Blank Subframe Research Articles

Performance Improvement Using ICIC for UAV-Assisted Public Safety Networks with Clustered Users during Emergency

The application of drones, also known as unmanned aerial vehicles deployed as unmanned aerial base stations (UABSs), has received extensive interest for public safety communications (PSC) to fill the coverage gaps and establish ubiquitous connectivity. In this article, we design a PSC LTE-Advanced air–ground-based HetNet (AG-HetNet) that is a scenario representation of a geographical area during and after a disaster. As part of the AG-HetNet infrastructure, we have UABSs and ground user equipment (GUE) flocking together in clusters at safe places or evacuation shelters. AG-HetNet uses cell range expansion (CRE), intercell interference coordination (ICIC), and 3D beamforming techniques to ensure ubiquitous connectivity. Through system-level simulations and using a brute-force technique, we evaluate the performance of the AG-HetNet in terms of fifth-percentile spectral efficiency (5pSE) and coverage probability. We compare system-wide 5pSE and coverage probability when UABSs are deployed on a hexagonal grid and for different clustering distributions of GUEs. The results show that reduced power subframes (FeICIC) defined in 3GPP Release-11 can provide practical gains in 5pSE and coverage probability than the 3GPP Release-10 with almost blank subframes (eICIC).

Improved almost blank subframe technology with cooperative interference suppression

AbstractAlmost blank subframe (ABS) is a classic and efficient technology to cancel interference in cellular networks and could be applied in future networks such as ultra‐density network. However, the existence of ABS will result in the deterioration of the communication capacity of the macro base station (BS), particularly for applications with large number of edge users. To solve this problem, an improved ABS technology with an interference cancelation scheme is proposed. For the considered scenario, the macro BS and the micro BS work in a cooperative manner, where the signal transmitted by the macro BS interferes with the communication between the micro BS and its edge terminals. At the terminal side, both the nonlinearity of the macro BS transmitter and the propagation model between the edge user and the macro BS are estimated using neural networks (NNs), which are then sent to the micro BS for interference elimination through the ABS. At the micro BS side, firstly, the nonlinearity and channel parameters from the ABS frame are used to generate a cancelation signal. Secondly, the cancelation signal is sent from the micro BS to the edge user to eliminate the disturbance from the macro BS. This enhanced technology can alleviate the disturbance for the edge user. Meanwhile, since it massively decreases the occupancy of ABS in the macro BS, the capacity of the macro cell can be improved.

Research on Interference Coordination Optimization Strategy for User Fairness in NOMA Heterogeneous Networks

In order to comprehensively improve the performance of edge users in heterogeneous cellular networks and the fairness of network users, a downlink interference coordination optimization strategy in heterogeneous cellular networks with non-orthogonal multiple access (NOMA) based on the cell range expansion (CRE) and the almost blank subframe (ABS) technology is proposed. Different from the traditional interference coordination strategy, a NOMA user pairing scheme combined with ABS technology and a dynamic NOMA power allocation scheme are designed to maximize the network fairness based on the optimized throughput of the edge users. The simulation results show that the proposed optimization strategy can balance the performance of network users more effectively to improve the throughput of edge users and network fairness than other NOMA user pairing and power allocation algorithms without the complexity being increased.

Performance evaluation of the eICIC technique applied to a heterogeneous 4G mobile network

