Long Term Evolution Femtocell Research Articles

Software-Defined Networking-Enabled Heterogeneous Wireless Networks and Applications Convergence

A software-defined networking (SDN) architecture is capable of integrating all radio frequency and optical wireless small cell networks (e.g. fifth generation (5G), long-term evolution (LTE) femtocell, wireless fidelity (WiFi), light fidelity (LiFi)) in one network domain. This paper considers a SDN-enabled heterogeneous network (HetNet) comprised of LiFi, LTE femtocell and WiFi access points (APs). The HetNet control plane maintains the state of the network topology and wireless resources, which can support the development of intelligent service provisioning and efficient data communications in x generation (xG) wireless networks. The SDN applications use the network state to provide services in the data plane. However, when the state of network and wireless resources constantly changes, the SDN applications cannot provide reliable and guaranteed services to the wireless user equipments. This paper develops a queuing theoretic framework, which provides a performance evaluation for the SDN-enabled HetNet and applications convergence. A traffic engineering (TE) scheme is developed to support dynamic agnostic downlink flows routing to APs and differentiated granular services across the HetNet. Network and user centric policies are developed to make applications aware of network resource availability on the northbound and southbound interfaces of a SDN controller. Numerical models are introduced to study the impact of the computation and communication resources of northbound and southbound interfaces on the SDN-enabled HetNet scalability and the quality-of-service (QoS) guarantee of applications. Also, simulation scenarios are conducted to evaluate the performance of the TE scheme in provisioning effective and reliable services for subscribers.

Performance analysis of resource scheduling in LTE femtocell with hybrid access mode

<p>Femtocell is a promising technology that intends in solving the indoor coverage problems so as to enhance the cell capacity. The overall network performance, in turn depends on the access methods used by the femtocells. The access method is used to identify about the user’s connectivity with the femtocell network. There are three access mechanisms defined in Third Generation partnership Project (3GPP) specification for Long Term Evolution (LTE) femtocells: open, closed and hybrid access mechanisms. Hybrid access mechanism is mostly preferred by the network for the effective utilization of resources. But, it is important to regulate the proper scheduling scheme for them. In this paper, scheduling in femtocell is investigated, where, among the non subscribers, preference is given to the users who have high throughput priority metric, thereby increasing overall throughput of the network.</p>

Enhanced handover algorithm in LTE femtocells network

Data rate and Coverage are the main secret factors for customer satisfaction. Today, small cell technology as femtocell can achieve the upcoming demand for higher data rate for cellular networks as well as can extend the coverage area. Femtocells are known as low cost, low power and efficient way to enhance the signal in indoor/outdoor areas with little mobile coverage.Deploying femtocells networks result in more frequent initiation of a handover (HO) procedure. The reduction of unnecessary handovers challenges is getting more considerable while more femtocells are used in the network. We propose a novel HO algorithm to eliminate the redundant handovers in Long Term Evolution (LTE) femtocells network and to nominate the most proper target femtocell for HO among many candidates. This algorithm based on the transition probability matrix to predict the user movement using Markov Chain equations. Toward this goal, we are considering Reference Symbol Received Quality (RSRQ) and Reference Symbol Received Power (RSRP), User Equipment (UE) moving direction and in which zone the UE inside the femtocell as decision criteria.

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

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

QoS-aware cooperative power control and resource allocation scheme in LTE femtocell networks

Home Evolved Node B (HeNB), which is the base-station of femtocell, is a popular research topic in the future Long Term Evolution (LTE) networks. It can serve many indoor users and improve the spectrum utility. However, the large amount of HeNBs also causes heavy interference. In this paper, we propose a novel scheme called QoS-aware cooperative power control and resource allocation (QCPR) to maintain the QoS of user constraints and reduce the interference in femtocell networks by considering each HeNBs troubling and servicing aspects. QCPR is composed by two operation stages. First, the chief troubling HeNBs transmission power is adjusted according to its interference and service factors. Then, a probabilistic-based resource allocation algorithm is executed to arrange each HeNBs transmission time/frequency to further enhance the overall spectrum reuse. The simulation results illustrate that, comparing to other existing power control and resource allocation schemes, QCPR effectively avoids the interferences between neighbor HeNBs, and thus better satisfies QoS connections and improves aggregate throughput of the femtocell networks.

