Browsing by Author "Su, Yu T."

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A codeword weight lower bound for a class of tail-biting turbo codes
(2007)
Yan-Xiu, Zheng
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
This paper presents an achievable codeword weight lower bound associated with weight-2 input sequences of a class of turbo codes. The class of codes has an interleaver structure that encompasses most practical interleavers used by turbo codes. It partitions the incoming information sequence into blocks of the same size and the interleaver performs intra-block and inter-block permutations. Both pre- and post-permuted blocks are individually tail-biting encoded. Following [4], we refer to the codeword associated with a weight-2 input sequence as a weight-2 error event We apply a special permutation function that incorporates the separate encoding concept to derive a lower bound of the weight-2 error event. This lower bound reveals that (i) a larger component code period gives better distance for the weight-2 error events, and (ii) separate encoding results in improved distance if the block length is suitably chosen and is large enough.
A Linear Programming Approach for PAPR Reduction in OFDM Systems
(2009)
Tung, Yuan-Hao
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Lin, Kuhn-Chang
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
Peak-to-average-power ratio (PAPR) is a key design concern of an OFDM system as it determines the system's power efficiency. Clipping is a simple and efficient way of reducing PAPR. A suboptimal recursive clipping and filtering (RCF) method was proposed in [5] to reduce PAPR. This paper presents an alternate RCF approach which selects an error (clipping) vector that minimizes the peaks in both I-and Q-channels while satisfying some time and frequency domain distortion bounds. We formulate the design problem as a constrained linear programming (CLP) problem and extend it to include the tone-reservation option. Like the RCF method, our approach does not need side information and incurs no data rate loss. Since the error vector used in RCF has not been optimized, our approach offers improved PAPR reduction. It also provide tradeoff between PAPR reduction and bit error rate (BER) degradation.
A Particle-Swarm-Driven Cross-Entropy Method for MIMO Signal Detection
(2010)
Wang, Chun-Lin
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Lin, Yu-Ting
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Su, Yu T.
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傳播研究所
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Institute of Communication Studies
In this paper, we apply simulation-based optimization methods to detect quadrature amplitude modulated (QAM) MIMO signals. The first one is the so-called Cross-Entropy (CE) method which enables the corresponding CE-based detector to provide bit-error-rate (BER) performance close to that achievable by the maximum-likelihood (ML) detector when the signal-to-noise ratio (SNR) is relatively low. Unfortunately, the performance curves exhibit error floors in the high SNR region. To improve the performance in the high SNR region, we borrow the concept of Particle Swarm Optimization (PSO) and refer to the resulting iterative detector as the Particle-Swarm-driven Cross-Entropy (PSD-CE) MIMO detector. This detector gives a significant BER performance improvement in the medium-to-high SNR region. We also consider the case when the channel state information is imperfect and suggest a robust detector structure based on a modified score function.
A random graph-based model to analyze packet interference between frequency hopping systems with an application to Bluetooth
(2008-09-05)
Naik, Kshirasagar
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Wei, David S. L.
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Su, Yu T.
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Shiratori, N.
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電信工程研究所
In this paper, we present a graph-based model for analyzing interference between two frequency hopping systems for wireless communication. Informally, frequency hopping means that successive packets are transmitted on different frequencies from a pseudo-random sequence. The frequency band occupied by a packet may be narrow or wide. Our model is based on the concept of probabilistic graphs, where a node represents a "channel" and an edge denotes the probability of interference between two packets belonging to two different channels. Two packets on two channels are said to be mutually interfering if the two packets overlap in time and are transmitted on the same frequency. Thus, from the viewpoint of probabilistic graphs, the expected number of nodes with at least one incident edge is a measure of packet interference in a collection of wireless channels. We apply this model of packet interference to a heterogeneous cluster of Bluetooth piconets, where a piconet could be either of 79-hop type or of 23-hop type. Though the 23-hop type has been phased out, we use it as an example in this paper. (C) 2008 Elsevier B.V. All rights reserved.
A Sequential Test Based Cooperative Spectrum Sensing Scheme for Cognitive Radios
(2008)
Shei, Yeelin
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
Fast and accurate spectrum sensing is crucial in realizing a reliable cognitive network. Cooperative spectrum sensing can help reducing the mean detection time and increasing the agility of the sensing process. However, when the number of cognitive users is large, the bandwidth need for the control channel that are used to report the secondary user nodes' results to the fusion center may become excessively large. In this paper, we apply the sequential probability ratio test (SPRT) to control the average number of the reporting bits. It is shown that the proposed technique not only reduces the mean detection time and bandwidth but also outperforms its non-sequential counterpart. We derive the relationships amongst the global performance, miss probability and false alarm probability and show how to control the average number of reports by thresholding the distributed cognitive users.
