Downlink scheduling in LTE: Challenges, improvement, and analysis

The recent wireless communication networks rely on the new technology named Long Term Evolution (LTE) to offer high data rate real-time (RT) traffic with better Quality of Service (QoS) for the increasing demand of customer requirement. LTE provide low latency for real-time services with high throughput, with the help of two-level packet retransmission. Hybrid Automatic Repeat Request (HARQ) retransmission at the Medium Access Control (MAC) layer of LTE networks achieves error-free data transmission. The performance of the LTE networks mainly depends on how effectively this HARQ adopted in the latest communication standard, Universal Mobile Telecommunication System (UMTS). The major challenge in LTE is to balance QoS and fairness among the users. Hence, it is very essential to design a down link scheduling scheme to get the expected service quality to the customers and to utilize the system resources efficiently. This paper provides a comprehensive literature review of LTE MAC layer and six types of QoS/Channel-aware downlink scheduling algorithms designed for this purpose. The contributions of this paper are to identify the gap of knowledge in the downlink scheduling procedure and to point out the future research direction. Based on the comparative study of algorithms taken for the review, this paper is concluded that the EXP Rule scheduler is most suited for LTE networks due to its characteristics of less Packet Loss Ratio (PLR), less Packet Delay (PD), high throughput, fairness and spectral efficiency.

Wireless internet access was introduced to the world, which led to more mobile phone subscriptions. Data services were first available in the second generation. Later after working past a lot of challenges to achieve the needs and higher performance, the Third Generation Partnership Project (3GPP) created High Speed Packet Access (HSPA). There is a lot of demand on the mobile applications, which then requires higher data rates and low latency. So the 3GPP further started working on Long Term Evolution (LTE), that improves all necessities. The introduction of Orthogonal Frequency Division Multiplexing (OFDM) further improved throughput rate but scheduling algorithm has a greater part in increasing overall performance of network. The scheduling algorithms are used to allocate time, space and resources to the users. These algorithms have also been employed in downlink (i.e. the communication from base station to the mobile) since it requires high data rates with lower packet loss compared to uplink therefore efficient algorithms are required for downlink. This paper focuses on the detailed study and comparisons of existing downlink scheduling algorithms which are namely Proportional Fair (PF), Max-Rate, Maximum Largest Weighted Delay First, Round Robin(RR), and Exponential Rule(EXP-Rule). Moreover, this paper provides some of improvements that can be done in the above mentioned algorithms.

Long Term Evolution (LTE) mobile networks, time-frequency radio resources are allotted with respect to Quality of Service (QoS) requirements using scheduling algorithms. Buffer Occupancy (BO), Average Cellular Throughput (ACT), Average User Throughput (AUT), Blocking Probability (BP) and Fairness Index (FI) are the parameters to be considered when designing a scheduler. A new scheduling policy is proposed in this paper, called “Channel Aware Optimized Proportional Fair (CAOPF)” to optimize the channel behavior based on Channel Quality Indicator (CQI). The performance of the introduced scheduler is investigated and compared with the other schedulers such as Round Robin (RR) and Proportional Fair (PF). Simulation results indicate that the new scheduler gives the best level of QoS performance in terms of the above said parameters when compared with the other schedulers taken into account. It provides no pending data of users in good channel condition, higher ACT, higher improvement in user throughput in good and average channel conditions. In addition, very low blocking of user data in good channel condition and optimized FI and resource block (RB) allocated to the users in all channel conditions are seen.

