy and Competitiveness under the project HEDYT-GBB (TEC2012-33302) and the European Regional Development Fund (ERDF)

Cloud Transmission: System Performance and Application Scenarios

[EN] Cloud Transmission (Cloud Txn) System is a flexible multi-layer system that uses spectrum overlay technology to simultaneously deliver multiple program streams with different characteristics and robustness for different services (mobile TV, HDTV and UHDTV) in one RF channel. The transmitted signal is formed by superimposing a number of independent signals at desired power levels, to form a multilayered signal. The signals of different layers can have different coding, bit rate, and robustness. For the top layer, system parameters are chosen to provide very robust transmission that can be used for high speed mobile broadcasting service to portable devices. The bit rate is traded for more powerful error correction coding and robustness so that the Signal to Noise Ratio (SNR) threshold at the receiver is a negative value in the range of -2 to -3 dB. The top layer is designed to withstand combined noise, co-channel interference and multipath distortion power levels higher than the desired signal power. The lowerlayer signal can be DVB-T2 signal or other newly designed system to deliver HDTV/UHDTV to fixed receivers. The system concept is open to technological advances that might come in the future: all new technologies, BICM/Non Uuniform-QAM, rotated constellations, Time Frequency Slicing or MIMO techniques can be implemented in the Cloud Txn lower (high data) rate layer. The main focus of this paper is to thoroughly describe the performance of this newly presented Cloud Transmission broadcasting system.This work has been financially supported in part by the University of the Basque Country UPV/EHU (UFI 11/30), by the Basque Government (IT-683- 13 and SAIOTEK), by the Spanish Ministry of Science and Innovation under the project NG-RADIATE (TEC2009-14201), and by the Spanish Ministry of Economy and Competitiveness under the project HEDYT-GBB (TEC2012- 33302

Channel phase processing in wireless networks for human activity recognition

The phase of the channel state information (CSI) is underutilized as a source of information in wireless sensing due to its sensitivity to synchronization errors of the signal reception. A linear transformation of the phase is commonly applied to correct linear offsets and, in a few cases, some filtering in time or frequency is carried out to smooth the data. This paper presents a novel processing method of the CSI phase to improve the accuracy of human activity recognition (HAR) in indoor environments. This new method, coined Time Smoothing and Frequency Rebuild (TSFR), consists of performing a CSI phase sanitization method to remove phase impairments based on a linear regression transformation method, then a time domain filtering stage with a Savitzky–Golay (SG) filter for denoising purposes and, finally, the phase is rebuilt, eliminating distortions in frequency caused by SG filtering. The TSFR method has been tested on five datasets obtained from experimental measurements, using three different deep learning algorithms, and compared against five other types of CSI phase processing. The results show an accuracy improvement using TSFR in all the cases. Concretely, accuracy performance higher than 90% in most of the studied scenarios has been achieved with the proposed solution. In few-shot learning strategies, TSFR outperforms the state-of-the-art performance from 35% to 85%.This work has been financially supported by the Basque Government (under grant IT1436-22) and by the Spanish Government (under grant PID2021-124706OB-I00, funded by MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe )