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Low Complexity Equalization Method for ZP-OFDM under Highly Mobile Environments
(2020-02-01)
Tanangsanakool, Saha
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Reangsuntea, Pongsathorn
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Mori, Kazuo
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Boonsrimuang, Pisit
Many Interferences from multipath fading channels in the mobile channels, there are many types of research trying to compensate for such interferences. The Zero-padded OFDM (ZP-OFDM) is a popular method that has much attention as an efficient technique to improve the performances. In the high-speed mobile channel, the Doppler frequency destroyed orthogonality among subcarriers and inter-carrier interference (ICI), It would degrade the bit error rate (BER) performance. We proposed both equalization (TDE) method and CIR estimation with less computation complexity for the ZP-OFDM signal that can solve this problem. The salient feature of our proposed method is using a training sequence (TS) instead of using Zero-padded which enables for estimation of CIR. And we show that the proposed method shows the less computational complexity when compared with the conventional frequency-domain equalization, the proposed TDE method employs an iterative solution instead of using the direct inverse matrix method. We validate the proposed methods presented by computer simulations under highly mobile environments. The simulation results show a comparison of the effectiveness of the proposed TDE method and conventional TDE methods.
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Low-complexity based TDE Method for OFDM signal in higher time-varying fading channels
(2020-01-01)
Tanangsanakool, Saha
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Reangsuntea, Pongsathorn
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Mori, Kazuo
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Boonsrimuang, Pisit
Orthogonal Frequency Division Multiplexing (OFDM) signal would be damaged significantly by inter-carrier interference (ICI) in higher time-varying fading channels. The ICI leads to fatal degradation of bit error rate (BER) performance due to the loss of orthogonality among subcarriers. To solve this problem, this paper proposes a high accuracy time-domain channel impulse response (CIR) estimation method and low-complexity based time-domain equalization (TDE) method for solving the simultaneous equations instead of using an inverse matrix calculation which can achieve better BER performance and lower computation complexity even in higher time-varying fading channels. The salient features of proposed method are to employ a time-domain training sequence (TS) in the estimation of channel impulse response (CIR) instead of using pilot subcarriers in the frequency domain and to employ the time domain equalization (TDE) method with maximum likelihood (ML) estimation instead of using a conventional frequency domain equalization (FDE) method. This paper also proposes a low-complexity iterative method for solving the simultaneous equations instead of using an inverse matrix calculation, which remains the computation complexity up to 7.8% of inverse matrix calculation with the same BER performance but achieves the BER performance when compared with the conventional method. This paper presents various simulation results in higher time-varying fading channels (vehicle speed ≈ 381 km/hrs) to demonstrate the effectiveness of the proposed method as compared with conventional FDE and TDE methods.
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Channel Estimation and Equalization Methods for ZP-OFDM under Highly Mobile Environments
(2019-04-29)
Tanangsanakool, Saha
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Reangsuntea, Pongsathorn
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Mori, Kazuo
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Boonsrimuang, Pisit
Zero-Padded OFDM (ZP-OFDM) has been attracted a lot of attention as an efficient technique to improve the performance in severe multipath fading channels. Many works were devoted to the equalization method for ZP-OFDM in quasi-static channel model. However, an inter-carrier interference (ICI) which occurred under highly mobile environments would be destroyed orthogonality among subcarriers and causes the degradation of bit error rate (BER) performance due to the time domain channel impulse responses (CIRs) are assumed to be constant over one OFDM symbol. The time domain equalization (TDE) method in conjunction with a time domain CIR estimation method is proposed to solve this problem for the ZP-OFDM signal in the time domain. The advantage of the proposed method is to apply a training sequence (TS) instead of using ZP which enables for estimation of CIR. And also to reduce computational complexity, the proposed method is employed time domain equalization based on the minimum mean squared error (MMSE-TDE) instead of using the conventional frequency domain equalization based on MMSE (MMSE-FDE) method. This paper presents various simulation results under highly mobile environments to demonstrate the effectiveness of proposed TDE method as compared with conventional demodulation methods.
