We address the post-compensation of nonlinear distortion in precoded orthogonal frequency division multiplexing signals caused by power amplifier impairments. An iterative message-passing receiver is proposed, using generalized approximate message passing to perform OFDM demodulation and nonlinearity compensation, while deriving new messages towards the equalizer to establish a turbo-equalization scheme. Additionally, the complex integral required for GAMP is simplified, reducing it to a one-dimensional integral that can be computed numerically. The proposed receiver significantly outperforms previous GAMPbased distortion compensation techniques.

We address joint channel estimation and data detection under unknown non-linearity caused by impaired power amplifiers. Using a Bayesian model with hidden variables for data, channel, and amplifier characteristics, we design a semi-blind probabilistic receiver for channel and non-linearity compensation coupled with decoding to minimize the number of pilot symbols. Simulations show high tolerance of the proposed receiver to unknown linear and non-linear impairments, with reasonable computation complexity.

In the fifth generation (5G) Vehicle-to-Everything (V2X) autonomous mode, vehicles may select radio resources for their packet transmissions without the support of the base station (BS). For periodic traffic, the same resources can be accessed at consecutive reservation intervals to improve the selection procedure. However, potential collisions occurring during this period may remain undetected and persist over time. Previous studies introduced algorithms leveraging in-band full-duplex (FD) transceivers to detect and react to collisions by performing resource reselection. However, as demonstrated in this paper, in more realistic scenarios where part of the data traffic is not periodic, performing reselections after collisions, regardless of the traffic type, may not be effective and could even be counterproductive. To address this issue, this work introduces two novel alternative schemes, each with its own advantages and drawbacks, both based on FD transceivers. Simulation results demonstrate that both solutions effectively handle scenarios with mixed traffic. Without penalising the aperiodic traffic, the range of periodic traffic is improved by up to 38% over the legacy Mode 2 under heavy traffic conditions.

The Third Generation Partnership Project (3GPP) recently introduced the fifth-generation (5G) new radio (NR) sidelink to enable vehicle-to-everything (V2X) communications supporting advanced safety services. Nevertheless, improvements over the previous generation still pose challenges to meet the reliability and latency requirements of V2X communications, particularly in the allocation of distributed resources, i.e., Mode 2. In Mode 2, vehicles autonomously select radio resources for their message transmissions and can maintain the selected resources for a given reservation period to efficiently handle periodic data traffic. However, potential collisions during this period may remain undetected due to half-duplex communications and unacknowledged broadcast transmissions, resulting in persistent message losses and posing a threat to road safety. This paper aims to improve the 5G NR-V2X sidelink for systems beyond 5G-Advanced by exploiting full-duplex transceivers. We propose a novel medium access control (MAC) scheme where vehicles can detect collisions while transmitting, dynamically adapt the collision detection threshold according to the measured channel load, and react to detected collisions through appropriate resource reselection and retransmission procedures. Extensive simulations conducted under various settings show that this MAC scheme brings substantial performance gains in terms of reliability and latency, compared to the current legacy Mode 2 procedure and a benchmark full-duplex scheme from the literature.

Grant-free non-orthogonal multiple access is an emerging communication paradigm, where devices transmit to an access point without explicit permission. However, unknown user activities add discrete latent variables on top of the usual hidden variables (accounting for channels and data), thus rendering exact inference - in the form a mixture of underlying distributions growing with time - intractable. Thus low-complexity user activity detection with reliable approximate distributed inference in the form of message-passing is relevant. We propose a new generic expectation propagation solution in the form of complex Gaussian distributions, that are consistently derived using a Wirtinger calculus-based second-order approximation. The proposed algorithm is then integrated with expectation propagation for other tasks (channel estimation, symbol detection and decoding) in a fully Bayesian inference setting. The main outcome is an excellent tradeoff between user missed detections and false alarms in a non-orthognal multiple access context, thus enabling further complexity reduction by gradually disabling message-passing for successfully identified inactive users. Numerical results demonstrate the superiority of the proposed method over similar approximations.

Applications envisioned to enable connected and autonomous vehicles entail the exchange of data through reliable and low-latency direct communications between vehicles. The current specifications for the cellular-vehicle-to-everything (C-V2X) technology can still barely match such requirements. To tackle this issue, we investigate here the joint application to the C-V2X sidelink with autonomous resource allocation of two techniques that are being considered for the evolution of cellular systems, i.e., in-band full-duplex (FD) and non-orthogonal multiple access (NOMA). In particular, we consider FD capabilities to detect ongoing collisions while transmitting and thus resolve persistent resource allocations, which are causing repeated errors at the neighboring receivers. Regarding NOMA, we consider the use of successive-interference cancellation (SIC) for the decoding of multiple signals when different vehicles are transmitting simultaneously using the same resources, thus converting packet losses into improved spectral efficiency. The investigation is based on the latest fifth generation (5G) New Radio (NR)-V2X specifications and focuses on broadcast transmissions, which are expected to cover the majority of the exchanged traffic in V2X contexts. As shown through simulations in large-scale scenarios, the two techniques, both relying on signal processing at the receiver to cancel the (self or successive) interference, provide complementary advantages under different conditions. FD is in fact very effective to improve the delivery performance at short distances when periodic data traffic is assumed, while SIC-based NOMA improves the reception probability at medium distances both under periodic and aperiodic data traffic conditions.

