LTE-Advanced System Research Articles

Multiplexing SRS with Periodic CSI on Shortened PUCCH Format 2/2a/2b

In order to avoid dropping the SRS report frequently in case of collision between SRS and a periodic CSI report in LTE-Advanced system, this paper gives shortened PUCCH (Physical Uplink Control Channel) format 2/2a/2b for multiplexing SRS (Sounding Reference Signal) with periodic CSI (Channel State Information). The result of simulation shows that the shortened PUCCH format 2/2a/2b can effectively support simultaneous transmission periodic CSI and SRS. What’s more, on shortened PUCCH format 2/2a/2b with the first and last two encoded bits punctured, periodic CSI and HARQ-ACK feedback have the same performance as on PUCCH format 2/2a/2b without multiplexing SRS. Hence through the shortened PUCCH format 2/2a/2b, we can not only enhance simultaneous transmission of periodic CSI and SRS, but also guarantee the similar performance of periodic CSI and HARQ-ACK feedback as transmitting them on PUCCH format 2/2a/2b without multiplexing SRS.

이종 망을 위한 QoS 관리 체계

Because each resource in LTE-Advanced system and network`s shapes such as bandwidth, error rate change variably, it is judged that it is impossible to control service continuity with procedural, artificial, and static control method applied to the existing voice service. This research suggests a QoS management mechanism to support the service continuity effectively based on policy control. It means a method in which a subscriber`s terminal collects information about its current condition and base station around, and a base station, through the data collected by monitoring inner or adjacent base station, shares related data and converges, controlling service continuity on its own.

Enhancing spectral-energy efficiency forLTE-advanced heterogeneous networks: a users social pattern perspective

The development of LTE-Advanced and beyond cellular networks is expected to offer considerably higher data rates than the existing 3G networks. Among the many potential technologies in LTE-Advanced systems, users? characteristics and social behavior have been studied to improve the networks? performance. In this article we present the concept of user social pattern (USP), which characterizes the general user behavior, pattern, and rules of a group of users in a social manner, and utilize USP as an optimization basis for network performance enhancement. From large-scale traffic traces collected from current mobile cellular networks, the USP model is evaluated and verified. Furthermore, to evaluate the potential of spectral efficiency and energy efficiency enhancement based on USP in LTE-A HetNets, we establish a complete system and link-level HetNet simulation platform according to 3GPP LTE-A standards. Then, based on the platform, simulations are performed to evaluate the impact of USP on spectral and energy efficiency in an LTE-A network, and a USP-based spectral efficiency and energy efficiency enhancement scheme is proposed for a HetNet of the LTE-A system. Simulation results validate that USP can be used as an effective concept for network performance optimization in an LTE-A system.

QoS Priority Based Femtocell User Power Control for Interference Mitigation in 3GPP LTE-A HetNet

In recent years, development of femtocells are receiving considerable attention towards increasing the network coverage, capacity, and improvement in the quality of service for users. In 3GPP LTE-Advanced (LTE-A) system, to efficiently utilize the bandwidth, femtocell and macro cell uses the same frequency band, but this deployment poses a technical challenge of cross-tier interference to macro users. In this paper, the novel quality of service based fractional power control (QoS-FPC) scheme under the heterogeneous networks environment is proposed, which considers the users priority and QoS-requirements during the power allocation. The proposed QoS-FPC scheme has two focal points: firs, it protects the macrocell users uplink communication by limiting the cross-tier interference at eNB below a given threshold, and second, it ensures the optimization of femtocell users power allocation at each power adjustment phase. Performance gain is demonstrated with extensive system-level simulations to show that the proposed QoS-FPC scheme significantly decreases the cross-tier intereference and improves the overall users throughput.

