Macro Cell Research Articles

A spectrum auction algorithm based on joint power control and beamforming in small cell networks

Spectrum auction is considered as a suitable approach to efficiently allocate spectrum among unlicensed users. However, in previous studies of spectrum auction, competition can hardly be reflected in the traditional spectrum allocation and the spectrum efficiency is still not high after the allocation. In this paper, we enhance the factor of competition in the auctions, in which bidders need to pay for the competition and the interference to macro cell users (MUs). We consider a communication system with one macro cell and several small cells, thus a licensed radio spectrum is shared by both MUs and small cell users (SUs). A truthful auction algorithm is proposed for spectrum allocation and the spectrum is divided into multiple channels in different time slots, so that SUs can make their choice for bidding under the guidance of history. In order to raise the communication quality, we propose a power control and beamforming algorithm in the heterogeneous network to enhance the system performance. Simulation results are presented to verify the effectiveness of the proposed algorithm in the small cell network.

A Joint CAC and Dynamic Bandwidth Allocation Technique for Capacity and QoS Analysis in Heterogeneous LTE based BWA Network: Few Case Studies

Broadband Wireless Access (BWA) network such as LTE brings heterogeneity in terms of different radio access technologies, multi-tier architectures and co-implementation of various protocols to support various types of services with desired Quality of Service (QoS) for the subscribers. However, due to limited bandwidth and high demand of LTE-BWA networks, effective network planning is required to utilize the available radio resources in an efficient way. To achieve this target, this paper aims to implement a unique Radio Resource Management scheme for a heterogeneous LTE based BWA network (BWA Het-Nets) which consists of Small cells along with Macro cells. The proposed analysis has two components: (1) Received Signal Strength (RSS) based CAC policy; and (2) Dynamic Bandwidth Allocation (DBA) scheme for QoS provisioning. The novelty of this work lies on the integration of the RSS based CAC policy with DBA scheme for improved performance in terms of different QoS parameters like New Call Blocking Probability (NCBP), Hand off Call Dropping Probability (HCDP) and Bandwidth Utilization (BU). A Continuous Time Markov Chain based mathematical model is also developed for the realistic analysis of those QoS parameters. The Joint CAC and DBA scheme (JCAC-DBA) in two-tier LTE BWA Het-Nets significantly improves NCBP, HCDP, BU and overall capacity of the network under different combinations of macro/small cells for heterogeneous multimedia services.

Modeling and Performance Evaluation of a Context Information-Based Optimized Handover Scheme in 5G Networks

Recently, green networks are considered as one of the hottest topics in Information and Communication Technology (ICT), especially in mobile communication networks. In a green network, energy saving of network nodes such as base stations (BSs), switches, and servers should be achieved efficiently. In this paper, we consider a heterogeneous network architecture in 5G networks with separated data and control planes, where basically a macro cell manages control signals and a small cell manages data traffic. Then, we propose an optimized handover scheme based on context information such as reference signal received power, speed of user equipment (UE), traffic load, call admission control level, and data type. In this paper, the main objective of the proposed optimal handover is either to reduce the number of handovers or the total energy consumption of BSs. To this end, we develop optimization problems with either the minimization of the number of total handovers or the minimization of energy consumption of BSs as the objective function of the optimization problem. The solution of the optimization problem is obtained by particle swarm optimization, since the developed optimization problem is an NP hard problem. Performance analysis results via simulation based on various probability distributions of the characteristics of UE and BS show that the proposed optimized handover based on context information performs better than the previous call admission control based handover scheme, from the perspective of the number of handovers and total energy consumption. We also show that the proposed handover scheme can efficiently reduce either the number of handovers or the total energy consumption by applying either handover minimization or energy minimization depending on the objective of the application.

