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The impending spectrum congestion imposed by the emergence of new bandwidth-thirsty applications may be mitigated by the integration of radar and classic communications functionalities in a common system. Furthermore, the merger of a sensing component into wireless communication networks has raised interest in recent years and it may become a compelling design objective for 6G. This article presents the evolution of the hitherto separate radar and communication systems towards their amalgam known as a joint radar and communication (RADCOM) system. Explicitly, we propose to integrate a radio sensing component into 6G. We consider an ultra-dense network (UDN) scenario relying on an active multistatic radar configuration and on cooperation between the access points across the entire coverage area. The technological trends required to reach a feasible integration, the applications anticipated and the open research challenges are identified, with an emphasis on high-accuracy network synchronization. The successful integration of these technologies would facilitate centimeter-level resolution, hence supporting compelling high-resolution applications for next-generation networks, such as robotic cars and industrial assembly lines., 10 pages, 3 figures, accepted for publication in IEEE Vehicular Technology Magazine

Radar systems based on orthogonal ifrequency-division multiplexing (OFDM) are promising candidates for future intelligent transport networks because they combine target-estimation functions with communication network functions in one single system. By exploring this dual functionality, this paper presents a new cooperative method for distributed target tracking for multiple-input multiple-output (MIMO) OFDM radar systems. The proposed method employs a cascading information-fusion approach. First, the ego-vehicle performs a multi-target estimation by fusing the radar signals reflected by the targets with the communication signals it receives. Then, the ego-vehicle performs a tracking process, fusing its estimates with the estimates made by other in-network vehicles. By exploring the cooperation between vehicles, the proposed method enables the distributed tracking of targets. The result is a highly accurate multi-target tracking across the entire cooperative vehicle network, leading to improvements in transport reliability and safety. The proposed method is validated through simulations and laboratory measurements at 24 GHz.

This paper considers a cooperative bistatic scenario for integrated sensing and communication (ISAC) paradigm, where transmitter and receiver base stations (BS) are connected through the front-haul to a central unit (CU), enabling cooperation. A multiple-input multiple-output (MIMO) configuration is considered in combination with orthogonal frequency division multiplexing (OFDM). The communication and radio-sensing functions are performed in orthogonal sets of sub-carriers, where the sub-carriers allocated to radio-sensing are distributed among antennas in an interleaved way. The interleaved frame structure is exploited in the design of a new parameter estimation method. The proposed method is a two-stage algorithm to estimate the delay/Doppler shift and angular position of objects (paths) in the channel. First, the multiple signal classification (MUSIC) algorithm estimates the angle-of-arrival (AoA) of the paths. Then, the delay, Doppler shift and angle-of-departure (AoD) are jointly estimated for each AoA combining an extended search over the AoD domain and a two-dimensional periodogram. The simulations show that the delay, Doppler shift and AoA are estimated correctly, while the estimation of the AoD may report error, although it can be compensated. published

High-resolution delay-Doppler estimation is an important requirement for automotive radar systems, especially in multi-target scenarios that require better target separation performance. Orthogonal frequency-division multiplexing (OFDM) is a promising candidate waveform for future intelligent transport networks, since it enables the integration of both radar and communication functionalities. Exploring the dual functionality enabled by OFDM, this paper presents a new cooperative method for high-resolution delay-Doppler estimation. The proposed subspace-based method exploits the combination of both the radar and received communication signals to estimate target parameters. The procedure achieves high-resolution delay-Doppler estimation for both uncorrelated, partially correlated and coherent signals, and enables a significant reduction in the required bandwidth when compared to previous approaches which do not exploit the knowledge of the communication signals. Laboratory measurements at 24 GHz and simulation results demonstrate the efficacy of the proposed method for the estimation of multiple targets.

