LTE-Advanced System Research Articles

Decentralized Learning-Based Relay Assignment for Cooperative Communications

Cooperative communication exploits spatial diversity via relay node antennas to increase data rates in wireless networks. Relay node selection, therefore, plays a critical role in system performance. This paper examines the problem of relay node selection in cooperative networks, in which one relay node can be used by multiple source–destination transmission pairs, and all transmission pairs share the same set of relay nodes. Centralized approaches may exhibit higher complexity when the number of source nodes is increased. This paper gives source nodes self-optimizing and self-learning abilities and enables them to autonomously select relay nodes. A fully distributed approach, called a “Decentralized Learning-based Relay Assignment” (DLRA) algorithm, is proposed to achieve this goal. DLRA uses a reinforcement learning technique called stochastic learning automata, with each source node attaining the self-learning ability to find an appropriate relay node according to environmental feedback. This paper shows the convergency, optimality, and performance of DLRA via mathematical analysis and evaluates the performance of DLRA in two different network systems: a cooperative ad hoc network and a Long-Term Evolution (LTE)-Advanced relay network. The experimental results present several properties of DLRA: the effectiveness of DLRA in cooperative communication systems, the significant improvements made by DLRA in fairness, and the capacity of each node in LTE-Advanced systems.

Novel Handover Optimization with a Coordinated Contiguous Carrier Aggregation Deployment Scenario in LTE-Advanced Systems

The carrier aggregation (CA) technique and Handover Parameters Optimization (HPO) function have been introduced in LTE-Advanced systems to enhance system performance in terms of throughput, coverage area, and connection stability and to reduce management complexity. Although LTE-Advanced has benefited from the CA technique, the low spectral efficiency and high ping-pong effect with high outage probabilities in conventional Carrier Aggregation Deployment Scenarios (CADSs) have become major challenges for cell edge User Equipment (UE). Also, the existing HPO algorithms are not optimal for selecting the appropriate handover control parameters (HCPs). This paper proposes two solutions by deploying a Coordinated Contiguous-CADS (CC-CADS) and a Novel Handover Parameters Optimization algorithm that is based on the Weight Performance Function (NHPO-WPF). The CC-CADS uses two contiguous component carriers (CCs) that have two different beam directions. The NHPO-WPF automatically adjusts the HCPs based on the Weight Performance Function (WPF), which is evaluated as a function of the Signal-to-Interference Noise Ratio (SINR), cell load, and UE’s velocity. Simulation results show that the CC-CADS and the NHPO-WPF algorithm provide significant enhancements in system performance over that of conventional CADSs and HPO algorithms from the literature, respectively. The integration of both solutions achieves even better performance than scenarios in which each solution is considered independently.

D2D 통신에서 사이드링크를 위한 DFT 기반 채널 추정 기법

Recently, 3rd Generation Partnership Project (3GPP) has developed device-to-device (D2D) communication to cope with the explosively increasing mobile data traffic. The D2D communication uses sidelink based on single carrier-frequency division multiple access (SC-FMDA) due to its low peak-to-average power ratio (PAPR). In addition, demodulation reference signal (DMRS) is designed to support multiple input multiple output (MIMO). In this paper, we propose the DFT-based channel estimation scheme for sidelink in D2D communication. The proposed scheme uses the 2-Dimensional Minimum Mean Square Error (2-D MMSE) interpolation scheme for the user moving at a high speed. We perform the system level simulation based on 20MHz bandwidth of 3GPP LTE-Advanced system. Simulation results show that the proposed channel estimation scheme can improve signal-to-interference-plus-noise ratio (SINR), throughput and spectral efficiency of conventional scheme.

Reverse Rate Matching for Low-Power LTE-Advanced Turbo Decoders

In this paper, a reverse rate matching method is presented for LTE-Advanced turbo decoders. In LTE-Advanced systems, the turbo codes are highly punctured to achieve high data rate when the channel is reliable. In that case, since only a small part of the input frame memory contains meaningful data, accessing all entries of the memory is redundant. To reduce the meaningless accesses, the proposed reverse rate matching method evaluates whether each code bit is punctured or not. As a result, more than 30% of the power consumed in accessing the input memory can be saved when the code rate is high. Furthermore, a low-complexity hardware architecture realizing the proposed method is presented for parallel-SISO decoding. By making use of a specific relationship resident in parallel input indexes, the hardware complexity of the reverse rate matching unit is reduced by 44%.

