Long Term Evolution Downlink Research Articles

Crosstalk Mitigation for LTE-Over-Copper in Downlink Direction

Radio-over-copper is a niche idea that has potential to become a cornerstone in the deployment of dense 5G networks. We address one of the remaining hurdles and present an architecture for transparent crosstalk mitigation in long term evolution (LTE)-over-copper systems. By taking advantage of reference symbols present in the downlink LTE signals, we propose two methods for estimating the copper channel. System performance is evaluated using channel measurements and error vector magnitude calculations with promising results.

WE-MQS: A new LTE Downlink Scheduling Scheme for Voice Services based on User Perception

The Long Term Evolution (LTE) is a high data rates and fully All-IP network. Scheduling and resource allocation are very important tasks in LTE network. So that, the optimization of the real-time services transmission is very essential. However, there are many challenges when deploying the live multimedia services such as VoIP, Video, etc. This paper proposes a new scheduling scheme which based on the Wideband (WB) E-model, Channeland QoS-Aware (known as WE-MQS scheduler) for voice traffic in LTE downlink direction. The voice traffic flow is very sensitive to network impairments such as delay, packet loss, jitter, etc. The proposed scheduling scheme is based on the extension of the WB E-model and the consideration of Maximum Queue Size (MQS) as a factor for the metric. Since this scheduling scheme considers Mean Opinion Score (MOS) values, thus, it gets higher user perception. The simulation results show that the proposed scheme has the performance which not only satisfies QoS requirements of voice services but also outperforms well-known schedulers such as Frame Level Scheduler (FLS), Modified Largest Weighted Delay First (MLWDF) and Exponential/Proportional Fair (EXP/PF) schedulers in terms of delay for all the number of user (NU) and Packet Loss Rate (PLR) when the NU is more than 47. For the cell throughput, Fairness Index (FI), and Spectral Efficiency, the proposed scheduler is always in the middle of the remaining schedulers. The performance evaluation is compared in terms of Delay, PLR, Throughput, FI, and FI for FLS, M-LWDF, EXP/PF schedulers and the proposed one.

Interference Analysis Between Digital Terrestrial Television (DTT) and 4G LTE Mobile Networks in the Digital Dividend Bands

With the introduction of digital terrestrial television (DTT) and the analogue television switch-off, terrestrial broadcast spectrum in the UHF band is being released for mobile communications, in particular for fourth generation (4G) long term evolution (LTE) mobile services. This spectrum is known as digital dividend. An impending problem when deploying 4G LTE mobile networks in the digital dividend bands is that interferences may appear in the adjacent radio frequency channels used for DTT. In this paper, we analyze the adjacent coexistence of DTT and 4G LTE networks in the digital dividend bands at 700 MHz and 800 MHz. A generic framework is adopted such that results can be easily extrapolated to different scenarios and bands. Results are presented as a function of the guard band between technologies, for both LTE uplink and downlink adjacent to the DTT signals, and for fixed outdoor and portable indoor DTT reception. Also, the effect of using anti-LTE filters is studied.

Improved MLWDF scheduler for LTE downlink transmission

ABSTRACTIn long-term evolution (LTE) downlink transmission, modified least weighted delay first (MLWDF) scheduler is a quality of service (QoS) aware scheduling scheme for real-time (RT) services. Nevertheless, MLWDF performs below optimal among the trade-off between strict delay and loss restraints of RT and non-RT traffic flows, respectively. This is further worsened with the implementation of hybrid automatic retransmission request (HARQ). As these restraints grow unabated with increasing number of user demands, the performance of MLWDF further reduces. In order to ameliorate this situation, there is a need to directly incorporate the variations in user demands and HARQ implementation as parameters to the MLWDF scheduler. In this work, an improvement to the MLWDF scheduler is proposed. The improvement entails adding two novel parameters that characterise user demand and HARQ implementation. The scheduler was tested using varying three classes of service in QoS class identifiers (QCIs) table standardised by Third Generation Partnership Project for LTE network to characterise different services. It was also tested on the basis of packet prioritisation. The proposed scheduler was simulated with LTE-SIM simulator and compared with the MLWDF and proportional fairness schedulers. In terms of delay, throughput and packet loss ratio; the proposed scheduler increased overall system performance.

