Different Channel coding techniques in MIMO-OFDM

In this paper, we propose an optimal power allocation scheme for joint pilot placement and space frequency (SF) code design for multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) wireless channels. OFDM is combined with multiple antennas to increase data diversity gain on a time varying multipath fading channel, resulting in a MIMO-OFDM system. A set of fast time-varying and frequency-selective fading channels is considered. The proposed pilot assisted transmission scheme multiplexes known symbols with information bearing data to estimate the channel in the presence of inter symbol interference (ISI). The channel is assumed to be unchanged for the duration of one OFDM block and change independently from one OFDM block to the other. The number of pilot symbols for each OFDM block is held constant and the symbols are dispersed throughout the block for efficient channel estimation. However, equally distributing the total power between the data and pilots doesn't optimize the transmission over a frequency-selective fading channel. We propose an optimal power allocation scheme for the joint pilot placement and space frequency code design scheme based on the channel response and the bit error rate (BER) values. This leads to substantial improvement in performance for a 2 times 2 MIMO-OFDM system. The results can be extended to MIMO-OFDM systems with any number of transmit and receive antennas.

Multiple Input Multiple output Orthogonal Frequency division Multiplexing (MIMO-OFDM) is a prepossessing modulation technique that have achieve notable heed in wireless environment nowadays. It improves the bandwidth efficiency and increases system capacity so as to provide a reliable transmission. However it has a high increase in PAPR (peak-to-average power ratio) due to the use of large number of sub carriers which result in many restrictions for practical applications. A novel hybrid approach is presented in this paper for the PAPR reduction by merging PTS and clipping together. This paper consists of various technique for reducing peak-to-average power ratio that are developed in last two decades such as PTS, clipping, CMA etc. The simulation result shows a collation between different PAPR reduction techniques. We propose and demonstrate an algorithm using two different techniques together and the results are verified using MATLAB software. We also comment on the computational complexity and practicability of these approaches.

In this new information age, high data rate and strong reliability features our wireless communication systems and is becoming the dominant factor for a successful deployment of commercial networks. MIMO-OFDM (multiple input multiple output-orthogonal frequency division multiplexing), a new wireless broadband technology, has gained great popularity for its capability of high rate transmission and its robustness against multi-path fading and other channel impairments. A major challenge to MIMO-OFDM systems is how to obtain the channel state information accurately and promptly for coherent detection of information symbols and channel synchronization. In the first part, this dissertation formulates the channel estimation problem for MIMO-OFDM systems and proposes a pilot-tone based estimation algorithm. A complex equivalent base-band MIMO-OFDM signal model is presented by matrix representation. By choosing equally-spaced and equally-powered pilot tones from sub-carriers in one OFDM symbol, a down-sampled version of the original signal model is obtained. Furthermore, this signal model is transformed into a linear form solvable for the LS (least-square) estimation algorithm. Based on the resultant model, a simple pilot-tone design is proposed in the form of a unitary matrix, whose rows stand for different pilot-tone sets in the frequency domain and whose columns represent distinct transmit antennas in the spatial domain. From the analysis and synthesis of the pilot-tone design in this dissertation, our estimation algorithm can reduce the computational complexity inherited in MIMO systems by the fact that the pilot-tone matrix is essentially a unitary matrix, and is proven an optimal channel estimator in the sense of achieving the minimum MSE (mean squared error) of channel estimation for a fixed power of pilot tones. In the second part, this dissertation addresses the wireless location problem in WiMax (worldwide interoperability for microwave access) networks, which is mainly based on the MIMO-OFDM technology. From the measurement data of TDOA (time difference of arrival), AOA (angle of arrival) or a combination of those two, a quasi-linear form is formulated for an LS-type solution. It is assumed that the observation data is corrupted by a zero-mean AWGN (additive white Gaussian noise) with a very small variance. Under this assumption, the noise term in the quasi-liner form is proved to hold a normal distribution approximately. Hence the ML (maximum-likelihood) estimation and the LS-type solution are equivalent. But the ML estimation technique is not feasible here due to its computational complexity and the possible nonexistence of the optimal solution. Our proposed method is capable

