Chi-chao Chao's research while affiliated with National Tsing Hua University and other places
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Publications (62)
In this paper, the hybrid beamforming design for multiple-input multiple-output (MIMO) orthogonal frequencydivision multiplexing (OFDM) systems is studied over the indoor millimeter wave (mmWave) channels. Under practical hybrid beamforming constraints for multi-carrier systems and the study of sub-systems, we propose the sub-system SVD (SS) hybrid...
In this paper, algebraic constructions of quasi-cyclic low-density parity-check (QC-LDPC) codes with the unequal error protection (UEP) property are considered. A criterion for constructing such codes via the masking technique is proposed, based on which explicit conditions on the base parity-check matrices and masking matrices to achieve UEP are p...
A new low-complexity parallel symbol-flipping decoding algorithm for non-binary low-density parity-check (NB-LDPC) codes is proposed. The algorithm outperforms quite a number of existing reliability-based message-passing algorithms, and its computation complexity is smaller than that of almost all the previously proposed iterative decoding algorith...
This paper examines the use of channel feedback to adaptively determine pilot placement among subcarriers in amplify-and-forward (AF) orthogonal frequency-division multiplexing (OFDM) relay systems. With feedback of the previous channel estimate, pilot subcarriers at the source and relay can be reassigned to reduce channel estimation error and ensu...
In this paper, the signal-to-interference-plus-noise ratio (SINR) analysis of orthogonal frequency-division multiplexing (OFDM) systems over the IEEE 802.15.3c 60 GHz channel models is investigated. The derivation precisely captures the distinctive path clustering phenomenon in the spatial-temporal domain and provides the exact SINR. Based on the a...
In this paper, a generalized construction of quasi-cyclic low-density parity-check (QC-LDPC) codes for unequal error protection (UEP) is proposed based on the masking technique. We can obtain UEP QC-LDPC codes as long as the Tanner graph of the masking matrix satisfies a general condition which can include our previous UEP construction as a special...
Subcarrier allocation, power allocation, and partner selection (PS) algorithms are examined for amplify-and-forward (AF) cooperative multicarrier systems. Consider a network that consists of multiple cooperative pairs that employ a two-phase cooperation scheme, where the users first transmit their own messages on each of their subcarriers in phase...
The advantage of using channel feedback informa- tion to determine the optimal pilot placement is examined for amplify-and-forward OFDM relay links. This work extends upon the previously proposed feedback-aided pilot placement scheme to systems that employ subcarrier pairing at the relay. With channel feedback, the pilot subcarriers can be properly...
This paper presents two low-complexity reliability-based message-passing algorithms for decoding LDPC codes over non-binary finite fields. These two decoding algorithms require only finite field and integer operations and they provide effective trade-off between error performance and decoding complexity compared to the non-binary sum product algori...
Subcarrier allocation, power allocation, and partner selection algorithms are examined for amplify-and-forward cooperative multicarrier systems. Consider a network that consists of multiple cooperative pairs employing a two-phase cooperation scheme where the users first transmit their own messages on each of their subcarriers in Phase I and either...
This paper examines the use of channel feedback to determine the optimal pilot placement for channel estimation of amplify-and-forward OFDM relay links. With channel information from the previous symbol period, new pilot locations can be determined so that, on the one hand, channel estimation errors are controlled at a low level and, on the other h...
This paper presents a novel low-complexity iterative reliability-based decoding algorithm for LDPC codes over q-ary finite fields. This proposed algorithm has low complexity and hence provides an effective trade-off between error performance and decoding complexity compared to q-ary sum product algorithm. This decoding algorithm is devised based on...
In this paper, a new construction of irregular low-density parity-check convolutional codes (LDPC-CCs) is presented. Both upper and lower bounds on the free distance are derived as well. Compared with previously constructed irregular LDPC-CCs, our design can not only avoid a girth less than 8 but also provide an enlarged free distance. Since some u...
In this paper, a new direct construction of zero correlation zone (ZCZ) sequence sets based on the generalized Boolean functions is proposed. Different from quite a number of previous results in the literature, our method does not require other special sequences. The sequence length, the ZCZ length, the set size, and the constellation size are all...
