Frequency Selective Rayleigh Channel Research Articles

Adaptive dual-mode OFDM with index modulation

With the integration of the index modulation concept, the popular OFDM has gained an appealing new dimension. However, OFDM with index modulation (OFDM-IM) causes a decrease in data rate for higher order modulations due to its unused subcarriers. Recently, dual-mode OFDM with index modulation (DM-OFDM-IM) has been proposed to prevent this decrease in data rate. The spectral efficiency (SE) of both techniques depends on the selection of different parameters, such as modulation types and number of active subcarriers. However, the quality of the wireless channel has not been taken into account yet to increase the data rate. In this paper, we propose a new adaptive DM-OFDM-IM (A-DM-OFDM-IM) system to enhance the bit error probability (BER) performance considering the channel conditions and obtain a substantial increase in SE. Unlike the previous DM-OFDM-IM and the classical OFDM-IM schemes, our proposed system enables the use of different types of modulations for different subblocks in one OFDM signal. We demonstrate that the SE of the proposed system is comparable with that of its OFDM-IM and DM-OFDM-IM counterpart under frequency selective Rayleigh channels. Moreover, computer simulations corroborate that the derived theoretical results are considerably accurate for the SE of A-DM-OFDM-IM systems.

Performance of Convolution Coded Multicarrier CDMA System in Frequency Selective Rayleigh Channel

Performance of Convolution Coded Multicarrier CDMA System in Frequency Selective Rayleigh Channel

Performance analysis of filter bank multicarrier system with non‐linear high power amplifiers for 5G wireless networks

The filter bank multicarrier (FBMC) with offset quadrature amplitude modulation (OQAM) is one of the alternative modulation schemes to orthogonal frequency division multiplexing for next generation broadband wireless access systems. The non-linearity of high-power amplifiers (HPA) has a crucial effect on the performance of FBMC systems. In this study, the impacts of non-linear distortion effects are considered in a FBMC-OQAM system when the signal is passed through a HPA for medium- and high-power signals which are modelled as amplitude and phase distortions. Specifically, memory-less HPA non-linear distortion models such as solid-state power amplifier (SSPA), soft-envelope limiter (SEL), travelling wave tube amplifier are proposed for FBMC systems. A closed-form expression for bit error rate expression is derived and analysed for SSPA and SEL models for FBMC/OQAM system with non-linear HPA in frequency-selective Rayleigh channel by varying constellation size in OQAM modulation and input back-off. The performance is compared for the models with 64 sub-channels and input back-off for 6 and 8 dB. In lieu of validating the obtained simulation results, theoretical results are being compared.

Spatial Diversity, Low PAPR and Fast Decoding for OFDM using L2-Orthogonal CPM ST-Codes

Orthogonal Frequency Division Multiplexing (OFDM) schemes provide high data rates and good robustness against frequency selective fading for communication systems. Space-Time Block Coding (STBC) is an efficient way to introduce space-time diversity in Multiple-Input Multiple-Output (MIMO) systems. Using non-linear modulations such as Continuous Phase Modulation (CPM) with its constant envelope property may be a way to construct MIMO OFDM systems that alleviates the typical Peak to Average Power Ratio (PAPR) issue of OFDM. However, CPM based systems are usually plagued by decoding complexity issues. In this paper, we introduce space-time-frequency diversity techniques based on L2-orthogonal multi-h CPM Space-Time codes designed for OFDM transmission. We benchmark these codes under frequency selective Rayleigh channels and show how they achieve full spatial diversity at full rate for any number of antennas, good spectral compactness, low PAPR and robustness to frequency fading. Furthermore, L2-orthogonality allows fast decoding with complexity growing only linearly in the number of Tx antennas.

