Power consumption constitutes a major challenge for electronics circuits. One possible way to deal with this issue is to consider it very soon in the design process in order to explore various design choices. A typical design flow often starts with a high-level description of a full system, which imposes to provide accurate models. Power modeling techniques can be employed, providing a way to find a relationship between power and other metrics. Furthermore, it is also important to consider efficient power characterization techniques. The role of this article is, first, to provide an overview of the register transfer level to transistor level power modeling and estimation techniques for FPGAs and ASICs devices. Second, it aims at proposing a classification of all approaches according to defined metrics, which should help designers in finding a particular method for their specific situation, even if no common reference is defined among the considered works.

In this article, we present a new, simple, accurate, and fast power estimation technique that can be used to explore the power consumption of digital system designs at an early design stage. We exploit the machine learning techniques to aid the designers in exploring the design space of possible architectural solutions, and more specifically, their dynamic power consumption, which is application-, technology-, frequency-, and data-stimuli dependent. To model the power and the behavior of digital components, we adopt the Artificial Neural Networks (ANNs), while the final target technology is Application Specific Integrated Circuit (ASIC). The main characteristic of the proposed method, called NeuPow, is that it relies on propagating the signals throughout connected ANN models to predict the power consumption of a composite system. Besides a baseline version of the NeuPow methodology that works for a given predefined operating frequency, we also derive an upgraded version that is frequency-aware, where the same operating frequency is taken as additional input by the ANN models. To prove the effectiveness of the proposed methodology, we perform different assessments at different levels. Moreover, technology and scalability studies have been conducted, proving the NeuPow robustness in terms of these design parameters. Results show a very good estimation accuracy with less than 9% of relative error independently from the technology and the size/layers of the design. NeuPow is also delivering a speed-up factor of about 84× with respect to the classical power estimation flow.

In this paper, we present a flexible, simple and accurate power modeling technique that can be used to estimate the power consumption of modern technology devices. We exploit Artificial Neural Networks for power and behavioral estimation in Application Specific Integrated Circuits. Our method, called NeuPow, relies on propagating the predictors between the connected neural models to estimate the dynamic power consumption of the individual components. As a first proof of concept, to study the effectiveness of NeuPow, we run both component level and system level tests on the Open GPDK 45 nm technology from Cadence, achieving errors below 1.5% and 9% respectively for component and system level. In addition, NeuPow demonstrated a speed up factor of 2490X.

Analog Beamsteering (ABS) has emerged as a low complexity and power efficient solution for Wave (mmWave) massive Multiple Input Multiple Output (Massive-MIMO) systems. Driven by the ability to exploit the low spatial correlation between the User Terminals (UTs) when a high number of transmit antennas is available at the Base Station (BS), ABS can be used to support Multi User (MU) MIMO scenarios instead of digital or Hybrid Beamforming (HBF) approaches. In this paper, we analytically characterize the Spectral Efficiency (SE) of MU-Massive-MIMO systems relying on ABS and theoretically define the asymptotic saturation level of the SE at high SNR. On the other hand, we provide a tight theoretical approximation for the SE of the system when implementing HBF with ABS at the analog stage and Zero Forcing precoding at the digital layer.

Receive Antenna Shift Keying (RASK) is a MIMO transmission scheme that is based on the Spatial Modulation (SM) concept applied at the receiver. In this scheme, the so-called spatial symbol is mapped to the index of one receive antenna that will be targeted during the symbol duration. In this paper, the performance of RASK is studied when the Maximum Ratio Transmission (MRT) precoding is used at the transmitter to focus toward the targeted antenna using coherent or non-coherent detection with different detection algorithms at the receiver. For coherent detection, the ML- based detector, and the Maximum Real Amplitude (MR) detector are studied, and we propose a specific detector called Maximum Real Minimum Imaginary (MRMI). For non-coherent detection, the ML-based detector and the Maximum Received Power (MP) are studied. The expressions of the Pairwise Error Probability for the coherent ML, MR and MP are derived and validated by simulations, and the performance of all detectors are compared by simulations. Finally, the computation complexity of the detectors is compared.

In this paper, we demonstrate an experimental visible light communication (VLC) transmission compliant with illumination standards consisting of low-cost components. We therefore employ the carrierless amplitude and phase (CAP) modulation technique over a low-cost white light emitting diode (LED), and we experimentally investigate the maximum achievable data rate while limiting the illumination level to that of a typical office environment. For a given optical power and using a low-cost silicon PIN photodiode, we achieved a throughput of 184 Mbps with a 16-CAP signal and with a bit error rate (BER) below 0.001. Moreover, those experimental results are compared to a simulation model we developed.

