Efficient joint channel equalization and tracking for V2X communications using SC-FDE schemes

Our aim with this paper is to present a solution suitable for vehicle-to-everything (V2X) communications, particularly, when employing single-carrier modulations combined with frequency-domain equalization (SC-FDE). In fact, we consider the V2X channel to be doubly-selective, where the variation of the channel in time is due to the presence of a Doppler term. Accordingly, the equalization procedure is dealt by a low-complexity iterative frequency-domain equalizer based on the iterative block decisionfeedback equalization (IB-DFE) while the tracking procedure is conducted employing an extended Kalman filter (EKF). The proposed system is very efficient since it allows a very low density of training symbols, even for fast-varying channels. Furthermore only two training symbols are required to initialize the tracking procedure. Thus, ensuring low latency together with reduced channel estimation overheads.publishe

Frequency-Domain Channel Estimation and Equalization for Single Carrier Underwater Acoustic Communications

A new frequency-domain channel estimation and equalization (FDE) scheme is proposed for single carrier (SC) underwater acoustic communications. The proposed SC-FDE employs a small training signal block for initial channel estimation in the frequency domain and converts the estimated transfer function to a desired DFT (discrete Fourier transform) size for channel equalization of the data blocks. The frequency domain equalizer is designed using the linear minimum mean square error criterion. A new phase coherent detection scheme is also proposed and deployed to combat the phase drift due to the instantaneous Doppler in the underwater channels. The channel transfer functions and group-averaged phase drift are re-estimated adaptively in a decision-directed manner for each data block in a packet, which contains M blocks of QPSK data. The proposed SC-FDE method is applied to single input multiple output (SIMO) systems using the experimental data measured off the coast of Panama City, Florida, USA, June 2007. The uncoded bit error rate of the SIMO systems varies between 1.3% to 6.8 x 10^-5 when 4 ~ 8 receive hydrophones are utilized, and the source-receiver range is 5.06 km

Robust frequency-domain turbo equalization for multiple-input multiple-output (MIMO) wireless communications

This dissertation investigates single carrier frequency-domain equalization (SC-FDE) with multiple-input multiple-output (MIMO) channels for radio frequency (RF) and underwater acoustic (UWA) wireless communications. It consists of five papers, selected from a total of 13 publications. Each paper focuses on a specific technical challenge of the SC-FDE MIMO system. The first paper proposes an improved frequency-domain channel estimation method based on interpolation to track fast time-varying fading channels using a small amount of training symbols in a large data block. The second paper addresses the carrier frequency offset (CFO) problem using a new group-wise phase estimation and compensation algorithm to combat phase distortion caused by CFOs, rather than to explicitly estimate the CFOs. The third paper incorporates layered frequency-domain equalization with the phase correction algorithm to combat the fast phase rotation in coherent communications. In the fourth paper, the frequency-domain equalization combined with the turbo principle and soft successive interference cancelation (SSIC) is proposed to further improve the bit error rate (BER) performance of UWA communications. In the fifth paper, a bandwidth-efficient SC-FDE scheme incorporating decision-directed channel estimation is proposed for UWA MIMO communication systems. The proposed algorithms are tested by extensive computer simulations and real ocean experiment data. The results demonstrate significant performance improvements in four aspects: improved channel tracking, reduced BER, reduced computational complexity, and enhanced data efficiency --Abstract, page iv

Cyclic prefix assisted block transmission for low complexity communication system design

This thesis presents new results on cyclic prefix (CP) assisted block transmission for low complexity communication system design. Two important aspects are studied: the CP based low-complexity schemes for channel equalization and channel estimation. Specifically, based on the simple frequency domain equalization, a low complexity joint receiver is proposed for CP-CDMA system, which is a special application of block transmission. And in this work the finite impulse response (FIR) model is used for the unknown communication channels. To identify an unknown FIR channel, a novel channel estimation method is proposed by exploiting the cyclic prefix technique. Compared to a conventional method, the proposed method delivers the similar estimation accuracy, yet at much lower system overhead and lower computational complexity. In order to minimize the channel total mean square error in channel estimation, the criteria and solutions to optimal training sequence design are also presented. Finally, the performance study is carried out on the proposed channel estimation scheme for BPSK block transmission system as well as CP-CDMA system using simulation along with analysis