Overlapping coalition formation games based interference coordination for D2D underlaying LTE-A networks

In the device-to-device (D2D) underlaying LTE-Advanced (LTE-A) systems, unlike the existing works which formulate the resources sharing problem as a disjoint coalition formation game, in this letter we propose a novel overlapping coalition formation game (OCFG) based scheme to coordinate the interference between these two subsystems. By sharing uplink spectrums, in this game each D2D pair is allowed to join multiple coalitions simultaneously to improve the spectral efficiency and maximize the system utility. The merge-and-split rule is designed to adapt to the dynamic environment and a discrete-time Markov chain based analysis is utilized to present the stability. Compared with traditional methods, simulations demonstrate the significant performance enhancement of the proposed algorithm in terms of the complexity and D2D system sum throughput.

백홀 시스템에서 시스템 레벨 시뮬레이션 기반 하이브리드 수신기 설계 및 성능 분석

폭발적으로 증가하고 있는 모바일 데이터 트래픽을 수용하기 위하여 셀 간 간섭을 제어할 수 있는 향상된 수신기에 대한 연구가 필요하다. 이를 위해 3GPP(3rd Generation Partnership Project) 에서는 인접 셀의 간섭 신호를 억제 및 제거하여 수신기의 SINR(Signal-to-Noise-plus-Interference Ratio)을 향상시켜 수신 성능을 올리는 NAICS(Network Assisted Interference Cancellation and Suppression)가 표준에서 논의되고 있다. 본 논문에서는 이웃셀로 부터 간섭의 영향을 줄이기 위하여 연판정 기반의 향상된 수신기를 제안한다. 제안한 수신기는 MMSE (Minimum Mean Square Error) 또는 IRC (Interference Rejection Combing) 수신기를 통해 간섭 신호의 불편 추정 (unbiased estimation) 값을 계산 하고 간섭 신호를 억제 및 제거한다. 간섭 신호는 LLR (Log-Likelihood Ratio)로 표현되는 소프트 정보를 통해 업데이트 한다. 시스템 레벨 시뮬레이션은 3GPP LTE-Advanced 하향링크 시스템의 20㎒ 대역을 기반으로 이루어 졌으며, 시뮬레이션 결과 제안한 수신기를 통해 기존 수신기보다 SINR, 전송률 및 스펙트럼 효율 측면에서 성능 향상을 가져다주는 것을 확인하였다.

An Efficient Scheduling Scheme for OFDMA Resource Blocks with Joint User Scheduling based on Earliest Deadline First with Carrier Aggregation (CA) in LTE-A System

This paper focuses on the resource planning within the downlink of Long Term Evolution Advanced (LTE-A) in addition to Carrier Aggregation (CA) technology. Every time CA is being put to use, it is very vital to complement the LTE-A system with a robust and suitable resource scheduling plan. The two basic resource scheduling schemes are Separate Random User Scheduling and Joint User Scheduling (JUS). The former scheme is simpler, but less efficient, while the latter performs optimally at the expense of higher computation complexity. As a matter of fact, LTE-Advanced networks are designed to render minimal latency and additional broadcast rates, coupled with increased spectral operational performance beyond the benchmark of 3G networks. Nevertheless, concerning the insufficient radio resources, the efficient application and management of these scarce resources are most desirable. Hence, the best approach for profitable resource allocation must be of central focus to meet the Quality of Service (QoS) standard. For the purpose of enhancing the system equity and refraining from high complexity of the system, it is recommended that the JUS is based on Earliest Deadline First (EDF), to offer QoS guarantees and equitable distribution of radio resources. From the simulation results, the following improvements were made: The proposed JUS based on EDF, improved the throughput of the users by adjusting the deadline for the allocated resource blocks of the users. The JUS-EDF has improved the users throughput by 10 % as compared to simple JUS. It also enhanced the system fairness by adjusting the priority of each user according to Earliest Deadline compared to JUS, by 8.88 %. Also JUS-EDF reduced packet delays by 1 s, as compared to the conventional JUS. This paper has introduced a sub-optimized packet scheduling algorithm to fully utilize the new feature in LTE-A downlink system.