Energy-Efficient NOMA-Enabled Traffic Offloading via Dual-Connectivity in Small-Cell Networks

The recent small-cell dual-connectivity (DC) in 3GPP specification enables a mobile user (MU) to communicate with the macrocell and offload traffic through a small cell, which facilitates a flexible traffic offloading. The advanced non-orthogonal multiple access (NOMA) further enables small/macro cells to simultaneously accommodate multiple MUs’ offloading using the same channel, which improves spectrum-efficiency. In this letter, driven by the growing demand for greening cellular systems, we investigate the energy-efficient NOMA-enabled traffic offloading through DC, which aims to minimize the total power consumption of the small and macro cells, while satisfying each MU’s QoS-requirement. The optimal traffic offloading corresponds to a two-sided power allocation problem, which, however, is nonconvex. By exploiting the feature of DC, we equivalently transform this power allocation problem into a convex rate-splitting problem, which can be efficiently solved. Numerical results are provided to validate the advantage in saving power consumption by using the proposed optimal NOMA-enabled traffic offloading scheme.

Dual-Scheduler Design for C/U-Plane Decoupled Railway Wireless Networks

Previously, we have proposed a C/U-plane (Control/User plane) decoupled railway wireless network in which higher frequency bands are adopted by small cells to provide wider available spectra for the U-plane of passengers’ services. In order to guarantee reliable connectivity to wayside eNodeBs (eNBs), an onboard mobile relay (MR), consisting of two components, namely, MR-UE (User Equipment) and MR-AP (Access Point), is employed to forward passengers’ services over backhaul links between MR-UE and wayside eNBs. The remaining problem here is how to utilize spectra effectively and efficiently under this new configuration. Since a given wayside eNB hosts only one single accessed user most of the time, we design an additional uplink scheduler for the MR-UE to self-manage the usage of uplink resources, avoiding the complicated uplink grant procedure commonly used in the conventional cellular systems. Moreover, we develop eNB schedulers to coordinate the spectra in small cells. To deal with occasional multi-user scenarios, we propose an uplink scheduler switcher for the macro cell to judge which uplink scheduler should be activated. Furthermore, an uplink resource allocation scheme with high spectrum efficiency is deliberately designed for the new dual-scheduler configuration. Finally, we carry out theoretical analysis and numerical simulations to demonstrate the effectiveness of our proposed scheme.

User Association and Resource Allocation Optimization in LTE Cellular Networks

As the demand for higher data rates is growing exponentially, homogeneous cellular networks have been facing limitations when handling data traffic. These limitations are related to the available spectrum and the capacity of the network. Heterogeneous networks (HetNets), composed of macro cells (MCs) and small cells (SCs), are seen as the key solution to improve spectral efficiency per unit area and to eliminate coverage holes. Due to the large imbalance in transmit power between MCs and SCs in HetNets, intelligent user association (UA) is required to perform load balancing and to favor some SCs attraction against MCs. As long term evolution (LTE) cellular networks use the same frequency sub-bands, user equipment may experience strong intercell interference (ICI), especially at cell edge. Therefore, there is a need to coordinate the resource allocation (RA) among the cells and to minimize the ICI. In this paper, we propose a generic algorithm to optimize UA and RA in LTE networks. Our solution, based on game theory, permits to compute cell individual offset and a pattern of power transmission over frequency and time domain for each cell. Simulation results show significant benefits in the average throughput and also cell edge user throughput of 40% and 55% gains respectively. Furthermore, we also obtain a meaningful improvement in energy efficiency.

Energy-Efficient Resource Allocation for Phantom Cellular Networks With Imperfect CSI

Multi-tier heterogeneous networks have become an essential constituent for next-generation cellular networks. Meanwhile, energy efficiency (EE) has been considered a critical design criterion along with the traditional spectral efficiency (SE) metric. In this context, we study power and spectrum allocation for a two-tier phantom cellular network. The optimization framework includes both EE and SE. We consider densely deployed phantom cellular networks and model the EE optimization problem considering the inevitable interference in this setup and imperfect channel estimation impairments. To this end, we propose three resource allocation strategies aiming at optimizing this network EE performance metric. Furthermore, we investigate the effect of changing some system parameters on the performance of these strategies, such as phantom cells resource units share, number of deployed phantom cells within a macro cell, number of pilots, and the phantom cells transmission power budget. It is found that increasing the number of pilots will deteriorate the EE performance of the whole setup, while increasing phantom cells transmission power budget will not affect the EE of the whole setup significantly. In addition, we observed that it is always useful to allocate most of the network resource units to the phantom cells tier.