Today reducing power consumption is a major concern especially when it concerns small embedded devices. Power optimization is required all along the design flow but particularly in the first steps where it has the strongest impact. In this work, we propose new power models based on neural networks that predict the power consumed by digital operators implemented on Field Programmable Gate Arrays (FPGAs). These operators are interconnected and the statistical information of data patterns are propagated among them. The obtained results make an overall power estimation of a specific design possible. A comparison is performed to evaluate the accuracy of our power models against the estimations provided by the Xilinx Power Analyzer (XPA) tool. Our approach is verified at system-level where different processing systems are implemented. A mean absolute percentage error which is less than 8% is shown versus the Xilinx classic flow dedicated to power estimation.

Millimeter-Wave (mmWave) channels are characterized as being sparse and Line of Sight (LoS) dominated. Applying hybrid beamforming in mmWave systems guarantees Multi-User (MU) transmission with low hardware requirements. Zero Forcing (ZF) precoding can be utilized at the digital layer of the hybrid beamformer to mitigate the Inter User Interference (IUI). However, due to the sparse nature of the mmWave channels, a ZF precoder may provide limited performance due to the highly correlated MU channel matrix. The aim of this paper is hence to address the interference mitigation problem in the analog domain before handling it at the ZF digital level. Signal to Leakage and Noise Ration (SLNR) based users selection algorithm is introduced for maximizing the Spectral Efficiency (SE) of the system with low complexity requirements. We finally highlight by simulations the potential gains achieved by the introduced interference aware users selection approach.

Spatial modulation (SM) schemes use the index of the transmit (resp. the receive) antenna to transmit additional data, and therefore allow for a new exploitation of the space dimension to increase the spectral efficiency of MIMO systems. The baseline of the proposed study relies on the so-called extended receive antenna shift keying (ERASK) concept consisting in transmitting the spatial bits by focusing the transmit energy towards subsets of receive antennas. With ERASK, the subsets of targeted antennas can be of any size leading to an amount of additional spatial bits directly equal to the number of receive antennas. However, an ON/OFF keying is used to carry the spatial symbols meaning that a zero power level is associated with non targeted antennas. Consequently, the transmission of additional IQ symbols in ERASK is not compatible with every spatial symbol configurations. In this paper, we propose a novel scheme referred to as Extended RSM (ERSM) that sends additional IQ modulated signals in ERASK, in order to increase the overall spectral efficiency. The key idea is to associate a non zero power levels for all spatial symbols. Two power levels are used to transmit the spatial and the IQ symbols, and an optimal ratio of the power is calculated. The theoretical performance of the proposed ERSM scheme is derived and then validated through simulations.

Millimeter-Wave (mmWave) systems offer extremely large Band-Width (BW) and highly Line-of-Sight (LOS) dominant channels. Many beamforming and power allocation techniques have recently emerged to leverage such channel characteristics in order to enhance the sum capacity and the coverage for multi-user transmissions. However, most of the existing algorithms are practically limited due to full channel knowledge and high complexity requirements. In this paper we introduce a novel, low complexity, angular based beamforming and power allocation framework, that requires the knowledge of the main contributive Directions of Arrival/Departure (DoAs/DoDs) of the propagation channel only. Exploiting the fact that propagation conditions are highly driven by the geometrical structure of the channel in mmWave scenarios, our method relies on the estimation of the leakage caused by each User Equipment (UE) on all the other UEs, approximated from the DoAs contributions. We prove with the simulation results that this approach, in addition to be practically plausible, can enhance the network Spectral Efficiency (SE) alongside with maintaining acceptable data rates for the cell edge UEs.

Spatial modulations (SM) use the index of the transmit (or the receive) antennas to allow for additional spectral efficiency in MIMO systems by transmitting spatial data on top of classical IQ modulations. Extended Receive Antenna Shift Keying (ERASK) exploits the SM concept at the receiver side and yields the highest overall spectral efficiency in terms of spatial bits compared to the conventional SM schemes. To perform efficiently, ERASK may use zero-forcing precoding to target spatial streams towards the selected receive antennas, therefore requiring the Channel State Information CSI at the transmitter. In this paper, we evaluate the theoretical performance degradation of the ERASK scheme under imperfect CSI. In addition, correlation between antennas at the transmitter and the receiver using the Kronecker correlation model is integrated in our analysis. Analytical approach for the Bit Error Rate performance is provided and validated through simulations.