Our aim with this paper is to present a solution suitable for vehicle-to-everything (V2X) communications, particularly, when employing single-carrier modulations combined with frequency-domain equalization (SC-FDE). In fact, we consider the V2X channel to be doubly-selective, where the variation of the channel in time is due to the presence of a Doppler term. Accordingly, the equalization procedure is dealt by a low-complexity iterative frequency-domain equalizer based on the iterative block decisionfeedback equalization (IB-DFE) while the tracking procedure is conducted employing an extended Kalman filter (EKF). The proposed system is very efficient since it allows a very low density of training symbols, even for fast-varying channels. Furthermore only two training symbols are required to initialize the tracking procedure. Thus, ensuring low latency together with reduced channel estimation overheads. published

The line spectral estimation problem has applications in radar, wireless communications, spectroscopy, and power electronics, among others. The signal is modeled as a sparse linear combination of complex sinusoids and the problem target is to estimate the number of sinusoids in the mixture, and respective parameters of each individual sinusoid, such as magnitude, phase, and frequency. In this work, we first introduce a novel formulation of the rank function, which involves the solution of a multi-convex optimization problem. Using the multi-convex reformulation of the rank function an over-parameterization of the line estimation problem is proposed together with a cyclic minimization procedure to obtain a solution. The cyclic method iterates between the optimization of the signal subspace and null-space and stops when the two are orthogonal. Every limit point of the sequence of iterates is shown to be a stationary point of the original problem. Numerical experiments show that only a small number of iterations is required for convergence. The signal subspace optimization is a semidefinite program (SDP) and the null-space optimization has a closed-form solution. The cost per iteration of a general-purpose interior point method (IPM) to solve the SDP is a quartic function of the problem dimension. It is shown that by exploiting the problem structure the cost per iteration of the IPM may be reduced to a cubic function of the problem dimension, comparable to the cost of the alternating direction method of multipliers (ADMM). However, contrarily to the latter, the former achieves the precision necessary for fine frequency localization. A large set of numerical experiments show the effectiveness of the proposed approach.

This paper proposes a hybrid multi-user equalizer for the uplink of broadband millimeterwave massive multiple input/multiple output (MIMO) systems with dynamic subarray antennas. Hybrid subconnected architectures are more suitable for practical applications since the number of required phase shifters is lower than in fully connected architectures. We consider a set of only analog precoded users transmitting to a base station and sharing the same radio resources. At the receiver end, the hybrid multi-user equalizer is designed by minimizing the sum of the mean square error (MSE) of all subcarriers, considering a two-step approach. In the first step, the digital part is iteratively computed as a function of the analog part. It is considered that the digital equalizers are computed on a per subcarrier basis, while the analog equalizer is constant over the subcarriers and the digital iterations due to hardware constraints. In the second step, the analog equalizer with dynamic antenna mapping is derived to connect the best set of antennas to each radio frequency (RF) chain. For each subset of antennas, one antenna and a quantized phase shifter are selected at a time, taking into account all previously selected antennas. The results show that the proposed hybrid dynamic two-step equalizer achieves a performance close to the fully connected counterpart, although it is less complex in terms of hardware and signal processing requirements. published

In this paper, we propose the usage of Generalized Frequency Division Multiplexing (GFDM), a non-orthogonal multicarrier waveform for radar. We presented a novel method that cancels the effect of interference caused by the non-orthogonality of GFDM waveform in the radar processing, thus not affecting the performance of the radar. We show the viability of GFDM for radar with communications systems and the benefits of using it over Orthogonal Frequency Division Multiplexing (OFDM). Finally, we also present GFDM as a solution to mitigate inter-system interference in radar with communications (RadCom) systems, thus showing that GFDM may prove to be a better candidate than OFDM for RadCom applications. This method is validated with simulations and practical measurements at 24 GHz.

Emerging research in game theory based power control applied to ad hoc opportunist networks shows much promise to help understand the complex interactions between OR nodes in this highly dynamic and distributed environment. Also, the employment of game theory in modeling dynamic situations for opportunist ad hoc networks where OR nodes have incomplete information has led to the application of largely unexplored games such as games of imperfect monitoring. Ad hoc security using game theory is the future area of research in ORs we have considered an ah hoc behavior in the opportunists radio (ORs) and suggested that by implementing ah hoc features in the ORs will improve the overall performance of system.

