Robust adaptive coding schemes for multipath fading channels

This paper investigates the capacity of spread spectrum multiple access (SSMA) in a non-cellular environment under additive white Gaussian noise (AWGN) conditions. A theoretical system model is proposed that allows one to evaluate such a system. The probability density function of the average degradation due to the interuser interference is determined by simulations and the validity of approximating the interuser interference as a Gaussian random variable is verified. The capacity of SSMA is shown to be low compared to TDMA when operated in a non-cellular environment without forward error control (FEC) coding.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reliable image transmission over wireless channels is difficult due to the presence of multipath fading, noise, and limited bandwidth. MIMO-OFDM has proven to be an effective solution to these challenges by jointly exploiting spatial diversity and frequency-selective transmission. In this work, a MIMO-OFDM-based image transmission system is designed and evaluated using MATLAB simulations. The input image is converted into a binary bitstream, encoded, modulated, and transmitted over fading wireless channels. At the receiver, channel equalization and decoding techniques are applied to recover the transmitted image. System performance is assessed in terms of bit error rate (BER), reconstructed image quality, and robustness under additive white Gaussian noise and Rayleigh fading conditions. Simulation results demonstrate that the proposed MIMO-OFDM framework achieves improved BER performance and enhanced visual image quality, as reflected by higher PSNR values.

Wireless networks have dynamic transmission properties as the wireless channel conditions randomly change over time due to several environmental factors. When transmitting real-time applications such as video, the dynamic properties of wireless networks can have detrimental effects on the quality of the video delivered to a user. Many Quality of Service (QoS) guarantee techniques to improve video quality in wireless networks are available. However, these mainly focus on traffic shaping based on bandwidth requirements and prioritization and do not take into account the effects a changing wireless channel might have on the transmitted video. With an increasing amount of video applications being transmitted over wireless networks, alternative methods to provide QoS guarantees should be investigated. This research proposes an adaptive Forward Error Control (FEC) mechanism that dynamically adjusts the number of error control packets based on the traffic load in the network and the state of the wireless channel. When the wireless channel is bad, such as during a rain storm, the proposed mechanism reduces the amount of FEC packets added thereby reducing computational overhead in the network. This enables the receiver to recover the information sent by the transmitter faster with fewer errors than it otherwise would. Simulation results using video trace files show an improvement over existing solutions in terms of the number of FEC packets added while overall the user-perceived quality of the video streaming session is maintained at the same level, even when the network is experiencing a high Packet Error Rate (PER).

Bit-error rate (BER) performance analyses are presented for Reed-Solomon coded fast frequency-hopping binary frequency-shift-keying (FFH/BFSK) spread-spectrum (SS) systems under the conditions of additive white Gaussian noise (AWGN) and the worst-case band multitone jamming (MTJ). The FFH system employs the soft-decision linear-combining receiver to obtain the diversity-combining output. The corresponding hard decision of the diversity-combining output is then used to decode the Reed-Solomon codes. The analytical expressions of the BER performance of the coded FFH systems are derived and shown to be applicable to higher diversity levels without much more computational complexity. Numerical results show that there is an optimum code rate for the Reed-Solomon coded system under the worst-case multitone jamming conditions.

Channel coding is a fundamental procedure in wireless telecommunication systems and has a strong impact on the data transmission quality. This effect becomes more important when the transmission must be characterised by low latency and low bit error rate, as in the case of vehicle-to-everything (V2X) services. Thus, V2X services must use powerful and efficient coding schemes. In this paper, we thoroughly examine the performance of the most important channel coding schemes in V2X services. More specifically, the impact of use of 4th-Generation Long-Term Evolution (4G-LTE) turbo codes, 5th-Generation New Radio (5G-NR) polar codes and low-density parity-check codes (LDPC) in V2X communication systems is researched. For this purpose, we employ stochastic propagation models that simulate the cases of line of sight (LOS), non-line of sight (NLOS) and line of sight with vehicle blockage (NLOSv) communication. Different communication scenarios are investigated in urban and highway environments using the 3rd-Generation Partnership Project (3GPP) parameters for the stochastic models. Based on these propagation models, we investigate the performance of the communication channels in terms of bit error rate (BER) and frame error rate (FER) performance for different levels of signal to noise ratio (SNR) for all the aforementioned coding schemes and three small V2X-compatible data frames. Our analysis shows that turbo-based coding schemes have superior BER and FER performance than 5G coding schemes for the vast majority of the considered simulation scenarios. This fact, combined with the low-complexity requirements of turbo schemes for small data frames, makes them more suitable for small-frame 5G V2X services.

