Impact Of Imperfect Channel State Information Research Articles

Performance of SWIPT-Enabled FD TWR Network With Hardware Impairments and Imperfect CSI

Cooperative communication with energy harvesting capability increases network coverage and provides a green and sustainable solution for future wireless technologies. In this article, we analyze the performance of a two-way relay network, where bidirectional information exchange between two nodes takes place via simultaneous wireless information and power transfer-enabled relay node, operating in full-duplex (FD) mode over generalized Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> fading channels. Different nonlinear power amplifier (NLPA) models, such as solid-state power amplifier, traveling wave tube amplifier, and soft envelope limiter, are considered at the relay node. The effect of practical constraints, such as imperfect channel state information (CSI) and transceiver hardware impairments (HIs), is considered. Further, we consider the impact of residual self-interference (RSI) due to imperfect successive interference cancellation in the FD mode. For performance analysis, the closed-form expressions of outage probability (OP), asymptotic OP, system throughput, energy efficiency, ergodic capacity, and asymptotic ergodic capacity are derived. The diversity order of the considered network is evaluated. Further, the impact of imperfect CSI, NLPA, HIs, RSI, and other parameters are highlighted on the system performance. The performance of FD and half-duplex mode is also compared. Monte Carlo simulations confirm the accuracy of the derived closed-form expressions.

Physical layer security for space–time-block-coded MIMO system in Rician fading in the presence of imperfect feedback

We investigate physical layer security (PLY) of space–time-block-coded (STBC)–multi-input–multi-output (MIMO) wiretap channel in the presence of imperfect channel state information (ICSI) over Rician fading channel. Secrecy for data transmission to legitimate user in the presence of eavesdropper is metered in terms of average secrecy capacity (ASC), probability of non-zero secrecy rate (PNZSR) and secrecy outage probability (SOP). We derive the closed form expression for security parameter by using the probability distribution function and cumulative distribution function of output signal to noise ratio (SNR). Simulation results are presented to validate our analytical results and demonstrate the impact of ICSI on the secrecy performance of STBC–MIMO system.

Multi-User Relay Selection for Full-Duplex Radio

This paper investigates a user-fairness relay selection (RS) problem for decode-and-forward (DF) full-duplex (FD) relay networks, where multiple users cooperate with multiple relays in each coherence time. We consider two residual self-interference (RSI) models with or without direct links. We propose a sub-optimal relay selection (SRS) scheme which requires only the instantaneous channel state information (CSI) of source-to-relay and relay-to-destination links. To evaluate the performance, the outage probability of SRS is derived for different scenarios depending on RSI models and the availability of direct links. To further investigate, asymptotic expressions are derived for the high-transmit power regime. For comparison purposes, 1) the average throughputs of the FD and half-duplex (HD) modes are derived; 2) non-orthogonal transmission is considered and its performance is discussed with approximations; and 3) the impact of imperfect CSI is investigated with the aid of analysis. While simulation results are provided to verify the analytical results, they reveal interesting fundamental trends. It turns out that a significant throughput degradation occurs with FD mode over HD mode when self-interference is fully proportional to the transmit power. Since all users can communicate in the same coherence time with the FD mode, these joint RS schemes are useful for user-fairness low-latency applications.

Impact of Imperfect CSI on ASER of Hexagonal and Rectangular QAM for AF Relaying Network

In this letter, we derive the closed-form expression of outage probability for a dual-hop variable-gain amplify-and-forward relay network. The maximal ratio combining receiver over independent and non-identically distributed frequency flat Nakagami-m fading channels with integer-valued fading parameter and imperfect channel state information (CSI) is considered. Asymptotic analysis on outage probability is also performed. Average symbol error rate (ASER) expressions are derived for general-order hexagonal and rectangular QAM schemes using the cumulative distribution function-based approach. The impact of the fading parameter and imperfect CSI are highlighted on the system performance. Comparative analysis of ASER performance for different QAM constellations is also illustrated. Monte Carlo simulations are performed to validate the derived analytical results for both perfect and imperfect CSI.

