• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.46 no.5
• /
• pp.19-25
• /
• 2009

In this paper, the constellation rearrangement method for retransmission based on Chase combining, is introduced. And the effectiveness of the recommended constellation rearrangements is analyzed with statistics. Their performance for turbo-coded or convolutional coded bit streams is evaluated with simulation under additive white Gaussian noise environment.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37 no.5A
• /
• pp.311-316
• /
• 2012

In this paper, a bit-mapping scheme is proposed for partial Chase combining in LDPC-coded systems. Contrary to the previously known bit mapping that assigns the information bits to more reliable channels, the proposed mapping assigns the codeword bits of irregular LDPC codes to distinct Gaussian channels by considering the characteristics of LDPC codes and channels. The recursion equation for partial Chase combining is derived by using the density evolution technique, based on it, the best bit mapping among the various bit-mapping schemes is derived, and the validity of them is confirmed through simulation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.12C
• /
• pp.1135-1141
• /
• 2007

In this paper, an adaptive bit-reliability mapping is proposed for the bit-level Chase combining in LDPC-coded high-order modulation systems. Contrary to the previously known bit-reliability mapping that assigns the information (or parity) bits to more (or less) reliable bit positions, the proposed mapping adaptively assigns codeword bits to the bit positions of various reliabilities by considering the characteristics of code and protection levels of bits in high-order modulation symbol. Compared with the symbol-level Chase combining and the constellation rearrangement bit mapping, the proposed mapping gives $0.7{\sim}1.3$ dB and $0.1{\sim}1.0$ dB performance gain at $FER=10^{-3}$ with no additional complexity, respectively. Adaptive bit-reliability mappings are derived for various environments and the validity of them is confirmed through simulation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38A no.9
• /
• pp.750-758
• /
• 2013

In this paper, we introduce the low-density parity-check (LDPC) coded orthogonal frequency division multiplexing (OFDM) subframe reordering scheme for achieving equal combined power allocation in type I hybrid automatic repeat request (H-ARQ) systems and analyze the performance improvement by using the channel capacity. Also, it is confirmed that the layered decoding for subframe reordering scheme in H-ARQ systems gives faster convergence speed. It is verified from numerical analysis that a subframe reordering pattern having larger channel capacity shows better bit error rate (BER) performance. Therefore the subframe reordering pattern achieving equal combined power allocation for each subframe maximizes the channel capacity and outperforms other subframe reordering patterns. Also, it is shown that the subframe reordering scheme for achieving equal combined power allocation gives better performance than the conventional Chase combining scheme without increasing the decoding complexity.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.21 no.4
• /
• pp.718-723
• /
• 2017

We propose a pilot hopping scheme that improves the limited system capacity due to pilot contamination in multi-cell environment with large-scale antenna arrays at a base station, assuming the infinite number of antennas. In the conventional fixed pilot scheme, each user obtains the same signal-to-interference ratio (SIR) over a long period of time. Therefore, a user with strong interference has continuously low SIR which degrades its service quality. In the proposed pilot hopping scheme, different pilot signals are used for each time slot, and different amounts of interference are received every time. When such a pilot hopping technique is applied, the SIR fluctuates at every time slot. When the Hybrid Automatic Repeat & reQuest (HARQ) technique is applied in such a channel, the outage probability and transmission rate are improved. We show that there is the performance gain of the proposed scheme over the conventional scheme through computer simulations.