Efforts are underway to finalize the fifth generation (5G) vehicle-to-everything (V2X) communication technology. Direct communication among vehicles over the sidelink interface through the autonomous selection of radio resources is among the main and more challenging capabilities of such a connectivity solution. Nonetheless the crucial enhancements conceived by the Third Generation Partnership Project (3GPP) in Release 16, the autonomous resource allocation (a.k. a. Mode 2) still suffers from collisions due to the wrong estimation of the resource occupancy status enforced by half-duplex (HD) transceivers. In this paper, we argue in favour of the usage in vehicles of in-band full-duplex (FD) transceivers, gaining momentum in the research towards sixth generation (6G) systems thanks to their simultaneous transmission and reception capability. Exploiting FD, we propose to enhance the autonomous mode by detecting collisions and triggering resource reselection procedures in a more conscious manner. Simulation results show that the conceived proposal allows sidelink V2X to achieve significant improvements in terms of reliability and timeliness when compared against the legacy Mode 2.

In grant-free non-orthogonal multiple access, the set of active users is unknown a priori. We address the challenging problem of dynamic channel estimation in this context. Assuming that inactive users are completely muted (in order to avoid unwanted pilot/preamble interference on active users), we investigate a channel estimation method performed jointly with user activity detection, multi-user detection and decoding. Leveraging conditional independence assumptions in probabilistic modeling, we introduce a low-complexity channel estimation performing expectation propagation in parallel for the measurements over all receive antennas. The proposed channel estimation technique is evaluated under different receive antenna correlation models and shows a good performance/complexity tradeoff with respect to joint measurement processing.

Vehicle-to-everything (V2X) connectivity is deemed crucial to enable upcoming cooperative automated driving applications. The Cellular-V2X (C-V2X) technology supports direct interactions among vehicles over the sidelink interface. According to the autonomous mode, vehicles select sidelink radio resources for their message transmissions in a completely distributed manner, without the support of the base station. The majority of works focused so far on periodic message transmissions, for which sidelink resources can be semi-persistently reserved after a channel sensing procedure. In this paper, we take a step forward by considering both periodic and high-priority aperiodic messages, such as sporadic decentralized environmental notification messages (DENMs), competing for the same resources. The impact of some new sidelink features devised in 5G-V2X (Release 16) for the autonomous mode, such as the new radio (NR) flexible numerology, the short-term sensing, the pre-emption mechanism, are preliminarily investigated in this paper. They are coupled with a newly proposed resource reservation scheme for the repetitions of DENMs. Results showcase the improvements of our proposal in terms of higher DENM reliability achieved with little-to-none additional signaling, with a negligible impact on periodically transmitted messages.

The first set of specifications for the Cellular-Vehicle-to-Everything (C-V2X) technology has been issued by the Third Generation Partnership Project (3GPP) in Release 14 to enable the exchange of periodic cooperative awareness messages supporting basic safety applications. Enhancements towards 5G New Radio (NR) V2X are under study in Release 16 in order to support advanced vehicular use cases with stricter latency and reliability demands, and different traffic patterns (e.g., aperiodic messages, unicast delivery). In this paper, we focus on the support of aperiodic traffic like Decentralized Environmental Messages (DENMs), which are sent out asynchronously to vehicles alerting them to road hazard events such as anomalous traffic conditions, road-works or signal violation, emergency braking. DENMs can be repeatedly transmitted in a relevant area to increase message reliability during the event lifetime. Simulations have been conducted to analyze scenarios where periodic and event-triggered messages share the same radio resource pool(s) in the autonomous sidelink mode of NR V2X. The main parameters of the autonomous resource allocation mechanism affecting the DENM delivery have been investigated as well as the benefits of DENM repetitions, while also considering their impact over periodically transmitted messages, under different simulation settings.

Broadcast traffic in IEEE 802.11 vehicular networks is known to suffer from poor performance due to the lack of recovery mechanisms from packet losses, based on the rules of the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. This may have a detrimental impact on cooperative vehicular safety applications that build on the reliable regular broadcasting of status messages by vehicles in a local neighborhood. Full-Duplex (FD) techniques can improve the broadcast CSMA/CA performance by letting a sending vehicle sense the channel while transmitting, thus enabling “collision detection”. The vehicle, consequently, can abort the packet prone to collision and reattempt a later transmission. In this paper, we define a stochastic geometry model that captures the collision detection capability of FD-enabled vehicles, while accurately characterizing the interference power generated by other vehicles on a road segment, and the dynamics of the backoff mechanism used for broadcast packet retransmissions. The model provides helpful insights into the FD broadcast CSMA/CA behaviour, highlighting a clear relationship between the settings for the carrier sense threshold and the collision detection threshold and the number of covered receivers on the road.