3GPP LTE Downlink PHY Transceiver using Closed-loop Spatial Multiplexing in Frequency Selective Fading Environment

LTE (Long Term Evolution) is a 3GPP (Third Generation Partnership Project) wireless standards that gives us wideband CDMA (Code Division Multiple Access) and HSPA (High Speed Packet Access) a third generation connectivity. LTE is the fourth generation (4G) of wireless communication technologies that brings the standard OFDMA (Orthogonal Frequency Division Multiple Access) modulation , MUMIMO (Multiuser Multiple Input Multiple Output) technology and different multipath fading model EVA (Extended Vehicular a), ETU (Extended Typical Urban) and EPA (Extended Pedestrian A) which allows the operator to use spectrum more efficiently to deliver high speed data. This paper characterizes the downlink performance of LTE. There are many metric to characterize the performance, but one of the most convenient and informative metric is the BER (Bit Error Rate). So the performance is characterized in terms of BER. In this paper the LTE system is modeled and simulated using MATLAB and the BER for 2×2 and 4×4 MIMO using QPSK and 16QAM modulation is obtained against different SNR values. General Terms Mobile Communication

WE-MQS-VoIP Priority: An enhanced LTE Downlink Scheduler for voice services with the integration of VoIP priority mode

The Long Term Evolution (LTE) is a high data rates and fully All-IP network. It is developed to support well to multimedia services such as Video, VoIP, Gaming, etc. So that, the real-time services such as VoIP, video, etc. need to be optimized. Nevertheless, the deployment of such live stream services having many challenges. Scheduling and allocating radio resource are very important in LTE network, especially with multimedia services such as VoIP. When voice service transmitted over LTE network, it is affected by many network impairments where there are three main factors including packet loss, delay, and jitter. This study proposes a new scheduler which is based on VoIP priority mode,Wideband (WB) E-model, QoS- and Channel-Aware (called WE-MQS-VoIP Priority scheduler) for voice services in LTE downlink direction. The proposed scheduling scheme is built based on the WB E-model and Maximum Queue Size (MQS). In addition, we integrate the VoIP priority mode into our scheduling scheme. Since the proposed scheduler considers the VoIP priority mode and user perception, thus, it improves significantly the system performance. The results demonstrate that the proposed scheduler not only meets QoS demands of voice calls but also outperforms Modified Largest Weighted Delay First (M-LWDF) in terms of delay, Packet Loss Rate (PLR) for all number of user (NU) and excepting NU equals 30, respectively. For Fairness Index (FI), cell throughput, and Spectral Efficiency (SE), the difference among the packet schedulers is not significant. The performance evaluation is compared in terms of Delay, PLR, Throughput, FI, and SE.

Impact of CSI Feedback Strategies on LTE Downlink and Reinforcement Learning Solutions for Optimal Allocation

The constant increase in wireless handheld devices and the prospect of billions of connected machines has led the cellular community to research many different technologies that can deliver a high data rate and quality of service to mobile users (MUs). One of the problems that is usually overlooked by the community is that more devices mean higher signaling necessary to coordinate transmission and to allocate resources effectively. In particular, channel state information (CSI) of the users' channels is necessary in order for the base station to assign frequency resources. On the other hand, this feedback (FB) information comes at a cost of uplink (UL) bandwidth, which is traditionally not considered. In this paper, we analyze the impact that reduced user FB information has on a Long-Term Evolution (LTE) network. A model, which considers the tradeoff between downlink (DL) performance and UL overhead, is presented. We introduce different FB-allocation strategies, which follow the same structure as the ones in the LTE standard, and study their effects on the network for varying number of users and different resource-allocation strategies. We show that dynamically allocating FB resources can be beneficial for the network. In order for the base station to determine which FB-allocation strategy is the most beneficial, in specific network conditions, we propose two reinforcement learning (RL) algorithms. The first solution allows the base station to allocate one homogeneous FB strategy valid for all the users served, whereas the second more complex solution determines a different strategy for each user based on its channel conditions. The RL methods show that, even in dynamic scenarios, each base station is capable of determining an optimal operating point autonomously, hence optimally balancing FB overhead and benefits.