3D-MIMO codebook aided multiple user pairing scheme in LTE-Advanced systems

Two-dimensional (2D) multiple-input multiple-output (MIMO) is currently concentrated on propagation in horizontal plane, but the impact of elevation angle is not considered. However, due to the three-dimensional (3D) character of the real MIMO channel, 2D MIMO cannot achieve the optimal system throughput. A multiple-user MIMO (MU-MIMO) user pairing scheme was proposed, in which the vertical dimension was taken into consideration. In the proposed scheme, a 3D codebook based on full dimension MIMO channel was designed; then two 3D MU-MIMO user's pairing schemes are proposed combining the proposed joint and separate 3D codebook. Simulation evaluates the proposed 3D codebook aided user pairing scheme and compares with the previous 2D MU-MIMO user pairing technology. Owing to the additional spatial degree of freedom in vertical dimension, the proposed 3D MU-MIMO user pairing schemes can effectively improve the overall system performance.

Service Self-Organization Based on SON in LTE-Advanced Heterogeneous Networks

Since global service providers consider seamless interworking with existing networks as the most important factor, it is most likely that LTE-Advanced of 3GPP is selected as international standard for 4G wireless communication. As such, we suggest SON based service self-organization which provides users with service continuity even when mobile users have terminal mobility and session mobility, and enable service providers to implement “heterogeneous multi-network of integrated” which guarantees better service in terms of wireless communication access, transmission speed, and Quality of Service (QoS). It is also expected to allow fast handover service such as VOD, and streaming in LTE-Advanced system. Moreover, this study could be conducted with various research institutions and manufacturers, leading joint research and technology transfer in the future.

LTE 시스템을 위한 다중 대역 안테나 설계

In this paper, a multiband LTE antenna satisfying LTE octa-band is proposed. The proposed antenna consists of a modified PIFA structure and a folded monopole which has the height of 4 mm. Each parts operates at lower and upper LTE band. Measured bandwidth(6 dB return loss) was 118 MHz(870~988 MHz) at the lower band and 1,107 MHz(1,650~2,757 MHz) at the upper band. The proposed antenna has a omni-directional radiation pattern and measured peak gains were 3.21 dBi at the lower band and 4.19 dBi at the upper band, respectively. The proposed antenna is expected to be utilized for future LTE-advanced system.

Multiplexing Periodic CSI with HARQ-ACK on PUCCH Format 3 in LTE-A

In order to avoid dropping the periodic CSI report frequently in case of collision between a periodic CSI report and HARQ-ACK feedback in LTE-Advanced system, this paper gives two coding schemes for multiplexing periodic CSI (Channel State Information) with HARQ-ACK (Hybrid Automatic Repeat request Acknowledgement) feedback on PUCCH (Physical Up Control Channel) format 3. The result of simulation shows that both of the two coding schemes can effectively support simultaneous transmission periodic CSI and HARQ-ACK feedback on PUCCH format 3. What’s more, with joint coding scheme, periodic CSI and HARQ-ACK feedback have the same performance, while HARQ-ACK feedback has better performance than periodic CSI with separate coding scheme. Hence through the separate coding scheme, we can not only enhance simultaneous transmission of periodic CSI and HARQ-ACK feedback, but also guarantee the similar performance of HARQ-ACK feedback as transmitting it alone.

Adaptive Handover Decision Algorithm Based on Multi-Influence Factors through Carrier Aggregation Implementation in LTE-Advanced System

Although Long Term Evolution Advanced (LTE-Advanced) system has benefited from Carrier Aggregation (CA) technology, the advent of CA technology has increased handover scenario probability through user mobility. That leads to a user’s throughput degradation and its outage probability. Therefore, a handover decision algorithm must be designed properly in order to contribute effectively for reducing this phenomenon. In this paper, Multi-Influence Factors for Adaptive Handover Decision Algorithm (MIF-AHODA) have been proposed through CA implementation in LTE-Advanced system. MIF-AHODA adaptively makes handover decisions based on different decision algorithms, which are selected based on the handover scenario type and resource availability. Simulation results show that MIF-AHODA enhances system performance better than the other considered algorithms from the literature by 8.3 dB, 46%, and 51% as average gains over all the considered algorithms in terms of SINR, cell-edge spectral efficiency, and outage probability reduction, respectively.

