A Novel GBSM for Non-Stationary V2V Channels Allowing 3D Velocity Variations

A new non-stationary (NS) geometry-based stochastic model (GBSM) is presented for developing and testing the communication systems of vehicle-to-vehicle (V2V) applications, which considers the three-dimensional (3D) scattering environments and allows 3D velocity as well. In this paper, the proposed GBSM for NS V2V channels allowed 3D velocity variations and was more suitable for actual V2V communications because it provided smoother transitions between the consecutive channel segments. The time-variant channel coefficient and the channel parameters, i.e., Doppler frequencies, path delay and power, angle of arrival (AoA), and angle of departure (AoD), were analyzed and derived. Likewise, the theoretical statistical properties as the probability density function (PDF), the auto-correlation function (ACF), and Doppler power spectral density (DPSD) were also analyzed and derived under the von Mises–Fisher (VMF) distribution. Finally, the theoretical and measured results were well coordinated alongside the implemented results, which confirmed the feasibility of the introduced model along with the theoretical expressions.

Autoencoder-bank based design for adaptive channel-blind robust transmission

The idea of employing deep autoencoders (AEs) has been recently proposed to capture the end-to-end performance in the physical layer of communication systems. However, most of the current methods for applying AEs are developed based on the assumption that there exists an explicit channel model for training that matches the actual channel model in the online transmission. The variation of the actual channel indeed imposes a major limitation on employing AE-based systems. In this paper, without relying on an explicit channel model, we propose an adaptive scheme to increase the reliability of an AE-based communication system over different channel conditions. Specifically, we partition channel coefficient values into sub-intervals, train an AE for each partition in the offline phase, and constitute a bank of AEs. Then, based on the actual channel condition in the online phase and the average block error rate (BLER), the optimal pair of encoder and decoder is selected for data transmission. To gain knowledge about the actual channel conditions, we assume a realistic scenario in which the instantaneous channel is not known, and propose to blindly estimate it at the Rx, i.e., without any pilot symbols. Our simulation results confirm the superiority of the proposed adaptive scheme over existing methods in terms of the average power consumption. For instance, when the target average BLER is equal to $$10^{-4}$$ 10 - 4 , our proposed algorithm with 5 pairs of AE can achieve a performance gain over 1.2 dB compared with a non-adaptive scheme.

Secret Key Generation Assisted by Intelligent Reflecting Surface with Discrete Phase Shift in Static Environment

<a>Physical layer secret key generation is a promising candidate to achieve one-time-pad encryption approach for wireless communication system. The main issue of this method is the insufficient secret key rate. Especially in a static environment, the entropy of the channel complex coefficient is limited due to the lack of channel time-variation. To solve the problem, this paper proposes a novel secret key generation scheme assisted by intelligent reflecting surface (IRS) with discrete phase. We construct a dynamic time-varying channel by switching the phase of the reflection elements rapidly and randomly, and use channel estimation samples to update the secret key. Based on the common IRS channel model, we derive the expression of secret key rate. Monte Carlo simulation and numerical results show that the scheme can update secret key even if the channel coefficient is constant, and the secret key rate is higher than schemes based on artificial random signal. In addition, we comprehensively analyze the influence of various factors, such as the number of reflection elements and the IRS switching frequency on the secret key rate. </a>

Secret Key Generation Assisted by Intelligent Reflecting Surface with Discrete Phase Shift in Static Environment

<a>Physical layer secret key generation is a promising candidate to achieve one-time-pad encryption approach for wireless communication system. The main issue of this method is the insufficient secret key rate. Especially in a static environment, the entropy of the channel complex coefficient is limited due to the lack of channel time-variation. To solve the problem, this paper proposes a novel secret key generation scheme assisted by intelligent reflecting surface (IRS) with discrete phase. We construct a dynamic time-varying channel by switching the phase of the reflection elements rapidly and randomly, and use channel estimation samples to update the secret key. Based on the common IRS channel model, we derive the expression of secret key rate. Monte Carlo simulation and numerical results show that the scheme can update secret key even if the channel coefficient is constant, and the secret key rate is higher than schemes based on artificial random signal. In addition, we comprehensively analyze the influence of various factors, such as the number of reflection elements and the IRS switching frequency on the secret key rate. </a>

Secret Key Generation Assisted by Intelligent Reflecting Surface with Discrete Phase Shift in Static Environment

<a>Physical layer secret key generation is a promising candidate to achieve one-time-pad encryption approach for wireless communication system. The main issue of this method is the insufficient secret key rate. Especially in a static environment, the entropy of the channel complex coefficient is limited due to the lack of channel time-variation. To solve the problem, this paper proposes a novel secret key generation scheme assisted by intelligent reflecting surface (IRS) with discrete phase. We construct a dynamic time-varying channel by switching the phase of the reflection elements rapidly and randomly, and use channel estimation samples to update the secret key. Based on the common IRS channel model, we derive the expression of secret key rate. Monte Carlo simulation and numerical results show that the scheme can update secret key even if the channel coefficient is constant, and the secret key rate is higher than schemes based on artificial random signal. In addition, we comprehensively analyze the influence of various factors, such as the number of reflection elements and the IRS switching frequency on the secret key rate. </a>

Relay Selection Schemes for FSO Communications over Turbulent Channels

Free Space Optics (FSO) Communication has attracted the attention of the researchers in the last decade due to its high data rate, security, and low cost. Relay-assisted techniques are used to divide the distance to shorter hops in order to mitigate the effects of turbulence, weather attenuation, pointing error, and geometric loss. Choosing an active relay per time slot has been proven to enhance the performance of the system and decrease the loading effect on the system when compared to all active relays. This paper investigates the best relay that can be selected according to the source to relay (S-R) channel coefficient, relay to destination (R-D) channel coefficient, and source to destination (S-D) channel coefficient. A comprehensive comparison is applied to the three following cases: (a) Broadcast phase from source to relay to select the best (Proactive-Relay); (b) Broadcast phase from relay to destination after broadcasting to all relays then select (Reactive-relays); and, (c) Direct link from source-to-best relay-to-destination to conclude which method is better for different scenarios, such as turbulence regime, number of relays, different pointing error effect, and severity of S-R as compared to R-D and vice versa. The selection methods regard to four aspects: (1) Number of relays (two or three relays); (2) Distance between Source-Relay and Relay-Destination (D = 400–600 m, 500–500 m, and 600–400 m); (3) The different turbulence of Log-normal channel and Gamma-Gamma channel (with a refractive index coefficient( C n 2 = 0.5 × 10−14, 2 × 10−14 and 5 × 10−14)); and finally, (4) Beam waist ω z (pointing error).

Directional AF Cooperative Communication System Based on Outage Probability

In order to improve outage property of cooperative communication system, directional antenna technology could be introduced. The paper proposes single relay AF cooperative communication protocol based on directional antenna and deduces the outage probability of system in fully directional mode theoretically so as to deduce the lower bound. With the minimum system outage probability to be the target, the paper analyzes OPA (Optimum Power Allocation) and makes detailed analysis and comparison of the system property of the established model by combining with specific simulation value. The simulation result shows that on the condition of high SNR (Signal to Noise Ratio) or greater difference of channel coefficient between two terminals and relay, the lower bound and accurate value are approximated and the outage property of fully directional cooperative communication is superior to that of traditional mode. Under the situation of limited power, OPA can enhance the outage property of system effectively.