Downlink Performance of Pilot-Reused HetNet With Large-Scale Antenna Arrays

Considering a heterogeneous network where both macro base station (BS) and small cell (SC) nodes are equipped with massive number of antennas, this paper studies the performance for multiple-input multiple-output downlinks when the macro and small cells share the same spectrum, and hence interfere with each other. Suppose that the large-scale antenna arrays at both macro BS and SC nodes employ maximum-ratio transmission (MRT) or zero-forcing transmission (ZFT) precoding, and transmit data streams to served users simultaneously. A new pilot reuse pattern among SCs is proposed for channel estimation. Taking into account imperfect channel state information (CSI), capacity lower bounds for MRT and ZFT are derived, respectively, in closed-form expressions involving only statistical CSI, followed by asymptotic analyses for massive arrays under specific power scaling laws. Subsequently, two user scheduling algorithms, greedy scheduling and asymptotical scheduling algorithm (ASA), are proposed based on derived capacity lower bounds and asymptotic analyses, respectively. ASA is demonstrated to be a near optimal in the asymptotic regime and has low complexity. Finally, the derived closed-form expressions are verified to be accurate predictors of the system performance by Monte Carlo simulations. Numerical results demonstrate the effectiveness of the asymptotic analysis and proposed user scheduling schemes.

Power efficient and coordinated eICIC-CPC-ABS method for downlink in LTE-advanced heterogeneous networks

In 2020, mobile data traffic is expected to be a thousand times more than the current scenario. In order to handle this increased capacity, improvement in spectral efficiency is one of the challenging task. In long term evolution (LTE) and long term evolution advanced (LTE-A), deployment of small cell base station (SBS) and hotspot are step to handle the increased capacity of the network and quality of service. In this scenario, the SBSs are deployed under the coverage of macro cell base station (MBS). Neighbour MBS and neighbour SBS create intra and inter-cell interference to the users in the overlapped region. In order to mitigate interference, coordination between base stations is required. In this paper, we propose an enhanced intercell interference coordination by considering centralized processing controller with almost blank subframe (eICIC-CPC-ABS) for heterogeneous networks (HetNets). Centralized processing controller (CPC) at MBS decides the radio resource allocation of each SBSs based on user location. The dynamic frequency and reduced transmission power depend on the user locations. The analytical and simulation results demonstrate that the proposed method (eICIC-CPC-ABS) provides higher signal to interference plus noise ratio (SINR) compared to existing models: inter cell interference coordination (ICIC) and enhanced inter cell interference coordination (eICIC). The proposed method provides significant savings in transmitting power. Additionally, it increases the network capacity and coverage.

Dual Connectivity Enabled User Association Approach for Max-Throughput in the Downlink Heterogeneous Network

The architecture of dual connectivity (DC) allows each user's equipment to simultaneously communicate with a macro and a small cell via two different radio-interfaces. User association (UA) with DC is considerably more challenging than traditional single one, because each user must be associated with the best combination of serving macro cell and small cell. This paper focuses on DC architecture and proposes an efficient DC-enabled UA approach to maximize the overall system throughput for downlink wireless heterogeneous network (HetNet). In this approach, we formulate it as a non-linear and integer optimization problem in a sum-of-ratios form. Since the formulated problem is non-deterministic polynomial hard (NP-hard), it is challenging to achieve its optimal solutions. To this end, this problem is relaxed and then transformed into a tractable form, which can be solved iteratively to obtain its solution. Numerical results show that, compared with the existing methods, the proposed algorithm can enhance system throughput and improve offloading performance of small cells.

Multilayer Optimization of Heterogeneous Networks Using Grammatical Genetic Programming.

