Impact Of Channel Estimation Errors Research Articles

Impact of co-channel interference on the performance of VANETs under [formula omitted] fading

Vehicular Ad hoc Networks (VANETs) are considered to be a novel solution for provisioning of infotainment services and reduction of accidents on the road. However, communication in VANETs is significantly hampered by multipath fading and co-channel interference. In this context, we analytically model VANETs based on the well-known cluster model. The closed form expression for packet error probability is derived in the presence of co-channel interference under α-μ fading. Impact of α and μ on interference is also characterized in detail. We also incorporate the impact of channel estimation errors of main and interfering link to provide more realistic evaluation of packet error probability. We then provide performance evaluation of VANETs under cooperative communication and quantify the improvements in the performance of cluster. We also evaluate the importance of fading parameters α and μ in the presence of interfering signal from nearby cluster. Our findings disclose that an error floor is introduced at high signal-to-noise-ratio (SNR) due to imperfect channel estimation. Additionally, the error probability considerably reduces by applying cooperative scheduling. Extensive simulations are performed in MATLAB to validate our results, which also prove the practicality of our analytical model.

Decode-and-forward with quadrature spatial modulation in the presence of imperfect channel estimation

The performance of quadrature spatial modulation (QSM) multiple-input multiple-output (MIMO) system with cooperative decode and forward (DF) relays is analyzed in this paper. QSM is a new MIMO transmission technique that enhances the overall performance of conventional spatial modulation through exploiting quadrature spatial dimension. A practical scenario is considered where the channel is estimated at the relays and the destination and the impact of channel estimation error is investigated. Two cooperative systems are considered in the study. In the first system, multiple single-antenna DF relays are assumed, whereas, in the second system, single multiple-antennas DF relay is considered. For both systems, an analytical expression for the pair wise error probability (PEP) is obtained. As well, an asymptotic expression for the PEP at high and pragmatic signal to noise ratio is derived. Derived expressions are used to provide an upper bound on the average bit error ratio. The derived analysis is corroborated through Monte Carlo simulations and results demonstrate a close-match for a wide range of SNR values.

Intrinsic Interference Based Physical Layer Encryption for OFDM/OQAM

A physical layer encryption method is proposed for orthogonal frequency division multiplexing with offset quadrature amplitude modulation. The proposed method uses intentionally added pure imaginary symbols as keys, so that their intrinsic interferences can obfuscate true data symbols at the eavesdroppers. The key generation method and four loading patterns are proposed. Also, the impact of channel estimation error, the robustness against ciphertext attacks, and the information leakage at the eavesdropper are analyzed. Finally, the performance of the proposed method is evaluated through numerical simulations.

Secrecy performance analysis of TAS/MRC system in the presence of channel estimation error

This paper presents secure transmission in transmit antenna selection with maximal ratio combining (TAS/MRC) over Rayleigh fading channel for multiple input multiple output (MIMO) taking channel estimation error into account. In this paper, we evaluate the probability of non-zero secrecy capacity (PNZSC) and secrecy outage probability (SOP) for TAS/MRC system considering the impact of channel estimation error (CEE). The numerical results show that the system is valid for any transreceiving and eavesdropping antennas in general.

Efficient Channel Estimation for Reconfigurable MIMO Antennas: Training Techniques and Performance Analysis

Multifunctional and reconfigurable multiple-input multiple-output (MR-MIMO) antennas are capable of dynamically changing the operation frequencies, polarizations, and radiation patterns, and can remarkably enhance system capabilities. However, in coherent communication systems, using MR-MIMO antennas with a large number of operational modes may incur prohibitive complexity due to the need for channel state estimation for each mode. To address this issue, we derive an explicit relation among the radiation patterns for the antenna modes and the resulting channel gains. We propose a joint channel estimation/prediction scheme where only a subset of all the antenna modes is trained for estimation, and then, the channels associated with the modes that are not trained are predicted using the correlations among the different antenna modes. We propose various training mechanisms with reduced overhead and improved estimation performance, and study the impact of channel estimation error and training overhead on the MR-MIMO system performance. We demonstrate that one can achieve significantly improved data rates and lower error probabilities utilizing the proposed approaches. For instance, under practical settings, we observe about 25% throughput increase or about 3-dB signal-to-noise ratio improvement under the same training overhead with respect to non-reconfigurable antenna systems.