Channel estimation in Underwater Acoustic Communication (UAC) faces significant challenges due to the non-Gaussian, impulsive noise in ocean environments and the inherent high dimensionality of the estimation task. This paper introduces a robust channel estimation algorithm by solving an l1−l1 optimization problem via the Alternating Direction Method of Multipliers (ADMM), effectively exploiting channel sparsity and addressing impulsive noise outliers. A non-monotone backtracking line search strategy is also developed to improve the convergence behavior. The proposed algorithm is low in complexity and has robust performance. Simulation results show that it exhibits a small performance deterioration of less than 1 dB for Channel Impulse Response (CIR) estimation in impulsive noise environments, nearly matching its performance under Additive White Gaussian Noise (AWGN) conditions. For Delay-Doppler (DD) doubly spread channel estimation, it maintains Bit Error Rate (BER) performance comparable to using ground truth channel information in both AWGN and impulsive noise environments. At-sea experimental validations for channel estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems further underscore the fast convergence speed and high estimation accuracy of the proposed method.

The increasing demand for high-density and high-speed digital optical recording systems has made the development of advanced coding and signal processing techniques for fast and reliable data recovery increasingly important. In recent years, the parity-check (PC)-code-based reception technique has been widely studied for magnetic recording systems, and it is projected to be highly promising for high-density optical recording. The PC code is an inner error correction code (ECC), which can detect dominant short error events of the system, using only a few parity bits. This reduces the loss in error correction capability of the outer ECC due to random short errors and results in a simple and efficient solution to improve the overall performance. This thesis is dedicated to the design and analysis of PCcode- based recording systems to achieve higher recording capacity with low implementation complexity, for high-density blue laser disc systems. In particular, most of the key components of the PC-code-based optical recording system have been designed and optimized for different recording densities, and different proportions of white noise and media noise. During the development of advanced coding and detection techniques, it becomes necessary to investigate the system’s performance with different coding schemes and recording densities. In Chapter 2 of the thesis, we propose a generalized Braat-Hopkins model for optical recording channels, which provides a fair basis for the performance comparison of detection schemes over different coding schemes and recording densities, for channels with additive, white Gaussian noise (AWGN) and media noise. Various basic issues associated with the PC-code-based systems are investigated in Chapter 3. These include bounds for bit error rates and error event probabilities, the dominant error events at channel detector output, different PC codes, simple and efficient post-processors, the impact of error events that are split across data block boundaries and the corresponding remedy, as well as the effects of code rates and recording densities. Simulation results show that a 4-bit PC code achieves the best performance. The corresponding bit error rates (BERs) are very close to the performance bounds, at both nominal and high densities. Constrained codes, which serve as a key component in the read-write channel of data storage systems, are desired to have a high code rate with low-complexity encoder/decoder. In Chapter 4, we investigate the design of certain capacity-approaching constrained codes for optical recording systems. In particular, we derive analytically the relationship between the number of encoder states and the maximum size of these codes. We identify the minimum number of encoder states that maximizes the code rate, for any desired codeword length. The design of constrained PC codes is key to the development of PCcode- based systems, and the systematic design of efficient constrained PC codes remains a challenging problem. In Chapter 5, we propose a general and systematic code design technique for constructing capacity-approaching constrained PC codes, which can detect any type of error events of the system, with the minimum code rate loss. Compared to the rate 2/3 code without parity, the newly designed constrained 4-bit PC code achieves a performance gain of 2 dB at nominal density, and 1.5 dB at high density, at BER = 10-5. As the dominant noise for high-density optical recording systems, media noise severely degrades the performance of channel detectors and postprocessors that are designed for AWGN. In Chapter 6, we propose two novel modifications to the bit detector to combat media noise. We further develop a data-dependent post-processing scheme for error correction. Compared to the system designed without considering media noise and without PC codes, the overall performance gain of the developed scheme can be more than 11 dB at high media noise levels. In data storage systems, the ECC failure rate (EFR) serves as the ultimate measure of the data recovery performance. In Chapter 7, we develop semi-analytical approaches for estimating the EFR, and analyze EFRs for the developed PC-code-based systems, for the cases without and with interleaving. Our analysis shows that with the optimum interleaving degrees, compared to the rate 9/13 code without parity, the 2-bit PC code achieves a gain of around 0.5 dB, and the 4-bit PC code gains 0.6 dB, at high record ing density and EFR = 10-16. The thesis concludes in Chapter 8 with some suggestions for further work.