Long Term Evolution(LTE) 시스템은 멀티미디어 서비스와 같은 다양한 서비스를 이동 사용자에게 제공할 수 있다. 실제로 HSPA+(High Speed Packet Access plus)는 다운링크의 비트 율(bit rate)을 크게 향상 시켰으나, 다양한 멀티미디어 서비스에서 요구하는 서비스 품질을 어떻게 만족시킬 것인가에 대한 연구는 매우 미비한 상태이다. 본 논문에서는 proportional fair(PF) 알고리즘을 기반으로 하여 LTE를 위한 효율적인 패킷 스케쥴링 알고리즘을 제안하였다. 제안된 알고리즘에서는 패킷 스케쥴링을 할 때 패킷의 우선순위를 결정하는 가장 중요한 요소인 트래픽 클래스의 가중치와 순간 사용자 데이터 전송율을 최적화 하였다. 또한 다중 셀(multi-cell) 환경에서 LTE를 통해서 사용자에게 전송되는 멀티미디어 트래픽을 시뮬레이션 함으로써 제안된 알고리즘의 성능이 향상되었음을 보였다. The Long Term Evolution (LTE) system is already able to provide a background of variety services for mobile users with multimedia services such as audio, video, and data. In fact, the High Speed Packet Access plus (HSPA+) solution can greatly enhance bit rates on down-link. However, the supporting for multimedia applications with different QoS (Quality of Service) requirements is not devised yet. Hence, in this paper we propose an effective packet scheduling algorithm based on Proportional Fairness (PF) scheduling algorithms for the LTE. In this proposed packet scheduling scheme, we optimized instantaneous user data rates and the traffic class weight which prioritize user's packets. Finally, we evaluated and showed the performance of the proposed scheduling algorithm through simulations of multimedia traffics being transmitted to users over LTE links in a multi-cell environment.

Handover (HO) algorithms, managed by Mobility Management Entity (MM), and Scheduling algorithms, managed by Radio Resource Management Entity (RRM) are both the most important aspects in the next-generation cellular systems 3GPP Long Term Evolution (LTE). When a User Equipment (UE) is in motion, the constraints of offering better Quality of Service (QoS), especially in Real Time applications, increase. This is why the design of a powerful handover algorithm is essential, in order to ensure a seamless transfer of a UE to a new cell. In this article, we propose a new HO algorithm based on the Available Bandwidth prediction at the eNBs level. The improvements proposed by our scheme compared to other HO algorithms such as LTE Hard Handover Algorithm (LHHA), Integrator Handover and LTE Hard Handover Algorithm with Average RSRP Constraint (LHHAARC) has been shown via different parameters namely throughput, system delay and Packet Loss Ratio (PLR). Using LTE-Sim simulator, all HO algorithms were simulated against the three well-known scheduling schemes, namely, Proportional Fair (PF), Exponential Proportional Fairness (EXP / PF) and Modified Largest Weighted Delay First (MLWDF). The objective is to define a synthesis allowing the automatic choice of the proper scheduling scheme to use, according to the HO decision algorithm predefined by the system.

Recently, there has been a tremendous increase in mobile data usage with widespread proliferation of smartphone like devices and increasing popularity of video streaming services such as YouTube. This is already causing overloading of 3G cellular access networks. It is estimated that even the 4G LTE (Long Term Evolution) technology which has significantly higher spectral efficiency than 3G will also face overloading in near future. As a result, it has become important to find out ways and means of offloading the traffic from the LTE network. One possible solution is offloading it to Wi-Fi to gain extra capacity and improve overall network performance. In this paper we have considered an outdoor macro cell LTE Network being offloaded by a Wi-Fi network. We study the loading of LTE Network in different types of user and traffic distribution and investigate how offload to Wi-Fi APs can help in easing the congestion in LTE network and thereby lead to better per user throughputs and better quality of experience to end users using NS-3. Also, among the various scheduling algorithms that have been defined for efficient resource allocation in LTE, three schedulers have been considered: Round Robin (RR), Proportional Fair (PF) and Priority Set Scheduler (PSS) schedulers and their performance has been evaluated in the offloading scenario.

Curitiba is a city in south Brazil with an estimated population of 1.8 million inhabitants [3]. The teledensity in this city is over 1.2 cellular for each person and, four players, actually are working with Long Term Evolution (LTE) in the city. However, the quality of the LTE cell coverage has not yet reached the standard of the Third Generation Partnership Project (3GPP) group. Considering the growing demand for better quality of service provided by telecom operators, this study aims to develop a methodology for analyzing the quality of cellular LTE coverage in Curitiba that can easily be extended to any other big city in Brazil, since we consider a dense urban region, in the frequency range of 2600 MHz and a bandwidth of 20 MHz. The methodology includes conducting a proper drive test in a commercial network with the processing of data obtained through the commercial software, as well as developing a spreadsheet to perform a theoretical project for the purpose of comparing and validating the methodology.

