Interference Scenarios Research Articles

Surrogate modeling based cognitive decision engine for optimization of WLAN performance

Due to the rapid growth of wireless networks and the dearth of the electromagnetic spectrum, more interference is imposed to the wireless terminals which constrains their performance. In order to mitigate such performance degradation, this paper proposes a novel experimentally verified surrogate model based cognitive decision engine which aims at performance optimization of IEEE 802.11 links. The surrogate model takes the current state and configuration of the network as input and makes a prediction of the QoS parameter that would assist the decision engine to steer the network towards the optimal configuration. The decision engine was applied in two realistic interference scenarios where in both cases, utilization of the cognitive decision engine significantly outperformed the case where the decision engine was not deployed.

Optimum transmitted power spectral distribution for broadband power line communication systems considering electromagnetic emissions

The study prior to the installation of a power-line communication (PLC) system requires detailed knowledge of the channel properties, such as transfer function, noise levels, and channel capacity in order to assess the services that can be provided. The channel capacity is greatly affected by the transmitted power over the available frequency range. At the same time, the values of transmitted power determine the electromagnetic field magnitude to the vicinity of the system. The simultaneous operation of different systems which share parts of the same frequency range, in the context of smart grid communications, has to be regulated in order to avoid excessive interference scenarios. Therefore, an algorithm that calculates the optimum power allocation of the transmitted power for PLC systems is proposed. The algorithm takes into account the maximum permitted values of electric field emitted from the PLC system and determines the transmitted power. The proposed algorithm is implemented for several test cases, while the corresponding channel capacities are calculated. It is shown that the proposed scheme better exploits the available frequency range and the transmission margins.

Joint Downlink and Uplink Tilt-Based Self-Organization of Coverage and Capacity Under Sparse System Knowledge

Concurrent self-organization of coverage and capacity in both downlink (DL) and uplink (UL) is an ambitious task since 1) Coverage and capacity are conflicting key performance indicators (KPIs), and 2) an adequate DL performance does not necessarily entail an adequate UL performance because the DL and UL interference scenarios are fundamentally different. However, considering the UL when self-organizing the network is crucial because the UL transmission becomes more important due to the emergence of new applications and services, such as social networking, video calls, or sensor networks, which require either parity between DL and UL traffic or even more UL than DL traffic. In this paper, we propose a general concept for the self-organization of multiple KPIs while having only very sparse knowledge about the network. Using this concept, we propose an effective tilt-based algorithm that manages to jointly optimize coverage and capacity in DL and UL. In an urban scenario with real Long-Term Evolution (LTE) site locations, we were able to increase the cell-edge user throughput by 70% (DL) and 24% (UL) while concurrently decreasing the number of uncovered users by 21% (DL) and 25% (UL), compared with a well-chosen reference tilt setting.

A fractional path-loss compensation based power control technique for interference mitigation in LTE-A femtocell networks

Introduction of Femtocells in heterogeneous network enhances the capacity, indoor coverage of the existing macrocell based network. It also allows high-speed data services for the multi-media application and software. However, in dense co-channel deployment scenarios femtocells cause severe interference to the neighbouring cells users. In this paper, a downlink-power-control scheme is presented for femtocell with no overhead signalling exchange with the macrocell. The femtocell adjusts the transmit power subject to home user equipment (HUE) measurements. The minimum level of transmit power is determined by the target Signal to Interference and Noise Ratio (SINR) of femtocell user that is set according to the required Quality of Service (QoS) of the femtocell users. The system level simulations confirm that, the proposed scheme reduces the outage probability of the nearby macrocell user equipment (MUE) up to 16.7% compared to fixed power setting, while maintaining the spectral efficiency of femtocell users. Furthermore, the transmit power can be reduced by 52.6% which leads to power effective solution of the interference scenario.