Impact of Feedback Channel Delay over Joint User Scheduling Scheme and Separated Random User Scheduling Scheme in LTE-A System with Carrier Aggregation

In Long Term Evolution-Advanced (LTE-A), the signal quality in a wireless channel is estimated based on the channel quality measurements. The measurement results are used to select suitable modulation and coding scheme for each transmission, feedback, and processing delay, which can cause a mismatch between channel quality information (CQI) and current channel state at the base station. However, prospect delays in the reception of such CQI may lead to a system performance degradation. This study analyzes the impact of CQI feedback delay on joint user scheduling (JUS) scheme and separated random user scheduling (SRUS) scheme in LTE-A system over carrier aggregation. The analysis will be compared with the system having delayed channel and perfect knowledge at different deployment scenario. We will study the throughput performance of both scheduling schemes with different deployment scenario, and then recommend the suitable deployment scenario to keep the desired QoS for a specific number of users. Results show that, in main beam directed at sector boundaries and diverse coverage, JUS scheme performs better than SRUS, which can justify the intensive use of user equipment power and extra control signaling overhead.

Mobility Management for Femtocells in LTE-Advanced: Key Aspects and Survey of Handover Decision Algorithms

Support of femtocells is an integral part of the Long Term Evolution - Advanced (LTE-A) system and a key enabler for its wide adoption in a broad scale. Femtocells are short-range, low-power and low-cost cellular stations which are installed by the consumers in an unplanned manner. Even though current literature includes various studies towards understanding the main challenges of interference management in the presence of femtocells, little light has been shed on the open issues of mobility management (MM) in the two-tier macrocell-femtocell network. In this paper, we provide a comprehensive discussion on the key aspects and research challenges of MM support in the presence of femtocells, with the emphasis given on the phases of a) cell identification, b) access control, c) cell search, d) cell selection/reselection, e) handover (HO) decision, and f) HO execution. A detailed overview of the respective MM procedures in the LTE-A system is also provided to better comprehend the solutions and open issues posed in real-life systems. Based on the discussion for the HO decision phase, we subsequently survey and classify existing HO decision algorithms for the two-tier macrocell-femtocell network, depending on the primary HO decision criterion used. For each class, we overview up to three representative algorithms and provide detailed flowcharts to describe their fundamental operation. A comparative summary of the main decision parameters and key features of selected HO decision algorithms concludes this work, providing insights for future algorithmic design and standardization activities.

Network access for M2M/H2H hybrid systems: a game theoretic approach

Long Term Evolution-Advanced (LTE-A) is prospering as one of the promising mobile communication systems. In the near future, it is expected that in addition to traditional humanto- human (H2H) communications, an LTE-A system needs to support many applications with the technique of machine type communications (MTC), or machine-to-machine communications (M2M). Since M2M features a large number of devices, a mechanism to guarantee the performance of H2H and M2M in the random access procedure of LTE-A (RACH procedure) should be considered. However, little research provides dynamic RACH resource allocation approaches for H2H and M2M. In this paper, we propose a game-theoretic framework, which divides its random access resources into three groups: for H2H, for M2M, and for the hybrid usage. Under this framework, the Nash Equilibrium (NE) guarantees the system throughput by adaptively redistributing the traffic loading, and the NE can be approached rapidly even if the information of traffic loading is quite limited.

On Swarm Intelligence Inspired Self-Organized Networking: Its Bionic Mechanisms, Designing Principles and Optimization Approaches

Inspired by swarm intelligence observed in social species, the artificial self-organized networking (SON) systems are expected to exhibit some intelligent features (e.g., flexibility, robustness, decentralized control, and self-evolution, etc.) that may have made social species so successful in the biosphere. Self-organized networks with swarm intelligence as one possible solution have attracted a lot of attention from both academia and industry. In this paper, we survey different aspects of bio-inspired mechanisms and examine various algorithms that have been applied to artificial SON systems. The existing well-known bio-inspired algorithms such as pulse-coupled oscillators (PCO)-based synchronization, ant- and/or bee-inspired cooperation and division of labor, immune systems inspired network security and Ant Colony Optimization (ACO)-based multipath routing have been surveyed and compared. The main contributions of this survey include 1) providing principles and optimization approaches of variant bio-inspired algorithms, 2) surveying and comparing critical SON issues from the perspective of physical-layer, Media Access Control (MAC)-layer and network-layer operations, and 3) discussing advantages, drawbacks, and further design challenges of variant algorithms, and then identifying their new directions and applications. In consideration of the development trends of communications networks (e.g., large-scale, heterogeneity, spectrum scarcity, etc.), some open research issues, including SON designing tradeoffs, Self-X capabilities in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)/LTE-Advanced systems, cognitive machine-to-machine (M2M) self-optimization, cross-layer design, resource scheduling, and power control, etc., are also discussed in this survey.

