Effect Of Imperfect Channel Estimation Research Articles

Physical Layer Security in Downlink of Cell-Free Massive MIMO With Imperfect CSI

This paper investigates the threat of passive eavesdropping on downlink cell-free massive MIMO (CF-MaMIMO) systems, examining in a particular system under the effects of imperfect channel estimation. Physical layer security (PLS) techniques and power allocation algorithms are typically adopted to deteriorate the quality of eavesdropped signals. In the downlink stream, artificial noise (AN) is broadcasted simultaneously with the users’ data streams, with the aim of jamming the eavesdropper’s signal without sacrificing the quality of service (QoS). However, imperfect channel estimation results in AN leakage to legitimate users. Our work considers this condition, and the power allocation algorithms we present determine the minimum power that is needed to maintain the user’s Qos even in the presence of leaked AN. We first propose the cooperative PLS algorithm (COP), which facilitates AN broadcasting via access point (AP) cooperation. Unfortunately, this cooperation wastes some of the power used to send the AN and, in most cases, increases the computational complexity. We then present the independent PLS algorithm (IND), where the goal is to regain this power by allowing each AP to broadcast AN independently. However, to meet the feasibility criterion, this occurs at the cost of increasing the number of used antennas. This technique reduces the power allocation complexity but increases the computational complexities of the precoder design and the channel estimation process. Our results reveal that the proposed algorithms enhance the security performance of CF-MaMIMO. We evaluate such performance from numerous angles including the number of users, number of APs, QoS, beamforming, AN leakage, and channel estimation techniques.

CSIN-assisted AF dual-hop relaying communication systems over imperfect Nagakami-[formula omitted] fading channels: Exact error performance

Relaying-based communication techniques are promising for current and future wireless systems. Amplify-and-forward (AF) relaying is more attractive due to the low cost and simplicity in its relay implementation. As compared to other AF schemes, the channel-state-information (CSI)-and-noise (CSIN)-assisted one is optimal and practically recommended. However, up to this moment, the exact symbol error rate (SER) performance of CSIN-assisted AF dual-hop relaying systems has been analytically derived only for Rayleigh fading environments, while for other more generic fading models, including Nakagami-m, it has been computed either approximately or via long-running time computer simulations. Thus, in this paper, we consider a CSIN-assisted AF dual-hop relaying system with independent and non-identical Nakagami-m fading channels and derive a new expression for its exact SER performance under the effect of imperfect channel estimation. The derived expression includes infinite series that can truncate quickly using a few terms, requires short computational time as compare to simulation, shows perfect matching with the simulation results, and offers remarkable accuracy enhancement over its approximate peer derived in literature. In addition, it helps in demonstrating some useful insights into the system’s realistic error performance considering different system and fading severity conditions. For example, results show that the system’s exact SER performance is dominated by the worse fading hop, does not change when the system’s two fading hops exchange their fading conditions, and improves faster with the per symbol average SNR when the fading severity conditions are better.

Linear MMSE Channel Estimation for Underlay Cognitive Radio Networks

Channel estimation techniques applied to cognitive radio networks (CRN) are analyzed for simultaneously primary and secondary channel estimations operating in underlay cognitive radio networks (uCRN). A complete base-band transmission including pilot sequence transmission, channel matrix estimation and optimal precoder matrix generation based on imperfect channel estimation are described. Also, the effect of imperfect channel estimation has been studied to provide means of developing techniques to overcome problems while enhancing the MIMO communication performance.