In this paper, we investigate centralized scheduling strategies for cooperative incremental redundancy retransmissions in the slow-fading half-duplex multiple access multiple relay channel. Time Division Multiple Access is assumed for the sources and the relays. Sources transmit successively in time slots for the first phase. The second phase consists of a limited number of time slots for retransmissions. In each time slot, the destination schedules a node (being a relay or a source) to retransmit, conditional on the knowledge of the correctly decoded source sets of each node (which is itself for a source). A scheduled relay retransmission uses Joint Network and Channel Coding on its correctly decoded source messages (cooperative retransmission). Several node selection strategies are proposed based on the maximization of the long-term aggregate throughput under a given constraint of fairness. Monte-Carlo simulations show that these strategies outperform the state of the art one based on the minimization of the probability of the common outage event after each time-slot. Moreover, the long-term aggregate throughput reached with these strategies is close to the upper-bound, calculated by the exhaustive search approach. The same conclusion remains valid for both symmetric and asymmetric source rate scenarios.

On the path to zero fatalities on the roadways, all vehicles have to periodically broadcast cooperative awareness messages (CAMs) in a timely and reliable manner, even in areas of high traffic density. The carrier senses multiple access with collision avoidance (CSMA/CA) scheme of IEEE 802.11, the de-facto standard for vehicular communications, is known to offer no reliability to broadcast packets that cannot be acknowledged, and to poorly perform at high network load due to collisions and interference. In this paper, an enhanced CSMA/CA protocol is analyzed for vehicular networks, which improves the CAM timeliness and reliability by leveraging full-duplex (FD) transceivers on board. FD devices can listen to the channel while transmitting, thus making collision detection viable. A FD vehicle can detect a CAM collision while sending, promptly abort the packet and retransmit it later. Results achieved through an analytical model under mathematically tractable assumptions, and through extensive system-level simulations in a complex urban environment, show the effectiveness of the protocol to cope with direct collisions, especially in high traffic areas, paving the way towards the realization of cooperative automated driving.

Digital self-interference cancellation is a major challenge for orthogonal frequency division multiplexing full-duplex transmissions. Therefore, reliable estimation of both the signal-of-interest and the self-interference channel, becomes the limiting factor in a mobile radio context. In this letter, improved estimation of the time-varying channels is obtained by solving the problem jointly with self-interference cancellation and decoding using a factor graph approach. Taking advantage of the per-subcarrier structure of message-passing, a low-complexity receiver is obtained. Our semianalytical and numerical results show the superiority of the proposed scheme over state-of-the art self-interference cancellation methods under limited pilot overhead.

Reliable and timely exchange of periodic beacons, a.k.a. cooperative awareness messages (CAMs), in the one-hop neighborhood is essential in vehicular networks to support cooperative driving applications. The problem is that broadcasted CAMs are neither acknowledged nor retransmitted in case of failure, e.g., due to channel errors or collisions, and this makes data transmission unreliable and without any delivery guarantee. In this paper, we propose in-band full-duplex communications to improve the reliability of vehicle-to-vehicle beacon exchanges. The FD capability to simultaneously transmit and receive on the same channel can be beneficially exploited by a vehicle to detect a collision while transmitting, and to promptly retransmit to recover from the packet failure. Achieved simulation results show that the proposed solution provides several improvements in terms of reliability and timeliness in CAMs delivery when compared against a naïve half-duplex broadcasting and a simple CAM repetition technique.

In this paper, we study the benefit of Joint Network Channel Coding (JNCC) and Decoding (JNCD) for half-duplex slow fading Multiple-Access Multiple-Relay Channels (MAMRC), defined as follows: (1) Multiple statistically independent sources communicate with a single destination with the help of multiple relays; (2) Each relay is half-duplex; (3) The links between the different nodes are subject to slow fading and additive white Gaussian noise; (4) Some links interfere. Channel State Information (CSI) is available only at the receivers (relays or destination) and assumed perfect. While the Multiple Access (MA) function is presented generically depending on how the resources are allocated to the sources and relays, the emphasis is on the most spectrally-efficient Non-Orthogonal Multiple-Access (NOMA) where sources and cooperating relays interfere. The relays perform JNCC in combination with Selective Relaying (SR), meaning that they forward a function of the correctly decoded sources' packets to the destination. Practical linear JNCC schemes and the corresponding JNCD architectures are described in detail for NOMA, and shown to perform close to the theoretical limits.