Channel-Aware Random Access in the Presence of Channel Estimation Errors

In this work, we consider the random access of nodes adapting their transmission probability based on the local channel state information (CSI) in a decentralized manner, which is called CARA. The CSI is not directly available to each node but estimated with some errors in our scenario. Thus, the impact of imperfect CSI on the performance of CARA is our main concern. Specifically, an exact stability analysis is carried out when a pair of bursty sources are competing for a common receiver and, thereby, have interdependent services. The analysis also takes into account the compound effects of the multipacket reception (MPR) capability at the receiver. The contributions in this paper are twofold: first, we obtain the exact stability region of CARA in the presence of channel estimation errors; such an assessment is necessary as the errors in channel estimation are inevitable in the practical situation. Secondly, we compare the performance of CARA to that achieved by the class of stationary scheduling policies that make decisions in a centralized manner based on the CSI feedback. It is shown that the stability region of CARA is not necessarily a subset of that of centralized schedulers as the MPR capability improves.

On the Joint Impact of Hardware Impairments and Imperfect CSI on Successive Decoding

In this paper, a spatial multiplexing multiple-input multiple-output (MIMO) system when hardware along with radio-frequency imperfections occur during the communication setup is analytically investigated. More specifically, the scenario of hardware impairments at the transceiver and imperfect channel state information (CSI) at the receiver is considered when successive interference cancelation (SIC) is implemented. Two popular linear detection schemes are analyzed, namely, zero-forcing SIC (ZF-SIC) and minimum mean-square-error SIC (MMSE-SIC). New analytical expressions for the outage probability of each SIC stage are provided when independent and identically distributed Rayleigh fading channels are considered. In addition, the well-known error propagation effect between consecutive SIC stages is analyzed, while closed-form expressions are derived for some special cases of interest. Finally, useful engineering insights are manifested, such as the achievable diversity order, the performance difference between ZF- and MMSE-SIC, and the impact of imperfect CSI and/or the presence of hardware impairments to the overall system performance.

Novel Markov channel predictors for interference alignment in cognitive radio network

In cognitive radio (CR) network, how to mitigate interference between different users is a key task. Interference alignment (IA) is a promising technique to tackle the multi-user interference in communication system. Compared with other interference management methods (such as zero-forcing), IA can not only effectively eliminate the interference, but also greatly increase the system capacity. However, the perfect channel state information (CSI) is required for both transmitters and receivers to apply the IA algorithm, which is hard to achieve in practical applications. In this paper, the effect of imperfect CSI on IA in CR system is analyzed in terms of signal to interference plus noise ratio and achievable sum rate. A linear finite state Markov chain (LFSMC) predictor, which incorporates the finite state Markov chain into the AR predictor, is proposed to reduce the impact of imperfect CSI on system performance of CR network. Moreover, for the sake of simplifying the initialization of LFSMC predictor, a simplified LFSMC (S-LFSMC) predictor is provided. Simulation results indicate that both of the LFSMC and S-LFSMC predictor can greatly improve the performance of IA system with the inaccurate CSI. Specifically, the LSFMC predictor can achieve satisfied performance compared with other predictors mentioned in this paper. And the LSFMC predictor which is simpler and its performance is still much better than traditional predictors. Therefore, we can choose a suitable predictor (LAFMC or S-LSFMC) based on the different requirements.

Joint relay selection and power allocation in energy harvesting AF relay systems with ICSI

In various wireless networks, power allocation scheme promises significant benefits in energy harvesting (EH) wireless networks. However, these benefits depend on the knowledge of the channel state information (CSI), which is hardly perfect. Therefore, in this study, the authors investigate an EH two-way relaying network with channel estimation error taking into consideration. First, the system outage performance is studied and closed-form expressions for the outage probability are derived. On the basis of minimising the outage probability, an optimal power allocation (OPA) scheme is proposed and the effective ways to solve this OPA scheme are presented. In addition, a joint relay selection and the OPA scheme is provided to further improve the system performance. Finally, by comparing the OPA scheme with conventional power allocation schemes via simulations, the superiority of the OPA scheme is demonstrated. Moreover, the impact of imperfect CSI on the system performance is analysed and the simulation results show the robustness of the OPA scheme.

Outage Performance of Decode-and-Forward in Two-Way Relaying With Outdated CSI

In this paper, we analyze the outage behavior of decode-and-forward (DF) relaying in the context of selective two-way cooperative systems. First, a new relay selection metric is proposed to take into consideration both transmission rates and instantaneous link conditions between cooperating nodes. Afterward, the outage probability of the proposed system is derived for Nakagami- $m$ fading channels in the case when perfect channel state information (CSI) is available and then extended to the more realistic scenario where the available CSI is outdated due to fast fading. New expressions for the outage probability are obtained, and the impact of imperfect CSI on the performance is evaluated. Illustrative numerical results, Monte Carlo simulations, and comparisons with similar approaches are presented to assess the accuracy of our analytical derivations and confirm the performance gain of the proposed scheme.

