Browsing by Author "Cheng, Chien-Chun"

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Enhanced Spatial Modulation with Multiple Constellations
(2014)
Cheng, Chien-Chun
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Sari, Hikmet
;
Sezginer, Serdar
;
Su, Yu T.
;
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
;
Sari, Hikmet
;
Sezginer, Serdar
;
Su, Yu T.
;
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
;
Sari, Hikmet
;
Sezginer, Serdar
;
Su, Yu T.
;
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
;
Sari, Hikmet
;
Sezginer, Serdar
;
Su, Yu T.
;
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-Domain Spatial Modulation
(2016)
Arrano, Hernan F.
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Sari, Hikmet
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Cheng, Chien-Chun
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電機工程學系
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Department of Electrical and Computer Engineering
Spatial modulation (SM) is a multiple-input multiple-output (MIMO) technique, which was introduced for wireless communication systems in which the number of transmit RF chains is smaller than the number of antennas. The basic principle in this technique is to select transmit antennas using information bits and transmit data symbols from these antennas. Obviously, SM involves symbol-rate antenna switching, which leads to serious problems and degradations in practice due to the non-rectangular pulse shaping used. Combining SM with orthogonal frequency-division multiplexing (OFDM) leads to what we call Frequency-Domain SM (FDSM). This technique avoids antenna switching and eliminates the related problems. However, the number of RF chains required to implement it is no longer smaller than the number of transmit antennas, but the power requirements are reduced as compared to conventional MIMO/OFDM. In this paper, we investigate the requirements in terms of high-power amplifiers and we introduce a Balanced FDSM scheme, which further reduces these requirements.
Linear Interference Suppression with Covariance Mismatches in MIMO-OFDM Downlink
(2014-01-01)
Cheng, Chien-Chun
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Sezginer, Serder
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Sari, Hikmet
;
Su, Yu T.
;
電機資訊學士班
Interference cancellation is a key design concern for next-generation communication systems. One practical approach is the so-called interference rejection combining (IRC) scheme which treat interference as a stationary Gaussian process to simplify interference suppression design. However, this stationary assumption does not hold in practice; in particular, the statistics of the pilot and the data parts from an interfering eNodeB (eNB) are quite different. This considerably impacts the possible improvements of interference-aware receivers. In this paper, novel interference suppression schemes are proposed, which handle separately the interfering pilot and data signals. The proposed schemes take into account channel estimation errors and also the errors in covariance estimation of interference plus noise.
Linear Interference Suppression With Covariance Mismatches in MIMO-OFDM Systems
(2014-12-01)
Cheng, Chien-Chun
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Sezginer, Serdar
;
Sari, Hikmet
;
Su, Yu T.
;
電子工程學系及電子研究所
Interference cancellation is a key design concern for next-generation communication systems. One practical approach is the interference rejection combining (IRC) scheme, which is already being considered as the base receiver for next-generation 3GPP specifications. IRC treats interference as a stationary Gaussian process to facilitate simple interference suppression. However, this stationary assumption does not hold in practice; for example, the variances of the pilot signal and of the data signal from the interfering base station (eNB) are quite different. This considerably impacts the possible improvements of an interference-aware receiver. In this paper, novel interference suppression schemes are proposed, which handle separately the interfering pilot and the interfering data signals. The proposed schemes take into account channel estimation errors and the errors in estimating the covariance of interference plus noise. The performance of the proposed schemes is validated by using realistic channel models and asynchronous scenarios for MIMO-OFDM systems.
Model-Based Channel Estimation and Codeword Selection for Correlated MIMO Channels
(2012)
Cheng, Chien-Chun
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Chen, Yen-Chih
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Su, Yu T.
;
Sari, Hikmet
;
電機工程學系
For a closed loop MIMO system to provide outstanding performance, the receiver needs to feedback accurate channel state information, which in turn requires a large codebook size. In this paper, we present a new codeword selection scheme based on a model-based channel estimator. Our scheme performs simultaneous channel estimation and codeword selection by exploiting the structures of the associated MIMO spatial channel and the codebook used. For a DFT-based codebook with arbitrary size, only a quantization operation is needed to select a proper codeword in a correlated fading environment. Using industry-approved standard channel models in simulating the system performance, we show that our low-complexity codeword selection scheme does outperform the scheme based on the conventional least-square estimator.
