Time Correlation Of Channel Research Articles

Characterization and modeling of high-speed underwater acoustic communication channels

High-speed mobile underwater acoustic communication (HSM-UAC) is a relatively unexplored terrain, but its importance is expected to increase with the widespread application of flexible underwater mobile platforms such as AUVs and UUVs. Knowledge of HSM-UAC channels is a prerequisite to achieving reliable communication. This work conducted two HSM-UAC channel measurement experiments with a maximum speed of 20knots. The analysis of channel time-varying characteristics demonstrates the shortcomings of traditional consistent Doppler frequency offset channel model. The experimental findings reveal the presence of two non-stationary modes in the HSM-UAC channel. For short moving distances, the changes in channel geometry result in each path experiencing a different Doppler scale, thus observing the multiscale-multilag (MSML) channels. For long moving distances, the alteration in sound ray propagation tracks entirely reshapes the channel impulse response (CIR) structure, leading to a rapid decline in channel time correlation. In further analysis, the correlation coefficient of the power delay profile (PDP) is used to measure channel stationarity. Subsequently, the stationary time and corresponding stationary distance are calculated as characterization parameters for the time-varying channel model. The quantitative evaluation results are helpful for the communication signal design and determining the update frequency of channel state information.

The Complexity–Performance Tradeoff in Resource Allocation for URLLC Exploiting Dynamic CSI

The challenging applications envisioned for the future Internet of Things networks are making it urgent to develop fast and scalable resource allocation algorithms able to meet the stringent reliability and latency constraints typical of the ultra-reliable, low-latency communications (URLLCs). However, there is an inherent tradeoff between complexity and performance to be addressed: sophisticated resource allocation methods providing optimized spectrum utilization are challenged by the scale of applications and the concomitant stringent latency constraints. Whether nontrivial resource allocation approaches can be successfully applied in large-scale network instances is still an open question that this article aims to address. More specifically, we consider a scenario in which channel-state information (CSI) is used to improve spectrum allocation in a radio environment that experiences channel time correlation. Channel correlation allows the usage of CSI for longer time before an update, thus lowering the overhead burden. Following this intuition, we propose a dynamic pilot transmission allocation scheme in order to adaptively tune the CSI age. We systematically analyze the improvement of this approach applied to a sophisticated, recently introduced graph-based resource allocation method that we extend here to account for CSI. The results show that even in very dense networks and accounting for the higher computational time of the graph-based approach, this algorithm is able to improve spectrum efficiency by over 12% as compared to a greedy heuristic, and that dynamic pilot transmissions allocation can further boost its performance in terms of fairness, while concomitantly further increase spectrum efficiency of 3%-5%.

Channel estimation for reconfigurable intelligent surface assisted wireless communication systems in mobility scenarios

Reconfigurable intelligent surface (RIS) can manipulate the wireless propagation environment by smartly adjusting the amplitude/phase in a programmable panel, enjoying the improved performance. The accurate acquisition of the instantaneous channel state information (CSI) in the cascaded RIS chain makes an indispensable contribution to the performance gains. However, it is quite challenging to estimate the CSI in a time-variant scenario due to the limited signal processing capability of the passive elements embedded in a RIS pannel. In this work, a channel estimation scheme for the RIS-assisted wireless communication system is proposed, which is demonstrated to perform well in a time-variant scenario. The cascaded RIS channel is modeled as a state-space model based upon the mobility situations. In addition, to fully exploit the time correlation of channel, Kalman filter is employed by taking the prior information of channels into account. Further, the optimal reflection coefficients are derived according to the minimum mean square error (MMSE) criterion. Numerical results show that the proposed methods exhibit superior performance if compared with a conventional channel estimation scheme.

The Security of Cognitive Multiuser Networks Over Space-and-Time Correlated Channels

In this paper, we investigate the secrecy performance of cognitive multi-input multi-output multiuser (MIMO-MU) wiretap networks over space-and-time correlated fading channels. Specifically, we propose a joint transmit antenna selection (TAS) and multiuser scheduling scheme to improve the security of the considered system. To thoroughly analyze the impact of the joint TAS and multiuser scheduling scheme and the channel correlation on the physical layer security, the new exact and asymptotic closed-form expressions for the secrecy outage probability of cognitive MIMO-MU wiretap networks are derived in two distinct scenarios, i.e., space-and-time correlated fading channels and independent-and-perfect fading channels. From the theoretical and simulation results, several important remarks are concluded as follows. 1) The channel space correlation does not affect the achievable secrecy diversity order in a high main-to-eavesdropper ratio (MER) regime. While it produces different impacts on the secrecy performance with different values of the MER in a low MER regime. 2) The channel time correlation on the main channel can reduce the achievable secrecy diversity order from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{\rm A}N_{\rm B}$</tex-math></inline-formula> to 1. 3) The joint TAS and multiuser scheduling scheme can achieve better performance than the traditional random scheduling scheme over space-and-time correlated fading channels.