Modern wireless communication systems rely on limited feedback for Fast Link Adaptation (FLA). FLA in presence of advanced receivers needs new physical layer abstractions (PHY abstractions) that are able to capture their performance in order to derive the limited feedback metrics (e.g., Channel Quality Indicators). Recently, a PHY abstraction was proposed for the class of iterative linear minimum mean square error based soft interference cancellation and decoding also referred to as turbo Linear Codeword Interference Cancellation (turbo L-CWIC) receivers in 3GPP. This PHY abstraction needs to be calibrated and a first one-dimensional (1D) calibration method was proposed. In this paper, we revisit the calibration method by proposing a more rigorous framework to minimize the predicted throughput error that dramatically influences the FLA mechanisms. We also suggest a novel multi- dimensional calibration approach. Monte Carlo simulations show that it outperforms the 1D at the expense of the knowledge of the number of independent fading blocks experienced by a codeword.

In this paper, we study the individual and common symmetric ϵ-outage achievable rates of various cooperative strategies adapted to the slow fading Multiple Access Multiple Relay Channel (MAMRC). Channel links are independent and subject to slow Rayleigh fading and additive white Gaussian noise. No Channel State Information at the Transmitter (CSIT) is available. Common to all investigated cooperation schemes are the following assumptions: (1) The sources are independent and want to communicate their messages to a single destination with the help of multiple relays using Joint Network Channel Coding (JNCC) and Decoding (JNCD); (2) Each relay is half-duplex and applies a Selective Decode and Forward (SDF) cooperative strategy, i.e., it forwards a deterministic function of the source messages that are decoded without errors. The cooperation schemes differ in the assignment of the available channel uses to the sources and the relays, ranging from the less efficient orthogonal assignment where sources and relays are given non-overlapping channel uses to the most efficient one where sources and relays can transmit simultaneously in all available channel uses.

In this paper, we tackle the problem of link adaptation in closed-loop turbo coded multiple-input multiple-output antenna systems with non-linear turbo receivers performing iterative linear minimum mean-square error (soft) interference cancellation (LMMSE-IC) and turbo decoding. The proposed link adaptation scheme relies on a low rate feedback and operates joint spatial precoder selection (e.g., antenna selection) and modulation-coding scheme selection so as to maximize the average rate subject to a target block error rate constraint. The paper first revisits in detail the architecture of the whole turbo receiver, then presents a semi-analytical performance prediction method to analyze its evolution through the stochastic modeling of each of the components. Based on this PHY-layer abstraction, average predicted and simulated throughputs are shown for different communication scenarios.

In this paper, we investigate the benefit of Joint Network Channel Coding (JNCC) for a new class of Multiple Access Relay Channel (MARC), defined as follows: (1) Independent sources communicate with a single destination in the presence of a relay; (2) The relay is half-duplex and applies a Selective Decode and Forward (SDF) strategy, i.e, it forwards only a deterministic function of the error-free decoded messages; (3) The sources are allowed to transmit simultaneously during both the listening phase and the transmission phase of the relay. We refer this model to as Non-Orthogonal MARC (NOMARC), which better leverages the broadcast nature of the radio channel than its more conservative orthogonal counterpart, i.e., Orthogonal MARC (OMARC). This paper aims at measuring the advantage brought by NOMARC/JNCC over OMARC/JNCC from both an information-theoretic and a practical code design perspectives.

In this paper, a novel semi-analytical performance prediction method is proposed for iterative MMSE-IC detection and semi-blind channel estimation. It is examplified in the context of single-user MIMO-OFDM transmission which we model by a discrete-input MIMO P-block fading flat Rayleigh channel in the frequency domain. The proposed method extends existing symbolwise Mutual Information Effective SNR Metric (MIESM) link-to system approach to the context of imperfect channel state information and semi-blind channel estimation at the receiver side. It allows to compute the average Block Error Rate (BLER) conditional on an initial pilot-assisted channel estimation and long term channel distribution information. Thus, the proposed method takes advantage of all the available a priori information before actual data transmission and could be equally employed for slow and fast link adaptation.

In this paper, we investigate the benefit of joint network-channel distributed coding for the multiple-access half-duplex relay channel. In contrast with previous work, the medium access is not orthogonal and the source-to-relay links are not error-free, which render the reality of wireless environments and notably complicate the problem. Indeed, due to the broadcast nature of wireless media, transmitted signals interfere at the relay and at the destination and form multiple-access channels. This entails the need of more sophisticated joint multiuser detection and decoding procedures. Moreover, improper (erroneous) distributed codes may result from unsuccessful decoding at the relay. This second issue is handled with selection relaying. We describe in detail the structure of the encoders, when and how JNC coding is performed, and the structure of the joint multiuser detectors and decoders. For a given spectral efficiency, we show through simulations that our approach provides substantial performance gains compared to conventional joint network-channel distributed coding for the orthogonal multiple-access half-duplex relay channel. Equivalently, for a targeted performance, our approach allows to transmit at higher rates.