Imperfect CSI-Based Joint Resource Allocation in Multirelay OFDMA Networks

Radio resource allocation is very important in relay orthogonal frequency-division multiple-access (OFDMA) networks. Since perfect channel state information (CSI) is hardly obtained, the robust design that takes into account the CSI imperfection plays a crucial role in the development of efficient resource-allocation schemes. As to the chunk-based resource-allocation scheme, this paper focuses on the imperfect CSI-based resource-allocation problem to jointly optimize the chunk assignment, transmission link selection (direct or relay link), and power allocation in multirelay OFDMA systems. The optimization formulation minimizes the total transmit power with transmission requirement constraints and is considered a mixed-integer optimization problem, and a dual-maximization-based joint resource-allocation algorithm is proposed. The proposed dual-maximization-based algorithm is shown to be optimal. We also develop a low-complexity but near-optimal resource-allocation algorithm. The numerical results validate the performance gains offered by the proposed joint resource-allocation algorithms. The results also show that the impact of imperfect CSI is nonnegligible, which highlights the importance of robust designs in practical wireless networks.

Improving spectrum access using a beam‐forming relay scheme for cognitive radio transmissions

Cognitive radio (CR) systems allow unlicensed secondary users to transmit on the licensed frequency bands without degrading the transmissions of licensed primary users. Combining CR with other emerging techniques such as multi-antenna relaying may bring many benefits for the secondary transmissions. In this study, the authors propose and investigate a new relay-based cooperation scheme for a CR network to improve the secondary access to the licensed spectrum band without causing additional interference to the simultaneous primary transmission. The proposed scheme considers one multi-antenna relay node that can assist either the primary or the secondary transmission using beam-forming (BF). In the proposed new scheme, the BF weights are designed in the presence of imperfect channel state information (CSI). Simulation results show that the secondary's channel capacity is significantly improved and outperforms conventional transmission schemes. The results also reveal the impact of imperfect CSI on the primary outage performance and the efficiency of the proposed solution for minimising the interference due to imperfect CSI.

Wireless Energy and Information Transfer Tradeoff for Limited-Feedback Multiantenna Systems With Energy Beamforming

In this paper, we consider a multi-antenna system where the receiver should harvest energy from the transmitter by wireless energy transfer to support its wireless information transmission. In order to maximize the harvesting energy, we propose to perform adaptive energy beamforming according to the instantaneous channel state information (CSI). To help the transmitter to obtain the CSI for energy beamforming, we further propose a win-win CSI quantization feedback strategy, so as to improve the efficiencies of both power and information transmission. The focus of this paper is on the tradeoff of wireless energy and information transfer by adjusting the transfer duration with a total duration constraint. Through revealing the relationship between transmit power, transfer duration and feedback amount, we derive two wireless energy and information transfer tradeoff schemes by maximizing an upper bound and an approximate lower bound of the average information transmission rate, respectively. Moreover, the impact of imperfect CSI at the receiver is investigated and the corresponding wireless energy and information transfer tradeoff scheme is also given. Finally, numerical results validate the effectiveness of the proposed schemes.

Precoder Design for BICM-MIMO Systems Under Channel Estimation Error

If properly designed, the use of a linear precoder can achieve the maximum coding gain and diversity order in bit-interleaved coded modulation with multiple-input multiple-output systems. However, such maximum coding gain and diversity order are compromised under the practical scenario of having imperfect channel state information (CSI) at the receiver. To alleviate the impact of imperfect CSI on the coding gain and diversity order, joint linear precoder and training pattern are designed in this paper. The design is carried out by considering both the pairwise error probability and the mean square error of the channel estimator. The effectiveness of the proposed design is illustrated by comparing its performance with the performance obtained when only the training pattern is designed for an precoder optimized under the perfect CSI. In particular, simulation results show that a $$1.5$$ 1.5 dB gain is achieved by the proposed design.

Imperfect CSI Based Joint Bit Loading and Power Allocation for Deadline Constrained Transmission

This paper studies the imperfect channel state information (CSI) based joint resource scheduling problem for deadline constrained transmission. We present a holistic system model in terms of performance constraints of imperfect CSI, scheduling deadline and bit loading. By tackling channel estimation error, robust scheduling problems are formulated with the ellipsoidal approximation and transmission reliability constraints respectively. Dynamic programming (DP) based robust scheduling schemes are derived. The numerical results show that the proposed robust scheduling schemes are efficient in solving the jointly scheduling problem. It is also shown that the impact of imperfect CSI is non-negligible, thus highlighting the importance of robust design in time-sensitive communications.