Effect of Imperfect Artificial Noise on the Performance of Physical Layer Security for MU-Massive MIMO System

Physical Layer Security (PLS) in Multiple Input Multiple Output (MIMO) systems is crucial to achieving reliable communication. Artificial Noise (AN) is a commonly employed technique to provide PLS-based secure communication. This requires perfect knowledge of the channel between transmitter (Alice) and legitimate user (Bob). However, this channel information may be imperfect due to estimation errors. Thus, the claimed performance of AN-based PLS is questionable and requires thorough investigation. In this work, the effect of imperfect channel estimation on the performance of PLS for multiuser Massive (MU-Massive) MIMO system is investigated. The channel estimation error is modeled as a complex Gaussian variable. The performance measure in terms of Bit-error-rate (BER) is evaluated for different levels of channel estimation error. This investigation provides a good illustration of how the performance of AN-based PLS is affected by the channel estimation error in the MU-Massive MIMO system. This work shows the trend in BER increase with the increase in AN mismatch.

Performance Analysis of Energy Beamforming WPCN Links With Channel Estimation Errors

In this paper, we analyze the performance of a wireless-powered communication network that consists of a multiple-antenna hybrid access point (AP) and a single-antenna user. The AP transmits radio frequency (RF) power in the downlink (DL) using maximal ratio transmission (MRT) type energy beamforming. The user harvests it and transmits data to the AP in the uplink (UL), which is received with maximal ratio combining (MRC). Previous analyses have assumed the availability of perfect channel estimation. In contrast, we eliminate this unrealistic assumption and consider the effect of imperfect channel estimates. We first derive the distributions of the received AP signal-to-noise ratio (SNR). We then analyze the average throughput performance of delay-limited and delay-tolerant modes by evaluating the outage probability (OP) and ergodic capacity (EC). We also derive the exact bit error rates (BERs) and symbol error rates (SERs) of several digital modulations. Asymptotic performance expressions in the high SNR regime and the large antenna regime are also developed. Finally, analytical and asymptotic results are validated by Monte-Carlo simulations. The impacts of the transmit power, the energy harvesting (EH) time, the number of antennas and the efficiency of EH are investigated.

Effect of Imperfect Channel Estimation on the Performance of Cognitive Satellite Terrestrial Networks

The incorporation of cognitive radio (CR) techniques into satellite communication systems, has been considered as one of the most promising approaches to address the spectrum scarcity, which constitutes an advanced infrastructure known as cognitive satellite terrestrial network (CSTN). Due to the estimation error or feedback delay, perfect channel state information (CSI) of satellite and/or terrestrial links in CSTNs are normally unavailable. This paper investigates the effect of imperfect CSI on the performance of CSTN, where a secondary satellite network coexists with a primary terrestrial network by employing the underlay cognitive mechanism according to which the satellite user is allowed to access the licensed spectrum without deteriorating the operation of terrestrial user. Specifically, we derive the analytical expressions for the outage probability and ergodic capacity of the cognitive network, which provides an efficient approach to jointly evaluate the impacts of imperfect channel estimations for different links on the performance of considered network. Moreover, simple asymptotic outage probability formula in the high signal-to-noise ratio regime is presented to reveal the diversity order and coding gain of the CSTNs. Finally, numerical results are provided to confirm the validity of the theoretical analysis, as well as quantitatively analyze the effects of various system parameters on the performance of the CSTNs with CSI imperfection.

Performance Analysis of Media-Based Modulation With Imperfect Channel State Information

Media-based modulation (MBM) is an attractive modulation scheme where information bits are conveyed by digitally controlling the on/off status of radio frequency mirrors (which are parasitic elements) placed near the transmit antenna. The MBM alphabet (which is the set of channel fade coefficients corresponding to all possible mirror on/off status vectors) is estimated at the receiver through pilot transmissions. In this paper, we analyze the effect of imperfect channel estimation on the bit error performance of MBM. We present the analysis for generalized spatial modulation MBM (GSM-MBM). We analyze the performance for two types of detectors, namely the commonly studied mismatched detector, and the true maximum-likelihood (ML) detector that maximizes the likelihood by taking the statistics of the channel estimate into account. First, we derive an exact average pairwise error probability (PEP) expression for the mismatched detector using characteristic function approach, and obtain a union bound based upper bound on the average bit error probability (BEP). Next, given the estimate of the MBM alphabet, we derive the true ML detector for GSM-MBM, and derive an exact average PEP expression (by averaging the conditional PEP over the statistics of the channel estimate) and an upper bound on the average BEP. The exactness of the average PEP and the tightness of the average BEP upper bounds of the detectors are validated through simulations.