The new MIMO schemes commonly referred to as spatial modulations (SM) use the index of the transmit (resp. the receive) antenna to transmit additional data and hereby increase the spectral efficiency of digital communication systems. Most of proposed SM schemes allow for simultaneously transmitting two types of symbols, the classical IQ-symbols of a M-order modulation, and a spatial information related to the index of the transmit or targeted receive antenna(s). In this paper, we propose a complete uplink and downlink transmission system between a Base Station and a Connected Device for Internet-of-Things application based on SM. We thus concentrate on SM schemes only conveying spatial information for both downlink (from a base station to a connected device) and uplink (from a connected device to a base station) transmissions and leading to low complexity at the device. For the downlink we propose the use of an existing receive SM, the ERASK that is an extension of a very simple receive spatial modulation known as RASK (Receive Antenna Shift Keying) which aims at increasing the spectral efficiency. For the uplink, we firstly propose a new scheme which analogy with ERASK is highlighted. Both ERASK and ESSK can be efficiently used in the global system while keeping very low complexity at the device side. All complexity is reported at the base station with pre-processing function used to concentrate the signal energy towards the device targeted antenna(s). The channel estimation is also only needed at the base station for pre-processing of the ERASK and detection process of the ESSK.

This paper discusses the problem of user association and downlink resource allocation in heterogeneous wireless networks (HWNs) where a mobile node (MN) can associate to a single network at a time. A context-aware optimization problem is formulated to maximize the aggregate user-centric profit in the system while taking into consideration the network constraints, user preferences, and the amount of data rate requested by each MN. To achieve its purpose, the formulated problem employs contextual information related to the MN measurements and requirements, the HWN architecture, and the available resources at each network. The user-centric profit is based on the quality of the received signal and the power consumption at the MN. The formulated optimization problem is discrete (binary) with high complexity; based on the continuous relaxation of the problem, a solution with polynomial-time complexity is proposed. It is shown through simulations that the proposed solution achieves a near-optimal performance in terms of average user-centric profit and percentage of blocked data rate. Moreover, the proposed solution requests lower number of handovers.

Integrating different types of wireless access technologies in heterogeneous networks provides flexible choices for users to handover to a more preferable network that satisfies their needs. In this paper, we discuss the recent 802.21.1 Software Defined Radio Access Network (SDRAN) architecture that couples the Software Defined Networking (SDN) mechanisms by the IEEE 802.21 Media Independent Handover Services. Based on this architecture, we propose a centralized handover algorithm that manages user association and downlink capacity resource allocation. The algorithm is formulated as a Generalized Assignment Problem (GAP) which maximizes the overall profit of mobile nodes which is studied in terms of power consumption and Received Signal Strength (RSS). Comprehensive simulation has been conducted; It is shown that the formulated algorithm reduces the overall consumed power and increases the average relative received signal strength while demanding an extra number of HOs.

Time-Reversal (TR) precoding schemes are regarded as promising candidates for robust and energy efficient wireless systems. These schemes are characterized by their low computational complexity at the receiver side. In multipath Rayleigh fading channel, this paper presents analytical expressions of the average bit error rate (BER) of TR technique and the Equal Gain Transmission (EGT) scheme in MISO-OFDM systems. It further provides simple and tight upper bounds on the ergodic capacity of these schemes. Hence, these theoretical analyses might be very useful to avoid lengthy simulations. It also provides an interesting conclusion: for large number of transmit antennas, i.e. in Massive MIMO, TR technique outperforms the EGT scheme and its performance approaches that of Maximum Ratio Transmission (MRT) scheme. Hence, it confirms the applicability of TR scheme in the future Massive MIMO systems. Results with LTE-A system parameters are provided in order to corroborate our analysis.

Real-life ants use pheromone trails to guide themselves back and forth from food, without the help of a map. In this paper, we introduce a new protocol for wireless networks, called Time Reversal for Ant Trails (TRAT) which mimics ants by using electromagnetic virtual beacons generated by Time Reversal focusing instead of pheromones. Simulations show that for a given trajectory, the performance of the proposed scheme increases with the number of transmit antennas at the network side, with the precision of the scanning, and decreases with inter-beacon spacing and the carrier frequency.

