A joint channel estimation and turbo equalization scheme for doubly selective fading channels

Research into cutting-edge systems that can satisfy the rising needs for greater data rate and increased reliability is becoming more and more necessary as wireless communication technologies continue to evolve. To enhance the spectral and energy efficiencies, this study examine the performance of massive multiple input multiple output (mMIMO) communication systems using wavelet-order orthogonal frequency division multiplexing (W-OFDM). Also, a communication system was created based on W-OFDM Massive MIMO using MATLAB to model its operation. The simulated system's various stages of operation was examined through detailed analysis and its performance was compare with prior studies and practical networks on OFDM. Key performance metrics, specifically the data throughput, was evaluated to assess the effectiveness and viability of the system. The simulation results indicates that W-OFDM can achieve up to 35% reduction in peak-to-average-power-ratio (PAPR) compared to the traditional OFDM, with a 20% improvement in BER performance under Rayleigh fading conditions. Also, the spectral efficiency of W-OFDM mMIMO outperforms convectional OFDM by 15%, making it a viable technology for future communication networks requiring high data rates and reliability. This implies that, the analytical evaluation confirms that W-OFDM mMIMO provides substantial benefits for improving energy and spectral efficiencies in wireless communication systems, addressing the challenges of increased user demands for high spectrum. This study contributes to the understanding of MIMO systems' performance optimization, highlighting the importance of antenna configuration and cell distance. Comprehensive analysis of spectral efficiency and energy efficiency trade-offs in MIMO systems and identification of optimal antenna configuration for maximum energy efficiency, addressing some of the challenges of future wireless communication systems.

Turbo equalization schemes based on minimum mean square error (MMSE) criteria available in the literature for multiple-input multiple-output (MIMO) systems are computationally expensive, as they require a relatively large matrix inversion. In this paper, we propose a low complexity turbo equalization (TE) scheme with successive interference cancellation for orthogonal frequency division multiplexing (OFDM) based MIMO receiver systems (TE-SIC-MIMO). TE-SIC-MIMO leverages on the soft feedback symbol estimate to selectively remove the intercarrier interference (ICI) and co-antenna interference (CAI) from the received data, thus turning the system matrix into an easily invertible form. Extrinsic Information Transfer (EXIT) chart analysis supplemented with numerical simulation results shows that TE-SIC-MIMO performance under static and rapidly time varying multipath conditions is mostly on par with MMSE turbo equalization scheme available in the literature, that is based on a sub-matrix of the system matrix at signal-to-noise ratios (SNR) of practical interest. However, the computation complexity of TE-SIC-MIMO turns out to be much lesser than the TE scheme considered.

In this paper, we propose a joint channel estimation and decoding scheme using soft bit output information in OFDM-based systems. In order to estimate the complex OFDM channel amplitudes, the estimation algorithms usually rely on the pilot signal assisted modulation (PSAM). We enhanced this method by using the soft code bits after each turbo decoding iteration in a feedback loop. This way, the quality of the initial channel estimation can be significantly increased without the need of using additional pilot symbols. The proposed algorithm is tested on a selection of different time and frequency selective fading channels based on Rayleigh fading discrete taps of an exponentially decaying average power delay profile. We compare the performance of our algorithm with other channel estimation techniques for two different sizes of the data frame and demonstrate gains in order of 1-2 dB. We also show that our algorithm is better suited for fast changing, highly frequency-selective channels.

Communication over HF-ionospheric channel requires the use of a performant receiver based on turbo equalization scheme. In this receiver, channel estimation can be improved for each iteration using soft information fed back from the decoder. We propose a turbo equalizer based on a soft-input Kalman estimator that can operate without channel impulse response knowledge. Performance analysis of the channel estimator is tested using four paths channel for two Doppler spread values and records of realistic channel. Simulation results show the convergence of the algorithm versus the frequency dispersion of the paths and compare the BER of the proposed Kalman based turbo equalizer with that of the conventional turbo equalizer. Results show that the proposed equalizer provide a significant gains in BER performance and convergence without the need for training data.

