This paper introduces a novel resource allocation framework for the coexistence of enhanced mobile broadband (eMBB) and ultra-reliable low latency communication (URLLC) services in a non-orthogonal multiple access (NOMA) system. The proposed solution utilizes a two-layer deep reinforcement learning (DRL) algorithm to optimize the dynamic allocation of subbands and power for both URLLC and eMBB users. In the top layer, a deep Q-network (DQN) is employed for discrete subband allocation while the bottom layer uses a multi-agent DRL approach to refine the continuous power allocation. This hierarchical approach ensures that low latency and reliability requirements of the URRLC services are met, without compromising the high throughput demands of eMBB. Extensive simulations validate the efficiency of the proposed algorithm, demonstrating improved system performance in terms of power and subband optimization for both user types.

This work presents a novel approach for estimating the minimum distance of concatenated convolutional codes. Unlike most prior methods, the proposed approach relies solely on encoder-side properties, eliminating the need for a decoder in the estimation process. To this end, we introduce an alternative method for identifying return-to-zero sequences, enabling a lowcomplexity, reliable minimum distance estimation. The proposed method is flexible and applicable to both serial and parallel concatenated structures. The results confirm that this approach produces exact minimum distance values for several sizes of the LTE turbo code family while significantly reducing processing time and computational complexity compared to existing methods. For example, in a challenging case study, applying the method to an LTE turbo code with tailbiting termination of length$K=6144$bits yields an estimated minimum distance of 50 and a multiplicity of 12288 in 100 minutes on a standard personal computer - a reduction by several orders of magnitude in comparison to state of the art methods.

This work proposes a novel pilot structure (PS) to improve channel estimation (CE) in massive multiple-input multiple-output filter bank multi-carrier (mMIMO-FBMC) communications using offset quadrature amplitude modulation (OQAM). Accurate CE is essential to fully benefit from the corresponding spectral efficiency (SE) advantages and robustness against dispersive channels. Unlike orthogonal frequency division multiplexing (OFDM), FBMC/OQAM shows only real-field orthogonality. Therefore, corresponding signals suffer from intrinsic interference, motivating the use of alternative CE techniques. Furthermore, typical CE methods for mMIMO-FBMC systems require large training overheads, particularly for a large number of users or for flat-fading channel conditions over each subcarrier band. To address these issues, this paper proposes a PS that reduces the training overhead by interleaving user pilots in frequency while using conventional OFDM CE techniques, particularly the least squares (LS) method in the context of single-user (SU) and multi-user (MU) scenarios. Analytical expressions for the mean square error (MSE) and the Cramer-Rao lower bound (CRLB) are derived for the estimation technique considering the proposed PSs. Furthermore, performed simulations over the 5G QuaDRiga channel show that the proposed PS improves SE while delivering optimal performance in both preamble-based MU-mMIMO and SU systems.

International audience

Massive multiple-input multiple-output (mMIMO) systems and filtered multi-carrier waveforms have recently emerged as hot research topics in next-generation wireless networks. This paper extends the use of Overlap-Save Filter Bank Multi-Carrier (FBMC) receivers to mMIMO communication systems and investigates the corresponding FBMC transceiver advantages over OFDM. To this aim, we derived the signal-to-interference ratio (SIR) expressions analytically under several channel impairments such as timing offsets and carrier frequency offsets. Furthermore, we conducted an asymptotic study on the performance of FBMC augmented with our proposed receivers in the context of massive MIMO systems. While still outperforming OFDM, results for FBMC show that increasing the number of base station (BS) antennas does not increase the SINR unboundedly. We have validated the proposed analytical study by comparing its results with those obtained from Monte Carlo simulations and confirmed the superiority of the proposed receivers over those in mMIMO literature. Moreover, analytical and simulation results confirm that the Overlap-Save FBMC receiver can support asynchronous communications in the context of mMIMO, a cornerstone for grant-free communications and massive access.

A crucial element of cellular communication networks is the achievable spectral efficiency (SE). Indeed, motivated by the continuous growth in mobile data traffic in wireless networks, improving SE has represented one of the key goals of the 3rd Generation Partner Project (3GPP) along several generations of communication standards. In this paper, we propose a novel transmission scheme based on intentionally overlapping the subcarriers of adjacent users considering two state-of-the-art waveforms: the orthogonal frequency division multiplexing (OFDM) and the filter bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM). We investigate the achievable spectral efficiency improvement of the proposed transmission scheme in the presence and absence of timing offset impairments under the tapped delay line B (TDL-B) multipath 3GPP model of the 5G QuaDRiGa channel. According to the test results, the proposed transmission technique achieves up to 20% SE improvement for FBMC/OQAM when associated to the overlap-save FBMC receiver and 12% for OFDM.

