Signal-to-interference Plus Noise Power Ratio Research Articles

Adaptive interference mitigation space‐time array reconfiguration by joint selection of antenna and delay tap

AbstractSpace‐time adaptive processing (STAP) array has found extensive use in the global navigation satellite system for interference suppression. Nevertheless, the conventional space‐time array necessitates multiple antennas and time delay taps, resulting in a heavy burden on both hardware and computation resources. Thus, lowering the cost and complexity of STAP becomes a considerable problem demanding prompt solutions. This work designs a space‐time array reconfiguration scheme based on the joint selection strategy of the antenna and delay tap to address this problem. The reconstructed array can induce a high signal to interference plus noise power ratio (SINR) when using fewer antennas and delay taps. The space‐time correlation coefficient (STCC) is first presented to manifest the influence of reconfiguration on output SINR. Then, we formulate the space‐time array reconfiguration mathematical model, aiming to minimise STCC. Two reconfiguration methods are provided to solve the optimal array configuration of antennas and delay taps that can reach the minimum STCC and maximum SINR. The optimal antenna‐delay tap pairs are finally selected to comprise the reconstructed array. Substantial simulation experiments verify that the presented scheme and strategy are effective and reliable in space‐time array reconfiguration.

Performance analysis of subspace projection algorithm with respect to projection length for GNSS jamming mitigation

Non-stationary jamming signals broadcast by jammers severely threaten the reliability of global navigation satellite systems (GNSS). The instantaneous frequency (IF) based subspace projection algorithm is an attractive solution for GNSS jamming mitigation. However, its theoretical performance analysis is rare and not well discussed. To better apply subspace projection, we develop the theoretical post-correlation signal-to-interference-plus-noise power ratio (SINR) of receivers incorporating subspace projection to facilitate performance analysis. Different from existing work, this paper assumes that IF errors are independent and identically distributed instead of instantaneous phase errors, which is more reasonable. Numerical simulation results validate the derived theoretical SINR. The results show that the performance of subspace projection highly depends on the selection of projection length. Subspace projection with a well-designed projection length can perform much better than a conventional long projection length. Utilizing the theoretical SINR, the jamming mitigation performance of subspace projection with different projection lengths can be quickly evaluated, which provides an important theoretical guidance for the application of the algorithm.

Intelligent-Reflecting-Surface-Assisted Multicasting with Joint Beamforming and Phase Adjustment

In this paper, a set of transmission schemes are proposed for the delivery of multicast (MC) signals, in which an intelligent reflecting surface (IRS) assists the transmission from an access point (AP) to a set of multicast users. It is known that the large number of IRS reflecting elements have the potential to improve the transmission efficiency by forming an artificial signal path with strong channel gain. However, the joint optimization of the AP beamformer and the phases of the IRS reflecting elements is challenging due to the non-convex nature of the phase elements as well as the high computational complexity required for a large number of elements. A set composed of two AP beamformer schemes and a set with two IRS phase adjustment algorithms are proposed, which are sub-optimal but less computationally demanding. A semi-definite relaxation (SDR)-based scheme is considered along with a least squares (LS) based one for the AP beamformer design. For the IRS phase adjustment, an LS based optimization and a grouping method for the phase elements are suggested. From these two sets, four combinations of overall optimization can be built, and their performances can be compared with their merits and weaknesses revealed. The signal-to-interference-plus-noise power ratio (SINR) performance results are verified in various parameter conditions by simulation.

Random Beam-Based Non-Orthogonal Multiple Access for Low Latency K-User MISO Broadcast Channels.