QoE-aware Optimization of Video Stream Downlink Scheduling Over LTE Networks Using RNNs and Genetic Algorithm

Long Term Evolution (LTE) is the initial version of fourth-generation (4G) networks which provides ubiquitous broadband access. LTE supports multimedia Quality of Service (QoS) traffic with high data transfer speed, fast communication connectivity, and high security. Multimedia traffic over LTE networks is one of the highest percentages of mobile traffic and it has been growing rapidly in recent years. Our approach focuses on the development of Quality of Experience (QoE) aware optimization downlink scheduling video traffic flow. QoE is the overall acceptability of a service or application, as perceived subjectively by end users. In this work we aim to maximise QoE of video traffic streaming over LTE networks. This work introduces a novel integration framework between genetic algorithm (GA) and random neural networks (RNN) applied to QoE-aware optimization of video stream downlink scheduling. The proposed framework has been applied and evaluated using an open source simulation tool for LTE networks (LTE-Sim). A comparison between our framework and state-of-the-art LTE downlink scheduling algorithms (FLS, EXP-rule, and LOG-rule) has been done under different network conditions. Simulation results have shown that our scheduler can achieve better performance in terms of QoE (∼10% increase), throughput and fairness.

Linearity Enhanced Wide-Bandwidth Pulse-Modulated Polar Transmitters for LTE Femtocell Applications

The pulse-modulated polar transmitter (PMPT) uses envelope information to pulse modulate phase information to implement highly linear and highly efficient polar transmitters. Previous implementations of the PMPT successfully achieved bandwidths up to 5 MHz. However, as the bandwidth of the signal increases, nonidealities of the PMPT limit the performance of this architecture. The nonidealities are predominantly aliasing from pulsewidth modulation (PWM) and distortions from switching, which degrade the spectral performance. By using aliasing-free digital PWM and digital pre-distortion concurrently, spectral performance of the PMPT can be improved for wide bandwidth applications. For validation, a prototype transmitter was tested with a 20-MHz bandwidth downlink long-term evolution (LTE) signal at 836.5 MHz. Using the proposed method, the prototype transmitter achieved an output power of 19.8 dBm and drain efficiency of 24.4% while passing the spectral requirements of the LTE standard for femtocell base stations.

Self-Optimization Algorithm for Outer Loop Link Adaptation in LTE

In this letter, a novel algorithm for improving outer loop link adaptation (OLLA) convergence speed in the downlink of Long Term Evolution (LTE) is presented. The proposed heuristic algorithm adjusts the OLLA initial offset parameter based on OLLA adjustment histograms of large activity connections. The algorithm is validated with a connection-level simulator, fed with real connection traces collected from a live LTE network. Results show that average network block error rate, user throughput and spectral efficiency can be improved by properly adjusting the initial OLLA offset parameter.

Packet Scheduling Study For Heterogeneous Traffic In Downlink 3gpplte System

Long Term Evolution (LTE) network deploys Orthogonal Frequency Division Multiple Access (OFDMA) technology for downlink multi-carrier transmission. To meet the Quality of Service (QoS) requirements for LTE networks, packet scheduling has been employed. Packet scheduling determines when and how the user’s packets are transmitted to the receiver. Therefore effective design of packet scheduling algorithm is an important discussion. The aims of packet scheduling are maximizing system throughput, guaranteeing fairness among users, andminimizing either or both PacketLoss Ratio (PLR)and packet delay. Inthis paper, the performance of two packet scheduling algorithms namely Log Maximum-Largest Weighted Delay First (LOG-MLWDF) and Max Delay Unit (MDU), developed for OFDM(Orthogonal Frequency Division Multiplexing)networks, has been investigated in LTE downlink networks, and acomparison of those algorithmswith a well-known scheduling algorithm namely Maximum-Largest Weighted Delay First(MLWDF) has been studied.The performance evaluation was in terms of system throughput, PLR and fairness index. This study was performed forboth real time (voice and video streaming)and non-real time (best effort)perspectives. Results show that for streaming flows,LOG-MLWDF shows best PLR performance among the considered scheduling schemes, and for best effort flows, it outperforms theother two algorithms in terms of packet delay and throughput.