Massive MIMO and filtered multi-carrier waveforms are considered as key enabling technologies for next-generation wireless networks. In this work, the Filter Bank Multi-Carrier (FBMC) waveform solution applying our previously proposed short filter and advanced receivers is extended to massive MIMO systems and evaluated in comparison to OFDM. Simulation results are presented for the non-line of sight (NLOS) 3D Urban-Macrocell (UMa) model of the 5G QuaDRiGa channel. Results show that the solution applying the proposed Overlap-Save (OS) and Overlap-Save-Block FBMC (OSB) receivers out-performs OFDM under timing offsets, carrier frequency offsets and Doppler spreads. Moreover, they confirm that the Overlap-Save FBMC receiver can support asynchronous communications in the context of massive MIMO, a cornerstone for grant-free communications and massive access.

The Internet of Things (IoT) is a major driving use case of future communication systems. 5G and beyond networks should be properly designed to meet the quality of service (QoS) requirements of IoT devices in terms of massive access, data rates, latency and reliability. In this paper, we study the uncoordinated spectrum and power allocation problems in an uplink IoT network. In the considered setting, IoT devices aim at organizing their transmissions, without any coordination, on the available frequency channels and power levels. To enhance performance, we propose the deployment of full-duplex relays as well as the use of non-orthogonal multiple access and queuing at the level of the relays. A new algorithm, based on the multi-player multi-armed bandits framework, is proposed with the aim of reducing the transmit power of IoT devices. Simulation results validate the convergence of the proposed algorithm. Results also confirm the superior performance of the proposed technique in terms of satisfying QoS requirements and reducing the needed user transmit power when compared to two baseline schemes.

Device to device (D2D) and nonorthogonal multiple access (NOMA) are promising technologies to meet the challenges of the next generations of mobile communications in terms of network density and diversity for Internet of Things (IoT) services. This article tackles the problem of maximizing the D2D sum throughput in an IoT system underlaying a cellular network, through optimal channel and power allocation (PA). NOMA is used to manage the interference between cellular users (CUs) and full-duplex (FD) IoT devices. To this aim, mutual successive interference cancellation (SIC) conditions are identified to allow simultaneously the removal of the D2D devices interference at the level of the base station and the removal of the CUs interference at the level of D2D devices. To optimally solve the joint channel and PA problem, a time-efficient solution of the PA problem in the FD context is elaborated. By means of graphical representation, the complex nonconvex PA problem is efficiently solved in constant time complexity. This enables the global optimal resolution by successively solving the separate PA and channel assignment problems. The performance of the proposed strategy is compared against the classical state-of-the-art FD and half-duplex (HD) scenarios, where SIC is not applied between CUs and IoT devices. The results show that important gains can be achieved by applying mutual SIC NOMA in the IoT-cellular context, in either HD or FD scenarios.

To achieve better connectivity in future communication networks, the deployment of different types of access points (APs) is underway. APs are expected to be equipped with self-organizing capabilities to reduce costs. Moreover, due to the spectrum crunch, frequency reuse among the deployed APs is inevitable, exacerbating the problem of inter-cell interference (ICI). Therefore, ICI mitigation in self-organizing networks (SONs) is commonly identified as a key radio resource management mechanism to enhance performance. To this end, this paper proposes a novel solution for the uncoordinated channel and power allocation problems. Based on the multi-armed bandits (MAB) framework, the proposed technique does not require any communication between the APs. The case of varying channel rewards across APs is considered. In contrast to previous work on channel allocation using the MAB framework, APs are permitted to choose multiple channels for transmission. Moreover, non-orthogonal multiple access is used, allowing multiple APs to access each channel simultaneously. This results in an MAB model with varying channel rewards, multiple plays and non-zero reward on collision. The proposed algorithm has an expected regret in the order ofO(log2T), with extensive numerical results revealing it significantly outperforms a well-known baseline algorithm in terms of energy efficiency.