Accurate channel state information is the foundation of the receiver design for power line communication (PLC) system. However, the presence of impulsive noise makes the problem more complex. As traditional impulsive noise mitigation methods are based on the assumption that the channel state information is known in advance, which limits their applications. In this paper, by exploiting the parametric sparsity, we propose a joint channel and impulsive noise estimation scheme based on compressed sensing theory for narrowband PLC systems. Observing the strong coherence of measurements matrix, we adopt the sparse Bayesian learning (SBL) to solve the compressed sensing problem. Simulation results verify our proposed algorithm has smaller mean square error and bit error rate.

Frame synchronization, channel estimation scheme and signal compensation using regression method in OFDM systems

OFDM modulation, which has been adopted for the digital video broadcasting (DVB-T) standard in Europe, has been recognized for its good performance for high data rate wireless communications. Therefore, the study of the robust transmission of multimedia data over OFDM systems has attracted extensive research interest. In the past, channel estimation, which is an important aspect in OFDM systems, has not been exploited for multimedia transmission. When using block-training based channel estimation schemes, there exists a periodic variation of the error rates due to channel estimation imprecision. We use this property to provide unequal error protection (UEP) for video transmission. Compared with systems using pilot-training based channel estimation schemes, which are recommended in the DVB-T standard, a performance gain of about 2dB in the PSNR of the reconstructed images is achieved.

Orthogonal frequency division multiplexing (OFDM) modulation, adopted by the digital video broadcasting (DVB-T) standard, has been recognized for its good performance for high data rate wireless communications. Therefore, the study of the robust transmission of multimedia data over OFDM systems has attracted extensive research interests. In the past, channel estimation, which is an important aspect in OFDM systems, has not been exploited for multimedia transmission. When using the block training based channel estimation, OFDM data blocks experience unequal decoding error rate due to the imprecision of channel estimation. We use this property to provide unequal error protection (UEP) for transmission of SPIHT coded images. Compared with the systems using pilot training channel estimation schemes, which are recommended in the DVB-T standard, the proposed scheme improves the PSNR of reconstructed images by up to 2 dB.

Reconfigurable intelligent surfaces (RISs) have been recently considered as a promising candidate for energy-efficient solutions in future wireless networks. Their dynamic and low-power configuration enables coverage extension, massive connectivity, and low-latency communications. Due to a large number of unknown variables referring to the RIS unit elements and the transmitted signals, channel estimation and signal recovery in RIS-based systems are the ones of the most critical technical challenges. To address this problem, we focus on the RIS-assisted wireless communication system and present two joint channel estimation and signal recovery schemes based on message passing algorithms in this paper. Specifically, the proposed bidirectional scheme applies the Taylor series expansion and Gaussian approximation to simplify the sum-product procedure in the formulated problem. In addition, the inner iteration that adopts two variants of approximate message passing algorithms is incorporated to ensure robustness and convergence. Two ambiguities removal methods are also discussed in this paper. Our simulation results show that the proposed schemes show the superiority over the state-of-art benchmark method. We also provide insights on the impact of different RIS parameter settings on the proposed schemes.

The ability to receive broadcast content in highly mobile scenarios plays an important role in determining the success of broadcast systems in general. The second generation of Terrestrial Digital Video Broadcasting (DVB-T2) has made several technical enhancements to increase the data carrying capacity that enabled the reception of High Definition (HD) content. Due to its properties, Orthogonal Frequency-Division Multiplexing (OFDM) is chosen as the transmission scheme in the physical layer. However, in highly mobile environments, a doubly-selective or a time-varying multipath channel that exhibits selectivity in both the time as well as the frequency domain, deteriorates the performance of the receiver. Furthermore, DVB-T2 allows up to 32k carriers on the same channel raster resulting in a smaller carrier spacing that further amplifies the effects of mobility at the receiver. Thus, channel estimation and equalization techniques play a vital role in overcoming the effects of a doubly-selective channel and enabling high mobility in a DVB-T2 receiver. Channel estimation schemes must not only be able to model the wireless channel accurately but also be computationally efficient in order to enable implementation on resource constrained consumer hardware. Compressed Sensing (CS) schemes like the Rake-Matching Pursuit (RMP) algorithm are proven to perform well in vehicular communication systems and the associated computational complexity is significantly smaller than competing state-of-art estimation schemes. In this paper, we show that the RMP algorithm for channel estimation is suitable to be used with DVB-T2 under varying channel conditions. The results show that the proposed schemes produce significantly better results when compared to the conventional channel estimation and equalization schemes. Furthermore, a detailed analysis on the computational complexity will further strengthen the need for the proposed scheme to estimate doubly-selective channels.