Heterogeneous cellular networks are composed of macro cells (MCs) and small cells (SCs) in which all cells occupy the same bandwidth. Provision has been made under the third generation partnership project-long term evolution framework for enhanced intercell interference coordination (eICIC) between cell tiers. Expanding on previous works, this paper instruments grammatical genetic programming to evolve control heuristics for heterogeneous networks. Three aspects of the eICIC framework are addressed including setting SC powers and selection biases, MC duty cycles, and scheduling of user equipments (UEs) at SCs. The evolved heuristics yield minimum downlink rates three times higher than a baseline method, and twice that of a state-of-the-art benchmark. Furthermore, a greater number of UEs receive transmissions under the proposed scheme than in either the baseline or benchmark cases.

Energy estimation and optimization platform for 4g and the future base station system early-stage design

There are already several power models to estimate the power consumption of base stations at system level. However, there is so far no model that can predict power consumption of the future base station designs based on algorithms and hardware selections with insufficient physical information. We present such an energy model for typical base stations. This model can help designers in estimating, evaluating and optimizing energy/ power consumption of candidate designs in early design stages. The proposed model is verified by an LTE extreme scenario. The estimated results show that digital front-end, channel equalization and channel decoding are three major power greedy modules (consuming 39.4%, 16.3%, 13.4%) in a digital baseband subsystem. The power estimation error of the proposed power amplifier (PA) power model is 3.5% (macro cell). The major contribution of this paper is that the proposed models can rapidly estimate energy/power consumption of 4G and the future base stations (such as 5G) in early design stages with well acceptable precision, even without sufficient implementation information.

Einfluss einer Betonbeschichtung auf die Mechanismen der Bewehrungskorrosion in gerissenem Stahlbeton

AbstractDie Dauerhaftigkeit von chloridexponierten Stahlbetonbauwerken kann durch Rissbildung erheblich reduziert werden. Durch die Risse können Chloride vergleichsweise rasch zur Bewehrung gelangen und Bewehrungskorrosion initiieren. Daher wird in einschlägigen Regelwerken [1, 2] vorgegeben, bei besonders gefährdeten Bauwerken wie Parkdecks dem Eindringen von Chloriden durch zusätzliche Maßnahmen dauerhaft entgegenzuwirken. Das DBV‐Merkblatt „Parkhäuser und Tiefgaragen” [3] enthält verschiedene Entwurfsgrundsätze und Ausführungsvarianten zur Sicherstellung der Dauerhaftigkeit. Eine Variante sieht vor, gemäß dem Instandsetzungsprinzip W‐Cl nach RL SIB [4] bzw. dem Verfahren 8.3 nach DIN EN 1504‐9 [5] die Betonoberfläche mit einem rissüberbrückenden Oberflächenschutzsystem (OS) nach abgeschlossener Rissbildung zu verschließen, um eine weitere Chlorid‐ und Feuchtezufuhr zu verhindern und damit den elektrischen Widerstand des Betons zu erhöhen.In einem umfangreichen Experimentalprogramm konnte für die Situation „bewehrungskreuzende Biegerisse” gezeigt werden, dass nach zeitweiser Chloridexposition, wie sie in Parkhäusern über eine Winterperiode im unbeschichteten Zustand zu erwarten ist, durch eine Betonbeschichtung zuvor bereits aktivierte Makroelementströme maßgeblich reduziert bis vollständig gestoppt wurden. Der Erfolg dieser Maßnahme beruht auf dem Anstieg des anodischen Polarisationswiderstands aufgrund von Deckschichtbildung und/oder unzureichendem Nachschub von Chloriden. Der Einfluss der Erhöhung des Elektrolytwiderstands auf das Makrokorrosionselement durch Austrocknung des Betons ist vernachlässigbar. Noch nicht abschließend geklärt ist die Frage nach dem höchstzulässigen Chloridgehalt, der im Beton verbleiben darf, damit auch nach einer Beschichtung keine Bewehrungskorrosion mit standsicherheitsrelevanten Querschnittsverlusten initiiert bzw. aufrecht erhalten wird.

