Browsing by Author "Ku, Meng-Lin"

Now showing 1 - 10 of 10

A Derivation on the Equivalence Between Newton's Method and DF DFT-Based Method for Channel Estimation in OFDM Systems
(2008-10-01)
Ku, Meng-Lin
;
Huang, Chia-Chi
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we derive the decision-feedback (DF) discrete Fourier transform (DFT)-based channel estimation method from Newton's method for space-time block code (STBC)/orthogonal frequency division multiplexing (OFDM) systems. Through our derivation, the equivalence between Newton's method and the DF DFT-based method is established. Computer simulations are also used to demonstrate the equivalence of the two methods in terms of BER and normalized square error (NSE) performance. Finally, the results presented in this paper also hold for conventional OFDM systems.
A modified DVB-T system architecture with multi-carrier multi-code transmission and MPIC based reception
(2008)
Jeng, You-Tsai
;
Ku, Meng-Lin
;
Huang, Chia-Chi
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we propose a modified DVB-T system architecture with a multi-carrier multi-code transmission format. The main techniques we use in the system include the orthogonal Walsh code spreading and soft multipath interference cancellation (soft MPIC). Both techniques are used to combat the system degradation caused by the multipath effect. With the spreading gain and the path diversity gain achievable from the used techniques, the proposed system architecture shows much better performance compared with the original DVB-T system.
A Refined Channel Estimation Method for STBC/OFDM Systems in High-Mobility Wireless Channels
(2008-11-01)
Ku, Meng-Lin
;
Huang, Chia-Chi
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we investigate channel estimation for orthogonal frequency division multiplexing (OFDM) systems with space-time block code (STBC) in mobile wireless channels. Our proposed method consists of two-stage processing and is developed on the basis of the classical discrete Fourier transform (DFT)-based channel estimation method. In the initialization stage, we employ a multipath interference cancellation technique to estimate multipath delays and multipath complex gains. In the tracking stage, we develop a refined decision-feedback (DF) DFT-based channel estimation method in which a few pilot tones inserted in OFDM data symbols are applied to form an optimal gradient vector at the first iteration such that the error propagation effect is mitigated. In order to reduce computational complexity, an approximate weighting matrix is adopted to avoid matrix inversion. We demonstrate the proposed method through computer simulation of an STBC/OFDM system with two transmit antennas and a single receive antenna. The results show that our method outperforms the classical DFT-based method, the STBC-based minimum mean square error (MMSE) method, and the Kalman filtering method as well, and that significant signal-to-noise ratio (SNR) performance improvement can be achieved, especially when a high-level modulation scheme, e.g. 16QAM, is adopted in high-mobility environments.
A Robust Channel Estimator for High-Mobility STBC-OFDM Systems
(2010-04-01)
Chen, Hsiao-Yun
;
Ku, Meng-Lin
;
Jou, Shyh-Jye
;
Huang, Chia-Chi
;
電機工程學系
In this paper, a robust channel estimator for high-mobility space-time block code-orthogonal frequency division multiplexing (STBC-OFDM) systems is proposed and applied in IEEE 802.16e systems. A high-performance two-stage channel estimation method is adopted. The proposed architecture reduces computational complexity effectively and improves 85.2% of the hardware implementation. The performances of the proposed design have been demonstrated through the simulation of an STBC-OFDM system with two transmit antennas and one receive antenna. At the vehicle speed of 120 and 240 km/hr for quadrature phase shift keying (QPSK) modulation, the proposed design can achieve the bit-error rate (BER) of about 10(-4) and 10(-3) without using channel coding. Moreover, it has significant performance improvement as compared with interpolation-based channel estimation methods. The proposed channel estimator implemented in 90 nm CMOS technology can support up to 29.03 Mbps (uncoded) downlink data transmission. The design only requires 859.6 K gates and dissipates 43.71 mW at 83.3 MHz operating frequency with 1 V power supply.