Propagation Characteristics of Millimeter-Wave Band for 5G Mobile Communications

Background: Millimeter wave band has been identified as a potential frequency band to meet out the high data traffic targeted in 5G Mobile Communications. At this band, the losses during its propagation pose greater challenges in its use for communication. Methods: Propagation characteristics of millimeter wave band have been analyzed through simulation considering the MIMO-OFDM system in Matlab. The propagation characteristics in terms of losses, bit-error rate, cell edge performance and cell throughput are analyzed. Findings: The MIMO-OFDM using millimeter wave band is capable of delivering an average cell throughput and cell-edge throughput performances better than the current LTE Advanced Systems. Application: Higher throughput performance of the MIMO-OFDM in millimeter wave band necessitates its use in 5G Mobile Communication Systems.Keywords: 5G System, Millimeter Wave, Propagation, Mobile Communication

Improved Carrier Frequency Offset Estimation Algorithms for PUCCH Format 1 in LTE-Advanced

Physical Uplink Control Channel (PUCCH) is an important narrow-band channel in LTE-Advanced system, which carries the uplink control information, such as acknowledge/non-acknowledge (ACK/NACK) bits, downlink channel quality indicator (CQI), HARQ-ACK feedback information, and it requires much higher transmission quality than the other channels. With the aid of orthogonal CDMA, multiple users share the same time-frequency resource, the multiuser interference has been the main factor that limits the transmission quality of the control information [1]. In the high-speed mobile scenario, there exists a large Doppler frequency shift, which leads to loss of code orthogonality and also introduces inter-carrier interference (ICI) within a single SCFDMA symbol. Besides, the multiuser interference in high-speed mobile environment is severe. In this paper, the carrier frequency offset estimation algorithms are analyzed, and a double-iteration carrier frequency offset (CFO) estimation algorithm is proved to perform the best for PUCCH Format 1 in high-speed mobile scenario. The estimation process is achieved by coarse estimation and fine estimation, which enlarges the estimation range and improves the estimation accuracy.

The digital predistortion of the SC-FDMA signals in LTE uplink system

ABSTRACTThe single-carrier frequency-division multiple access (SC-FDMA) is used in the uplink of the long-term evolution (LTE) and LTE-advanced systems because of the lower peak-to-average-power ratio (PAPR) compared with the widely used orthogonal frequency-division multiplexing (OFDM) scheme. However, the non-linearity caused by the characteristic of the radio frequency (RF) power amplifiers (PAs) is still a critical problem, and there are few researches about the linearisation for the SC-FDMA signals. The digital predistorter is widely applied by employing digital baseband distortion ahead of the amplifier to compensate for the non-linearity effects and provide efficiency enhancements for high PAs in the different communication systems. This letter presents an efficient and flexible inverse autoregressive moving-average (ARMA) model-based digital predistorter to linearise the PA distortion with memory in the LTE uplink system. The proposed digital predistortion (DPD) algorithm is for the first time applied to SC-FDMA signals and verified with a series of experimental measurements. The spectrum regrowth of SC-FDMA signals is improved by up to 12 dB from both simulation and measurement. The proposed predistorter has been shown to solve the distortion problem caused by the memory effect effectively in RF PA.

Vertical sectorization in self-organizing LTE-advanced networks

Cellular radio networks continuously evolve to respond the exponential growth in data traffic volume in mobile communications. Active antenna technology contributes to this evolution by introducing vertical sectorization, which splits the horizontal sector into two subsectors with respect to the elevation plane and doubles the number of cells that can be deployed. However, in order to guarantee a reliable and near-optimal operation of vertical sectorization in a system that applies universal frequency reuse, such as LTE-advanced, co-channel interference mitigation is essentially needed. In this article we propose a decentralized self-optimization method that can be used to mitigate the undesirable inter-cell interference by self-tuning the electrical antenna downtilt toward the optimal antenna elevation angle. The performance evaluations for the proposed self-optimization method are carried out for both coordinated and uncoordinated subsector transmission scenarios within the LTE-advanced framework using a dynamic LTE-advanced compliant system level SON simulator. Based on the extensive performance evaluations carried out for a realistic urban scenario, it is found that self-optimization improves the vertical sectorization performance 25 % in terms of virtual load. Furthermore, the performance gain reaches up to 30 % when vertical vectorization is provided with dynamic point selection and muting feature. Therefore, the article concludes that in LTE-advanced networks vertical sectorization can largely benefit from the antenna self-optimization and outperform the traditional horizontal sectorization approach with low algorithmic complexity .

