Showing papers on "LTE Advanced published in 2013"

Random access for machine-to-machine communication in LTE-advanced networks: issues and approaches

Abstract: Machine-to-machine communication, a promising technology for the smart city concept, enables ubiquitous connectivity between one or more autonomous devices without or with minimal human interaction. M2M communication is the key technology to support data transfer among sensors and actuators to facilitate various smart city applications (e.g., smart metering, surveillance and security, infrastructure management, city automation, and eHealth). To support massive numbers of machine type communication (MTC) devices, one of the challenging issues is to provide an efficient way for multiple access in the network and to minimize network overload. In this article, we review the M2M communication techniques in Long Term Evolution- Advanced cellular networks and outline the major research issues. Also, we review the different random access overload control mechanisms to avoid congestion caused by random channel access of MTC devices. To this end, we propose a reinforcement learning-based eNB selection algorithm that allows the MTC devices to choose the eNBs (or base stations) to transmit packets in a self-organizing fashion.

Trends in small cell enhancements in LTE advanced

Abstract: 3GPP LTE, or Long Term Evolution, the fourth generation wireless access technology, is being rolled out by many operators worldwide. Since LTE Release 10, network densification using small cells has been an important evolution direction in 3GPP to provide the necessary means to accommodate the anticipated huge traffic growth, especially for hotspot areas. Recently, LTE Release 12 has been started with more focus on small cell enhancements. This article provides the design principles and introduces the ongoing discussions on small cell enhancements in LTE Release 12, and provides views from two active operators in this area, CMCC and NTT DOCOMO.

Resource allocation for device-to-device communications underlaying LTE-advanced networks

Abstract: The Long Term Evolution-Advanced (LTEAdvanced) networks are being developed to provide mobile broadband services for the fourth generation (4G) cellular wireless systems. Deviceto- device (D2D) communications is a promising technique to provide wireless peer-to-peer services and enhance spectrum utilization in the LTE-Advanced networks. In D2D communications, the user equipments (UEs) are allowed to directly communicate between each other by reusing the cellular resources rather than using uplink and downlink resources in the cellular mode when communicating via the base station. However, enabling D2D communications in a cellular network poses two major challenges. First, the interference caused to the cellular users by D2D devices could critically affect the performances of the cellular devices. Second, the minimum quality-of-service (QoS) requirements of D2D communications need to be guaranteed. In this article, we introduce a novel resource allocation scheme (i.e. joint resource block scheduling and power control) for D2D communications in LTE-Advanced networks to maximize the spectrum utilization while addressing the above challenges. First, an overview of LTE-Advanced networks, and architecture and signaling support for provisioning of D2D communications in these networks are described. Furthermore, research issues and the current state-of-the-art of D2D communications are discussed. Then, a resource allocation scheme based on a column generation method is proposed for D2D communications. The objective is to maximize the spectrum utilization by finding the minimum transmission length in terms of time slots for D2D links while protecting the cellular users from harmful interference and guaranteeing the QoS of D2D links. The performance of this scheme is evaluated through simulations.

LTE release 12 and beyond [Accepted From Open Call]

Abstract: As the specification of Release 11 of the LTE standards is approaching its completion, 3GPP is gradually moving its focus toward the next major step in the evolution of LTE. The drivers of the LTE evolution include the increasing demand for mobile broadband services and traffic volumes as well as emerging usage scenarios involving short-range and machine-type communications. In this article we provide an overview of the key technology areas/components that are currently considered by 3GPP for Rel-12, including support for further enhanced local area access by tight interaction between the wide area and local area layers, signaling solutions for wireless local area network integration, multi-antenna enhancements, improved support for massive MTC, and direct device-to-device communications.

