User Signal-to-interference-plus-noise Ratio Research Articles

Optimal Transmit Power and Channel-Information Bit Allocation With Zeroforcing Beamforming in MIMO-NOMA and MIMO-OMA Downlinks

In downlink, a base station (BS) with multiple transmit antennas applies zeroforcing beamforming to transmit to single-antenna mobile users in a cell. We propose the schemes that optimize transmit power and the number of bits for channel direction information (CDI) for all users to achieve the max-min signal-to-interference plus noise ratio (SINR) fairness. The optimal allocation can be obtained by a geometric program for both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA). For NOMA, 2 users with highly correlated channels are paired and share the same transmit beamforming. In some small total-CDI rate regimes, we show that NOMA can outperform OMA by as much as 3 dB. The performance gain over OMA increases when the correlation-coefficient threshold for user pairing is set higher. To reduce computational complexity, we propose to allocate transmit power and CDI rate to groups of multiple users instead of individual users. The user grouping scheme is based on K-means over the user SINR. We also propose a progressive filling scheme that performs close to the optimum, but can reduce the computation time by almost 3 orders of magnitude in some numerical examples.

IRS-Assisted Full Duplex Systems Over Rician and Nakagami Fading Channels

Intelligent reflecting surface (IRS) has been deemed as an energy and spectral-efficient technology, that can potentially enhance network coverage and transmission reliability, with minimum impact on transceivers' complexity. Motivated by this, we develop a comprehensive analysis on the performance of integrating IRS into full-duplex (FD) cellular or Internet of Things (IoT) networks in both realistic Rician and Nakagami fadings. Firstly, in the context of reciprocal channels in Rician fadings, we derive the closed-form approximations of the users' outage probability (OP) and ergodic capacity (EC), under the non-central Chi-square distribution assumption on the signal-to-interference-plus-noise ratio (SINR). Further following by the Gamma distribution assumption on the SINR, we derive the cumulative distribution function (CDF) expression of the user's SINR, which is then leveraged to obtain simple yet effective closed-form expressions in terms of OP and EC. Subsequently, in Nakagami fading scenarios with the reciprocal and non-reciprocal channels, the closed forms of both users' OP and EC are obtained. Finally, the correctness of all the theoretical expressions is verified through substantial Monte Carlo simulations. The results indicate that the OP and EC deduced from Gamma distribution exhibit the fairly precise results for the arbitrary number of IRS elements, especially in Nakagami fadings.

Linear Precoding for Space-Time Line Code-Based Multicast Systems

In this article, a linear precoding weight vector is designed to enhance the minimum signal-to-interference plus noise ratio (SINR) of a space-time line code (STLC)-based multicast users. To solve the intractable minimum SINR maximization problem, the optimal weight vector for each STLC user is derived, and then, the individual optimal weight vectors are linearly combined. The designed linear precoding vector improves the minimum and average SINR of the multicast users as verified by numerical results. Numerical results also verify that the STLC-based multicast is a promising scheme, especially, if a transmitter has a large number of transmit antennas and the additive noises are severe at the users.

A novel pilot power allocation method based on energy efficiency maximization in massive MIMO systems for future generation wireless technologies

SummaryIn this paper, we propose a novel pilot power allocation method that focuses on the maximization of the energy efficiency. The core algorithm of this method, which is a dynamic approach that takes into account signal‐to‐interference‐plus‐noise ratio (SINR), is called pilot power allocation polarizing SINRs (PS‐PPA). The aim is to maximize the energy efficiency of the system along with the proposed pilot power allocation method using this algorithm in a multi‐cell multi‐user massive multiple‐input multiple‐output (MIMO) system. The algorithm determines difference between average SINR per cell and SINRs of users individually, during the scan of the whole cells sequentially. Therefore, it always updates the allocation for the latest SINR of users in power updates to improve the energy efficiency of the system. In power updates, PS‐PPA calculates weights using an exponential function of the SINR difference. This weighting function is defined for each real number, so it can always result in a specific number. In addition, the weighting function is performed in the [ ] range where the power values are predefined. The energy efficiency of the system is measured in a number of simulations by calculating the average SINR per cell. Furthermore, all these performance results are obtained for equal pilot power allocation (EPPA) and water‐filling pilot power allocation (WF‐PPA) schemes. As a result of simulation results, proposed pilot power allocation method has proven to be more superior than EPPA and WF‐PPA methods.

