Highest Channel Gain Research Articles

Resource Optimization in H-CRN with Supervised Learning Based Spectrum Prediction Technique

Cognitive radio network shows potential means of granting intensifying demand for wireless applications. In this model, an efficient resource optimization scheme with Priority Pricing Technique (PPT) is proposed with supervised learning-based SVM to tackle limited spectrum availability and underutilization in Hybrid-Cognitive Radio Networks (H-CRN). H-CRN works under the principle of detection of PUs states (active/inactive). If spectrum sensing is made in favor of active PUs, then the CSI (Channel State Information) is estimated and works in underlay principle. If it is made in favor of inactive PUs, then the transmission is performed in overlay manner. In the proposed PPT the PUs and SUs with highest channel gain have the highest priority to use the spectral resources. SVM is used as an effective technique of spectrum sensing to provide higher probability of detection of PUs as soon as possible. The proposed method faces following challenges such as in order to enhance the CRN transmission performance, the PUs have to withstand more interference power and transmit power control is needed in improving the sum rates when the interference is severe in H-CRN. With Simulation outcomes, the assessment of the proposed (PPT) model among (Fixed Pricing Technique and Without Pricing Technique) indicates the proposed method's improved efficiency. The results reveal significant effectiveness in obtaining better classification accuracy with less computation complexity, increased throughput, spectral efficiency and energy efficiency of the network.

On the Performance of Noma Systems with Different User Grouping Strategies

This paper investigates several critical issues on the ergodic sum capacity and system outage performance of downlink non-orthogonal multiple access (NOMA) systems with different numbers of users per cluster sharing the same resource. The outcomes from this work suggest that NOMA systems with more users per cluster perform better under a low channel gain, while those with fewer users per cluster perform better under a high channel gain. It discloses a fact that a traditional NOMA system with a fixed user grouping scheme may not be a good choice to deal with complex channel conditions with diverse applications. To address the issue, this paper introduces a concept of mixed user grouping NOMA, which outperforms OMA and traditional NOMA significantly. The work in this paper lays a foundation for more further investigations on mixed user grouping NOMA systems.

Massive MIMO-NOMA Based MEC in Task Offloading for Delay Minimization

Mobile edge computing (MEC) has been considered a promising technology to reduce task offloading and computing delay by enabling mobile devices to offload their computation-intensive tasks. Non-orthogonal multiple access (NOMA) is regarded as a promising method of increasing spectrum efficiency, while Massive multiple-input multiple-output (MIMO) can support a larger number of users for simultaneous offloading. These two technologies can effectively facilitate offloading and further improve the performance of MEC systems. In this work, we propose a NOMA and Massive MIMO assisted MEC system for delay-sensitive applications. Our objective is to minimize the overall computing and transmission delay under users’ transmit power and MEC computing capability. Through the pairing scheme for Massive MIMO-NOMA, the users with the higher channel gain can offload all their data, while the users with the lower channel gain can offload a portion of their data to the MEC. Performance results are provided regarding to the sum data rate and overall system delay compared with the orthogonal multiple access (OMA)-MIMO based and Massive MIMO (M-MIMO) based MEC systems.

Capacity Maximization in Cell Free Massive MIMO Network with Access Point Selection Method

Background: Cell Free massive MIMO, containing a very large number of distributed access points (APs), which is a promising technology to provide high data rate, spectral efficiency (SE), and energy efficiency (EE). The system performance of cell-free M-MIMO is maximum when selecting optimal access points (AP) from the large number of APs. The linear precoding methods of zeroforcing (ZF) and minimum mean square error (MMSE) are utilized in this study because they are devoid of self-interference and so improve the system capacity. Objective: The objective of this study is to maximize the system data rate in a cell-free M-MIMO network. Method: To maximize the system data rate, the maximum channel gain-based Access Point Selection (MCGAPS), Distance based Access Point Selection (DAPS), and Random-Access Point Selection (RAPS) algorithms are used to pick access points (APs) in a cell-free M-MIMO network. Because the MCGAPS algorithm selects those APs with the highest channel gain, the system’s rate is improved. Result & Discussion: The DAPS algorithm is used to choose the closest APs to the user. The APs were randomly chosen using RAPS. Random user selection (RUS) algorithm schedules the same number of users. Conclusion: It is observed that the DAPS and RUS algorithms jointly improve the system rate significantly in cell-free massive MIMO system compared to the other proposed algorithms.