The evolution of LTE-A (Long Term Evolution -Advanced) has enabled the development of the Heterogeneous Network (HetNet) which uses multiple cell types due to the explosion in the number of connected subscribers. Different cell types of different sizes are deployed to share the load in the heterogeneous network. Unplanned deployment of small cells with low power, planning of the existing network, the power difference between cells; physical and meteorological phenomena affect the signal quality of radio links; crowded areas of metropolises with extremely high traffic hotspots force operators to increase the network capacity in a more economical way by installing small cells Several techniques have been developed in the literature. Among them, eICIC has emerged as the best and is used to overcome these interference problems in the heterogeneous 4G network. The performance evaluation of eICIC has been performed analytically and numerically in the time domain due to its use with the ABS (Almost Blank Subframe) of the OFDM system. The simulation areas are in center of the picocells, in the cell range extension (CRE) areas and in the macrocells. Analytically, we used the signal-to-interference-plus-noise ratio (SINR) to evaluate the bit rate, RSRP and RSRQ. The numerical method consists in proposing an algorithm for calculating the analytical parameters using Matlab software. The results obtained from the simulations are convincing and are not far from those obtained in the literature. The values obtained from the SINR correspond to the SINR-CQI table found in the literature. The throughput calculated in this work in relation to radio conditions (RSRP, RSRQ) reflects everyday realities.

Comparative Study of Scheduling Algorithms in LTE HetNets with Almost Blank Subframe

Comparative Study of Scheduling Algorithms in LTE HetNets with Almost Blank Subframe

Inter-cell interference mitigation using adaptive reduced power subframes in heterogeneous networks

With the remarkable impact and fast growth of the mobile networks, the mobile base stations have been increased too, especially in the high population areas. These base stations will be overloaded by users, for that reason the small cells (like pico cells) were introduced. However, the inter-cell interference will be high in this type of Heterogeneous networks. There are many solutions to mitigate this interference like the inter-cell interference coordination (ICIC), and then the further enhanced ICIC (Fe-ICIC) where the almost blank subframes are used to give priority to the (victim users). But it could be a waste of bandwidth due to the unused subframes. For that reason, in this paper, we proposed an adaptive reduced power subframe that reduces its power ratio according to the user’s signal-to-interference-plus-noise ratio (SINR) in order to get a better throughput and to mitigate the intercell interference. When the user is far from the cell, the case will be considered as an edge user and will get a higher priority to be served first. The results show that the throughput of all users in the macro cells and pico cell will be improved when applying the proposed scheme in term of throughput for the users and the cells.

Heuristic approach for jointly optimising FeICIC and UAV locations in multi‐tier LTE‐advanced public safety HetNet

Unmanned aerial vehicles (UAVs) enabled networks can enhance wireless connectivity and support emerging services. However, this would require system-level understanding to modify and extend the existing terrestrial network infrastructure. In this study, the authors integrated UAVs as user equipment and base stations into an existing long term evolution (LTE)-Advanced heterogeneous network (HetNet) and provide system-level insights of this three-tier LTE-Advanced air-ground HetNet (AG-HetNet). The performance of AG-HetNet was evaluated through brute-force technique and heuristics algorithms in terms of the fifth percentile spectral efficiency (5pSE) and coverage probability. In particular, system-wide 5pSE and coverage probability were compared, when unmanned aerial base stations (UABSs) are deployed on a fixed hexagonal grid and when their locations are optimised using a genetic algorithm (GA) and elitist harmony search algorithm based on the genetic algorithm (eHSGA); while jointly optimising the inter-cell interference coordination (ICIC) and cell range expansion (CRE) network parameters for different ICIC techniques. The simulation results show that the heuristic algorithms (GA and eHSGA) outperform the brute-force technique and achieve better peak values of coverage probability and 5pSE. Simulation results also show that a trade-off exists between peak values and computation time when using heuristic algorithms. Furthermore, the three-tier hierarchical structuring of reduced power subframes further-enhanced ICIC (FeICIC) defined in 3GPP Rel-11 provides considerably better 5pSE and coverage probability than the 3GPP Rel-10 with almost blank subframes eICIC. They also investigated the network performance for different practical deployment heights of UABS and they found low-altitude UABSs to perform sparsely better than medium-altitude UABSs.