In this paper we consider a multipath channel subject to variations in time due to the presence of a Doppler drift which imposes a phase rotation on the original channel impulse response. Accordingly, a decision-directed state-space approach based on the extended Kalman filter (EKF) is proposed to track the channel variation. This approach is particularly efficient since we are able to reduce the number of training symbols used for channel tracking to be as few as two times the number of transmitters. These training symbols are required to initialize the EKF. Furthermore, using a decision-directed approach we are able to provide the EKF with state-observations without additional training symbols. Our approach is specially designed to work with hybrid analog/digital multiple-input multiple-output (MIMO) architectures.

In this paper we consider a multipath channel subject to variations in time due to the presence of a Doppler term which imposes a phase rotation on the original channel impulse response. Accordingly, a decision-directed state-space approach based on the extended Kalman filter (EKF) is proposed to track the channel variation. This approach is particularly efficient since we are able to reduce the number of pilot symbols used for channel tracking by using a decision-directed approach. In fact, only two training symbols are required to initialize the EKF. Our approach is validated considering orthogonal frequency-division multiplexing (OFDM) schemes.

In this paper, a novel method for tracking targets using OFDM radar with an integrated communication system (RadCom) for automotive applications is presented. OFDM-based radar schemes are promising candidates for future intelligent transportation networks. However, due to system resolution limitations, improvements in estimation and tracking of targets are required. Correct and accurate object tracking is a critical aspect of advanced driver assistance systems. The proposed method takes advantage of the dual functionality of RadCom systems through an information fusion approach that combines the radar signal reflected by the targets with received communication signals. The main idea is to explore cooperation between vehicles to improve safety and accuracy during tracking. Tracking results of laboratory measurements at 24 GHz and simulation results in a multi-target environment are presented.

Although millimeter-wave (mmWave) and massive multiple input multiple output (mMIMO) can be considered as promising technologies for future mobile communications (beyond 5G or 6G), some hardware limitations limit their applicability. The hybrid analog-digital architecture has been introduced as a possible solution to avoid such issues. In this paper, we propose a two-step hybrid multi-user (MU) equalizer combined with low complexity hybrid precoder for wideband mmWave mMIMO systems, as well as a semi-analytical approach to evaluate its performance. The new digital non-orthogonal multi carrier modulation scheme generalized frequency division multiplexing (GFDM) is considered owing to its efficient performance in terms of achieving higher spectral efficiency, better control of out-of-band (OOB) emissions, and lower peak to average power ratio (PAPR) when compared with the orthogonal frequency division multiplexing (OFDM) access technique. First, a low complexity analog precoder is applied on the transmitter side. Then, at the base station (BS), the analog coefficients of the hybrid equalizer are obtained by minimizing the mean square error (MSE) between the hybrid approach and the full digital counterpart. For the digital part, zero-forcing (ZF) is used to cancel the MU interference not mitigated by the analog part. The performance results show that the performance gap of the proposed hybrid scheme to the full digital counterpart reduces as the number of radio frequency (RF) chains increases. Moreover, the theoretical curves almost overlap with the simulated ones, which show that the semi-analytical approach is quite accurate.

In this paper, we propose a hybrid multiuser equalizer combined with low complexity hybrid precoder for wideband millimeter-wave massive MIMO systems. We consider a generalized frequency division multiplexing (GFDM) modulation scheme, which is a new digital non-orthogonal multi-carrier modulation, aiming to achieve higher spectral efficiency, better control of out-of-band (OOB) emissions, and obtain a reduction in peak to average power ratio (PAPR) compared to OFDM. At the transmitter side, a simple yet efficient pure analog precoder is applied. At the base station, the hybrid multiuser linear equalizer is optimized by minimizing the mean square error between the hybrid approach and the full digital counterpart. The analog phase shifters have constant amplitude being constant over the bandwidth due to the hardware constraints. The results show that the performance of the proposed hybrid scheme is very close to the full digital counterpart as the number of RF chains increases.