LTE-Advanced 환경에서 D2D 통신을 위한 송수신 기법

We treat device-to-device direct communication (D2D) by reusing cellular uplink resources in LTE-Advanced systems. Conventional schemes assume that D2D transmitter employs SC-FDMA scheme for the date transmission. In the conventional schemes, however, it is very difficult to reduce the interference between the users, D2D communication cannot be used when the interference caused by cellular uplink signal is high. In this paper, we propose D2D transmission scheme which employes MC-CDMA technology and D2D detection scheme which uses MMSE algorithm to reduce interference from the cellular uplink signal. Therefore, in the proposed scheme the D2D communication becomes possible even in the high interference scenario. Through simulation, we show that the proposed scheme has better BER performance than the conventional scheme.

Intra and Inter-Cell Resource Management in Full-Duplex Heterogeneous Cellular Networks

Full-duplex communication is drawing high attention as a means of enhancing wireless capacity considerably by enabling simultaneous transmission and reception on the same frequency spectrum. While it had been considered infeasible for a long time due to strong self-interference, recent researches have made substantial progress on addressing this challenge. This paper focuses on designing full-duplex cellular networks with co-channel femtocells. Due to relatively high transmit power, cancellation of self-interference by existing techniques could still be imperfect for cellular systems and thus residual interference may impact performance significantly. To overcome this in OFDMA systems, a new radio resource management scheme assigning downlink and uplink transmissions jointly while considering the gain of self-interference cancellation is developed. Three available transmission modes of a frequency resource block and crossover points between their achievable capacities are identified for the mode selection of each resource block. Users are then assigned resource blocks and transmit power levels are determined such that the total utility sum is maximized. To handle new femtocell interference scenarios, the transmit powers of femtocells and their connected users are adjusted by a coordination algorithm such that both data transmission and mode selection of an underlying macrocell are protected.

A compact fractal UWB antenna with reconfigurable band notch functions

ABSTRACTIn this paper, a compact reconfigurable single/dual notch band ultrawideband (UWB) antenna with triple notch band characteristics is presented for portable UWB applications. The desired compactness and wideband is achieved using fractals in antenna design. It has the compact dimensions of 24.5 mm × 20 mm. The single/dual notch band reconfigurability is demonstrated in WiMAX band as well as in X‐band using two p‐i‐n diodes for efficient utilization of UWB bands in case of no interference scenarios. The band rejections are obtained by introducing two C‐shaped slots in the fractal monopole, whereas band rejection in WLAN band is achieved by placing two C‐shaped single split ring resonator on either sides of feed line. In addition, the time‐domain characteristic of antenna is also evaluated in terms of fidelity factor, which is more than 0.71. These results illustrates that the presented antenna is appropriate candidate for portable UWB applications. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:509–514, 2016

Massive MIMO for Maximal Spectral Efficiency: How Many Users and Pilots Should Be Allocated?

Massive MIMO is a promising technique for increasing the spectral efficiency (SE) of cellular networks, by deploying antenna arrays with hundreds or thousands of active elements at the base stations and performing coherent transceiver processing. A common rule-of-thumb is that these systems should have an order of magnitude more antennas $M$ than scheduled users $K$ because the users’ channels are likely to be near-orthogonal when $M/K > 10$ . However, it has not been proved that this rule-of-thumb actually maximizes the SE. In this paper, we analyze how the optimal number of scheduled users $K^\star$ depends on $M$ and other system parameters. To this end, new SE expressions are derived to enable efficient system-level analysis with power control, arbitrary pilot reuse, and random user locations. The value of $K^\star$ in the large- $M$ regime is derived in closed form, while simulations are used to show what happens at finite $M$ , in different interference scenarios, with different pilot reuse factors, and for different processing schemes. Up to half the coherence block should be dedicated to pilots and the optimal $M/K$ is less than 10 in many cases of practical relevance. Interestingly, $K^\star$ depends strongly on the processing scheme and hence it is unfair to compare different schemes using the same $K$ .

