Intae Hwang

Intercell Interference Coordination Using Threshold-Based Region Decisions

IMT-Advanced mobile communication systems make it possible for any devices to access high-speed networks anytime and anywhere. To meet the needs of IMT-Advanced systems, cellular systems must solve the problem of intercell interference caused by frequency reuse. Intercell interference problems become severe when orthogonal frequency division multiplexing (OFDM) transmission, which is a key technology for 4G communication systems, is used in a cellular system. In this paper, a zone-based intercell interference coordination (ICIC) scheme with high flexibility and low cost is proposed, and its performance is evaluated through multicell system-level simulations carried out according to the simplified 3GPP (3rd Generation Partnership Project) Long Term Evolution (LTE) system parameters. In the proposed algorithm, each cell is divided into several regions based on threshold values. Each region reuses frequencies in different ways, and the regions have different maximum transmit (TX) powers according to the interference environment. Even though the proposed scheme can be implemented with low complexity by using only the existing user equipment (UE) measurement, simulation results have confirmed that it provides significant improvements in geometry distribution.

Improving the System-on-a-Chip Performance for Mobile Systems by Using Efficient Bus Interface

Minimizing the communication delay is one of the most important design considerations in System-on-a-Chip (SoC) design for mobile systems. In this paper, we present a bus interface design technique, called Efficient Bus Interface (EBI), to reduce the communication delay between the Intellectual Property (IP) core and the memory connected through AMBA3 AXI bus for mobile systems. Several mobile systems require huge multimedia data in the memory to be transferred to the IP core through bus. The EBI is designed to reduce the memory access time by using double buffering, open row access, and bank interleaving. According to our simulations, the proposed EBI improves the performance of the target system by up to 49%.

Cell Range Expansion and Time Partitioning for Enhanced Inter-cell Interference Coordination in Heterogeneous Network

In this paper, we propose a cell selection scheme and interference management scheme in Heterogeneous Network (HetNet). The cell selection scheme is based on the SINR, and the cell expansion range can vary through the offset value. We can manage the interference between the macro cell and Picocell, using ABS in the time domain. Also, a flexible ABS density is applied, to increase the spectrum efficiency. We show the simulation results of the selection scheme based on SINR with different offset values (6dB, 12dB) and the interference management scheme. Simulation results show that the proposed scheme can improve the user spectrum efficiency of the macro cell and Pico cell user. Eventually, the proposed scheme can improve overall user performance.

Novel MCS Based Relay Protocols for Throughput Optimization Using AMC in LTE-Advanced System

In this paper, we propose a throughput optimization scheme for relay protocols based on Adaptive Modulation and Coding (AMC). The performance of relay protocols with the AMC scheme and show that relay protocols with the AMC scheme are capable of providing better average throughput at a lower Signal to Noise Ratio (SNR) level as compared to the conventional scheme with no AMC. We perform 3GPP Long Term Evolution-Advanced (LTE-A) parameters based simulations to prove the performance comparison of adaptive Modulation and Coding Scheme (MCS) relay protocols with non-adaptive MCS relay protocols. The simulation results of the proposed system with adaptive MCS prove that among the Amplify-and-Forward (AF), Decode-and-Forward (DF) and De-Modulate-and-Forward (DMF), the DMF protocol performs best, at a lower SNR value and higher average throughput.

Interference Management with Cell Selection Using Cell Range Expansion and ABS in the Heterogeneous Network Based on LTE-Advanced

Long term evolution-advanced has developed the heterogeneous network (HetNet) that consists of a mix of macrocells and low-power nodes, such as picocells, to improve the system performance. Also, to encourage data offloading in HetNet, cell range expansion has been introduced. In this paper, we propose a cell selection scheme based on signal to interference plus noise ratio for optimal offloading effect. Also, we manage interference for the user located cell range expanded region using almost blank subframe (ABS) with flexible ABS ratio, to improve the spectrum efficiency in the time domain. Simulation results show that the proposed scheme can improve the spectrum efficiency of the macrocell and picocell user. Eventually, the proposed scheme can improve overall user performance.

