Hyun-Seok Yu

Transmit selection diversity technique in the MIMO-OFDM systems for HSDPA

To support the increasing requirement for additional services demanding very high bit rates and higher system capacity, high speed downlink packet access (HSDPA) is provided in the UMTS standard. Orthogonal frequency division multiplexing (OFDM) is a technology that has been shown to be well suited to HSDPA for high data rate transmission. Selective transmit diversity is a well-known technique to combat the detrimental effects of multipath fading and obtain diversity gain from multiple antennas. We consider transmit selection diversity applied to the OFDM-HSDPA system. The proposed OFDM architecture adopts antenna selection diversity and a novel groupwise subcarrier allocation algorithm in closed-loop mode. In the conventional closed-loop mode, user equipment (UE) should feed back channel quality information (CQI) bits for each associated subcarrier, and there may be a lot of feedback information. We try to reduce the feedback bandwidth compared to previous allocation methods while the system performance should not be degraded by grouping adjacent subcarriers. Through simulation results, we found that the throughput, capacity, coverage and reliability can be dramatically increased by employing the proposed scheme.

Hybrid chip-rate equalization of downlink CDMA in SFN channel

We consider a simple downlink code division multiple access (CDMA) system in which user signals are transmitted in a single-frequency network (SFN) channel. The SFN channel has always been a problem in mobile communication or broadcasting channel due to its huge delay spread. Generally, we suffer from multiple access interference (MAI) caused by the multipath channel and MAI becomes worse when the terminal meets the SFN channel. In this paper we present a receiver algorithm which performs adaptive channel equalization efficiently in the harsh SFN mobile channel with considerably low complexity. We will cover some methods for a chip equalizer implementation and evaluate their performances in a simple short delay channel and SFN channel. Also, effects of frequency offsets of the base-station (repeater) are investigated as a consideration for practical applications.

Design of pilot signal for MC-CDMA uplink systems

Coherent demodulation needs to maintain the symbol timing synchronization and to estimate the channel response in multicarrier code division multiple access systems. The use of inverse DFT (IDFT) is often considered to generate a pilot signal for this propose. However it requires a large implementation complexity, making it impractical for real applications. In this paper, we consider the design of a novel pilot signal for both symbol synchronization and channel estimation. By controlling the design parameters, the pilot signal can be generated to provide a desired signal-to- interference noise power ratio, while maintaining an acceptable peak-to-average power ratio. Simulation results show that the use of the proposed pilot signal can improve the detection performance compared to the use of conventional IDFT-based pilot signal, while significantly reducing the implementation complexity.