Browsing by Author "Chang, Tofar C. -Y."

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Adaptive Group Shuffled Decoding for LDPC Codes
(2017-10-01)
Chang, Tofar C. -Y.
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Su, Yu T.
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交大名義發表
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National Chiao Tung University
We propose new grouping methods for group shuffled (GS) decoding of both regular and irregular low-density parity check cods. These methods are applicable for the belief-propagation as well as the min-sum-based GS decoders. Integer-valued metrics for measuring the reliability of each tentative variable node (VN) decision and the associated likelihood of being corrected are developed. The metrics are used to determine the VN updating priority, so the grouping may vary in each iteration. We estimate the computation complexity needed to adaptively regroup VNs. Numerical results show that our GS algorithms improve the performance of some existing GS belief-propagation decoders.
An HARQ Scheme with Large Rate Adaptation Range and Inter-Packet Cooperative Decoding
(2016)
Lu, Chia-Chi
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Chang, Tofar C. -Y.
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Chien, Tsu-Hsuan
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Su, Yu T.
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傳播研究所
The throughput of a conventional rate-compatible code based hybrid automatic repeat request (HARQ) protocol is lower-bounded by the rate of the mother code used. The mother code rate along with the highest puncture rate determine the operation range of the protocol in terms of the average received signal-to-noise ratio (SNR). In this paper, we propose a new HARQ protocol based on rate-compatible punctured and shortened low-density parity-check (LDPC) code so that it admits a large operating SNR range. The large dynamic coding rate range is also useful for link adaptation applications. A distinct feature of the new HARQ protocol is: when a packet (frame) fails to pass the cyclic redundancy check (CRC) test and the system is operating at a rate lower than that of the mother code, the corresponding re-transmitted packet will consists of a coded payload resulted from systematic encoding a fraction of the CRC-failed bits plus new data bits. The re-encoded part plays the role of bridging two (component) codes, or equivalently, building a larger code out of smaller codes. Various decoding schedules that exchange messages between two or among more packets (component codes) become available and much decoding performance improvement can be obtained. Numerical results show that, compared with the conventional HARQ protocol, our approach provides significant better throughput performance in the low SNR region.
Distributed Clustering and Spectrum-Based Proximity Device Discovery in a Wireless Network
(2016)
Chang, Tofar C. -Y.
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Wei, Chun-Yi
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Hsu, Min-Chien
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Lin, Chih-Yu
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Su, Yu T.
Direct short-range device-to-device (D2D) conununication enjoys many advantages, such as high transmission rates, low propagation delays, low transmit power and interference. In order to realize the advantages, a device or user equipment participating in the D2D communications have to determine that the devices discovered are in a proximity area and are suitable to establish links with them. Hence, an accurate and efficient clustering scheme, which can organize the devices nearby into multiple D2D communication groups is necessary. Against this background, in this paper we propose a self-clustering scheme which requires no assistance from Cellular Network. The philosophy of our design is to group the devices with similar sensed spectrum profiles. In order to facilitate this self-clustering scheme, we adopt Reed-Solomon (RS) code into our proposed design. More specifically, in our design, a D2D communication group is formed by the D2D devices whose sensed spectrum vectors are mapping to the same valid RS codeword which is broadcast by the form of frequency-hopping (141) pattern. Additionally, the collision event could happen when multiple D2D devices transmit signals to discovery their group members. Hence, we design the FH probing sequence based on a randomly cyclic-shifted non-binary RS codeword to eliminate the possible collision events and interference exited in clustering procedure. In this paper, we provide our detail sequence design and the self-clustering procedure. In the simulation results, we show that the proposed self-clustering is efficient and effective.
Dynamic Weighted Bit-Flipping Decoding Algorithms for LDPC Codes
(2015-11-01)
Chang, Tofar C. -Y.
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Su, Yu T.
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傳播研究所
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電機資訊學士班
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Institute of Communication Studies
Bit-flipping (BF) decoding of low-density parity-check codes is of low complexity but gives inferior performance in general. To improve performance and provide new BF decoder options for complexity-performance tradeoffs, we propose new designs for the flipping function (FF), the flipped bit selection (FBS) rule and the checksum weight updating schedule. The new FF adjusts the checksum weights in every iteration while our FBS rules take more information into account. These two modifications represent efforts to track more closely the evolutions of both check and variable nodes\' reliabilities. Two selective update schedules are proposed to offer more performance and complexity tradeoffs. The combinations of the new FBS rule and known FFs result in new BF decoders with improved performance and a modest complexity increase. On the other hand, combining the new FF and FBS rule gives a new decoder with performance comparable to that of the normalized min-sum algorithm while if we use a much simpler FBS rule instead, the decoder suffers little performance loss with reduced complexity. We also present a simple decision-theoretical argument to justify the new checksum weight formula and a time-expanded factor graph model to explain the proposed selective weight-updating schedules.
Multi-Stage Bit-Flipping Decoding Algorithms for LDPC Codes
(2019-09-01)
Chang, Tofar C. -Y.
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Wang, Pin-Han
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Su, Yu T.
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電機工程學系
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電信工程研究所
We present two general multi-stage (MS) bit-flipping (BF) decoding algorithms for low-density parity-check (LDPC) codes. Both algorithms consist of soft-decision (SD) and hard-decision BF decoding parts. In comparison with known MS LDPC decoders, our approach is much simpler as all stages share the same BF structure. The only complexity increase is due to the use of an adaptive stage-switching (SS) mechanism which gives near-optimal SS timing. A new design issue we address is that the first-stage algorithm's parameter has to be re-tuned to achieve the optimal overall performance. The numerical results demonstrate that the proposed decoding methods can significantly improve the error-rate performance of the conventional SD BF decoders.