Dong-Seung Kwon

An adaptive time slot allocation strategy for W-CDMA/TDD system

The code division multiple access system with time division duplex mode (CDMA/TDD) where the same frequency allocation is made for both uplink and downlink is a good solution when the traffic asymmetry between uplink and downlink exists. However, when the asymmetry of each cell may be significantly different from each other, the traffic may experience severe interference from each other when each cells own slot allocation is made according to the level of traffic asymmetry in each cell. The interference in the W-CDMA/TDD system when the slot allocations are made according to traffic patterns of each cell is analyzed, and a time slot allocation scheme considering the traffic asymmetry is proposed. In this paper, system performances are simulated under the proposed time slot allocation strategy and its optimal operation of the strategy is investigated.

Performance analysis of a multistage MPIC in 16-QAM CDMA systems over multipath Rayleigh fading channels

In this paper, a multipath interference canceller (MPIC) of a code division multiple access (CDMA) signal at the RAKE receiver of the mobile unit is considered. An analytical method of 16-QAM CDMA systems using a MPIC is proposed over multipath Rayleigh fading channels. Furthermore, numerical results obtained by the proposed analysis show that a MPIC is required for 16-QAM CDMA systems in order to mitigate the defects of multipath interferences and effectively obtain the path diversity of the RAKE receiver. In addition, it is verified that the receiver with three or four stages MPIC is sufficient in practical system.

The Pilot Design for Channel Estimation in a Practical MIMO OFDM System

The locations of the pilot subcarriers can’t be equally spaced because the practical system utilize the virtual subcarriers. Thus, the minimum mean square error (MSE) performance of the maximum likelihood (ML) estimate is difficult to be obtained. Previously tried to search the locations of the pilot subcarriers when the virtual subcarriers are used. However, it is difficult to apply to the case of that the number of total pilot subcarriers is 512 or 1024 in the practical MIMO OFDM system of the IEEE 802.16e standards. For the case of the practical system such as the IEEE 802.16e standards, the locations of the pilot subcarriers will be found with proposed methods. One is a modified scheme, the others are new schemes for the practical MIMO OFDM system. Proposed methods result in the MSE performance of the channel estimate lower than 0:5dB degradation from the minimum MSE performance of the ML channel estimate on the time domain in the four transmitted antennas. This paper proposes the methods, which can apply to the practical MIMO OFDM system such as the IEEE 802.16e standards and, the obtained locations, and, the power of the pilot subcarriers.

Programmable architecture for NFA-based string matching

In this paper, we propose a programmable string matching architecture to process multiple characters at a single cycle. To simplify the architecture of the previous works, we employ a method of realigning the input data stream by offsets. We show that some registers can be eliminated by using the method. Additionally, we present two different approaches to implement a programmable hardware for string matching on FPGA. We show the synthesis results for these two approaches.

Mobile WiMAX Performance Measurements and the selection of path loss model for UGV

Mobile WiMAX is a rapidly growing broadband wireless access technology based on IEEE 802.16e-2005 air-interface standards. It provides high-speed internet service anytime, anywhere, from anyone and any device with seamless mobility and the service is located between mobile phone and wireless LAN. For special activities purpose, we have developed Mobile WiMAX communication systems for UGV (Unmanned Ground Vehicle). This paper present performance results and path loss model for Mobile WiMAX communication system for cell coverage prediction. As little or no published data exists about measurements in LOS (Line of Sight) field trials for Mobile WiMAX, we set up a test-bed and performed cell coverage measurements. We predicted a optimal path loss model through calculating RSSI (Received Signal Strength Indicator). In this paper, the 2-ray ground reflection model was selected an optimal path loss model in this Mobile WiMAX Performance Measurements.

Multi-Axes Modulation for MC-CDMA Systems

In this paper, we analyze the signals of MC-CDMA system with linear combining for single user detection in a mulitpath Rayleigh fading channel. The multi-user interference (MUI) of other users is closely related with modulation methods. The multi-axes modulation scheme which rotates such one dimensional signaling as BPSK or ASK et al. is presented. It can be shown that MUI is effectively reduced by using this scheme. The proposed scheme has better performance up to 6 dB in Eb/No under reasonable assumption

Network capacity and reliable transmission in ultra-dense networks sharing multiple carriers

Explosive demands for mobile data are leading to fundamental changes in the design of future fifth generation (5G) cellular networks to meet the challenging requirements of higher capacity and improved quality of user experience. To be close to these requirements, advanced technologies have been studied, such as user-centric architectures, massive MIMO, millimeter wave, heterogeneous networking, advanced self-configuration and optimization technologies, etc. This paper is focused on analytical models for performance evaluation of ultra-dense networks. Using the stochastic geometry approach, the SINR distributions and the outage probabilities are derived in circumstance with heterogeneous radio access systems and multiple carrier deployment. Moreover, the network capacity is defined in terms of performance metric of ultra-dense networks. We also show numerical results in various deployment scenarios and discuss them.

Impacts of joint packet scheduling for heterogeneous component carriers in multi-carrier systems

Component carriers (CCs) in a Long Term Evolution - Advanced (LTE-A) system are limited by maximum 100 radio bearers (RBs) on a 20 MHz CC due to a fixed 15 KHz subcarrier bandwidth. However it is able to be changed in the future, so that a study regarding heterogeneous CCs which have diverse RBs above 100 on a CC is needed at this moment. To support non-contiguous carrier aggregation (CA) with the these conditions, a heterogeneous joint CC packet scheduling algorithm interacting with a radio resource control (RRC) is considered in this paper. The performance of the joint CC packet scheduling algorithm on heterogeneous CCs with different channel characteristics has been analyzed and compared through computer simulations as well. According to the results, we found that an 800 MHz CC exhibits approximately 4 dB better channel gains than a 2.1 GHz CC. We also obtained a capacity increase of about 15-40% for a joint CC maximum rate (MR) algorithm and about 2-28 % for a joint CC proportional fair (PF) algorithm when the number of users is increased. On the other hand, in a round-robin (RR) scenario, we were unable to notice any differences between the independent CC and joint CC packet scheduling policies. Furthermore, looking at the impacts of different amounts of RBs on 800 MHz + 2.1 GHz CCs, we can conclude that a one-to-one RB ratio with respect to the MR, PF, and RR algorithms has a better performance compared to other cases, and thus, owing to the better channel gain, the smaller the RBs of the 800 MHz CC, the better the performance achieved.

An analytical study on the 802.16m sleep mode with M/G/1 queuing model

So far, many studies have been made for the 802.16m sleep mode operations. However, in the previous work, the equation derivations are too complicated to be used or analytical models are not accurate. We introduce an accurate analytical model through simple derivations in case when a sleep cycle is constant assuming M/G/1 queuing model.

A Relay and Transmission Mode Selection Scheme to Enhance the Bit Error Rate Performance in Relay Systems

In a cooperative communication system with a source node and multiple relays equipping single antenna and a destination node equipping multiple antennas, the selective cooperative spatial multiplexing scheme can obtain spatial multiplexing gain and additional selection diversity gain. But it can degrade a bit error rate performance because some received symbols forwarded from particular relays may be lost by attenuation due to path-loss. We propose a relay and transmission mode selection scheme which selects minimum number of multiple relays having the channel capacity larger than a given data rate and transmission mode which switches spatial multiplexing and spatial diversity mode in cooperation phase to enhance the bit error rate performance. The proposed scheme achieves 1.5~2dB gain at the low SNR range compared with the conventional scheme by obtaining additional spatial diversity gain.