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Time domain equalization method for TS-OFDM signal under higher mobile environments
(2017-12-01)
Reangsuntea, Pongsathorn
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Boonsrimuang, Pisit
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Mori, Kazuo
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Kobayashi, Hideo
In higher time-varying fading channels, the signal quality of orthogonal frequency division multiplexing (OFDM) technique would be degraded relatively due to the occurrence of inter-carrier interference (ICI). To solve this problem, this paper firstly proposes a new design of time domain training sequence (TS) in the estimation of channel impulse response (CIR) for the TS-OFDM signal which can reduce the leakage of power spectrum density (PSD) at the outside of OFDM allocated frequency bandwidth with keeping higher CIR estimation accuracy. Secondly, this paper proposes a time domain equalization (TDE) method which can achieve better bit error rate (BER) performance with keeping lower computation complexity even in higher time-varying fading channels. The salient feature of the proposed TDE method is to employ a partial differentiation for the time domain CIR matrix for solving the maximum likelihood (ML) equation in which the time domain CIR matrix becomes a symmetric banded matrix. From this feature, a low-complexity parallel block inverse matrix algorithm can be employed in the calculation of inverse matrix in keeping the same accuracy as that of the direct inverse matrix calculation. This paper presents various computer simulation results to demonstrate the effectiveness of the proposed TDE method for the TS-OFDM signal as compared with conventional frequency domain equalization (FDE) methods under higher mobile environments.
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Transmit diversity for TS-OFDM signal in higher time-varying fading channels
(2017-11-03)
Danchai, Anusan
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Reangsuntea, Arttapol
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Boonsrimuang, Pisit
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Reangsuntea, Pongsathorn
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Mori, Kazuo
This paper proposes a channel estimation and equalization methods for a transmit diversity system of using time domain training sequence inserted orthogonal frequency division multiplexing (TS-OFDM) signal in higher time-varying fading channels. The salient feature of the proposed channel impulse response (CIR) estimation method for the transmit diversity system with a space frequency block coding is to employ a new design of training sequence (TS) signal which can reduce the leakage of power spectrum density (PSD) and keep higher CIR estimation accuracy. In the proposed equalization method, the estimated CIR at every sampling time and the known TS signals are employed at the receiver for removing the inter-symbol interference (ISI) caused in higher time-varying fading channels so as to employ the overlap and add (OLA) operation. This paper presents various simulation results to demonstrate the effectiveness of the proposed transmit diversity system as comparing with the conventional methods.
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Cell throughput based sleep control scheme for heterogeneous cellular networks
(2017-11-03)
Phaiwitthayaphorn, Prapassorn
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Boonsrimuang, Pisit
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Reangsuntea, Pongsathorn
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Fujii, Takashi
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Sanada, Kosuke
Recently, the concept of heterogeneous networks (HetNets) has been proposed as an alternative solution to provide higher coverage and capacity for cellular networks. In HetNets concept, many of small base stations (SBSs) are employed in the existing cell of macro base stations (MBSs) to increase the coverage and system capacity. However, the employment of many SBSs in the existing macro cells would causes the increase in power consumption with decreasing the energy efficiency in downlink cellular networks. To solve this problem, this paper proposes a cell throughput based sleep control scheme for the SBSs in HetNets. In the proposed scheme, the cell capacity ratio for the SBSs is employed as decision criteria to put the SBSs into sleep state. From various simulation results, the proposed scheme can achieve better energy efficiency and better system throughput than the conventional schemes.
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Low-complexity MMSE-FDE method for TS-OFDM signal under high mobile environments
(2016-12-16)
Reangsuntea, Pongsathorn
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Sanada, Kousuke
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Mori, Kazuo
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Kobayashi, Hideo
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Boonsrimuang, Pisit
This paper proposes a minimum mean square error-frequency domain equalization (MMSE-FDE) method for training sequence inserted orthogonal frequency division multiplexing (TS-OFDM) signal under high mobile environments. The salient features of proposed method are to enable the acquisition of frequency diversity gain by using the enhanced CIR matrix and to enable the reduction of complexity by employing the fast algorithm for inverse matrix calculation. From the simulation results, this paper confirms that the proposed method can achieve better bit error rate (BER) performance than the conventional MMSE-FDE methods with keeping lower complexity.