A turbo coding system for high speed communications
(2007-10-01)
Zheng, Yan-Xiu
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
This paper presents a new turbo coding scheme for high data rate applications. It uses a special interleaver structure that is naturally suited for parallel processing and a multiple-round early stopping test involving both sign check and a CRC code. A memory (storage) management mechanism is included as a critical part of the decoder. The proposed coding scheme offers new design options and tradeoffs that are not available to conventional convolutional turbo codes (CTCs). In particular, it becomes possible for the decoder to employ an efficient inter-block collaborative decoding algorithm, passing the information obtained from stopping test proved blocks to other unproved blocks. It also becomes important to have a proper decoding schedule. The combined effect is improved performance and reduction in the average decoding latency. We show that the memory manager has a modular-like effect in that additional memory units render enhanced performance due not only to less forced early stopping but to possible increases of the interleaving depth. It also provides additional design tradeoff amongst performance, speed and required memory size. Depending on the decoding schedule, the degree of parallelism and other decoding resources available, the proposed scheme admits a variety of decoder architectures that meet a large range of speed and performance demands.
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.
An iterative resource allocation algorithm for cooperative multimedia communications
(2007)
Lin, Yuan-Bin
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Chiu, Tai-Hsiang
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Su, Yu T.
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Kao, M. S.
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電信工程研究所
Transmit diversity through user cooperation is an attractive proposal for performance enhancement in a mobile communication network. Given the availability of multiple transmission channels from multiple users, we are concerned with the channel, power and rate assignment scheme that offers the maximum capacity while satisfying the multimedia multi-rate requirements. Earlier cooperative schemes often assume that a central processing device is available to find the optimal or suboptimal solution. The corresponding high computing complexity, however, makes the implementation of an energy-efficient cooperative transmission not very practical. In this paper, we present a simple resource allocation scheme that enables each participant user to easily and independently find a near-optimal channel assignment matrix and power allocation vector. under certain constraints. Our solution can be used for both mono-rate and multi-rate applications. It is optimal for the former case and gives near-optimal performance for the latter case.
Constraint relaxation and annealed belief propagation for binary networks
(2007)
Chen, Yen-Chih
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
In this paper, we propose two novel generalized belief propagation (BP) algorithms to improve the convergence behavior of the conventional BP algorithm. By incorporating a dynamic temperature into the free energy formulation, message passing is performed on a dynamic surface of energy cost. The proposed cooling process helps BP converge to a stable fixed point with a lower energy value that leads to better estimations. For decoding turbo-like error correcting codes, we adopt a parametric Gaussian approximation to relax the binary parity check constraints and generalize the conventional binary networks as well. Both the computational complexity and the convergence rate of the proposed annealed BP algorithms are almost the same as those of the conventional BP algorithm. Simulated performance of the proposed algorithms when they are used to decode a low density parity check (LDPC) code and the (23,12) Golay code is presented to validate our proposals.
Detection of Carrier-Interferometry Code Based Overloaded Multi-carrier CDMA Signals
(2017-01-01)
Li, Ming-Xiu
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
We consider a multi-carrier CDMA system based on carrier-interferometry (CI) sequences. The CI sequences are selected because of their outstanding cross-correlation property and are used to spread multi-stream data over transform (frequency) domain. The system is overloaded by allowing an user to transmit K data streams on N < K orthogonal subcarriers or time-frequency units. This paper investigates the problem of multi-stream detection for such an overloaded system. Several suboptimal receiver structures are studied and their performance in uncoded and coded systems is investigated. We discuss the effects and usages of the channel state information on the performance of various receivers.
Detection of Spatial-Modulated Signals in the Presence of CSI Error and Time-Spatial Correlation
(2013-01-01)
Chang, Hsuan-Cheng
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Liu, Yen-Cheng
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Su, Yu T.
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傳播研究所
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Institute of Communication Studies
Most of the studies on spatial modulation (SM) signal detection assume perfect channel state information (CSI) and ignore the channel\'s time-spatial correlation. Performance degradation incurs in the presence of imperfect CSI and channel correlations when estimating or predicting channel state based on periodic pilots. Detector structures that take into account both the channel estimation error and time-spatial correlation are investigated in this paper. We propose the CSI error and channel correlation aware ML detectors in conjunction with two channel estimation methods and present numerical results to quantify the associated performance improvements.
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 Resource Allocation for Relay-based OFDMA Systems With Fairness Considerations
(2010)
Lu, Yen-Shuo
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Lin, Yuan-Bin
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
Capacity and coverage of a Frequency Division Multiple Access (OFDMA) network can be greatly enhanced by dynamically allocate the radio transmission resources. By including the radio resources of cooperative nodes and taking into account the fairness issue, we present a simple suboptimal solution to the problem of radio resource allocation in relay-based OFDMA cellular systems. We restrict our investigation to a single-cell system with several cooperative relay stations and mobile stations (MSs). An IEEE 802.16e-like TDD scenario is assumed and only the uplink transmission with the base station (BS) handling the resource allocation is of concern. We propose two suboptimal algorithms that assign power, subcarriers and cooperative relay stations to a group of MS's to meet their QoS and minimum rate requirements. Our low-complexity solutions maximize the sum rate and a fairness index while satisfies the QoS and total transmit power constraint. Numerical results show that the proposed algorithms provide robust fairness and achieve near optimal sum rate performance.