This work presents the coder and decoder of block mBnB of the type 1B2B or Manchester. In the coder 1B2B each block/word of 1 input bit is coded in the block / word of 2 output bits. In the decoder 1B2B happen the inverse, each block of 2 input bits is newly converted in the original block of 1 output bit. The coder injects in the transmission line a number of 1’s exactly equal to the number of 0’s, what guarantees a DC constant component and maximizes the transitions number. The objective is to implement the pair coder and decoder 1B2B so that it improves the transmission quality and increases the information security. Keywords: Block codes, Digital systems, Transmission lines

This work presents the coder and decoder of block 7B8B simplified with auxiliary channel. The coder 7B8B converts an input 7 bits word in an output 8 bits word. It transmits approximately an equal number of 1’s and 0’s to provide a DC constant component. It increases the transitions number, improves the system quality and security. The objective is also to improve the system potentialities with an auxiliary channel to monitor the communication (alarm.) The main channel is real, but the auxiliary channel is fictitious. Keywords: Block Codes, Advanced digital systems, Transmission lines

In this paper we consider a multi-input multi-output (MIMO) channel subject to time variations. These channel variations are due to the presence of a Doppler term which imposes a phase rotation on the original channel impulse response (CIR). On one hand, modern equalization schemes require the knowledge of the CIR or, equivalently, the channel frequency response (CFR). On the other hand, channel estimation procedures consume significant resources, particularly when transmitting training sequences. Therefore, we propose the use of a statespace approach, namely the extended Kalman filter (EKF), to interpolate the channel estimates obtained during the training stage onto the data transmission stage. Our approach is validated considering single-carrier frequency-domain equalization (SCFDE) transmissions.

The high capacity demands of 5G communications require multiple input multiple output (MIMO) technologies and millimeter wave communications to enables the required multi-Gbps. The small wavelengths of millimeter wave communications allow packing a huge number of antennas in a small space, enabling massive MIMO schemes, with the associated high capacity gains. The hardware impairments inherent in low complexity hardware implementations are characteristic of these systems. This means strong nonlinear effects throughout the transmission chain that will have negative impact on the system’s performance. In this paper we study the impacts of these nonlinear effects on the overall performance of an OFDM massive MIMO communication employing a hybrid analog/digital architecture. For this purpose, we develop analytical and semi-analytical tools for performance evaluation of nonlinear effects in those systems. These tools are shown to be very accurate. They make it possible to predict the nonlinearities’ penalties in hybrid systems and/or to assess the optimal operation point for a specific nonlinear amplifier.

This work addresses the security of a two-user broadcast channel. The challenge of protecting a broadcast channel is associated with the necessity of securing the system, not only against eavesdropping attacks originating from external nodes, but also to ensure that the inside users do not eavesdrop on each other&rsquo, s information. To address this issue, the present work proposes a cooperative jamming scheme that provides protection against eavesdropping attacks carried out simultaneously by inside users and external eavesdroppers. To achieve this goal, the developed scheme combines real interference alignment with a blind cooperative jamming technique defined in the literature. An information theoretical analysis shows that positive secure degrees of freedom are achievable using the proposed solution.

Most of the previous work on hybrid transmit and receive beamforming focused on narrowband channels. Because the millimeter wave channels are expected to be wideband, it is crucial to propose efficient solutions for frequency-selective channels. In this regard, this paper proposes an iterative analog&ndash, digital multi-user equalizer scheme for the uplink of wideband millimeter-wave massive multiple-input-multiple-output (MIMO) systems. By iterative equalizer we mean that both analog and digital parts are updated using as input the estimates obtained at the previous iteration. The proposed iterative analog&ndash, digital multi-user equalizer is designed by minimizing the sum of the mean square error of the data estimates over the subcarriers. We assume that the analog part is fixed for all subcarriers while the digital part is computed on a per subcarrier basis. Due to the complexity of the resulting optimization problem, a sequential approach is proposed to compute the analog phase shifters values for each radio frequency (RF) chain. We also derive an accurate, semi-analytical approach for obtaining the bit error rate (BER) of the proposed hybrid system. The proposed solution is compared with other hybrid equalizer schemes, recently designed for wideband millimeter-wave (mmWave) massive MIMO systems. The simulation results show that the performance of the developed analog&ndash, digital multi-user equalizer is close to full-digital counterpart and outperforms the previous hybrid approach.

The future Internet of Things will integrate sensing and wireless communications. Among the multiple types of sensors to be used, sensors based on the radar principles are of interest for several applications, namely automotive. Dual functionality devices that integrate reflectometry and communication capabilities will be important to reduce development costs through the reuse of modules and to optimise the usage of radio resources, e.g. spectrum. This paper reviews the main trends that push for the merging of radar type sensors and wireless communications (RadCom). It presents the most important use cases that can be currently foreseen and identifies the main technology trends and issues to reach a mature technology, focusing on OFDM type waveforms that will enable a smooth integration with 4G and 5G.

