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This chapter provides fundamental indications about wireless communications beyond LTE/LTE‐A (5G). We start by identifying the drivers for making the transition to 5G networks, and we make clear that the strict paradigm of synchronism and orthogonality as applied in LTE prevents efficiency and scalability. We challenge this paradigm and propose new key PHY‐layer technology components, the core being a unified frame structure concept, which supports an integrated 5G air interface, capable of dealing both with broadband data services and small packet services within the same band. It is essential for this concept to introduce waveforms that are more robust than OFDM, for example with respect to time‐frequency misalignment. Encouraging candidate waveform technologies are presented and discussed with their respective results. This goes along with the corresponding multiple access technologies, using multi‐layered signals and advanced multi‐user receivers. In addition, we introduce new strategies to enable “one shot transmission”, with greatly reduced control signaling, particularly for sporadic traffic. These components enable an efficient and scalable air interface supporting the highly varying set of requirements originating from the 5G drivers.

International audience; Low Power Wide Area (LPWA) networks aim at connecting low cost devices with high constraints on the link budget. Focusing on the physical layer, the combination of Frequency Shift Keying (FSK) modulation and coding in the same process has been shown efficient when associated to a turbo receiver. This paper considers the optimization of Turbo-FSK parameters for the LPWA context using the EXtrinsic Information Transfer (EXIT) Chart analysis. After adapting the metric to the FSK waveforms, EXIT chart performance results are extended and compared to short packet lengths using extensive Bit Error Rate (BER) computations.

With the increasing demand for mobile data traffic, enhanced frequency localized transmissions are considered for the generation of wireless networks to come. Filter Bank Multi-Carrier modulation, with the use of Offset-QAM, proves to be an interesting candidate to satisfy those spectrum constraints. Contrary to CP-OFDM, FBMC does not use any CP. Its spectral efficiency is improved but it also weakens the transmissions over highly frequency selective channels. Complex detection stage based on precoding or multi-tap equalization is thus necessary to prevent orthogonality losses. Another solution can be the use of the Frequency-Spreading scheme which improves the frequency resolution. In this paper, we propose to extend probabilistic decoding to linear FBMC receivers. The performances of the two common FBMC receiver structures, PolyPhase Network and Frequency-Spreading, are assessed over frequency-selective LTE channel models. The analytical formulae of the likelihood metrics are also derived.

Low Power Wide Area networks aim at connecting low cost devices with high constraints on the link budget. Focusing on the physical layer, the combination of orthogonal modulation and coding in the same process has been shown efficient when associated with a turbo receiver. This work shows how this scheme, based on frequency shift keying modulation, can be efficiently implemented on today low-end platform based on a flexible radio frequency semiconductor component combined with a low power microcontroller. A link budget improvement of 4.6dB is demonstrated with a low-end receiver, enabling a coverage extension by a factor of 1.78 or a reduction of the transmit power by a factor 3, while keeping the same quality of service.

International audience; In Low Power Wide Area networks, terminals are expected to be low cost, low power and able to achieve successful communication at long range. Communication should be low rate compared to cellular mobile networks. Most of the current technologies dedicated to Machine-to-Machine communication rely on the use of a spreading factor to achieve low levels of sensitivity. To contain power consumption at the terminal side, the cost of complexity should be paid by the receiving side. We propose to use turbo processing schemes as potential physical layers. We compare these schemes to a standard and an industrial solution, and show that a significant gain in sensitivity can be achieved, and very energy efficient scheme can be designed by mixing turbo processing and orthogonal modulation concepts.

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Flexible and efficient use of all available spectrums for different network deployment scenarios is one challenge for the future 5G. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and time resources. In this work, we study and fairly compare the performance of different waveforms (UFMC, FBMC, and legacy LTE waveforms) in cellular networks with relaxed synchronization. First, a unified frame structure is discussed to introduce the context. Then we compare the robustness of the waveform contenders in the envisaged scenario. Based on these results, a bit loading algorithm is proposed to cope with the non-uniform distribution of the interference across the carriers in order to increase the spectral efficiency.