Measurement and Evaluation Techniques to Estimate the Degradation Produced by the Radiated Transients Interference to the GSM System

A common source of noise for digital communication systems is the radiated transient interference. As an example, it has been reported that the degradation is produced to the Global System for Mobile (GSM)-Railway signaling system when the impulsive noise is generated by sparks caused by the discontinuity between the catenary and the pantograph. Concerning the measurement and evaluation procedures defined in the electromagnetic compatibility standards, they are not suitable for these types of transient disturbances. Therefore, new techniques must be developed to determine, with a high confidence level, the degradation that impulsive noise will produce in communication systems. In this paper, novel time-domain measurement procedures are carried out to acquire transient interferences generated by sparks properly. Moreover, two different evaluation methodologies, employing base-band simulation and amplitude probability distribution detector, are used to analyze the impact of the disturbance applied into a GSM system interference scenario. Finally, the results obtained with the developed methodologies are successfully compared with a reference measure where the GSM downlink channel quality is monitored by a mobile station test unit.

Design and evaluation of ANR algorithm for LTE real scenario with high interference

The operation of mobile networks has three basic objectives to fulfil: quality–coverage–capacity, at a cost of efficient operation. Quality can be expressed as the network's ability to maintain a call or data session, which must be terminated at will by users. When the network is not able to fulfil this condition, dropped calls occur. To ensure quality and user mobility, it is necessary to design a proper neighbour cell list to allow transfer between cells. In this sense, the 3GPP standard considers the ANR (automatic neighbour relation) technique for LTE as an automatic method of defining neighbour lists that optimises network performance. Presented is a method to define an optimised neighbour cell list, which is designed and implemented in a real UMTS network of Telefonica within a high interference scenario, and which is easily extrapolated to the LTE network.

Minimum Energy Block Technique Against Pulsed and Narrowband Mixed Interferers for Single Antenna GNSS Receivers

In this letter, we propose to mitigate the mixture of a pulsed interference and a narrowband interference (NBI). By exploiting the periodicity of pulsed interference, we proposed a minimum energy block technique to segment inputs into blocks and group consecutive blocks into batches. We choose these minimum energy blocks in all batches to estimate the power spectrum density (PSD) of NBI. The mixed interference can be suppressed by frequency-domain blanking (FDB) and time-domain blanking (TDB) techniques in serial. The proposed technique only requires prior knowledge of the period range of pulsed interference to control the block size and block number of each batch. The receiver operating characteristic (ROC) curves show that the proposed technique outperforms the conventional one and achieves a performance close to the ideal mitigation under harsh mixed interference scenarios.

Linear Precoder Design for Simultaneous Information and Energy Transfer Over Two-User MIMO Interference Channels

Communication strategies that utilize wireless media for simultaneous information and power transfer offer a promising perspective for efficient usage of energy resources. With this motivation, we focus on the design of optimal linear precoders for interference channels utilizing such strategies. We formulate the problem of minimizing the total minimum mean-square error while keeping the energy harvested at the energy receivers above given levels. Our framework leads to a non-convex problem formulation. For point-to-point multiple-input multiple-output channels, we provide a characterization of the optimal solutions under a constraint on the number of transmit antennas. For the general interference scenario, we propose two numerical approaches, one for the single antenna information receivers case, and the other for the general case. We also investigate a hybrid signalling scheme, where the transmitter sends a superposition of two signals: a deterministic signal optimized for energy transfer and an information carrying signal optimized for information and energy transfer. It is illustrated that if hybrid signalling is not incorporated into the transmission scheme, interference can be detrimental to the system performance when the number of antennas at the receivers is low.