Goodput Maximization of HARQ-IR Over Arbitrarily Correlated Rician Fading Channels

This paper investigates the optimal design of hybrid automatic repeat request with incremental redundancy (HARQ-IR) over arbitrarily correlated Rician fading channels for goodput maximization. With practical consideration of both the channel time correlation and line-of-sight (LOS) links, theoretical analysis and optimal design of HARQ-IR become very challenging. To address them, asymptotic outage analysis is first carried out to not only gain meaningful insights but also facilitate the optimal design. With simple forms of asymptotic expressions derived, joint optimization of the transmission powers and rate aiming at goodput maximization under average total transmission power constraint is enabled and solved analytically. The optimal goodput is also derived in closed form, with which meaningful insights can then be extracted. Particularly, the scaling law of the optimal goodput with respect to the transmit signal-to-noise ratio is found, and the harmfulness of time correlation and the benefit of LOS links are revealed. Finally, the analytical results are validated through extensive simulations.

Asymptotic Outage Analysis of HARQ-IR Over Time-Correlated Nakagami- $m$ Fading Channels

In this paper, outage performance of hybrid automatic repeat request with incremental redundancy (HARQ-IR) is analyzed. Unlike prior analyses, time-correlated Nakagami- $m$ fading channel is considered. The outage analysis thus involves the probability distribution analysis of a product of multiple correlated shifted Gamma random variables and is more challenging than prior analyses. Based on the findings of the conditional independence of the received signal-to-noise ratios, the outage probability is exactly derived by using conditional Mellin transform. Specifically, the outage probability of HARQ-IR under time-correlated Nakagami- $m$ fading channels can be written as a weighted sum of outage probabilities of HARQ-IR over independent Nakagami fading channels, where the weightings are determined by a negative multinomial distribution. This result enables not only an efficient truncation approximation of the outage probability with uniform convergence but also asymptotic outage analysis to further extract clear insights, which have never been discovered for HARQ-IR even under fast fading channels. The asymptotic outage probability is then derived in a simple form, which clearly quantifies the impacts of transmit powers, channel time correlation, and information transmission rate. It is proved that the asymptotic outage probability is an inverse power function of the product of transmission powers in all HARQ rounds, an increasing function of the channel time correlation coefficients, and a monotonically increasing and convex function of information transmission rate. The simple expression of the asymptotic result enables optimal power allocation and optimal rate selection of HARQ-IR with low complexity. Finally, numerical results are provided to verify our analytical results and justify the application of the asymptotic result for optimal system design.

On the Generation of Correlated Short- and Long-Term Fading for Multiple BANs

This letter presents a time-varying channel model implementation for multiple body area networks including both on-body an body-to-body links. Channel time-correlation properties are modeled with an autoregressive method with the exception of body-to-body short-term fading. This last component shows an important dependence on the body positions and specifically on the mutual orientation of the bodies. For this reason, it requested a dedicated implementation a method based on Cholesky decomposition. Simulated results of the implementation are validated with measurements, and a good agreement between the two is found.

Inverse Moment Matching Based Analysis of Cooperative HARQ-IR over Time-Correlated Nakagami Fading Channels

This paper analyzes the performance of cooperative hybrid automatic repeat request with incremental redundancy (HARQ-IR) and proposes a new approach of outage probability approximation for performance analysis. A general time-correlated Nakagami fading channel covering fast fading and Rayleigh fading as special cases is considered here. An efficient inverse moment matching method is proposed to approximate the outage probability in a closed form. The effect of approximation degree is theoretically analyzed to ease its selection. Moreover, diversity order of cooperative HARQ-IR is analyzed. It is proved that the diversity order is irrelevant to the time correlation coefficient $\rho$ , as long as $\rho , and full diversity from both spatial and time domains can be achieved by cooperative HARQ-IR under time-correlated fading channels. The accuracy of the analytical results is verified by computer simulations, and the results reveal that cooperative HARQ-IR scheme can benefit from high fading order and low channel time correlation. Optimal rate selection to maximize the long-term average throughput given a maximum allowable outage probability is finally discussed as one application of the analytical results.

Performance Analysis of Space-Time Spreading DS-CDMA Systems over Fast-Fading General Time-Correlated Channels

This paper examines the performance of the space-time spreading (STS), DS-CDMA in a fast-fading general time-correlated Rayleigh channel. The transmitter employs two orthogonal codes to space-time spread the incoming symbols and generates STS symbols for transmission from two transmit antennas over a frequency flat channel. We present an analytical study of the performance of such system when the channel is rapidly varying from one symbol to another and show that it depends on the channel time correlation coefficient. A closed form expression for the probability of bit error as a function of the channel correlation and the input signal to noise ratio is also derived, showing that it increases as the channel correlation increases for a given signal-to-noise ratio. As expected, a lower bound on the bit error rate (BER) is achieved when the channel varies independently from one symbol to another while the upper bound is achieved when the channel is quasi-static. The analytical results depict total agreement with the simulation results.

Link Adaptation Considering Mobility in OFDMA Systems with Multiple Transmit Antennas

Link adaptation is investigated for OFDMA systems with multiple transmit antennas, where the transmission rate is adapted and where the subcarriers to be used and the multiple antenna transmission scheme to be applied are adaptively selected, according to instantaneous SNR and user mobility. The throughputs (defined as the transmission rate multiplied by 1-(outage probability)) of several transmission modes, which are differentiated by their use of subcarriers and multiple antennas, are compared. Numerical examples are presented showing that the best transmission mode depends on the instantaneous SNR, user mobility (or time-correlation of channel), and a rate adaptation scheme.