On the performance of ECF-based multi-threshold receiver in NOMA systems for vehicular communications with unknown impulsive noise

In this paper, we derive an analytical expression for the bit error probability of a multi-threshold (MTh) detector in the downlink three-user non-orthogonal multiple access (NOMA) based vehicular communication system with unknown noise. The MTh detector directly detects the signal of vehicle user with the highest channel gain without detecting the signals of weaker users and removing their effects. It is shown that the bit error probability performance of the MTh detector is superior to that of the successive interference cancellation (SIC) detector in a special case. Then, we propose a blind empirical characteristic function (ECF) based method to estimate the signal levels of vehicle users, required to implement the MTh detector, in unknown noise. Next, we derive an analytical expression for the variance of the proposed ECF-based estimator which is validated via computer simulations. It is shown that the ECF-based estimator is asymptotically unbiased and consistent. Furthermore, we obtain the normalized Cramér-Rao lower bound (NCRLB) for the estimators of signal levels which shows that the ECF-based estimator is almost efficient in small generalized signal-to-noise ratio (GSNR) values. Numerical results show that the ECF-based MTh detector outperforms the absolute median-based SIC detector in the mixture of Gaussian and α-stable noise.

Capacity and Fairness Maximization-Based Resource Allocation for Downlink NOMA Networks

Non-orthogonal multiple access (NOMA) is one of the leading technologies for 5G communication. User pairing (UP) and power allocation (PA) are the key controlling mechanisms for the optimization of the performance of NOMA systems. This paper presents a novel UP and PA (UPPA) technique for capacity and fairness maximization in NOMA called (CFM-UPPA). The impact of the power allocation coefficient and the ratio between the channel gains of the paired users on the sum-rate capacity and the fairness in NOMA is firstly investigated. Then, based on this investigation, the PA and UP algorithms of the CFM-UPPA technique are proposed. The power allocation coefficient of the proposed PA is formulated as an exponentially decaying function of the ratio between the channel gains of the paired users to maximize the capacity and the fairness, and its maximum value is adjusted to guarantee the successive interference cancellation (SIC) constraints. The proposed UP is based on selecting the user that has the highest channel gain per subcarrier as the strong user to maximize the capacity and selecting the user that has the closest lower channel gain to the strong user’s channel gain as the weak user to improve the fairness and capacity. The performance evaluation of the proposed CFM-UPPA technique in terms of capacity, fairness, and outage probability demonstrates that its performance significantly outperforms that of the orthogonal multiple access (OMA) system and that of the NOMA system with random UP. Also, the simulation results demonstrate the efficiency of the proposed PA in improving the performance of other UP algorithms, such as the random UP algorithm.

1-bit feedback-based beamforming scheme for an uplink FSO-NOMA system with SIC errors.

In this paper, we study the effect of a beamforming scheme for a multiple-input-single-output (MISO) uplink free-space optical (FSO) communication system with nonorthogonal multiple access (NOMA) over negative exponential fading channels. 1-bit feedback about the channel state information is required by the proposed beamforming scheme. The feedback is considered to be error-free in this work; however, an error due to successive interference cancellation (SIC) is taken into consideration. It is inferred by bit error rate (BER) analysis that a higher weight given to the channel with higher channel gain and a slightly lower weight given to the channel with lower channel gain gives the best performance as compared to all arbitrary schemes in a 2×1 FSO-NOMA system. Further, it is also analytically shown that using a 1-bit feedback-based beamforming scheme in an FSO-NOMA system suppresses the effect of SIC error; hence the BER performance of both the transmitters (TXs) is the same, which is not the case for a conventional NOMA scheme. A simplified asymptotic upper bound of BER of the proposed scheme is obtained by using the order statistics, and an optimized beamforming vector is found by minimizing this upper bound. It is then established analytically as well as through simulations that the beamforming vector is independent of average signal-to-noise ratio as long as the two channels remain independent and identically distributed. We further compare the proposed scheme with an FSO-NOMA system without feedback and beamforming and with single-input single-output FSO system using 4-ary pulse amplitude modulated signaling. It is shown by simulations that the proposed scheme outperforms both of them and has a huge coding gain advantage. A numerical analysis of this scheme is also provided for gamma-gamma (GG) and log-normal (LN) turbulence regime. The proposed scheme is extended to 3×1 and 4×1 MISO systems, and it is revealed that the performance of the system degrades as the number of TX increases.