The orbital angular momentum (OAM) is a physical property of an electromagnetic (EM) radiation, distinct from polarization, carrying a mechanical moment. In radio frequency range, OAM can be viewed as a phase gradient on the wave front. In this paper, the problem of the detection of the orbital angular momentum (OAM) order (or topological charge) for electromagnetic (EM) radiation is addressed. The OAM order detection problem is first presented as a multiple hypothesis testing problem. The maximum likelihood test leading to the error probability on the OAM order detection in additive white Gaussian noise (AWGN) channel is derived when the transmitting and receiving arrays are perfectly aligned and misaligned. A simpler receiver based on fast fourier transform (FFT) is then presented. The performances of this receiver are then presented through extensive simulation runs for various degrees of misalignment between the transmitter and the receiver.

Elimination of alien crosstalk in coordinated digital subscriber line systems is investigated in this study. In the upstream, the process of crosstalk elimination may take advantage of available coordination at the receiver side. As the signal received at the coordinated terminals can be corrupted by alien crosstalk, the reception process involves passing the signals received at the coordinated terminals through a spatial whitening operation. As part of the contribution in this study, a method is proposed to obtain the spatial whitening filter coefficients. These coefficients are estimated from the cyclic spectrum of alien crosstalk received at the coordinated system terminals, where transmission at the coordinated system is controlled to allow separating the cyclic spectra of both coordinated system and alien crosstalk signals. This study includes evaluation of the whitening receiver performance taking into account the effects of estimation errors. Theoretical derivations are illustrated by numerical results obtained for VDSL2 application.

Low complexity Multiple Input Multiple Output (MIMO) precoders for Orthogonal Frequency Division Multiplex (OFDM), such as Maximum Ratio Transmission (MRT) and Minimum Mean Square Error (MMSE) precoders enable to multiplex data streams in the spatial domain, without breaking OFDM orthogonality in the frequency domain, and therefore achieve a high spectral efficiency. OFDM using Offset Quadrature Amplitude Modulation (OFDM/OQAM) is an alternate modulation which is more spectrally efficient than OFDM. Unfortunately, when applied to OFDM/OQAM, traditional low complexity precoders introduce an inter-carrier interference (ICI) which is complex to cancel at the receiver side. This paper proposes a new family of low complexity precoders, called “Make-It-Real” (MIR) precoders. These precoders are designed so that the equivalent channel including precoding and propagation is “made real” and does not break the orthogonality of OFDM/OQAM in the frequency domain. At the receiver side, a simple extraction of the real part of the demodulated signal is necessary. Simulations show that OFDM/OQAM with MIR MMSE precoder outperforms all studied MIMO OFDM solutions, without requiring a complex ICI cancellation at the receiver.

Recently, polymer optical fiber (POF) became a popular solution for the indoor communications. In this paper, a multi-band discrete-Fourier-transform spread (MB-DFT-S) discrete multi-tone (DMT) system is proposed to study and optimize in terms of POF communications. A joint optimization of used subcarrier number, used bandwidth and multi-band number is investigated. The transmission of MB-DFT-S DMT over 50 m POF link is implemented. Both theoretical and experimental results demonstrate that optimized MB-DFT-S DMT system outperforms the original DMT and DFT-S DMT systems, which means that it is a promising technique for future POF transmission systems.

In this paper we study the Time Reversal (TR) technique in a large MISO-OFDM system. This technique has been proven to provide good beamforming gains at a price of a channel estimation availability at the transmitter side. Moreover, the greater the number of transmit antennas, the better the spatial and temporal focusing gains, which makes TR a good candidate for large MISO systems while keeping a low complexity. The capacity of the system and the bit error rate (BER) performances are first derived and simulated and compared with systems applying the maximum ratio transmission technique. The time focusing gain of the TR technique is then exploited to show that the equivalent channel is shortened when the number of antennas increases, allowing a reduction of the guard interval and an increase of the spectral efficiency of the system. Finally, the robustness of the system to channel estimation errors is evaluated by adding simple channel estimation techniques in the system and evaluating the BER performance.

In this work, a new fast-decodable space-time block code (STBC) is proposed. The code is full-rate and full-diversity for 4 × 2 multiple-input multiple-output (MIMO) transmission. Due to the unique structure of the codeword, the proposed code requires a much lower computational complexity to provide maximum-likelihood (ML) decoding performance. It is shown that the ML decoding complexity is only O(M4,5) when M-ary square QAM constellation is used. Finally, the proposed code has highest minimum determinant among the fast-decodable STBCs known in the literature. Simulation results prove that the proposed code provides the best bit error rate (BER) performance among the state-of-the-art STBCs.