MACD e-ICIC: a dynamic LTE interference coordination method based on trend and trading know-how

Mobile communications are preparing for the incredible changes from $$4\mathrm{th} \,\hbox {Generation (4G)}$$ to $$5\mathrm{th}\hbox { Generation (5G)}$$ in the coming years. In this new generation, co-channel interference is one of the critical challenges to be tackled due to network densification by providing high data rates through several macro and small cells working together, configuring the so-called $$\hbox {Heterogeneous Network (HetNet)}$$ . The umbrella of 3GPP system (including LTE and its evolution towards 5G) provides the $$\hbox {Almost Blank Subframe (ABS)}$$ as a scheme of the $$\hbox {Enhanced Inter-Cell Interference Coordination (e-ICIC)}$$ framework to mitigate interference among macro and small cells. The ABS mutes some of the macro cell transmissions in selected subframes to decrease interference to small cells, thus orthogonalizing macro and small cell transmissions in time-domain. In this paper, we use a $$\hbox {moving average convergence/divergence}$$ technique based on trading know-how to propose a $$\hbox {real time ABS e-ICIC}$$ algorithm. Our proof-of-concept simulation results show relative capacity gains of 112% compared to the case without $$\hbox {ABS}$$ .

Enhanced ABSF Algorithm with a Relay Function in LTE Heterogeneous Networks

In this study, we enhance the almost blank subframe (ABSF) algorithm in a Long Term Evolution (LTE) heterogeneous network (HetNet) by providing a relay function. The ABSF is a technique proposed by the Third Generation Partnership Project to reduce interference in a HetNet. Despite the fact that the ABSF effectively mitigates intercell interference, it has two major disadvantages. First, the ABSF algorithm alters the scheduling policy of macro base stations. Second, it degrades the capacity of users served by femto base stations. Our proposed enhanced algorithm applies a relay function to assist victim macro user equipment (VMUE), and it reduces the side effects caused by the ABSF algorithm. Taking resource allocation and power control into account, the relay function assists VMUE in such a way that interference with other users is minimized. Via simulation results, the proposed algorithm exhibits improvements of 18% and 8% for system throughput and user satisfaction, respectively, in comparison with the conventional ABSF.

Analysis of Acquired Indoor LTE-A Data from an Actual HetNet Cellular Deployment

Increasing the user downlink throughput is always a task of utmost importance for any cellular network service provider. However, most of the research is only focused on system simulations due to environmental simplicity. In this paper, instead of focusing on theoretical simulations, we aim to find the best practical solution to increase user throughput in an actual HetNet deployment where many small cells are deployed inside a building. An inter-frequency deployment is implemented in the actual LTE-A HetNet environment. A series of data collections were conducted in an actual indoor LTE-Advanced HetNet (heterogeneous network) environment with optimization strategies such as ABS (Almost Blank Subframe) and turning off/on interfering antennas. Detailed findings and analysis are provided to better understand the complicated actual HetNet environment. This work is also important to understand the future 5G network since the small cells and HetNet will continue to play an important role in the 5G network.

Analysis of the Geographical-Information Impact on the Performance of ABS-CRE HetNets

In this paper, we analyze the performance of Heterogeneous Networks (HetNets) that are operating under Almost Blank Subframes (ABS) and Cell Range Expansion (CRE) by taking into consideration the effect of geographical information. In order to achieve such analyses, we develope a simulator that incorporates data from a Geographic Information System (GIS); specifically, a set of parameters that define the morphology of buildings and streets in urban areas. We describe the implemented methods to estimate the received power, as well as the average throughput, over an area of interest. Our numerical results clearly demonstrate that the overall network performance significantly depends on geographical information; hence our main contribution consists in developing a simulator that incorporates such information in the analysis and evaluation of ABS-CRE HetNets, which allows proposing design guidelines to improve the performance of these networks in realistic scenarios. To the best of our knowledge, this kind of proposal has not been reported in previous works.