Turbo codes are a well-known code class used for example in the LTE mobile communications standard. They provide built-in rate flexibility and a low-complexity and fast encoding. However, the serial nature of their decoding algorithm makes high-throughput hardware implementations difficult. In this paper, we present recent findings on the implementation of ultra-high throughput Turbo decoders. We illustrate how functional parallelization at the iteration level can achieve a throughput of several hundred Gb/s in 28 nm technology. Our results show that, by spatially parallelizing the half-iteration stages of fully pipelined iteration unrolled decoders into X-windows of size 32, an area reduction of 40% can be achieved. We further evaluate the area savings through further reduction of the X-window size. Lastly, we show how the area complexity and the throughput of the fully pipelined iteration unrolled architecture scale to larger frame sizes. We consider the same target bit error rate performance for all frame sizes and highlight the direct correlation to area consumption.

This paper studies the combination of full-duplex (FD) and half-duplex (HD) device-to-device (D2D) communications while underlaying a cellular system. Non-orthogonal multiple access (NOMA) is used to manage the interference between devices and cellular users using mutual successive interference cancellation (SIC) and to boost the performance of D2D underlay systems, which are mainly interference-limited. For this purpose, we derive the conditions allowing for the application of mutual SIC in FD-D2D and HD-D2D systems. We compare the performance of the proposed strategy against state-of-the-art, where SIC is not applied between D2D devices and cellular users. The results show that important gains can be achieved by using NOMA in this context and highlight the importance of SIC factors for determining the best transmission mode.

Recently the Local-SOVA algorithm was suggested as an alternative to the max-Log MAP algorithm commonly used for decoding Turbo codes. In this work, we introduce new complexity reductions to the Local-SOVA algorithm, which allow an efficient implementation at a marginal BER penalty of 0.05 dB. Furthermore, we present the first hardware architectures for the computational units of the Local-SOVA algorithm, namely for the add-compare select unit and the soft output unit, targeting radix orders 2, 4 and 8. We provide place & route implementation results for 22nm technology and demonstrate an area reduction of 46-75% for the soft output unit for radix orders ≥ 4 in comparison with the respective max-Log MAP soft output unit. These area reductions compensate for the overhead in the add compare select unit, resulting in overall area saving of around 27-46% compared to the max-Log-MAP. These savings simplify the design and implementation of high throughput Turbo decoders.

In this paper, an algorithm based on the multiplayer multi-armed bandit (MAB) framework is proposed to solve an uncoordinated spectrum access problem. The proposed technique does not require any communication or coordination between users. The case of varying channel rewards across users is considered. In contrast to previous work, the users are permitted to choose multiple channels for transmission, resulting in a MAB model with multiple plays. The proposed algorithm has an expected regret of the order O(log2T), which is validated by simulation results.

Decoding using the dual trellis is considered as a potential technique to increase the throughput of soft-input soft-output decoders for high coding rate convolutional codes. However, the dual Log-MAP algorithm suffers from a high decoding complexity. More specifically, the source of complexity comes from the soft-output unit, which has to handle a high number of extrinsic values in parallel. In this paper, we present a new low-complexity sub-optimal decoding algorithm using the dual trellis, namely the dual Max-Log-MAP algorithm, suited for high coding rate convolutional codes. A complexity analysis and simulation results are provided to compare the dual Max-Log-MAP and the dual Log-MAP algorithms. Despite a minor loss of about 0.2 dB in performance, the dual Max-Log-MAP algorithm significantly reduces the decoder complexity and makes it a first-choice algorithm for high-throughput high-rate decoding of convolutional and turbo codes.

In this paper, we present two new hardware architectures for Turbo Code decoding that combine functional, spatial and iteration parallelism. Our first architecture is the first fully pipelined iteration unrolled architecture that supports multiple frame sizes. This frame flexibility is achieved by providing a set of interleavers designed to achieve a hardware implementation with a reduced routing overhead. The second architecture efficiently utilizes the dynamics of the error rate distribution for different decoding iterations and is comprised of two stages. First, a fully pipelined iteration unrolled decoder stage applied for a pre-determined number of iterations and a second stage with an iterative afterburner-decoder activated only for frames not successfully decoded by the first stage. We give post place & route results for implementations of both architectures for a maximum frame size of K = 128 and demonstrate a throughput of 102.4 Gb/s in 2S nm FDSOI technology. With an area efficiency of 6.19 and 7.15 Gb/s/m$m^{2}$ our implementations clearly outperform state of the art.

