Systems In Rayleigh Fading Channels Research Articles

Power Control of Reed–Solomon-Coded OFDM Systems in Rayleigh Fading Channels

Power control in an RS-coded orthogonal frequency division multiplex (OFDM) system with error-and-erasure correction decoding in Rayleigh fading channels was investigated. The power of each symbol within a codeword was controlled to reduce the codeword error rate (WER). Several RS-coded OFDM systems with power control are proposed. The WERs of the proposed systems as a function of the signal-to-noise ratio per bit were derived. We found that channel inversion at the transmitter in combination with the erasure generation by ordering fading amplitudes at the receiver provided the lowest WER among the considered systems. Furthermore, the erasure generation by ordering fading amplitudes was found to be better than the erasure generation by comparing fading amplitudes with a threshold.

A Rotated-Constellation Based Method for BER Analysis in Uplink NOMA Systems

Non-orthogonal multiple access (NOMA) is one of candidate technologies in the next generation radio access networks, in which the joint maximum-likelihood (JML) detector has the optimal estimation performance. In this paper, we propose a rotated-constellation based method to regularize the decision boundaries of received constellation. Through regular decision boundaries, we further derive the approximate closed-form BER expressions of uplink NOMA systems in Rayleigh fading channels. Numerical results verify the effectiveness of rotated-constellation based method and conform to our derivation. It is also shown through simulations that the proposed analysis method outperforms conventional method in terms of accuracy.

Hybrid Cramer-Rao Bound on Carrier and Sampling Frequency Offset Estimation for OFDM Systems in Rayleigh Fading Channels

For the carrier frequency offset (CFO) and sampling (clock) frequency offset (SFO) estimation, the hybrid Cramer-Rao bound (HCRB) is developed when the CFO, SFO, information-bearing symbols are deterministic and channel coefficients are random. Both noise and channel coefficients are complex Gaussian. The HCRB is a lower bound on the mean squared estimation error for any unbiased estimator of a parameter. For the HCRB to be applicable, it is necessary for deterministic parameters to be identifiable (uniquely determined). Some necessary identifiability conditions of some deterministic parameters are found and presented. The HCRB is dependent on the initial time instant. The HCRB is used to assess the performances of some existing methods via simulation. Our results demonstrate that even the best performance is still around 10 dB higher than the HCRB. Further effort is needed to develop more accurate methods.

Copula-Based Modeling of RIS-Assisted Communications: Outage Probability Analysis

Statistical characterization of the signal-to-noise ratio (SNR) of reconfigurable intelligent surface (RIS)-assisted communications in the presence of phase noise is an important open issue. In this letter, we exploit the concept of copula modeling to capture the non-standard dependence features that appear due to the presence of discrete phase noise. In particular, we consider the outage probability of RIS systems in Rayleigh fading channels and provide joint distributions to characterize the dependencies due to the use of finite resolution phase shifters at the RIS. Numerical assessments confirm the validity of closed-form expressions of the outage probability and motivate the use of bivariate copula for further RIS studies.

Beamforming Using Exact Evaluation of Leakage and Ergodic Capacity of MU-MIMO System.

Closed-form evaluation of key performance indicators (KPIs) of telecommunication networks help perform mathematical analysis under several network configurations. This paper deals with a recent mathematical approach of indefinite quadratic forms to propose simple albeit exact closed-form expressions of the expectation of two significant logarithmic functions. These functions formulate KPIs which include the ergodic capacity and leakage rate of multi-user multiple-input multiple-output (MU-MIMO) systems in Rayleigh fading channels. Our closed-form expressions are generic in nature and they characterize several network configurations under statistical channel state information availability. As a demonstrative example of the proposed characterization, the derived expressions are used in the statistical transmit beamformer design in a broadcast MU-MIMO system to portray promising diversity gains using standalone or joint maximization techniques of the ergodic capacity and leakage rate. The results presented are validated by Monte Carlo simulations.

Hermite Expansion Model and LMMSE Analysis for Low-Resolution Quantized MIMO Detection

In this paper, the Hermite polynomials are employed to study linear approximation models of narrowband multiantenna signal reception (i.e., MIMO) with low-resolution quantizations. This study results in a novel linear approximation using the second-order Hermite expansion (SOHE). The SOHE model is not based on those assumptions often used in existing linear approximations. Instead, the quantization distortion is characterized by the second-order Hermite kernel, and the signal term is characterized by the first-order Hermite kernel. It is shown that the SOHE model can explain almost all phenomena and characteristics observed so far in the low-resolution MIMO signal reception. When the SOHE model is employed to analyze the linear minimum-mean-square-error (LMMSE) channel equalizer, it is revealed that the current LMMSE algorithm can be enhanced by incorporating a symbol-level normalization mechanism. The performance of the enhanced LMMSE algorithm is demonstrated through computer simulations for narrowband MIMO systems in Rayleigh fading channels.

