Future generation cellular networks are expected to provide ubiquitous broadband access to a continuously growing number of mobile users. In this context, LTE systems represent an important milestone towards the so called 4G cellular networks. A key feature of LTE is the adoption of advanced Radio Resource Management procedures in order to increase the system performance up to the Shannon limit. Packet scheduling mechanisms, in particular, play a fundamental role, because they are responsible for choosing, with fine time and frequency resolutions, how to distribute radio resources among different stations, taking into account channel condition and QoS requirements. This goal should be accomplished by providing, at the same time, an optimal trade-off between spectral efficiency and fairness. In this context, this paper provides an overview on the key issues that arise in the design of a resource allocation algorithm for LTE networks. It is intended for a wide range of readers as it covers the topic from basics to advanced aspects. The downlink channel under frequency division duplex configuration is considered as object of our study, but most of the considerations are valid for other configurations as well. Moreover, a survey on the most recent techniques is reported, including a classification of the different approaches presented in literature. Performance comparisons of the most well-known schemes, with particular focus on QoS provisioning capabilities, are also provided for complementing the described concepts. Thus, this survey would be useful for readers interested in learning the basic concepts before going into the details of a particular scheduling strategy, as well as for researchers aiming at deepening more specific aspects.

/pdf/downlink-packet-scheduling-in-lte-cellular-networks-key-1z27kezket.pdf

Downlink Packet Scheduling in LTE Cellular Networks: Key Design Issues and a Survey

Recent analysis by manufacturers and network operators has shown that current wireless networks are not very energy efficient, particularly the base stations by which terminals access services from the network. In response to this observation the Mobile Virtual Centre of Excellence (VCE) Green Radio project was established in 2009 to establish how significant energy savings may be obtained in future wireless systems. This article discusses the technical background to the project and discusses models of current energy consumption in base station devices. It also describes some of the most promising research directions in reducing the energy consumption of future base stations.

/pdf/green-radio-radio-techniques-to-enable-energy-efficient-3j1elryk04.pdf

Green radio: radio techniques to enable energy-efficient wireless networks

The explosive development of Information and Communication Technology (ICT) has significantly enlarged both the energy demands and the CO 2 emissions, and consequently contributes to make the energy crisis and global warming problems worse. However, as the main force of the ICT field, the mobile networks, are currently focusing on the capacity, variety and stability of the communication services, without paying too much severe concerns on the energy efficiency. The escalating energy costs and environmental concerns have already created an urgent need for more energy-efficient "green" wireless communications. In this paper, we survey and discuss various remarkable techniques toward green mobile networks to date, mainly targeting mobile cellular networks. We also summarize the current research projects related to green mobile networks, along with the taxonomy of energy-efficiency metrics. We finally discuss and elaborate future research opportunities and design challenges for green mobile networks.

A Survey of Green Mobile Networks: Opportunities and Challenges

With years of tremendous traffic and energy consumption growth, green radio has been valued not only for theoretical research interests but also for the operational expenditure reduction and the sustainable development of wireless communications. Fundamental green tradeoffs, served as an important framework for analysis, include four basic relationships: 1) spectrum efficiency versus energy efficiency; 2) deployment efficiency versus energy efficiency; 3) delay versus power; and 4) bandwidth versus power. In this paper, we first provide a comprehensive overview on the extensive on-going research efforts and categorize them based on the fundamental green tradeoffs. We will then focus on research progresses of 4G and 5G communications, such as orthogonal frequency division multiplexing and non-orthogonal aggregation, multiple input multiple output, and heterogeneous networks. We will also discuss potential challenges and impacts of fundamental green tradeoffs, to shed some light on the energy efficient research and design for future wireless networks.

Fundamental Green Tradeoffs: Progresses, Challenges, and Impacts on 5G Networks

We present a design of a complete and practical scheduler for the 3GPP Long Term Evolution (LTE) downlink by integrating recent results on resource allocation, fast computational algorithms, and scheduling. Our scheduler has low computational complexity. We define the computational architecture and describe the exact computations that need to be done at each time step (1 milliseconds). Our computational framework is very general, and can be used to implement a wide variety of scheduling rules. For LTE, we provide quantitative performance results for our scheduler for full buffer, streaming video (with loose delay constraints), and live video (with tight delay constraints). Simulations are performed by selectively abstracting the PHY layer, accurately modeling the MAC layer, and following established network evaluation methods. The numerical results demonstrate that queue- and channel-aware QoS schedulers can and should be used in an LTE downlink to offer QoS to a diverse mix of traffic, including delay-sensitive flows. Through these results and via theoretical analysis, we illustrate the various design tradeoffs that need to be made in the selection of a specific queue-and-channel-aware scheduling policy. Moreover, the numerical results show that in many scenarios strict prioritization across traffic classes is suboptimal.