LTE and the Evolution to 4G Wireless: Design and Measurement Challenges

Abstract: A practical guide to LTE design, test and measurement, this new edition has been updated to include the latest developmentsThis book presents the latest details on LTE from a practical and technical perspective. Written by Agilents measurement experts, it offers a valuable insight into LTE technology and its design and test challenges. Chapters cover the upper layer signaling and system architecture evolution (SAE). Basic concepts such as MIMO and SC-FDMA, the new uplink modulation scheme, are introduced and explained, and the authors look into the challenges of verifying the designs of the receivers, transmitters and protocols of LTE systems. The latest information on RF and signaling conformance testing is delivered by authors participating in the LTE 3GPP standards committees.This second edition has been considerably revised to reflect the most recent developments of the technologies and standards. Particularly important updates include an increased focus on LTE-Advanced as well as the latest testing specifications.Fully updated to include the latest information on LTE 3GPP standardsChapters on conformance testing have been majorly revised and there is an increased focus on LTE-AdvancedIncludes new sections on testing challenges as well as over the air MIMO testing, protocol testing and the most up-to-date test capabilities of instrumentsWritten from both a technical and practical point of view by leading experts in the field

Performance Evaluation of LTE and Wi-Fi Coexistence in Unlicensed Bands

Abstract: The deployment of modern mobile systems has faced severe challenges due to the current spectrum scarcity. The situation has been further worsened by the development of different wireless technologies and standards that can be used in the same frequency band. Furthermore, the usage of smaller cells (e.g. pico, femto and wireless LAN), coexistence among heterogeneous networks (including amongst different wireless technologies such as LTE and Wi-Fi deployed in the same frequency band) has been a big field of research in the academy and industry. In this paper, we provide a performance evaluation of coexistence between LTE and Wi-Fi systems and show some of the challenges faced by the different technologies. We focus on a simulator-based system- level analysis in order to assess the network performance in an office scenario. Simulation results show that LTE system performance is slightly affected by coexistence whereas Wi-Fi is significantly impacted by LTE transmissions. In coexistence, the Wi-Fi channel is most often blocked by LTE interference, making the Wi-Fi nodes to stay on the LISTEN mode more than 96% of the time. This reflects directly on the Wi-Fi user throughput, that decreases from 70% to ≈100% depending on the scenario. Finally, some of the main issues that limit the LTE/Wi-Fi coexistence and some pointers on the mutual interference management of both the systems are provided.

Fractional frequency reuse for interference management in LTE-advanced hetnets

Abstract: Improvement of cell coverage and network capacity are two major challenges for the evolving 4G cellular wireless communication networks such as LTE-Advanced networks. In this context, hierarchical layering of cells with macro base stations coexisting with low-power and shortrange base stations (corresponding to picocells or femtocells) in a service area is considered to be an efficient solution to enhance the spectralefficiency of the network per unit area. Also, such a hierarchical cell deployment, which is referred to as a heterogeneous network, or Het- Net, provides significant improvement in the coverage of indoor and cell edge users and ensures better QoS to the users. Interference mitigation between different layers is one of the key issues that needs to be resolved for successful deployment of HetNets. To this end, fast frequency response, FFR, is considered to be an efficient intercell interference coordination technique for OFDMA-based HetNets. This article focuses on evaluating three state-of-the-art FFR deployment schemes: strict FFR, soft FFR, and FFR-3 schemes for OFDMA-based two-tier HetNets comprising macrocells overlaid with femtocells. Also, a variation of the FFR-3 scheme, which is referred to as the optimal static FFR (OSFFR) scheme, is proposed. A broad comparison among all these FFR schemes is performed by using Monte Carlo simulations considering performance metrics such as outage probability, average network sum rate, and spectral efficiency. Simulation results show that, the average gains in spectral efficiency (b/s/Hz) of the network are significantly higher for the proposed scheme when compared to the strict FFR, soft FFR, and FFR-3 schemes.

Self-configuration and self-optimization in LTE-advanced heterogeneous networks

Abstract: Self-organizing network, or SON, technology, which is able to minimize human intervention in networking processes, was proposed to reduce the operational costs for service providers in future wireless systems. As a cost-effective means to significantly enhance capacity, heterogeneous deployment has been defined in the 3GPP LTEAdvanced standard, where performance gains can be achieved through increasing node density with low-power nodes, such as pico, femto, and relay nodes. The SON has great potential for application in future LTE-Advanced heterogeneous networks, also called HetNets. In this article, state-of-the-art research on self-configuring and self-optimizing HetNets are surveyed, and their corresponding SON architectures are introduced. In particular, we discuss the issues of automatic physical cell identifier assignment and radio resource configuration in HetNets based on selfconfiguring SONs. As for self-optimizing SONs, we address the issues of optimization strategies and algorithms for mobility management and energy saving in HetNets. At the end of the article, we show a testbed designed for evaluating SON technology, with which the performance gain of SON algorithms is demonstrated.