Performance Analysis for SWIPT Cooperative DF Communication Systems with Hybrid Receiver and Non-Linear Energy Harvesting Model.

In this paper, we study the outage and throughput performance for the simultaneous wireless information and power transfer (SWIPT) cooperative decode-and-forward (DF) communication systems. The hybrid receiver that uses both time switching (TS) and power splitting (PS) methods for energy harvesting (EH) and information decoding (ID), and the piece-wise linear EH model that captures the non-linear input-output characteristic of the EH circuit, are considered. We present exact analytical expressions of the outage probability (OP) and throughput, which are expressed as single definite integral on finite interval and can be easily evaluated, for the systems in Rayleigh fading channel. For further simplicity of calculation, we derive novel and closed-form approximate expressions of the OP and throughput. The impact of different system parameters on the system performance is investigated. Numerical results show the high accuracy of the proposed closed-form approximate expressions especially in the region of higher signal-to-noise ratio (SNR). It is also shown that the system performance is greatly overestimated when the ideal linear EH model is used instead of the practical non-linear EH model. A different result to the non-hybrid receiver with both linear EH model and non-linear EH model that there exists an optimal location to minimize the OP for the hybrid receiving relay node with non-linear EH model is also demonstrated.

SαS noise suppression for OFDM wireless communication in rayleight channel

Orthogonal frequency division multiplexing (OFDM) is a form of multi-carrier transmission technique widely used in the modern wireless network to achieve high-speed data transmission with good spectral efficiency. However, in impulsive noise environement BER performances of these systems, originally designed for a Gaussian noise model, are much degraded. In this paper, a new symmetric-alpha-stable (SαS) noise suppression technique based conjointly on adaptive modulation, convolutional coding (AMC) and Recursive Least Square (RLS) filtering is presented. The proposed scheme is applied on OFDM system in Rayleigh fading channel. The transmissions are analyzed under different combinations of digital modulation schemes (BPSK, QPSK, 16-QAM, 64-QAM) and convolutional code rates (1/2, 2/3, 3/4). Simulation results show that our proposed hybrid technique provides effective impulsive noise cancelation in OFDM system and exhibits better BER performance.

Performance analysis of multiple-relay cognitive communication system in Rayleigh fading channel

The spectrum scarcity in communication systems has attracted many researches in the area of cognitive communication which is known as a precious solution to overcome this problem. Overlay (OL) and underlay (UL) strategies are two main techniques in the cognitive systems (CSs). On the other side, cooperative communication improves the reliability and capacity of data communications when using the multiple-relay scheme. In this paper, assuming the multiple-relay cooperative cognitive communication system, the quality of service (QoS) parameters as effective capacity (EC) and outage probability (OP) are analyzed in details. A closed-form mathematical expression is obtained for OP and EC in Rayleigh fading channel considering different constraints on the CS such as false detection of busy/idle state of primary user (PU), or interference threshold of secondary user on PU in OL and UL strategies, respectively. Moreover, the comparison of OL and UL strategies in terms of the QoS parameters is done. As will be shown in this paper, simulation and numerical results verify each other and follow the mathematical analysis of the QoS parameters.

Channel Estimation Based on IOTA Filter in OFDM/OQPSK and OFDM/OQAM Systems

In this paper, we present a study of bit error rate (BER) for orthogonal frequency division multiplexing/offset quadrature phase shift keying (OFDM/OQPSK) and OFDM/offset quadrature amplitude modulation (OQAM) systems with an isotropic orthogonal transfer algorithm (IOTA) filter. The novel noise suppression method based on an IOTA filter is proposed to reduce the error of channel estimation caused by additive white Gaussian noise (AWGN). The OFDM/OQPSK and OFDM/OQAM systems do not insert the guard interval (GI) and pilots in the signal frames, thus they possess transmission efficiency. An analysis was carried out for convolutional coded OFDM/OQPSK and OFDM/OQAM systems in Rayleigh fading channels with generator polynomials and constraint lengths. Compared with conventional OFDM/QPSK and OFDM/QAM systems with the insertion of comb-type pilots, the proposed IOTA filter-based channel estimation method can provide significant energy per bit to time-varying noise power spectral density ratio gains over time and frequency-selective propagation Rayleigh fading channels in OFDM/OQPSK and OFDM/OQAM systems.