In the past decades, researchers/scientists have paid attention to the physical layer of underwater communications (UWCs) due to a variety of scientific, military, and civil tasks completed beneath water. This includes numerous activities critical for communication, such as survey and monitoring of oceans, rescue, and response to disasters under the sea. Till the end of the last decade, many review articles addressing the history and survey of UWC have been published which were mostly focused on underwater sensor networks (UWSN), routing protocols, and underwater optical communication (UWOC). This paper provides an overview of underwater acoustic (UWA) physical layer techniques including cyclic prefix orthogonal frequency division multiplexing (CP-OFDM), zero padding orthogonal frequency division multiplexing (ZP-OFDM), time-domain synchronization orthogonal frequency division multiplexing (TDS-OFDM), multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM), generalized frequency division multiplexing (GFDM), unfiltered orthogonal frequency division multiplexing (UF-OFDM), continuous phase modulation orthogonal frequency division multiplexing (CPM-OFDM), filter bank multicarrier (FBMC) modulation, MIMO, spatial modulation technologies (SMTs), and orthogonal frequency division multiplexing index modulation (OFDM-IM). Additionally, this paper provides a comprehensive review of UWA channel modeling problems and challenges, such as transmission loss, propagation delay, signal-to-noise ratio (SNR) and distance, multipath effect, ambient noise effect, delay spread, Doppler effect modeling, Doppler shift estimation. Further, modern technologies of the physical layer of UWC have been discussed. This study also discusses the different modulation technology in terms of spectral efficiency, computational complexity, date rate, bit error rate (BER), and energy efficiency along with their merits and demerits.

In this paper, we propose a receiver architecture that can demodulate multiple data streams with different frequency offsets and propagation delays in multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) ad hoc networks. The receiver performs joint synchronization and interference cancellation to separate these interfering data streams and achieve synchronization for each stream. We propose a novel training-based minimizing mean square error (MMSE) algorithm to jointly obtain the frequency offsets and the equalization delays. The effects of frequency offsets and propagation delays are compensated with these estimated parameters. We also propose a direct training-based equalizer design algorithm to obtain the equalizer coefficients. This algorithm involves solving an optimization problem that considers symbol error rate. Simulation shows good uncoded bit error rate performance for our proposed algorithms.

The MIMO-OFDM (multiple input multiple output-orthogonal frequency division multiplexing) system recently received considerable attention because of its potential ability to enable the higher transmission data rate while keeping the high signal quality. In practical MIMO-OFDM systems, the efficient and highly accurate channel estimation method is the mandatory requirement to achieve the potential system performance over MIMO channels. This paper proposes the discrete cosine transform (DCT) interpolation-based channel estimation (DCTI-CE) method, which could meet the above requirements. The salient feature of the proposed DCTI-CE method is to enable the estimation of all link channel responses with high accuracy by using only one preamble symbol even under the severe multi-path fading channel for wireless LAN systems.

Ambient backscatter communication (ABC) is a promising technology for future wireless systems due to its ultra-low-power operation and simplicity. To further enhance its performance, multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) has been adopted in this work. However, carrier frequency offset (CFO) can disrupt the orthogonality of the MIMO-OFDM signal, which significantly degrades the performance of the reader’s receiver. To address this issue, we consider an asynchronous ABC system and propose a deep learning (DL) algorithm to estimate and compensate the CFO at the reader, ensuring reliable communication in MIMO-OFDM-based ABC systems. The proposed architecture integrates a hybrid attention mechanism, which captures inter-dependencies between the two types of extracted features, and a squeeze-and-excitation network that adaptively refines channel-wise feature responses. The proposed architecture can also work for conventional OFDM and MIMO-OFDM systems. Furthermore, to validate the model’s robustness and generalization capability, additional test datasets are generated for various modulation schemes and different 3GPP TR38.901 tapped delay line channel models. The simulation results indicate its outperformance over existing approaches and has lower computational complexity than the existing methods.

In multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems, several detection schemes have been developed for high error performance and low complexity. In several detection schemes, maximum likelihood (ML) and QRD-M have optimal error performance. However, these detection schemes have very high complexity. Thus, this paper proposes reduced complexity of QRD-M detection scheme in MIMO-OFDM systems. The proposed detection scheme has two stages, i.e. partial zero-forcing (ZF) and conventional QRD-M. The proposed detection scheme has higher error performance and lower complexity than the decision feedback equalizer (DFE).