In this paper, we propose a distributed coding/modulation scheme for wireless broadcast networks with relays. We consider a scenario where a source communicates with a single destination assisted by a relay which aids transmission to the destination. Orthogonal frequency division multiplexing (OFDM) transmission is considered where the available bandwidth is allocated simultaneously to the source and the relay. Real value data symbols are transmitted by the source. The relay decodes the information from the sources and it re-encodes them to generate some extra redundancy, which is modulated onto real data symbols and transmitted to the destination with a time offset equal to half the signal interval. Hence, the proposed scheme can be regarded as a distributed OFDM/OQAM scheme between the source and the relay. The proposed scheme achieves good performance in terms of bit error rate. Moreover, it does not require insertion of guard interval achieving therefore spectral efficiency gain.

Traditionally, cellular radio communication systems define a spectrum mask to avoid inter-channel interference between services operated in adjacent frequency bands. In this paper, we intend to optimize the spectrum efficiency of wireless systems by frequency band reused, which is performed by partial channel overlapping of adjacent bands. The impact of interchannel interference is studied for both single and multicarrier modulations. Then time reversal (TR) with multiple-input-single-output (MISO) is applied to depress the inter-channel interference thanks to the TR focusing properties. The spectral efficiency of the system is evaluated according to the overlap ratio τ and the number of transmitting antennas. The optimal τmaxis identified and, as a result, channel overlapping is proved to be interesting at low SNR regime in a range depending on the number of antennas.

Time Reversal (TR) is a multiple-input single-output (MISO) pre-filtering technique that allows a signal to be sent towards a target antenna by focusing the wave at the receiver both in the time and in the space domains. Recently, TR has been advertised for both green communications and confidential communications. This paper proposes an experimental characterization of the confidentiality of an indoor MISO-TR communication. The transmit system is made of 16 transmit antennas distributed within a room and the data stream is transmitted with a 256-Quadratic Amplitude Modulation (256QAM). The received signal is demodulated by the target user but also by a spy or eavesdropper antenna, both using a Single Tap Receiver. The Bit Error Rate (BER) achieved by the spy is then evaluated for variable positions of the spy nearby the target. The “spy BER” is plotted as a function of the spy-to-target distance. This experimental measurement clearly shows the presence of a spy BER “sink” centered on the target.

The 3D MIMO code is a robust and efficient spacetime coding scheme for the distributed MIMO broadcasting. However, it suffers from the high computational complexity if the optimal maximum-likelihood (ML) decoding is used. In this paper we first investigate the unique properties of the 3D MIMO code and consequently propose a simplified decoding algorithm without sacrificing the ML optimality. Analysis shows that the decoding complexity is reduced from O(M8) to O(M4.5) in quasi-static channels when M-ary square QAM constellation is used. Moreover, we propose an efficient implementation of the simplified ML decoder which achieves a much lower decoding time delay compared to the classical sphere decoder with Schnorr-Euchner enumeration.

With the data explosion coming, research on green communications experiences a growing interest in the Information and Communication Technologies (ICTs) world. At the same time, Time Reversal (TR) has been identified as a good green candidate owing to its low-complexity and its ability to focus energy in both spatial and temporal domains allowing for reduction of interference between users and to improve Signal to Noise Ratio (SNR) gains. Nevertheless, applying TR requires channel estimation at the transmitter side and therefore induces overhead in packet-switched system because of the sounding frames transmission. In this paper, we propose a very simple method to apply TR for packet switching under green constraints. We demonstrate that the proposed system offers a good compromise between the physical layer energy-efficiency gains owing to focusing properties of TR and the Medium Access Control (MAC) layer additional consumption due to the overhead caused by the sounding frames. The influence of different channel estimation protocols and medium access methods are studied leading to some recommendations. We also describe the application of TR to Multi-Users Multiple-Input Multiple Output (MU-MISO) Orthogonal Frequency Division Multiplex (OFDM) packet-switching system. The expected green performance of TR is then confirmed by link level simulations.