White space communications have attracted a particular interest after some national regulators have authorized TVWS unlicensed secondary usage. The IEEE 1900.7 working group has defined a specific air interface tailored to these applications. The standard, is based on an Filter Bank Multi Carrier (FBMC) physical layer and a CSMA-CA MAC sublayer. In this paper, the Modulation and Coding Schemes (MCS) of the IEEE 1900.7-2015 are considered to assess simulated expectations on throughput and coverage under various typical TVWS deployment scenarios: Fixed Long Range Access, campus WLAN (in Fixed Urban/Suburban environments), Indoor Femtocells (a TVWS low power transceiver for WLAN-like applications). Expected rate and coverage maps are provided for these scenarios.

International audience; —The number of Machine to Machine (M2M) applications is increasing rapidly especially in cellular communication systems. These applications should support a very high number of stations (STAs) and facilitate communication without any human intervention. To fulfill these requirements random access protocols are a possible choice. Carrier sense multiple access collision avoidance (CSMA/CA) protocol with request to send and clear to send (RTS/CTS) mechanism presents high degradation of the throughput and packet drop probability performance especially when the packets size are small. The medium access control (MAC) overhead caused by the RTS and CTS messages is high comparing to the total duration of successful transmission. In order to reduce the MAC overhead we propose in this work a new strategy to serve many users successively. This strategy consists on sending many RTS in parallel by different stations on different frequency sub-bands. Once the RTS messages do not collide with each other, there will be no need to resend the RTS and wait for a CTS to gain the channel access. In this paper, this proposed strategy is investigated and we demonstrate that it reaches better saturation throughput and packet drop probability especially in loaded networks. Index Terms—Multiband Carrier sense multiple access/collision avoidance (M-CSMA/CA), throughput, MAC protocol, scheduling, M2M, overhead reduction, finite retransmission, packet drop probability.

Non synchronous random access is envisaged for sporadic traffic to limit the amount of the exchanged signaling messages. Burst data transmission is commonly used in wireless communication systems. Each burst begins with a preamble which is used to synchronize the receiver. When the initial estimation of the Carrier Frequency Offset is coarse, and/or the burst duration is relatively long, a phase tracking algorithm is required to track any residual phase during the payload transmission. In this paper we investigate a blind phase tracking algorithm for Filter Bank Multicarrier waveforms. Different algorithms are described and evaluated. A comparison with state of the art algorithms is discussed. Finally we describe an algorithm based on sign statistics that outperforms the state of the art algorithms while reducing the complexity.

International audience; The Internet of Things aims to connect several billions of devices. Terminals are expected to be low cost, low power, and able to achieve successful communication at long range. While current Machine-to-Machine technologies tend to use spreading factors to meet the required specifications, we propose a more sophisticated use of redundant waveforms in a scheme called Turbo-FSK. This scheme involves Frequency-Shift-Keying (FSK) modulation at the transmission, and a turbo-decoder dedicated to the FSK waveforms at the receiver. Highly robust communication is achieved with a mere transmitter, as complexity is deported on the receiver side. Results are compared to common modulations using spreading factors, a significant gain in performance is achieved even with small packet sizes.

International audience; We present in this paper a new medium access control (MAC) scheme devoted to orthogonal frequency division multiple access (OFDMA) systems which aims at reducing collision probabilities during the channel request period. The proposed MAC relies on the classical carrier sense multiple access/collision avoidance (CSMA/CA) protocol with RTS / CTS ("Request To Send" / "Clear To Send") mechanism. The proposed method focus on the collision probability of RTS messages exploiting a multi-channel configuration for these messages while using the whole band for data transmissions. The protocol may be interpreted as an asynchronous frequency multiplexing of RTS messages. This method achieves strong performance gains in terms of throughput and latency especially in crowded networks. Index Terms—Carrier sense multiple access/collision avoidance (CSMA/CA), multiband, throughput, MAC protocol.

International audience; Filter Bank MultiCarrier modulation (FBMC) is a promising waveform technology envisaged for future mobile communication networks. For many transmission scenarios, the combination of multiple non-contiguous spectrum bands is foreseen. Because of coexistence issues, very low Adjacent Channel Leakage is required making FBMC waveforms of particular interest. However the fair frequency localization of FBMC results in a time spreading of the waveform: the filter impulse response introduces transitions which increase the duration of the burst with respect to classical multicarrier schemes such as Orthogonal Frequency Division Multiplexing and may reduce the overall spectral efficiency. In this work, we propose to study the performance of a FBMC waveform considering Carrier Sense Multiple Access with Collision Avoidance. Two mechanisms are employed for packet transmission: a basic access and a reservation scheme (based on RTS/CTS). We study how effective the RTS/CTS handshake is under ideal channel conditions by taking into account the specificities of the FBMC physical layer. Furthermore, we discuss about the RTS threshold value on packet size that maximizes throughput performance by employing one of both possible schemes and the impact of subchannel aggregation strategies on throughput and latency.

