Eui-Hak Lee

Adaptive cooperative communications with multiple antennas

Although multiple-input multiple-output antenna transmission is advantageous on orthogonal frequency division multiple access system, it may not be possible that practical systems have more than two antennas because of its size and cost. Therefore, cooperative communication has been recently studied as a way to solve this problem in a wireless environment. However, if cooperative communication system selects relay in a bad channel environment between source and relay, the relay has a bad effect on the bit error ratio performance. Thus, selective relay technique is proposed in this paper. The proposed system can select the best relay which has the best SNR between source and relay among the candidates. The proposed system also easily finds the best relay with low complexity.

Adaptive Femtocell Design Scheme in Mobile Communication Systems

Mobile communication technologies have been evolving very rapidly and providing many advantages with mobile users. However, the amount of data traffic has increased significantly due to rapid expansion of mobile market. Recently, femtocell which is known as indoor base station is considered as the key solution to combat the data traffic. Femtocell provides mobile users with better quality of service. However, deployment of femtocell is not so easy due to inter-cell-interference (ICI) with existing macrocell. Signals from base stations are transmitted by a form of electronic magnetic waves. So, these waves undergo interference each other. Thus, this paper proposes the design scheme for femtocell which can reduce the influence of ICI. And also, proposed femtocell operates adaptively in accordance with reliability of system. With this proposed scheme, free and easy deployment of femtocell is expected.

Adaptive Channel Coding Based on Channel Condition in Cooperative Communication System

A multiple input multiple output (MIMO) system presents the disadvantage that the system has high cost if receiver size is limited. A cooperative communication system overcomes disadvantages of MIMO system. So, many cooperative communication transmission schemes have been studied. In this paper, the proposed scheme considers channel condition of source to destination and then decides on a usage for channel coding. The channel coding is used for transmission in badly conditioned channel to improve the performance. If channel condition is good, the channel coding is not used, whet increases the throughput. The channel condition is determined using the cyclic redundancy check code. The simulation results show that the proposed scheme has better trade-off between the performance and throughput than the conventional scheme.