Many of the new mobile communication devices will be things that power and monitor our homes, city infrastructure and transport. Controlling drones thousands of miles away, performing remote ...surgeries or being immersed in video with no latency will also be a huge game changer. Those are some of the few things that make the fifth generation (5G) a revolution expected to be a thrust to the economy. To that end, the design and density of deployment of new networks is also changing becoming more dense, what introduces new challenges into play. What else will it add to previous generations? The MOOC about Ultra-dense networks for 5G and its evolution has been prepared by the researchers of an European MSCA ITN, named TeamUp5G, and introduces the most important technologies that support 5G mobile communications, with an emphasis on increasing capacity and reducing power. The content spans from aspects of communication technologies to use cases, prototyping and the future ahead, not forgetting issues like interference management, energy efficiency or spectrum management. The aim of the MOOC is to fill the gap in graduation and post-graduation learning on content related to emerging 5G technologies and its applications, including the future 6G. The target audience involves engineers, researchers, practitioners and students. This paper describes the content and the learning outcomes of the MOOC, the main tasks and resources involved in its creation, the joint contributions from the academic and non-academic sector, and aspects like copyright compliance, quality assurance, testing and details on communication and enrollment, followed by the discussion of the lessons learned.
An efficient implementation of several tasks at the receiver becomes crucial in OFDM-based high-speed WLAN systems, such as automatic gain control, time and frequency synchronization, and offset ...tracking. This paper deals with fixed point constraints and accuracy requirements for implementation of those algorithms. Also, a complete set of thresholds for the practical implementation of time and frequency synchronization sub-blocks is obtained. Moreover, a technique to mitigate the remaining frequency offset after coarse acquisition is proposed, yielding a good trade-off between performance and complexity. Finally, we propose the implementation of a simple and effective automatic gain control procedure.
Terahertz (THz) band communication has abundant spectral resources to accommodate multiple broadband carriers. However, the strong path loss attenuation and the limited transmission power affect the ...maximum number of carriers that can be activated. A simple way to address this limitation consists in transmitting the same message from multiple transmission points, using Joint-Transmission (JT) Coordinated Multi-Point (CoMP). However, the distance-frequency-dependent molecular absorption that THz channels experience makes the implementation of JT-CoMP challenging. In this paper, we propose a decentralized scheme that takes into account the effect of distance to select the per-carrier transmit beamforming weights and powers. For this purpose, low-rate feedback information is reported from the receiver to the transmission points, such that decisions performed locally take into account the ones made in the coordinated set. Notable sum data rate gains are observed when compared to the baseline schemes, where transmission power is equally divided among carriers or independently allocated using waterfilling. As expected, the accuracy of the reported channel phase information, the number active transmission points, and the distance-dependent frequency selectivity of the THz channel affect the sum data rate that multi-carrier JT-CoMP can provide.
The multipath diversity and coding gain metrics for cyclic-prefixed single-carrier (SC-CP) systems, which characterize the bit error rate (BER) at high SNR, have not been carefully studied in the ...literature. We first show that, unlike OFDM, the diversity and coding gains for SC-CP are data-realization-dependent. Then, we show that there is a signal-to-noise ratio (SNR) threshold beyond which the dominant diversity order starts deviating from the maximum diversity order to eventually reduce to one at higher SNRs. Using the averaged pairwise probability, we derive an analytical expression for this SNR threshold. The latter is shown to increase with the block length and to be unrealistically high for moderate/high block lengths. Comparisons of SC-CP with rotated constellations and zero-padded SC systems are also provided.
Code diversity using space-time block codes was developed for single-carrier and single-receiver systems. In this paper, the extension of code diversity by phase rotation to multi-user and ...multi-carrier systems is proposed and analyzed. We show that code diversity with reduced feedback is possible in this new scenario and the coding gain has a mild logarithmic decrease with the number of users and the number of sub-carriers. In addition, we develop an analytical upper bound for the average error probability whose accuracy is verified by simulation.PUBLICATION ABSTRACT
Global Communications Newsletter Campista, Miguel Elias M.; Moraes, Igor M.; Costa, Luís Henrique M. K. ...