This paper introduces a software-defined radio implementation of an OFDM-based transceiver for the prototyping and testing of 5G physical layer algorithms. The implementation uses high level abstraction tools to develop and test the algorithms, significantly reducing the time and effort needed to test new features. The proposed architecture adopts interconnecting FIFOs between each functional block, reducing the critical paths and enabling complex designs to be implemented at higher clock rates. The proposed LTE-like transceiver is implemented using COTS FPGA and RF development boards. The real-time over-the-air demonstrator has an on-the-fly scalable bandwidth from 20 to 61.44 MHz, attaining close to 500 Mb/s when using 256-QAM modulation.

Remarkable research activities and major advances have been occurred over the past decade in multiuser multiple-input multiple-output (MU-MIMO) systems. Several transmission technologies and precoding techniques have been developed in order to exploit the spatial dimension so that simultaneous transmission of independent data streams reuse the same radio resources. The achievable performance of such techniques heavily depends on the channel characteristics of the selected users, the amount of channel knowledge, and how efficiently interference is mitigated. In systems where the total number of receivers is larger than the number of total transmit antennas, user selection becomes a key approach to benefit from multiuser diversity and achieve full multiplexing gain. The overall performance of MU-MIMO systems is a complex joint multi-objective optimization problem since many variables and parameters have to be optimized, including the number of users, the number of antennas, spatial signaling, rate and power allocation, and transmission technique. The objective of this literature survey is to provide a comprehensive overview of the various methodologies used to approach the aforementioned joint optimization task in the downlink of MU-MIMO communication systems., Comment: 45 pages, 12 figures, accepted in IEEE Communications Surveys and Tutorials

Network densification through the deployment of small cells along the coverage area of a macro-cell, employing massive multiple input multiple output (MIMO) and millimeter-wave (mmWave) technologies, is a key approach to enhancing the network capacity and coverage of future systems. For ultra-dense mmWave heterogeneous scenarios with a massive number of users, one should address both inter- and intra-tier interferences contrary to the low-density scenarios, where the network is mainly noise limited. Therefore, this paper proposes low complex hybrid analog-digital receive and transmit beamforming techniques for ultra-dense uplink massive MIMO mmWave heterogeneous systems to efficiently mitigate these interferences. At the small cells, the hybrid analog-digital receive beamforming/equalizer is computed in a distributed fashion, where the analog processing is performed at the small cell base stations or access points and the digital part at a central unit for joint processing. To optimize the analog part of the hybrid equalizer and the precoders used at the user terminals, we consider as a metric the distance relative to the fully digital counterpart induced by the Frobenius norm. In the optimization problem, apart from the analog constraints usually considered in the homogeneous systems, we further impose the constraints inherent to the distributed nature of the access points. To cancel the inter-tier interference, the digital parts of the precoders employed at the small cell user terminals are designed so that this interference resides in a low-dimensional subspace at the macro base station. The results show that the performance of the proposed hybrid analog-digital precoder/equalizer scheme is close to the fully digital counterpart and is able to efficiently remove both inter- and intra-tier interferences.

In this paper, we consider a $K$ -user $M\times N$ MIMO interference channel, with outdated channel state information at the transmitters (CSIT). Based on the technique introduced by Cadambe and Jafar, for the IC with perfect and up-to-date CSIT, we propose and analyze a scheme that guarantees interference alignment with outdated CSIT. The interference is aligned by the transmitters, and removed by the receivers using zero-forcing by Cadambe and Jafar. However, this is not feasible for the IC with outdated CSIT, since there is no up-to-date CSIT to compute the interference alignment precoders. To overcome this limitation, we propose that the interference should be aligned by the receivers instead. With this approach, the interference caused by a transmitter spans the same subspace at all receivers, i.e., the interference at receiver $k \neq m$ may be obtained through a linear map from the interference at receiver $m$ . Therefore, one interference retransmission per transmitter is enough to cancel all the interference. This reduces the overhead required for interference removal from $K(K-1)$ to $K$ interference terms.