In this paper, a joint channel-network coding is proposed for the multiple access half duplex relay channel. To improve performance, the classical constraints of orthogonality between links are partially relaxed, i.e., in the first transmission phase the two sources are allowed to transmit simultaneously, while in the second phase, the relay transmits alone and the sources are silent. In order to resolve the subsequent collisions occurring at the relay and destination, related iterative multiuser detection structures are suggested. Simulation results demonstrate the superiority of the proposed semi-orthogonal transmission protocol compared to the orthogonal one.

In this paper, two semi-analytical performance prediction methods are proposed and compared for multiuser MIMO transmission over block-fading multipath channels and iterative MMSE successive interference cancellation based joint decoding. In the first method, we develop a completely analytical parameterisation of the whole turbo receiver up to the users' channel decoders. The method which follows the classical framework of extrinsic information transfer charts tracks the evolution of the average mutual information defined at coded bit level and circulating between the multiuser detector and the bank of channel decoders. The modelling of the demapping output in the multiuser detector is based on an explicit calculation of the (conditional) mutual information for each symbol digit in a symbol label under arbitrary (possibly non-uniform) a priori probability distributions on others. Then, shifting in viewpoint and considering user demapping and decoding as a joint process, we present an alternative method which tracks the evolution of the average mutual information defined at symbol level and circulating between the MMSE successive interference based interface and the bank of joint demappers and channel decoders. This allows to avoid the critical issue of parameterising the demapping. Numerical results demonstrate the superiority of the second method for high-order non-linear mapping.

We consider an idealized synchronous single-carrier single-cell uplink communication where K users equipped with multiple antennas transmit their data to a base station also equipped with multiple antennas. Users have no (or very limited) channel state information. They employ space-time trellis codes to improve the reliability of their transmission link. Transmission occurs on fading multipath channels. Prior to transmission, users' spacetime codewords are interleaved in order to break channel memory. The multiuser joint decoding at the base station (assuming perfect channel state information) is reformulated as the computation of marginal probabilities on dense layered factor graphs with loops. This computation is done by means of the sum-product algorithm. We derive several instances of the sum-product algorithm by modifying the topology of the loopy graph and the definition of the corresponding exchanged messages and show through simulations that those variations can substantially impact the final delivered marginals.

Abstract-This paper presents a semi-analytical method to predict the performance of iterative interference cancellers used in advanced multiuser MIMO CDMA systems. At the receiver side, the orthogonality between codes is restored by a chip rate equalization allowing the transmitted symbols to be subsequently estimated by a simple correlations. The proposed prediction method is based on Signal to Interference-plus-Noise Ratio (SINR) tracking and Average Mutual Information (AMI) compression. Therefore, the SINR at symbol level after despreading is analytically derived and injected into the algorithm. Simulations confirm that the method provides accurate performance prediction and is fast enough to be integrated in radio resource management and link adaptation mechanisms of advanced MIMO CDMA/MC-CDMA systems using powerful interference cancellation techniques.

This paper generalizes the information-theoretic optimality of minimum mean square error successive interference cancellation in layered space-time coding with rate and power control. Based on this derivation, a new concept relying on partial feedback is introduced, whose core idea is to exploit an additional degree of freedom relative to the partitioning of transmit antennas. Taking into account this additional degree of freedom, together with power control and decoding order, allows the reduction of the quantization noise induced by the use of finite discrete-rate sets at the transmitter. However, the simultaneous optimization of all those degrees of freedom proves to be computationally intensive and would result in a tremendous feedback load. Practical algorithms are thus proposed to achieve this optimization with a reasonable complexity and a limited amount of feedback. Monte-Carlo simulations show that those algorithms perform close to the theoretical limits.

This paper presents a novel fast performance prediction method for iterative minimum-mean square error interference cancellation based joint decoding in a very general multiuser MIMO setting considering a transmission over block-fading frequency-selective channels. A Gaussian approximation is made for all propagated messages between the outer codes and the space-time multiuser detector. The method relies on a signal-to-interference-plus-noise ratio compression, by means of the mutual information effective signal-to-noise metric (MIESM), which allows a one-dimensional AWGN look-up table to capture the soft decoding result of each distinct user. Simulations show that this method while being extremely simple and fast keeps very accurate and is thus adequate for radio resource management and link adaptation purposes.

This paper investigates the effect of channel estimation errors in presence of spatial correlation for fading MIMO multiple access channels (MACs). Specifically, the capacity is derived under the notion of reliable communication based on the average of the error probability over all channel estimation errors. Although not necessarily optimality in presence of channel estimation errors, we restrict the channel inputs to be Gaussians, allowing a closed-form expression for the mutual information, which leads to an inner bound of the capacity region. For different types of transmitter information (e.g. instantaneous and covariance information), we study optimal transmission schemes that permit to maximize the sum-rate. Numerical results show that the performance of covariance feedback is quite sensitive to channel accuracy while the gap between the open-loop and the closed-loop scenario increases with the channel uncertainty. Simulations also assess the performance degradation of transmit/receive correlation and reveal that their impact behaves independently of the estimation errors.