A Survey of Radio Resource Management for Spectrum Aggregation in LTE-Advanced

In order to satisfy the requirements of future IMT-Advanced mobile systems, the concept of spectrum aggregation is introduced by 3GPP in its new LTE-Advanced (LTE Rel. 10) standards. While spectrum aggregation allows aggregation of carrier components (CCs) dispersed within and across different bands (intra/inter-band) as well as combination of CCs having different bandwidths, spectrum aggregation is expected to provide a powerful boost to the user throughput in LTE-Advanced (LTE-A). However, introduction of spectrum aggregation or carrier aggregation (CA) as referred to in LTE Rel. 10, has required some changes from the baseline LTE Rel. 8 although each CC in LTE-A remains backward compatible with LTE Rel. 8. This article provides a review of spectrum aggregation techniques, followed by requirements on radio resource management (RRM) functionality in support of CA. On-going research on the different RRM aspects and algorithms to support CA in LTE-Advanced are surveyed. Technical challenges for future research on aggregation in LTE-Advanced systems are also outlined.

New Remapping Strategy for PDCCH Scheduling for LTE-Advanced Systems

In LTE-A, efficient Physical Downlink Control Channel (PDCCH) scheduling is fundamental to ensuring not only users' Quality of Service (QoS) but also bursty data channels. However, the limited resource available for PDCCH has proven to be a major issue that hampers users' scheduling. By principle, every user equipment (UE) admitted into the network is expected to be scheduled by the control channel prior to gaining access to data channel's resources (i.e. Physical Resource Blocks-PRBs). However, the limited PDCCH resources in traditional systems usually result to some UEs being deprived from accessing PRBs because they have not been scheduled for resource access by PDCCH. This situation is a major connectivity challenge in LTE-A systems. As such, we have proposed a new remapping strategy for PDCCH resource scheduling based on linear transformation matrix. Our scheme remaps the users' search spaces using a transformation function derived from their previous search spaces and the available resources in order to efficiently address PDCCH resource utilization issue. Extensive simulation results show that our new scheme is able to reduce UEs' average blocking probability and as well improve PDCCH resource utilization. Notwithstanding this enhancement, our scheme still maintains the decoding procedure and search space concept in LTE-A systems. Terms — Physical downlink control channel (PDDCH), aggregation level, search space, control channel element, u ser equipment (UE).

A Framework for LTE-A Proximity-based Device-to-Device Service Registration and Discovery

Device-to-Device (D2D) communications in Long Term Evolution (LTE) networks has been proposed as a promising concept as part of the LTE-Advanced (LTE-A) framework, whose aim is to improve user experiences and resource utilization, taking advantage of users’ proximity to each other. In order to extend the current LTE-A system to support D2D communication, there is a need to work on enhancements on the network architecture level. In this paper, we survey the work proposed so far by researchers and propose a design that extends the Third Generation Partnership Project's (3GPP) definition of proximity based services, describing by this the necessary supporting elements.

