Guillaume Ferré

STBC-Based (Turbo) STTC Codes Built by Set Partitioning for Three Transmit Antennas: Construction and Performances

This paper introduces new studies on the codes named Super Orthogonal Space Time Trellis Codes (SOSTTC). Using set partitioning rules combined with a set of orthogonal designs, SOSTTCs are able to combine the coding gain of STTCs together with diversity advantage of orthogonal STBCs. We propose new application fields of these codes in the particular context of three transmit antenna systems. We introduce new STTCs built on STBC designs that outperform some STTCs schemes based on the determinant and rank criteria. Further- more, we demonstrate by simulation that the use of these codes in a turbo parallel concatenated scheme permits working very close to the channel outage probability.

Performances of LDPC based multi-user space frequency diversity system design for uplink multi-carrier CDMA

We present the performance of a new multi-user detector for space frequency uplink transmission in multi-carrier CDMA systems. In our proposed architecture, the data symbols are parallelized and then each of the symbols is spread by a spreading code before sending the chips as multiple OFDM codeword. The SFBC decoder is placed at the last stage of our multi-user receiver and the user separation is done after the OFDM demodulator. We show that, the system is particularly easy to implement, and besides, the performance is comparable to the case of a single user SFBC system. We also point out the need of additional interleaver when the system is used with a LDPC channel encoder

EM Based Channel Estimation and Decoding in OFDM Turbo Blast Detectors

Channel parameter estimation is an important task for coherent detection and constitutes a key challenge in MIMO systems. Turbo-Bell Labs Laboratory Architecture Systems (T-BLAST) with orthogonal frequency division multiplexing (OFDM) can be used to improve communication quality and capacity. This paper proposed a modified expectation maximization (EM) algorithm for T-BLAST systems in frequency selective channels. It is based on a combination of data and pilot based channel estimate with approximated coefficients. These coefficients are obtained by resolving an optimization problem using the Lagrangian multipliers. The algorithm we present takes advantage of the exchange message between the two soft input soft output (SISO) modules of the turbo receiver to attain the best estimation performance. The effectiveness of this technique is demonstrated through the simulation of an OFDM T-BLAST system with two-transmit and three-receive antennas.

Collision and packet loss analysis in a LoRaWAN network

Internet of things (IoT) is considered as the next technological revolution. Therefore, many solutions are developed either in free, i.e. ISM bands or in non free bands with the ultimate aim of affording connectivity over several kilometers. Based on this feature, in urban environment the density of IoT devices will be extremely high. In this paper we propose to analyze the collision and packet loss when LoRaWAN is considered. Based on the LoRaWAN features, we develop closed-form expressions of collision and packet loss probabilities. Simulation results confirm our theoretical developments. We also show that our theoretical expressions are more accurate than the Poisson distributed process to describe the collisions.

New Layered Space-Time Schemes Based on Group of Three Transmit Antenna

We present a new architecture of layered space-time codes as a combination of Bell Laboratory Layered Space-Time (BLAST) architecture and of special Space Time Trellis (STTC) Codes which are variations about the Super Orthogonal Space-Time Trellis Codes (SOSTTC) first introduced by Ionescu et al in [1] [2] and further improved by Jafarkhani et al. in [3]. The system we propose is named Super Quasi Orthogonal Horizontal Layered Space Time Trellis Code (SQOHLSTTC). It consists in a powerful Space-Time Block Code (STBC) based STTC originally derived for a three transmit antenna system, together with an original block based decoding algorithm. The decoding algorithm of SQOHLSTTC combines group interference suppression and group interference cancellation techniques. To implement the system, we propose a low complexity hard decision iterative decoding method. System performances confirm the great interest of the proposed transmission scheme.

Multi-user detection in OFDM space time block code for high rate uplink application

In this paper, we propose a multi-user detector for space-time uplink transmission in multi-carrier CDMA systems using a new combination of STBC, OFDM and CDMA spreading. To achieve high rate, CDMA spreading codes are shared between a few users and we use linear STBC decoding to further separate users. The OFDM codewords are built from chips issued from different symbols. The STBC encoder and decoder are placed at the last stage of our multi-user transmitter and receiver respectively. We show that the system is particularly easy to implement when exploiting the space diversity after CDMA detection. Besides, the performance is comparable to the case of a single user STBC system. The proposed system allows for a very high rate multi-user system compared to the conventional CDMA system or combined array-processing technique previously proposed.

Layered Space-Time Coding for 3×n Transmit Antenna Communication Systems

We present a new architecture of layered space-time codes as a combination of BLAST architecture and of special STTC codes which are variations about the codes first introduced by Jafarkhani et al. and named super orthogonal space-time trellis codes (SOSTTC). Using powerful set partitioning, these codes are able to combine the coding advantage of STTCs together with the advantage diversity of orthogonal space-time block codes (STBC). The system we propose is named super quasi orthogonal horizontal layered space time trellis code (SQOHLSTTC). It consists in a powerful STBC based STTC originally derived for a three transmit antenna system, together with an original block based decoding algorithm which enables to use a higher number of transmit antennas. The decoding of SQOHLSTTC combines group interference suppression and group interference cancellation techniques. To implement the system, we propose a low complexity hard decision iterative decoding method. System performances are illustrated and confirm the great interest of the proposed transmission scheme

Improving frequency synchronization by means of new correlation criteria for fine time synchronization in MIMO system

In this paper, a precise timing synchronization technique is proposed for multiple-input multiple- outpzrt MMO system. The proposed algorithm can be used for iEEE 802. I la wireless LAN system. We modified the existing algorithm in literature to obtain exact packet arrival timing. We then use this advantage to better estimate frequency ofsset due to locd oscillator imperfections or Doppler effect.

LDPC-based space-time coded OFDM systems: Turbo-EM receiver design with channel state information guessing algorithms

In this paper we study some turbo receiver architectures employing low-density parity check (Ldpc) codes together with orthogonal frequency division multiplexing (Ofdm) for high data rate wireless transmissions. Different demodulation schemes based on expectation-maximization (Em) algorithm are studied along with the channel impulse response (Em) algorithms. We studied differentCir guessing algorithms including the EM-based algorithms such as a space-alternating generalized expectation-maximization algorithm (Sage). It is shown that the proposed turbo-Em receiver employing a soft maximum a posteriori (Map)Em demodulator and a belief propagationLdpc decoder can perform within 1 dB from the ergodic capacity of the studiedMimo ofdm channels. Besides, we find that a suboptimum structure based on a soft interference cancellationMmse filtering demodulator exhibits negligible loss in non-correlated fadingMimo channels but suffer extra performance loss in highly correlatedMimo channels.RésuméDans cet article, nous étudions les performances de récepteurs de type turbo utilisant des codesLdpc dans le contexte de transmissions hauts débits enOfdm. Différents types de démodulateurs utilisant l’algorithmeEm sont présentés ainsi que divers algorithmes d’apprentissage du canal de propagation toujours basés sur I’Em. En particulier nous proposons une variante de l’algorithmeEm baptiséeSage Space-Alternating Generalized Expectation-Maximization algorithm. Nous montrons alors que le récepteur turboMap-em combiné avec un codeurLdpc permet de travailler à 1 dB de la capacité ergodique du canal lorsque le canal est parfaitement estimé. De plus, nous montrons qu ’une structure sous-optimale utilisant un annuleur d’interférences avec un filtrage des moindres carrés présente des pertes négligeables dans le cas de canaux indépendants mais est plus sensible que la structureMap-em à la présence de canaux fortement corrélés.