SER analysis of multi-way relay networks with M-QAM modulation in the presence of imperfect channel estimation

Multi-way relay networks (MWRNs) allow multiple users to exchange information with each other through a single relay terminal. MWRNs are often incorporated with capacity achieving lattice codes to enable the benefits of high-rate signal constellations to be extracted. In this paper, we analytically characterize the symbol error rate (SER) performance of a functional de- code and forward (FDF) MWRN in the presence of channel estimation errors. Considering M-ary quadrature amplitude modulation (QAM) with square constellations as an important special case of lattice codes, we obtain asymptotic expressions for the average SER for a user in FDF MWRN. The accuracy of the analysis at high signal-to-noise ratio is validated by comparison with the simulation results. The analysis shows that when a user decodes other users with better channel conditions than itself, the decoding user experiences better error performance. The analytical results allow system designers to accurately assess the non-trivial impact of channel estimation errors and the users� channel conditions on the SER performance of a FDF MWRN withM-QAM modulation.

Generalized Selection Combining Scheme for Orthogonal Space—Time Block Codes with M-QAM and M-PAM Modulation Schemes

Multiple-input multiple-output (MIMO) systems implement multiple antennas to enhance diversity gain of wireless communication systems. Earlier work in generalized selection combining (GSC) focused on single-input multiple-output systems without space---time coding. Recently, with the aid of space---time coding, diversity gain became possible using multiple transmit antennas. In this paper, GSC scheme is applied to orthogonal space---time block codes (OSTBC) for 4 × L and 8 × L MIMO systems with various modulation schemes like M-PSK, M-QAM, and M-PAM in a slowly fading Rayleigh channel. The performance of GSC for half rate-full diversity, full rate-full diversity, and 3/4 rate-full diversity OSTBC is discussed and compared. Approximate closed-form expressions for symbol error rate (SER) and ergodic capacity for various OSTBCs are derived. The impact of channel estimation errors on system performance is also examined. Approximate closed-form expressions for performance bounds on SER and ergodic capacity of GSC for MIMO OSTBC are also derived and plotted.

On the Spectral Efficiency of Rate and Subcarrier Bandwidth Adaptive OFDM Systems Over Very Fast Fading Channels

In this paper, rate and subcarrier bandwidth adaptation (RSBA) on the average spectral efficiency of orthogonal frequency-division multiplexing (OFDM) systems using $M$ -ary quadrature amplitude modulation ( $M$ -QAM) is investigated in the presence of frequency-selective and very rapidly time-varying fading channels. The closed-form expressions for rate and capacity with perfect channel state information (CSI) and imperfect CSI are derived. In this paper, imperfect CSI is caused jointly by channel estimation error and unavoidable delay between when CSI is estimated and when the estimation results are used for actual transmission. The capacity with perfect CSI is just a special case of imperfect CSI. Based on the closed-form expressions of the maximum capacity, optimal RSBA algorithms with perfect and imperfect CSI are proposed, respectively. Theoretical and numerical results show that the RSBA scheme can improve the system performance effectively under the perfect-CSI case. It can make a tradeoff between intercarrier interference (ICI) and transmission efficiency by considering the cyclic prefix. The results also show that the RSBA scheme is effective in repelling the impact of outdated CSI, as well as in reducing the impact of channel estimation error, but to a lesser extent.

Energy‐efficiency resource allocation for cognitive heterogeneous networks with imperfect channel state information

In this study, the authors focus on the downlink resource allocation to optimise energy-efficiency (EE) of orthogonal frequency division multiplexing-based cognitive heterogeneous network (HetNet), where network service providers operate multi-radio access technologies. A more practical case is considered, in which imperfect channel state information (CSI) is available for wireless channels between secondary base stations and secondary users (SUs), primary users (PUs). Since imperfect CSI may result in outage in secondary networks and make collision occur in primary networks, a joint subcarrier and power allocation scheme for the cognitive HetNet is proposed to guarantee quality of service requirements for both SUs and PUs in probabilistic manners. Then the probabilistic EE optimisation scheme is approximated into a deterministic convex form, and the optimal solutions for the scheme are derived by double-loop iteration method. Afterwards, the authors develop a low-complexity algorithm in the presence of imperfect CSI with a small reduction of system performance. Simulation results are provided to show the impact of channel estimation error on the EE optimisation problem and to highlight the performance improvement from considering channel estimation error in the joint subcarrier and power allocation scheme for the cognitive HetNet system.

Physical layer security of MIMO STBC over Rayleigh fading channels in the presence of channel estimation error

This paper presents secure transmission in orthogonal space time block codes (OSTBC) in the presence of channel estimation error over multiple input multiple output (MIMO) wiretap channels. In this paper, we evaluate probability of non-zero secrecy capacity (PNZSC) and secrecy outage probability (SOP) for OSTBC system over Rayleigh fading channels considering the impact of channel estimation error (CEE). The numerical result demonstrates that the system is generic and valid for any transceiving and eavesdropper antennas.