In this paper, we propose random beam-based non-orthogonal multiple access (NOMA) for low latency multiple-input single-output (MISO) broadcast channels, where there is a target signal-to-interference-plus-noise power ratio (SINR) for each user. In our system model, there is a multi-antenna transmitter with its own single antenna users, and the transmitter selects and serves some of them. For low latency, the transmitter exploits random beams, which can reduce the feedback overhead for the channel acquisition, and each beam can support more than a single user with NOMA. In our proposed random beam-based NOMA, each user feeds a selected beam index, the corresponding SINR, and the channel gain, so it feeds one more scalar value compared to the conventional random beamforming. By allocating the same powers across the beams, the transmitter independently selects NOMA users for each beam, so it can also reduce the computational complexity. We optimize our proposed scheme finding the optimal user grouping and the optimal power allocation. The numerical results show that our proposed scheme outperforms the conventional random beamforming by supporting more users for each beam.

Dimensionality reduction of interference subspace for multiuser massive MIMO null-space expansion

This paper proposes a dimensionality reduction of interference subspace to improve the interference suppression capability of null-space expansion (NSE) for multiuser massive multiple-input-multiple-output (MIMO) systems. The fundamental concept of the NSE is to nullify the interference subspace generated by the combined multiple past channel state information (CSI) vectors. It can suppress inter-user interference (IUI) leaked due to outdated CSI in a mobility environment. It is enabled by plentiful degrees of freedom (DoF) brought by massive antenna elements the base station has, and hence NSE can outperform existing channel prediction based precoding approaches. However, additive noise-induced CSI estimation error limits its effectiveness; expanded dimension of null-space cannot be appropriately spanned to interference subspace. The key idea of our new proposal is to extract principal interference subspace channel. Null-space can be appropriately expanded with reduced its dimension, and remaining DoF can be assigned to beamforming. It results in improving overall signal-to-interference-plus-noise power ratio (SINR) performance which is verified via numerical simulation.

Performance Analysis of Large-Scale NGSO Satellite-Based Radio Astronomy Systems

Large-scale non-geostationary orbit (NGSO) satellite communication systems (SCSs) are emerging to play an important role for future global wireless communication. However, downlink transmissions from these mega-constellation SCSs can cause disruptive radio frequency interference (RFI) to the radio astronomy systems (RASs) on the ground or in space. Therefore, the satellite-based RASs including low earth orbit (LEO)-based or medium earth orbit (MEO)-based RASs are further considered to lower the impact from SCSs on the higher orbit onto the ground RASs and the lower orbit RASs. In this paper, we first analyze and compare the impact of RFI on LEO satellite-based RAS and MEO satellite-based RAS. The RFI results show that for both systems, RFI from higher orbit SCSs can totally undermine the RAS continuum observation adjacent to the SCS downlink bands when using the emission mask defined by National Telecommunications and Information Administration (NTIA). To solve the observation issues for both systems, we find out the required SCS emission mask for each RAS so that both systems can avoid RFI. Secondly, this paper also investigates three typical radio astronomy metrics such as maximum baseline distance (MBD), the number of simultaneously observing telescopes, and the signal to interference plus noise power ratio (SINR) performance. Our evaluation results show that the satellite-based RASs have greater MBD, thus, better spatial resolution, than the ground-based RAS. Due to the greater antenna gain of the ground telescopes, the SINR performance of satellite-based RASs may have limitations comparatively. However, because of more RFI sources at ground RASs in reality, satellite-based RASs have better chances to avoid RFI impact and potential SINR advantages. Additionally, we also explore the advantages of NGSO satellite-based RAS from a communication side. Our analysis shows that the large-scale NGSO satellite-based RAS can offer more spectrum access to both SCS and RAS.

