Orthogonal frequency division multiplexing (OFDM) is a multicarrier transmission system that can achieve high data rate over wireless channels At the same time, multiple input multiple output OFDM

Compensation of Non-linear Distortion Effects in MIMO-OFDM Systems Using Constant Envelope OFDM for 5G Applications

Due to recent advancements in virtual reality (VR) and augmented reality (AR), the demand for high quality immersive contents is a primary concern for production companies and consumers. Similarly, the topical record-breaking performance of deep learning in various domains of artificial intelligence has extended the attention of researchers to contribute to different fields of computer vision. To ensure the quality of immersive media contents using these advanced deep learning technologies, several learning based Stitched Image Quality Assessment methods have been proposed with reasonable performances. However, these methods are unable to localize, segment, and extract the stitching errors in panoramic images. Further, these methods used computationally complex procedures for quality assessment of panoramic images. With these motivations, in this paper, we propose a novel three-fold Deep Learning based No-Reference Stitched Image Quality Assessment (DLNR-SIQA) approach to evaluate the quality of immersive contents. In the first fold, we fined-tuned the state-of-the-art Mask R-CNN (Regional Convolutional Neural Network) on manually annotated various stitching error-based cropped images from the two publicly available datasets. In the second fold, we segment and localize various stitching errors present in the immersive contents. Finally, based on the distorted regions present in the immersive contents, we measured the overall quality of the stitched images. Unlike existing methods that only measure the quality of the images using deep features, our proposed method can efficiently segment and localize stitching errors and estimate the image quality by investigating segmented regions. We also carried out extensive qualitative and quantitative comparison with full reference image quality assessment (FR-IQA) and no reference image quality assessment (NR-IQA) on two publicly available datasets, where the proposed system outperformed the existing state-of-the-art techniques.

https://www.mdpi.com/1424-8220/20/22/6457/pdf

DLNR-SIQA: Deep Learning-Based No-Reference Stitched Image Quality Assessment.

Generation of wireless network from past to present deals with many fatal problems such as - spectrum scarcity, lower data rates, power deficiency, synchronization, unfavorable diversity, inferior QoS, and Interference. Many of the above problems are resolved in some manner using a better modulation and multiplexing technique using Orthogonal Frequency Division Multiplexing (OFDM), however, it still interlocks with Interference hindrance. In the paper, we surveyed all about OFDM interference's - Inter Symbol Interference (lSI), Inter Carrier Interference (ICI) and Co- Channel Interference (CCI) which greatly inhibits the Bit Error Rate (BER) of OFDM. Moreover, this paper also reviews some of the good research on interference mitigation techniques. We also surveyed the work on wavelet transform which is quite effective in OFDM system compare to conventional Fourier transform. Channel coding is a measurable parameter which is a mere technique in reducing the CCI effect from the wireless system, for that we elaborate Space Time Block Code-OFDM (STBC-OFDM) to reduce ICI and CCI.

A Survey on OFDM Interference Challenge to improve its BER

In this paper, challenges regarding the provision of channel state information (CSI) in multiple-input multiple-output (MIMO) systems based on space time block codes (STBC) over slow time-varying Rayleigh fading channels are addressed. We develop a novel MIMO channel estimation algorithm that adopts a pilot symbol assisted modulation (PSAM) which has been proven to be effective for fading channels. In this approach, pilot symbols are periodically inserted into the data stream that is sent through the orthogonal STBC encoder. At the receiver, we propose a straightforward MIMO channel estimation method before being used by STBC decoder. Simulation results indicate that the proposed pilot-assisted MIMO concept provides accurate channel estimates. The impact of Doppler frequency on performance scheme is also investigated by simulation.

Pilot assisted channel estimation in MIMO-STBC systems over time-varying fading channels

Underwater communication is one of the paramount parts of communication. It avails us in scientific research, studies and is used by the coast guard and the navy for our country’s protection. We know that the underwater communication is difficult due to water currents, Doppler effect, ISI (Inter Symbol Interference), ICI (Inter Carrier Interference), surface noise, thrust noise, multiple path delay and it is also affected by any movement between the transmitter and receiver. OFDM (Orthogonal Frequency Division Multiplexing) is the most desirable mode of modulation underwater. It is spectrally efficient and immune to selective fading. We have implemented this OFDM to submarines with MIMO (Multiple Input Multiple Output), technology modelled using the equalizers ZF-MMFE for better Bit Error Rate (BER) Performance. This will overcome the present performance degradation in the single carrier domain equalization due to noise reconstruction in OFDM and the spectral scarcity due to the single user communication.