Impact of channel estimation error on zero‐forcing‐based multiple‐input–multiple‐output two‐way relaying

In this study, the authors investigate the impact of channel estimation error (CEE) on the performance of a multiple-input–multiple-output (MIMO) two-way relay system under Rayleigh fading. Herein, transmit/receive zero-forcing (ZF) is employed at the two source nodes, whereas analogue network coding is used at the relay node. Fundamentally, for making use of transmit/receive ZF, all nodes must be aware of channel state information (CSI). As perfect CSI may not always be available in practical scenarios, the CEE does exist in the considered system. By taking the imperfect CSI into account, they enucleate that the residual self-interference and additional noise pertaining to the CEE have effect of reducing end-to-end signal-to-noise ratios (SNRs) at the two source nodes. Based on the statistical characterisations of these post-processing SNRs, they carry out the overall system outage probability analysis. Further, they investigate the asymptotic outage behaviour to deduce the achievable diversity order. They substantiate that the diversity order may reduce to zero under severe impact of CEE. In addition, they derive a closed-form expression of ergodic sum-rate of the considered system with CEE. Numerical and simulation investigations are conducted to support all the theoretical findings using various values of CEE and antenna configurations.

Impact of loop-back interference and channel estimation errors on full-duplex relay networks

This paper investigates the rate performance of full-duplex (FD) relay systems under the effect of channel estimation error and residual loop-back interference. The study considers both one-way and two-way amplify and forward (AF) relaying schemes. Power allocation techniques, applied at the sources and the relay, are proposed and shown to be effective that leads to near optimal solution. Comparison between the half-duplex (HD) and FD systems using optimum power allocation are made. Also, the impact of channel estimation error and loop-back interference on the rate of FD transmission are compared. It is shown that the destructive effect of loop-back interference dominates the effect of channel estimation error. Finally, assuming a bidirectional network, the performance of two-way analog network coding (ANC) scheme is compared to the plan of using two one-way AF relaying connections. The results show that it is better to use FD ANC for low transmission power and HD one for high power than using two one-way relaying schemes.

Achievable rate and error performance of an amplify and forward multi‐way relay network in the presence of imperfect channel estimation

In this paper, we investigate the impact of channel estimation error on the achievable common rate and error performance of amplify and forward (AF) multi-way relay networks (MWRNs). Assuming lattice codes with large dimensions, we provide the analytical expressions for the end-to-end SNR at the users and obtain upper bounds on the achievable common rate for an AF MWRN. Moreover, considering binary phase shift keying (BPSK) modulation as the simplest case of lattice codes, we obtain the average bit error rate (BER) for a user in an AF MWRN. The analysis shows that the average BER is a linearly increasing function and the achievable common rate is a linearly decreasing function of the channel estimation error. On the other hand, the average BER decreases and the achievable common rate increases with increasing correlation between the true and the estimated channel. Also, we observe that the AF protocol is robust against increasing number of users in terms of error performance. We show that when the decoding user has better channel conditions compared to other users, AF relaying gives a better error performance and common rate. Finally, simulation results are provided to verify the validity of our analysis.

Channel capacity of TAS/MRC system with adaptive transmission and channel estimation errors

This correspondence presents the impact of channel estimation error (CEE) on the channel capacity analysis of multiple-input multiple-output (MIMO) system employing transmit antenna selection and maximal ratio combining (TAS/MRC) under adaptive transmission (ADT) techniques over frequency-flat Rayleigh fading channels. In this paper, we evaluated exact closed-form expressions of channel capacity for TAS/MRC system with CEE under different variable power and variable rate adaptation techniques: (i) optimal power and rate adaptation (opra) (ii) constant power with rate adaptation (cpra) (iii) channel inversion with fixed rate (cifr). The channel state information (CSI) consisting of the signal-to-noise ratio (SNR) level is estimated by the decoder and fed back to the transmitter. Further, the ADT schemes can be operated frame by frame, hence permitting for distinct compromises among the attainable capacity and the corresponding implementation complexity. Numerical outcomes illustrate the impact of CEE on the link capacity and outline the performance characteristics among the distinctive adaptation techniques.

Performance Analysis of Relay Selection in Two-Way Relay Networks With Channel Estimation Errors

The impact of channel estimation errors is investigated in two-way relay networks (TWRNs) with two different channel state information (CSI) estimation schemes, namely separate and cascaded. In the former scheme, the relay node is chosen in accordance with the CSI of the individual channels between the source nodes and the relay node. By contrast, in the latter scheme, relay node selection is performed in accordance with the CSI of the cascaded channel between the two source nodes. For both estimation schemes, the effect of the CSI estimation error on the outage probability is examined by means of the Cramer–Rao lower bound. Moreover, in contrast to previous studies, the source nodes in the TWRN are assumed to have different estimation errors. The numerical results confirm the validity of the derived expressions and show that the presence of different estimation errors at the two source nodes has a significant effect on the performance of the TWRN.