The densification of mobile networks should enable the fifth generation (5G) mobile networks to cope with the ever increasing demand for higher rate traffic, reduced latency, and improved reliability. The large scale deployment of small cells and distributed antenna systems in heterogeneous environments will require more elaborate interference mitigating techniques to increase spectral efficiency and to help unlock the expected performance leaps from the new network topologies. Coordinated multi-point (CoMP) is the most advanced framework for interference management enabling the cooperation between base stations to mitigate inter-cell interference and boost cell-edge user performance. In this paper, we study the combination of CoMP with mutual SIC, an interference cancellation technique based on power-domain non-orthogonal multiple access (NOMA) that enables multiplexed users to simultaneously cancel their corresponding interfering signals. A highly efficient inter-cell interference cancellation scheme is then devised, that can encompass several deployment configurations and coordination techniques. The obtained results prove the superiority of this approach compared to conventional NOMA-CoMP systems.

This paper proposes a new soft-input soft-output decoding algorithm particularly suited for low-complexity high-radix turbo decoding, called local soft-output Viterbi algorithm (local SOVA). The local SOVA uses the forward and backward state metric recursions just as the conventional Max-Log-MAP algorithm does, and produces soft outputs using the SOVA update rules. The proposed local SOVA exhibits a lower computational complexity than the Max-Log-MAP algorithm when employed for high-radix decoding in order to increase throughput, while having the same error correction performance even when used in a turbo decoding process. Furthermore, with some simplifications, it offers various trade-offs between error correction performance and computational complexity. For instance, employing the local SOVA algorithm for radix-8 decoding of the LTE turbo code reduces the complexity by 33% without any performance degradation and by 36% with a slight penalty of only 0.05 dB. Moreover, the local SOVA algorithm opens the door for the practical implementation of turbo decoders for radix 16 and higher.

In this paper, we study the traffic-aware resource allocation problem for a system with mixed traffic types. The considered framework encompasses real-time (RT) users having strict QoS requirements (in terms of amount of data and latency), and best-effort (BE) users for which the system tries to strike a balance between throughput and fairness. The resource allocation problem is studied in different contexts: orthogonal and non-orthogonal multiple access (OMA and NOMA respectively) in either centralized or distributed antenna systems (CAS and DAS respectively). Following the formulation of the resource optimization problem, we propose a low complexity suboptimal solution based on matching theory for each system context. We also propose an iterative approach to determine the number of subbands per antenna for the DAS contexts. The proposed techniques aim at guaranteeing the requirements of RT users while maximizing the utility function of BE users. Simulation results show that the proposed allocation method based on matching theory greatly outperforms a previously proposed greedy approach, especially in terms of RT users satisfaction.

Future communication systems are foreseen to support several services with different requirements. Waveform designs based on filter-bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) can offer interesting advantages in this context, such as low out-of-band power leakage and high spectral efficiency due to the lack of guard intervals. However, downsides of FBMC/OQAM with respect to a typical orthogonal frequency-division multiplexing (OFDM) solution include higher latency, higher complexity and difficulties in adapting some existing OFDM techniques such as MIMO Alamouti. To address these issues, novel FBMC receivers suitable for short prototype filters are proposed. Based on the Overlap-Save algorithm, the proposed receivers improve error-rate performance on multipath channels and support asynchronous communication. We show that complexity can be further reduced by efficiently processing blocks of FBMC symbols jointly, and that user mobility support can be traded off for additional complexity reductions in a flexible way through polynomial decomposition of the equalizer stage. Finally, we show that a block-Alamouti scheme can be applied, and we propose a MIMO equalizer with improved error-rate performance on time-varying channels, compared to the typical FBMC block-Alamouti equalizer.

Unmanned aerial vehicle (UAV)-base stations (BS) are envisioned to provide wireless access to areas where the existing wireless infrastructure is either not deployed, damaged or simply congested. In this paper, the problem of minimizing the transmit power of a UAV-BS, while serving users with their QoS requirements and accounting for the wireless backhaul limitation of the UAV, is investigated. To this end, an algorithm that finds the optimal bandwidth assignment in the backhaul link, the optimal 3D position of the UAV, as well as the transmit power distribution in the access and the backhaul links is proposed. Simulation results show that, using the proposed approach, the needed power is greatly reduced, when compared to a strategy that separates between the frequency band used in the access and the backhaul links. In addition, the performance enhancement of a UAV-enabled system over a traditional one in which the macro base station (MBS) directly serves users is shown.

