We propose a low-power mobile low earth orbit (LEO) satellite communication architecture, employing double reconfigurable intelligent surfaces (RIS) to enhance energy efficiency and signal performance. With a distance between RISs that satisfies the far-field requirement, this architecture positions one small RIS each in the near-field of the satellite's antenna and the user on the ground. Moreover, we develop a path loss model for the double- Ris communication link, considering the near-field and far-field effects. Further, with the help of dual-stage beamforming, the proposed system maximizes the signal power and minimizes power consumption. Simulation results show that the proposed architecture can reduce the power consumption with 40 dB in the uplink, with a small$0.25^{2}\mathbf{m}^{2}$RIS near the user, to communicate in energy-constrained LEO satellite communication circumstances.

We propose a joint polarization and spatial modulation (JPSM) scheme using reconfigurable intelligent surface (RIS). In this scheme, a RIS equipped with dual-polarized (DP) reflecting elements is used to assist the communication between a transmitter of a single polarized antenna and a receiver equipped with a uniform linear array of DP antennas, while additionally encoding the reflected waves on the RIS to perform JPSM scheme. The information data is encoded in terms of the receiver DP antenna index as well as the polarization state of the received signal. Furthermore, we develop exhaustive and heuristic RIS phase shift design solutions to enable the RIS-JPSM scheme. Moreover, both an optimum maximum likelihood and a low complexity greedy detectors are formulated. The proposed scheme enhances the data rate by operating higher-order polarization modulation in comparison to the conventional RIS-based spatial modulation scheme.

Estimation of a radio receiver's location from single-antenna observations - the received signal strength - is well known for its limited accuracy and lack of robustness. Yet, for reasons of energy- and space efficiency, emerging IoT devices will often be equipped with a single antenna. In this paper, we show how reconfigurable intelligent surfaces (RISs) can bring robustness and precision to this estimation problem. We propose a novel RIS-assisted SISO location scheme, based on new dynamic RIS reconfiguration protocols and an associated Maximum Like-lihood location estimation. We derive the Fisher information, the Cramér- Rao bound, and evaluate through simulations the effects of various relative RIS geometries and RIS reconfiguration pro-tocols. Our results indicate that the deployment of multiple RISs in the far-field allows for centimeter-level estimator accuracy. Reconfiguring RISs in a (pseudo-) random manner outperforms a deterministic orderly protocol by about 4 dB.

In line-of-sight (LoS) environments, point-to-point (P2P) multiple-input multiple-output (MIMO) channel matrix turns out to be rank deficient such that spatial multiplexing becomes unattainable. In this paper, we propose the deployment of distributed intelligent reflecting surfaces (IRSs) to act as artificial scatterers and synthesize a sort of multi-path propagation such that additional degrees of freedom are created. We show that given the far-field deployment of the IRS, it simply resembles a full-duplex relay with a single effective reflection coefficient. However, to maximize the channel capacity both the effective reflection coefficients of all IRSs and the transmit covariance matrix should be jointly optimized, which is a nonconvex optimization problem. Thus, we develop an alternating optimization algorithm to iteratively find a sub-optimal solution. Moreover, we propose different schemes to enhance the composite channel power which would result in an improvement to the achievable rate. Our simulation results show that the deployment of distributed IRSs with P2P MIMO systems in LoS environments increases the rank of the channel matrix, and improves the achievable rate by making spatial multiplexing possible.

Because of low potential revenue, network operators have mainly focused on providing connectivity in urban areas rather than in rural areas resulting in technology improvement in favour of urban areas; and consequently, most of remote areas suffer from poor or lack of connectivity. In this paper, we present the potential of massive‐MIMO to provide connectivity to sparse areas. We show that we can cover large rural areas with radius of tens of km using massive‐MIMO mounted on existing infrastructure of TV towers. We also show that, in contrast with common belief, higher frequencies, e.g., 3500 MHz rather than 700 MHz, can reach farther utilizing massive‐MIMO, provided that the antenna area is the same.

This work studies the joint design of spectral precoding, to avoid spectral out-of-band power emissions, and spatial precoding, to suppress spatial multiuser interference, in MIMO-OFDM systems. In current state-of-art approaches the transmit signals are precoded using two independently designed spectral and spatial precoders. In contrast this paper proposes a joint precoding of the signal to achieve a better performance. We analyse the performance of the proposed precoder in terms of spectral characteristics, system spectral efficiency and transmitter complexity. We show in particular that, interestingly, the proposed joint maximum-ratio precoder has a simple transmitter structure of two separate and consecutive banks of spectral and spatial precoders which in fact can be designed independently, while in case of zero-forcing the off-the-shelf precoders are far from the optimal. The joint zero-forcing precoder has a coupled structure and hence, we can not decompose it.

N-continuous orthogonal frequency division multiplexing (OFDM) is a promising solution to the out-of-band (OOB) emission issue in OFDM systems where theNth-order continuity between OFDM symbols leads to lower OOB emission than the plain OFDM; however, high self-interference in such systems is an obstacle. In this paper, we propose a new class of quasi-cyclic symbol extensions, which makes the OFDM systemN-continuous. The new extension leads to low OOB emission while the additive interference is less than otherN-continuous OFDM systems. Moreover, we propose a general analysis of the spectrum and interference that occurs in a linear precoded OFDM system. The framework is applicable to manyN-continuous OFDM systems including our proposed method.

In this paper we present a joint precoded and windowed OFDM system. This new hybrid method provides flexibility to suppress the out-of band (OOB) emission in non-contiguous OFDM systems used in cognitive radio. This method also provides the possibility of shortening the cyclic prefix without sacrificing the OOB emission or increasing the additional interference which is the case in low-latency future systems.