Recent trend of multiuser MIMO in LTE-advanced

Abstract: Recently, the mobile communication industry is moving rapidly toward Long Term Evolution, or LTE, systems. The leading carriers and vendors are committed to launching LTE service in the near future; in fact, a number of major operators such as Verizon have initiated LTE service already. LTE aims to provide improved service quality over 3G systems in terms of throughput, spectral efficiency, latency, and peak data rate, and the MIMO technique is one of the key enablers of the LTE system for achieving these diverse goals. Among several operational modes of MIMO, multiuser MIMO (MU-MIMO), in which the base station transmits multiple streams to multiple users, has received much attention as a way of achieving improvement in performance. From the initial release (Rel. 8) to the recent release (Rel. 10), so called LTE-Advanced, MUMIMO techniques have evolved from their premature form to a more elaborate version. In this article, we provide an overview of design challenges and the specific solutions for MU-MIMO systems developed in the LTE-Advanced standard.

System performance of LTE and IEEE 802.11 coexisting on a shared frequency band

Abstract: This paper presents the system performance analysis of 3GPP Long-Term Evolution (LTE) and IEEE 802.11 Wireless Local Area Networks (WLAN) in a situation where LTE downlink (DL) has been expanded over to unlicensed frequency band usually used by WLAN. Simple fractional bandwidth sharing mechanism is used to allow both technologies to transmit. The system performance is evaluated by means of fully dynamic network simulations.

LTE-Advanced: A Practical Systems Approach to Understanding 3GPP LTE Releases 10 and 11 Radio Access Technologies

Abstract: This book is an in-depth, systematic and structured technical reference on 3GPP's LTE-Advanced (Releases 10 and 11), covering theory, technology and implementation, written by an author who has been involved in the inception and development of these technologies for over 20 years. The book not only describes the operation of individual components, but also shows how they fit into the overall system and operate from a systems perspective. Uniquely, this book gives in-depth information on upper protocol layers, implementation and deployment issues, and services, making it suitable for engineers who are implementing the technology into future products and services. Reflecting the author's 25 plus years of experience in signal processing and communication system design, this book is ideal for professional engineers, researchers, and graduate students working in cellular communication systems, radio air-interface technologies, cellular communications protocols, advanced radio access technologies for beyond 4G systems, and broadband cellular standards.An end-to-end description of LTE/LTE-Advanced technologies using a top-down systems approach, providing an in-depth understanding of how the overall system works Detailed algorithmic descriptions of the individual components' operation and inter-connection Strong emphasis on implementation and deployment scenarios, making this a very practical book An in-depth coverage of theoretical and practical aspects of LTE Releases 10 and 11 Clear and concise descriptions of the underlying principles and theoretical concepts to provide a better understanding of the operation of the system's components Covers all essential system functionalities, features, and their inter-connections based on a clear protocol structure, including detailed signal flow graphs and block diagrams Includes methodologies and results related to link-level and system-level evaluations of LTE-Advanced Provides understanding and insight into the advanced underlying technologies in LTE-Advanced up to and including Release 11: multi-antenna signal processing, OFDM, carrier aggregation, coordinated multi-point transmission and reception, eICIC, multi-radio coexistence, E-MBMS, positioning methods, real-time and non-real-time wireless multimedia applications

On the Evolution of Multi-Cell Scheduling in 3GPP LTE / LTE-A

Abstract: This paper provides a holistic overview of multi-cell scheduling strategies in emerging wireless systems. Towards this objective, the evolution of interference management techniques is thoroughly investigated from simple inter-cell interference coordination (ICIC) techniques towards more advanced coordinated multipoint transmissions (CoMP), while comparing and contrasting their common features and differences. Finally CoMP is explored in detail as an advanced and challenging mechanism to fully cooperate between adjacent cells in order to have an efficient resource allocation and inter-cell interference mitigation in multi-cell environments.