Comparative Analysis of Downlink Packet Scheduling Algorithms in 3GPP LTE Networks

Long Term Evolution (LTE) mobile network aims to support high speed network services even in highmobility scenarios. To achieve this goal, LTE adopts some advanced features in Radio Resource Management (RRM) procedures. Among them, LTE packet scheduling plays a fundamental role in maximising system performance. In this paper, a comparative analysis on the performances of Proportional Fair (PF), Exponential/Proportional Fair (EXP/PF), Exponential (EXP) Rule, MaximumLargest Weighted Delay First (M-LWDF), Logarithmic (LOG) Rule and Frame Level Scheduler (FLS) LTE downlink packet scheduling algorithms is reported. Performance is evaluated in single cell with interference environment while increasing user number and user speed. Results show that for multimedia flow, FLS scheme outperforms other five schemes in terms of packet delay, packet loss ratio, and average throughput, whereas for best-effort flow, EXP-PF scheme shows better average throughput performance on average as compared with other algorithms being considered herein.

Iterative channel estimation method for long‐term evolution downlink transmission

Long-term evolution (LTE) standard employs orthogonal frequency division multiplexing (OFDM) for downlink (DL) data transmission. As pilot subcarriers are non-uniformly and sparsely spaced in the OFDM DL transmission, more complicated channel estimation methods may have to be adopted in the mobile devices to ensure adequate performance. An iterative approach is proposed for the channel estimation task, in which an inverse fast Fourier transform and fast Fourier transform pair is iteratively used to smooth channel estimates provided by decision feedback. The performance of this approach is compared with two two-dimensional interpolation methods and one discrete Fourier transform-based estimation method that have been proposed for the LTE DL transmission. Simulation results show that the performance of the proposed method surpasses all the other methods except at high signal-to-noise ratio, and moreover, not a single estimation method consistently performs better than the proposed method for all the channel models considered. Thus, the proposed method is the best among the considered methods for LTE DL transmission.

Coverage enhancement techniques for machine-to-machine communications over LTE

The tremendous growth of machine-tomachine (M2M) applications has been a great attractor to cellular network operators to provide machine-type communication services. One of the important challenges for cellular systems supporting M2M terminals is coverage, because terminals can be located in spaces in buildings and structures suffering from significant penetration losses. Since these terminals are also often stationary, they are permanently without cellular coverage. To address this critical issue, the third generation partnership project (3GPP), and in particular its radio access network technical specification group, commenced work on coverage enhancement (CE) for long-term evolution (LTE) systems in June 2013. This article reviews the CE objectives defined for LTE machine-type communication and presents CE methods for LTE downlink and uplink channels discussed in this group. The presented methods achieve CE in a spectrally efficient manner and without notably affecting performance for legacy (non- M2M) devices.

Buffer-aware adaptive resource allocation scheme in LTE transmission systems

Dynamic resource allocation scheme is a key component of 3GPP long-term evolution (LTE) for satisfying quality-of-service (QoS) requirement as well as improving the system throughput. In this paper, a buffer-aware adaptive resource allocation scheme for LTE downlink transmission is proposed for improving the overall system throughput while guaranteeing the statistic QoS and keeping certain fairness among users. Specifically, the priorities of the users’ data queues in the base station are ranked by their remaining life time or their queue overflow probability which is estimated by applying large deviation principle. An online measurement based algorithm which requires no statistical knowledge of the network conditions uses the queue priorities to dynamically allocate the resource blocks (RBs) for avoiding buffer overflow and providing statistic QoS guarantee. The simulation results show that the proposed algorithm improves the throughput and fairness while considerably reducing the average bit loss rate.