Wireless communication systems based on Time Reversal (TR) and a Single Tap Receiver (STR) are optimum at low Signal-to-Noise Ratio (SNR), while keeping low complexity at the receiver. Thus, they are interesting for low order Phase and Amplitude Modulations, such as Binary Phase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK). However, at higher Signal to Noise Ratio, Inter-Symbol Interference prevents from using higher order modulations such as 16 Quadrature Amplitude Modulation (16QAM) or 64QAM. This paper presents a new spatial modulation technique called Received Antenna Shift Keying (RASK), enabling the use of higher order modulation with TR and STR. Information is not conveyed by Phase and Amplitude Modulation (PAM). Instead, at the transmitter side, Time Reversal pre-filtering technique is used to focus a signal with constant amplitude and phase onto a single receive antenna among several receive antennas. Every symbol duration, the transmitter updates the target receive antenna. The index of the antenna is simply equal to the integer value coded by the binary sequence of information that has to be transmitted during the considered symbol. At the receiver side, each antenna has a Single Tap Receiver. The output of the Single Tap Receivers are used by a simple detector to determine the target receive antenna among all antennas. The detected antenna index is then converted into a binary sequence. If N is the number of receive antennas, a N-RASK system transmits Log2(N) bits per symbol. The performance of 16RASK is compared to 16QAM, with Time Reversal, and 1 bit Time Reversal, using simulations modeling inter-symbol and un-perfect spatial focusing. The study shows that 16RASK outperforms 16QAM, under strong multipath or when the number of transmit antennas is high.

This paper investigates the distributed space-time (ST) coding proposals for the future Digital Video Broadcasting-Next Generation Handheld (DVB-NGH) standard. We first theoretically show that the distributed MIMO scheme is the best broadcasting scenario in terms of channel capacity. Consequently we evaluate the performance of several ST coding proposals for DVB-NGH with practical system specifications and channel conditions. Simulation results demonstrate that the 3D code is the best ST coding solution for broadcasting in the distributed MIMO scenario.

This paper studies the energy efficiency (bits/joule) in relay assisted networks using Chase combining hybrid-ARQ (HARQ-CC) retransmission technique. As energy efficiency depends on the average delay and the packet error probability (PER), we start by deriving an approximation of the PER for HARQ-CC retransmission scheme. This approximation is really simple compared to the existing expressions in the literature and is proved to be tight enough to address the energy efficiency study. In particular, the energy efficiency is investigated in terms of destination position and in terms of transmission power of the source and the relay. The results give some insights on the optimal transmission power according to the maximum number of retransmissions maximizing the energy efficiency.

This paper proposes a new pre-coding technique called Frequency Division Duplex Time Reversal (FDD TR) for FDD Multiple Input Multiple Output (MIMO) wireless communications which relies on unquantized uncoded channel feedback. This technique is compared in terms of performance and overhead to Time Reversal (TR), 1bit Time Reversal (1bit TR). The performance assessment of a 16x2 MIMO system, is based on post receiver Signal To Noise Ratio (SINR) formulas and simulated indoor propagation channels. Results show that FDD TR outperforms 1bit TR in terms of overhead and throughput.

In this paper, two new coordination and resource allocation schemes based on zero-forcing and maximum ratio transmission pre-coding for densely deployed femtocells connected through a high data rate backhaul are proposed. These schemes aim at offering a uniform rate in a given building, i.e. equal rate simultaneously achieved by all users in that building. New link adaptation and power allocation mechanisms that maximize the uniform rate are proposed. The performance of the proposed schemes is assessed in terms of per user spectral efficiency and backhaul control overhead using system level simulations under realistic propagation models. The study shows that zero-forcing outperforms maximum ratio transmission in terms of spectrum efficiency while being penalizing in terms of backhaul control overhead.

In this paper we consider channel estimation for MIMO-OFDM systems, specifically when null carriers are placed at the border of the spectrum in order to limit interference with neighboring spectrums. Indeed, the presence of these null carriers leads to degradation on the transform domain channel estimation (TD-CE) because of a "border effect" phenomenon. Truncated singular value decomposition (TSVD) based method allows to improve the accuracy of the TD-CE by significantly reducing each "border effect". However, its application to MIMO systems may cause problem due to its high complexity. We propose in this paper, a solution based on the power profile of the transfer matrix in order to considerably reduce the complexity. The efficiency of the proposed solution is demonstrated within 3GPP system context.

This paper analyzes the outage probability of cooperative communications over asymmetric fading environments. This work investigates the scenario where cooperative nodes are located at different geographical locations. Some cooperative nodes experience line of sight (LOS) signals and some nodes may experience non-LOS (NLOS) signals. As a result, signals in different links are affected by different fading distributions, one link may undergo Rician fading distribution and others links may undergo Rayleigh fading distribution. Such scenario is referred to as asymmetric fading channel. Assuming decode-and-forward, we provide an analytical model of outage probability for repetition-based relaying over different asymmetric fading channels. We show that the outage performance is better when the relays are in LOS situation with respect to the source rather than to the destination for the large number of relay nodes regime. The conclusions are verified through analytical and Monte-Carlo simulation studies.