Waterfilling enables a dramatic increase in capacity of multiple antenna systems, but requires perfect knowledge at transmitter.When a finite discrete rate is available, this algorithm is no more optimal since the interest lies in maximizing the sum discrete-rate. In this paper, motivated by a feedback reduction, we introduce a transceiver that partially decouples the channel into parallel subchannels. From the analogy between multi-user and single-user channels, we propose a discrete rate iterative waterfilling procedure. It first relies on the classical iterative waterfilling, and then rounds continuous rates to discrete rates with an efficient use of residual power. Simulations show that a substantial enhancement of the discrete bit loading process is provided. We further investigate the trade-off feedback-performance of different waterfilling-based systems. Simulations point out that the proposed scheme outperforms the waterfilling with nearly 60% of feedback reduction in the moderate to high SNR region, while achieving nearly 90% of the sum discrete-rate waterfilling at low SNR.

This paper investigates a new concept that combines space-time coding with the layered architecture of successive interference cancellation with per antenna rate control (PARC- SIC) for wireless MIMO channels, relying on partial feedback. The key element is to exploit an additional degree of freedom (DoF), namely antenna partitioning, in addition to decoding order and power control considering that the set of transmit antennas can be grouped into subsets. It is proved that this design theoretically achieves the open-loop capacity. In presence of a finite discrete modulation and coding scheme (MCS) rate set at transmitter, this new DoF allows to either fight back the resulting quantization noise or to reduce the feedback without much performance loss.

Antenna selection, as a special case of power adaptation, can enhance the capacity of layered space time codes under rate control without any overhead feedback. To efficiently fight back rates quantization, this contribution considers a joint optimization of the best active transmit antennas associated to rate control together with antenna partitioning (i.e., layered multidimensional coding) and decoding order degrees of freedom. We propose an iterative antenna selection, which initializes the decoding order, so as to keep a low computational complexity while achieving near-optimal performance. Gains get all the more important as the signal-to-noise ratio increases.

This paper investigates the combination of spatial multiplexing and overloading as an evolution of the UMTS-HSDPA (high speed downlink packet access) toward very high spectral efficiencies in the case of no (or very limited) channel state information at transmitter. Overloaded spreading is carried out in the time domain only (independent per antenna), transmit space diversity is partially recovered employing Space-Time BICM for each user. A low complexity soft interference cancellation based iterative receiver for channel estimation, space-time chip-equalization and multiuser detection is proposed. Two scenarios are considered for the intracell interference: either the spreading codes and the modulation of the interfering users are known or no-knowledge of the interfering signals is available at the receiver whatsoever.

This paper investigates the combination of spatial multiplexing and overloading as an evolution of the UMTSHSDPA (High Speed Downlink Packet Access) toward very high spectral efficiencies. The base station employs single-carrier space-time bit-interleaved coded modulations with linear precoding for each user. From an information-theoretic point of view, this scheme is potentially capacity achieving but puts high stakes on the receiver complexity. Channel estimation is made particularly difficult by the superimposition of pilot symbols and data. Indeed, the classical channel estimation method based on matched filtering and accumulation clearly fails to give satisfactory performance in a spatial multiplexing and overloading context. Thus, we propose a sophisticated iterative receiver which includes channel estimation, MMSE-based chip-equalization and MMSE-based multiuser detection together with decoding of the turbo-code. Simultaneous downlink transmission to several users is investigated in this paper which brings out the overloading flexibility in terms of Space-Time Modulation and Coding Scheme (ST-MCS) design and radio resource allocation.

In this paper, frequency-domain implementation of a block turbo-equalizer where ISI suppression and CAI resolution are performed separately is presented. This functional split allows deriving efficient low complexity structures based on a modified doubly iterative architecture which ensure better tradeoff between performance and complexity. We focus on a modified doubly-iterative and hybrid structure where further complexity reduction is obtained by relaxing the criterion retained for ISI suppression (max-SNR instead of MMSE) from a given iteration. Simulation results show the efficiency of such modified architectures in the case of a realistic spatially correlated MIMO channel

This paper investigates the combination of spatial multiplexing and overloading as an evolution of the UMTS-HSDPA (high speed downlink packet access) toward very high spectral efficiencies. The base station employs single-carrier space-time bit-interleaved coded modulations with linear preceding for each user. From an information-theoretic point of view, this scheme is potentially capacity achieving but puts high stakes on the receiver complexity. Channel estimation is made particularly difficult by the superimposition of pilot symbols and data. Indeed, the classical channel estimation method based on matched filtering and accumulation clearly fails to give satisfactory performance in a spatial multiplexing and overloading context. Thus, we propose a sophisticated iterative receiver which includes channel estimation, MMSE-based chip-equalization and MMSE-based multiuser detection together with decoding of the turbo-code. Simultaneous downlink transmission to several users is investigated in this paper which brings out the overloading flexibility in terms of space-time modulation and coding scheme (ST-MCS) design and radio resource allocation

