Jae Kyun Kwon’s scientific contributions

We previously proposed an Orthogonal Code Hopping Multiplexing(OCHM) scheme as a new statistical multiplexing scheme in synchronous downlink. OCHM enables a large number of users to share a limited number of code channels through statistical multiplexing. In this paper, we obtain the optimal code rate in several traffic load environments by simulation and summarize the appropriate traffic load region for each code rate as the optimal code rate. An adaptive code rate control scheme is proposed and the base station adaptively changes the code rate according to traffic environments in order to save power.

For orthogonal downlink and statistical multiplexing, three modes of orthogonal code hopping multiplexing (OCHM) are proposed to accommodate more orthogonal downlink channels than orthogonal codewords for downlink channels, and they are compared. The performance comparison shows that the hybrid mode OCHM outperforms both the division mode and the hopping mode.

We previously proposed the Orthogonal Code Hopping Multiplexing(OCHM) scheme as a new statistical multiplexing scheme in synchronous downlink and applied the OCHM scheme to IS-95 and Wideband CDMA. OCHM enables a large number of users to share the limited number of code channels through statistical multiplexing. In this paper, we compare OCHM with HDR through link-level simulation. OCHM outperforms HDR in medium and high mobility conditions, while HDR operates better in a low mobility condition.

We propose a subband spreading technique to average a frequency selective fading channel which produces different signal-to-noise ratios (SNR) per subcarrier in orthogonal frequency division multiplexing (OFDM) systems. Data symbols are spread over a subband using orthogonal codes and transmitted. Each subband is composed of a group of subcarriers. Received symbols in a subband have the same reliability even in a frequency selective fading channel due to the subband spreading at the transmitter. As the number of subcarriers per subband increases, the averaging effect increases even though the complexity to multiplex the symbols increases. We compare the bit error rate (BER) performance of the proposed scheme with that of the conventional OFDM systems including the pre-equalization scheme. Furthermore, we propose an adaptive modulation scheme using the subband spreading technique in order to reduce signaling overhead and complexity. The proposed scheme can outperform the conventional subcarrier-by-subcarrier adaptation scheme in terms of throughput when the channel varies quickly.