Performance Analysis of Coordinated Multi-point with Scheduling and Precoding Schemes in the LTE-A System

To meet the requirements of users for quality of data services, techniques which can support a high data rate to users located within the cell edge as well as the cell center would be indispensible. Accordingly, the need for efficient methods to control the interference between transfer points is increasing. In current standards and academic issues the way of how to control the interference from point-to-point transmission naming coordinated multi-point (CoMP) was selected as the work items for 3rd Generation Partnership Project (3GPP) long term evolution-advanced (LTE-A) Release 11. This paper proposes a combined system of CoMP with Scheduling and Precoding, which solves the problem of conventional cellular system and improves the spectral efficiency of overall system. We design and analyze the performance of the Coordinated Beamforming technique, which is one major category of CoMP. The parameters are included in order to fulfill the requirements of the 3GPP LTE-A Standard. Finally, we make a performance analysis of the proposed system through the system level simulation in Homogeneous Network and Heterogeneous Network. We confirm the performance through a graph of the cumulative distribution function about signal to interference plus noise ratio.

Cell Selection and Resource Allocation for Interference Management in a Macro-Picocell Heterogeneous Network

A heterogeneous network (HetNet) based on the long-term evolution advanced standard has been developed to improve the system performance; in this HetNet, macrocells and low-power nodes, such as picocells, coexist. Further, cell range expansion has been introduced to encourage data offloading in a HetNet. In this paper, we propose a cell selection scheme based on the signal-to-interference-plus-noise ratio to achieve an optimal offloading effect. We also propose a resource allocation scheme in the frequency and time domains, to reduce interference in a HetNet. In the frequency domain, the macrocells allocate a frequency band by using soft frequency reuse, and the picocells choose the sub-bands that are not used in the macrocell sector, to avoid interference. In addition, we found that it was difficult to allocate a limited frequency resource. Therefore, the cross-tier interference can be managed by using an almost blank subframe (ABS) with a flexible ABS ratio, to improve spectrum efficiency in the time domain. The simulation results show that the proposed schemes can improve the spectrum efficiency of both the macro-user equipment and the pico-user equipment, as well as improve the overall UE performance.

Cooperative Multiuser Relay Communications Employing Hierarchical Modulation

Relay-assisted cooperative communications are a promising solution for error-performance improvement and cell coverage extension. However, additional resources such as time slots or frequency bands are required for the relay, which reduce the overall throughput. This paper proposes two cooperative relay schemes that employ hierarchical modulation to overcome this limitation. One scheme is for symmetric downlink communications and the other is for asymmetric downlink communications. These schemes exploit the hierarchical modulation symbols for users in the network and allow the system to transmit two or more independent data streams simultaneously. The proposed schemes reduce the number of transmission phases to the same as conventional schemes without diversity gain. The symbol-error rates of the proposed systems are a function of the distance parameter of hierarchical modulation. By flexibly controlling the distance parameter based on specific scenarios, it allows an extra degree of freedom to guarantee error performance of receivers whose signals undergo different losses.

Smart cooperative relay schemes in LTE-advanced system

Cooperative relaying is considered as the most cost-efficient method in 3GPP LTE-Advanced in terms of coverage prolongation and transmission efficiency. In this paper, we analyze the best performing cooperative relaying scheme between the Amplify-- and--Forward (AF) and Decode-and--Forward (DF) schemes for LTE-Advanced systems. The comparison between AF and DF Relay Nodes (RN) is important because both approaches are currently under consideration for 3GPP LTE-Advanced (LTE-A). The performance analysis of these two relay nodes considers the criteria of: (1) Linear equalization techniques such as Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) and (2) Cooperative Diversity using 2x2 Multiple Input and Multiple Output (MIMO) Alamouti scheme also termed as Space Frequency and Block Coding. Simulation results show that the Bit Error Rate (BER) performance of AF RN and DF RN improves in LTE-Advanced system and that DF RN clearly outperforms AF RN.

Design of New Quasi-Orthogonal STBC with Minimum Decoding Complexity for Four Transmit Antennas

A new Space-Time Block Code (STBC) achieving full rate and full diversity for general QAM and four transmit antennas is proposed. This code also possesses a quasi-orthogonal (QO) property like the conventional Minimum Decoding Complexity QO-STBC (MDC-QO-STBC), leadingg to joint ML detection of only two real symbols. The proposed code is shown to exhibit the identical error performance with the existing MDC-QO-STBC. However, the proposed code has an advantage in transceiver implementation since this code can be modified so that the increase of PAPR occurs on only two transmit antennas, whereas MDC-QO-STBC incurs a PAPR increase on all transmit antennas.