Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS o... more Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS operates on the L1 frequency (1575.42 MHz) and is currently still of interest since all GNSS satellites and receivers do not fully support additional frequencies such as L5 (1176.45 MHz). Although the Global Positioning System (GPS) aided Geo Augmented Navigation (GAGAN) SBAS is available, the performances are degraded due to the discrepancies of the ionospheric correction over Thailand and surrounding areas. Hence, in this work, we propose a new method based on the geometry-free ionospheric delay estimation with a single frequency (L1) and a single reference station requirement. The local ionospheric delays are estimated based on the proposed method with the observed GPS and GAGAN data in Thailand. Then the ionospheric corrections are obtained from the estimated local ionospheric delays. The analysis shows that using the estimated corrections, the positioning errors are reduced both on q...
2021 18th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON)
Although GAGAN satellite-based augmentation system (SBAS) provides ionospheric correction service... more Although GAGAN satellite-based augmentation system (SBAS) provides ionospheric correction service to India and surrounding areas, the correction values do not cover the entire region of Thailand and even at provided grids, they may not be sufficiently accurate. Hence, this work, we propose a local ionospheric delay estimation method based on the geo-free ionospheric delay estimation. Then the estimated ionospheric delays are applied together with the fast and long-term corrections of GAGAN SBAS to improve the positioning errors. The results show that the estimated ionospheric delays can improve the user positioning errors in terms of horizontal and vertical errors up to 0.5 and 1 meter, respectively.
Constrained codes in single-reader/two-track reading bit-patterned magnetic recording AIP Advance... more Constrained codes in single-reader/two-track reading bit-patterned magnetic recording AIP Advances 11, 015009 (2021);
Bit-patterned media recording (BPMR) is a promising technology for ultra-high density media, howe... more Bit-patterned media recording (BPMR) is a promising technology for ultra-high density media, however, there are some challenges that need to be addressed including two-dimensional (2D) interference, and track mis-registration (TMR). The system can experience TMR due to misalignment of the head and the track center. Conventionally, TMR is tackled using a servo system in which the head position offset is estimated by processing the overhead servo sequences before reading the data sequences. However, TMR impairment can also occur when the head is reading data sequences that are beyond the servo mechanism. To address this problem, we proposed TMR detection and correction techniques based on our previous work involving a single-track equalization method for a BPMR system using cross-correlation functions between the single readback signal and each of the training sequences from three adjacent tracks. In this proposed technique, the presence and level of TMR is detected and estimated based on the changes in the value of mean square error (MSE) between the equalized and feedback signals from the detectors after passing through a one-dimensional (1D) target for each sequence. Then, the estimated TMR levels are used in selecting the appropriate equalizer and the generalized partial response (GPR) target pair to tackle the TMR from the readback signal. The simulation results show improvement in the data recovery of a BPMR system using the proposed method when the system is experiencing 2D interference and TMR impairment.
2019 34th International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC), 2019
For multi-track read channel of high areal density magnetic recording systems, two-dimensional (2... more For multi-track read channel of high areal density magnetic recording systems, two-dimensional (2-D) equalizer is normally considered to shape the readback signal to the desired 2-D generalized partial response (GPR) target. However, the equalizer can correlate the additive noise in the signal and the noise can become the correlated/colored noise which will have a negative impact on the performance of the detector. In the literature, a noise predictive detector using a linear noise predictor (a finite impulse response (FIR) filter) is proposed to tackle the performance loss due to the color/correlated noise. Integrating noise prediction into a detector can grow the complexity of the detector depending on the number of taps in the FIR filter. Alternatively, the noise predictor can also be implemented using an infinite impulse response (IIR) filter. Moreover, IIR predictor can provide the performance gain without requiring a large number of filter's taps. Therefore, in this paper,...
2020 35th International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC), 2020
The ASEAN IVO project currently supports the research related to GNSS and ionospheric data produc... more The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. Satellite-Based Augmentation System (SBAS) is vital to air navigation in many regions around the world. In Thailand, the L1-frequency SBAS corrections can be received from the GPS Aided Geo Augmented Navigation (GAGAN) system which is intended for use over Indian airspace. In this work, we analyze the performances of the GAGAN system in Thailand on quiet and disturbed days in March 2019 by applying the entire corrections received at King Mongkut’s Institute of Technology Ladkrabang station. The 95-percent horizontal and vertical accuracies on quiet days are 1.52 and 3.18 meters, respectively. In contrast, on disturbed days they are 1.97 and 3.41 meters, respectively.
The ASEAN IVO project currently supports the research related to GNSS and ionospheric data produc... more The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. In the positioning system, the atmosphere is the main medium along the propagation path that includes some ions, water vapor, and noise. These are the causes of the propagation delay time especially the ions in the ionosphere. At the present, there are many Global Positioning System (GPS) stations worldwide. Therefore, we can check the performances of the positioning system by using the positioning error calculation. In this work, the positioning errors are calculated from the 16 GPS stations at the low geomagnetic latitude region (Thailand) with the single frequency algorithm on a disturbance day. Then, we compute the 95-percentile and the maximum of the positioning errors. The results show approximately the difference of 95-percentile value 1.799 meters on the horizontal axis and 2.289 meters on the vertical axis and maxi...
Paper published as part of the special topic on 62nd Annual Conference on Magnetism and Magnetic ... more Paper published as part of the special topic on 62nd Annual Conference on Magnetism and Magnetic Materials and Chemical Physics ARTICLES YOU MAY BE INTERESTED IN Effects of head field and AC field on magnetization reversal for microwave assisted magnetic recording AIP Advances 8, 056505 (2018);
The readback signal of patterned media storage (PMS) is corrupted by a two-dimensional interferen... more The readback signal of patterned media storage (PMS) is corrupted by a two-dimensional interference consisting of inter-symbol interference (ISI) and inter-track interference (ITI). In this paper, we apply the turbo equalization to mitigate the ITI effects. The codeword of the outer code is divided and then written on three separate tracks. After the first iteration, the bit estimates from the outer code provide partial ITI estimates for the branch metric computation in the soft-output viterbi algorithm (SOVA) detectors. Unlike previous works, the number of states of the channel trellis is due to the ISI only since the ITI information is not embedded in the parallel branches. When compared with the modified SOVA detectors with multi-parallel branches, simulation results show that a significant performance gain is achieved by our proposed method.
Songklanakarin Journal of Science and Technology, 2010
In this paper, we studied the performance of the iterated Viterbi detection methods using the mul... more In this paper, we studied the performance of the iterated Viterbi detection methods using the multi-track multi-head processing for a bit patterned media (BPM) channel with a two-dimensional interference consisting of inter-symbol interference (ISI) and inter-track interference (ITI). In each method, three Viterbi detectors are employed to process the three readback signals. In their trellises, the number of states is designed based on the ISI only. After the first iteration, the estimated output sequences are exchanged between the adjacent detectors as the ITI estimations and then used in the metric calculation of next iteration. When compared with other methods, the simulation results show that the proposed methods achieve significant gains. We also investigated the performance of the proposed methods for the BPM channel with different media noise levels. Finally, the computational complexity of all detectors is compared.
Paper published as part of the special topic on Chemical Physics ARTICLES YOU MAY BE INTERESTED I... more Paper published as part of the special topic on Chemical Physics ARTICLES YOU MAY BE INTERESTED IN Reduced complexity of multi-track joint 2-D Viterbi detectors for bit-patterned media recording channel AIP Advances 7, 056502 (2017);
ABSTRACT In multi-track detection, the simultaneous recovery of user data of all tracks is obtain... more ABSTRACT In multi-track detection, the simultaneous recovery of user data of all tracks is obtained from multi-head or single-head reader with buffer. Due to incomplete inter-track interference (ITI) information of the outer tracks, unequal error rates exist among tracks. For a system with three-track processing, the center track exhibits a better performance than the others. In this work, we propose the unequal error protection (UEP) schemes to improve the overall system performance of a 2-D interference bit-patterned recording system with multi-track detection. The performances of the proposed schemes are investigated for the BPM channels with and without the media noise. Based on the simulation results, the proposed schemes offer the gain of about 0.2–0.3 dB over the equal error protection (EEP) scheme at a bit error rate of 10−4.
ABSTRACT In this paper, we studied the performance of the iterated Viterbi detection methods usin... more ABSTRACT In this paper, we studied the performance of the iterated Viterbi detection methods using the multi-track multi-head processing for a bit patterned media (BPM) channel with a two-dimensional interference consisting of inter-symbol interfer-ence (ISI) and inter-track interference (ITI). In each method, three Viterbi detectors are employed to process the three readback signals. In their trellises, the number of states is designed based on the ISI only. After the first iteration, the estimated output sequences are exchanged between the adjacent detectors as the ITI estimations and then used in the metric calcula-tion of next iteration. When compared with other methods, the simulation results show that the proposed methods achieve significant gains. We also investigated the performance of the proposed methods for the BPM channel with different media noise levels. Finally, the computational complexity of all detectors is compared.
Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS o... more Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS operates on the L1 frequency (1575.42 MHz) and is currently still of interest since all GNSS satellites and receivers do not fully support additional frequencies such as L5 (1176.45 MHz). Although the Global Positioning System (GPS) aided Geo Augmented Navigation (GAGAN) SBAS is available, the performances are degraded due to the discrepancies of the ionospheric correction over Thailand and surrounding areas. Hence, in this work, we propose a new method based on the geometry-free ionospheric delay estimation with a single frequency (L1) and a single reference station requirement. The local ionospheric delays are estimated based on the proposed method with the observed GPS and GAGAN data in Thailand. Then the ionospheric corrections are obtained from the estimated local ionospheric delays. The analysis shows that using the estimated corrections, the positioning errors are reduced both on q...
2021 18th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON)
Although GAGAN satellite-based augmentation system (SBAS) provides ionospheric correction service... more Although GAGAN satellite-based augmentation system (SBAS) provides ionospheric correction service to India and surrounding areas, the correction values do not cover the entire region of Thailand and even at provided grids, they may not be sufficiently accurate. Hence, this work, we propose a local ionospheric delay estimation method based on the geo-free ionospheric delay estimation. Then the estimated ionospheric delays are applied together with the fast and long-term corrections of GAGAN SBAS to improve the positioning errors. The results show that the estimated ionospheric delays can improve the user positioning errors in terms of horizontal and vertical errors up to 0.5 and 1 meter, respectively.
Constrained codes in single-reader/two-track reading bit-patterned magnetic recording AIP Advance... more Constrained codes in single-reader/two-track reading bit-patterned magnetic recording AIP Advances 11, 015009 (2021);
Bit-patterned media recording (BPMR) is a promising technology for ultra-high density media, howe... more Bit-patterned media recording (BPMR) is a promising technology for ultra-high density media, however, there are some challenges that need to be addressed including two-dimensional (2D) interference, and track mis-registration (TMR). The system can experience TMR due to misalignment of the head and the track center. Conventionally, TMR is tackled using a servo system in which the head position offset is estimated by processing the overhead servo sequences before reading the data sequences. However, TMR impairment can also occur when the head is reading data sequences that are beyond the servo mechanism. To address this problem, we proposed TMR detection and correction techniques based on our previous work involving a single-track equalization method for a BPMR system using cross-correlation functions between the single readback signal and each of the training sequences from three adjacent tracks. In this proposed technique, the presence and level of TMR is detected and estimated based on the changes in the value of mean square error (MSE) between the equalized and feedback signals from the detectors after passing through a one-dimensional (1D) target for each sequence. Then, the estimated TMR levels are used in selecting the appropriate equalizer and the generalized partial response (GPR) target pair to tackle the TMR from the readback signal. The simulation results show improvement in the data recovery of a BPMR system using the proposed method when the system is experiencing 2D interference and TMR impairment.
2019 34th International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC), 2019
For multi-track read channel of high areal density magnetic recording systems, two-dimensional (2... more For multi-track read channel of high areal density magnetic recording systems, two-dimensional (2-D) equalizer is normally considered to shape the readback signal to the desired 2-D generalized partial response (GPR) target. However, the equalizer can correlate the additive noise in the signal and the noise can become the correlated/colored noise which will have a negative impact on the performance of the detector. In the literature, a noise predictive detector using a linear noise predictor (a finite impulse response (FIR) filter) is proposed to tackle the performance loss due to the color/correlated noise. Integrating noise prediction into a detector can grow the complexity of the detector depending on the number of taps in the FIR filter. Alternatively, the noise predictor can also be implemented using an infinite impulse response (IIR) filter. Moreover, IIR predictor can provide the performance gain without requiring a large number of filter's taps. Therefore, in this paper,...
2020 35th International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC), 2020
The ASEAN IVO project currently supports the research related to GNSS and ionospheric data produc... more The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. Satellite-Based Augmentation System (SBAS) is vital to air navigation in many regions around the world. In Thailand, the L1-frequency SBAS corrections can be received from the GPS Aided Geo Augmented Navigation (GAGAN) system which is intended for use over Indian airspace. In this work, we analyze the performances of the GAGAN system in Thailand on quiet and disturbed days in March 2019 by applying the entire corrections received at King Mongkut’s Institute of Technology Ladkrabang station. The 95-percent horizontal and vertical accuracies on quiet days are 1.52 and 3.18 meters, respectively. In contrast, on disturbed days they are 1.97 and 3.41 meters, respectively.