Location-Aware Transmission for Two-Cell Wireless Networks With Caching

A novel downlink transmission selection scheme based on the locations of users for network coded cache-enabled, Multiple-Input Multiple-Output (MIMO) systems is proposed in this paper. Caches are available at both base stations (BSs) and mobile terminals (MTs) and network coding is employed in order to reduce power consumption. We compare the analysis of the proposed scheme with a simple direct transmission scheme in terms of achievable sum rate and outage probability. It is shown that the proposed scheme is preferred for high transmit signal-to-noise ratio (SNR) and/or high cross-link channel gain ratio scenarios, while the simple direct transmission scheme is better for low SNR and/or low cross-link channel gain ratio. Motivated by this analytical results, we present a selection algorithm for location-aware transmission scheme for two-cell networks. Numerical results confirm our theoretical analysis.

Effective Secrecy Rate for a Downlink NOMA Network

In this paper, a novel approach is introduced to study the achievable delay-guaranteed secrecy rate, by introducing the concept of the effective secrecy rate (ESR). This study focuses on the downlink of a non-orthogonal multiple access (NOMA) network with one base station, multiple single-antenna NOMA users and an eavesdropper. Two possible eavesdropping scenarios are considered: 1) an internal, unknown, eavesdropper in a purely antagonistic network; and 2) an external eavesdropper in a network with trustworthy peers. For a purely antagonistic network with an internal eavesdropper, the only receiver with a guaranteed positive ESR is the one with the highest channel gain. A closed-form expression is obtained for the ESR at high signal-to-noise ratio (SNR) values, showing that the strongest user’s ESR in the high SNR regime approaches a constant value irrespective of the power coefficients. Furthermore, it is shown the strongest user can achieve higher ESR if it has a distinctive advantage in terms of channel gain with respect to the second strongest user. For a trustworthy NOMA network with an external eavesdropper, a lower bound and an upper bound on the ESR are proposed and investigated for an arbitrary legitimate user. For the lower bound, a closed-form expression is derived in the high SNR regime. For the upper bound, the analysis shows that if the external eavesdropper cannot attain any channel state information (CSI), the legitimate NOMA user at high SNRs can always achieve positive ESR, and the value of it depends on the power coefficients. Simulation results numerically validate the accuracy of the derived closed-form expressions and verify the analytical results given in the theorems and lemmas.

A Green Coordinated Multi-Cell NOMA System With Fuzzy Logic Based Multi-Criterion User Mode Selection and Resource Allocation

We consider a multi-cell non-orthogonal multiple access (NOMA) system with coordinated base stations and investigate its downlink user coordination mode selection and resource allocation to green the system while maintaining high spectral efficiency, in the presence of inter-cell interference. To the best of our knowledge, this is the first work to consider multiple criteria in user coordination mode selection for coordinated NOMA systems, and a fuzzy logic (FL) based approach is proposed to balance among multiple criteria to achieve higher robustness against the combined effect of shadowing, fading and inter-cell interference, compared to the previous single-criterion-based user coordination mode selection methods. This is also the first known effort to investigate multi-subchannel resource allocation for coordinated NOMA where the previous work on coordinated orthogonal multiple access is not applicable. Two resource allocation algorithms are proposed: first, a serving channel gain based subchannel allocation (SCG-SA) algorithm, based on the theoretical proof that the total transmission power is mono-decreasing with respect to the SCG of the non-coordinated user in each cell with the highest channel gain on the shared subchannel; second, a low-complexity FL user ranking order based joint resource allocation algorithm, which requires no separate user ranking process in subchannel allocation, thanks to the FL ranking list generated from user coordination mode selection. Also, the effects of imperfect channel state information and successive interference cancellation are considered. Numerical results show that the proposed multi-criterion based schemes significantly outperform the previous schemes based on single-criterion user coordination mode selection, in terms of transmission power and energy efficiency, contributing to a greener system.

Distribution of the Residual Self-Interference Power in In-Band Full-Duplex Wireless Systems

This paper derives the distribution of the residual self-interference (SI) power in an analog post-mixer canceler adopted in a wireless in-band full-duplex communication system. We focus on the amount of uncanceled SI power due to SI channel estimation errors. Closed form expressions are provided for the distribution of the residual SI power when Rician and Rayleigh fading SI channels are considered. Moreover, the distribution of the residual SI power is derived for low and high channel gain dynamics, by considering the cases when the SI channel gain is time-invariant and time-variant. While for time-invariant channels the residual SI power is exponentially distributed, for time-variant channels the exponential distribution is not a valid assumption. Instead, the distribution of the residual SI power can be approximated by a product distribution. Several Monte Carlo simulation results show the influence of the channel dynamics on the distribution of the residual SI power. Finally, the accuracy of the theoretical approach is assessed through the comparison of numerical and simulated results, which confirm its effectiveness.