Interference management through CoMP in 3GPP LTE-advanced networks

Abstract: Intercell interference management has become a critical issue for future cellular mobile systems. Coordinated multipoint transmission/reception, or CoMP, is an effective way of managing intercell interference, and has been regarded as a key technology of LTE-Advanced. This article first provides an overview of downlink CoMP techniques specified in 3GPP LTE Rel-11, which mainly focuses on transmission schemes, channel state information reporting, interference measurement, and reference signal design. Then uplink CoMP is discussed in brief as most of the coordination gain can be achieved by implementation with little standardization support. Evaluation results are provided to show the efficiency of CoMP. The challenges as well as possible solutions for future CoMP standardization are also discussed.

WiFi Direct and LTE D2D in action

Abstract: With the evolution of high-performance multi-radio smartphones, Device-to-Device (D2D) communications became an attractive solution for enhancing the performance of cellular networks. Although D2D communications have been widely studied within past few years, the majority of the literature is confined to new theoretical proposals and did not consider implementation challenges. In fact, the implementation feasibility of D2D communications and its challenges are still a relevant research question. In this paper, we introduce a protocol that focuses on D2D communications using LTE and WiFi Direct technologies. We also show that currently available WiFi Direct features permits to deploy the D2D paradigm on top of the LTE cellular infrastructure, without requiring any fundamental change in LTE protocols.

LTE/LTE-A signal compression on the CPRI interface

Abstract: The Centralized, Cooperative, Cloud Radio Access Network (C-RAN) is a next-generation wireless access network architecture based on centralized processing, collaborative radio, and real time cloud infrastructure. In this architecture, different access technologies (Global System for Mobile Communications (GSM)/Time Division Synchronous Code Division Multiple Access (TD-SCDMA)/Wideband Code Division Multiple Access (WCDMA)/Long Term Evolution (LTE)) can be supported on the same hardware platform in a baseband pool system, which can largely reduce system costs. Long Term Evolution (LTE) and Long Term Evolution-Advanced (LTE-A), which are based on Orthogonal Frequency Division Multiplexing (OFDM) and multiple input multiple output (MIMO) technologies, are regarded as the main wireless access technologies in the evolution from 3G to 4G. A variety of novel technologies such as multi-antenna MIMO, carrier aggregation (CA), and coordinated multipoint have been introduced in LTE/LTE-A to improve system performance, especially in the C-RAN architecture. However, one of the technical challenges for the C-RAN architecture is the fiber bandwidth required for data transmission between the remote radio unit (RRU) and the baseband unit (BBU). We propose using a low-latency baseband signal compression algorithm to solve this problem by reducing the fiber data rate. Using the characteristics of the LTE signal data, we remove the redundancy in the spectral domain. We also leverage block scaling in conjunction with using a linear or nonlinear (non-uniform) quantizer to minimize quantization error. This algorithm effectively reduces the amount of data transmitted between the BBU and RRU, and facilitates the deployment of LTE in the C-RAN architecture. We verified the robustness of the algorithm via simulations and lab tests. The proposed algorithm yields good system performance at a 1/2 compression rate and at a 1/3 compression rate in a practical propagation environment.

Multicell cooperation for LTE-advanced heterogeneous network scenarios

Abstract: In this article we present two promising practical use cases for simple multicell cooperation for LTE-Advanced heterogeneous network scenarios with macro and small cells. For co-channel deployment cases, we recommend the use of enhanced interference coordination, or eICIC, to mitigate cross-tier interference and ensure sufficient offload of users from macro to small cells. It is shown how the eICIC benefit is maximized by using a distributed inter-base station control framework for dynamic adjustment of essential parameters. Second, for scenarios where macro and small cells are deployed at different carriers an efficient use of the fragmented spectrum can be achieved by using collaborative inter-site carrier aggregation. In addition to distributed coordination/collaboration between base station nodes, the importance of explicit terminal assistance is highlighted. Comprehensive system-level simulation results illustrate the performance benefits of the presented techniques.