Full Phased MIMO Radar with Colocated Antennas

A Phased Multi-Input Multi-Output (PMIMO) radar employs a transmit array of antennas that are divided into overlapping subarrays with same number of elements in order to exploit the main advantage of a phased array (coherent gain) and that of MIMO (waveform diversity). This paper proposes Full Phased MIMO (FPMIMO) approach in which both transmit and receive arrays are divided into overlapping subarrays with same number of elements. In this structure various waveform combinations can be adopted simultaneously on both transmit and receive sides, including coherent waveforms, non-coherent subarray waveforms and non-coherent waveforms in order to increase coherent gain, waveform diversity as well as radar system flexibility to adapt to given requirements at any time. The increase in coherent gain and waveform diversity makes radar performance more robust against noises and interferences for the desired target. Radar performance in terms of transmit-receive gain, SINR (Signal-to-Interference-plus-Noise-Power Ratio), and maximum range has been formulated and its effectiveness has been compared to Phased Array (PA), MIMO, and PMIMO radars. FPMIMO radar promises flexibility in adapting itself to condition of the targets as exemplified by the design of bird radar with its mission requirements using the FPMIMO approach. The impact of the use of cos(θ)-type elements is also presented.

Characterization of SINR Region for Multiple Interfering Multicast in Power-Controlled Systems

This paper considers a wireless communication network consisting of multiple interfering multicast sessions. Different from a unicast system where each transmitter has only one receiver, in a multicast system, each transmitter has multiple receivers and broadcasts a common message to all of them. It is a well-known result for wireless unicast systems that the feasibility of a signal-to-interference-plus-noise power ratio (SINR) without power constraint is decided by the spectral radius of a nonnegative matrix. We generalize this result and obtain necessary and sufficient conditions for the feasibility of an SINR in a wireless multicast system with and without power constraint. The feasible SINR region and its geometric properties are studied. Besides, an iterative algorithm is proposed, which can efficiently check the feasibility condition and compute the boundary points of the feasible SINR region.

Dual-polarized GPS antenna array algorithm to adaptively mitigate a large number of interference signals

Intentional or unintentional interference experienced by the Global Positioning System (GPS) is a significant concern for GPS-based critical infrastructures and services including aviation. An effective way to mitigate GPS interference is to utilize a GPS antenna array capable of electronically changing its gain pattern. Although a conventional GPS antenna array consists of single-polarized antenna elements, a dual-polarized antenna array has the potential to mitigate approximately twice the number of interference signals in the spatial domain as a single-polarized array because of the additional degrees of freedom provided. This paper proposes an adaptive beamforming algorithm using a dual-polarized GPS antenna array for mitigation of interference signals with various polarizations. In this paper, a dual-polarized antenna element specifically refers to two co-located crossed linearly polarized dipole antennas. The proposed minimum-variance-distortionless-response (MVDR)-based space–time adaptive processing (STAP) method utilizes a novel constraint vector that is specially designed for a dual-polarized GPS array. As the proposed constraint vector considers realistic radiation patterns of the antenna, the performance of the proposed method in terms of the signal-to-interference-plus-noise power ratio (SINR) is noticeably superior to that of previous methods under a representative interference scenario. The performance of the proposed method is compared with three previous methods utilizing dual-polarized antenna arrays.

BER analysis and power control for interfering visible light communication systems

This paper studies the error performance of visible light communication systems consisting of multiple transmitter–receiver pairs, where mutual interference exists. Unlike the traditional method which approximates the interference signal as a Gaussian random process and express the bit error rate (BER) as a function of the signal-to-interference-plus-noise power ratio (SINR), we conduct a detailed analysis that captures the signal structure of the interference in terms of the number of light sources, and derive the BER explicitly. Simulation results show that under a realistic small-room scenario with basic illumination requirement, the BER predicted by the Gaussian model is much higher than the exact BER. To provide an alternative metric for resource allocation purpose, we also propose a new approximate expression for the BER. A power control problem is further investigated to ensure that the system is operated in an effective manner.