Frequency-Domain Turbo Equalization for MIMO Underwater Acoustic Communications

This paper investigates a low-complexity frequency-domain turbo equalization (FDTE) based on linear minimum mean square error (LMMSE) criterion for single-carrier (SC) multiple-input multiple-output (MIMO) underwater acoustic communications (UAC). The receiver incorporates both the equalizer and the decoder which exchange the extrinsic information on the coded bits for each other to implement the iterative detection. The channel impulse responses (CIRs) required in the equalization are estimated in the frequency domain (FD) by inserting the well-designed pilot blocks which are frequency-orthogonal Chu sequences. The proposed SC-MIMO-FDTE architecture is applied to the fixed-to-fixed underwater data gathered during SPACE08 ocean experiments in October 2008, where multiple transducers and hydrophones are deployed in communication ranges of 200m and 1000m, and the channel bandwidth is 9.765625 kHz. The phase shift keying (PSK) signals are transmitted from multiple transducers in various block sizes. The proposed transceiver has been demonstrated to improve the bit-error-rate (BER) performance significantly by processing the QPSK data blocks with block length of 1024 in 200m and 1000m ranges. The average BERs obtained by turbo detection with 3 iterations can achieve approximately 1.4 × 10-4 for the 200m system and 4.4 × 10-5 for the 1000m system

On the Performance of LDPC-Coded MIMO Schemes for Underwater Communications Using 5G-like Processing

UIDB/EEA/50008/2020This article studies the underwater acoustic (UWA) communications associated with multiple input–multiple output (MIMO), single carrier with frequency-domain equalization (SC-FDE), and with low-density parity-check (LDPC) codes. Low-complexity receivers such as equal gain combining (EGC), maximum ratio combining (MRC), and iterative block—decision feedback equalization (IB-DFE) are studied in the above-described scenarios. Furthermore, due to the low carrier frequencies utilized in UWA communications, the performance of the proposed MIMO scenarios is studied at different levels of channel correlation between antennas. This article shows that the combined schemes tend to achieve good performances while presenting low complexity, even in scenarios with channel correlation between antennas.publishersversionpublishe

Uplink of base station cooperation systems with SC-FDE modulations and IB-DFE receivers

This paper considers the uplink transmission in BS (Base Station) cooperation schemes where users in adjacent cells share the same physical channel and the signals received by each BS are sent to a CPU (Central Processing Unit) that combines the different received signals associated to a given user and/or performs the user separation. The signals are modulated through SC (Single-Carrier) schemes combined with FDE (Frequency- Domain Equalization) techniques and with iterative frequency-domain receivers based on the IB-DFE concept (Iterative Block Decision Feedback Equalization). Our performance results show performance results close to the MFB (Matched Filter Bound), where the proposed receivers allow enhancement in macro-diversity gains as well as an efficient user separation, making these techniques an excellent choice for the uplink transmission in future broadband wireless systems employing BS cooperation schemes

Design and performance evaluation of turbo FDE receivers

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Electrotécnica e de ComputadoresIn recent years, block transmission techniques were proposed and developed for broadband wireless communication systems, which have to deal with strongly frequency-selective fading channels. Techniques like Orthogonal Frequency-Division Multiplexing (OFDM)and Single Carrier with Frequency Domain Equalization (SC-FDE) are able to provide high bit rates despite the channel adversities. In this thesis we concentrate on the study of single carrier block transmission techniques considering receiver structures suitable to scenarios with strongly time-dispersive channels. CP-assisted (Cycle Pre x) block transmission techniques are employed to cope with frequency selective channels, allowing cost-e ective implementations through FFT-based (Fast Fourier Transform) signal processing. It is investigated the impact of the number of multipath components as well as the diversity order on the asymptotic performance of SC-FDE schemes. We also propose a receiver structure able to perform a joint detection and channel estimation method, in which it is possible to combine the channel estimates, based on training sequences, with decision-directed channel estimates. A study about the impact of the correlation factor estimation in the performance of Iterative Block-Decision Feedback Equalizer (IB-DFE) receivers is also presented