This paper presents a new class of block turbo-equalizers for single-carrier transmission over multiple-input multiple-output (MIMO) broadband wireless channels. The key underlying idea consists in equalizing (nonoverlapping) groups of symbols and detecting their individual space-time components in a disjoint and iterative fashion. This functional split naturally induces new design options that have been accurately listed and described, i.e., choice of distinct criteria for intergroup interference (IGI) equalization and intragroup components detection, yielding hybrid structures, multiple iterative loops, and related scheduling variants. Selected algorithms in the proposed class are compared in terms of performance under various transmission scenarios. For all of them, minimum mean square error IGI equalization certainly occupies a central role (at least for the first iteration) and may be identified as the computational bottleneck. Fortunately, block spread transmission together with cyclic prefix operations make the channel matrix block circulant, thus allowing low-complexity inversion in the Fourier domain

This paper addresses the problem of transmitting space-time interleaved coded signals over Multiple-Input Multiple-Output (MIMO) block fading channels with InterSymbol Interference (ISI). At the the receiver, we investigate a cooperative approach in which data detection, decoding, and channel estimation are performed separately and iteratively. Computationally efficient methods based on the Expectation-Maximization (EM) algorithm are developed for multiple path gain estimation.

This paper addresses the issue of advanced equalization methods for space-time communications over multiple-input multiple-output block fading channel with intersymbol interference. Instead of resorting to conventional multiuser detection techniques (based on the straightforward analogy between antennas and users), we adopt a different point of view, and separate time equalization from space equalization, thus introducing a higher degree of freedom in the overall space-time equalizer design. Time-domain equalization relies on minimum mean-square error criterion and operates on multidimensional modulation symbols, whose individual components can be detected in accordance with another criterion. In particular, when the optimum maximum a posteriori criterion is chosen, substantial performance gains over conventional space-time turbo equalization have been observed for different transmission scenarios, at the price of an increased, albeit manageable, computational complexity.

In this paper, we propose a class of iterative equalizers for space-time bit interleaved coded modulation over MIMO block fading multipath AWGN channel. Simulations show that the proposed receivers are able to reach the matched-filter bound and that the tested space-time coding schemes have the potential to get close to the Shannon theoretical limit.

This paper addresses the problem of decoding the space-time bit-interleaved coded signals transmitted over multiple-input multiple-output block fading multipath channel when channel state information is not perfect at the receiver. We develop a cooperative approach in which the channel estimation, channel equalization, data detection, and outer decoding are performed separately and iteratively. A computationally efficient method is proposed where most of the inner modules rely on the suboptimal MMSE criterion. The approach is validated through Monte-Carlo simulations.

We present some new results on a recently introduced multiple access technique which accommodates more than TV users on a channel whose bandwidth is N times the bandwidth of the individual user signals. For K = N + M users, the technique makes use of two sets of orthogonal signal waveforms, one for the first N users and one for the M additional users. Considering a combination of time-division multiple access (TDMA) and orthogonal code-division multiple access (OCDMA), this multiple access scheme is evaluated using quaternary phase-shift keying (QPSK) and 16-state quadrature amplitude (16-QAM) modulations. When used in conjunction with soft iterative interference cancellation (IC), the technique offers substantial overloads.

The paper aims at comparing the respective benefits of STBICM (space-time bit-interleaved coded modulation) and space-time trellis codes (STTC) for a MIMO block fading multipath channel. Giving a general framework for the calculation of the outage probability, we try to point out the best transmit scheme that approaches the closest the outage probability, assuming the most efficient receiver (i.e., disregarding any complexity aspect). We conclude that iteratively decoded STBICM should be used in preference to STTC.

We propose the building of high rate space-time codes for multiple-input multiple-output (MIMO) block fading multipath additive white Gaussian noise channels by layering small compound space-time trellis codes. To recover part of the spatial diversity between the different layers, we also study their concatenation with an outer code. Naturally, our space-time coding architecture puts the burden on the receiver complexity. As a main contribution of this paper, a near-optimal soft-input soft-output reduced-complexity trellis search algorithm is suggested for joint MIMO detection and inner decoding.

This letter presents a new receiver for Q-ary transmission, where all receiver blocks are embedded in an iterative structure. Packet data transmission in Global Systems for Mobile communications (GSM) and Enhanced Data rates for Global Evolution (EDGE) are considered as examples. A low-complexity soft-in-soft-out detector for EDGE is introduced and its modification suitable for iterative detection is derived. Application of iterative detection and channel estimation techniques in GSM/EDGE shows a significant performance enhancement. Additional improvement may be obtained if the iterative processing is applied to packet retransmission schemes.