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Low-complexity FDE method for TS-OFDM signal under higher time-varying channels
(2016-09-06)
Reangsuntea, Pongsathorn
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Mori, Kazuo
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Kobayashi, Hideo
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Reangsuntea, Arttapol
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Boonsrimuang, Pisit
A losing of orthogonality among subcarriers in higher time-varying fading channels causes an inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) signal which leads a fatal degradation both for the channel estimation accuracy and bit error rate (BER) performances. To solve this problem, this paper firstly proposes a channel estimation method with a new design of time domain training sequence (TS) of using a triangular window function which can achieve higher channel estimation accuracy with keeping lower leakage of power spectrum density (PSD) at the outside of OFDM allocated frequency bandwidth than the conventional TS signal. Secondly, this paper proposes a low-complexity frequency domain equalization (FDE) method which can achieve better BER performance than the conventional one-tap FDE method. The feature of proposed FDE method is to enable the reduction of complexity by using a Maclaurin's expansion algorithm in the inverse matrix calculation. This paper presents various computer simulation results to demonstrate the effectiveness of proposed FDE method as comparing with the conventional FDE methods.
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Iterative based time domain equalization method for DFTS-OFDM under highly mobile environments
(2016-09-06)
Reangsuntea, Arttapol
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Boonsrimuang, Pisit
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Reangsuntea, Pongsathorn
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Mori, Kazuo
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Kobayashi, Hideo
Under highly mobile environments, the bit error rate (BER) performance of DFT spreading-orthogonal frequency division multiplexing (DFTS-OFDM) signal with a frequency domain equalization method would be degraded relatively due to the loss of orthogonality among subcarriers. To solve this problem, this paper proposes an iterative based time domain equalization (TDE) technique with a time domain channel impulse response (CIR) estimation method for the DFTS-OFDM signal. The salient features of proposed method are to employ a time domain training sequence (TS) in the estimation of CIR instead of using the conventional pilot subcarriers method and to employ the TDE technique with a maximum likelihood (ML) estimation method instead of using the conventional minimum mean square error frequency domain equalization (MMSE-FDE) method. This paper also proposes a low-complexity iterative method for the TDE method by using the preconditioned conjugate gradient squared (PCGS) algorithm for solving the simultaneous equations instead of using a direct calculation of inverse matrix. This paper presents various simulation results under highly mobile environments to demonstrate the effectiveness of proposed iterative based TDE with the CIR estimation method for the DFTS-OFDM signal as comparing with the conventional MMSE-FDE method.
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Time domain equalization method for DFTS-OFDM signal without GI under high mobile environments
(2015-08-17)
Reangsuntea, Pongsathorn
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Mori, Kazuo
;
Kobayashi, Hideo
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Boonsrimuang, Pisit
In higher time-varying fading channels, the DFT Spreading-Orthogonal Frequency Division Multiplexing (DFTS-OFDM) signal would be damaged significantly by inter-channel interference (ICI) due to the loss of orthogonality among subcarriers which leads a fatal degradation of bit error rate (BER) performance. To solve this problem, this paper proposes a time domain equalization (TDE) technique in conjunction with a time domain channel impulse response (CIR) estimation method for the DFTS-OFDM signal. The salient features of proposed method are to employ a time domain training sequence (TS) in the estimation of CIR at every sampling time instead of using the conventional scattered pilots inserted in the frequency domain and to employ the TDE with a maximum likelihood (ML) estimation method in the demodulation of received time domain signal at every symbol instead of using the conventional frequency domain equalization (FDE) method. This paper presents various simulation results to demonstrate the effectiveness of proposed method for the DFTS-OFDM signal as comparing with the conventional FDE method.

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