Traffic‐aware resource allocation schemes for HetNet based on CDSA

The control-data separation architecture (CDSA) has been regarded as a promising solution to effectively manage the heterogeneous network (HetNet) in the fifth-generation mobile communication systems. Thus, this study investigates the resource allocation problems in CDSA-based HetNet. To meet various requirements of data transmission, the authors first present a new framework with flexible resource management and efficient traffic control. In this framework, the control-data transmission supported by macro cell evolved nodeB is time-sensitive and continuous with high reliability. On the basis of it, a traffic-aware resource allocation approach is proposed to improve the resource efficiency. Once the traffic-congestion requirements of the pattern are satisfied with the minimum spectrum, the throughput of small cells is simultaneously maximised due to orthogonal spectrum between macro and small cells by using this approach. Moreover, the traffic-congestion analytical result is elaborately derived in terms of current network state. Three adaptive resource allocation schemes for implementing this approach are also designed with different complexities. Numerical results validate the accuracy of the proposed analytical method, and also indicate that the traffic-aware resource allocation approach is more efficient than the static one.

Joint Backhaul-Access Analysis of Full Duplex Self-Backhauling Heterogeneous Networks

With the successful demonstration of in-band full-duplex (IBFD) transceivers, a new research dimension has been added to wireless networks. This paper proposes an interesting use case of this capability for IBFD self-backhauling heterogeneous networks (HetNet). IBFD self-backhauling in a HetNet refers to IBFD-enabled small cells backhauling themselves with macro cells over the wireless channel. Owing to their IBFD capability, the small cells simultaneously communicate over the access and backhaul links, using the same frequency band. The idea is doubly advantageous, as it obviates the need for fiber backhauling small cells every hundred meters and allows the access spectrum to be reused for backhauling at no extra cost. This work considers the case of a two-tier cellular network with IBFD-enabled small cells, wirelessly backhauling themselves with conventional macro cells. For clear exposition, the case considered is that of FDD network, where within access and backhaul links, the downlink (DL) and uplink (UL) are frequency duplexed ($f1$, $f2$ respectively), while the total frequency spectrum used at access and backhaul ($f1+f2$) is the same. Analytical expressions for coverage and average downlink (DL) rate in such a network are derived using tools from the field of stochastic geometry. It is shown that DL rate in such networks could be close to double that of a conventional TDD/FDD self-backhauling network, at the expense of reduced coverage due to higher interference in IBFD networks. For the proposed IBFD network, the conflicting aspects of increased interference on one side and high spectral efficiency on the other are captured into a mathematical model. The mathematical model introduces an end-to-end joint analysis of backhaul (or fronthaul) and access links, in contrast to the largely available access-centric studies.

Secure massive MIMO‐enabled full‐duplex 2‐tier heterogeneous networks by exploiting in‐band wireless backhauls

AbstractTo enhance the spectrum efficiency and secrecy performance, by using in‐band full‐duplex (FD) wireless backhaul technique, a secure massive multiple input multiple output (MIMO)–enabled heterogeneous cellular network (HCN) model is presented, where the macro base stations (MBSs) are equipped with massive MIMO antenna array, whereas the small cell base stations (SBSs) and user equipment have the single antenna. The ultradense small cells underlay the macro cells and offload traffic from macro cells. With FD mode, the massive MIMO MBSs and single‐antenna SBSs are responsible, respectively, for the access traffic of macro and small cells as well as the backhaul transmission between MBSs and SBSs over the same time‐frequency resource. The transmissions of macro and small cells are exposed to non‐colluding and passive eavesdroppers that attempt to decode the signals of legitimate users. For such HCN with in‐band wireless backhaul, by modeling the network elements as the independent Possion point processes and using the stochastic geometry, we first investigate the secrecy probabilities of the macro cell downlink and small cell uplink transmissions. At the same time, to achieve a comprehensive view, we also investigate the corresponding signal‐interference‐noise ratio (SINR) coverage performance. The presented numerical results show that when the intensity of user equipment is small relatively, exploiting the in‐band backhaul interference as jamming signals can enhance the secrecy probabilities of both the macro and small cell transmissions so that the in‐band FD backhaul mode outperforms the out‐band FD one. However, for the SINR coverage, the opposite results are achieved. That is to say, the in‐band backhaul transmission degrades the SINR coverage probabilities because of the existence of wireless backhaul interference. Besides of these, in numerical analysis, we also investigate the effect of the network parameters on the secrecy and coverage performance of both the macro and small cells. The derived results can be used for guiding the design of HCNs.