Max–min fair robust beamforming design for underlay device‐to‐device communications in cellular networks

SummaryThis paper investigates the robust downlink beamforming designs based on max–min fairness and base station (BS) power consumption constraint for device‐to‐device (D2D) communications underlaying cellular network, under the assumption of imperfect channel state information (CSI) at the BS. Our objective is to maximize the minimum signal‐to‐interference‐plus‐noise ratio (SINR) or non‐outage probability of users while guaranteeing that the consumed power at the BS is less than a threshold. In particular, three max–min fairness scenarios are considered. In the first scenario, the worst‐case SINR of cellular users (CUs) is maximized where the D2D SINR is guaranteed to be above a specified predetermined threshold. In the second scenario, we extend the first scenario and maximized D2D SINR while maximizing CUs' SINR. In these two scenarios, it is assumed that the errors are upper bounded in their Frobenius norms. In the third scenario, the minimum non‐outage probability of users is maximized, while a probabilistic model is considered for the uncertainty of channel covariance matrices. Although such optimization problems are not convex, the semidefinite relaxation (SDR) approach is used to obtain the optimal beamforming matrix, which always complies the rank‐one constraint. Simulation results show that significant improvement in terms of minimum SINR of CUs, the minimum non‐outage probability of CUs, and the probability of feasibility and the fairness index can be achieved with our proposed algorithms in comparison with other beamforming schemes.

Reconfigurable Intelligent Surface Assisted Two–Way Communications: Performance Analysis and Optimization

In this paper, we investigate the two-way communication between two users assisted by a reconfigurable intelligent surface (RIS). The scheme that two users communicate simultaneously over Rayleigh fading channels is considered. The channels between the two users and RIS can either be reciprocal or non-reciprocal. For reciprocal channels, we determine the optimal phases at the RIS to maximize the signal-to-interference-plus-noise ratio (SINR). We then derive exact closed-form expressions for the outage probability and spectral efficiency for single-element RIS. By capitalizing the insights obtained from the single-element analysis, we introduce a gamma approximation to model the product of Rayleigh random variables which is useful for the evaluation of the performance metrics in multiple-element RIS. Asymptotic analysis shows that the outage decreases at (log(ρ)/ρ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sup> rate where L is the number of elements, whereas the spectral efficiency increases at log(ρ) rate at large average SINR p. For non-reciprocal channels, the minimum user SINR is targeted to be maximized. For single-element RIS, closed-form solution is derived whereas for multiple-element RIS the problem turns out to be non-convex. The latter one is solved through semidefinite programming relaxation and a proposed greedy-iterative method, which can achieve higher performance and lower computational complexity, respectively.

Secrecy Rate Analysis of Satellite Communications With Frequency Domain NOMA

Due to the inherent broadcasting nature and broad coverage of satellite, satellite communications are well known to be vulnerable to security threats. Since the distance difference from satellite to terrestrial terminals is negligible, the channels of different users are similar, posing a challenge of achieving secure satellite downlink transmission in the presence of eavesdroppers (Eves). In this paper, we consider satellite communications in areas without terrestrial networks converge, and investigate the physical layer security in the satellite downlink. To achieve a positive secrecy rate, a frequency domain non-orthogonal multiple access (FD-NOMA) scheme and an according multiuser cooperative scheme are proposed. Particularly, by adopting the FD-NOMA, the spectrum efficiency can be improved at the cost of raising inter-user interference (IUI), and the inherent IUI is elegantly leveraged to suppress the signal-to-interference-plus-noise ratio (SINR) of Eves while the intended SINR of legitimate users can be enhanced by the cooperative scheme. The secrecy rate of satellite communications with FD-NOMA is analyzed, and a tight lower bound is derived, which is validated via numerical results. In addition, the secrecy rate is found to be affected by the level of spectral overlapping, and there exists an optimal spectral overlapping factor (SOF) which can maximize the secrecy rate.