This paper reports intermediate transceiver and frame structure concepts and corresponding results from the European FP7 research project 5GNOW. The core is the unified frame structure concept which supports an integrated 5G air interface, capable of dealing both with broadband data services and small packet services within the same band. It is essential for this concept to introduce waveforms which are more robust than OFDM, e.g., with respect to time-frequency misalignment. Encouraging candidate waveform technologies are presented and discussed with respective results. This goes along with the corresponding multiple access technologies using multi-layered signals and advanced multi-user receivers. In addition we introduce new (compressive) random access strategies to enable "one shot transmission" with greatly reduced control signaling particularly for sporadic traffic by orders of magnitude. Finally, we comment on the recent results on the 5GNOW networking interface. The intermediate results of 5GNOW lay the ground for the standardization path towards a new 5G air interface beyond LTE-A.

Relaxed synchronization and access to fragmented spectrum are considered essential for future generations of wireless networks in order to reduce physical channel signaling. Frequency Division Multiple Access for Filter Bank Multicarrier (FBMC) modulation provides promising performance without strict synchronization requirements contrary to conventional Orthogonal Frequency Division Multiplexing (OFDM). In this paper, the architecture of a FBMC receiver suitable for this scenario is considered and its performance is compared against OFDM. The maximum achievable capacity of an asynchronous uplink transmission is analyzed when limited amount of feedback information on timing misalignment and power control is available. The proposed receiver architecture based on frequency domain processing combined with the fair frequency localization of the FBMC prototype filter provides an architecture that allows for more efficient multiuser asynchronous reception compared to OFDM.

International audience; —In this work we study the collision probability, saturation throughput and statistical delay for the carrier sense multiple access collision avoidance (CSMA/CA) protocol with request to send and clear to send (RTS/CTS) mechanism in the case of frequency channel division. We propose in this paper a modified version of CSMA/CA-RTS/CTS to be compatible with the channel repartition technique and we prove that an important gain is introduced in terms of system performance especially for loaded networks. Simulations highlight that dividing the channel into independent sub-channels reduces drastically the RTS collision probability. Moreover, a gain in terms of saturation throughput and delay is shown especially in dense networks. Index Terms—Carrier senses multiple access/collision avoid-ance (CSMA/CA), Frequency channel division, RTS/CTS, MAC protocol.

We investigate the problem of sequence detection in a non linear channel for a contactless air interface. The work presented in this study is based on the the VHBR (Very High Bit-Rate) amendments of the ISO 14443 international standard. We focused more particularly on the part of the standard extension that defines the phase modulation (PSK) from the Proximity Coupling Device (PCD) to the Passive Inductive Coupled Card (PICC). We propose an efficient detector to overcome both Inter Symbol Interference (ISI) due to the high data rates, and system non linearities introduced by the differential detection at the receiver side. The proposed detector is an adaptation of the Viterbi algorithm for constraint-ternary alphabet. Our numerical results show that a rate of 13.56 Mbps can be achieved using a 15-states sequence detector.

International audience; Many of the current LDPC implementations of DVB-S2, T2 or WiMAX standard use the so-called layered architecture combined with pipeline. However, the pipeline process may introduce memory access conflicts. The resolution of these conflicts requires careful scheduling combined with dedicated hardware and/or idle cycle insertion. In this paper, based on the DVB-T2 example, we explain explicitly how the scheduling can solve most of the pipeline conflicts. The two contributions of the paper are 1) how to split the matrix to relax the pipeline conflicts at a cost of a reduced maximum available parallelism 2) how to project the problem of the research of an efficient scheduling to the well-known "Travelling Salesman Problem" and use a genetic algorithm to solve it.

International audience; Layered decoding is known to provide efficient and high-throughput implementation of LDPC decoders. However, the implementation of the layered architecture is not always straightforward because of the memory access conflicts in the a-posteriori information memory. In this paper, we focus our attention on a particular type of conflict introduced by the existence of multiple diagonal matrices in the DVB-T2 parity check matrix structure. We illustrate how the reordering of the matrix reduces the number of conflicts, at the cost of limiting the level of parallelism. We then propose a parity extending process to solve the remaining conflicts. Fixed point simulation results show coherent performance without modifying the layered architecture.

