On Secrecy Outage Probability for Downlink NOMA Systems With Relay-Antenna Selection

Secure transmission is essential for future non-orthogonal multiple access (NOMA) system. This paper investigates relay-antenna selection (RAS) to enhance physical-layer security (PLS) of cooperative NOMA system in the presence of an eavesdropper, where multiple antennas are deployed at the relays, the users, and the eavesdropper. In order to reduce expense on radio frequency (RF) chains, selection combining (SC) is employed at both the relays and the users, whilst the eavesdropper employs either maximal-ratio combining (MRC) or selection combining (SC) to process the received signals. Under the condition that the channel state information (CSI) of the eavesdropping channel is available or unavailable, two e↵ective relay-antenna selection schemes are proposed. Additionally, the closed-form expressions of secrecy outage probability (SOP) are derived for the proposed relay-antenna selection schemes. In order to gain more deep insights on the derived results, the asymptotic performance of the derived SOP is analyzed. In simulations, it is demonstrated that the theoretical results match well with the simulation results and the SOP of the proposed schemes is less than that of the conventional orthogonal multiple access (OMA) scheme obviously.

Performance Analysis and Simulation of Millimeter Wave Cell-Free mMIMO Networks

5G networks and beyond can provide high data rate for the served users. Small cells, massive multiple input multiple outputs (mMIMO) as well as working in millimeter wave bands are emerging tools toward empowering 5G and beyond networks. The cellular mMIMO networks can provide high data rate for users, however their performance is not satisfied for the cell-edge users and shadowed users. Fortunately, the cell-Free mMIMO network can provide a satisfied performance for all users even if they are in shadowed areas or at cell edges. The distributed access points (APs) through the coverage area can allow users to get benefit of the best serving AP. Furthermore, the users can have services anywhere due to the existence of one AP at least. The cell-Free mMIMO networks can provide a high throughput when they are operated in the millimeter wave bands due to the high available bandwidth. The operation in millimeter wave bands can let the 5G networks and beyond have a high data rate. Therefore, this paper gives a great attention to the millimeter wave bands. In this paper, the performance of the cell-Free mMIMO network, operating in the millimeter wave bands, is mathematically evaluated and simulated. The performance can include the spectral efficiency (SE), bit error rate (BER), and energy efficiency (EE). It is observed that the centralized cooperation among the APs, level 4, can provide a high SE and EE even if the maximal ratio combining (MRC) is applied. Moreover, the cell-Free four cooperation levels can perform better than cellular mMIMO when the millimeter wave non-line-of-sight (NLOS) models are applied.

MmWave V2X Cooperative Diversity Relay Channel with Feedback Delay and Link Blockage

In this work, we present a framework analysis of a millimeter wave (mmWave) vehicular communications systems. Communications between vehicles take place through a cooperative relay which acts as an intermediary base station (BS). The relay is equipped with multiple transmit and receive antennas and it employs decode-and-forward (DF) to process the signal. Also, the relay applies maximal ratio combining (MRC), and maximal ratio transmission (MRT), respectively, to receive and forward the signal.As the vehicles' speeds are relative high, the channel experiences a fast fading and this time variation is modeled following the Jake's autocorrelation model. We also assume narrowband fading channel. Closed-form expressions of the reliability metrics such as the outage probability and the mean rate are derived. Capitalizing on these performances, we derive the high signal-to-noise-ratio (SNR) asymptotes to get full insights into the system gains such as the diversity and coding gains.

Performance Analysis in DF Energy Harvesting Full-Duplex Relaying Network with MRC and SC at the Receiver under Impact of Eavesdropper

This paper investigates the decode-and-forward (DF) full-duplex (FD) relaying system under the presence of an eavesdropper. Moreover, the relay node is able to harvest energy from a transmitter, and then it uses the harvested energy for conveying information to the receiver. Besides, both two-hop and direct relaying links are taking into consideration. In the mathematical analysis, we derived the exact expressions for intercept probability and outage probability (OP) by applying maximal ratio combining (MRC) and selection combining (SC) techniques at the receiver. Next, the Monte Carlo simulation is performed to validate the mathematical analysis. The results show that the simulation curves match the mathematic expressions, which confirms the analysis section.

The Curious Case of Effective Isotropic Sensitivity

This paper establishes a solid mathematical model for Over the Air (OTA) test and characterization of 5G millimeter wave User Equipment (UE) in Compact Antenna Test Ranges (CATR). Special attention is paid to receiver characteristics and polarization mismatch problem which is encountered in spherical coverage tests. The received power of a UE with dual-polarized antenna system is derived and output SNR is calculated using Maximal Ratio Combining (MRC) principle. And finally, some of the misconceptions in 3rd Generation Partnership Project (3GPP) standards publications is addressed<br>

The Curious Case of Effective Isotropic Sensitivity

This paper establishes a solid mathematical model for Over the Air (OTA) test and characterization of 5G millimeter wave User Equipment (UE) in Compact Antenna Test Ranges (CATR). Special attention is paid to receiver characteristics and polarization mismatch problem which is encountered in spherical coverage tests. The received power of a UE with dual-polarized antenna system is derived and output SNR is calculated using Maximal Ratio Combining (MRC) principle. And finally, some of the misconceptions in 3rd Generation Partnership Project (3GPP) standards publications is addressed<br>