This paper considers the problem of impulse response shortening for discrete multitone (DMT) transceivers. The proposed channel shortening filter shortens the effective channel impulse response (CIR) while concentrating energy in a predetermined window. This approach is based on convolution operation and filter coefficients decomposition which over constraint the effective CIR and allows achieving better performance. Simulation results show that the proposed algorithm outperforms the classical channel shortening approaches in terms of achievable bit rate and computational complexity.

This paper deals with a novel transform domain channel estimation (TD-CE) based on discrete cosine transform (DCT) for the MIMO-OFDM system. After the description of the conventional DCT based method, a channel estimation scheme improved in terms of both performance and complexity using small DCT blocks is proposed. Finally the efficiency of this estimator is evaluated within IEEE802.11n and 3GPP/LTE system contexts.

This paper describes a blind crosstalk channel identification method and its application to discrete multitone (DMT)-based digital subscriber line (DSL) systems. Cyclostationarity inherited in these systems is exploited to isolate effects of different sources, which allows separate selection and identification of crosstalk channels. Second-order statistics-based source separation is performed by controlling part of the cyclic-extension in the transmitted DMT block. The minimum changes required by this method facilitate its implementation in current DSL systems. All mentioned theoretical derivations are illustrated by numerical results obtained with measured DSL channels.

In this paper, hardware implementation of a 4 times 4 MIMO MMSE Equalizer based on a matrix triangularization is analysed. An architecture is proposed, where the 81 rotations required in the triangularization process are performed using pipelined CORDIC. Based on this architecture, the trade-off between complexity and data rate is studied through two FPGA implementations of the MMSE equalizer, computing MMSE filtering every 6 clock cycles or 38 clock cycles. Hardware complexity evaluations shows that due to the irregular computational need of the triangularization, it is more efficient to pipeline operations as much as possible to obtain the best complexity/data rate trade-off.

Today iterative receivers have proved their efficiency in cancelling interference within the field of wireless communications. However their complexity is often seen as a brake for their use in real systems. In this paper an efficient iterative receiver real-time implementation for a 4 times 4 MIMO system is presented. An architecture of MMSE iterative receiver for MIMO-OFDM systems is proposed to limit latency and complexity due to iterative process: MMSE equalization implementation is realized using CORDIC operators; the scheduling between MIMO detection and channel decoding is optimized and specific interleaving functions are introduced to reduce latency and accelerate the convergence process. The implemented receiver is integrated in a real-time FPGA testbench and compared in terms of complexity and performance with a non iterative solution.

In this paper, performance comparison of frequency-domain (FD) minimum mean square error (MMSE) turbo equalization for OFDM and single-carrier (SC) transmission in ST-BICM systems is investigated. In particular, we propose a joint formulation of the frequency- domain OFDM and SC MMSE turbo equalizer which enable to bring out similarities and differences between the two transmission schemes. This provides a new view on the topic. The relevance of the proposed approach is confirmed by comparing the lower bound of the iterative equalizing process with the corresponding analytical results. Simulation results over multipath Rayleigh block fading channels for various MIMO configurations show the benefits provided by each scheme.

Multi-carrier modulations (MCM) and especially orthogonal schemes such as orthogonal frequency division multiplexing (OFDM) are currently used in many radio transmission standards. Among these modulations, OFDM/OQAM (also referred as OFDM/Offset QAM) is an interesting alternative to classical OFDM modulation, as it does not require the use of guard interval. This characteristic makes its spectral efficiency optimal. In this paper we investigate the combination of OFDM/OQAM and multiple-input multiple-output (MIMO) over radio channels associated to non iterative and iterative receivers. We focus on spatial data multiplexing (SDM) which is a well known MIMO technique designed to improve the capacity.

In this paper a FPGA implementation of a 4 times 4 MIMO MMSE Equalizer based on the QR factorization technique is presented. Considering fast varying channels a new filter is computed at each new channel realization thanks to an efficient architecture of matrix triangularization. The QR decomposition is performed with only 6 unrolled coordinate rotation digital computer (CORDIC) operators, which are efficiently exploited to minimize the latency of computation. Soft LLR obtained in output of the equalizer are validated on an FPGA hardware bench including a 4 times 4 Rayleigh fading channel and turbo- coding.

In this paper an iterative receiver including a duo-binary turbo code is proposed for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. A double iterative loop allows to obtain good performance by efficiently cancelling co-antenna interference and profiting from the gain of duo-binary turbo decoding. Nevertheless, in order to limit complexity of the receiver, a MMSE interference canceller is considered and a new sequencing is proposed to compute in parallel turbo decoding and MIMO detection. By this way, calculation power is evenly distributed and processing time is reduced. The performance of this MIMO-OFDM system is validated by simulations for a 4times4 spatial multiplexed case under BRAN E channel.