In this paper, a new construction of quasi-cyclic low-density parity-check (QC-LDPC) codes for unequal error protection (UEP) is proposed. We first give a new class of UEP block codes. QC-LDPC codes with binomial-term parity-check matrices which can avoid girths less than 8 and achieve an enlarged upper bound on the minimum distance are also introd...
Due to the large signal bandwidth of an ultra-wideband (UWB) transmitted reference (TR) system, the clustering channel statistics, as defined in the IEEE 802.15.3a channel models, should be taken into account in performance characterization. In this paper, we address the optimal mean channel energy capture for the maximal signal-to-interference-plu...
In this paper, convolutional codes are studied for unequal error protection (UEP) from an algebraic theoretical viewpoint. We first show that for every convolutional code there exists at least one optimal generator matrix with respect to UEP. The UEP optimality of convolutional encoders is then combined with several algebraic properties, e.g., syst...
In this paper, we consider estimation and compensation of the I/Q imbalance generated by the direct-conversion receiver in orthogonal frequency division multiplexing (OFDM) systems. Two methods for I/Q imbalance compensation are proposed: the maximum-likelihood estimation (MLE)-based method and the least-square estimation (LSE)-based method. Comput...
Due to ideal autocorrelation and cross-correlation properties, complete complementary codes (CCCs) can be employed in CDMA systems to eliminate the multiple-access interference. In this letter, we propose a direct general construction of CCCs from cosets of the first-order Reed-Muller codes, which includes previous results as a special case. The la...
One of the unique characteristics of ultra-wideband channels is the clustering phenomenon resolved by the ultra-wide signal bandwidth. Channel structures extended from the Saleh-Valenzuela model, e.g., the IEEE 802.15.3a and IEEE 802.15.4a models, have been proposed to describe such phenomenon. It is, however, noticed that a clear and systematic pr...
Ultra-wideband (UWB) communications exhibit many unique characteristics, one of which is the random clustering phenomenon in the resolved channel multipaths. The randomness in path arrivals will, however, make exact performance analysis quite challenging. In this paper, an analytical framework for precise performance characterization of communicati...
In this paper, we propose a new construction of (3, t)-regular low-density parity-check convolutional codes by properly including binomial entries in the parity-check matrices. Both of the upper and lower bounds on free distance are derived for the new codes. Compared with previous constructions, our design can not only avoid codes of girth less th...
In this paper, canonical convolutional encoders are studied for unequal error protection (UEP) from an algebraic theoretical viewpoint. We show that for any convolutional code there exists at least a canonical generator matrix which has the greatest separation vector, and hence the optimal UEP capability, among all canonical ones. A procedure for o...
Establishing a radio link in cell-based mobile communication systems involves searching and synchronizing the downlink known pattern of sequences associated with the base stations. The performance of the searching process, often referred to as cell search, depends greatly on the employed preamble sequences. In this paper, we propose a construction...
In this paper, exact signal-to-interference-plus-noise ratio (SINR) analysis of direct-sequence ultra-wideband (UWB) systems with Rake receiving in the presence of inter-symbol interference and multiple-access interference over a generalized Saleh-Valenzuela (GSV) channel with a generic pulse shaping function is provided. The SINR expression, for s...
In this paper, exact signal-to-interference-plus-noise ratio (SINR) analysis of direct-sequence ultra-wideband (UWB) systems with rake receiving in the presence of inter-symbol interference and multiple-access interference over realistic UWB channel models is conducted. The SINR expression, considering the code correlation functions and a generic r...
In this paper, we investigate a novel coding idea proposed previously to enable under-sampled receivers. An under-sampled receiver can sample the received baseband signals at only a fraction of the Nyquist rate and turns out to be an effective solution to the bottleneck of high-rate sampling and processing in ultra-wideband (UWB) communications. Th...
One of the disadvantages of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio
(PAPR) of OFDM signals. Golay complementary sets have been proposed to tackle this problem. In this paper, we develop several
theorems which can be used to construct Golay complementary sets and multiple-shift complementary...
Orthogonal frequency division multiplexing (OFDM) has been proposed for use as the physical layer of ultra-wideband (UWB) systems for high-rate, short-range personal area networking (PAN). For ultra-wideband systems, there is a constraint on the maximum power spectral density for the transmitted signal. Therefore, the bandwidth of the transmitted s...