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.
Enhanced Spatial Modulation with Multiple Constellations
(2014)
Cheng, Chien-Chun
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Sari, Hikmet
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Sezginer, Serdar
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Su, Yu T.
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電機工程學系
Spatial modulation (SM) has recently drawn a great deal of attention, particularly due to the low complexity that it promises for both the transmitter and the receiver sides. However, this technique has a significant spectral efficiency loss with respect to spatial multiplexing (SMX) with the same number of transmit (Tx) antennas, and when the modulation order is increased to achieve the same spectral efficiency, it loses in terms of the bit error rate (BER). In this paper, a new type of SM (referred to as Enhanced SM) is proposed which increases the number of bits transmitted per channel use compared to conventional SM. Note that conventional MIMO techniques including SMX and SM employ a fixed signal constellation. In our proposed technique, some information bits select not only the index(es) of the active antenna(s), but also the constellations to be transmitted from each of them. Both the closed-form analysis and the numerical results demonstrate that the proposed technique achieves better performance than conventional SM and that in most cases it also outperforms SMX.
Enhanced Spatial Modulation with Multiple Constellations and Two Active Antennas
(2014)
Cheng, Chien-Chun
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Sari, Hikmet
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Sezginer, Serdar
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Su, Yu T.
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電機學院
In this paper, we focus on spatial modulation (SM) which uses two active transmit (TX) antennas, and we introduce an Enhanced Spatial Modulation (ESM) technique, which conveys information bits not only by the indexes of the active antennas, but also by the constellations transmitted from each of them. The main feature of the proposed technique is that in addition to a primary modulation, it uses a secondary modulation that is obtained through geometric interpolation in the signal space. The secondary modulation has a reduced transmit energy compared to the primary modulation, and this leads to significant performance gains for the same spectral efficiency. We also describe other variants of the proposed ESM scheme in which the primary modulation is partitioned into two or more subsets and the lower-energy subsets are used in a larger number of combinations. We give design examples using four transmit antennas and 16QAM and 64QAM as primary modulations. The proposed techniques are compared to Conventional SM (CSM) and the results indicate that they provide a significant performance gain over CSM in terms of the symbol vector error rate (SVER) performance.
Enhanced Spatial Modulation With Multiple Signal Constellations
(2015-06-01)
Cheng, Chien-Chun
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Sari, Hikmet
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Sezginer, Serdar
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Su, Yu T.
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電子工程學系及電子研究所
In this paper, we introduce a new spatial modulation (SM) technique using one or two active antennas and multiple signal constellations. The proposed technique, which we refer to as Enhanced SM or ESM, conveys information bits not only by the index(es) of the active antenna(s), but also by the constellations transmitted from each of them. The main feature of ESM is that it uses a primary signal constellation during the single active antenna periods and some other secondary constellations during the periods with two active transmit antennas. The secondary signal constellations are derived from the primary constellation by means of geometric interpolation in the signal space. We give design examples using two and four transmit antennas and QPSK, 16QAM, and 64QAM as primary modulations. The proposed technique is compared to conventional SM as well as to spatial multiplexing (SMX), and the results indicate that in most cases, ESM provides a substantial performance gain over conventional SM and SMX while reducing the maximum-likelihood (ML) decoder complexity.
Enhanced Spatial Multiplexing - A Novel Approach to MIMO Signal Design
(2016)
Cheng, Chien-Chun
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Sari, Hikmet
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Sezginer, Serdar
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Su, Yu T.
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電機工程學系
In this paper, we present a new type of Spatial Multiplexing (SMX) schemes based on the multiple signal constellation concept, which was recently introduced in the context of Spatial Modulation (SM) by the present authors. The proposed technique, which we refer to as Enhanced SMX or E-SMX, conveys information not only by the transmitted symbols, but also by the antenna and constellation combinations used. In addition to the primary constellation, these schemes make use of one or more specifically-designed secondary constellations, obtained through geometric interpolation in the signal constellation plane. We present the general concept and describe specific schemes for different numbers of transmit antennas and using 16QAM as primary modulation. Our analysis and the simulation results indicate that the proposed schemes provide a significant performance gain over conventional SMX.
Frequency estimators for MIMO-OFDM systems
(2007-12-01)
Chiang, David C. -H.
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Su, Yu T.
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電信工程研究所
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Institute of Communications Engineering
Orthogonal frequency division multiplexing (OFDM) systems are known to be sensitive to carrier frequency offset (CFO). This paper is concerned with the CFO estimation for multiple input multiple output (MIMO) systems employing OFDM waveforms. We present two approaches to derive maximum likelihood (ML) pilot-assisted frequency estimators that use either two or multiple identical training symbols. It is shown that the resulting ML frequency estimators are similar to maximum ratio combining versions of Moose estimator and Yu-Su solution, respectively. Numerical examples demonstrate that the proposed frequency estimators are robust against spatial Signal-to-noise ratio (SNR) variation and they yield performance superior to that of the corresponding single-antenna system.