A compact UWB antenna with reconfigurable dual notch bands

ABSTRACTTo effectively utilize the entire ultrawideband (UWB) spectrum in case of no interference scenarios, a UWB antenna having reconfigurable dual band notch characteristics at WiMAX and WLAN band of frequencies is presented in this article. The p‐i‐n diodes and capacitors are properly placed in the UWB antenna to achieve the reconfigurable band notch function. The proposed antenna has the wide impedance bandwidth of 8 GHz (from 2.7 to 10.7 GHz). The four possible combinations of three p‐i‐n diodes are used to obtain single/dual reconfigurable notch bands in entire UWB band. The rejected WiMAX and WLAN band of frequencies are centered at 3.6 GHz and 5.5 GHz, respectively. The size of the proposed antenna is 27 × 32 mm2. The measured results are in good agreement with the simulated results. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2737–2742, 2015

Rethinking Interference Mitigation Spectrum Efficiency Model in Femtocell Networks using FFR

a wireless communication cellular network, call activity can be more intensive in some regions than others. In present scenario of society and city development such as metro-cities and NCR-regions in which, high speed, slow speed as well as pedestrian subscribers are available with high-density may decrease the system performance. Splitting the cell size and reduce the transmission distance is one of the effective technique. But, cell splitting technique does not provide efficient solution in the regions in which high speed, slow speed as well as pedestrian subscribers are available. Deploying the femtocell over cellular networks has recently attracted growing interests in academia, industry, and research places. Deploying femtocells over cellular networks is an attractive solution in current scenario for the improvement of cellular network's services providing better coverage and speed. Femtocell provides attractive indoor coverage with high throughput and promising satisfaction of subscribers. Coexisting femtocells and cellular networks lead to severe interference scenarios. However, inter cell interference decreases the system performance, capacity as well as throughput. Therefore, challenge still remaining is to efficiently allocate spectrum to this technology. This paper focuses on interference mitigation techniques in femtocell/macrocell networks and proposes a fractional frequency reuse (FFR) mechanism that leads to increase overall system performance. In particular, the mechanism aims to maximize throughput via a variety of combinations between inner cell radius and frequency allocation to the cellular networks. Additionally, a position minded frequency allocation to the femtocells targets to further reduce the cross- tier interference in femtocell networks.

Beamforming design with proactive interference cancelation in MISO interference channels

Abstract In this paper, we design coordinated beamforming at base stations (BSs) to facilitate interference cancelation at users in interference networks, where each BS is equipped with multiple antennas and each user is with a single antenna. By assuming that each user can select the best decoding strategy to mitigate the interference, either canceling the interference after decoding when it is strong or treating it as noise when it is weak, we optimize the beamforming vectors that maximize the sum rate for the networks under different interference scenarios and find the solutions of beamforming with closed-form expressions. The inherent design principles are then analyzed, and the performance gain over passive interference cancelation is demonstrated through simulations in heterogeneous cellular networks.

Fast Time-Varying Channel Estimation for OFDM Systems With Narrowband Interference

The problem of channel estimation in OFDM with narrowband interference (NBI) has been only investigated for slow time-varying channels. For the first time, a novel estimation framework is proposed for fast time-varying channels. The noise variances and channel are jointly estimated via the maximum a posteriori (MAP) expectation maximization (EM) algorithm. By considering in the EM formulation the channel as the unwanted parameter and the noise variances as the parameters to be estimated, a closed-form analytical expression for the estimation of the noise variances is obtained; the channel being given by the Kalman smoother. Mean square error (MSE) and bit error rate (BER) simulations confirm the effectiveness and robustness of the approach against mobility and its adequacy for practical interference scenarios.

Noise Robust Direction of Arrival Estimation for Speech Source With Weighted Bispectrum Spatial Correlation Matrix