This paper evaluates at the various modulation and coding techniques suitable for adaptive data communication system. The techniques evaluated are applicable to HF spectrum. Examples of modulation and coding scheme that are evaluated include PACTOR I, PACTOR II, PACTOR III, GTOR and STANAG 4285. Analysis of system performance is made in the presence of AWGN with future extension for multipath fading conditions. Comparison will be made based on the bit-error rate (BER), packet-error rate (PER) and the throughput. In addition, the effective data rate for all the schemes is compared with the Shannon capacity limit to ensure the optimal utilization of the given channel bandwidth. The modulation and coding scheme that meets all of the above requirements will be used for future adaptive data communication system.

Fundamental to all wireless communication is modulation, the process in which the message data is transmitted on a high frequency radio carrier. Most of the wireless transmissions today are digital as it has more advantages than analog; the effect of distortion, noise, interference is minimized through the use of ingenious digital signal processing as compared to analog communication system. In this paper, we have considered binary frequency shift keying (BFSK) as the modulation technique to send data over a wireless channel. The corresponding demodulator is responsible for retrieving the transmitted data from the noisy, faded signal as impacted by the channel. The metric usually used to evaluate a digital modulation scheme is its average probability of bit error. We have evaluated the bit error rate (BER) of BFSK signals in both the additive white Gaussian noise (AWGN) and flat Rayleigh fading channels. The evaluation has been carried out in both MATLAB and SIMULINK platforms which are subsequently validated by the corresponding theoretical values. After the simulated, BER values are verified and matched with their corresponding theoretical values, hardware realizations have been attempted. The contribution of this paper is (a) the BER evaluation of BFSK through MATLAB simulation and SIMULINK platform, followed by theoretical validations in two different channels and (b) investigation of a hardware platform called Field Programmable Analog Array (FPAA) to build and test a BFSK modulator demodulator (MODEM). Test results show promising outcomes as to the suitability of such MODEM. Indeed data is retrieved at the expense of a small delay.KeywordsFSKBERAWGNRayleigh flat fadingSIMULINKFPAA

The bit error rate (BER) performance of digital cellular radio systems was investigated in a Nakagami (1960) fading, correlated lognormal shadowing and additive white Gaussian noise (AWGN) environment for noncoherent differential phase shift keying (DPSK) modulation. Two models were used to determine the BER; the first one is based on the cumulative power levels of cochannel interferers while the second one is based on instantaneous cochannel interference power. The relative advantages of the two models were presented for various design parameters. The effects of bit energy to noise ratio, frequency reuse distance, cluster size, correlation coefficient, shadow spread, and fading parameter were studied. The BER was observed to be lower in a correlated shadowing environment compared with the uncorrelated case. The near-far effect was studied by assuming that both the desired and interfering mobiles are randomly located in their corresponding cells.

In recent years, there has been enormous interest in millimeter (mm) wave communication systems such as IEEE 802.11ad and IEEE 802.15.3c operating in higher and unused frequency bands. To make system more resilient in time varying, multipath fading channels, a modulation scheme called π/2-quadrature phase shift keying (QPSK) along with a forward error control (FEC) scheme has been proposed in these systems. The performance of the FEC decoder is improved when soft information in the form of log likelihood ratio (LLR) is given to it In this paper, we propose a method for soft demapping of π/2-QPSK symbols. This method is also applicable to other schemes such as differential QPSK (DQPSK) and offset QPSK (OPSK). The complexity of the proposed method is very less and requires one adder and one multiplier. We demonstrate the bit error rate (BER) performance of the proposed method using simulations and compare it with that of other methods.