Multiple-input multiple-output OFDM systems receive a great deal of attention due to their great potential in achieving high data rates in wireless communications. Nevertheless, performance of MIMO-OFDM systems can severely degrade due to inaccurate channel estimation especially over frequency-selective fast-varying channels. In this paper, a new efficient iterative channel estimation process based on linear regression algorithm is proposed in order to iteratively improve calculation of channel coefficients during data stage by taking into account multi-antenna interference. The efficiency of the proposed solution is demonstrated for non-orthogonal MIMO schemes over frequency selective fast-time varying channels thanks to comparison with other turbo-channel estimation techniques.

In this paper, we study the impact of carrier phase jitter on the performance of an interleaved frequency division multiple access (IFDMA) system. With this aim, we compute the signal to interference plus noise ratio (SINR) degradation caused by the phase jitter at the input of the decision device. Furthermore, we compare IFDMA systems with MC-CDMA systems with respect to their sensitivity to carrier phase jitter by means of numerical results

Multiple-input multiple-output (MIMO) systems combined with orthogonal frequency-division multiplexing (OFDM) receive a great deal of attention due to its great potential in achieving high data rates in wireless communications. Nevertheless for coherent detection systems, performance of these MIMO-OFDM systems can severely degrade due to inaccurate channel estimation especially over frequency-selective fast-varying channels. In this paper, we address a MIMO-OFDM coherent transmission with a pilot aided turbo channel estimation improved by addition of a linear regression algorithm in the iterative process. The efficiency of the proposed channel estimation is demonstrated over fast time varying channels thanks to comparison with other turbo-channel estimation systems

Linear precoded OFDM systems with channel coding have already been demonstrated to efficiently exploit frequency and time diversities of the transmission channel. Iterative receivers which iteratively perform channel decoding and deprecoding provide very good performance. In the literature, these iterative receivers are based on maximum likelihood based functions for both linear deprecoding and channel decoding leading to a high complexity for large size of preceding matrices or high modulation order. In this paper, a simple linear operation instead of a maximum likelihood based one is carried out for deprecoding allowing the use of large preceding matrices and thus an optimal exploitation of the signal diversity.

In this paper, the combination of spatial multiplexing with coded multi-carrier code division multiplex access (MC-CDMA) for a multiple input multiple output (MIMO) Rayleigh fading multipath channel is considered. A practical receiver structure performing the iteratively MIMO detection, multi-user despreading and channel decoding is presented. The MIMO detector, employing a linear minimum mean square error (MMSE) parallel soft interference canceller (PSIC) equalizer, allows to cope with the co-antenna interference (CAI). Simulation results show the efficiency of the iterative receiver for spatial multiplexed coded MC-CDMA that brings spatial diversity, increasing data rate, and multi-user flexibility.

An analysis of two crucial devices of turbo-equalization, the equalization part and the interleaving part, is developed for a frequency-selective fading channel, representative of an HF channel. First of all, we explain why the interference canceller of A. Gersho and T.L.Lim (see Bell System Technical Journal, vol.60, no.11, p.238-47, 1981) plays a key role in the convergence of turbo-equalization. Since this technique is an iterative process including the concatenation of an equalizer and a channel decoder, interleaving is also a very important task. Thanks to an analogy with coded modulation, we pinpoint the influence of the type of interleaving (bit or symbol) on the global performance.

Two multicarrier techniques are considered, coded orthogonal frequency division multiplexing (COFDM) and multicarrier CDMA (MC-CDMA). The paper presents the radio performance of these techniques at 60 GHz over Doppler and frequency-variant propagation channel models produced from wideband indoor measurements. Under system parameters derived from the ACTS MEDIAN project, the performances exhibit a very good robustness against multipath spread in an MC-CDMA transmission scheme.

This paper presents convincing results obtained with the self-adaptive decision feedback equalizer (SADFE) previously described by Labat et al. (1996). This equalizer is successfully applied to 64 and 256-QAM signals transmitted over channels corrupted by severe intersymbol interference (ISI) with specific examples concerning the digital television transmission. It clearly appears that with the same computational complexity, this new blind decision feedback equalizer that can be used when no training sequence is available exhibits nearly the same performance as the classical trained DFE in terms of convergence speed, residual mean-square error (MSE) and bit error rate (BER).