Gilsang Yoon

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%.

Improvement of the sphere decoding complexity through an adaptive OSIC-SD system

Sphere decoding is a decoding technique able to achieve the maximum likelihood error performance in fading environments; nevertheless, it exhibits a high complexity, especially in poor channel conditions. In this paper, we present an adaptive hybrid algorithm which reduces the complexity of conventional sphere decoding without sacrificing its error performance. Through simulations, we prove that the proposed system maintains almost the same bit error rate of the conventional sphere decoding, and exhibits a lower, quasi-constant complexity.

Improvement of the throughput-SNR trade-off using a 4G adaptive MCM system

The MIMO-OFDM Adaptive MCM System changes MIMO scheme, channel coding rate, and modulation scheme, adaptively, according to the channel conditions. And the addition of Pre-coding and Antenna Subset Selection assures a better performance and higher data rate. The MIMO-OFDM Adaptive MCM System achieves a better average throughput performance than a Non Adaptive-MCM system; as SNR increases, the throughput increases almost linearly. Based on the simulation results, we conclude that the proposed MIMO-OFDM Adaptive MCM System represents a feasible solution for improving the throughput-SNR tradeoff in the next generation of mobile communication systems.

Performance analysis of an adaptive-MCM system with combining AMC and MIMO schemes

In this paper, we proposed a system that combines AMC and MIMO schemes. While conventional AMC system changes only the coding rate and modulation, the proposed Adaptive-MCM system also selects the MIMO scheme (diversity, multiplexing) according to channel condition. Furthermore, by applying pre-coding and antenna subset-selection we not only produce optimal performance but also increase the data rate. In case of Non-Adaptive-MCM, the simulation results show that even thought, this system secures enough SNR, and its maximum throughput is limited. As for the Adaptive-MCM System, the simulation shows an overall average data rate increase, and a maximum throughput of 1440kbps that can be achieved because the schemes corresponding to the MCM levels are assigned dynamically. This probes that the Adaptive-MCM system increases the average data rate by improving the trade-off between SNR and throughput.

Loop Detection for Energy-Aware High Performance Embedded Processors

The energy consumed in instruction fetching accounts for a significant portion of total processor energy consumption. Energy consumption as well as performance should be considered when designing high performance embedded processors. In this paper, we present a hardware-based loop detection technique to reduce the energy consumption in the instruction fetch unit (instruction cache and branch prediction logic) for high performance embedded processors. The proposed instruction fetch unit reduces the energy consumed in the instruction cache by replacing the accesses to the large main instruction cache with those to the small selectively accessed cache (SAC). It also reduces the energy consumed in the branch prediction logic by reducing unnecessary accesses to the branch prediction logic. We evaluate the proposed design using a simulation infrastructure based on SimpleScalar and CACTI. Simulation results show that the proposed technique reduces the energy consumption in the instruction cache and the branch prediction logic by 20% and 24% on the average, respectively. Moreover, the proposed scheme shows little performance loss compared to the traditional scheme.

Performance Improvement of the Combined AMC-MIMO Systems with MCS Level Selection Technique

In this paper, we propose and observe a system that adopts independent MCS (modulation and coding scheme) level for each layer in the combined AMC-V- BLAST (adaptive modulation and coding-vertical- bell-lab layered space-time) system. Also, comparing with the combined system using common MCS level, the proposed system applied to Independent MCS level shows how much throughput performance is improved. As a result of simulation, Independent MCS level case adapts modulation and coding scheme for maximum throughput to each channel condition in separate layer, resulting in improved throughput compared to common MCS level case. Especially, the results show that the combined AMC-V-BLAST system with Independent MCS level achieves a gain of 700 kbps in 7~9 dB SNR (signal-to-noise ratio) range.

Throughput improvement of Adaptive Modulation System with optimal Turbo Coded V-BLAST technique using a STD Scheme

In this paper, we propose and analyze an Adaptive Modulation System with optimal Turbo Coded V-BLAST (Vertical-Bell-lab Layered Space-Time) technique that adopts the extrinsic information from MAP (Maximum A Posteriori) Decoder with Iterative Decoding as a priori probability in two decoding procedure of V-BLAST scheme; the ordering and the slicing. Also, comparing with the Adaptive Modulation System using conventional Turbo Coded V-BLAST technique that is simply combined V-BLAST scheme with Turbo Coding scheme, we observe how much throughput performance can be improved. In addition, we apply a STD (Selection Transmit Diversity) scheme to the systems for more performance improvement. The results show that the proposed system applying a STD scheme gains about 1.77 Mbps at 11 dB SNR (Signal to Noise Ratio) compared to the conventional system using 2 transmit and 2 receive antennas.