/pdf/downlink-scheduling-for-multiclass-traffic-in-lte-3r8j3biwor.pdf

Downlink scheduling for multiclass traffic in LTE

This paper explores the potential gain of joint diversity in both frequency domain and time domain which can be exploited to achieve spectral efficiency gains whilst simultaneously facilitating QoS/fairness in an OFDMA system (particularly in 3GPP Long Term Evolution (LTE)). The performance of several joint time-frequency schedulers is investigated. Simulation results show that joint time frequency schedulers achieve significantly superior performance compared to a more conventional time domain (only) proportional fair scheduler. The joint schemes show promising throughput gain while meeting stringent fairness criteria.

/pdf/joint-time-frequency-domain-proportional-fair-scheduler-with-3kb63h6q4m.pdf

Joint Time-Frequency Domain Proportional Fair Scheduler with HARQ for 3GPP LTE Systems

Expectations and requirements for future wireless communication systems continue to grow and evolve. Thus, recently, the third generation partnership project (3GPP) has considered the long term evolution (LTE) of 3G - also known as super 3G - to ensure its competitiveness in the future. It is generally assumed that the downlink of the new air interface would be OFDMA based and that some form of hybrid ARQ (HARQ) might be employed. This paper aims to evaluate the performance of various HARQ schemes over the OFDMA downlink of the currently proposed 3GPP LTE specification. Schemes are compared in terms of throughput and PER in the context their differing memory requirements for implementation. Simulation results show that type II incremental redundancy offers the best throughput performance but at the cost of higher memory requirement. However, when the schemes are enhanced with subcarrier and constellation rearrangement techniques, the performance gap between the different HARQ types is reduced significantly.

/pdf/performance-evaluation-of-hybrid-arq-schemes-of-3gpp-lte-240qbs5tj8.pdf

Performance Evaluation of Hybrid ARQ Schemes of 3GPP LTE OFDMA System

This paper presents a link level analysis of the rate and energy efficiency performance of the LTE downlink considering the unitary codebook based precoding scheme. In a multi-user environment, appropriate radio resource management strategies can be applied to the system to improve the performance gain by exploiting multi-user diversity in the time, frequency and space domains and the gains can be translated to energy reduction at the base station. Several existing and novel resource scheduling and allocation algorithms are considered for the LTE system in this paper. A detailed analysis of the performance gain of different algorithms in terms of throughput, rate fairness, and power efficiency is presented.

/pdf/power-efficient-dynamic-resource-scheduling-algorithms-for-3k6xoo6nc4.pdf

Power Efficient Dynamic Resource Scheduling Algorithms for LTE

LTE (Long Term Evolution) is a next major step in mobile radio communications, and will be introduced as Release 8 in the 3rd Generation Partnership Project (3GPP). The new evolution aims to reduce delays, improve spectrum flexibility and reduce cost for operators and end users [1]. To fulfil these targets, new enabling technologies need to be integrated into the current 3G radio network architectures. Multiple Input and Multiple Output (MIMO) is one of the crucial enabling technologies in the LTE system particularly in the downlink to achieve the required peak data rate. The unitary codebook based precoding technique is proposed in the standard to increase the capacity of the system. This paper presents a link level analysis of the LTE downlink and an investigation of the performance of both Single User (SU) MIMO and Multi User (MU) MIMO with codebook based unitary precoding.

/pdf/on-the-performance-of-su-mimo-and-mu-mimo-in-3gpp-lte-38kbt7e4qg.pdf

On the performance of SU-MIMO and MU-MIMO in 3GPP LTE downlink

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. The objective of the Green Radio research programme (Core 5) of Mobile VCE is to deliver reduced power consumption of radio access networks. This paper attempts to show that an efficient exploitation of multiple antenna techniques and multiuser diversity in both the time, frequency as well as the space domain can significantly ease the power requirements of a base station, whilst maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity are examined.

/pdf/power-efficient-mimo-techniques-for-3gpp-lte-and-beyond-5rq5fuaia1.pdf

Kian Chung Beh

Papers

Joint Time-Frequency Domain Proportional Fair Scheduler with HARQ for 3GPP LTE Systems

Performance Evaluation of Hybrid ARQ Schemes of 3GPP LTE OFDMA System

Power Efficient Dynamic Resource Scheduling Algorithms for LTE

On the performance of SU-MIMO and MU-MIMO in 3GPP LTE downlink

Power Efficient MIMO Techniques for 3GPP LTE and Beyond