New control plane in 3GPP LTE/EPC architecture for on-demand connectivity service

Abstract: The on-demand connectivity service is one of the main requirements of the cellular data network. It consists in moving sessions transparently and temporarily from one network equipment to another without causing user session interruption. This service enables networks to cope with the ever-changing network condition such as sudden congestion or arbitrary network equipment failure. In this paper, we argue that the cellular data networks such as LTE/EPC lack the network visibility and control elasticity that enable the on-demand connectivity service. The Software Defined Networking (SDN) is an emerging trend that should be considered to overcomes the above drawback. As a first step, we propose an OpenFlow-based control plane for LTE/EPC architectures. Using resiliency and load balancing use cases, we show that our proposal guarantees the on-demand connectivity service.

LTE/SAE Security Issues on 4G Wireless Networks

Abstract: The authors give an overview on the state of the art of potential security issues that occur in the deployment of the LTE/SAE (Long-Term Evolution/System Architecture Evolution) protocol in emerging 4G wireless technologies. Although security concerns and challenges in wireless networks will remain a hot topic in the future, the LTE/SAE standard could adapt to these rising challenges, becoming more robust and secure. By looking at the authentication and ciphering algorithms, such as EAP-AKA (Extensible Authentication Protocol for Authentication and Key Agreement), currently operating within the LTE protocol, the authors analyze several vulnerabilities in LTE/SAE security architecture—specifically, insecure AKA key derivation procedures and the lack of fast reauthentications during handovers.

Enhanced inter-cell interference coordination in co-channel multi-layer LTE-advanced networks

Abstract: Different technical solutions and innovations are enabling the move from macro-only scenarios towards heterogeneous networks with a mixture of different base station types. In this article we focus on multi-layer LTE-Advanced networks, and especially address aspects related to interference management. The network controlled time-domain enhanced inter-cell interference coordination (eICIC) concept is outlined by explaining the benefits and characteristics of this solution. The benefits of using advanced terminal device receiver architectures with interference suppression capabilities are motivated. Extensive system level performance results are presented with bursty traffic to demonstrate the eICIC concepts ability to dynamically adapt according to the traffic conditions.

Energy-efficient inter-frequency small cell discovery techniques for LTE-advanced heterogeneous network deployments

Abstract: Heterogeneous network, or HetNet, deployments are one of the key enablers in providing ubiquitous coverage and capacity enhancements for LTE-Advanced networks. They play an important role in achieving high data rate and quality of service requirements defined for next generation wireless networks. In this article we evaluate various cell discovery techniques tailored for energy-efficient detection of small cells deployed in a carrier other than the serving macrocell. The presented schemes are evaluated using extensive system simulations conducted in a 3GPP LTE-Advanced HetNet scenario. Shortcomings of the currently standardized mechanism are analyzed, and advantages of the evaluated schemes are presented. Both the offloading opportunity utilization and savings in UE battery power consumption are analyzed. The results show that using the considered flexible, adaptive, and intelligent schemes for small cell discovery, significant UE power savings can be achieved with small loss in offloading - giving benefits both on system level as well as in user experience.

Mobility enhancements for LTE-advanced multilayer networks with inter-site carrier aggregation

Abstract: In this article we first summarize some of the most recent HetNet mobility studies for LTEAdvanced, and use these to highlight the challenges that should be further addressed in the research community. A state-of-the-art HetNet scenario with macros and small cells deployed on different carriers, while using inter-site carrier aggregation, is hereafter studied. Hybrid Het- Net mobility solutions for such cases are derived, where macrocell mobility is network controlled, while small-cell mobility is made UE-autonomous. The proposed scheme is characterized by having the UE devices autonomously decide small cell addition, removal, and change without any explicit signaling of measurement events to the network or any signaling of hand - over commands from the network. Hence, the proposed solution effectively offloads the network from having to perform frequent small cell handoff decisions, and reduces the signaling overhead compared to known network controlled mobility solutions. Results from extensive dynamic system-level simulations are presented to demonstrate the advantages of the proposed technique, showing significant savings in signaling overhead.