The Method of Anti-Multipath for Recombination CDMA Users Based on Chip Waveform Compensation

In cognition radio system, the technology using CDMA users with controllable spectrum nulls as cognitive user possess the advantage of both CDMA and cognition radio. The existing method to obtain controllable spectrum nulls for cognition CDMA is to use recombination sequence. The autocorrelation performance is turned out to lower through derivation and analysis, which result in the lower of anti-multipath performance of CDMA users with recombination sequence through giving the variance of decision variables at the Rake receiver for asynchronous DSCDMA system in Rayleigh fading channel. Moreover, the performance of antimultipath for CDMA users depended on both chip waveform and spread-spectrum sequence. Thus, the performance of anti-multipath for CDMA users can be compensated by introducing chip waveform with satisfactory autocorrelation performance. The amendatory Hermite function (AHF) was turned out to possess 1properties of fine autocorrelation and cross-correlation, energy concentration in time and frequency domain, which turned out to be appropriate to compensate the antimultipath performance of CDMA users with recombination sequence. What is more, the spectrum nulls of AHF change when the order changes. It means that only the order of AHF used by CDMA users need to be changed when the frequency band of interference or authorized users change. It was turned out that the bit error rate (BER) performance of recombination CDMA users with AHF outweighed that with classic waveforms whenever there were multiple-access interference (MAI), multiple-path interference(MPI), narrow band interference(NBI). The proposed method possesses better performance of anti-MAI, anti-MPI, anti-NBI.

Weighted Selection Combinings for Differential Decode-and-Forward Cooperative Networks

Two weighted selection combining (WSC) schemes are proposed for a differential decode-and-forward relaying system in Rayleigh fading channels. Compared to the conventional selection combining scheme, the decision variable of the relay link is multiplied by a scale factor to combat the error propagation phenomenon. Average bit-error rate (ABER) expressions of the two proposed WSC schemes are derived in closed-form and verified by simulation results. For the second WSC scheme, asymptotic ABER expression and diversity order are derived to gain more insight into this scheme. Moreover, it is demonstrated that both WSC schemes can overcome the extra noise amplification induced by the link adaptive relaying scheme. The first WSC scheme is slightly inferior to the second one, which has a higher complexity. Both proposed WSC schemes outperform the conventional selection combining scheme.

Degrading the Effect of Channel Impairment on STBC-OFDM System in Rayleigh Fading Channel

This paper indicates the space time block code provides transmit diversity in wireless fading channel during the STBC-OFDM system. OFDM is enforced in broadband wireless access systems as the way to beat wireless channel impairments and to enhance and breadth potency. This research is to analyze the performance of non STBC-OFDM system and STBC-OFDM system. The performance has been evaluated for construction modulation (QAM) technique for orthogonal frequency division multiplexing (OFDM) systems using multiple transmit diversity antenna system in the channel. Conjointly the equation of SNR and BER has been derived for 16-QAM for multiple transmit and receive antenna for STBC-OFDM system by considering the have an effect on of Inter-symbol interference (ISI), phase noise and temporal arrangement noise in Raleigh fading channel.

Buffer-Aided Non-Orthogonal Multiple Access Relaying Systems in Rayleigh Fading Channels

Non-orthogonal multiple access (NOMA) is a promising technology in future communication systems. In this paper, we propose a buffer-aided NOMA relaying system, which consists of a source, a relay, and two destinations. In the relaying system, the relay helps the source transmit packets to two destinations simultaneously using NOMA scheme. We theoretically derive outage probabilities of source-to-relay link and relay-to-destinations links considering two scenarios that the relay does and does not know the channel state information (CSI) from itself to two destinations. When the relay knows CSI, the obtained outage probability of relay-to-destinations links involves integration operation. Thus, we derive an upper bound and two lower bounds. Simulation results demonstrate that two lower bounds approach exact outage probability at low and high signal-to-noise ratios, respectively. We also propose a relay decision scheme for the buffer-aided NOMA relaying system. Based on the obtained system outage probability, we theoretically derive the diversity order. It is found that no matter whether the relay knows CSI or not, the diversity order of 2 can be achieved when the buffer size is larger than or equal to 3.