Distributed Speech Recognition (DSR) systems rely on efficient transmission of speech information from distributed clients to a centralized server. Wireless or network communication channels within DSR systems are typically noisy and bursty. Thus, DSR systems must utilize efficient Error Recovery (ER) schemes during transmission of speech information. Some ER strategies, referred to as forward error control (FEC), aim to create redundancy in the source coded bitstream to overcome the effect of channel errors, while others are designed to create spread or delay in the feature stream in order to overcome the effect of bursty channel errors. Furthermore, ER strategies may be designed as a combination of the previously described techniques. This chapter presents an array of error recovery techniques for remote speech recognition applications. This chapter is organized as follows. First, channel characterization and modeling are discussed. Next, media-specific FEC is presented for packet erasure applications, followed by a discussion on media-independent FEC techniques for bit error applications, including general linear block codes, cyclic codes, and convolutional codes. The application of unequal error protection (UEP) strategies utilizing combinations of the aforementioned FEC methods is also presented. Finally, framebased interleaving is discussed as an alternative to overcoming the effect of bursty channel erasures. The chapter concludes with examples of modern standards for channel coding strategies for distributed speech recognition (DSR). 8.1. Distributed Speech Recognition Systems Throughout this chapter various error recovery and detection techniques are discussed. It is therefore necessary to present an overview of a complete experimental DSR system, including feature extraction, a noisy channel model, and an automatic speech recognition engine at the server end (Fig. 8.1). 2 Bengt J. Borgstrom, Alexis Bernard, and Abeer Alwan Feature Extraction Source Coding Channel Coding Channel Decoding Source Decoding Speech Recognition Client Server Noisy Channel input speech

This keynote discusses the behavior of noise in indoor power line communications (PLC) channels. Some ideas to improve system performance based on the knowledge of PLC noise are also introduced. The power-line noise at an outlet is the sum of noise waveforms produced and emitted to the lines from the appliances connected to the power-line network. In the design and the analysis of wireless communication systems, stationary additive white Gaussian noise (AWGN) is often assumed. In PLC systems, however, the statistical behavior of the man-made noise is quite different from that of the stationary AWGN. The fact that the noise in power-lines is not AWGN is often believed to be a cause of low quality of communications. However, Gaussian is the distribution of the largest entropy, and communications under non-Gaussian noise may achieve better performance if the system is designed to adapt the noise statistics. In other words, PLC systems retain large potential for performance improvement if the behavior of the noise is clarified and taken into account in the system design. For narrow-band indoor PLC, we have a mathematically tractable and accurate model based on experimental measurements. In this model, the noise is expressed as a Gaussian process whose instantaneous variance is a periodic time function. With this assumption and representation, the cyclostationary features of power-line noise can be described in close form formula with a small set of parameters. In wide-band indoor PLC, we have made measurements with high speed sampling (50MHz) with long observation duration (10.4s).

The Orthogonal Frequency Division Multiplexing (OFDM) is also known as multicarrier technology. Wideband digital communications in the recent past have increasingly utilized OFDM. It can withstand difficult channel circumstances, efficiently utilize spectrum resources, decrease ISI, and operate at a high data rate, among many other benefits. It has been used in several wireless and wired communication systems, including fourth generation Long-Term Evolution (4G LTE) mobile communications. The performance assessment and analysis of the OFDM system under Additive White Gaussian Noise (AWGN) channel has been carried out in this work. The factors in which system performance is assessed include the signal quality, Bit Error Rates (BERs), and Signal to Noise Ratios (SNRs) of the received signals. To improve performance while employing multicarrier modulation, the subcarriers must be kept orthogonal to one another, in the process known as OFDM. The sole focus of this study is the performance analysis of PAPR, BER, and SNR utilizing various modulation methods and schemes.

The algorithm and the results of a blind multiuser detector using a machine learning technique called support vector machine (SVM) on a chaos-based code division multiple access system is presented in this paper. Simulation results showed that the performance achieved by using SVM is comparable to existing minimum mean square error (MMSE) detector under both additive white Gaussian noise (AWGN) and Rayleigh fading conditions. However, unlike the MMSE detector, the SVM detector does not require the knowledge of spreading codes of other users in the system or the estimate of the channel noise variance. The optimization of this algorithm is considered in this paper and its complexity is compared with the MMSE detector. This detector is much more suitable to work in the forward link than MMSE. In addition, original theoretical bit-error rate expressions for the SVM detector under both AWGN and Rayleigh fading are derived to verify the simulation results.