New Scheduling Algorithm Proposed for Real Time Traffic Over LTE Femto-Cell

Due to the inadequate indoor signal penetration, the indoor environment coverage becomes poor, which diminishes the quality of voice and video applications and slows down high-speed data services, which leads to customer churn, who expect high quality of service. To keep customers satisfied, Long Term Evolution (LTE) has developed a new advanced technology called FemtoCell, conceived to boost cellular network performance and is achieved with the use of access points installed by home users. The purpose of this paper is to analyze the performance of new proposed algorithm for voice and video over LTE FemtoCell, and to compare its performances with some well-known algorithms such as the proportional fair algorithm (PF), Exponential Proportional Fairness (EXP/PF), Logarithm Rule (LOG-Rule), Exponential Rule (EXP-Rule) and Modified Largest Weighted Delay First (MLWDF), The performance evaluation is conducted in terms of system throughput, delay, and Packet Loss Ratio. Finally it will be concluded that the proposed scheduler satisfies the quality of service (QoS) requirements of the real-time traffic in terms of packet loss ratio (PLR), average throughput and packet delay. This paper also discusses the key issues of scheduling algorithms to be considered in future traffic requirements.

Analysis of handover based on the use of femtocells in LTE networks

One of the key elements in the networks LTE (Long Term Evolution) is the possibility of deploying multiple femtocells for the improvement of coverage and data rate. However, arbitrary overlapping coverage of these cells makes the handover mechanism complex and challenging. In this paper, simulations of deploying LTE femtocells in a scenario were evaluated. With this objective, measure impact and correlation of the use of femtocell parameters of QoS (Quality of Service) and handover. Possible limitations of this integration are discussed. Will be the integration of LTE femtocell a panacea? Despite this promising alternative estimates are fraught with uncertainty. The results show that the use of femtocell got worse on indicators of handover, impact on indicators of QoS.

Seamless LTE connectivity in high‐speed trains

AbstractHigh‐speed train (HST) is revitalizing the train as a preferred mid‐range transportation system. The provision of broadband Internet connectivity onboard trains is one of the key challenges in the competition among train operators. Unprecedented spectral efficiency and data rates (up to 100Mbps in high mobility) of the Universal Mobile Telecommunications System long‐term evolution (LTE) are expected to offer the solution for high‐speed Internet access onboard in HSTs. Massive wireless access and frequent handovers (HOs) of a large number of users might potentially cause service interruptions, and this, in turn, degrades intolerably the quality of experience (QoE) of users' onboard Internet access. In this paper, we propose a solution based on distributed antenna system that combines directional and omni‐directional antennas as train‐to‐ground radio‐access terminals (T‐RATs) and LTE femtocells in each carriage. Directional antennas are deployed at both ends of the HST to provide multi‐cell access by diversifying the HOs over multiple LTE cells. This mechanism virtually elongates the train size by connecting the front and rear carriages' T‐RATs to the faraway eNodeBs and augmenting the number of cells the HST can be simultaneously connected to. An ad hoc distributed load‐balancing mechanism that consists in offloading backlogged packets to the on‐service T‐RATs is mandatorily paired with multi‐cell access scheme to tie up with the request of seamless onboard Internet service at high QoE level. Copyright © 2015 John Wiley & Sons, Ltd.

Study of coexistence between indoor LTE femtocell and outdoor-to-indoor DVB-T2-Lite reception in a shared frequency band

Nowadays, the demand for high-quality multimedia services (video, audio, image, and data) is rapidly increasing. The Digital Video Broadcasting - terrestrial (DVB-T) standard, its second-generation version (DVB-T2), and the Long-Term Evolution (LTE) standard are the most promising systems to fulfill the demand for advanced multimedia services (e.g., high-definition image and video quality), especially in Europe. However, LTE mobile services can operate in a part of the UHF band allocated to DVB-T/T2 TV services previously. The main purpose of this work is to explore the possible coexistences of DVB-T2-Lite and LTE systems in the same shared frequency band (co-channel coexistence) under outdoor-to-indoor and indoor reception conditions. Furthermore, an applicable method for evaluating coexistence scenarios between both systems is shown with a particular example. These coexistence scenarios can be noncritical and critical. In the first case, both systems can coexist without significant performance degradation. In the second one, a partial or full loss of DVB-T2-Lite and/or LTE signals can occur. We consider an indoor LTE femtocell and outdoor-to-indoor DVB-T2-Lite signal reception in a frequency band from 791 up to 821 MHz. Simulations of combined indoor and outdoor signal propagation are performed in MATLAB using 3rd Generation Partnership Project (3GPP) channel models, separately for both DVB-T2-Lite and LTE systems. Correctness of path loss simulation results is verified by measurements. Afterwards, an appropriate linear model is proposed which enables to evaluate the impact of coexistence on performance of both systems in outdoor-to-indoor and indoor-to-indoor reception scenarios. The results are related to an actual location in the building and are presented in floor plans. The floor plans include different coexistence conditions (different power imbalance and different amount of overlay of the radio channels). Service availability of both systems is verified again by measurements. The resulting maps help better understand the effect of coexistence on achievable system performance under different indoor/outdoor reception situations considering real transmission conditions.