In this paper, reduced complexity channel estimation techniques that was first proposed in case of Single Input Single Output Orthogonal Frequency Division Multiplexing (SISO-OFDM) is generalized in case of multiple-input multiple-output — OFDM (MIMO-OFDM) systems. The impact of complexity reduction is analyzed through floating point simulation, fixed point simulation and FPGA implementation using rapid prototyping.

Physical layer security is a crucial issue in wireless networks to prevent legitimate communication from eavesdropping. This paper investigates the physical layer security of a wireless multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) communication system in the presence of a multiple-antenna eavesdropper. We first propose a minimum mean square error (MMSE)-based-filter secure MIMO–OFDM system which can destroy the orthogonality of eavesdropper’s signals. The MMSE-based-filter is used at the receiver to suppress the inter-subcarrier interference and disturb the reception of eavesdropper while maintaining the quality of legitimate transmission. Next, we propose another artificial noise (AN)-assisted secure MIMO–OFDM system to further improve the security of the legitimate transmission. The time-domain AN signal is designed to be canceled out at the legitimate receiver. Therefore, AN will disturb the reception of eavesdropper while the legitimate transmission will not be affected. Finally, power allocation for AN signals and subcarriers will be discussed since AN is generated utilizing the residual power of the MIMO–OFDM system. Simulation results are presented to demonstrate the security performance of the proposed transmit filter design and AN-assisted scheme in the MIMO–OFDM system.

Rapid development of wireless services, leads to ubiquitous personal connectivity in the world. The demand for multimedia interactivity is higher in the world which leads to the requirement of high data transmission rate. Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) is a future wireless service which is used to overcome the existing service problems such as development of subscriber pool and higher throughput per user. Although it overcomes the problems in existing services, resource allocation becomes one of the major issues in the MIMO-OFDM systems. Resource allocation in MIMO-OFDM is the optimization of subcarrier and power allocation for the user. The overall performance of the system can be improved only with the efficient resource allocation approach. The user data rate is increased by efficient allocation of the subcarrier and power allocation for each user at the base station, which is subject to constraints on total power and bit error rate. In this study, the problem of resource allocation in MIMO-OFDM system is tackled using hybrid artificial bee colony optimization algorithm based on a crossover operation along with Poisson-Jensen in equation. The experimental results show that the proposed methodology is better than the existing techniques.

Channel estimation is very important for MIMO (Multiple Input Multiple Output) OFDM (Orthogonal Frequency Division Multiplexing) systems, but its precision is reduced due to the noise in channel. In this letter, circularly slipping window is introduced to resist the noise. It can be proved by simulation that with the same channel model, optimal slipping window length is the same with different vehicle speed. MSE (Minimum Square Error) of channel is greatly reduced with circularly slipping window, and performance of the system is closed to that with correct channel estimation.

This paper proposes a novel channel tracking method based on radial basis function neural network (RBFNN) and particle filter (PF) in multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) system. First, we use the RBFNN to obtain the initial values of the MIMO channels, and then apply the PF method to track the variation of the channels. The fading channels are modeled as autoregressive (AR) process and the transmit signals are encoded by space-time block code (STBC) scheme. Simulation results show that the proposed method has effective tracking performance.

In orthogonal frequency division multiplexing (OFDM) systems, since virtual subcarriers are not used for transmission, approach of conventional uniformly placed pilot tones is not applicable in some situations. In this letter, based on nonuniform pilot tone placement, we derive optimal pilot sequences, which can achieve the minimum mean square error of the least squares estimate for multiple-input multiple-output (MIMO) OFDM systems. Simulation results demonstrate the effectiveness of the proposed approach.

In this paper, we analyze the Bit Error Rate (BER) performance of Golden coded Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over Rician multipath fading channel. We also compare the performance of the MIMO-OFDM system using Golden code in Rayleigh and Rician multipath fading channels. We discuss the effects of the presence of line-of-sight (LoS) component in the multipath fading environment which renders the improvement in the overall performance of the Golden coded MIMO-OFDM. This paper discusses the performance of Golden codes in a frequency selective Rician fading channel. To deal with the frequency selective fading channel, we use the OFDM (Orthogonal Frequency Division Multiplexing) modulation. The BER performance of the Golden coded MIMO-OFDM system under several propagation conditions has been evaluated. Keywords—MIMO, OFDM, Golden STBC, Rayleigh fading, Rician fading.