Long Term Evolution (LTE) network is a promising wireless technology which provides mobile users with high data rate and low latency. LTE has been developed by the 3rd Generation Partnership Project (3GPP) to improve the end to end system delay and support higher Quality of Services (QoS). However, 3GPP has not defined a firm provision to handle the scheduling process, so that scheduling becomes an open issue for researchers. Instead, they defined nine classes with their corresponding Quality of Services (QoS) requirements. In this paper, a novel scheduling algorithm is proposed based on class service using cooperative game theory technique. The available resources are fairly distributed among classes as proportion which results in higher fairness level among classes. In the second level, the users with tightest delay requirements are prioritized. The proposed algorithm is compared with Proportional Fairness (PF) and Exponential (EXP) rule algorithms in terms of throughput, delay and fairness index. The proposed model outperforms PF and EXP schemes in all comparative parameters.

A new concept such as smart city was introduced in the last years where the Intelligent Transportation system (ITS ) plays a critical role to provide road safety and manage Vehicular Ad Hoc Networks (VANETs) traffic. Nevertheless, VANETs have significant constraints like nodes high mobility, intermittent connectivity, variable network density and heterogeneity. However, the different types of traffic, the different Quality of Service requirements, the need to exchange mobile data, multi-services and data diversity leads mainly to load and time constraints in this specific and stringent type of networks. The main characteristic of this kind of networks is the very changing topology that poses supplementary constraints and makes achieving QoS constraints a very challenging task. In VANET network the vehicle generated traffic will be transferred to the data center from road side unit to the base station by using Long Term Evolution (LTE) in an urban area. Despite LTE has a larger system capacity and it provides a higher transmission speed, the network performance is affected by the implemented scheduling algorithm. In this context, we study the efficiency of LTE scheduler algorithms such as Proportional Fairness, Round Robin, Priority Set Scheduler, Maximum Throughput Scheduler and Throughput to Average Scheduler and Blind Equal Throughput mainly at the road side unit using Network Simulator 3(NS3) to determinate the most suitable scheduler for VANET traffic. Results demonstrate that the round robin algorithm is more effective for volumetric VANET traffic in terms of throughput, delay, packet loss rate and fairness.

Emerging multimedia services are spreading significantly thanks to the availability of high speed wireless networks. Network operators are facing the challenges to accommodate these services (e.g. Skype, interactive gaming, and other multimedia applications) with high user satisfaction. This paper presents a Quality of Experience (QoE) driven approach to allocate the radio resources in Long Term Evolution (LTE) wireless networks, in order to get higher user satisfaction. The main objective is to enhance the user experience while using the multimedia services such as VoIP, by jointly considering the user QoE and available wireless radio resources in the LTE-Advanced (LTE-A) network. Specifically, we propose a new downlink scheduling algorithm known as “QoE Scheme” for multimedia VoIP service in LTE-A networks. The main advantage of the proposed QoE Scheme is its measurement of user satisfaction and its feedback mechanism to the scheduler at evolving NodeB (eNodeB) in order to make the scheduling decision.

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LTE (Long Term Evolution), a 4G mobile communication standard has a support for higher data rates and lower latency. Since LTE is completely an Internet Protocol (IP) based technology, Network operators of LTE can handle voice via a “fall-back” technique by using previously existed circuit switched networks. To avoid this, Voice over IP (VoIP) services need to be used to deliver the voice over IP networks, such as Internet. Voice Codec is one of the critical components in VoIP used to convert analog signals to compressed digital packets and vice-versa that can be sent over the internet. But there are different kinds of codecs exist that optimize the voice stream based on bandwidth and application requirement. Unfortunately, there is no standard codec that is acceptable for all circumstances, some codecs provides better quality, some other uses lesser bandwidth. All these features will effect on the ultimate selection of codec by an organization. This paper focuses on the quality of service (QOS) analysis of VoIP traffic over LTE by configuring different voice codecs such as G.711, G.722.2, G.723.1 and G.729. To analyze the performance of these codecs ns-3 simulator is being used since its core has a support for LTE models. The comparative study of above selected VoIP codecs over LTE network in terms of Packet Loss, End to End delay, Jitter, and Throughput in normal and error prone scenarios has been done. From the analyzed results and the performance evaluated, the selection of codec will become easy to provide better VoIP services for customer satisfaction.