An Approach to Reduce Interference Using FFR in Heterogeneous Network

As the world is progressing towards 5G technology, its primary requirement is high throughput, low latency, high spectrum and energy efficiency and guaranteed QoS. High throughput is achievable when the user (UE) and the base station/Macro eNodeB (MeNB) are close to each other. This is achieved by using femtocell or Home eNodeB (HeNB). It is a kind of small cell. The femtocell needs to exist along with macrocell. Hence, they will share the resource along with the macrocell. There arises serious inter-channel and intra-channel interference (ICIC). To mitigate the interference, various solution methodologies, e.g. power control, co-operative communication and absolute blank sub-frame, can be used. In this research work, fractional frequency reuse method is discussed where the cell is segregated into centred and edge regions. All the centred, i.e. inner, regions can be assigned with the same frequency sub-band. Edge regions, i.e. outer region, can be assigned with different frequency sub-band with reuse factor of three. In this technique, ICIC can be reduced significantly. Hence, QoS can be improved and throughput of the system can also be enhanced. The outage probability can be reduced since cell-edge users are assigned with different sub-bands with high power.

On Developing Techniques for Sharing Satellite Spectrum with Indoor Small Cells in 5G

In this paper, we present two spectrum sharing techniques for a multisystem, incorporating an integrated satellite-mobile system and an autonomous terrestrial-mobile system (iSMS/aTMS), namely orthogonal spectrum sharing (OSS) and non-orthogonal spectrum sharing (nOSS) techniques. aTMS consists of numerous small cells deployed in several buildings, and iSMS consists of a satellite station integrated with complementary ground component (CGC) stations deployed within buildings. By exploiting the high external wall penetration loss of a building, the iSMS spectrum is shared with small cells per building in OSS, and small cells per 3-dimensional (3D) cluster per building in nOSS. An interference management scheme, to avoid interference in apartments with collocated CGC stations and small cells, was developed and an optimal number of almost blank subframes (ABSs) per ABS pattern period (APP) was defined. System-level capacity, spectral efficiency, and energy efficiency performance metrics were derived. Furthermore, we present an algorithm for both OSS and nOSS techniques. With extensive simulation and numerical analysis, it is shown that the proposed nOSS significantly outperforms OSS in terms of spectral efficiency and energy efficiency, and both techniques can meet the expected spectral efficiency and energy efficiency requirements for the fifth-generation (5G) mobile networks.

EICIC Optimization Improvements in Downlink Resource Allocation in LTE-A HetNets

Resource allocation mechanisms and management of inter-cell interference coordination (ICIC) are fundamental characteristics of the LTE-A network for achieving maximum capacity. Cell densification serves as a promising candidate solution for meeting the demand posed by mobile users, as well as optimizing coverage. However, the transmit power difference between the introduced picocells and the legacy macrocells essentially leads to challenges that limits system performance, especially for those users located at the edge of the cell. As a means of providing a clear understanding, the authors thus formulate the optimization problem as game theory, in order to maximize a modified utility function, which aims at making improvements on the eICIC. Based on exact potential game formulation, we optimize almost blank subframe (ABS) and cell selection bias (CSB) settings for both macrocells and picocells in a distributed manner. Simulation results illustrate important performance gains on the service fairness of the users, and especially for cell edge users, where the averaged throughput increases by up to 51%, when compared to eICIC optimization without our modified utility function.

Energy Efficiency Optimization Based on eICIC for Wireless Heterogeneous Networks

To solve the problem of load imbalance and system interference in heterogeneous networks (HetNets), an energy efficiency (EE) optimized strategy based on enhanced intercell interference coordination (eICIC) technology is proposed. The optimization of the EE of the system is established by taking into account four components which are the connection between the users and base stations (BSs), almost blank subframe (ABS) ratio, resource allocation in the frequency domain, and the power transmission of the macro BSs (MBSs). In our optimized strategy, the user’s optimal BS connection status are determined according to the overall EE change of the system, and the allocation of subframes and resource blocks of the MBSs both in the time domain and frequency domain are optimized, respectively. We use the Gauss–Seidel method to iteratively solve the optimization problem. Simulation results show that the optimized strategy outperforms other solutions in terms of EE and user fairness in average. The proposed optimization strategy increases the system EE by 24.2% and 19.1%, respectively, when compared with the maximal reference signal received power (MAX-RSRP) and the low power-ABS (LP-ABS) strategies. The Jain fairness index of our proposed optimization strategy is averagely increased by 33.8% and 23.4%, respectively. In addition, the proposed strategy can further improve the user satisfaction and the performance in the system.