Performance Evaluation of DS-CDMA System based Orthogonal Chaotic Vectors over Rayleigh Fading Channel

codes with low cross-correlation values are needed to suppress the effect of multiple access interference (MAI). The chaotic system can be used to generate very large number of sequences due to its sensitive property to initial conditions but due to the quasi-orthogonal nature of chaotic sequences the MAI between active users is generated which leads to degrade the performance of the system. Another type of chaotic sequences with zero values of cross-correlation called orthogonal chaotic vectors (OCVs) are generated by using logistic map and the basic idea of Gram-Schmidt ortho- normalization process. In this paper, performance of OCVs in DS-CDMA system for transmission data for different active users over different channels (Rayleigh Flat fading channel and Rayleigh Frequency selective channel) is given. Simulation results show that the DS-CDMA based on OCVs gives better BER performance than other systems. The results also show that the system based on OCVs has the same BER performance regardless of the number of users under the effect of flat fading channel. While at BER=10 −3 , number of active users =8 and spread factor 160 there is about 6dB performance difference between the system based on OCVs and system based on Non-OCVs under the effect of time invariant frequency selective fading channel and this difference is decreased to 1dB when spread factor is 320. Keywordsrthogonal chaotic vectors, Non-Orthogonal chaotic vectors, Gram-Schmidt ortho-normalization process, Fading channel.

Modelling and Simulation of Interference Cancellation Receiver for MIMO Multicarrier CDMA based Cognitive Radio

In this paper, modeling and simulation of a receiver with interference cancellation technique for the downlink transmission of multiple input multiple output (MIMO) multicarrier code-division multiple access (MC-CDMA) based cognitive radio is investigated. Synchronous transmission of multiple users’ signals over frequency selective Rayleigh channel is considered. Linear MMSE frequency domain equalization is utilized to overcome channel effect. Orthogonal Variable Spreading Factor (OVSF) codes are used to support users of different data bit rates. An adaptive subcarrier deactivation method is proposed for deactivating a set of subcarriers used for downlink transmission by the cognitive radio base station that overlap with primary user’s transmission in order to avoid causing interference to the primary user. Orthogonality between the spreading codes is lost due to subcarrier deactivation which causes interference among secondary cognitive radio users. In this paper a modified Group-wise Successive Interference Cancellation (m-GSIC) technique is proposed to suppress the interference caused due to subcarrier deactivation. The simulation results show that the proposed interference cancellation technique results in better BER performance over conventional interference cancellation techniques

The Capacity Performance of ASTC-MIMO-OFDM System in a Correlated Rayleigh Frequency-Selective Channel

Algebraic Space-Time Codes (ASTC) for Multiple Input Multiple Output (MIMO) systems are based on quaternion algebras. Thanks to their algebraic construction, the ASTC codes are full-rank, full-rate and have the non-vanishing determinant property. These codes have been proposed for MIMO flat fading channels in order to increase the spectral efficiency and to maximize the coding gain. The purpose of this work is to analyze the performance of the ASTC in a frequency selective Rayleigh channel. To deal with the frequency selectivity, we use the OFDM modulation. The capacity performances of an ASTC-MIMO-OFDM system, under correlated Rayleigh frequency-selective channel, have been evaluated.

Equalization: Analysis of MIMO Systems in Frequency Selective Channel

Due to the increased demand of wireless communication systems because of the features of the system which provides a wide coverage, high throughput and reliable services, the MIMO systems communication has come into existence. Features provided by these systems ensure the improved system coverage and increased data transmission rate by considering multiple numbers of transmitter and receiver antennas. In this paper, we are considering the equalization; a filtering approach that minimizes the error between actual output and desired output by continuous updating its filter coefficients for Rayleigh Frequency selective fading channel. We concluded that MMSE and ZF give the worst performance in Rayleigh frequency selective channel as compare to Rayleigh Flat fading Channel [35] due to a constant BER for large SNR’s. We have also observed that the successive interference methods provide better performance as compare to others, but their complexity is high. ML provides the better performance in comparison to others and BER doesn’t remain constant for a large SNR in this case. Simulation results shows that ML equalizer with BPSK gives better performance as compare to QPSK. Finally we concluded that Sphere decoder provides the best performance.