Three-phase two-way relaying with imperfect channel estimation and asymmetric traffic requirements: performance analysis and optimization

We study the effect of imperfect channel estimation (ICE) and asymmetric traffic requirements (ATRs) on the performance of bidirectional relaying with a direct link by employing three-phase analog network coding under Nakagami-m fading. Under such a realistic scenario, a tight lower bound on the overall outage probability is derived in closed-form, while a useful expression is presented for the asymptotically low outage regime. We also deduce the tight closed-form expression for the ergodic sum-rate. Furthermore, we formulate and solve analytically three optimization problems viz., relay power allocation under fixed location of the relay, relay position with fixed relay power allocation, and joint optimization of relay power allocation and location. Our results reveal that for given ICE, the optimal relay location offers significant system performance enhancement under ATRs, whilst the optimal relay power allocation has a more noticeable impact under symmetric traffic. It is also shown that the joint optimization of relay power allocation and location can further enhance the system performance, regardless of ATRs and ICE. Above all, based on the direct link quality, we show that the considered scheme outperforms its two-phase counterpart, even in the low signal-to-noise ratio regime.

Performance analysis of SFBC‐OFDM system with channel estimation error over generalized fading channels

AbstractIn this paper, the performance of space‐frequency block code orthogonal frequency‐division multiplexing (SFBC‐OFDM) system is analyzed over different fading channels using a generalized approach. General closed‐form expressions of average bit error rate (ABER) are derived for SFBC‐OFDM system. Both M‐ary phase‐shift keying and M‐ary quadrature amplitude modulation techniques have been considered in this analysis. The effect of imperfect channel estimation on ABER is included while deriving the ABER expression. The derived expressions are applicable under any given fading conditions provided that the moment‐generating function of fading channel is known. Simulation results are provided to verify the numerical results obtained from the derived expressions.

Antijamming Performance of Adaptive Chaos Based CDMA System with MRC in Imperfect Channel Estimation Environment

This paper presents the antijamming performance of adaptive multiuser DS-CDMA system using maximal ratio combining technique in slow switching pulse noise jammer. Complex flat fading channel coefficients are assumed to be unknown at the receiver. Pilot symbols are used to estimate the fading coefficients using least mean square (LMS) algorithm, and effect of imperfect channel estimation on bit error rate (BER) is studied. Under the perfect synchronization conditions, probability of error in closed form is derived.

On the Achievable Rate of a Class of Acoustic Channels and Practical Power Allocation Strategies for OFDM Systems

In this paper, we consider a class of single-input–multiple-output (SIMO) underwater acoustic communication channels, where each propagation path can be characterized by a complex-valued Gaussian block-fading model. The capacity of such channels is computed and analyzed using three power allocation strategies: waterfilling, uniform, and on–off uniform power allocation across the signal bandwidth. Our analysis considers the effects of imperfect channel estimation, delayed feedback, and pilot overhead, which are found to contribute to about 1 (b/s)/Hz loss from 4 (b/s)/Hz at 20-dB signal-to-noise ratio (SNR) for the experimental channel. We find that given the long feedback delays associated with acoustic channels, all-on uniform power allocation, which does not require feedback and is simple to implement, emerges as a justified practical solution that outperforms the other strategies. Furthermore, when considering acoustic-specific propagation effects, such as frequency-dependent attenuation and colored noise, considerable gain can be achieved by selecting the frequency band according to the attenuation pattern and the available transmit power, e.g., at least 6-dB gain for a 10-km link when compared to transmission over a preselected frequency band of 10–15 kHz.