Primary Synchronization Signal for D2D Communications in LTE-Advanced

In this letter, we present a general construction of synchronization signals specifically tailored for device-to-device (D2D) communications in the 3GPP LTE-Advanced system. Major properties of these signals are shown analytically, and some practical examples are further analyzed numerically. It is shown that these synchronization signals can provide 50% complexity reduction of the corresponding matched filters by utilizing central-symmetry signal properties.

Service Block Based Resource Allocation Scheme for Macrocell-Femtocell Networks

The heterogeneous LTE (Long Term Evolution)-Advanced networks comprising a macrocell and femtocells can provide an efficient solution not only to extend macrocell coverage but also to deal with packet traffics increasing explosively within macrocells. An efficient resource management scheme is necessary to maintain the QoS (Quality of Service) of mobile multimedia services because the LTE-Advanced system should support not only voice but also mobile applications such as data, image and video. This paper proposes a resource management scheme to guarantee QoS continuity of multimedia services and to maximize the resource utilization in OFDMA (Orthogonal Frequency Division Multiple Access) based LTE-Advanced systems. This scheme divides the resources into several service blocks and allocates those resources based on the competition between macrocell and femtocell. Simulation results show that it provides better performances than the conventional one in respect of handover failure rate and blocking rate.

Fast Implementation of Different LTE Physical Downlink Control Channels Using FPGA

Hardware implementation of LTE-advanced systems using FPGA technology is a highly promising technology for mobile communications and wireless networks researchers. The objective of this paper is to improve the processing speed; the system capabilities; the power consumption, and the processing delay of LTE-advanced downlink control channels due to the parallel processing nature of FPGA. Basically, the physical downlink control channel (PDCCH) is used to carry downlink control information (DCI). In which, an optimized HDL design for both transmitter and receiver of PDCCH will be presented. The design process of PDCCH transmitter and receiver are carried out in architecture under different antenna configurations including: single input single output: 1 × 1; multiple input multiple output (MIMO) 2 × 2, and MIMO 4 × 4. The complete LTE-advanced physical layer has been coded using VHDL as one of the most famous HDL languages. Designs have been synthesized using Xilinx Integrated Software Environment tool 14.2 on Xilinx Virtex-5 XC5VLX220T_FF1738 as well as Xilinx Spartan-6 XC6SLX45_2CSG324, the performance indices of these two FPGA kits, will be compared. To simulate the system on ModelSim SE 6.5, based on synthesize and implementation, in terms of register transfer level design, FPGA editor, and Xilinx Power Analyzer are discussed into an FPGA kit from the Xilinx vendor. As a result of the system implementation process, it was found that speed; number of registers and power consumption are improved. Finally, it is clear that the hardware is much faster than the software, as well as, reducing the power dissipation in Spartan-6 with respect to Vitex-5 FPGA configurations.

Novel power control and collision resolution schemes for device-to-device discovery

Device-to-Device (D2D) communications allow devices to communicate directly without going through infrastructure. It is considered a promising solution to improve communication performance and network capacity of LTE-Advanced system. In addition, the direct proximity communication implies reduced delay and energy consumption. However, from the perspective of D2D networks, co-existence of multiple D2D User Equipments (UEs) is a challenging issue because of the proximity interference management, especially, without a central controller in a distributed scheme. In this article, we propose a novel distributed power control and collision resolution schemes, which can enhance discovery success of proximity devices conforming to LTE-A networks. The simulation results demonstrate that our proposed schemes can significantly improve the performance of discovery success and detectable coverage by mitigating D2D interference.