Resource Allocation Scheme for Interference and Throughput Performance Improvement in LTE Femtocell Networks

Femtocells are one of the key enabling technologies for indoorcoverage extension and system capacity enhancement in LongTerm Evolution (LTE) cellular system. Cross-tier interferencebetween femtocells and macrocells is a great challenge. Inthis paper, a resource allocation scheme is proposed tominimize the interference and enhance the LTE femtocellthroughput. The fraction frequency reuse (FFR) scheme isconsidered for LTE cellular system. The proposed scheme isbased on using small number of resource blocks (RBs) whichefficiently selected according to their signal to interferenceplus noise ratio (SINR). Simulation results demonstrate thatthe proposed scheme increases the femtocell throughputusing small number of allocated resource blocks (RBs) andincreases SINR of femtocells users. Also, the proposedscheme significantly outperforms the conventional randomallocation scheme in terms of the achieved throughput andSINR values when the number of allocated RBs is only 20% ofthe total number of the available RBs.

QoS-Based Binary Signature Design for Secure CDMA Systems

Physical layer security, aiming at preventing the confidential information from eavesdroppers, has drawn significant attentions in recent years. In this paper, we address the problem of securing downlink single-user and multiuser transmissions in code division multiple-access systems. Particularly, we propose a novel binary signature design method to minimize the reception of the confidential messages at the eavesdropper. The popular signal-to-interference-plus-noise ratio (SINR) metric is adopted as a pragmatic security performance measurement. Specifically, for securing the single-user transmission, we aim to design a binary signature to minimize the eavesdropper's SINR while maintain the legitimate user's SINR at a desired level. However, the optimal exhaustive searching method has complexity growing exponentially with the signature length. Thus, we propose two suboptimal low-complexity semi-definite relaxation (SDR)-based and Rayleigh-quotient-based binary signature design algorithms, which have near optimal performance with much lower computational complexity. Furthermore, we extend the findings in the single-user case to multiuser scenario. Particularly, we propose to design a set of quasi-orthogonal signatures based on eavesdropping channel and select the conditionally optimal binary signature for each user iteratively until convergence. Simulation studies confirm our analytical performance predictions and demonstrate the benefits of the proposed secure signature design algorithms.

Multistream Multiuser Coordinated Beamforming for Cellular Networks With Multiple Receive Antennas

Multicell coordinated beamforming (CB) can mitigate intercell interference (ICI). However, existing work on CB focuses on systems that maximize overall throughput. This paper considers CB for systems with multiple receive antennas and further extends the CB to multiuser and multistream transmission. We consider fairness and pay close attention to cell-edge users. CB that maximizes the harmonic sum of signal-to-interference-plus-noise ratio (SINR) can be derived into a low-complexity algorithm that favors cell-edge users. Two iterative algorithms are developed. From the simulation results, the proposed algorithms can provide a better fifth-percentile user throughput compared with the CB algorithms minimizing mean square error, maximizing uplink SINR, and maximizing weighted sum rate. Furthermore, the computational complexity of the proposed algorithms is significantly lower than that maximizing the minimum SINR of users.

Performance Analysis of TDD Reciprocity Calibration for Massive MU-MIMO Systems With ZF Beamforming

This study analyzes a two-way signaling method for time division duplex reciprocity calibration (RC) in multiuser beamforming systems. The system model of RC is established, and the estimation error of the RC coefficient is derived. The effect of this error is examined in terms of the user signal-to-interference-plus-noise ratio (SINR) and capacity. Results reveal the relationship between the user SINR and RC errors as well as the number of antennas and users. Moreover, the findings show that the colocated antenna array is less sensitive to calibration errors than the case of distributed antennas even if the calibration signal-to-noise ratio (SNR) is identical. The interference resulting from imperfect calibration becomes the determinant that constrains the performance, particularly when a high user SNR is required.