An investigation of interference coordination in heterogeneous network for LTE-Advanced systems

The novel "femtocell" in Heterogeneous Network (HetNet) for LTE-Advanced (LTE-A) set-up will allow Malaysian wireless telecommunication operators (Maxis, Celcom, Digi, U-Mobile, P1, YTL and etc2.) to extend connectivity coverage where access would otherwise be limited or unavailable, particularly indoors of large building complexes. A femtocell is a small-sized cellular base station that encompasses all the functionality of a typical station. It therefore allows a simpler and self-contained deployment including private residences. For the Malaysian service providers, the main attractions of femtocell usage are the improvements to both coverage and capacity. The operators can provide a better service to end-users in turn reduce much of the agitations and complaints. There will be opportunity for new services at reduced cost. In addition, the operator not only benefits from the improved capacity and coverage but also can reduce both capital expenditure and operating expense i.e. alternative to brand new base station or macrocell installation. Interference is a key issue associated with femtocell development. There are a large number of issues associated with interference all of which need to be investigated, identified, quantified and solved. This is to ensure that the deployment of any femtocells will take place successfully. Among the most critical challenges in femtocell deployment is the interference between femtocell-to-macrocell and femtocell-to-femtocell in HetNets. In this paper, all proposed methods and algorithms will be investigated in the OFDMA femtocell system considering HetNet scenarios for LTE-A.

Enhancement of Geometry and Throughput in LTE Femtocells Cognitive Radio Networks

The mutual electromagnetic interference among macro users and femto users is a challenge, when femtocells are deployed in LTE and LTE advanced systems. When the used femtocells have a closed access, the macro users, who are indoors or near to the femtocells, are prone to a severe interference from the femto access points especially, in the case of the universal frequency reuse deployment. A power control is an effective way to improve the macro users' geometry at the expense of a drop in the femto users' geometry and capacity. The concept of a cognitive radio is proposed, as a novel approach, to mitigate the interference and improve the macro and femto users' geometry. The system is designed, mathematically analyzed, and simulated considering that the femto users are secondary users for the macro users. The macro users and the femto users' throughputs of the proposed system are estimated. Comparisons among the universal frequency reuse, the power control, and the suggested approach are held. The simulation results validate the efficiency of the proposed system. The average of femto users' throughput in the proposed system is better than the corresponding one employing the universal frequency reuse or the power control, even if only 20 % of the subcarriers are available to be accessed by the femto users. Moreover, the macro users' throughput in the proposed system is better than the corresponding one applying the universal frequency reuse or the power control, even if only 40 % of the subcarriers are available to be accessed by the macro users.

A prototype cognitive radio architecture for TVWS exploitation under the real time secondary spectrum market policy

This paper elaborates on the design and implementation of a prototype system architecture enabling for TVWS exploitation by LTE Advanced systems, under the real time secondary spectrum market policy. It describes a centralized infrastructure-based cognitive radio network, where dynamic TVWS allocation among unlicensed systems is administrated by a spectrum broker, carrying out radio-resource management and spectrum trading in real time. For efficient system performance as a matter of both maximum-possible radio resource exploitation and trading revenue, the paper discusses the design and implementation of a prototype mechanism at the spectrum broker side, which exploits the backtracking algorithm for obtaining the best-matching solution. Performance evaluation experiments carried-out under controlled conditions (i.e. simulation) verified the validity of the proposed architecture, besides establishing its capacity for maximum spectrum utilization and minimum fragmentation under a fixed-price trading policy.

LTE-Advanced and the evolution to Beyond 4G (B4G) systems

Cellular networks have been undergoing an extraordinarily fast evolution in the past years. With commercial deployments of Release 8 (Rel-8) Long Term Evolution (LTE) already being carried out worldwide, a significant effort is being put forth by the research and standardization communities on the development and specification of LTE-Advanced. The work started in Rel-10 by the Third Generation Partnership Project (3GPP) had the initial objective of meeting the International Mobile Telecommunications-Advanced (IMT-Advanced) requirements set by the International Telecommunications Union (ITU) which defined fourth generation (4G) systems. However, predictions based on the wireless traffic explosion in recent years indicate a need for more advanced technologies and higher performance. Hence, 3GPP’s efforts have continued through Rel-11 and now Rel-12. This paper provides a state-of-the-art comprehensive view on the key enabling technologies for LTE-Advanced systems. Already consolidated technologies developed for Rel-10 and Rel-11 are reviewed while novel approaches and enhancements currently under consideration for Rel-12 are also discussed. Technical challenges for each of the main areas of study are pointed out as an encouragement for the research community to participate in this collective effort.