Limited Feedback MU-MIMO in LTE-A System: Concepts, Performance, and Future Works

In wireless communications, interference is known as a major restricting factor in achieving system capacity. Therefore, in the Long-Term evolution (LTE) system, a transmitter and a receiver collaborate together to tackle the interference. To do so, in the frequency division duplex system, information of downlink channel must be shared among the transceivers via a limited feedback technique. In this regard, this paper discusses the downlink transmission of multi-user multiple-input multiple-output with limited feedback in the LTE-Advanced system. Extensive studies are conducted on all steps of downlink transmissions and receptions which include techniques such as receive antenna combining, channel state information (CSI) acquisition, CSI quantization, precoding, and user scheduling. By utilizing a LTE-A standard compliant simulator, the link-level performance of the system is evaluated under different receive antenna combiners and quantization codebooks. Moreover, the main system constraints such as channel delay and imperfect CSI are applied to the system which results show that the system performance severely degrades under imperfections, especially when the number of transmit antennas increases. The results mainly reveal that to achieve the capacity of LTE-A, with the presence of interference, delay, and limited feedback, more sophisticated methods are required. Hence, this study precisely addresses the future works on CSI quantization, precoding, and user scheduling.

Cooperative beamforming scheme using MIMO antenna array in LTE-A system

Beamforming (BF) technique using multiple input multiple output antenna array improves reliability, range of transmission, and cell capacity in the long-term evolution-advanced system. Especially, coordinated multi-point (CoMP) method based on the BF techniques has been studied to increase total cell capacity by reducing the inter-cell interference. If a downlink CoMP scheme is applied, more robust transmission is achieved to the user equipment located at the cell edge. There are several types of DL CoMP schemes already and system operator selects a proper scheme according to service property in a real wireless communication system. However, there is a trade-off between the reliability and the resource allocation. In this paper, the hybrid cooperative BF scheme considering this trade-off is proposed. The proposed scheme switches the transmission methods according to the channel state information. Consequently, this scheme can use resources more efficiently and the reliable transmission can be maintained even though a user is located at the cell edge.

Statistical model of OFDM and its application in nonlinearity analysis of LTE-Advanced systems

In this letter, to study the nonlinearity of RF power amplifiers (PAs), we showed that LTE-Advanced signals with large number of subcarriers can be expressed as a white Gaussian noise statistical model with flat power spectrum. This characteristic enables us to express the spectrum regrowth of LTE-Advanced signals up to an arbitrarily high order in an explicit form, in terms of the traditional PA nonlinearity parameter intercept points without complicated convolution. This general analytic expression would help RF designers to predict the PA distortion with simple intercept point expression, and provide insight for pre-distortion.

LTE-Advanced 시스템에서 모바일 IPTV 서비스 채널 변경 최소화 방법에 대한 분석

This paper presents our performance evaluation after the way of minimizing waiting times between channel switching for eMBMS(evolved Multimedia Broadcast/Multicast Services) technique in LTE-Advanced systems. Existing composition of MBMS using IGMP(Internet Group Management Protocol) transfers the data with Multicast from BM-SC(Broadcast Multicast Service Center) to eNB(evolevd Node B) and with Broadcast from eNB to UE(User Equipment). Therefore, in case of channel switching, IGMP Join report should be transferred to BM-SC and then wait user`s contents to be retransferred from eNB. To achieve this, Subscriber Channel technique of priorities is used for minimizing waiting times between channel switching as UE broadcasts favorite channels in advance.

A Low-Complexity Synchronization Method for LTE-A System Based on the Symmetric Time Domain Zadoff–Chu Sequence

Recently, Long Term Evolution Advanced (LTE-A) has been widely deployed for the fourth generation wireless communication system due to its high spectral utilization and throughput performance compared with the other systems. LTE-A adopts the Primary Synchronization Signal (PSS), which is generated from the frequency-domain Zadoff---Chu sequence to complete the synchronization and cell search at the receiver. Rather than the full cross-correlation search of the conventional synchronization method, in this paper, we propose a blind and low-complexity synchronization method that utilizes the time-domain symmetric property of PSS sequence. Results show that the proposed method can predict the arrival time and frequency offset of the received signal precisely and has the low-complexity advantage.