Performance Enhancement for Full-Duplex Relaying with Time-Switching-Based SWIPT in Wireless Sensors Networks

Full-duplex (FD) with simultaneous wireless information and power transfer (SWIPT) in wireless ad hoc networks has received increased attention as a technology for improving spectrum and energy efficiency. This paper studies the outage performance for a SWIPT-based decode-and-forward (DF) FD relaying network consisting of a single-antenna source S, a two-antenna relay R, and a multi-antenna destination D. Specifically, we propose four protocols, namely static time-switching factor with selection combining (STSF-SC), static time-switching factor with maximal ratio combining (STSF-MRC), optimal dynamic time-switching factor with selection combining (ODTSF-SC), and optimal dynamic time-switching factor with maximal ratio combining (ODTSF-MRC) to fully investigate the outage performance of the proposed system. In particular, the optimal time-switching factor from the ODTSF-SC and ODTSF-MRC methods is designed to maximize the total received data at the destination. In this context, we derive exact closed-formed expressions for all schemes in terms of the outage probability (OP). Finally, the Monte Carlo simulations are conducted to corroborate the theoretical analysis’s correctness and the proposed schemes’ effectiveness.

Performance enhancement techniques for variable spreading factor OFCDM systems

n this thesis we investigate the effect of Carrier Frequency Offset (CFO) on the performance of downlink Variable Spreading Factor (VSF) OFCDM systems when subcarrier grouping is used. An analytic expression of the SINR is derived for downlink VSF-OFCDM with CFO for the case of maximal ratio combining receiver. Numerical results show that, when the total spreading factor is fixed, the VSF-OFCDM system with higher frequency domain spreading factor is more sensitive to CFO than that with lower frequency domain spreading factor. Due to the adverse impact of the CFO on VSF-OFCDM systems, we propose a correction scheme based on the maximum likelihood principle. We derive the likelihood function for VSF-OFCDM system with CFO and use a gradient algorithm to estimate and minimize the effect of CFO in a tracking mode. Our results show that the BER performance in the low SNR environment can be improved significantly with few number of iterations for different spreading factors. We also propose a threshold-based group-adaptive modulation algorithm used with an adaptive subcarrier allocation technique for downlink VSF-OFCDM to increase the spectral efficiency for a given target BER. The proposed algorithm provides an increase in spectral efficiency without increasing the total transmit power for different spreading factors with and without coding.

Performance enhancement techniques for variable spreading factor OFCDM systems

n this thesis we investigate the effect of Carrier Frequency Offset (CFO) on the performance of downlink Variable Spreading Factor (VSF) OFCDM systems when subcarrier grouping is used. An analytic expression of the SINR is derived for downlink VSF-OFCDM with CFO for the case of maximal ratio combining receiver. Numerical results show that, when the total spreading factor is fixed, the VSF-OFCDM system with higher frequency domain spreading factor is more sensitive to CFO than that with lower frequency domain spreading factor. Due to the adverse impact of the CFO on VSF-OFCDM systems, we propose a correction scheme based on the maximum likelihood principle. We derive the likelihood function for VSF-OFCDM system with CFO and use a gradient algorithm to estimate and minimize the effect of CFO in a tracking mode. Our results show that the BER performance in the low SNR environment can be improved significantly with few number of iterations for different spreading factors. We also propose a threshold-based group-adaptive modulation algorithm used with an adaptive subcarrier allocation technique for downlink VSF-OFCDM to increase the spectral efficiency for a given target BER. The proposed algorithm provides an increase in spectral efficiency without increasing the total transmit power for different spreading factors with and without coding.

Performance Analysis Of VSF-OFCDM Femtocells

In this thesis, we analyze the performance of a variable spreading factor (VSF) OFCDM employed in femtocells, with OFDM used in macrocells in a hybrid heterogenous network. Orthogonal subcarriers are assigned to macro users and for femtocell users, non-contiguous subcarrier grouping is employed. We derive the analytic expression of the BER for uplink VSF-OFCDM femto and OFDM macro users for the case of maximal ratio combining receiver. We evaluate the performance of femto/macro users in VSF-OFCDM system through numerical and Monte Carlo simulation studies. Improvement in BER of the femtocell users is also noted. The relationship between the femto spreading factor and femto/macro BER is analyzed. We present, the relationship between the channel load and optimum spreading factor employed by femtocell users for the energy efficient performance of macro users. Femto wall penetration loss, that is the important parameter to evaluate the femto performance, is also taken into account. Also, effect of femto wall penetration on macro BER is evaluated for various spreading factors. Following our study, we find that interference-limited system favors increased time spreading especially when number of subcarriers is limited and noise-limited system favors increased frequency domain spreading. When large number of subcarriers are available, optimum spreading (from macro perspective) favors increased frequency domain spreading regardless of the femto-macro loads, or whether operating environment is noise or interference limited. Once the optimum spreading factor is determined, increase or decrease in the femto Eb/No does not matter. Also, femto wall penetration factor not only effects the femto BER directly, but also reduce the potential interference faced by macro user equipment (UEs). As a result macro BER is improved, but the choice of optimal spreading factor for macro UEs remain unaffected with the variation in femto wall penetration loss.