멀티모드 단말기를 위한 셀 경계 지역에서의 SINR 기반 사용자 선택 방법

We consider a cell edge environment. In cell edge, a user interfered by signal which is generated by a base stations not including the user. In cell edge environment, that is, there are inter cell interference (ICI) as well as multi user interference (MUI). Coordinated multi-point transmission (CoMP) is a technique which mitigates ICI between base stations. In CoMP, therefore, base stations can coordinate with each other by sharing user state information (CSI) in order to mitigate ICI. To improve sum rate performance in CoMP, each base station should generate optimal user group and transmit data to users selected in the optimal user group. In this paper, we propose a user selection algorithm in CoMP. The proposed method use signal to interference plus noise ratio (SINR) as criterion of selecting users. Because base station can`t measure accurate SINR of users, in this paper, we estimate SINR equation considering ICI as well as MUI. Also, we propose a user selection algorithm based on the estimated SINR. Through MATAL simulation, we verify that the proposed method improves the system sum rate by an average of 1.5 ~ 3 bps/Hz compared to the conventional method.

Fractional Frequency Reuse in DCO-OFDM-Based Optical Attocell Networks

In this paper a fractional frequency reuse (FFR) technique is considered in a direct-current optical orthogonal frequency-division multiplexing-based optical attocell network. An optical attocell network is proposed as a special type of visible light communication system that has the complete function of a cellular network. The cellular network is composed of many cells of extremely small size—the optical attocells. Two FFR schemes, strict fractional frequency reuse and soft frequency reuse, are considered. The signal-to-interference-plus-noise ratio (SINR) statistics and the spectral efficiency of the optical cellular system with FFR are analyzed. The performance of the systems with full frequency reuse and FFR is evaluated and compared. The results show that the FFR scheme can effectively achieve interference mitigation in an optical attocell network. The cell edge user SINR and spectral efficiency are significantly improved. Additionally, FFR provides improvements in average spectral efficiency. The effects of important parameters such as cell radius are also studied.

Base station beamforming technique using multiple signal‐to‐interference plus noise ratio balancing criteria

The authors propose a coordinated multi-cell beamforming technique for signal-to-interference plus noise ratio (SINR) balancing under multiple base station power constraints. Instead of balancing SINR of all users in all cells to the same level, the authors’ propose a new approach to balance SINR of users in various cells to different maximum possible values. This has the ability to allow users in cells with relatively more transmit power or better channel condition to achieve a higher balanced SINR than that achieved by users in the worst-case cells. This multi-level SINR balancing problem is solved using SINR constraints based SINR balancing criterion and subgradient method. The simulation results support the optimality of the results through comparison with semi-definite programming-based optimisation.

User selection for SINR-based uplink multiuser MIMO systems

To avoid the exhaustive search, we propose a fast user selection algorithm for Signal-to-Interference-plus-Noise-Ratio (SINR)-based multiuser Multiple-Input Multiple-Output (MIMO) systems with Alamouti Space-Time Block Code (STBC) transmit scheme. A locally optimal selection criterion is proposed at first. Then, the incremental selection approach is applied, which selects one among the residual available users to maximize the minimum user SINR step by step. Simulation results show that the fast algorithm gains over 90% of the diversity benefit achieved by the exhaustive search selection, and that the fast algorithm has much lower computational burden than the exhaustive search one, for the scenario where the number of all the available users is much greater than that of the selected users.

Large-System-Based Performance Analysis and Design of Multiuser Cooperative Networks

In this paper, the performance of the cooperative multiuser direct-sequence code-division multiple-access (DS-CDMA) system is analyzed in the asymptotic regime where both the spreading codes and the number of users grow unboundedly large with the same ratio. Assuming that each terminal is paired with another user which, in addition to transmitting its own data, estimates and relay the information transmitted from its partner, a simple approximate signal-to-interference-plus-noise ratio (SINR) expression is derived that is independent from the spreading codes and explicitly accounts for the effects of the multiple-access interference (MAI) and the relay noise. The so-obtained SINR expression is then computed based entirely on the available local information and without any knowledge about the interfering users. The results obtained above are then used to optimally design the cooperative system. In particular, it is shown how the amount of cooperation between each collaborating pair can be adjusted to simultaneously achieve a preassigned target SINR for both users. Based on the local information, the globally optimal amount of the relay power is obtained that maximizes the achieved SINR at the access point. It is shown that increasing the relay power does not necessarily result in improving the quality of reception at the access point and, to maximize each user's SINR, its relay power should be carefully adjusted based on the environmental parameters such as the interpartner channel link and the powers of MAI and the relay noise. The connection between the cooperative and the conventional multiuser systems is also studied and simulations are used to demonstrate the validity of the analytical results.