This study focuses on managing equity-conscious radio resources in OFDMA-based WIMAX networks with comparison of three algorithms, Max Rate, RR and PFS. Hence WiMAX Forum has been formed, which promotes the technology and provides compatibility and teroperability for 802.16-based products. The problem in heterogeneous WiMAX, users may possess different transmit power capabilities and experience independent channel realizations. As a result, those with lower power Capabilities or poor channel conditions will starve throughput share. It is observed that users with better channel conditions always dominate usage of the spectrum, causing low throughput for users with poor channel conditions. This paper studied the performance of downlink scheduling algorithms that perform radio resource allocation in order to improve the performance of the WiMAX system. These algorithms are Max Rate, Round Robin, and Proportional Fair. In addition, scheduling algorithm was implementing in order to explain the fairness concept. The algorithms were comparing to each other in terms of system throughput and fairness index. The performance evaluations are carrying out using MATLAB software. Simultaneous results show that the most suitable scheduling algorithm in terms of fairness index and system throughput for the WiMAX network is proportional fair. Meanwhile, Max Rate provides the highest throughput, even though the number of users is increased.

The LTE specification provides Quality of Service (QoS) of multimedia services with fast connectivity, high mobility, and security. However, 3GPP specifications have not defined scheduling algorithms to support real-time and non-realtime application services, this has led to the development of a variety of scheduling algorithms in the recent years. Performance is a key factor for assessing the scheduling algorithms. However, the performance analysis and evaluation for existing scheduling algorithms are limited to QoS parameters (e.g. in terms of throughput, packet loss and delay) and/or fairness metrics. It is not clear how these scheduling algorithms perform in terms of Quality of Experience (QoE) metrics (e.g. MOS score) which are more closely linked with end user experience or user perceived quality. In this paper, we investigate and evaluate the performance of three popular LTE downlink schedulers (proportional fairness (PF), exponential proportional fairness (EXP-PF), and modified largest weight delay first (M-LWDF)) in terms of QoE metric (i.e. MOS score) in addition to normal QoS metrics (e.g. packet loss and delay) for VoIP applications. Simulation results (based on LTE-Sim) show that the best suitable downlink scheduling algorithm is MLWDF, which has short end-to end delay (less than 50ms) and allowing maximum number of user access (more than 50 users) at acceptable MOS score (MOS over 3.5). The widely used scheduling algorithm (PF) will increase its end-to-end delay over 200ms, when number of user access is over 30. This will limit its application for VoIP when user access number increases. This work would help to assist the design and development of QoE-driven scheduling algorithms for mobile multimedia applications in the future.

The developments in wireless technology and applications in recent years have increased the interest in downlink scheduling and resource allocations among researchers. Moreover, fair scheduling and balanced Quality of Service (QoS) delivery for various forms of traffic are needed for Long-Term Evolution (LTE) wireless systems. This paper proposes hybrid QoS-aware downlink scheduling approaches that aim to address different traffic classes and balance the QoS delivery with improvements to the overall system performance under channel and bandwidth constraints. Moreover, this research introduces a taxonomy that classifies the scheduling algorithms into four main classes: delay aware, queue aware, target bit-rate aware and hybrid aware. The latter class is the scheduling class that is proposed in this paper; it considers channel, queue and delay parameters in its scheduling metric. Using simulations, we compare and analyze different downlink scheduling rules for their network-centric performance metrics, e.g., average packet loss ratio, average throughput, average packet delay, system fairness, and system spectral efficiency. The simulation results show that the queue-aware and delay-aware scheduling rules deliver the best QoS performance for video traffic classes, whereas our proposed hybrid scheduling rules deliver balanced QoS for various types of traffic classes. Employing QoS balancing scheduling rules in an LTE downlink is suggested to provide high QoS delivery for different traffic classes.