In this paper, we propose two methods to compensate the I/Q imbalance generated by the direct conversion receiver in orthogonal frequency division multiplexing (OFDM) systems. In our proposed methods, the channel is considered to be an unknown multipath channel with additive white Gaussian noise. Two methods for I/Q imbalance compensation are propo...
In this paper, the application of space-time codes (STCs) to orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) systems with under-sampled receivers is investigated. In this system, the total available bandwidth is divided into M<sub>t</sub> smaller sub-bands. OFDM modulation is adopted in each sub-band, and data are transmitted...
In this paper, a general reliability-updating formula is proposed for trellis-based soft-output decoding algorithms to optimize the tradeoff between performance and complexity. Based on the general formula, new algorithms are presented, and a concise interpretation is provided to relate new proposed algorithms and those reported previously. In addi...
![Fig. 2. Proposed spectrum bound for P ˜ c i ,c [k].](profile/Wei-De-Wu-2/publication/4062415/figure/fig1/AS:671510851235841@1537112071055/Proposed-spectrum-bound-for-P-c-i-c-k_Q320.jpg)
In this paper, we study the hopping code effects on the time-hopping spread-spectrum (TH-SS) ultra-wideband (UWB) signals to address the achievability of the desired signal properties. Specifically, we investigate the code features leading to the low averaged spectral power level and good receiver performance. For the former concern, an explicit re...
In this paper, we explore the analogy between queueing theory and information theory, especially in trac regulation and source coding. We consider a trac regulation problem, where an input sequence is mapped to an output sequence. The rate of a regulator is de ned to be the peak" rate of the output sequence and the performance of a regulator is in...
One of the disadvantages of orthogonal frequency division multiplexing (OFDM) systems is that OFDM signals may have high peak-to-average power ratio (PAPR). Almost all the previously proposed coding approaches dealing with this problem employ block codes. In this paper, we propose terminated convolutional codes with offset for PAPR reduction. The c...
Path pruning, a new coding concept to achieve free distance
enlargement for convolutional codes, is proposed. Through path pruning,
every convolutional code can be used for unequal error protection (UEP),
no matter whether it is originally a UEP code. To avoid undesired path
discontinuity and reduce possible path distance loss, a cascaded
implement...
In this paper we investigate analytically the convergence properties of the iterative turbo decoding with the Max-Log-MAP algorithm for soft-output generation. With respect to the iterative decoding scheme, several equivalent mathematical formulations are derived to facilitate the stability analysis, based on which we show that turbo decoding with...
This paper proposes new multiuser detectors for frequency-hopped spread spectrum multiple-access (FH-SSMA) based on binary frequency shift keying (BFSK) modulation and channelized frequency hopping. With knowledge of hopping sequences and envelopes of active users, the proposed scheme is a sub-optimal detector under maximum likelihood test. Diversi...
In this paper, we propose acombined variable-rate code-excited linearly predictive (QCELP)speech coding and unequal error protection (UEP) channel codingsystem for wireless communications. In contrast to theconventional schemes, our system employs a concatenatedsuper-imposed rate-compatible punctured convolutional (SI-RCPC)channel coding scheme whi...
In this paper, we concentrate on the study of combining the
optimality with respect to unequal error protection and canonicity of
generator matrices for convolutional codes. The transformation which can
keep the optimality of generator matrices is constructed, based on which
a procedure for obtaining a basic and optimal generator matrix with the
sm...
Path pruning and its application to convolutional codes for
unequal error protection (UEP), which result in path-compatible pruned
convolutional (PCPC) codes, together with a cascaded implementation are
proposed in this paper. Necessary and sufficient conditions are derived
for a sub-class of PCPC codes whose decoding can be conducted via only a
si...
In this paper, we investigate the connection admission control
problem in mobile personal communications networks. Since user mobility
and multimedia traffic are important factors in personal communications
networks, in contrast to other studies on this aspect which either
focused on only single-class call connections or ignored user mobility,
our...
Optimal encoding of convolutional codes for unequal error
protection (UEP) and its relations to basic, canonical, and minimal
generator matrices are studied in this paper. A generic lower bound on
length for UEP convolutional codes is also proposed
We investigate the connection admission control problem in mobile personal communications networks. In contrast to other studies on this aspect which either focused on only single-class call connections or ignored user mobility, our study directly addresses the connection admission control for multiple-class calls with user mobility. A generic clas...