EM-Based Iterative Receivers for OFDM and BICM/OFDM Systems in Doubly Selective Channels
(2011-05-01)
Ku, Meng-Lin
;
Chen, Wen-Chuan
;
Huang, Chia-Chi
;
電機工程學系
;
Department of Electrical and Computer Engineering
In this paper, we resort to the expectation-maximization (EM) algorithm to tackle the inter-carrier interference (ICI) problem, caused by time-variant multipath channels, for both orthogonal frequency division multiplexing (OFDM) systems and bit-interleaved coded modulation (BICM)/OFDM systems. We first analyze the ICI in frequency domain with a reduced set of parameters, and following this analysis, we derive an EM algorithm for maximum likelihood (ML) data detection. An ML-EM receiver for OFDM systems and a TURBO-EM receiver for BICM/OFDM systems are then developed to reduce computational complexity of the EM algorithm and to exploit temporal diversity, the main idea of which is to integrate the proposed EM algorithm with a groupwise ICI cancellation method. Compared with the ML-EM receiver, the TURBO-EM receiver further employs a soft-output Viterbi algorithm (SOVA) decoder to exchange information with a maximum a posteriori (MAP) EM detector through the turbo principle. Computer simulation demonstrates that the two proposed receivers clearly outperform the conventional one-tap equalizer, and the performance of the TURBO-EM receiver is close to the matched-filter bound even at a normalized maximum Doppler frequency (MDF) up to 0.2.
Joint Antenna Beamforming, Multiuser Scheduling, and Power Allocation for Hierarchical Cellular Systems
(2015-05-01)
Ku, Meng-Lin
;
Wang, Li-Chun
;
Liu, Yu-Lung
;
電機資訊學士班
;
Undergraduate Honors Program of Electrical Engineering and Computer Science
Cognitive radio (CR) is concretely embodied in hierarchical cellular systems by deploying an underlying microcellular system to reuse the underutilized spectrum of a macrocellular system. One of the key challenges to the success of hierarchical cellular systems is to manage the intercell interference between the macrocell and the microcell and to maximize the spectrum efficiency. In this paper, antenna beamforming, power allocation, and multiuser scheduling are jointly designed to opportunistically utilize the macrocell\'s uplink spectrum in serving multiple secondary microcellular users concurrently. The joint design of antenna beamforming, power allocation, and scheduling with the objective of maximizing the sum rate is indeed a mixed-integer nonlinear programming NP-hard problem. The proposed simpler iterative subgradient projection and semidefinite programming approach can obtain better performance than the conventional zero-forcing beamforming. Furthermore, unlike the optimal singular value decomposition (SVD) beamforming that requires all users to have channel knowledge at the receiver for cooperation, the proposed joint design methodology requires no channel knowledge at the receiver and can outperform the SVD beamforming without user scheduling. When considering both implementation complexity and performance enhancement issues, the proposed joint power allocation, multiuser scheduling, and antenna beamforming technique can help provide important insights into the design of interference management techniques for hierarchical CR systems.