Analysys of Blind adaptive multiuser detection receivers

In this paper, blind adaptive multiuser detection with Mean Output Energy (MOE) are designed in receivers for synchronous MC-DS-CDMA systems in Rayleigh fading channels. Pre and post detection in multiuser detectors are implemented in the system to detect their effects in the outputs. On the basic of the delayed received signals, we proposed Affine Projection Algorithm-link multiuser detector (APA) and its performance is evaluated with the existing multiuser blind detectors (Normalized blind LMS and Kalman Filter). Compared to existing multiuser detectors APA-link detector outperformed the BER performance and provided a tradeoff between performance and computation cost. The analysis if further extended by implementing, decorrelating multiuser detector based receivers in SC-DS-CDMA and MC-DS-CDMA to eliminate the MAI caused by other users.

Throughput of Coded DS CDMA/Unslotted ALOHA Networks with Variable Length Data Traffic and Two User Classes in Rayleigh Fading FSMC Model

Previous papers analyzed the throughput performance of the CDMA ALOHA system in Rayleigh fading channel, but they assume that the channel coefficient of Rayleigh fading was the same in the whole packet, which is not realistic. We recently proposed the finite-state Markov channel (FSMC) model to the throughput analysis of DS uncoded CDMA/unslotted ALOHA networks for fixed length data traffic in the mobile environment. We now propose the FSMC model to the throughput analysis of coded DS CDMA/unslotted ALOHA networks with variable length data traffic and one or two user classes in the mobile environment. The proposed DS CDMA/unslotted ALOHA wireless networks for two user classes with access control can maintain maximum throughput for the high priority user class under high message arrival per packet duration.

BIT ERROR RATE ANALYSIS OF MISO SYSTEM IN RAYLEIGH FADING CHANNEL

In wireless communication the performance of the system is an important characteristic. In this paper we will compare the analyzed performance of the multi antenna system in Rayleigh fading channel by using various digital modulation techniques (BPSK, QPSK-4, 8, 16). Basic idea in this scheme is by studying the channel characteristic and transmit the signal from the transmitter to analyze the performance and by transmit the same signal by changing the channel characteristic (Bit rate, SNR(signal-to-noise ratio), Doppler effect) to analyzed the performance. The resultant will be presented by comparing all the analyzed performances.

Mathematical model of bessel beamformer with automatic gain control for smart antenna array system in Rayleigh fading channel

This paper analyzes the mathematical model of a Bessel beamformer with automatic gain control (AGC) in a multipath scenario using a digital modulation technique and makes comparison with the one without AGC. The Bessel beamformer with AGC is designated here as the modified Bessel beamformer. The desired useful and interfering signals operate with the same carrier frequency and Doppler shifts but in different directions. Based on simulation results, this modified Bessel beamformer is shown to provide an optimum solution and to accommodate more users in real-time base stations of mobile communication system when implemented on smart antenna array systems. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Maximum diversity achieving decoders in MIMO decode-and-forward relay systems with partial CSI

We consider multiple-input multiple-output decode-and-forward relay systems in Rayleigh fading channels under the partial channel state information (CSI) that the channel statistics of the source-relay (SR) link and the instantaneous CSI of the source-destination and relay-destination links are known at the destination. In this paper, we propose a new near maximum likelihood (near-ML) decoder with two-level pairwise error probability (near-ML-2PEP) which uses the average PEP instead of the exact PEP. Then, we theoretically prove that the near-ML and near-ML-2PEP decoders achieve the maximum diversity, which is confirmed by Monte Carlo simulations. Moreover, we show that the near-ML-2PEP decoder can also achieve the maximum diversity by substituting the average PEP with the values that represent the error performance of the SR link.

Performance Analysis of Multi-Hop Amplify-and-Forward Relaying Systems in Rayleigh Fading Channels with a Poisson Interference Field

In this paper, we analyze the performance of multi-hop transmission systems that employ amplify-and-forward relays over a Rayleigh fading environment in the presence of a Poisson field of interferers. The interference model considers the effect of spatial distribution of co-channel interferers in the vicinity of the relays and the destination node. Using a tight upper bound on the end-to-end signal-to-interference ratio, a closed-form expression for the system outage probability is derived. Moreover, a lower bound for the average symbol error rate of general modulations, the exact average bit error rate (BER) of binary modulations and the average channel capacity are presented in the form of single-fold integrals that can be reliably evaluated numerically, whereas closed-form results are obtained for a special case of the dual-hop relaying system. Finally, asymptotic expressions for the system outage probability and the end-to-end BER are derived which provide useful insights regarding the factors affecting the performance of the considered system. The novel expressions can be used to show the impact of interference model parameters such as the transmit power, path loss exponent, and spatial density of interferers on the performance of multi-hop wireless systems. Simulation results are further provided to demonstrate the accuracy of the analytical expressions.