Symbol Error Rate Analysis of Joint Diversity System With Channel Estimation Error

In this paper, we investigate the impact of channel estimation error on symbol error rate (SER) for joint diversity (i.e., combining space–time block coding and user scheduling) in multiple-input–multiple-output systems with a channel estimation error. Under a Gaussian distributed channel estimation error, the exact expressions of the joint diversity for SER with both M-ary quadrature amplitude modulation (QAM) and phase-shift keying (PSK) modulation are derived. Using probability density function approximation, we quantify the diversity order and signal-to-noise ratio (SNR) gain of SER for joint diversity in the presence of a channel estimation error. From the analysis results, we show that the diversity order is enhanced as the number of user terminals increases, regardless of the modulation type. This is because user scheduling provides multiuser diversity. Moreover, the SNR gain decreases as the number of user terminals increases. This is because the peak effective SNR in joint diversity decreases as the number of user terminals increases.

Joint Relay and Jammer Selection and Power Control for physical Layer Security in Two-Way Relay Networks with Imperfect CSI

Physical layer security is an emerging security paradigm that can achieve secure information transmission from the source to the intended destination with the existence of malicious eavesdroppers. In this paper, joint relay/jammer selection and power control with friendly jammers for physical layer security in two-way relay networks are studied. First, several relay/jammer selection schemes are proposed to increase the secrecy capacity for source nodes and degrade the eavesdropper links simultaneously. The presented schemes select one conventional relay node and at most two friendly jammers among a number of intermediate nodes. The impact of channel estimation error on the wiretap channel is also considered. After the selection of optimal relay node and friendly jammers, a game-theoretic power control approach is introduced to deal with the interaction between the source nodes and the friendly jammers. The proposed power control approach is proven to be able to converge to the Stackelberg equilibrium, and both source nodes and friendly jammers can obtain their optimal benefits. The simulation results demonstrate the effectiveness of the relay/jammer selection schemes to enhance the secrecy capacity of the system, and validate the properties of optimization and convergence for the game-theoretic power control approach.

Impact of Channel Estimation Error on the Performance of Relay Selection in Cognitive Radio Networks

Channel estimation error, which adversely affects the performance of any wireless communication system, is inevitably available in receivers. However, its impact on the bit error rate (BER) performance of relay selection in underlay cognitive networks has not been investigated analytically. This paper fills in this literature gap by firstly proposing an exact single-integral form BER formula for general network topology. Based on this proposal, we further analyze the diversity gain to have insights into asymptotic performance and system design. Secondly, we derive a closed-form approximate BER formula, which has been shown highly accurate, for a typical network topology where relays are closely positioned for reduced simulation time. Various results demonstrate that the channel estimation error significantly degrades the performance of the relay selection in underlay cognitive networks and completely destroys its diversity gain. In addition, increasing the number of involved relays drastically remedies its impact.

Performance Analysis of Rayleigh Fading Channels with Hybrid Correlation Effects with 2-Branch Maximal Ratio Combining

This paper deals with the impact of channel estimation errors on the capacity of correlated fading MIMO channels. In this paper, closed-form expressions for cumulative density function and probability density function for Rayleigh fading channels with combined effects of impairments due to combining errors and branch correlation errors for 2-branch case are derived. We also derive closed-form expressions for capacities per unit bandwidth for fading channels with effects of hybrid correlation for two branch maximal ratio combining diversity reception case for different adaptation policies. We show that hybrid correlation leads to increased performance degradation when combining correlation is low and branch correlation is high and vice versa. Even though hybrid correlation exists between branches, capacity gains are significantly more for adaptation policies especially for OPRA policy as compared to other policies for both cases.

A full-cooperative diversity beamformingscheme in two-way amplify-and-forward relay systems

Consider a simple two-way relaying channel in which two single-antenna sources exchange information via a multiple-antenna relay. For such a scenario, all the existing approaches that can achieve full cooperative diversity order are based on antenna/relay selection, for which the difficulty in designing the beamforming lies in the fact that a single beamformer needs to serve two destinations. In this paper, a new full-cooperative diversity beamforming scheme that ensures that the relay signals are coherently combined at both destinations is proposed, and analytical results are provided to demonstrate the performance gains. Moreover, the impact of channel estimation error is also evaluated. Finally, numerical results are provided to verify the accuracy of the provided analytical results, and also to show that this proposed scheme can outperform existing schemes based on antenna selection.