Electromagnetic Lens-Focusing Antenna Enabled Massive MIMO: Performance Improvement and Cost Reduction

Massive multiple-input-multiple-output (MIMO) techniques have been recently advanced to tremendously improve the performance of wireless communication networks. However, the use of very large antenna arrays at the base stations brings new issues, such as the significantly increased hardware and signal processing costs. In order to reap the performance gains of massive MIMO and yet reduce its cost, this paper proposes a novel system design by integrating an electromagnetic (EM) lens with the large antenna array, termed the EM-lens enabled MIMO. The EM lens has the capability of focusing the power of an incident wave to a small area of the antenna array, whereas the location of the focal area varies with the angle of arrival (AoA) of the wave. Hence, in scenarios where the arriving signals from geographically separated users have different AoAs, the EM-lens enabled receiver provides two new benefits, namely, energy focusing and spatial interference rejection. By taking into account the effects of imperfect channel estimation via pilot-assisted training, in this paper, we analytically show that the average received signal-to-noise ratio in both the single-user and multiuser uplink transmissions can be improved by the EM-lens enabled system. Furthermore, we demonstrate that the proposed design makes it possible to considerably reduce the hardware and signal processing costs with only slight degradations in performance. To this end, two complexity/cost reduction schemes are proposed, which are small-MIMO processing with parallel receiver filtering applied over subgroups of antennas to reduce the computational complexity, and channel covariance based antenna selection to reduce the required number of radio frequency chains. Numerical results are provided to corroborate our analysis and show the great potential advantages of our proposed EM-lens enabled MIMO system for next generation cellular networks.

Performance Analysis of Dual-Hop Amplify-and-Forward Systems with Multiple Antennas and Co-channel Interference

This paper investigates the performance of a dual-hop amplify-and-forward relaying system with co-channel interference at both the relay and destination nodes. The source node is equipped with multiple antennas and adopts the orthogonal space-time block code to increase the system performance. Both the outage probability and the average bit error rate under the presence of multiple Rayleigh fading interferers are obtained in closed form for the variable and fixed-gain relaying schemes. Moreover, the effect of imperfect channel estimation on the variable-gain relaying scheme is also discussed. The effect of co-channel interference at both the relay and destination nodes are discussed. Simulation experiments are also conducted to verify the theoretical derivations.

Joint Cooperative Temporal Sensing and Distributed Estimation for Bayesian Optimal Threshold

Cooperative temporal sensing and distributed estimation are two vital aspects of cognitive radio. This paper studies a joint cooperative temporal sensing and distributed estimation scheme for Bayesian optimal threshold. This scheme studies the impact of distributed estimation error on the performance of cooperative temporal sensing by using Bayesian cost, and the Bayesian optimal threshold is obtained by minimizing the Bayesian cost. Finally, we examine the performances of other optimal thresholds with different criterions, and the effect of imperfect channel estimation is also tested. Numerical results show the performance of proposed scheme and validate our analysis.

Link Performance Estimation Techniques for MIMO-OFDM Systems with Maximum Likelihood Receiver

Link adaptation allows a communication system to adapt its transmission modes according to channel conditions. Although a maximum likelihood (ML) receiver for multiple-input multiple-output (MIMO) systems provides optimal performance, estimating its link performance has been a difficult problem. In this paper, we propose a new link performance abstraction technique for MIMO orthogonal frequency-division multiplexing systems with the ML receiver. The performance of ML detection (MLD) is estimated by employing capacity bounds of two simple linear receivers. Then, we give a simple parametrization to compute the desired per-stream signal-to-noise ratio (SNR) values, which can be applied for both vertically and horizontally coded MIMO systems. Based on the derived per-stream SNR estimates, the block error rate is obtained using the received-bit information rate metrics. We also examine the effect of imperfect channel estimation as well as spatial correlations among antennas. Finally, extensive simulation results show that the proposed method provides superior estimation accuracy in the MIMO-MLD link evaluation with very low computational complexity.