In this paper we propose a decoding architecture for turbo-like decoding algorithm of a particular class of Low-Density Parity Check codes. We define a methodology to design codes. In a first step a hardware architecture and the decoding scheduling are first selected. Then rules for the design of these codes are derived, aiming at improving the convergence of the decoding algorithm, while fitting with the proposed architecture. Last, performance results and details on the decoder implementation are provided to illustrate the interest of the approach.

This paper investigates cycle and distance properties of structured Low Density Parity Check (LDPC) codes based on circulant permutation matrices. A very simple algorithm to detect and construct codes with good cycle properties is proposed. A geometrical approach to design codes with good girth properties is then presented and illustrated, through the definition of rules for the design of parity check matrices without short length cycles. An upper bound on the minimal distance of the proposed structured code is also derived. The information provided by this bound can help the construction of the parity check matrices, in order to achieve a target minimum distance.

In this paper a new interleaver is proposed as turbo codes intern interleaver. This interleaver designed from shifted identity matrices has been developed to facilitate implementation of parallelized turbo decoding. The structure is first illustrated and then, implementation aspects are discussed. We demonstrate that the proposed interleaver is contention free and enables low complex implementation without performance loss.

This paper proposes a code design method for a particular class of serial concatenated codes named systematic with serially concatenated parity (S-SCP) codes. Using a particular family of S-SCP codes based on quasi cyclic code, we propose a code design taking into account both implementation and performance requirements. This design enables a particular scheduling of the decoding process enabling the reduction of the number of parallelized processes required to meet a target throughput.

Low-Density Parity Check codes have been widely investigated over the past few years, and construction of Low-Density Parity Check code enabling efficient implementation design represents one of the main topics of interest. This article proposes a new code family, based on a structures code construction with an inherent parallelism. This construction divides the parity check matrix into layers which can be processed simultaneously, improving encoding throughput and latency. Possible optimizations and example are proposed and illustrated.

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Among these latter, the flexible and efficient use of non-contiguous unused spectrum for different network deployment scenarios is considered a key challenge for 5G systems. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and radio resources. In this work, we propose a comparison of several 5G waveform candidates (OFDM, UFMC, FBMC and GFDM) under a common framework. We assess spectral efficiency, power spectral density, peak-to-average power ratio and robustness to asynchronous multi-user uplink transmission. Moreover, we evaluate and compare the complexity of the different waveforms. In addition to the complexity analysis, in this work, we also demonstrate the suitability of FBMC for specific 5G use cases via two experimental implementations. The benefits of these new waveforms for the foreseen 5G use cases are clearly highlighted on representative criteria and experiments.

A flexible data frame structure adapted to 5G operations and designed to support high bandwidth pipes or sporadic traffic is described. The frame structure imposes to consider receiver architectures that are adapted to orthogonal frequency division mutliplexing (OFDM) for structured synchronous traffic and alternative flexible asynchronous waveforms such as filterbank multicarrier (FBMC) for sporadic traffic. OFDM and FBMC receivers are reviewed and a new flexible receiver architecture is then proposed and described. The design of the new architecture is centered on a memory unit complemented with co-processor units improving the flexibility of the digital signal processing operations of the receiver. The architecture is particularly adapted to application specific integrated circuit. The throughput imposed on the memory and the associated data receiver bus has been evaluated. The evaluation concluded that the throughput is suitable for very large scale integration implementations.

Relaxed synchronization and access to fragmented spectrum are considered for future generations of wireless networks. Frequency division multiple access for filter bank multicarrier (FBMC) modulation provides promising performance without strict synchronization requirements contrary to conventional orthogonal frequency division multiplexing (OFDM). The architecture of a FBMC receiver suitable for this scenario is considered. Carrier frequency offset (CFO) compensation is combined with intercarrier interference (ICI) cancellation and performs well under very large frequency offsets. Channel estimation and interpolation had to be adapted and proved effective even for heavily fragmented spectrum usage. Channel equalization can sustain large delay spread. Because all the receiver baseband signal processing functionalities are proposed in the frequency domain, the overall architecture is suitable for multiuser asynchronous transmission on fragmented spectrum.