This paper presents a new concept of high-resolution direction-of-arrival (DoA) estimation in orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) radar with integrated communication system (RadCom) for automotive applications. High-resolution DoA estimation is an important requirement for automotive radar systems, especially in multi-target scenarios that require higher target separation performance. This paper introduces a subspace-based procedure for high-resolution DoA estimation for closely spaced targets in uncorrelated and partially correlated signals, and allows better DoA estimation in coherent signals. This procedure integrates the use of the radar signal together with the communication signal received from another user (one of the targets to be estimated).

In this paper we consider the use of a single- carrier with frequency-domain equalization (SC-FDE) scheme for the uplink in a cellular radio system. To cope with the doubly-selective nature of the channel we propose a receiver structure for the joint channel equalization and tracking. We use a low-complexity iterative frequency-domain equalizer based on the iterative block decision-feedback equalization (IB-DFE) concept for the channel equalization and an extended Kalman filter (EKF) for the channel tracking procedure. The tracking procedure works by, first, observing the channel through channel estimation based on training blocks and, then, by predicting the channel during data transmission. Alternatively, decision-directed channel estimation can be used also, resulting in an improved performance.

Most previous work on hybrid beamforming millimeter wave (mmWave) communications and massive multiple input multiple output (MIMO) systems focused on narrowband channels. However, it is expected that the mmWave channels will be wideband, and for that reason, it is important to design solutions for frequency-selective channels. Therefore, in this paper, we consider the design of a hybrid analog/digital multiuser linear equalizer for broadband mmWave massive MIMO systems, optimized using the bit error rate (BER) as a metric. For the digital part, a closed-form solution is obtained by showing that the minimum mean square error (MMSE) and minimum BER solutions are identical. The analog part, which is assumed to be the same for all subcarriers, is computed iteratively over the radio frequency (RF) chains, and it is shown that the solution obtained in a previous iteration may be updated inexpensively to obtain a solution for the current iteration. The simulation results show that the performance gap between the proposed hybrid broadband multiuser equalizer and full digital equalizer decreases monotonically and exponentially with the number of RF chains until reaching zero. Moreover, the gap decay rate is faster for sparser mmWave channels, where fewer RF chains are required to achieve the same performance of the full digital architecture.

This paper considers a hybrid two-step space-frequency receiver structure for multiuser uplink millimeter-wave (mmWave) massive MIMO based systems. We adopt constant envelope OFDM (CE-OFDM) since it is a promising modulation technique for future systems, which allows very efficient power amplification. We consider low-complexity user terminals employing a single RF chain and using an analog precoding based only on the average angles of departure of the channel. At the base station a non-linear multi-user equalizer, based on the iterative block decision feedback equalization (IB-DFE) principle, and using a hybrid analog-digital structure, is designed to efficiently remove the inter-user and inter-carrier interferences. This equalizer is designed to minimize the sum of the mean square errors of all subcarriers. Numerical results have shown that the proposed scheme outperforms the linear equalizers. Moreover, performance is already close to the full digital counterpart after only a few iterations.

The secrecy challenge of protecting a power domain non-orthogonal multiple access (NOMA) system is associated with the intrinsic superposition structure of the transmitted information. Because of this superposition operation, the interference generated by the other user’s information must be first decoded by the receiver in order to allow the intended information to be acquired. Therefore, a robust secrecy solution for this type of channel access techniques must consider not only the existence of attacks coming from undetectable passive eavesdroppers located outside of the network, but also attacks carried out by eavesdroppers registered as legitimate users inside the system. In this work, a cooperative jamming technique is combined with a secure channel training solution in order to protect a two user power domain NOMA system against eavesdropping attacks coming simultaneously from inside and outside of the network. The proposed secrecy solution is evaluated numerically and the evaluation demonstrates that weak secrecy is achieved against the inside and outside eavesdroppers.