SINR Maximizing Beamforming Schemes for the Full Duplex Amplify-and-Forward Relay Channel

We propose signal-to-interference-plus-noise power ratio (SINR) maximizing rank one beamforming schemes for the full-duplex (FD) relay systems. The non-regenerative amplify and forward (AaF) relay is considered with multiple transmit antennas and multiple receive antennas. The residual self-interference (SI) after analogue domain processing is to be suppressed by the proposed schemes so that the spectral efficiency of FD can be improved. We first analyze the correlation matrix of SI in a matrix power series and derive a convergent form of the correlation matrix so that the SINR expressions can be identified. Leveraging the structure of the SINR function on the beamformer (BF) vectors and power control parameter, two of the proposed schemes try to maximize SINR by optimizing a BF vector through iterative updates exploiting a bisection type search with the other BF vector being fixed. The third proposed scheme alternates over these two schemes to further enhance them by widening the search space that the BF vectors span. We compare the SINR of the proposed schemes with some reference schemes based on zero forcing approaches, maximum ratio reception, and maximum ratio transmission to characterize the performance improvement of the proposed schemes.

Radio Resource Management Based on User and Network Characteristics Considering 5G Radio Access Network in a Metropolitan Environment

In this paper, we clarify the issues in a metropolitan environment involving overlying frequency bands with various bandwidths and propose a cell selection scheme that improves the communications quality based on user and network characteristics. Different frequency bands with various signal bandwidths will be overlaid on each other in forthcoming fifth-generation (5G) radio access networks. At the same time, services, applications or features of sets of user equipment (UEs) will become more diversified and the requirements for the quality of communications will become more varied. Moreover, in real environments, roads and buildings have irregular constructions. Especially in an urban or metropolitan environment, the complex architecture present in a metropolis directly affects radio propagation. Under these conditions, the communications quality is degraded because cell radio resources are depleted due to many UE connections and the mismatch between service requirements and cell capabilities. The proposed scheme prevents this degradation in communications quality. The effectiveness of the proposed scheme is evaluated in an ideal regular deployment and in a non-regular metropolitan environment based on computer simulations. Simulation results show that the average of the time for the proposed scheme from the start of transmission to the completion of reception at the UE is improved by approximately 40% compared to an existing cell selection scheme that is based on the Maximum Signal-to-Interference plus Noise power Ratio (SINR).

Opportunistic Multiuser Two-Way Amplify-and-Forward Relaying With a Multiantenna Relay

We consider the opportunistic multiuser diversity in the multiuser two-way amplify-and-forward (AF) relay channel. The relay, equipped with multiple antennas and a simple zero-forcing beam-forming scheme, selects a set of two way relaying user pairs to enhance the degree of freedom (DoF) and consequently the sum throughput of the system. The proposed channel aligned pair scheduling (CAPS) algorithm reduces the inter-pair interference and keeps the signal to interference plus noise power ratio (SINR) of user pairs relatively interference free in average sense when the number of user pairs become very large. For ideal situations, where the number of user pairs grows faster than the system signal to noise ratio (SNR), the DoF of $M$ per channel use can be achieved when $M$ is the relay antenna size. With a limited number of pairs, the system is overloaded and the sum rates saturate at high signal to noise ratio (SNR) though modifications of CAPS can improve the performance to a certain amount. The performance of CAPS can be further enhanced by semi-orthogonal channel aligned pair scheduling (SCAPS) algorithm, which not only aligns the pair channels but also forms semi-orthogonal inter-pair channels. Simulation results show that we provide a set of approaches based on (S)CAPS and modified (S)CAPS, which provides system performance benefit depending on the SNR and the number of user pairs in the network.

WPAN 간섭원에 의한 MIMO-OFDM WLAN의 성능 열화 분석을 위한 실시간 주파수 간섭 분석 시스템

Abstract In this paper, we have proposed the frequency interference analysis system using both LabVIEW and Universal Software Radio Peripheral(USRP) for performance degradation analysis of Multi Input Multi Output-Orthogonal Frequency Division Multiplexing(MI-MO-OFDM) Wireless Local Area Network(WLAN) due to Wireless Local Area Network(WPAN) interferer. The proposed system consists of three part, i.e., victim, channel, and interferer. Both victim and interferer are implemented by LaBVIEW and a USRP board. Then interfering signal and additive white Gaussian noise are combined with the wanted signals of a victim. Measured Bit Error Rate(BER) at the victim receiver is compared with theoretical BER according to various signal to interference plus noise power ratio (SINR) values. Measured and theoretical BER curves show good agreement. Key words: Frequency Sharing, Frequency Interference, MIMO-OFDM, LabVIEW, USRP WXY9 Z[\]Y^((Department of Computer and Electronic Engineering, Myongji College) *_`9ZaY^GZ((Department of Electrical Engineering, Kookmin University)Manuscript received October 2, 2015 ; Revised November 26, 2015 ; Accepted November 26, 2015. (ID No. 20151002-19S)Corresponding Author: Byung-Jun Jang (e-mail: bjjang@kookmin.ac.kr)