Worst Cell Based Pilot Allocation in Massive MIMO Systems

Massive multiple-input multiple-output (MIMO) has been viewed as an advanced technique in future 5G networks. Conventional massive MIMO systems consist of cellular base stations (BS) equipped with a very large number of antennas to simultaneously serve many single-antenna users. Unfortunately, massive MIMO system’s performance is limited by pilot contamination (PC) problem. Conventionally, all users in massive MIMO systems are assigned pilot randomly. In this paper, we propose a pilot allocation algorithm based on a cell with the worst channel quality (WCPA) algorithm to improve the uplink achievable sum rate of the system. Specifically, WCPA exploits the large-scale coefficients of fading channels between the BSs and users. According to the number of available orthogonal pilot sequences, we choose some of the highest inter-cell interfering users and assign each of them a unique pilot sequence if the number of pilot sequences is more than the number of users in a cell. Next, we choose a target cell with the worst channel quality, and gather the highest channel gain user in the target cell and the lowest interfering user in the other cells in the same group in a sequential way by assigning them the same pilot sequence. The simulation results show the outperformance of the proposed algorithm compared to the conventional pilot allocation schemes.

Joint non-orthogonal multiple access (NOMA) & Walsh-Hadamard transform: Enhancing the receiver performance

Non-orthogonal multiple access (NOMA) is a new access method to achieve high performance gains in terms of capacity and throughput, so it is currently under consideration as one of the candidates for fifth generation (5G) technologies. NOMA utilizes power domain in order to superimpose signals of multiple users in a single transmitted signal. This creates a lot of interference at the receive side. Although the use of successive interference cancellation (SIC) technique reduces the interference, but to further improve the receiver performance, in this paper, we have proposed a joint Walsh-Hadamard transform (WHT) and NOMA approach for achieving better performance gains than the conventional NOMA. WHT is a well-known code used in communication systems and is used as an orthogonal variable spreading factor (OVSF) in communication systems. Application of WHT to NOMA results in low bit error rate (BER) and high throughput performance for both low and high channel gain users. Further, it also reduces peak to average power ratio (PAPR) of the user signal. The results are discussed in terms of comparison between the conventional NOMA and the proposed technique, which shows that it offers high performance gains in terms of low BER at different SNR levels, reduced PAPR, high user throughput performance and better spectral efficiency.

Performance Analysis of Buffer-Aided Priority-Based Max-Link Relay Selection in DF Cooperative Networks

In this paper, we propose a new relaying scheme, referred to as priority-based max-link relay selection, for buffer-aided decode-and-forward cooperative networks. We give the first priority to the relay buffers having status full, the second priority to the relay buffers having status empty, and the third priority to the relay buffers having status neither full nor empty. The best relay node is selected corresponding to the link having the highest channel gain among the links within a priority class. By adopting a Markov chain approach to analyze the state transition matrix that models the evolution of the buffers status, we derive analytical expressions for the outage probability and the average bit error rate. Analytical expressions for the steady-state probability vector are also obtained, and through these expressions, it is shown that states with the same probabilities can be grouped, thus reducing the size of the state transition matrix. We propose a general state-grouping-based method to obtain the reduced state transition matrix, which in turn reduces the computational complexity in obtaining the steady-state distribution. Our analytical and simulation results demonstrate that the proposed relaying scheme has better performance gain over the conventional max-link scheme.

Energy Efficiency of SISO and MISO in Visible Light Communication Systems

In this paper, we focus on maximizing energy efficiency problems for visible light communication (VLC) systems. Specifically, for single-input-single-output (SISO) VLC systems, we first systematically analyze the power consumption along the signal processing path and propose an explicit energy efficiency expression, which is a quasi-concave function of the power consumption at the power amplifier (PA). Then, we investigate the energy efficiency maximization problem under both the power constraint and rate requirement. By exploiting Dinkelbach's algorithm and Lagrangian method, the optimal power consumption of PA is obtained in a closed form. Numerical results are presented to evaluate the performance of the proposed optimal solution. Moreover, we analyze the power consumption of multi-LED and study the energy efficiency maximization problem for the multi-input-single-output (MISO) VLC system, under both per LED's power constraint and rate constraint. This problem is shown to be nonconvex. With leveraging Dinkelbach's algorithm, the original problem can be reformulated as a convex problem, and the optimal solution can be efficiently obtained by the interior point algorithm. Meanwhile, numerical results are presented to show the performance of the proposed optimal solutions. In particular, it is shown that the power is preferentially allocated to the subchannels with higher channel gain in the MISO VLC system.

Performance Comparison with Different Antenna Properties in Time Reversal Ultra-Wideband Communications for Sensor System Applications.