This paper evaluates BER performance of VHF band broadband mobile communication systems standardized as ARIB STD-T103 mode1. The ARIB STD-T103 mode 1 is based on IEEE 802.16-2009 standard with OFDMA because of its easy implementation. The IEEE 802.16-2009 based system is originally expected to operate in microwave bands such as 2.5 GHz with 512 FFT based OFDM in 5 MHz channel. However, the ARIB STD-T103 based system should tune the radio parameters of IEEE 802.16-2009 to suit for VHF band propagation characteristics because many multipath waves with long delay path are received in the VHF band. The ARIB STD-T103 mode 1 adopts OFDMA with 1024 FFT in 5 MHz channel and convolutional Turbo coding to cope with long delay multipath environments in VHF band such as IEEE 802.22 Profile A model. However, the BER performance in the environments has never been evaluated. This paper evaluates the BER performance with conventionally proposed receiving scheme by computer simulation. However, the performances of UL and DL with 64QAM do not achieve the required BER of ARIB STD-T103. To improve the BER performance this paper proposes three channel estimation schemes for DL. Although the BER performance with the schemes are not improved drastically, it is clarified that one of the proposals is expected to reduce size of storage in comparison with the conventional estimation schemes. With the estimation scheme and maximum ratio combined diversity achieves the required BER in both UL and DL.

This paper presents an optimized turbo equalizer based on Laot's turbo equalization scheme by means of soft intersymbol interference (ISI) cancellation. Due to Berrou's turbo-principle, common turbo equalization schemes use the extrinsic information as a-priori input for the equalizer. In contrast to this, we propose the use of the full soft output channel decoder's information for the turbo interference canceller. The performance of this improved turbo equalizer by means of soft interference cancellation is evaluated in the environment of two channels, which introduce severe ISI. Simulation results show that the proposed turbo equalizer achieves a performance gain of up to 4 dB compared to Laot's original approach. The performance gain is achieved without any increase of computational complexity. Moreover, we apply a modified extrinsic information transfer (EXIT) chart to the proposed turbo equalizer and illustrate the convergence advantages in comparison to Laot's approach.

In this paper, a new joint timing and channel estimation scheme is proposed for orthogonal frequency division multiplexing and single carrier block transmission ultra-wideband (UWB) systems. In particular, a new preamble pattern is used for both coarse timing and channel estimation. Despite of the presence of coarse timing error, the estimated channel impulse response (CIR) is simply the cyclic shifted version of the real CIR, thanks to the unique structure of the preamble. Then a new method is proposed to search for the first channel tap in the CIR vector, which can be employed to fine tune the timing position and adjust the channel estimation for later data block detection. The proposed scheme has low complexity, saves preamble overhead by performing joint synchronization and channel estimation, and outperforms existing timing acquisition methods in the literature by a large margin in dense multipath UWB channels. Moreover, this paper presents an analysis of the effect of residual timing error on the performance of single carrier systems with frequency domain equalization.

Joint channel estimation and data detection under fading on reconfigurable fabric

The turbo equalization principle, based on Berrou's (1993) turbo principle, is a high performance receiver scheme to mitigate intersymbol interference (ISI) caused by a frequency selective channel. Several turbo equalization (TEQ) schemes, like Douillard's (1995) MAP/MLSE TEQ, Laot's (1997) TEQ scheme by means of soft ISI cancellation and turbo equalization based on MMSE linear equalization have been presented different in performance and computational complexity. One of these schemes, turbo equalization based on MMSE linear equalization achieves nearly MAP/MLSE performance, while reducing the computational complexity tremendously. We extend this receiver scheme to 16-QAM and present simulation results for different ISI channels.