Performance Analysis and Enhancement for Opportunistic Analog Network Coding with Imperfect CSI

Imperfect channel state information (CSI) is among the main factors that affect system performance in wireless networks. In this paper, we investigate the impact of imperfect CSI on the performance...

A Worst-Case Robust Beamforming Design for Multi-Antenna AF Relaying

In this paper, we consider relay precoder optimization for a multi-antenna amplify-and-forward (AF) relaying system using imperfect channel state information (CSI) with either additive or multiplicative deterministic uncertainties. Adopting worst-case robustness, we aim to maximize the worst-case received signal-to-noise ratio (SNR) at the destination subject to the power constraint at the relay. Despite the non-convexity of the design problem, we obtain a closed-form solution and discover that beamforming along the nominal channel direction achieves the best performance with channel uncertainties. Based on the optimal solution, we further analyze the impact of imperfect CSI on the performance of the robust multi-antenna AF relaying system and carry out simulations to verify our analysis.

Cross-Layer Resource Allocation in OFDMA Systems for Heterogeneous Traffic With Imperfect CSI

In this paper, we propose a cross-layer resource-allocation scheme for orthogonal frequency-division multiple-access (OFDMA) systems with imperfect channel-state information (CSI). In our modeling, we consider two traffic types: 1) streaming traffic, which requires a maximum guaranteed average delay, and 2) elastic traffic with flexible rate requirements. We then consider queue-state information (QSI) and CSI in a cross-layer framework to maximize the total transmission rate of elastic users while the average delay constraint for streaming users and the maximum transmission power constraint are satisfied. We also consider the impact of imperfect CSI. An algorithm is then proposed based on the dual decomposition method to obtain the subcarrier assignment and power allocation for each user. Using simulations, we evaluate the impact of streaming traffic on the total achievable rate of elastic users for different values of the required outage probability. It is also shown by simulation that, by increasing the variance of CSI estimation, the total rate of elastic traffic is decreased.

Joint Channel State Based Random Access and Adaptive Modulation in Wireless LANs with Multi-Packet Reception

Conventional 802.11 medium access control (MAC) protocols have been designed separately from the characteristics of the physical layer so as to simplify the analysis, but this hardly optimizes the overall performance from a system point of view. In this paper, we propose a channel state information (CSI) based random access protocol that takes advantage of multi-packet reception (MPR) in IEEE 802.11-like wireless local area networks (WLANs). Specifically, the proposed MAC protocol dynamically adjusts each nodes transmission probability according to the network population, estimated channel condition, as well as the maximum number of packets that can be simultaneously decoded. System throughput is analyzed by taking adaptive modulation and transmission errors into consideration. Based on such analytical result, an optimal transmission policy is derived to maximize the system throughput. In addition, the impact of imperfect CSI on the throughput performance is investigated and the tradeoff between the CSI quality and average SNR at the receiver is demonstrated. It is shown that compared with the schemes using conventional models, our proposed approach can significantly increase the throughput without sacrificing system resources such as bandwidth and transmission energy.

A nakagami fading phase difference distribution and its impact on BER performance

We propose a new model for investigating the impact of complex imperfect channel state information (CSI) over Nakagami-m fading channels. The phase difference between two correlated complex Nakagami random variables (RVs) is proposed and its statistical properties are investigated. A closed-form expression for the distribution is obtained using an approach from [1] and depends on the Nakagami-m parameter and the power correlation coefficient (p) between two correlated complex RVs. A simple approximation is given when p is close to unity. The proposed phase difference is shown to accurately approximate that of the Ricean. We derive the joint density function of this phase difference and its associated correlated envelopes. This is given in a closed form in terms of a generalized hypergeometric function, but the RVs can be easily generated for simulation. We analyze the impact of imperfect CSI on the bit error rate (BER) of uncoded and coded modulation. For uncoded modulation, the average BER and a closed-form expression of the asymptotic BER or error floor are obtained. For coded modulation, we determine the error free feedback bound of bit-interleaved coded modulation with iterative decoding for both perfect and imperfect CSI. We show that imperfect phase estimation is the major cause of the error floor.