Efficient coordination of almost blank subframes with coupling macro cells in heterogeneous networks

SummaryHeterogeneous networking is an inevitable trend in mobile communication systems, where macrocells and small cells coexist to provide the service of wireless access. The technique of enhanced inter‐cell interference coordination (eICIC) is popularly used to mitigate signal interference among cells. A number of subframes are picked as almost blank subframes (ABSs), during which a macro‐cell base station suspends data transmissions to improve signal quality of small cells that it covers. Since the throughput of macro cells drops to zero in an ABS, how to decide the number of ABSs (ie, the ABS ratio) and their positions (ie, the ABS placement) is critical. Many studies implicitly consider that every small cell resides in only one macro cell and they manage ABSs for each individual macro cell accordingly. In practice, some macro cells may cover the same small cells (called coupling macrocells) which makes the management of their ABSs depend on each other. To address this issue, the paper proposes an efficient coordination of ABS with coupling macro cells (ECO) algorithm. It divides the network into component subnetworks depending on whether macro cells are coupling or not. Then, ECO computes the ABS ratios for the macro cells in each component subnetwork based on multiple factors, including data rate, traffic demand, and quality of service (QoS) support. Moreover, ECO jointly places the ABSs of coupling macro cells to shorten packet latency. Experimental results show that the ECO algorithm not only increases the network throughput but also reduces the loss rate of real‐time data.

Dual-Connectivity Enabled Resource Allocation Approach With eICIC for Throughput Maximization in HetNets With Backhaul Constraint

By introducing the concept of dual connectivity (DC), joint user association and resource allocation for heterogeneous networks (HetNets) with backhaul constraint have been investigated. However, co-channel scenario is rarely considered in DC-enabled HetNets due to inter-tier interference. To solve this issue, enhanced intercell interference coordination (eICIC) via almost blank subframe (ABS) is introduced into DC-enabled HetNets with backhaul constraint. The objective is to improve overall system throughout while providing quality-of-service (QoS) guarantees on user’s rate. First, the joint DC-enabled user association and resource allocation problem is formulated as an mixed integer nonlinear programming (MINLP) problem. Then, by linearizing the products of the variables, the original problem is reformulated into a linear problem. Last, a low-complexity heuristic method to achieve the near-optimal solution is proposed. Also, the numerical results show the superiority of our algorithm.

QoS-Guaranteed Radio Resource Management in LTE-A Co-Channel Networks with Dual Connectivity

