Byoung-Hoon Kim

Linear MMSE space-time equalizer for MIMO multicode CDMA systems

We propose an enhanced chip-level linear space-time (ST) equalizer for multiple-input multiple-output (MIMO) multicode code-division multiple-access (CDMA) systems. In the MIMO multicode CDMA systems, the reuse of the same spreading codes in different transmit antennas significantly degrades the equalization performance if the ST equalizer uses a minimum mean-squared error (MMSE) weighting vector that minimizes the mean-squared error of the equalizer output chip sequence. As the CDMA despreader concatenated to an ST equalizer distorts interstream interference components differently from multipath interference and background noise components, the chip-level MMSE weighting vector usually steers in suboptimal directions in the signal space. Therefore, we propose a new MMSE weighting vector that takes the despreading effect into account in this paper. Simulation results show a substantial performance improvement through the new weighting vector

WLC36-3: Selective Virtual Antenna Permutation for Layered OFDM-MIMO Transmission

In this paper we introduce selective virtual antenna permutation (S-VAP) for layered OFDM-MIMO transmission in downlink cellular environments. In the S-VAP scheme, the base station spatially permutes multiple independently encoded layers and then transmits the permuted layers over selected virtual antennas. The mobile station employs a successive interference cancellation (SIC) based receiver to maximize the spectral efficiency. The layer permutation enables a significant reduction of channel quality feedback information necessary to adjust the data rate of each layer. Transmission over selected virtual antennas instead of physical antennas enables efficient power amplifier utilization and thus brings out a quantized spatial water-filling gain.

Bidirectional iterative ISI canceller for high-rate DSSS/CCK communications

This paper proposes a new RAKE receiver incorporated with a bidirectional iterative intersymbol interference (ISI) canceller in order to reinforce multipath robustness of high-rate direct-sequence spread-spectrum complementary code keying (DSSS/CCK) systems. The proposed RAKE receiver first combines multipath signal components through a channel matched filter (CMF) and removes postcursor-ISI by employing a codeword decision feedback equalizer (DFE). Then, a CCK codeword detector tentatively determines the current CCK codeword symbol and reuses it to subtract precursor-ISI from the previous symbol. Therefore, the ultimate symbol decision is made using the delayed signal with both postcursor-ISI and precursor-ISI cancelled. The detection performance can be more improved through an iterative refinement processing between the postcursor and the precursor components. Simulation results exhibit a significantly improved error rate performance of the proposed receiver compared with that of the legacy RAKE receiver employing only a postcursor DFE. The additional cost for realization of the proposed receiver is one symbol decision delay and reuse complexity of the DFE and the codeword detector.

Codeword scrambling for multi-stream transmission in MIMO channel

We propose to independently scramble the codewords of the parallel data streams which are transmitted through multiple antennas in the multiple-input-multiple-output (MIMO) wireless channel. The codeword scrambling converts any possibly competing codewords of the interfering streams into invalid random words in the viewpoint of the decoder of the desired stream when the channel coefficient vectors of two or more parallel streams become very close. It also plays a role of effective interference variance reduction when the code rate is low enough to use a repetition rate matching after a baseline channel encoding. Simulation results show that the scrambling can improve the decoding performance especially when the MIMO channel is highly correlated in the transmitter side or the repetition rate is high.

An Enhanced Space-time Equalizer for MIMO Multi-code CDMA Systems

This paper proposes an enhanced chip-level linear space-time equalizer for multiple-input-multiple-output (MIMO) multi-code CDMA systems. In the MIMO multi-code CDMA systems, the reuse of the same spreading codes in different transmit antennas significantly degrades the equalization performance if the space-time equalizer uses a weighting vector that minimizes the mean squared error of the equalizer output chip sequence. As the CDMA despreader concatenated to a space-time equalizer distorts inter-stream interference components differently from multipath interference and background noise components, the traditional chip-level minimum mean squared error (MMSE) weighting vector usually steers in a sub-optimal direction in the signal space. Therefore, we propose a new MMSE weighting vector that takes the despreading effect into account in this paper. Simulation results show a substantial performance improvement through the new weighting vector