LTE-Advanced System Research Articles

LTE-Advanced에서 프리코딩에 의한 효율적인 상향링크 적응 방식

LTE-Advanced 시스템은 최대 15bps/Hz의 주파수 효율을 달성하기 위해 상향링크 다중 안테나 전송을 지원해야 한다 본 논문은 LTE-Advanced 상향링크 MIMO 시스템 구조를 제안하고 프리코딩에 의한 링크 적응방식을 고려하여 단말당 오류율을 줄이고 시스템 용량을 향상시키는데 기여할 수 있다 특히, <TEX>$2{\times}4$</TEX> MIMO 시스템에서 최적의 프리코딩 행렬을 선택하여 랭크를 결정하는 방식을 제안하고 MMSE(minimum mean squared error) 수신기에 대한 SINR(signal-to-interference and noise ratio)을 유도한다. 제안 방식의 성능 검증을 위해 실질적인 MIMO 채널 모델에서 BLER(BLock Error Rate) 시뮬레이션을 수행한다. 제안 방식이 full-rank로 고정해서 보내는 경우 보다 더 좋은 성능을 발휘하며 MCS가 낮거나 고속 이동시에 더 큰 이득을 얻을 수 있다. LTE-Advanced system requires uplink multi-antenna transmission in order to achieve the peak spectral efficiency of 15bps/Hz. In this paper, the uplink MIMO system model for the LTE-Advanced is proposed and an efficient link adaptation shceme using precoding is considered providing error rate reduction and system capacity enhancement. In particular, the proposed scheme determines a transmission rank by selecting the optimal wideband precoding matrix, which is based on the derived signal-to-interference and noise ratio (SINR) for the minimum mean squared error (MMSE) receivers of <TEX>$2{\times}4$</TEX> multiple input multiple output (MIMO). The proposed scheme is verified by simulation with a practical MIMO channel model. The simulation results of average block-error-rate(BLER) reflect that the gain due to the proposed rank adapted transmission over full-rank transmission is evident particularly in the case of lower modulation and coding scheme (MCS) and high mobility, which means the severe channel fading environment.

A cross-layer resource allocation scheme for ICIC in LTE-Advanced

As a new technology, inter-eNB coordination has been included in LTE-Advanced study items. Moreover, the network architecture in LTE-Advanced system is modified to take into account coordinated transmission. In our study, we explore the problem of jointly optimizing the power level and scheduling of resource blocks for LTE-Advanced network based on orthogonal frequency division multiplexing (OFDM). We propose a distributed optimization scheme based on evolutionary potential games, and in the process of objective function modeling we employ the Lagrangian multiplier method to solve the constraint objective optimization problem. Then particle swarm optimization (PSO) method is adopted to find the optimal power allocation and scheduling for each resource block in the multi-cell framework. Numerical results prove that proposed algorithm notably improves the overall throughput, while user fairness is guaranteed. Importantly, additional computation and communication cost introduced by cross-layer optimization is also evaluated.

LTE Advanced The 4G Mobile Broadband Technology

By the design and optimization of upcoming radio access techniques and a further evolution of the existing system, the Third Generation Partnership Project (3GPP) had laid down the foundations of the future Long Term Evolution (LTE) advanced standards-the 3GPP candidate for 4G. This paper offers an overview of the research work carried out to meet the requirements of 4G. The various technology components like wideband transmission and spectrum sharing, multiantenna solutions, coordinated multiple transmission/reception (CoMP) and relaying, introduced to meet the requirements for LTE Advanced systems, have been discussed.