Dual connectivity (DC) was first proposed in 3GPP Release 12 which allows one piece of user equipment (UE) to connect to two base stations in heterogeneous networks (HetNet) at the same time, to increase the flexibility of resource utilization. DC has been further extended to multiple connectivity in 5G New Radio (NR). On the other hand, different UE tends to have different bandwidth requirements. Thus, in DC, one of the challenging issues is how to integrate resources from two base stations to enhance the quality of service (QoS) as well as the data transfer rate of each UE. In this paper, we proposed novel resource management mechanisms to improve the QoS of UE in the co-channel dual connectivity network. In terms of resource allocation, we designed the (MTS) which, in principle, allocates a resource block to the UE with the best channel quality while considering the issues of intercell resource allocation and the QoS requirement of each UE. In order to balance the load of different cells, we designed a novel cell selection scheme based on the HetNet Congestion Indicator (HCI) which considers not only the signal quality of UE but also the remaining resources of each base station. To improve the QoS of cell edge UE, cell range expansion (CRE) and the Almost Blank Subframe (ABS) were proposed in 3GPP. In this paper, based on Q-learning, we designed an adaptive mechanism which dynamically adjusts the ABS ratio according to the network condition to improve resource utilization. Our simulation results showed that our MTS scheduler was able to achieve a 31.44% higher data rate than the Proportional Fairness Scheduler; our HCI cell selection scheme yielded a 2.98% higher data rate than the signal-to-interference plus noise ratio (SINR) cell selection scheme; the QoS satisfaction rate of our Q-learning dynamic ABS scheme was 4.06% higher than that of the Static ABS scheme. Finally, for the cell edge users who often suffer poor data transfer rate, by integrating the mechanisms of DC, CRE, and ABS, our experimental results showed that the QoS satisfaction ratio of cell edge UEs could be improved by 10.76% as compared to the single connectivity and no ABS situation.

Joint Optimization of Interference Coordination Parameters and Base-Station Density for Energy-Efficient Heterogeneous Networks.

Heterogeneous networks (HetNets), consisting of macro-cells and overlaying pico-cells, have been recognized as a promising paradigm to support the exponential growth of data traffic demands and high network energy efficiency (EE). However, for two-tier heterogeneous architecture deployment of HetNets, the inter-tier interference will be challenging. Time domain further-enhanced inter-cell interference coordination (FeICIC) proposed in 3GPP Release-11 becomes necessary to mitigate the inter-tier interference by applying low power almost blank subframe (ABS) scheme. Therefore, for HetNets deployment in reality, the pico-cell range expansion (CRE) bias, the power of ABS and the density of pico base stations (PBSs) are three important factors for the network EE improvement. Aiming to improve the network EE, the above three factors are jointly considered in this paper. In particular, we first derive the closed-form expression of the network EE as a function of pico CRE bias, power reduction factor of low power ABS and PBS density based on stochastic geometry model. Then, the approximate relationship between pico CRE bias and power reduction factor is deduced, followed by a linear search algorithm to get the near-optimal pico CRE bias and power reduction factor together at a given PBS density. Next, a linear search algorithm is further proposed to optimize PBS density based on fixed pico CRE bias and power reduction factor. Due to the fact that the above pico CRE bias and power reduction factor optimization and PBS density optimization are optimized separately, a heuristic algorithm is further proposed to optimize pico CRE bias, power reduction factor and PBS density jointly to achieve global network EE maximization. Numerical simulation results show that our proposed heuristic algorithm can significantly enhance the network EE while incurring low computational complexity.

E-Fi: Evasive Wi-Fi Measures for Surviving LTE within 5 GHz Unlicensed Band

The growing spectrum crunch has motivated exploratory efforts in the use of LTE in the 5 GHz bands for downlink traffic. However, this paradigm raises concerns of fair sharing of the spectrum and the adverse impact of scheduled LTE frames on Wi-Fi Packet Success Rates (PSR). To address this issue, we propose E-Fi, an interference-evasion mechanism that allows Wi-Fi devices to survive LTE transmissions without any cooperation between these two different standards. Different from existing approaches, we argue that the simple use of Almost Blank Subframes (ABS) within the LTE standard offering short channel access windows overestimates opportunities for Wi-Fi. The pilots embedded in the ABS not only interfere with Wi-Fi but also adversely impact the carrier sensing function. E-Fi mitigates this problem through a two-fold approach. It uses a combination of (i) Wi-Fi Direct with packet relaying and (ii) classical distributed coordination function to reach distant nodes. Second, it ensures load balancing for both Wi-Fi uplink and downlink traffic with high PSR by creating node-groups based with dedicated contention-based medium access intervals. Our approach is validated by comprehensive simulation and experimental results that indicate significantly higher throughput in E-Fi compared to classical Wi-Fi.