The N-continuous precoder for the suppression of OOB emission in OFDM systems that minimizes the EVM is introduced. We show that the minimum in-band interference due to the introduced precoding approach is 3 dB less than the inband interference of existing N-continuous precoders. Moreover, we introduce a novel practical block precoder that approaches the performance of the suggested optimal precoder. We analyze the spectrum of the OFDM signal after block precoding, the inband interference due to block precoding and the effect of block precoding on the BER. The price to pay for block precoding is the computational complexity that grows linearly with the block size.

In this paper, we describe and analyze the results of a radio channel measurement campaign in an extreme industrial environment; a large open-pit copper mine targeted by next generation's highly voiced device communications. We present a practical and efficient method to perform robust and high-sensitivity impulse response measurements without a common clock reference using the widely spread USRP hardware. With this technique, we performed channel sounding on a large number of locations within the mine. One important observation is that the radio channel's impulse response in an open-pit mine can often be more than 10 μs long, and much unlike the responses normally associated with Wi-Fi and mobile cellular radio systems, which poses serious design challenges for future 5G radio systems.

Dynamic spectrum management (DSM) improves the capacity utilization of twisted-pair cables by adapting the transmit power spectral density (PSD) of modems to the actual noise environment and channel conditions. Earlier proposed DSM algorithms do not take into account the standardized very high speed digital subscriber line (VDSL) constraints on the allowable transmit PSDs. However, VDSL modems support only restricted transmit PSD shapes resulting from the standardized power back-off (PBO) method, which is controlled by a small set of parameters. Furthermore, since all modems are currently using the same PBO parameters their bit rate performance is severely limited. In this paper, we show how to effectively exploit the standardized PBO concept for DSM to significantly boost bit rates. We also present a low complex DSM algorithm, the user unique PBO (UUPBO) algorithm, for calculating PBO parameters that are uniquely optimized for each modem.

Accurate upstream power back-off (PBO) parameters are needed by operators deploying very high-speed digital subscriber line (VDSL) modems. Although a standardized PBO method for VDSL exist, the standard gives little or no guidance to an operator how to establish these optimized PBO parameters for its particular network and customers. In this paper, we present an efficient algorithm based on the Nelder-Mead simplex search which calculates optimized upstream PBO parameters. To make the PBO parameter calculation independent of the network scenario we present a new method for establishing worst-case far-end crosstalk (FEXT) noise, which is based on virtual modems

In this paper we consider the estimation of improper noise in multicarrier DSL systems. We show that the improperness of baseband noise relates to the mirrored frequency components in the positive and negative frequency halves. Spectral leakage in the receiver requires in general widely linear estimation (WLE) techniques of the noise instead of less complex linear estimation (LE) techniques. We describe how to take into account for the improperness in the estimation and how it is possible to neglect it by using smooth receiver windowing. This is demonstrated by using two similar but conceptually different noise estimators, which are based on deterministic and stochastic noise models, combined with LE or WLE. We also describe some practical properties of improper noise estimation in multicarrier DSL systems by showing intuition pleasing connections to spectral leakage, receiver windowing, dimensionality and model parameters, residual noise interference, and complexity.

We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. We assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal's power spectral density as a priori information. Using a frequency invariant design, it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, show that, without perfect a priori information, this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal-to-noise ratio and symbol error rate degradation.

We present an algorithm that autonomously synchronizes all DMT-Zipper based VDSL modems in an unbundled access network, solving the problem with nonorthogonal NEXT that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL modem in the central office or in the street cabinet. We determine the other modems' relative frame offsets by exploiting their NEXT signal using the inherent cyclic redundancy found in DMT signals. By estimating the relative frame offsets of the other users, we can adjust a given user's own frame-timing relative to the mean of the others. With our method all modems in the network will be synchronized to within a small fraction of the total DMT frame-length, suppressing the nonorthogonal NEXT to a level far below the background noise-floor. This means that we can achieve the same performance in an unbundled access network without any master clock reference as in a system where all modems are perfectly synchronized using a master clock.

We present an algorithm for self-synchronizing all modems in a discrete multitone (DMT)-based very high-speed digital subscriber line (VDSL) system using the Zipper duplex method. This solves the problem with non-orthogonal near-end crosstalk (NEXT) that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL-modem. It uses the auto-correlation of the DMT-signal to determine the frame-offset of other users, and adjusts the own frame-timing to be better aligned with the other users. With our method all modems will be self-synchronized to within a small fraction of the total DMT frame-length. This self-synchronization suppresses the NEXT to a level far below the background noise-floor. This means that our self-synchronized system has the same performance as a system where all modems are perfectly synchronized to a master clock.

Previously the authors presented a novel duplex method for very high bit-rate digital subscriber lines (VDSL) called Zipper. With this method all VDSL-modems on different wires in the same bindergroup have to be time-synchronized to avoid near-end cross-talk (NEXT). We describe a method which enables Zipper to run in a time-asynchronous mode. By introducing pulse-shaping in the transmitter and windowing in the receiver the NEXT is almost completely suppressed even though the synchronization between modems on neighboring lines is skipped. The remaining NEXT and efficiency loss due to pulse-shaping and windowing results in only a small bit-rate performance loss, typically less than 10% compared to the time-synchronized Zipper. However, with the new freedom of optimizing the lengths of the cyclic suffices with asynchronous Zipper, there may even be a small improvement in bit-rate performance for short wires.

We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise sources.

We present performance results for a new duplex scheme, called Zipper, for DMT-based VDSL (very high bit rate digital subscriber lines) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream direction. It has a high flexibility to divide the capacity between the up- and downstream as well as good coexistence possibilities with other systems such as ADSL (asymmetrical digital subscriber line). Simulation results show a high bit rate performance in different environments such as mixed ADSL and VDSL traffic, under radio frequency interference, and with different background noise sources.