Designing Energy-Efficient Wireless Access Networks: LTE and LTE-Advanced

As large energy consumers, base stations need energy-efficient wireless access networks. This article compares the design of Long-Term Evolution (LTE) networks to energy-efficient LTE-Advanced networks. LTE-Advanced introduces three new functionalities--carrier aggregation, heterogeneous networks, and extended multiple-input, multiple-output (MIMO) support. The authors develop a power consumption model for LTE and LTE-Advanced macrocell and femtocell base stations, along with an energy efficiency measure. They show that LTE-Advanced's carrier aggregation and MIMO improve networks' energy efficiency up to 400 and 450 percent, respectively.

Mobility robustness optimization in self-organizing LTE femtocell networks

Femtocell is a promising solution for enhancing the indoor coverage and capacity in wireless networks. However, for the small size of femtocell and potentially frequent power on/off, existing handover schemes may not be reliable enough for femtocell networks. Moreover, improper handover parameters settings may lead to handover failures and unnecessary handovers, which make it necessary to enhance the mobility robustness for femtocells. In this article, we propose a gradient method and cost function-based mobility robustness optimization scheme for long term evolution (LTE) femtocell self-organizing networks. Moreover, signalling overhead of the scheme is analyzed. Simulation results show that the proposed scheme has a better performance than the fixed parameters method in terms of reduced the number of handover failures and unnecessary handovers with limited signalling modifications.

Collaborative Sub-Channel Allocation in Cognitive LTE Femto-Cells: A Cooperative Game-Theoretic Approach

In this paper, formation of stable coalitions of users, each exploiting resources in a femto-cell, and the resource allocation in each femto-cell is investigated in a UMTS long term evolution (LTE) network. We study a downlink scenario where users collaborate to increase network throughput and, simultaneously, attempt to increase their own payoffs. Payoffs to the users are defined as the monetary equivalent of the individual users' achievable throughput in the specified coalition structure. A distributed game-theoretic resource allocation mechanism is developed whereby users autonomously decide which sub-channel in which coalition to join. If each user operates according to the proposed algorithm, the sum throughput of all links converges with probability one to its maximum feasible value.

Traffic steering by self-tuning controllers in enterprise LTE femtocells

Abstract Femtocells have been suggested as a promising solution for the provision of indoor coverage and capacity. This article investigates the problem of re-distributing traffic demand between long-term evolution (LTE) femtocells with open access in an enterprise scenario. Several traffic sharing algorithms based on automatic tuning of femtocell parameters are considered. The proposed algorithms are implemented by fuzzy logic controllers. Performance assessment is carried out in a dynamic system-level simulator. Results show that localized congestion problems in these scenarios can be solved without impairing connection quality by jointly tuning handover margins and cell transmit power.