Modelling and Estimation of Correlated MIMO-OFDM Fading Channels
(2011)
Cheng, Chien-Chun
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Chen, Yen-Chih
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Su, Yu T.
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傳播研究所
;
Institute of Communication Studies
This paper presents a general reduced-rank channel model and a corresponding low-complexity estimation scheme for wideband spatial-correlated multiple-input multiple-output (MIMO) systems. We focus on orthogonal frequency division multiplex (OFDM) based systems. The proposed reduced-rank model is useful for many post-channel-estimation applications such as channel state information (CSI) feedback, precoder design and user/channel selection. Our work is an extension of an earlier investigation on narrowband MIMO channels. Like the narrowband case, the proposed wide-band channel estimator also offer the advantage of rendering both channel coefficients and mean angle of departure (AoD) simultaneously. By exploiting the time, frequency, and spatial correlations of the channel and with continuous-type pilot symbols, we found that, even with as high as a compression ratio of 1%, our channel estimator is capable of maintaining an acceptable mean squared errors (MSE) in highly correlated environments. Both mathematical analysis and computer simulation, based on some industry-approved standard channel models, indicate that our algorithm outperform the conventional least-square estimator within most range of interest.
Modified Decision Feedback Method for Mobile OFDM Channel Estimation
(2010)
Cheng, Chien-Chun
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Chang, Dah-Chung
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Chen, Yung-Fang
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傳播研究所
;
Institute of Communication Studies
In some frame-based OFDM applications such as WLAN and WMAN, the channel estimation is accomplished through the aid of the preamble. By means of the preamble, the estimated channel is only well applied under the assumption of a static channel status within the frame. If we consider a time-varying channel status in those applications, the channel tracking has to be performed without the aid of pilots. A past idea for channel tracking was to use a decision-feedback loop with a smoothing method to reduce the drawback of decision-error propagation. In our work, we design the error detectors for detecting error propagation and propose some compensation methods for reducing the influence of error propagation. In simulation results, the performance of the proposed decision-error detectors and compensation methods is compared. We show that the smaller bit error rate can be achieved for the proposed time domain decision feedback algorithm and thus, bandwidth efficiency can remain without the pilots used for channel tracking.
Moving-Average Based Interference Suppression on Frequency Selective SIMO Channels
(2014-01-01)
Cheng, Chien-Chun
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Sezginer, Serdar
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Sari, Hikmet
;
Su, Yu T.
;
電機資訊學士班
Co-channel interference suppression is a key design concern for next-generation communication systems. It is particularly challenging in the presence of frequency-selective fading as the covariance matrices of the interference plus noise vary across subcarriers. The moving average technique is an effective scheme for estimating the frequency-selective covariance matrices. But the problem of choosing the optimal window size is far from trivial. In this work, we propose a window selection scheme based on the mean square error (MSE) of the covariance estimate. It only requires information of the signalto- noise ratio (SNR) and signal-to-interference ratio (SIR) and is robust against variations of the interfering channel\'s power delay profile. Moreover, the results can be applied to time-varying channels by simply replacing the frequency correlation function by the time correlation function.
New Signal Design for Enhanced Spatial Modulation with Multiple Constellations
(2015)
Cheng, Chien-Chun
;
Sari, Hikmet
;
Sezginer, Serdar
;
Su, Yu T.
;
電機學院
In this paper, we introduce a new signal design for the Enhanced Spatial Modulation (ESM) concept, which was recently proposed by the present authors. The basic idea of ESM is to convey information bits not only by the indexes of the active transmit antennas, but also by the types of the multiple constellations used. Design of the original ESM schemes involved one or more secondary modulations, which were derived using a single step of geometric interpolation in the signal constellation plane. In the new design, we go one step further in the interpolation process and derive additional modulations leading to a significant increase of the number of active antenna and modulation combinations used. A design example is given for 10 bits per channel use (bpcu) transmission using four transmit antennas two of which are active at a time. The new design is compared to conventional multi-stream spatial modulation (MSM) and to our previously proposed ESM scheme. The analysis and the simulation results confirm a signal-to-noise ratio (SNR) gain of 2.2 dB over MSM and 0.4 dB over ESM when the three schemes are operated at the same spectral efficiency.