This paper proposes a new family of recursive systematic convolutional codes, defined in the non-binary domain over different Galois fields GF(q) and intended to be used as component codes for the design of non-binary turbo codes. A general framework for the design of the best codes over different GF(q) is described. The designed codes offer better performance than the non-binary convolutional codes found in the literature. They also outperform their binary counterparts when combined with their corresponding QAM modulation or with lower order modulations.

In this paper, a new filter-bank multi-carrier (FBMC) receiver targeted at short prototype filters (PFs) is presented. In addition to the typical advantages of FBMC modulation such as improved frequency containment and support of relaxed synchronization, the proposed receiver enables accurate one-tap equalization of the signal despite the use of a short PF, while significantly reducing the complexity by merging the equalization and the standard FBMC receiver. An adapted frame structure is proposed that occupies the same radio resources as a 4G/LTE orthogonal frequency-division multiplexing (OFDM) frame while providing a similar data rate. Moreover, this frame structure is shown to readily support block-based Alamouticoded multiple-input multiple-output transmissions. Simulation results show that the proposed FBMC receiver can outperform an OFDM system on 4G/LTE channel models in both single antenna and Alamouti configurations, while having a better robustness to synchronization errors than a frequency-spread FBMC receiver.

This paper proposes a new traffic-aware resource allocation technique, employing non-orthogonal multiple access (NOMA) in a downlink distributed antenna system (DAS). The studied framework consists of users with mixed traffic types: real-time (RT) users having strict QoS requirements (in terms of amount of data and latency), and best-effort (BE) users aiming to maximize their throughput and fairness. After formulating the resource and power optimization problem, we propose a low complexity sub-optimal algorithm that aims at guaranteeing the requirements of RT users while maximizing the utility function of BE users. Simulation results show a remarkable performance enhancement of the proposed algorithm over baseline techniques in terms of RT users satisfaction. Also, the proposed technique achieves near optimal fairness for BE users while maximizing their average throughput.

A method to design efficient puncture-constrained interleavers for turbo codes (TCs) is introduced. Resulting TCs profit from a joint optimization of puncturing pattern and interleaver to achieve an improved error rate performance. First, the puncturing pattern is selected based on the constituent code Hamming distance spectrum and on the TC extrinsic information exchange under uniform interleaving. Then, the interleaver function is defined via a layered design process taking account of several design criteria, such as minimum span, correlation girth, and puncturing constraints. We show that applying interleaving with a periodic cross connection pattern that can be assimilated to a protograph improves error-correction performance when compared to the state-of-the-art TCs. An application example is elaborated and compared with the long-term evolution standard: a significant gain in performance can be observed. An additional benefit of the proposed technique resides in the important reduction of the search space for the different interleaver parameters.

A weighted proportional fair (PF) scheduling method is proposed in the context of nonorthogonal multiple access (NOMA) with successive interference cancellation (SIC) at the receiver side. The new scheme introduces weights that adapt the classical PF metric to the NOMA scenario, improving performance indicators and enabling new services. The distinguishing value of the proposal resides in its ability to improve long‐term fairness and total system throughput while achieving a high level of fairness in every scheduling slot. Finally, it is shown that the additional complexity caused by the weight calculation has only a limited impact on the overall scheduler complexity, while simulation results confirm the claimed improvements, making the proposal an appealing alternative for resource allocation in a cellular downlink system.

In this paper, we consider a transmission scheme combining precoded Faster-Than-Nyquist signaling (FTN) and Orthogonal Frequency Division Multiplexing Offset Quadrature Amplitude Modulation (OFDM/OQAM). The precoding method, named Sparse Interference Pre-Cancellation (SIPC), aims at reducing the interference introduced by FTN signaling at the transmitter side. In order to further improve the receiver performance, we propose additional enhancements to the channel encoder, notably, the bit-to-symbol mapping and symbol to time-frequency-positions mapping. Via simulations, we show that the proposed modifications improve the Bit-Error-Rate (BER) performance of the considered transceiver.

This paper considers the problem of Base Station power minimization in downlink Orthogonal Frequency Division Multiple Access (OFDMA) systems. It aims at providing new solutions for the reduction of the total energy consumption. Such solutions rely on joint subcarrier and power allocation, under the constraints of requested per-user data rate. Practical results show that the proposed techniques allow a significant decrease of transmission power with an affordable complexity, compared to well-referenced methods from the literature.