Smart heterogeneous networks: a 5G paradigm

An exponential growth in data demand on wireless networks and wireless link capacity approaching its theoretical limits, bound us to find new solutions and innovative network designs to handle the enormous amount of traffic. In this paper, we discuss long term evolution-advance (LTE-A) heterogeneous networks (HetNets) being a most effective solution to break this wireless cellular capacity crunch. LTE-A HetNets provide adequate increase in capacity by utilizing multi-tier architecture consisting of different type of cells i.e macro cell, small cell, relay and device to device. However this increase in capacity comes with certain challenges in HetNets outlined in this article. Considering inter cell interference coordination (ICIC) as biggest challenge in LTE-A HetNets, this article surveys state of the art LTE-A HetNets deployments with focus on ICIC. Effective ICIC techniques allow further substantial capacity increase. We give state of the art ICIC on air-interface as well as backhaul strategies for effective ICIC in LTE-A HetNets. Operators perspective of LTE-A HetNets with some insight to future of 5G LTE-A HetNets is provided. We also provide simulation results to show how LTE-A HetNets lead to realize ambitious targets of 5G technology in terms of capacity.

Modeling Delay Timer Algorithm for Handover Reduction in Heterogeneous Radio Access Networks

Consisting of both small cells and a macro cell, the heterogeneous radio access network (Het-RAN) provides transmission service with higher data rate, offloads data traffic from the macro cell, and expands the service area of the macro cell. However, due to the small and non-continuous service areas of the small cells, frequent handover executions (i.e., significant handover cost) occur in the Het-RAN. To resolve the issue, we have proposed a delay timer algorithm (DTA) in our previous works. In this paper, we propose an analytical model to study the effects of the application traffic (based on the ETSI traffic model) and the user equipment (UE) mobility model on the performance of the DTA. We assume general distributions in the UE mobility model, so the analytical model is flexible enough for performance evaluation of the real Het-RAN system. We also construct a simulation model. The analytical model is validated against the simulation model. This analysis can help network operators run the Het-RAN more efficiently and effectively.

Interference Alignment With Finite Extensions in Partially Connected Networks

In this paper, we investigate the interference alignment (IA) for a class of partially connected multi-input multi-output heterogeneous networks, which consist of $L$ fully connected pico cells, $J$ partially connected pico cells, and one macro cell. In particular, we investigate the feasibility of IA conditions with no channel extensions, $T$ -independent channel extensions, and $T$ -dependent channel extensions, respectively, for the single beam case. We present three theorems to characterize some necessary conditions, which $L$ , $J$ , $T$ , and the channel diversity order $\overline L$ must jointly satisfy when IA conditions are feasible. These necessary conditions also implicitly impose the constraints on the upper bounds of achievable degrees of freedom with different channel extensions.

EICIC Configuration Algorithm with Service Scalability in Heterogeneous Cellular Networks

Interference management is one of the most important issues in heterogeneous cellular networks with multiple macro and pico cells. The enhanced inter cell interference coordination (eICIC) has been proposed to protect downlink pico cell transmissions by mitigating interference from neighboring macro cells. Therefore, the adaptive eICIC configuration problem is critical, which adjusts the parameters including the ratio of almost blank subframes (ABS) and the bias of cell range expansion (RE). This problem is challenging especially for the scenario with multiple coexisting network services, since different services have different user scheduling strategies and different evaluation metrics. By using a general service model, we formulate the eICIC configuration problem with multiple coexisting services as a general form consensus problem with regularization and solve the problem by proposing an efficient optimization algorithm based on the alternating direction method of multipliers. In particular, we perform local RE bias adaptation at service layer, local ABS ratio adaptation at BS layer, and coordination among local solutions for a global solution at a network layer. To provide the service scalability, we encapsulate the service details into the local RE bias adaptation subproblem, which is isolated from the other parts of the algorithm, and we also introduce some implementation examples of the subproblem for different services. The extensive simulation results demonstrate the efficiency of the proposed algorithm and verify the convergence property.