Reference Signal Transmission Schemes for Coordinated Multi-Point Transmission for 3GPP LTE-Advanced

In this study, we investigate reference signal (RS) transmission schemes that aim to efficiently support coordinated multi-point (CoMP) transmission by providing improved channel estimation accuracy so that transmission parameters can be appropriately chosen on a cellular network. First, we investigate typical scenarios for transmission parameter selection with the widely used CoMP transmission and precoding schemes aligned with those considered for Long Term Evolution (LTE)-Advanced systems. Second, we investigate an RS transmission scheme that can provide accurate channel estimation even with severe inter-cell interference. Finally, we verify the performance benefit of the investigated scheme by a multi-cell link level evaluation. The results obtained indicate: 1) the investigated scheme improves block error rate performance compared to conventional schemes for fixed modulation and coding schemes (MCSs) allocation with a better precoding control accuracy on the LTE-Advanced system downlink and 2) the investigated scheme provides a throughput performance gain compared to conventional schemes for adaptive MCS allocation and coordinated beamforming.

LTE update [Series Editorial

This issue includes four articles addressing some key technologies for LTE and LTE-Advanced systems.

Carrier aggregation for LTE-advanced mobile communication systems

In order to achieve up to 1 Gb/s peak data rate in future IMT-Advanced mobile systems, carrier aggregation technology is introduced by the 3GPP to support very-high-data-rate transmissions over wide frequency bandwidths (e.g., up to 100 MHz) in its new LTE-Advanced standards. This article first gives a brief review of continuous and non-continuous CA techniques, followed by two data aggregation schemes in physical and medium access control layers. Some technical challenges for implementing CA technique in LTE-Advanced systems, with the requirements of backward compatibility to LTE systems, are highlighted and discussed. Possible technical solutions for the asymmetric CA problem, control signaling design, handover control, and guard band setting are reviewed. Simulation results show Doppler frequency shift has only limited impact on data transmission performance over wide frequency bands in a high-speed mobile environment when the component carriers are time synchronized. The frequency aliasing will generate much more interference between adjacent component carriers and therefore greatly degrades the bit error rate performance of downlink data transmissions.

Multicell power allocation method based on game theory for inter-cell interference coordination

As a new technology, coordinated multipoint (CoMP) transmission is included in LTE-Advanced study item. Moreover, the network architecture in LTE-Advanced system is modified to take into account coordinated transmission. Under this background, a novel power allocation game model is established to mitigate inter-cell interference with cellular coordination. In the light of cellular cooperation relationship and centralized control in eNodeB, the power allocation in each served antenna unit aims to make signal to interference plus noise ratio (SINR) balanced among inter-cells. Through the proposed power allocation game algorithm, the users’ SINR can reach the Nash equilibrium, making it feasible to reduce the co-frequency interference by decreasing the transmitted power. Numerical results show that the proposed power allocation algorithm improves the throughput both in cell-center and cell-edge. Moreover, the blocking rate in cell-edge is reduced too.

Key Enabling Physical Layer Technologies for LTE-Advanced

The 3GPP Long Term Evolution Advanced (LTE-A) system, as compared to the LTE system, is anticipated to include several new features and enhancements, such as the usage of channel bandwidth beyond 20MHz (up 100MHz), higher order multiple input multiple output (MIMO) for both downlink and uplink transmissions, larger capacity especially for cell edge user equipment, and voice over IP (VoIP) users, and wider coverage and etc. This paper presents some key enabling technologies including flexible uplink access schemes, advanced uplink MIMO receiver designs, cell search, adaptive hybrid ARQ, and multi-resolution MIMO precoding, for the LTE-A system.

Performance Evaluation of Carrier Aggregation for Elastic Traffic in LTE-Advanced Systems

Carrier aggregation is a potential technology for the LTE-Advanced system to support wider bandwidth than the LTE system. This paper analyzes the performance of carrier aggregation under elastic traffic, and compares it to that of a simpler approach for the same purpose, referred to as the independent carrier approach. The queueing behaviors of these two approaches are formulated as one fast versus multiple slow state-dependent Processor Sharing servers, respectively. Both analytical and simulation results show that when there are L component carriers with uniform bandwidth in the system, the performance of the carrier aggregation approach is L times better than that of the independent carrier approach in terms of the average user delay and throughput under the same traffic load.