In this paper, we consider a generic model of space-time bit-interleaved coded modulation (ST-BICM) on a multiple-input multiple-output (MIMO) Rayleigh fading multipath channel. A practical low-complexity receiver structure performing iteratively MIMO data detection, channel decoding and channel estimation, is presented. The MIMO data detection, employing a reduced-state list-type soft output Viterbi algorithm enables to cope with severe channel intersymbol interference (ISI) without MIMO prefiltering. Among other results, simulations show that our approach can dramatically improve the downlink performance of time-division multiple access (TDMA) systems with high order modulation, keeping a reasonable complexity at the receiver side.

We propose two pilot symbol aided iterative algorithms for channel re-estimation to be used in iterative detection and decoding (turbo-detection) of signals transmitted over frequency selective channels. The first algorithm is based on the expectation-maximization (EM) algorithm that makes use of a signal decomposition to compute separate dosed form recursion expressions for the channel coefficient re-estimates. The a posterior conditional channel state probabilities required by the EM-based turbo-estimation can be easily provided by the forward-backward trellis search performed by the soft-in soft-out (SISO) ISI decoding task. The second algorithm is based on the well-known bootstrap algorithm where soft information from the outer decoder is used to make hard decisions on transmitted coded data, and the detected coded data are used in the channel turbo-estimation process via the conventional linear pseudo-inverse method. Both of the proposed channel turbo-estimation algorithms are naturally embedded in the framework of the turbo-detector, bringing almost no overhead to the receiver complexity.

A generic model of bit-interleaved coded modulation (BICM) on a multipath Rayleigh fading multiple-input multiple-output (MIMO) channel is derived. A practical low-complexity trellis-based receiver performing iteratively channel estimation, multilayer coded data detection and channel decoding is introduced. The inner multilayer data detector, employing reduced-state techniques together with generalized per-survivor processing, presents two-fold advantages. It enables one to cope with severe channel intersymbol interference and allows the use of more transmit antennas than receive antennas. Simulations show that our approach can dramatically improve the downlink performance of time division multiple access (TDMA) systems with high order modulation, such as EDGE, keeping a reasonable complexity at the receiver side.

The UMTS radio interface based on CDMA, has been designed to offer a wide range of data rates using variable spreading factor. It is ongoing standardization effort to include a high data rate packet mode in the downlink direction. This new mode is called high speed downlink packet access (HS-DPA) and is characterized by the giving up of closed loop power control, link adaptation using variable constellations (QPSK, MAQ16,MAQ64), and low spreading factor. The proposed receiver is particularly adapted to HSDPA mode has it gives close to optimal performance even in the case of high modulation order and low spreading factor while keeping a reasonable complexity.

We investigate a communication model made of an outer code interleaved with a space-time trellis coded modulation (ST-TCM). Such a scheme is very relevant for highly frequency selective and time-varying channels using turbo-detection at the receiver side, but inherently suffers from a low coding rate. One possible solution to alleviate this impairment (i.e., to increase spectral efficiency) is to use parallel (or multilayered) transmission as done in recent approaches (BLAST). However, parallel transmission and highly frequency selective channels involve tremendous complexity at the receiver side. We propose a low complexity turbo-detector based on reduced-state trellis search and generalized per survivor processing that proves to be very efficient in this resulting multiple-input multiple-output (MIMO) ISI channel context.

We analyze and compare several strategies for iteratively decoding trellis-encoded signals over channels with memory. Soft-in/soft-out extensions of reduced-complexity trellis search algorithms such as delayed decision-feedback sequence estimating (DDFSE) or parallel decision-feedback decoding (PDFD) algorithms are used instead of conventional BCJR and min-log-BCJR algorithms. It has been shown that for long channel impulse responses and/or high modulation orders where the BCJR algorithm becomes prohibitively complex, the proposed algorithms offer very good performance with low complexity. The problem of channel estimation in practical implementation of turbo detection schemes is studied in the second part. Two methods of channel reestimation are proposed: one based on the expectation-maximization (EM) algorithm and the second on a simple Bootstrap technique. Both algorithms are shown to dramatically improve the performance of the classical pseudo inverse channel estimation performed initially on a training sequence.

We investigate two iterative methods for decoding serially concatenated convolutional codes (SCCC) on multipath Rayleigh fading channels. One method employs optimal maximum a posterior (MAP) decoders or sub-optimum versions. The second slightly differs and is based on a soft-in soft-out (SISO) parallel decision-feedback decoder (PDFD), used for iteratively performing joint equalization and inner decoding together with outer decoding. Simulation results show that the first iterative process is only 0.7 dB better than the second one, which is however far less complex.

A turbo-detector concept assuring a favorable tradeoff between performance and complexity is investigated for the novel radio access scheme at enhanced data rates for GSM evolution (EDGE). The high level modulation employed in EDGE (8-PSK) precludes MAP or MLSE turbo-detection, and consequently, computationally efficient sub-optimum solutions have to be considered. A turbo-detector based on a generic SISO delayed decision-feedback sequence estimator (DDFSE) is shown to be a very promising candidate, so long as we couple it with a discrete-time allpass pre-filter turning channel impulse response into minimum phase.