The performance of synchronous spread-spectrum multiple-access
(SSMA) communications based on direct-sequence (DS), slow
frequency-hopped (SFH), and fast frequency-hopped (FFH) systems for
wireless local communications of micro-cellular personal communications
is analyzed. Using an indoor multipath fading channel model with
clusters of arriving ray...
The generalized Hamming weights introduced by Wei (1991) have been
shown to be fundamental descriptive parameters of a linear block code.
They have been found to be useful in certain cryptographic applications
and in the studies of minimal trellis diagrams of linear block codes. In
this correspondence, we determine the first few and the last few
ge...
We consider a practical maximum-likelihood sequence estimation
(MLSE) equalizer on multipath fading channels in conjunction with an
adaptive channel estimator consisting of a least mean square (LMS)
estimator and a linear channel predictor, instead of assuming perfect
channel estimates. A new LMS estimator model is proposed which can
accurately cha...
The method of the hidden Markov model (HMM) is used to develop a
faithful model for the burst error statistics of Viterbi decoding of
convolutional codes. One of the advantages of building such a model is
that it can be used to generate the output sequence with little cost and
can provide a basis for studying other system parameters. The HMM
develo...
Coexisting analog frequency modulation (FM) based on frequency
division multiple access (FDMA) and narrow-band code division multiple
access (N-CDMA) in adjacent spectrum is studied. The allocation on
different spectrum can avoid the serious performance degradation as
transitioning from fully loaded analog FM/FDMA to N-CDMA. The guard-band
needed b...
Bit error probabilities of direct-sequence (DS) systems with RAKE receivers and slow frequency hopped (SFH) systems with diversity receptions in indoor multipath fading channels are analyzed. Equal-gain and selective combinings for DS systems with binary phase-shift keying (BPSK) modulation and SFH systems with binary frequency-shift keying (BFSK)...
We propose a new construction of nonlinear unequal error
protection (UEP) block codes whose encoding complexity is approximately
equivalent to the decoding complexity of a linear block code. Some
classes of codes that are better than any linear UEP codes with the same
parameters are presented
Commentson a paper by Rouanne and Costello Jr. (IEEE Trans. Inform. Theory, vol.34, p.1011-20, 1988). It is shown that the derivation in the above paper is incorrect and hence the lower bound obtained is not valid for general trellis-coded modulation schemes. A corrected bound is presented to remedy this flaw. Also shown is a similar lower bound de...
The performance of synchronous spread spectrum multiple access
(SSMA) communications based on direct-sequence (DS), slow frequency
hopped (SFH) and fast frequency hopped (FFH) systems for wireless local
communications or micro-cellular personal communications is analyzed. By
assuming an indoor multipath fading channel model with clusters of
arrivin...
In the literature the performance of joint maximum-likelihood
sequence estimation for trellis-coded modulation systems was analyzed
under the assumption that fading is so slow that the channel does not
change during all error events. In this paper we extend the performance
analysis to general fading processes by considering the correlation
function...
In the literature, the performance of maximum-likelihood sequence
estimation (MLSE) equalization on multipath fading channels is analysed
under the assumption of perfect channel estimates. In reality, this
condition is difficult to attain, especially for fast fading channels.
It is therefore of great significance to study the performance
degradatio...
The performance of general binary block codes on an unquantized
additive white Gaussian noise (AWGN) channel at low signal-to-noise
ratios is considered. Expressions are derived for both the block error
and the bit error probabilities near the point where the bit
signal-to-noise ratio is zero. These expressions depend on the global
geometric struct...
In this paper we use random coding analysis to study the average distance properties of trellis codes. The generating function for the average number of error events with each distance from the transmitted code path in the ensemble of random trellis codes is fully determined. Summary The average distance structure of binary convolutional codes is d...
Citations
... The HBF design has been the subject of extensive research [10]- [28], with single user HBF being considered in [12], [15], [22], [24], [26] and multiuser (MU) HBF being considered in [13], [16], [18]- [21], [27], [28]. Due to the computationally challenging unit modulus constraints imposed on each entry of the ABF matrix, all these papers have only developed heuristic procedures, which do not guarantee convergence or predictable performance. ...