New Signal Designs for Enhanced Spatial Modulation
(2016-11)
Cheng, Chien-Chun
;
Sari, Hikmet
;
Sezginer, Serdar
;
Su, Yu Ted
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電子工程學系及電子研究所
In this paper, we present three new signal designs for enhanced spatial modulation (ESM), which was recently introduced by the present authors. The basic idea of ESM is to convey information bits not only by the index(es) of the active transmit antenna(s) as in conventional SM, but also by the types of the signal constellations used. The original ESM schemes were designed with reference to single-stream SM and involved one or more secondary modulations in addition to the primary modulation. Compared with single-stream SM, they provided either higher throughput or improved signal-to-noise ratio (SNR). In this paper, we focus on multi-stream SM (MSM) and present three new ESM designs leading to increasing SNR gains when they are operated at the same spectral efficiency. The secondary signal constellations used in the first two designs are derived through a single geometric interpolation step in the signal constellation plane, while the third design also makes use of additional constellations derived through a second interpolation step. The new ESM signal designs are described for MIMO systems with four transmit antennas out of which two are active, but we also briefly present extensions to higher numbers of antennas. Theoretical analysis and simulation results indicate that the proposed designs provide a significant SNR gain over MSM.
Robust MIMO Detection Under Imperfect CSI Based on Bayesian Model Selection
(2013-08)
Cheng, Chien-Chun
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Sezginer, Serdar
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Sari, Hikmet
;
Su, Yu T.
;
電子工程學系及電子研究所
A robust receiver for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems is proposed. We are interested in the scenario when only a limited number of observations in both time and frequency domains are available. For this scenario, perfect channel state information is impossible to obtain and the receiver suffers from statistical information mismatch. To overcome this limitation, we first propose the optimum receiver by performing jointly channel and data estimation. For statistical information mismatch, we construct a finite set of covariance matrices and derive a model-selection scheme based on Bayesian Model Selection. Finally, the sliding-window scheme is used in order to enhance the model selection accuracy. Simulation results are presented, showing that the proposed scheme outperforms the conventional scheme under imperfect channel knowledge.
Robust MIMO-OFDM Detection with Channel Estimation Errors
(2013-01-01)
Cheng, Chien-Chun
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Sezginer, Serdar
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Sarin, Hikmet
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Su, Yu T.
;
電子工程學系及電子研究所
A robust receiver for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems is proposed. We are interested in the scenario when only a limited number of pilot symbols in both time and frequency domains are available. For this scenario, perfect channel state information is impossible to obtain and the receiver suffers from channel estimation errors. To overcome this limitation, we apply two criterions to derive the optimal receiver in the sense: 1) maximum likelihood with the distribution of channel estimation and 2) jointly channel and data estimation. Simulation results are presented, showing that the proposed schemes outperform the conventional scheme under imperfect channel knowledge.
SINR Enhancement of Interference Rejection Combining for the MIMO Interference Channel
(2014-01-01)
Cheng, Chien-Chun
;
Sezginer, Serdar
;
Sari, Hikmet
;
Su, Yu T.
;
電機資訊學士班
Interference rejection combining (IRC) is an effective technique to suppress the spatial interference in multiple input multiple-output (MIMO) systems. In general, more receive antennas result in better interference-suppression capability. However, as the number of receive antennas increases, the receiver becomes more complex and loses its scalability. Therefore, an increased attention was turned by industry to find efficient ways to enable the use of more receive antennas, e.g., scaling the number of receive antennas to increase interference rejection capability. In this paper, a baseband preprocessing scheme is proposed by maximizing the signal-to-interference-plus noise ratio (SINR). It involves minimum modification of the existing receiver structure when additional receive antennas become available. The proposed process provides substantial improvements by exploiting the channel estimates or the SINR feedback from the original receiver. The main idea is to generate a new channel matrix for the original receiver such that the interference can be suppressed after the proposed processing. Since the proposed scheme does not rely on the receiver structure, it can be easily applied to different receivers.