This paper considers a multiuser broadband uplink massive multiple input multiple output (MIMO) millimeter-wave (mmWave) system. The constant envelope orthogonal frequency division multiplexing (CE-OFDM) is adopted as a modulation technique to allow an efficient power amplification, fundamental for mmWave based systems. Furthermore, a hybrid architecture is considered at the user terminals (UTs) and base station (BS) to reduce the high cost and power consumption required by a full-digital architecture, which has a radio frequency (RF) chain per antenna. Both the design of the UT’s precoder and base station equalizer are considered in this work. With the aim of maximizing the beamforming gain between each UT and the BS, the precoder analog coefficients are computed as a function of the average angles of departure (AoD), which are assumed to be known at the UTs. At the BS, the analog part is derived by assuming a system with no multi-user interference. Then, a per carrier basis nonlinear/iterative multi-user equalizer, based on the iterative block decision feedback equalization (IB-DFE) principle is designed, to explicitly remove both the multi-user and residual inter carrier interferences, not tackled in the analog part. The equalizer design metric is the sum of the mean square error (MSE) of all subcarriers, whose minimization is shown to be equivalent to the minimization of a weighted error between the hybrid and the full digital equalizer matrices. The results show that the proposed hybrid multi-user equalizer has a performance close to the fully digital counterpart.

This paper presents the development and evaluation of an orthogonal frequency-division multiplexing (OFDM) radar in a field-programmable gate array (FPGA) board. The work is realized with support of MATLAB and Xilinx System Generator software tools for computational simulations. The projected system is integrated in a FPGA board through the Xilinx Vivado software platform and its operability verified. The simulated and physical results show the possibility to distinguish several targets, with different characteristics, from the range versus velocity radar image.

Millimeter waves and massive multiple-input multiple output (MIMO) are two promising key technologies to achieve the high demands of data rate for the future mobile communication generation. Due to hardware limitations, these systems employ hybrid analog&ndash, digital architectures. Nonetheless, most of the works developed for hybrid architectures focus on narrowband channels, and it is expected that millimeter waves be wideband. Moreover, it is more feasible to have a sub-connected architecture than a fully connected one, due to the hardware constraints. Therefore, the aim of this paper is to design a sub-connected hybrid analog&ndash, digital multi-user linear equalizer combined with an analog precoder to efficiently remove the multi-user interference. We consider low complexity user terminals employing pure analog precoders, computed with the knowledge of a quantized version of the average angles of departure of each cluster. At the base station, the hybrid multi-user linear equalizer is optimized by using the bit-error-rate (BER) as a metric over all the subcarriers. The analog domain hardware constraints, together with the assumption of a flat analog equalizer over the subcarriers, considerably increase the complexity of the corresponding optimization problem. To simplify the problem at hand, the merit function is first upper bounded, and by leveraging the specific properties of the resulting problem, we show that the analog equalizer may be computed iteratively over the radio frequency (RF) chains by assigning the users in an interleaved fashion to the RF chains. The proposed hybrid sub-connected scheme is compared with a fully connected counterpart.

In order to fulfil the high capacity demands of 5G communications, massive MIMO and millimetre wave are two enabling key technologies considered for future wireless communication. Although these technologies allow huge capacity gains, the radio frequency transceivers employed in this systems induce several hardware impairments as noise quantization (due to resolution quantizers), nonlinear power amplifiers, frequency and phase offsets and in-phase and quadrature imbalance, which lead to a strong nonlinear distortion in the transmitted signal. The impact of these nonlinear effects on the overall performance of hybrid analog-digital massive MIMO millimetre wave OFDM systems is studied in this work, highlighting the importance of its knowledge to improve communication quality. Theoretical analysis of the distortion spectral signal in transmission is assessed and validated for these communication systems, using the quasi-Gaussian nature of the input nonlinear signals. The nonlinearity impact in these systems was observed for different scenarios, where the value of saturation level shows to have a strong influence on the overall system performance.

At the present time many studies have been carried out to jointly use the OFDM signal for communication and radar functions, but other waveforms have been shown to be better candidates than OFDM for communications applications. Therefore studies on evaluation of the application of these same signals to radar functions may be necessary. In this paper, we adapted the radar processing of the OFDM signal to be applied in a new Filter Bank Multicarrier (FBMC) scheme, which is shown to be much superior to the OFDM system since it presents the same bit error rate (BER) performance in multipath channels, a much higher spectral efficiency and as shown here, better performance in radar targeting. We evaluated its performance for radar applications with joint communications.