A novel differential multiuser detection algorithm for multiuser MIMO-OFDM systems

We propose an efficient low bit error rate (BER) and low complexity multiple-input multiple-output (MIMO) multiuser detection (MUD) method for use with multiuser MIMO orthogonal frequency division multiplexing (OFDM) systems. It is a hybrid method combining a multiuser-interference-cancellation-based decision feedback equalizer using error feedback filter (MIMO MIC DFE-EFF) and a differential algorithm. The proposed method, termed ‘MIMO MIC DFE-EFF with a differential algorithm’ for short, has a multiuser feedback structure. We describe the schemes of MIMO MIC DFE-EFF and MIMO MIC DFE-EFF with a differential algorithm, and compare their minimum mean square error (MMSE) performance and computational complexity. Simulation results show that a significant performance gain can be achieved by employing the MIMO MIC DFE-EFF detection algorithm in the context of a multiuser MIMO-OFDM system over frequency selective Rayleigh channel. MIMO MIC DFE-EFF with the differential algorithm improves both computational efficiency and BER performance in a multistage structure relative to conventional DFE-EFF, though there is a small reduction in system performance compared with MIMO MIC DFE-EFF without the differential algorithm.

Channel-based spoofing detection in frequency-selective rayleigh channels

The radio channel response decorrelates rapidly as the transmitter changes location in an environment with rich scatterers and reflectors. Based on this fact, a channel-based authentication scheme was previously proposed to discriminate between transmitters at different locations, and thus to detect spoofing attacks in wireless networks. In this paper, we study its application in frequency-selective Rayleigh channels, considering channel time variations due to environmental changes and terminal mobility, as well as the channel estimation errors due to the interference from other radios. We propose a generalized likelihood ratio test (GLRT) that is optimal but computationally cumbersome, and a simplified version that requires no a priori knowledge of channel parameters and is therefore more practical. We verify the efficacy of the channel-based spoofing detectors via numerical analysis, showing how performance is improved by using multiple antennas, higher transmit power, and wider system bandwidth. We show that, under a wide variety of practical conditions, spoofing can be detected with better than 90% probability while keeping the probability of falsely rejecting valid transmissions below 10%.

Mobile speed estimation for broadband wireless communications over Rician fading channels

In this paper, a new algorithm is proposed to estimate mobile speed for broadband wireless communications, which often encounter large number of fading channel taps causing severe intersymbol interference. Different from existing algorithms, which commonly assume that the fading channel coefficients are available for the speed estimators, the proposed algorithm is based on the received signals which contain unknown transmitted data, unknown frequency selective fading channel coefficients possibly including line-of-sight (LOS) components, and random receiver noise. Theoretical analysis is first carried out from the received signals, and a practical algorithm is proposed based on the analytical results. The algorithm employs a modified normalized auto-covariance of received signal power to estimate the speed of mobiles. The algorithm works well for frequency selective Rayleigh and Rician channels. The algorithm is very resistant to noise, it provides accurate speed estimation even if the signal-to-noise ratio (SNR) is as low as 0 dB. Simulation results indicate that the new algorithm is very reliable and effective to estimate mobile speed corresponding to a maximum Doppler up to 500 Hz. The algorithm has high computational efficiency and low estimation latency, with results being available within one second after communication is established.

Ergodic capacity formula of MIMO-OFDM systems under correlated frequency selective Rayleigh fading channels

An explicit formula for the ergodic capacity of Orthogonal Frequency Division Multiplexing (OFDM)-based Multiple-Input Multiple-Output (MIMO) systems under correlated frequency selective Rayleigh channels is derived, by simplifying the channel response matrix in frequency domain into the so-called Kronecker model composed of three kinds of correlations, i.e. multipath tap gain correlation and spatial fading correlations at both transmitter and receiver. The derived formula is very simple and convenient for one to estimate the effects of all three kinds of correlations on MIMO-OFDM capacity. If taps are independent, there is a very simple expression for the ergodic capacity. In case of tap correlation, the capacity formula could be further given in an integral expression. The validity of the new formula is verified and the effects of correlations, delay spread as well as the number of subcarriers on the ergodic capacity are evaluated via Monte Carlo simulations.