Reduction of the feedback delay effect on a proportional fair scheduler in LTE downlink using nonlinear support vector machine prediction

The scheduling of mobile users often relies on accurate feedback from the channel quality indicator (CQI). In this paper, we determine the strength of the effect of feedback delay on the scheduler in a Long-Term Evolution (LTE) system. We study this degradation under fairness constraints using a proportional fair scheduler. We propose a nonlinear support vector machine regression with a modified cost function in order to reduce the effect of feedback delay on the scheduler, which operates by predicting the CQI from previous feedback and using that for scheduling instead of the delayed feedback. The simulation results show important improvements in terms of throughput.

Comparative Analysis of Various Inter-Carrier Interference Cancellation Methods

This paper provides a review of various inter carrier interference cancellation methods used in Orthogonal Frequency Division Multiplexing (OFDM) in the downlink of Long Term Evolution (LTE) and in many other applications. It contains the analysis of different methods, their explanations, areas of implementation, advantages, drawbacks and finally a comparison of the methods has been made. The paper is based on the fact that during OFDM reception, the overlapping frequencies interfere due to various reasons and different methods have to be applied to avoid interference among the frequencies for a proper reception at the receiver.

An Optimal and Priority Based Rate Guaranteed Radio Resource Allocation Scheme for LTE Downlink

The problem of allocating radio resources for data transmission in the downlink of the Long Term Evolution (LTE) systems is studied. The scheduler present at the Evolved NodeB of the LTE network follows a specific scheduling algorithm to distribute the radio resources (available spectrum) among the users who request for carriers for data transmission. Generally scheduling algorithms aim at providing fairness, high throughput, reduced access delay, etc. Also with radio resource allocation/scheduling algorithms, different Modulation and Coding Schemes can be employed for different users in the same scheduling interval in order to achieve higher throughput. In this paper a new scheduling algorithm is proposed. The implementation of the proposed scheduling algorithm is followed with its comparison with the conventional scheduling algorithms like Round Robin, Best Channel Quality Indicator and Proportional Fair. In the proposed algorithm, the minimum data rate requirement of each user is taken into account. Two classes of users namely priority and non-priority users are considered. In this scenario, the algorithm is implemented in a way to satisfy the priority users first by allocating the available radio resources to them first and then allocating the remaining radio resources to the non-priority users. The algorithm also ensures optimized Resource Block (RB) allocation, so that users are allotted with minimum possible RBs required to satisfy their data rate requirement. The simulation results show that, compared to the conventional scheduling algorithms, the proposed algorithm performs well by efficient utilization of the scarce radio spectrum and in guaranteeing the rate requirement for the maximum number of active users especially to priority users.

Performance Analysis for LTE Wireless Communication

Long Term Evolution (LTE) is the new upgrade path for carrier with both GSM/UMTS networks and CDMA2000 networks. The LTE is targeting to become the first global mobile phone standard regardless of the different LTE frequencies and bands use in other countries barrier. Adaptive Modulation and Coding (AMC) is used to increase the network capacity or downlink data rates. Various modulation types are discussed such as Quadrature Phase Shift Keying (QPSK) and Quadrature Amplitude Modulation (QAM). Spatial multiplexing techniques for 4×4 MIMO antenna configurations are considered. This paper has outlined various estimation techniques to increase the throughput of the LTE network by simulating the estimation techniques with various parameters in the LTE downlink mode 4 (spatial multiplexing). Three techniques i.e. channel estimation technique, estimation of channel models and MIMO receiver algorithm are simulated to provide the ideal LTE wireless communication system.

Interference Management in Lte Downlink Networks

Two major challenges for evolving LTE (Long Term Evolution) networks are to achieve enhanced system capacity and cell coverage compared with WCDMA (Wideband Code Division Multiple Access) system. Effective utilization of radio resources as well as dense spectrum reuse are at the core to attain these targets. However, dense frequency reuse may increase inter-cell interference, which in turn severely limits the capacity of users in the system. Inter-cell interference can restrict overall system performance in terms of throughput and spectral efficiency, especially for the users located at the cell edge area. Hence, careful management of inter-cell interferences becomes crucial to improve LTE system performance. In this paper, interference mitigation schemes for LTE downlink networks are investigated.