On accurate simulations of LTE femtocells using an open source simulator

Long-term evolution (LTE) femtocells represent a very promising answer to the ever growing bandwidth demand of mobile applications. They can be easily deployed without requiring a centralized planning, to provide high data rate connectivity with a limited coverage. In this way, the overall capacity of the cellular network can be greatly improved. At the same time, the uncoordinated setup of femtocells poses new issues that require a deep and thorough analysis before spreading this technology worldwide. Unfortunately, to the best of our knowledge, no accurate simulation tools are freely available for enabling this kind of investigation. Thus, we present in this study a simulation tool for LTE femtocells, implemented as a module of the emerging open source LTE-sim framework. It encompasses heterogeneous scenarios with both macro and femtocells, spectrum allocation techniques, user mobility, femtocell access policies, and several other features related to this promising technology. After reviewing the status of the art on LTE femtocells, we detail the description of the module that we propose with a major emphasis on the newly devised loss models for indoor scenarios, the new network topology objects, and the most significant enhancements to the simulator protocol stack. Furthermore, to provide a clear understanding of the practical utility of this new simulator, we investigate two indoor and urban scenarios. A scalability test is also presented to demonstrate the efficiency of the proposed tool in terms of processing requirements. All presented results suggest that this new module can be very interesting for the research community, due to its great flexibility and limited computational cost.

Optimized spectrum sensing algorithms for cognitive LTE femtocells

In this article, we investigate to perform spectrum sensing in two stages for a target long-term evolution (LTE) signal where the main objective is enabling co-existence of LTE femtocells with other LTE femto and macrocells. In the first stage, it is required to perform the sensing as fast as possible and with an acceptable performance under different channel conditions. Toward that end, we first propose sensing the whole LTE signal bandwidth using the fast wavelet transform (FWT) algorithm and compare it to the fast Fourier transform-based algorithm in terms of complexity and performance. Then, we use FWT to go even deeper in the LTE signal band to sense at multiples of a resource block resolution. A new algorithm is proposed that provides an intelligent stopping criterion for the FWT sensing to further reduce its complexity. In the second stage, it is required to perform a finer sensing on the vacant channels to reduce the probability of collision with the primary user. Two algorithms have been proposed for this task; one of them uses the OFDM cyclic prefix for LTE signal detection while the other one uses the primary synchronization signal. The two algorithms were compared in terms of both performance and complexity.

Dynamic Reservation Scheme of Physical Cell Identity for 3GPP LTE Femtocell Systems

A large number of phone calls and data services will take place in indoor environments. In Long Term Evolution (LTE), femtocell, as a home base station for indoor coverage extension and wideband data service, has recently gained significant interests from operators and consumers. Since femtocell is frequently turned on and off by a personal owner, not by a network operator, one of the key issues is that femtocell should be identified autonomously without system information to support handover from macrocell to femtocell. In this paper, we propose a dynamic reservation scheme of Physical Cell Identities (PCI) for 3GPP LTE femtocell systems. There are several reserving types, and each type reserves a different number of PCIs for femtocell. The transition among the types depends on the deployed number of femtocells, or the number of PCI confusion events. Accordingly, flexible use of PCIs can decrease PCI confusion. This reduces searching time for femtocell, and it is helpful for the quick handover from macrocell to femtocell. Simulation results show that our proposed scheme re- duces average delay for identifying detected cells, and increases network capacity within equal delay constraints. The 3rd Generation Partnership Project (3GPP) is work- ing on the standardization of asynchronous communication systems. This technology is being enhanced gradually en- suring higher user data rate, bigger system capacity, and lower cost. The wideband CDMA (WCDMA) system is standardized with 3GPP release 99/4 which is being de- ployed in the world. Release 5 is related to High Speed Downlink Packet Access (HSDPA), and it improves the downlink packet transmission speed theoretically up to 14.4 Mbps. High Speed Uplink Packet Access (HSUPA) is enhanced up to 5.76 Mbps in uplink, and it is standardized with the Release 6. We simply mention both HSDPA and HSUPA as High Speed Packet Access (HSPA). In release 7, High Speed Packet Access Evolution (eHSPA, HSPA+) is standardized. eHSPA is based on the HSPA network with a simple upgrade, and it supports more bandwidth efficiency and lower latency. The maximum data rate is 28.8 Mbps in downlink and 11.5 Mbps in uplink (1). How- ever, users still require further system improvements. The technology is dramatically enhanced in release 8, where the standard of Long Term Evolution (LTE) is currently being established. The main objectives of LTE are higher data rates, lower latency, increased capacity, enhanced coverage, and an optimized system for the packet switching network (2). LTE also considers a femtocell, which is referred to as a home base station for an indoor coverage extension and overall network performance enhancement (3). Recently, LTE-Advanced standard targeting of 1Gbps for low mobil- ity is being discussed in release 9. We look into general features and requirements of fem- tocells. Important issues related to access control are de- scribed, followed by our contributions and organization of the paper.