THE EFFECT OF PARTIAL BAND INTERFERENCE ON MULTI-CARRIER DS-CDMA SYSTEMS

ABSTRACTIn this paper, a multi-carrier signaling technique is applied to a direct sequence code division multiple access (DS-CDMA) system. This type of signaling has the desirable properties of lower chip rate, exhibiting a narrow band interference suppression effect, along with robustness to fading, without the need of either an explicit RAKE receiver or an interference suppression filter. Band limited spreading waveforms are used to prevent self-interference. The system performance over a frequency selective Rayleigh channel is evaluated analytically and through computer simulation, in the presence of partial band interference.

Consistent estimation of Rayleigh fading channel second-order statistics in the context of the wideband CDMA mode of the UMTS

We address the problem of estimating the second-order statistics of a frequency-selective Rayleigh channel in the context of the wideband CDMA mode of the UMTS. The data to be transmitted are sent over slots on which the channel is assumed to remain constant. Each slot contains a pilot symbol sequence from which it is possible to estimate the current value of the channel. The covariance matrix of the channel is usually estimated by a denoised version of the empirical covariance matrix of the trained channel estimate. However, in the UMTS, this estimate is not consistent in the sense that if the number of slots used to estimate it tends to infinity, it does not converge to the true covariance matrix of the channel. We propose a new consistent estimate of the covariance matrix and evaluate the performances of two Wiener-like channel estimation schemes based on the proposed estimate. The performances of the new approach are evaluated by means of the bit error rate provided by a RAKE receiver based on the proposed channel estimates. It is shown that our estimate of the covariance matrix allows significant improvement in the performance of the RAKE receiver.

An Improved Linear MMSE Detection Technique for Multi‐Carrier CDMA Systems: Comparison and Combination with Interference Cancellation Schemes

AbstractIn this paper, various detection techniques are studied in the synchronous case of a multiuser MC‐CDMA system operating in frequency selective Rayleigh channel. First of all, an improved linear detection approach named MMSE per user detection technique, which takes into account the despreading process, is presented. Simulation results over a Rayleigh fading channel show that this novel technique offers for non full load systems a significant gain compared to the MMSE equalization per camer method. Then, the performance of various parallel and successive interference cancellation techniques is compared to the performance of the linear MMSE per user scheme. When the power of the interferers is roughly equal to the power of the useful signal, the performance of the linear MMSE per user is really close to the performance of the non linear PIC and SIC schemes.

BER Improvement of CSDD Scheme in Frequency-Selective Rayleigh Channels with CCI Using an Efficient Decision Feedback Technique

Article BER Improvement of CSDD Scheme in Frequency-Selective Rayleigh Channels with CCI Using an Efficient Decision Feedback Technique was published on May 1, 1997 in the journal Frequenz (volume 51, issue 5-6).

Performance of multicarrier DS CDMA systems

In this paper, we apply a multicarrier signaling technique to a direct-sequence CDMA system, where a data sequence multiplied by a spreading sequence modulates multiple carriers, rather than a single carrier. The receiver provides a correlator for each carrier, and the outputs of the correlators are combined with a maximal-ratio combiner. This type of signaling has the desirable properties of exhibiting a narrowband interference suppression effect, along with robustness to fading, without requiring the use of either an explicit RAKE structure or an interference suppression filter. We use bandlimited spreading waveforms to prevent self-interference, and we evaluate system performance over a frequency selective Rayleigh channel in the presence of partial band interference; we also compare system performance with that of a single-carrier RAKE system.

Novel high bit rate Viterbi decoder for monodimensional trellis coded modulation on fading channels

The Letter describes a novel high bit rate Viterbi decoder for 4AM and 8AM trellis coded modulation optimised for a Rayleigh frequency selective channel.