MIMO Cloud Transmission Based on BICM-ID for High Data Rate Local Contents Delivery

A novel cloud transmission (CTxn) technique is proposed based on the multiple-input multiple-output (MIMO), called MIMO CTxn. Even though conventional single-input single-output (SISO) CTxn is operated at a negative signal-to-interference plus noise power ratio (SINR), where interference power is the same as the desired signal power, a critical drawback of SISO CTxn is that the maximum achievable spectral efficiency is less than 1 bit/s/Hz. Applying a MIMO technique to the conventional SISO CTxn provides a very efficient way to support high-date-rate service for delivering local contents, even at a negative SINR. Simulation results show that MIMO CTxn outperforms SISO CTxn while supporting high-order modulation and a high code rate. For instance, 16-QAM code rate 1/3 MIMO CTxn outperforms 4-QAM code rate 1/3 SISO CTxn from the SINR point of view. Further, the performance of MIMO CTxn is invariant with respect to the power imbalance and the difference between the received signal strengths. This makes the coverage planning much easy because all the other regions operate well without any loss of data rate if the coverage is planned with respect to the worst case.

Hybrid coordinated strategy of downlink coordinated multi-point transmission

Coordinated multi-point (CoMP) transmission is put forward in the long term evolution-advanced (LTE-A) system to improve both average and cell-edge throughput. CoMP-joint processing (JP) scheme can get a larger cell-edge throughput and a lower bit error rate (BER) than the CoMP-coordinated beamforming (CB) scheme, but it also has higher complexity due to data sharing. A hybrid coordinated strategy with parameter α, which indicates the proportion of users employing the CoMP-JP scheme, is proposed to apply the CoMP-JP scheme to improve the poorer communication quality of cell edge and employ the CoMP-CB scheme for other users to enhance average throughput and spectral efficiency. This paradigm selects users defined by the certain threshold of signal to interference plus noise power ratio (SINR) corresponding to the parameter α to the CoMP-JP scheme. This paper compares the BER performance between the block diagonalization (BD) based precoding and the linear precoders by maximizing signal to leakage and noise ratio (SLNR), and also indicates that the SLNR based precoding algorithm gets lower BER than the BD based precoding algorithm with certain signal-to-noise ratios (SNRs). Finally, this paper discusses that the system performance is partially affected by the percentage of CoMP-JP users and concludes that 50% of users sorted to communicate under the CoMP-JP scheme will reach the best system performance.

Weighted-Combining Calibration on Multiuser MIMO Systems with Implicit Feedback

Implicit feedback is an approach that utilizes uplink channel state information (CSI) for downlink transmit beamforming on multiple-input multiple-output (MIMO) systems, relying on over-the-air channel reciprocity. The implicit feedback improves throughput efficiency because overhead of CSI feedback for change of over-the-air channel responses is omitted. However, it is necessary for the implicit feedback to calibrate circuitry responses that uplink CSI includes, because actual downlink and uplink channel responses do not match due to different transmit and receive circuitry chains. This paper presents our proposed calibration scheme, weighted-combining calibration (WCC); it offers improved calibration accuracy. In WCC, an access point (AP) calculates multiple calibration coefficients from ratios of downlink and uplink CSI, and then combines coefficients with minimum mean square error (MMSE) weights. The weights are derived using a linear approximation in the high signal to noise power ratio (SNR) regime. Analytical mean square error (MSE) of calibration coefficients with WCC and calibration schemes for comparison is expressed based on the linear approximation. Computer simulations show that the analytical MSE matches simulated one if the linear approximation holds, and that WCC improves the MSE and signal to interference plus noise power ratio (SINR). Indoor experiments are performed on a multiuser MIMO system with implicit feedback based on orthogonal frequency division multiplexing (OFDM), built using measurement hardware. Experimental results verify that the channel reciprocity can be exploited on the developed multiuser MIMO-OFDM system and that WCC is also effective in indoor environments. key words: multiple-input multiple-output (MIMO), channel reciprocity, implicit feedback, calibration, minimum mean square error (MMSE)