Adaptive OFDM Non-Uniform Modulation for Underwater Acoustic Communication

In this paper, the channel estimation technique for space time block code (STBC) based multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) is investigated for multipath fading channel. The channel estimation is based on the comb-type pilot arrangement where the pilot subcarriers are placed at regular interval of each OFDM symbol block and are orthogonal between different transmitting antennas. Due to the advantages of orthogonal pilot subcarrier, the original transmitted signal is completely recovered from the mixed transmitted signal at the receiver side. The least square (LS) algorithm is adopted for estimation of channel at pilot subcarrier while the interpolation is done at data subcarrier. The performance of the developed channel estimation technique is compared with the traditional single-input single-output (SISO) OFDM system on the basis of symbol error rate (SER). The simulation results show that the STBC OFDM gives better performance than SISO OFDM and the SER decreases as the signal to noise ratio (SNR) and the number of receive antenna increases.

A comb-type pilot symbol aided channel estimation for STBC based OFDM system over frequency selective channel

In time-selective fading channel, the Alamouti orthogonality principle is lost due to the variation of channel from symbol-to-symbol in space–time block-coded orthogonal frequency division multiple...

A Novel LMMSE-EM Channel Estimator for High Mobility STBC-OFDM System

In this paper, we propose two efficient signal detection methods for high mobility space–time block code based orthogonal frequency division multiplexing (OFDM) The first proposed method is based on order block decision feedback equalizer (OBDFE) which is the column norm ordering version of the conventional BDFE method To improve the system performance further, we have proposed a hybrid OBDFE–MPD method by cascading the OBDFE method with a multistage parallel decoder (MPD) The advantage of the OBDFE–MPD method is that it does not need additional complexity as most of the computations are performed in the initial stage by the OBDFE method These two proposed methods are compared with minimum mean square error (MMSE), block linear minimum mean square error (BLMMSE), block decision feedback equalizer (BDFE), vertical Bell laboratories layered space–time (VBLAST) and space alternating generalized expectation maximization (SAGE) in terms of performance and computational complexity From the simulation results and computational complexity, it is shown that both the proposed OBDFE and OBDFE–MPD methods provide a great trade-off between performance and computational complexity for high mobility OFDM system with transmit diversity

Efficient Signal Detection Methods for High Mobility OFDM System with Transmit Diversity

The Alamouti Space Time Block Code (STBC) based Orthogonal Frequency Division Multiplexing (OFDM) is very attractive in frequency selective channel as the channels remain constant over Alamouti code period (two consecutive OFDM symbol block). But when the channel is fast fading, this assumption does not holds good and causes co-channel interference (CCI). Hence, the simple Alamouti detection method is not sufficient to recover the original transmitted signal from the mixed transmitted signals at the receiver side. To cancel the effects of CCI, several detection techniques are addressed namely SIC, DMLD, DZFD, DF and ML. The ML method has the optimum performance but the computational complexity is very high. Therefore, we propose a suboptimal MDF detection which provides comparable performance to that of ML with very less computational complexity. Finally, the performances of the above detection methods are compared in terms of symbol error rate (SER) and computational complexity for STBC OFDM system over doubly selective channel.

Co-channel interference suppression techniques for STBC OFDM system over doubly selective channel

The performance analysis of Alamouti space time block code (STBC) based orthogonal frequency division multiplexing (OFDM) is often analyzed on the assumption that the channel is constant over Alamouti code period (two consecutive OFDM symbol block). But when the channel is fast fading, this assumption does not hold good and causes co-channel interference (CCI) and inter-carrier interference (ICI). In this paper, an iterative interference cancellation is proposed for STBC OFDM to suppress both the CCI and ICI effect jointly. The proposed scheme consists of two stage interference cancellation. In the first stage the CCI cancellation is performed based on Diagonalized Zero Forcing Detection (DZFD) method. In the latter stage a simplified parallel interference cancellation (PIC) scheme coupled with decision statistics combining (DSC) method is used to cancel the ICI effect and hence improves the system performance. The simulation results verify that the proposed scheme achieves good performance for STBC OFDM system in high mobility environment.

Jyoti P. Patra

Papers

A comb-type pilot symbol aided channel estimation for STBC based OFDM system over frequency selective channel

A Novel LMMSE-EM Channel Estimator for High Mobility STBC-OFDM System

Efficient Signal Detection Methods for High Mobility OFDM System with Transmit Diversity

Co-channel interference suppression techniques for STBC OFDM system over doubly selective channel

Joint iterative CCI and ICI cancellation for STBC-OFDM system in fast fading channel