IEEE communications magazine,
5/2023, Letnik:
61, Številka:
5
Magazine Article, Journal Article
Visible light communication (VLC) is a promising communication technology that paves the way to the Internet of Things. The forthcoming Industry 4.0 requires reliable high-speed communication links, ...which can be easily fulfilled with the massive adoption of the VLC technology. However, in VLC indoor communication environments, line-of-sight link blockages and strong misalignment losses between the light-emitting diode (LED) transmitters and the photodiode (PD) receivers are usual problems that must be tackled. This paper proposes a coordinated multi-point (CoMP) transmission technique to deal with both issues, and carries out a detailed evaluation of the VLC system performance as function of the PD receiver orientation and the density of obstacles in different scenarios. The proposed cooperative transmission scheme demonstrates an improvement in the average cell data rate and outage probability performance and, as a consequence, justifies the use of CoMP techniques to provide reliable VLC services in ultra-dense small cell scenarios indoors.
Users of wireless communications nowadays request everyday more and more data rate. In order to provide such as high transmission rates, multiple antennas in transmission and reception (MIMO) are ...used combined with the high efficient transmission scheme of OFDM (orthogonal frequency division multiplexing). Besides, enhanced systems must be designed to accomplish with the demand. One of the solutions to reduce interferences in wireless mobile channels is the block diagonalization (BD). However, a MIMO-OFDM-BD signal exhibits the drawbacks of OFDM counterparts in terms of power envelope fluctuations which degrades the signal if high efficiency nonlinear High Power Amplifiers (HPA) are used. Thus, in this paper, a novel technique for reducing the power envelope fluctuations based on Fuzzy logic is presented and analized. The proposal obtains the same reduction as the best MIMO-OFDM technique denoted as ACE (Active Constellation Extension) but with much less complexity over MIMO-OFDM-BD signals. More than 2 dB of reduction can be easily obtained by using our proposal.
Most of the turbo encoding schemes at standards are parallel-based, so different architectures for efficient implementation are common in the literature. However, a serial turbo decoder is not that ...common. This scheme is used in CCSDS 131.2-B-1 standard, which is attracting much of attention recently due to its higher performance for satellite communications. In this paper, an efficient architecture for the decoder is proposed and analyzed. It is intended to show an architecture that can be modeled in a circuit description language (such as VHDL and Verilog) in such a way that it can be easily implemented on a Field Programmable Gate Array (FPGA). This work describes in detail this architecture explaining the encoding operations that are performed at the transmitter and then, how to undo them at the receiver. The proposed algorithm works by using independent components to divide the tasks and to obtain a pipeline architecture to improve the efficiency. The results of simulating and implementing the proposed architecture on a Xilinx Zynq UltraScale+ RFSoC ZCU28DR board with XCZU28DR-2FFVG1517E RFSoC are shown. The final results presented demonstrate how the hardware operations give equivalent results to the software simulation and do not consume board resources aggressively as usually the turbodecoder does.
A Maximum Likelihood joint channel and Frequency Offset estimator is addressed for Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing systems in the presence of Inter Symbol ...Interference and Inter Carrier Interference due to an insufficient Cyclic Prefix. The use of known Pseudo Noise based Symmetric Sequences to perform the joint estimation is proposed. The periodicity of the cost function for the Frequency Offset estimator has been analytically derived. It has been found that the proposed Pseudo Noise based Symmetric Sequences achieve an acquisition range for normalized Frequency Offset within the interval ±0.5, while previously proposed symmetric sequences are limited to ±0.25. The performance of Frequency Offset and channel estimators has been evaluated by the Cramér–Rao Bound and the theoretical Mean Squared Error. Also, the analytical Mean Squared Error for channel estimation in case of an imperfect estimation of Frequency Offset has been developed to analyze its impact in the performance. Moreover, we have proven that the estimation with the second half of the symmetric preamble performs better than with the whole preamble.
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