Looking at LTE in Practice: A Performance Analysis of the LTE System Based on Field Test Results

Abstract: This article introduces a practical performance analysis of the long-term evolution (LTE) cellular system based on field test results from a commercially deployed Third-Generation Partnership Project's (3GPP?s) Release 8 LTE network in Band-3 (i.e., 1,800 MHz, sometimes termed LTE1,800 MHz) with 20-MHz channel bandwidth. The presented analysis demonstrates the downlink (DL) and uplink (UL) throughputs in mobility conditions in addition to other aspects of the LTE system such as link budget, cell coverage, spectral efficiency, and handover performance. LTE's key features such as multiple-input, multiple-output (MIMO) and higher-order modulation [i.e., 64 quadrature amplitude modulation (QAM)] are assessed in different radio frequency (RF) conditions. A comparison is presented between LTE and 3GPP Release 8 evolution of high-speed packet access (HSPA+) with a dual-cell high-speed DL packet access (DC-HSDPA) feature based on the universal mobile telecommunications system (UMTS) 2,100-MHz commercial network with 10-MHz bandwidth (i.e., 2x5-MHz adjacent carriers). The presented LTE network performance analysis and the comparison with the HSPA+ network can be used to benchmark the LTE system performance and evaluate the gains and merits of deploying the LTE network. It has been demonstrated that the LTE system outperforms the HSPA+ system in terms of spectrum efficiency, 64-QAM utilization, cell coverage, and handover delay. The LTE system offers a 34% improvement in spectrum efficiency, 40% 64-QAM utilization versus 7.4% for the HSPA+ system, and a 60% reduction in data interruption time during handover.

Long term evolution in high speed railway environments: Feasibility and challenges

Abstract: Long Term Evolution (LTE) is considered to be the natural evolution for the current Global System for Mobile Communications-Railways (GSM-R) in high speed railway environments, not only for its technical advantages and increased performance, but also due to the current evolution of public communication systems. In railway environments, mission critical services, operation assistance services, and passenger services must be supported by reliable mobile communication systems. Reliability and availability are key concerns for railway operators and as a consequence, railway operators are usually conservative adopters of information and communication technologies (ICT). This paper describes the feasibility of LTE as a successor to GSM-R for new railway mobile communication systems. We identify key features of LTE as a technology and analyze its ability to support both the migration of current railway services and the provisioning of potential future ones. We describe the key challenges to address specific requirements for railway communication services including the provisioning of voice service in LTE networks, handover performance, multicast multimedia transmission, and the provisioning of group communications service and railway emergency calls.

Pushing the Limits of LTE: A Survey on Research Enhancing the Standard

Abstract: Cellular networks are currently experiencing a tremendous growth of data traffic. To cope with this demand, a close cooperation between academic researchers and industry/standardization experts is necessary, which hardly exists in practice. In this paper, we try to bridge this gap between researchers and engineers by providing a review of current standard-related research efforts in wireless communication systems. Furthermore, we give an overview about our attempt in facilitating the exchange of information and results between researchers and engineers, via a common simulation platform for 3GPP long term evolution (LTE) and a corresponding webforum for discussion. Often, especially in signal processing, reproducing results of other researcher is a tedious task, because assumptions and parameters are not clearly specified, which hamper the consideration of the state-of-the-art research in the standardization process. Also, practical constraints, impairments imposed by technological restrictions and well-known physical phenomena, e.g., signaling overhead, synchronization issues, channel fading, are often disregarded by researchers, because of simplicity and mathematical tractability. Hence, evaluating the relevance of research results under practical conditions is often difficult. To circumvent these problems, we developed a standard-compliant opensource simulation platform for LTE that enables reproducible research in a well-defined environment. We demonstrate that innovative research under the confined framework of a real-world standard is possible, sometimes even encouraged. With examples of our research work, we investigate on the potential of several important research areas under typical practical conditions, and highlight consistencies as well as differences between theory and practice.