Non-Orthogonal Multiple Access (NOMA) has proven itself as a serious candidate for multiple access schemes in the 5thgeneration of wireless communication systems. In this paper, we propose new resource allocation techniques that allow the coupling of NOMA with multiple-input-multiple-output (MIMO) systems. As in most of downlink NOMA systems, the proportional fairness (PF) scheduler is used. As for power allocation (PA), most previous works assume an equal PA between antennas and subbands, which is sub-optimal. In this paper, we first propose a technique to reduce the complexity of the PF scheduler, and then we introduce an iterative waterfilling-based power allocation to the Single-User MIMO (SU-MIMO) case. Extensive simulations show that the novel PA technique improves the quality of experience of users suffering from bad channel conditions, as well as the user fairness.

DVB-T2 was the first industrial standard deploying rotated and cyclic Q delayed (RCQD) modulation to improve performance over fading channels. This enables important gains compared to conventional quadrature amplitude modulations (QAM) under severe channel conditions. However, the corresponding demodulation complexity still prevents its use for wider applications. This paper proposes several rotation angles for different QAM constellations and a corresponding low-complexity detection method. Results show that the proposed solution simplifies both the transmitter and the receiver with often better performance than the proposed angles in DVB-T2. Compared with the lowest complexity demappers currently used in DVB-T2, the proposed solution achieves an additional reduction by more than 60%.

This paper investigates a new strategy for radio resource allocation applying a non-orthogonal multiple access (NOMA) scheme. It calls for the cohabitation of users in the power domain at the transmitter side and for successive interference canceller (SIC) at the receiver side. Taking into account multi-user scheduling, subband assignment and transmit power allocation, a hybrid NOMA scheme is introduced. Adaptive switching to orthogonal signaling (OS) is performed whenever the non-orthogonal cohabitation in the power domain does not improve the achieved data rate per subband. In addition, a new power allocation technique based on waterfilling is introduced to improve the total achieved system throughput. We show that the proposed strategy for resource allocation improves both the spectral efficiency and the cell-edge user throughput. It also proves to be robust in the case of communications in crowded areas.

In this paper, we derive the exact expression of the finite-signal to noise ratio (SNR) diversity-multiplexing tradeoff (DMT) for Rayleigh fading multiple-input multiple-output (MIMO) channels with dual correlated antennas at the transmitter (2×Nr) and/or at the receiver (Nt×2). We first derive the exact outage probability versus SNR. While finite-SNR DMT and outage probabilities are usually only estimated, we show that the numerical results of our derived outage probability and finite-SNR DMT are identical to those obtained using Monte Carlo simulations. Furthermore, it is shown that achievable diversity gains at realistic SNRs are significantly lower than asymptotic values and that the DMT degrades as the spatial correlation increases. Space-time codes (STCs) for MIMO systems are conventionally designed to achieve the asymptotic DMT frontier. This finite-SNR DMT could provide a new insight to design STCs for practical MIMO systems optimized at realistic SNRs and propagation environments.

In this paper, the combination of a low-complexity Multiple-input Multiple-output based on belief propagation (MIMO-BP) detector with a Non-Binary Low-Density Parity-Check (NB-LDPC) decoder is investigated. Such detection and decoding algorithms can enable an equivalent representation based on a larger Joint Factor Graph (JFG). Shuffle schedule can therefore be used jointly and simultaneously on the detector and the decoder. Actions are undertaken at the detector, decoder and the iterative receiver levels in order to reduce overall complexity. Indeed, applying the proposed low-complexity BP-based detection greatly reduces the number of operations per iteration (divided by ten), with a negligible performance penalty. EXtrinsic Information Transfer (EXIT) charts enable to analyze the convergence behaviour of the proposed iterative receiver. This analysis is used to find the best set of parameters enabling a detection-decoding process with a performance closest to the full-complexity system.