Adaptive Power Loading for Multi-Relay OFDM Regenerative Networks with Relay Selection

In this paper, we propose an adaptive power loading algorithm for an OFDM (orthogonal frequency division multiplexing)-based multi-relay regenerative network with relay selection. The proposed scheme is based on selecting the "best" relay(s) according to different strategies and distributing the power adaptively among the subcarriers of source and selected relay(s) as to minimize an upper bound on the bit error rate (BER). Our Monte Carlo simulation results demonstrate superior performance gains through power loading with respect to conventional equal power loading schemes. The effects of imperfect channel estimation and relay location on the BER performance are further discussed.

Analysis of DS-CDMA System with Phase Synchronization Errors for Selection Diversity Scheme

Wireless communication is currently the most dynamic field with the invention of new technologies. Presently one of the main challenges in the wireless communication field is to combat fading. At the receiver, the signal may be lost completely due to destructive addition of multi paths signal components. Generally effect of fading is analyzed with channel compensation using different diversity combining schemes such as selection diversity, equal gain combining and maximal ratio combining techniques. Selection diversity is one of the preferred schemes due to its simplest implementation process. However, often channel estimation may not be perfect because of changing nature and other factors like correlation between the signals etc. The main aim of this paper is to observe the effect of imperfect channel estimation on the performance of the receiver. Analysis has been done for channel estimation along with selection diversity combining. Also, receiver may not be synchronized always with transmitter giving some phase errors. Such error is also incorporated along with selection diversity for performance evaluation of the system.

Dynamic physical resource block allocation algorithms for uplink long term evolution

The authors investigate dynamic physical resource block (PRB) allocation for the uplink long-term evolution (LTE) system with single carrier-frequency division multiple access (SC-FDMA). Three dynamic PRB allocation algorithms are proposed, which are referred to as the maximum greedy (MG), mean enhanced greedy (MEG) and single mean enhanced greedy (SMEG) algorithms, respectively. Simulation results show that the proposed algorithms significantly outperform the previous two-dimensional (2-D) algorithm in terms of bit error rate (BER) and data rate fairness. The MEG algorithm is shown to provide a performance close to the Hungarian algorithm (optimal algorithm to maximise the SE) in terms of spectral efficiency (SE), while requiring a much lower computational complexity. SMEG further reduces the complexity of MEG with little performance degradation. Furthermore, the effects of imperfect channel estimation, root mean square (RMS) delay, Doppler spread and channel estimate feedback delay on performance are investigated.

Performance Evaluation of Generalized Selection Combiners Over Slow Fading with Estimation Errors

In this paper we derive closed-form expressions for the single-user adaptive capacity of generalized selection combining (GSC) system, taking into account the effect of imperfect channel estimation at the receiver. The channel considered is a slowly varying spatially independent flat Rayleigh fading channel. The complex channel estimate and the actual channel are modelled as jointly Gaussian random variables with a correlation that depends on the estimation quality. Three adaptive transmission schemes are analyzed: (1) optimal power and rate adaptation; and (2) constant power with optimal rate adaptation, and (3) channel inversion with fixed rate. In addition to deriving an exact expression for the capacity of the aforementioned adaptive schemes, we analyze the impact of channel estimation error on the capacity statistics and the symbol error rate for GSC systems. The capacity statistics derived in this paper are the moment generating function, complementary cumulative distribution function and probability density function for arbitrary number of receive antennas. Moreover, exact closed-form expressions for M-PAM/PSK/QAM employing GSC are derived. As expected, the channel estimation error has a significant impact on the system performance.

A novel analytical method for maximum likelihood detection in MIMO multiplexing systems

This letter addresses the problem of symbol error probability (SEP) analysis for maximum likelihood (ML) detection in multiple-input multiple-output (MIMO) multiplexing systems. A new analytical method is presented based on the total probability theorem. The effects of imperfect channel estimation and power allocation scheme are investigated. The accuracy of the proposed method is demonstrated by Monte-Carlo simulations. It is shown that the analytical results match quite well with the simulation ones irrespective of the signal-to noise- ratio (SNR).