LTE/LTE-A Discontinuous Reception Modeling for Machine Type Communications

Abstract: Machine type communications (MTC) are considered as key applications in LTE/LTE-A networks, for which lowering power consumption is among the primary requirements. In this paper, we model the LTE/LTE-A discontinuous reception (DRX) mechanism for MTC applications based on a Semi-Markov chain model. With our model the power saving factor and wake up latency can be accurately estimated for a given choice of DRX parameters, thus allowing to select the ones presenting the best tradeoff. The proposed model is validated through simulations. We also investigate the effect of different DRX parameters on performance.

Carrier aggregation for LTE-advanced: design challenges of terminals

Abstract: Carrier aggregation is a key feature of 3GPP LTE that addresses the support of higher data rates and utilization of fragmented spectrum holdings. In this article, the relevant design challenges of terminals are discussed. The transmitter architectures are reviewed, and the minimum amount of power amplifier back-offs is evaluated. In addition, several receiver architectures are compared from the perspective of design tradeoff. The radio impairments affecting the receiver performance are analyzed and the simulation results are provided. The corresponding silicon implementation is presented together with the measurement results.

Transmitter Architecture for CA: Carrier Aggregation in LTE-Advanced Systems

Abstract: CA has already found its place in the deployment of 4G wireless networks. It successfully shows its value as an efficient way to increase the signal bandwidth within the available spectrum. This article is focused on demonstrating and analyzing the possible transmitter architecture solutions for CA. Further, the benefits and issues of using concurrent dual-band transmitter architecture are investigated. The recent progress on deploying concurrent dual-band PAs has been surveyed, where recent published literatures reported significant improvement on the concurrent dual-band PA design and achievable efficiency. The challenges present in the development of the linearization schemes for concurrent dual-band transmitters are addressed and possible solutions are studied.

Efficient small data access for machine-type communications in LTE

Abstract: In this paper, we address the emerging concept of Machine-Type Communications (MTC), where unattended wireless devices send their data over the Long Term Evolution (LTE) cellular network. In particular, we emphasize that future MTC deployments are expected to feature a very large number of devices, whereas the data from a particular device may be infrequent and small. Currently, LTE is not optimized for such traffic and its data transmission schemes are not MTC-specific. To improve the efficiency of small data access, we propose a novel contention-based LTE transmission (COBALT) mechanism and evaluate its performance with both analysis and protocol-level simulations. When compared against existing alternatives, our data access scheme is demonstrated to improve network resource consumption, device energy efficiency, and mean data access delay. We conclude that COBALT has the potential for supporting massive MTC deployments based on the future releases of the LTE technology.

Mobile relay in LTE-advanced systems

Abstract: Voice and data communications on high speed vehicles encounter bad channel condition, high call drop rate, serious signaling congestion and excessive power consumption of UE. Mobile relay technology which features on-board relay node is expected to improve the quality of service for passengers. However, the design for fixed relay in LTE-Advanced system cannot meet the requirements of mobile relay. In this article, the architecture for mobile relay is presented. The key techniques of supporting mobile relay are investigated, such as the group mobility, the local service support, the multi-RAT and RAN sharing, with the corresponding solutions. The potential system optimization, for example, the self-optimization network, power saving, measurement and system information acquisition are also presented where the efficiency of mobile relay can further be improved. Simulation and numerical results demonstrate the feasibility of the mobile relay.

Architecture and protocols for LTE-based device to device communication

Abstract: The evolution of cellular wireless communications has involved the introduction of technologies such as multiple antennas, OFDM, higher spectral efficiency through better modulation, denser deployments and carrier aggregation. A different approach to enhancing the cellular network by using direct communication between UEs is presented in this paper. Direct device-to-device (D2D) communication can be used for several purposes including network traffic offloading, public safety, and social applications such as gaming. The architectural and protocol enhancements required to extend the current 3GPP LTE-Advanced system to incorporate D2D communication are described, including the logical functions of a D2D server in the core network, the procedures for devices to discover each other and obtain D2D services, the steps involved in establishing and maintaining a D2D call and procedures for efficient mobility between a traditional cellular mode and a D2D mode of operation.