The complexity reduction of receivers in ultrawideband (UWB) communication when time reversal (TR) technique is applied makes it suitable for low-cost and low-power sensor systems. Larger antenna dispersion can generally lead to a less stable phase center and will increase the interference in UWB communications based on pulse radio, whereas a higher antenna gain will result in higher channel gain and further larger channel capacity. To find out the trade-off between antenna gain and dispersion, we performed the channel measurements using different antennas in a dense multipath environment and established the distribution of channel capacities based on the measured channel responses. The results show that the capacity loss caused by antenna dispersion cannot be compensated by antenna gain with line-of-sight transmission to some extent, the effect of phase center on the communication system is negligible, and antennas with smaller time dispersion will have a better energy focusing property and anti-interference performance in TR systems.

Mobile Robot Path Planners With Memory for Mobility Diversity Algorithms

Mobile robots (MRs) using wireless communications often experience small-scale fading so that the wireless channel gain can be low. If the channel gain is poor (due to fading), the robot can move (a small distance) to another location to improve the channel gain and so compensate for fading. Techniques using this principle are called mobility diversity algorithms (MDAs). MDAs intelligently explore a number of points to find a location with high channel gain while using little mechanical energy during the exploration. Until now, the location of these points has been predetermined. In this paper, we show how we can adapt their positions by using channel predictors. Our results show that MDAs, which adapt the location of those points, can in fact outperform (in terms of the channel gain obtained and mechanical energy used) the MDAs that use predetermined locations for those points. These results will significantly improve the performance of the MDAs and consequently allow MRs to mitigate poor wireless channel conditions in an energy-efficient manner.

Optimal transmission power determination to increase energy efficiency of large-scale MIMO antenna systems

Large-scale (LS) MIMO antenna systems use excessive amount of TX antennas and serve limited number of users to make very high channel gain, and it is obvious that the channel gain increases spectral efficiency of the system. The transmission power of LS-MIMO systems also can be reduced from the increment of channel gain to increase energy efficiency (EE). In this situation, a determination of transmission power which is reduced from total available transmission power can be an important scheme to achieve high EE. This paper proposes a determination scheme of the EE optimum transmission power for LS-MIMO systems. The approximated optimum transmission power is derived analytically as a closed-form function based on various parameters, such as number of TX antennas, number of users, system bandwidth, interference, and so on. Using the closed-form function with the measurable parameters, we can easily get the optimum EE transmission power in real-time. The effectiveness of proposed scheme is validated with numerical simulations. According to the results, the proposed scheme can significantly increase the EE with fairly small loss of channel capacity, compared with ordinary LS-MIMO systems.

Performance Evaluation of User Selection Protocols in Random Networks with Energy Harvesting and Hardware Impairments

In this paper, we evaluate performances of various user selection protocols under impact of hardware impairments. In the considered protocols, a Base Station (BS) selects one of available Users (US) to serve, while the remaining USs harvest the energy from the Radio Frequency (RF) transmitted by the BS. We assume that all of the US randomly appear around the BS. In the Random Selection Protocol (RAN), the BS randomly selects a US to transmit the data. In the second proposed protocol, named Minimum Distance Protocol (MIND), the US that is nearest to the BS will be chosen. In the Optimal Selection Protocol (OPT), the US providing the highest channel gain between itself and the BS will be served. For performance evaluation, we derive exact and asymptotic closed-form expressions of average Outage Probability (OP) over Rayleigh fading channels. We also consider average harvested energy per a US. Finally, Monte-Carlo simulations are then performed to verify the theoretical results.

A Power-Optimized Cooperative MAC Protocol for Lifetime Extension in Wireless Sensor Networks.

In wireless sensor networks, in order to satisfy the requirement of long working time of energy-limited nodes, we need to design an energy-efficient and lifetime-extended medium access control (MAC) protocol. In this paper, a node cooperation mechanism that one or multiple nodes with higher channel gain and sufficient residual energy help a sender relay its data packets to its recipient is employed to achieve this objective. We first propose a transmission power optimization algorithm to prolong network lifetime by optimizing the transmission powers of the sender and its cooperative nodes to maximize their minimum residual energy after their data packet transmissions. Based on it, we propose a corresponding power-optimized cooperative MAC protocol. A cooperative node contention mechanism is designed to ensure that the sender can effectively select a group of cooperative nodes with the lowest energy consumption and the best channel quality for cooperative transmissions, thus further improving the energy efficiency. Simulation results show that compared to typical MAC protocol with direct transmissions and energy-efficient cooperative MAC protocol, the proposed cooperative MAC protocol can efficiently improve the energy efficiency and extend the network lifetime.