The ASEAN IVO project currently supports the research related to GNSS and ionospheric data produc... more The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. In the positioning system, the atmosphere is the main medium along the propagation path that includes some ions, water vapor, and noise. These are the causes of the propagation delay time especially the ions in the ionosphere. At the present, there are many Global Positioning System (GPS) stations worldwide. Therefore, we can check the performances of the positioning system by using the positioning error calculation. In this work, the positioning errors are calculated from the 16 GPS stations at the low geomagnetic latitude region (Thailand) with the single frequency algorithm on a disturbance day. Then, we compute the 95-percentile and the maximum of the positioning errors. The results show approximately the difference of 95-percentile value 1.799 meters on the horizontal axis and 2.289 meters on the vertical axis and maxi...
Paper published as part of the special topic on 62nd Annual Conference on Magnetism and Magnetic ... more Paper published as part of the special topic on 62nd Annual Conference on Magnetism and Magnetic Materials and Chemical Physics ARTICLES YOU MAY BE INTERESTED IN Effects of head field and AC field on magnetization reversal for microwave assisted magnetic recording AIP Advances 8, 056505 (2018);
The readback signal of patterned media storage (PMS) is corrupted by a two-dimensional interferen... more The readback signal of patterned media storage (PMS) is corrupted by a two-dimensional interference consisting of inter-symbol interference (ISI) and inter-track interference (ITI). In this paper, we apply the turbo equalization to mitigate the ITI effects. The codeword of the outer code is divided and then written on three separate tracks. After the first iteration, the bit estimates from the outer code provide partial ITI estimates for the branch metric computation in the soft-output viterbi algorithm (SOVA) detectors. Unlike previous works, the number of states of the channel trellis is due to the ISI only since the ITI information is not embedded in the parallel branches. When compared with the modified SOVA detectors with multi-parallel branches, simulation results show that a significant performance gain is achieved by our proposed method.
Songklanakarin Journal of Science and Technology, 2010
In this paper, we studied the performance of the iterated Viterbi detection methods using the mul... more In this paper, we studied the performance of the iterated Viterbi detection methods using the multi-track multi-head processing for a bit patterned media (BPM) channel with a two-dimensional interference consisting of inter-symbol interference (ISI) and inter-track interference (ITI). In each method, three Viterbi detectors are employed to process the three readback signals. In their trellises, the number of states is designed based on the ISI only. After the first iteration, the estimated output sequences are exchanged between the adjacent detectors as the ITI estimations and then used in the metric calculation of next iteration. When compared with other methods, the simulation results show that the proposed methods achieve significant gains. We also investigated the performance of the proposed methods for the BPM channel with different media noise levels. Finally, the computational complexity of all detectors is compared.
Paper published as part of the special topic on Chemical Physics ARTICLES YOU MAY BE INTERESTED I... more Paper published as part of the special topic on Chemical Physics ARTICLES YOU MAY BE INTERESTED IN Reduced complexity of multi-track joint 2-D Viterbi detectors for bit-patterned media recording channel AIP Advances 7, 056502 (2017);
ABSTRACT In multi-track detection, the simultaneous recovery of user data of all tracks is obtain... more ABSTRACT In multi-track detection, the simultaneous recovery of user data of all tracks is obtained from multi-head or single-head reader with buffer. Due to incomplete inter-track interference (ITI) information of the outer tracks, unequal error rates exist among tracks. For a system with three-track processing, the center track exhibits a better performance than the others. In this work, we propose the unequal error protection (UEP) schemes to improve the overall system performance of a 2-D interference bit-patterned recording system with multi-track detection. The performances of the proposed schemes are investigated for the BPM channels with and without the media noise. Based on the simulation results, the proposed schemes offer the gain of about 0.2–0.3 dB over the equal error protection (EEP) scheme at a bit error rate of 10−4.
ABSTRACT In this paper, we studied the performance of the iterated Viterbi detection methods usin... more ABSTRACT In this paper, we studied the performance of the iterated Viterbi detection methods using the multi-track multi-head processing for a bit patterned media (BPM) channel with a two-dimensional interference consisting of inter-symbol interfer-ence (ISI) and inter-track interference (ITI). In each method, three Viterbi detectors are employed to process the three readback signals. In their trellises, the number of states is designed based on the ISI only. After the first iteration, the estimated output sequences are exchanged between the adjacent detectors as the ITI estimations and then used in the metric calcula-tion of next iteration. When compared with other methods, the simulation results show that the proposed methods achieve significant gains. We also investigated the performance of the proposed methods for the BPM channel with different media noise levels. Finally, the computational complexity of all detectors is compared.
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Papers by Lin M Myint