In this paper, an efficient iterative receiver for digital communication systems is investigated. It combines a Non-Binary Low-Density Parity-Check (NB-LDPC) decoder with a high-order constellation demapper and a Multiple-Input Multiple-Output (MIMO) detector. A suboptimal MIMO detector based on the Belief Propagation (BP) algorithm is investigated as an alternative to a Maximum Likelihood (ML) detector. Extrinsic information is exchanged between the detector and the decoder thanks to an iterative process. EXtrinsic Information Transfer (EXIT) charts enable to analyze the convergence behaviour of the proposed MIMO-BP detector. A suitable schedule for the different types of iterations is finally proposed to reduce the receiver latency and improve its error correction performance.

A fading channel emulator particularly suited for simulations of broadband communication systems is investigated. It is based on the overlap-save (OLS) method, traditionally used for efficient convolution. The resulting emulator shows a statistical accuracy comparable to the best known state-of-the-art techniques while greatly reducing complexity in terms of memory requirements. Therefore, it enables real-time simulation and makes the model particularly appealing for a hardware implementation. In addition, the introduction of an OLS-based interpolator enables simulation of very low Doppler frequencies with a high statistical precision.

Space time block codes (STBCs) are commonly designed according to the rank-determinant criteria, suitable for high signal to noise ratio (SNR) values. However, capacity approaching forward error correcting codes, used in practical communication systems, achieve iterative convergence at low to moderate SNR. In this paper we first present a non- asymptotic STBC design criterion based on the bitwise mutual information (BMI) maximization at a specific target SNR. According to this BMI criterion, we then optimize a trace-orthonormal- based STBC structure. Therefore, designed STBC becomes adaptive with respect to the SNR. Proposed adaptive trace-orthonormal STBC shows identical or better performance than 2×2 STBCs of a turbo-coded WiMAX system.

Bit-Interleaved Coded Modulation (BICM) offers a significant improvement in error correcting performance for coded modulations over fading channels compared to the previously existing techniques. Iterative processing at the receiver side can provide additional improvement to the BICM performance. In this paper, an efficient shuffled iterative receiver is investigated for the second generation of the terrestrial digital video broadcasting standard DVB-T2. The main contribution is scheduling an efficient message passing algorithm with low latency between the demapper and the IDPC decoder. A BER performance comparison between a fixed-point version that considers architectural constraints and a theoretical version over a fading channel with erasure is presented. It validates the potential of iterative receiver as practical and competitive solution for the DVB-T2 standard.

In this paper, serially concatenated continuous phase modulation (SCCPM) is considered for the uplink of satellite communications. A three-step design procedure is proposed to optimize the association of the outer code and the CPM for a wide range of spectral efficiencies, ranging from 0.75 to 2.25 bit/s/Hz. Firstly, EXIT chart analysis is applied to derive general guidelines for choosing SCCPM parameters. A significant result is that a high-rate outer code is required to achieve good convergence threshold, given a spectral efficiency. At a second stage, union bounds to the error probability are considered to choose the outer code under the constraints arising from the EXIT charts analysis. From this analysis, extended BCH codes and extended Hamming codes are proposed as outer code for broadband and narrowband transmission, respectively. For the latter, double-binary convolutional codes and symbol interleaving is also proposed as a valid alternative. Finally, combining both EXIT charts and union bounds we optimize the association of code and CPM to achieve both low error rates and good convergence. The proposed concatenated structure offers very low error floors and good performance in the waterfall region for all considered spectral efficiencies. A significant improvement with respect to previous concatenated CPM schemes is shown.

In this paper, serially concatenated continuous phase modulation (CPM) is considered. A concatenated structure consisting of a short extended BCH code as outer code is proposed, targeting a wide choice of spectral efficiencies, ranging from 0.75 to 2.25 bit/s/Hz. A two-step design procedure combining EXIT charts analysis and union bound techniques is used to optimize the association of the outer code and the CPM. An exhaustive study of several quaternary and octal CPM schemes is performed. The proposed concatenated structure offers very low error floors (frame error rate below 10-6) and good performance in the waterfall region for all spectral efficiencies. A significant improvement with respect to previous concatenated CPM schemes is shown. The envisaged application of the proposed scheme is the return link of broadband satellite communications.

A new approach for the association of the well known turbo codes to modulation schemes is presented. This method is designed for flat fading channels. It presents the advantage of lowering the error floor as the modulation order increases when compared to the traditional pragmatic turbo BICM approach. The improvement in performance comes at the price of a relatively small added complexity without sacrificing the iterative process convergence. The proposed modifications address mainly the modulator and the corresponding demodulator. An improvement exceeding 0.8 dB is observed at BER rates lower than 10-7.