... UEP is firstly proposed by B.Masnick and J.Wolf [19]. After that, numerous UEP schemes based on various forward error correction (FEC) codes [20][21][22] or modulations [23][24][25] are developed. UEP is most widely applied in the transmission of multimedia data like voices, images and videos [26][27][28], as they are usually progressive and easier to be prioritized. ...
... Continuing our previous research on performance analysis of single-user DS and SFH systems [20], we consider multipleuser DS-SSMA with binary phase-shift keying (BPSK) modulation and RAKE receivers, SFH-SSMA with continuousphase binary frequency-shift keying (BFSK) modulation and noncoherent detection, and FFH-SSMA with continuous-phase BFSK modulation and noncoherent detection, employing coding and diversity techniques over indoor multipath fading channels. Reed-Solomon (RS) codes with erasure decoding capability are considered to further improve the performance. ...
![[object Object]](https://i1.rgstatic.net/ii/profile.image/418667281043458-1476829466314_Q64/Kwang-Cheng-Chen.jpg)
... In [5]- [9], the authors have presented the channel capacity for hybrid beamforming based mm-Wave communication systems, whereas simulation and semi-analytical error performance analyses for 60 GHz band have analysed in [10], [11]. In [12], the author has examined the average SINR of orthogonal frequency division multiplexing (OFDM) system over IEEE 802.15.3c 60 GHz channel. Analytical expressions of interpath interference (IPI), inter-symbol interference (ISI), interchip interference (ICI) and multiple-access interference (MAI) for UWB system with coherent Rake receiver have been presented in [13], [14]. ...
![[object Object]](https://i1.rgstatic.net/ii/profile.image/279140558229511-1443563703855_Q64/Wei-De-Wu-2.jpg)
... Another algorithm termed as weighted algorithm B (wt.Algo B ) presented in [12] introduces the binary Hamming distance and plurality logic performance improvement. The parallel symbol flipping decoding (PSFD) algorithm in [13], has good performance only for parity check matrix of large column weight. A multiple voting based PSFD (MV-PSFD) algorithm was proposed in [14] for the improvement of PSFD algorithm. ...
![[object Object]](https://i1.rgstatic.net/ii/profile.image/902197323771904-1592112012307_Q64/Chao-Yu-Chen.jpg)
... Meanwhile, the relay that receives a message from a particular subcarrier in the first hop has an opportunity to forward the processed message to a different subcarrier in the second hop because of the independent fading in each subcarrier in each hop [7] [8]. Thus, subcarrier pairing (SP) has become a simple but effective method to enhance the transmission performance in broadband relay systems [7] [8] [9]. Although beamforming and equalization can be performed in the frequency-domain (FD) of a relay, SP has not been applied in CP-SC relay systems so far. ...
... The ZCZ sequences were also constructed using direct methods. The direct constructions do not need predefined sequences, some of the direct constructions of ZCZ sequences based on GBFs are provided in [39][40][41]. The connection between GRM codes and ZCZ sequences is also provided in [40,41]. ...
... To avoid such an unexpected distance loss due to hardswitching, we propose a new switching scheme called softswitching which processes c i,t 's by ci,t is allowed for transmission, if a i,t mod p (l)= 1 ci,t is deleted from the encoder outputs, if a i,t mod p (l)= 0 (4) as A(l) is used for puncturing in [t l ,t l ]. By soft-switching, as presented in Appendix, we can show that all codewords across the switching boundary between A(i) and ...
... This paper is extended from a previous conference version[29], where only preliminary results for IEEE 802.15.3a channel models with idealized effect of pulse shaping functions are provided. ...
... The joint estimation of the IQ and systems impairments with trained-based techniques has been addressed in many studies. In particular, several algorithms for the estimation of the receiver IQ imbalance and channel Finite Impulse Response (FIR) coefficients have been proposed in [7][8][9][10][11][12]. Extensions to the case where the communication system is also corrupted by Phase Noise (PN), Carrier Frequency Offset (CFO) and/or Direct Current (DC) offset have also been described in [13][14][15][16][17][18]. ...