One big challenge to the robust direction of arrival (DOA) estimation for the speech source is the environmental noise. In practical conditions, the noise can be undirected or emitted from a pointed source. In order to improve the reliability of DOA estimation in various adverse noisy conditions, we propose a novel DOA estimation method in this paper, and what lies in the core in the method is the “Weighted Bispectrum Spatial Correlation Matrix (WBSCM).” The bispectrum is a kind of higher order statistics (HOS) of a signal, and the WBSCM reflects the spatial correlation of the bispectrum phase differences (BPD) between different microphones. As the HOS of the Gaussian signal is theoretically zero, by formulating in the bispectrum domain, the proposed method has an inherent advantage against the Gaussian noise. Moreover, the BPD, which is embedded in the WBSCM, contains the redundant information related to the DOA of the speech source. This redundancy helps to improve the robustness in non-Gaussian noise conditions, especially for the directional interference scenarios. In addition, the WBSCM enables bispectrum weighting to select the speech units in the bispectrum, in order to highlight the effect of these units in the DOA estimation. Similar to the signal-to-noise estimation, a decision-directed method is proposed to compute the bispectrum weights. Finally, a new DOA estimator is proposed, which is based on the eigenvalue analysis of the WBSCM. We conduct experiments under various kinds of noisy environments, and the experimental results demonstrate the effectiveness of proposed method.

Adaptive reweighting homotopy algorithms applied to beamforming

We develop adaptive beamforming algorithms that are robust against sensor failure and ill-conditioning in the autocorrelation matrix (common in low-rank interference scenarios). Both goals are achieved simultaneously through the use of l1 regularization. The algorithms are based on the complex adaptive reweighting homotopy technique. We also develop iterative versions of the algorithms that take advantage of properties of homotopy l1 solvers and dichotomous coordinate iterations to reduce considerably the computational complexity, compared with other regularization methods.

비면허기기 간 실시간 주파수간섭 분석 테스트베드 구현

본 논문에서는 2.4 GHz 대역에서 동작하는 Wi-Fi나 Zigbee 등 비면허기기 간 주파수간섭을 실시간으로 분석할 수 있는 테스트베드를 제안하였다. 제안된 테스트베드는 피간섭원과 간섭원의 RF부는 범용 SDR 보드인 Universal Software Radio Peripheral(USRP)로 구현하고, 모뎀은 <TEX>$Labview^{TM}$</TEX>를 이용하여 프로그램하여 구현하였다. 따라서 주파수간섭과 관련된 동작 주파수, 출력전력, 모뎀 파라미터 등을 손쉽게 변경할 수 있어 다양한 주파수간섭 환경을 손쉽게 모델링할 수 있을 뿐만 아니라, 주파수간섭에 따른 물리계층의 Bit Error Rate(BER) 열화 특성을 실시간으로 파악할 수 있는 장점이 있다. 테스트베드의 검증을 위해 피간섭원으로 IEEE 802.15.4를, 간섭원으로 IEEE 802.11b를 구현하여 실시간으로 주파수간섭 영향을 측정하고, 이를 이론 및 MATLAB/Simulink 시뮬레이션 결과와 비교하여 1 dB 이내로 일치함을 확인하였다. In this paper, we suggested a real-time test-bed for analyzing frequency interference between 2.4 GHz unlicensed devices, such as WiFi, Zigbee, etc. Owing to versatile programming capability of Universal Software Radio Peripheral(USRP) and <TEX>$Labview^{TM}$</TEX>, frequency interference environments can be easily modeled. Therefore, performance degradation effects due to various parameters of interferer and victim receiver can be analyzed intuitively. For verification, we showed a frequency interference scenario, which consists of IEEE 802.15.4 as a victim and IEEE 802.11b as a interferer. Measured Bit Error Rate(BER) results showed good agreement with theory and simulation results.

Search for New Phenomena in Dijet Angular Distributions in Proton-Proton Collisions at sqrt[s]=8 TeV Measured with the ATLAS Detector.

A search for new phenomena in LHC proton-proton collisions at a center-of-mass energy of sqrt[s]=8 TeV was performed with the ATLAS detector using an integrated luminosity of 17.3 fb^{-1}. The angular distributions are studied in events with at least two jets; the highest dijet mass observed is 5.5 TeV. All angular distributions are consistent with the predictions of the standard model. In a benchmark model of quark contact interactions, a compositeness scale below 8.1 TeV in a destructive interference scenario and 12.0 TeV in a constructive interference scenario is excluded at 95% C.L.; median expected limits are 8.9 TeV for the destructive interference scenario and 14.1 TeV for the constructive interference scenario.