An Improved Adaptive Beamforming Method for Spatially Non-Collocated Vector Sensor Array

To reduce the mutual coupling effects among the collocated electromagnetic vector sensor and enhance the performance of the joint space-polarization filtering, an improved adaptive beamforming method is proposed for non-collocated vector sensor array in this paper. First, the distributed array geometry composed of the crossed dipole pair and the signal model are introduced. Second, theoretical derivation of the improved method is discussed. By projecting the weight vector of the joint space-polarization minimum variance distortionless response (SPMVDR) onto a signal subspace, the optimal weight vector of the improved method is obtained. The projection operation generates a lower power of the output noise and improves the signal to interference plus noise power ratio (SINR) compared with the conventional SPMVDR. Computer simulation results indicate that the improved algorithm can achieve a good joint filtering performance and enhance the robustness to array pointing error.

Joint Tx/Rx MMSE Filtering for Single-Carrier MIMO Transmission

In this paper, we propose a joint transmit and receive linear filtering based on minimum mean square error criterion (joint Tx/Rx MMSE filtering) for single-carrier (SC) multiple-input multiple-output (MIMO) transmission. Joint Tx/Rx MMSE filtering transforms the MIMO channel to the orthogonal eigenmodes to avoid the inter-antenna interference (IAI) and performs MMSE based transmit power allocation to sufficiently suppress the inter-symbol interference (ISI) resulting from the severe frequency-selectivity of the channel. Rank adaptation and adaptive modulation are jointly introduced to narrow the gap of received signal-tointerference plus noise power ratio (SINR) among eigenmodes. The superiority of the SC-MIMO transmission with joint Tx/Rx MMSE filtering and joint rank adaptation/adaptive modulation is confirmed by computer simulation. key words: single-carrier transmission, MIMO, MMSE filtering, rank adaptation, adaptive modulation

BICM-ID-Based IDMA: Convergence and Rate Region Analyses

This paper considers uplink interleave division multiple access (IDMA), of which crucial requirement is the proper operability at a very low signal-to-interference-plus-noise power ratio (SINR) range. The primary objectives of this paper are threefold: (1) to demonstrate the achievability of near-capacity performance of bit interleaved coded modulation with iterative detection (BICM-ID) using very low rate single parity check and irregular repetition (SPC-IrR) codes at a very low SINR range, and hence the technique is effective in achieving excellent performance when it is applied for IDMA, (2) to propose a very simple multiuser detection (MUD) technique for the SPC-IrR BICM-ID IDMA which does not incur heavy per-iteration computational burden, and (3) to analyze the impacts of power allocation on the convergence property of MUD as well as on the rate region, by using the extrinsic information transfer (EXIT) chart. The SPC-IrR code parameters are optimized by using the EXIT-constrained binary switching algorithm (EBSA) at a very low SINR range. Simulation results show that the proposed technique can achieve excellent near-capacity performance with the bit error rate (BER) curves exhibiting very sharp threshold, which significantly influences the convergence property of MUD. Furthermore, this paper presents results of the rate region analysis of multiple access channel (MAC) in the cases of equal and unequal power allocation, as well as of a counterpart technique. The results of the MAC rate region analysis show that our proposed technique outperforms the counterpart technique.