Joint channel estimation and data detection method for STBC/OFDM systems
(2008-07-10)
Ku, Meng-Lin
;
Huang, Chia-Chi
The present invention provides a joint channel estimation and data detection method for STBC/OFDM systems, comprising the following steps: a preliminary step, in which, after passing the received signals through an OFDM demodulator, frequency-domain signals R1[k] and R2[k] of the complementary-coded pilot preambles in two successive OFDM symbol times, as well as two successive OFDM data symbols R1(i)[k] and R2(i)[k] at the ith time slot, are obtained; an initial step for setting up the predetermined number Np of the channel path, using complementary-coded pilot preambles to estimate the channel impulse response, then using this estimation result of the channel impulse response to calculate a path selective set Sm,, and furthermore, in accordance with the path selective set Sm, determining the number Lm of the selected paths and the excess delay τm,l of the selected path, and then calculating the initial channel state information vector y(1,0) and the Hessian matrix F; a tracking step, in which the initial value v of the recursion index is set to 1 at first, and the maximum number of recursion is set to V; if the index v of recursion is 1, use sparse pilot subcarriers to calculate channel state information Ĥm[k], and calculate a searching direction vector Ψ that is obtained by using the sparse pilot subcarriers and then calculate a searching direction vector
Non-linear Effects of Receiver Amplifier for 60GHz Radio Communication
(2011)
Ku, Meng-Lin
;
Lu, Ssu-Han
;
Wang, Li-Chun
;
Yan, Sheng-Hong
;
電機工程學系
In this paper, we investigate the impact of a receiver amplifier on orthogonal frequency division multiplexing (OFDM) and single-carrier block transmission (SCBT) systems which are two potential air interfaces for future short-range wireless communications at 60GHz radio spectrum. We derive a generalized baseband equivalent model for the receiver amplifier by using a power series to capture the nonlinear distortion behavior with several parameters. Based on this model, we develop a simulation flow in the baseband domain for evaluating the system performance deterioration with the non-ideal receiver amplifier. Computer simulations are used to compare the performance of OFDM and SCBT systems under several radio frequency (RF) parameters, such as 1dB compression point, the 3rd-order intercept point, etc. The developed methodology across the baseband and RF can help us jointly optimize the system performance and implementation cost with the nonlinear amplifier at the receiver side.
On Hybrid Energy Utilization in Wireless Sensor Networks
(2017-12-01)
Tala't, Mohammad
;
Yu, Chih-Min
;
Ku, Meng-Lin
;
Feng, Kai-Ten
;
電機工程學系
In a wireless sensor network (WSN), many applications have limited energy resources for data transmission. In order to accomplish a better green communication for WSN, a hybrid energy scheme can supply a more reliable energy source. In this article, hybrid energy utilization-which consists of constant energy source and solar harvested energy-is considered for WSN. To minimize constant energy usage from the hybrid source, a Markov decision process (MDP) is designed to find the optimal transmission policy. With a finite packet buffer and a finite battery size, an MDP model is presented to define the states, actions, state transition probabilities, and the cost function including the cost values for all actions. A weighted sum of constant energy source consumption and a packet dropping probability (PDP) are adopted as the cost value, enabling us to find the optimal solution for balancing the minimization of the constant energy source utilization and the PDP using a value iteration algorithm. As shown in the simulation results, the performance of optimal solution using MDP achieves a significant improvement compared to solution without its use.
Toward Optimal Multiuser Antenna Beamforming for Hierarchical Cognitive Radio Systems
(2012-10-01)
Ku, Meng-Lin
;
Wang, Li-Chun
;
Su, Yu T.
;
電機資訊學士班
;
Undergraduate Honors Program of Electrical Engineering and Computer Science
In this paper, we present a joint antenna beamforming and power allocation technique to maximize the multiuser sum rate in an underlying microcellular system which reuses the same spectrum of a macrocellular system. One challenge in this kind of hierarchical cognitive radio (HCR) systems is to manage the interference between the macrocell and the microcell. The key contribution of this paper is to develop an optimization technique for antenna beamforming that can maximize the achievable sum rate of the underlying cognitive radio (CR) microcellular system and control the interference between the macrocell and the microcell with a satisfaction level. The proposed technique optimizes the sum rate performance by maximizing its lower bound and transfers the original non-convex problem into a convex optimization problem by introducing auxiliary variables to confine the intra-user interference power among the secondary system. Next, an iterative sum rate maximization (ISM) algorithm is developed to find the beamforming weights and the allocated power for each secondary user to simultaneously maximize system sum rate, coverage, and concurrent multiuser transmission probability in the HCR system. The developed joint design methodology provides valuable insights into the design of an optimal HCR system for various numbers of users as well as cell coverage, and can quantitatively optimize the performance tradeoffs in the hierarchical multiuser CR systems for current and future wireless communication applications.