This paper presents an injection method for synchronizing analog to digital converters (ADC). This approach can eliminate the need for precision routed discrete synchronization signals of current technologies, such as JESD204. By eliminating the setup and hold time requirements at the conversion (or near conversion) clock rate, higher sample rate systems can be synchronized. Measured data from an existing multiple ADC conversion system was used to evaluate the method. Coherent beams were simulated to measure the effectiveness of the method. The results show near theoretical coherent processing gain.
On Channel Estimation of OFDM-BPSK and -QPSK over Nakagami-m Fading ChannelsCSCJournals
This paper evaluates the performance of OFDM - BPSK & -QPSK based system with and without channel estimation over Nakagami-m fading channels. Nakagami-m variants are generated by decomposition of Nakagami random variable into orthogonal random variables with Gaussian distribution envelopes. Performance of OFDM system in Nakagami channel has been reported here. The results yield the optimum value of m based on BER and SNR. Using this optimum value of m, Channel estimation over flat fading has been reported here. It has been depicted clearly from simulated graphs that channel estimation has further reduced the BER. However, threshold value of m has played a vital role during channel estimation.
Improved Timing Estimation Using Iterative Normalization Technique for OFDM S...IJECEIAES
Conventional timing estimation schemes based on autocorrelation experience perfor- mance degradation in the multipath channel environment with high delay spread. To overcome this problem, we proposed an improvement of the timing estimation for the OFDM system based on statistical change of symmetrical correlator. The new method uses iterative normalization technique to the correlator output before the detection based on statistical change of symmetric correlator is applied. Thus, it increases the detection probability and achieves better performance than previously published methods in the multipath environment. Computer simulation shows that our method is very robust in the fading multipath channel.
Joint Timing and Frequency Synchronization in OFDMidescitation
With the advent of OFDM for WLAN
communications, as exemplified by IEEE 802.11a, it has become
imperative to have efficient and reliable synchronization
algorithms for OFDM WLAN receivers. The main challenges
with synchronization deal with the frequency offset and delay
spread introduced by the wireless channel. In this paper,
research is done into OFDM timing synchronization and
frequency synchronization techniques.
A novel delay dictionary design for compressive sensing-based time varying ch...TELKOMNIKA JOURNAL
Compressive sensing (CS) is a new attractive technique adopted for Linear Time Varying channel estimation. orthogonal frequency division multiplexing (OFDM) was proposed to be used in 4G and 5G which supports high data rate requirements. Different pilot aided channel estimation techniques were proposed to better track the channel conditions, which consumes bandwidth, thus, considerable data rate reduced. In order to estimate the channel with minimum number of pilots, compressive sensing CS was proposed to efficiently estimate the channel variations. In this paper, a novel delay dictionary-based CS was designed and simulated to estimate the linear time varying (LTV) channel. The proposed dictionary shows the suitability of estimating the channel impulse response (CIR) with low to moderate Doppler frequency shifts with acceptable bit error rate (BER) performance.
CS Based Channel Estimation for OFDM Systems under Long Delay Channels Using ...IJERA Editor
Orthogonal frequency division multiplexing (OFDM) is a technique which are used in the next-generation wireless communication. Channel estimation in the OFDM technique is one of the big challenges, ever since high-resolution channel estimation can significantly improve the equalization at the receiver and consequently enhance the communication performances. Channel computation using superimposed pilot sequences is also a fully new area, idea for using superimposed pilot sequences has been proposed by various authors for different applications. In this paper, we are introduced a high accurate, low complexity compressive sensing (CS) based channel estimation namely Auxiliary information based Subspace Pursuit (ASP) in TFT-OFDM systems. ASP based channel estimation in TFT-OFDM system is based on two steps. First is, by exploiting the signal structure of recently proposed TDM-OFDM scheme, the supporting channel information is obtained. Second is, we propose the supporting information based subspace pursuit (SP) algorithm to use a very small amount of frequency domain pilots embedded in the OFDM block used for the exact channel estimation. Moreover, the obtained auxiliary channel information is adopted to reduce the complexity of the conventional SP algorithm. Simulation results demonstrate a important reduction of the number of pilots relative to least-squares channel estimation and supporting high-order modulations like 256 QAM.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Review on Doubling the Rate of SEFDM Systems using Hilbert Pairsijtsrd
A novel multi carrier technique for spectrally efficient frequency division multiplexing SEFDM system for improving the spectral efficiency is discussed. A Hilbert pair is utilized as pulse shaping filters. At the the Hilbert pulse pair is generated using the square root raised cosine pulse and an equivalent matched filter configuration is utilized to generate the Hilbert pair at receiver. Simulations with different values of compression factor of the SEFDM signals were carried out to verify the data rate gain of the proposed system. The proposed system has no degradation in bit error rate performance with the data rate doubled relative to conventional SEFDM system. For system using turbo coding, there is significant BER improvement compared to uncoded transmission. Padmam Kaimal "Review on Doubling the Rate of SEFDM Systems using Hilbert Pairs" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-4 , June 2021, URL: https://www.ijtsrd.compapers/ijtsrd42348.pdf Paper URL: https://www.ijtsrd.comengineering/electronics-and-communication-engineering/42348/review-on-doubling-the-rate-of-sefdm-systems-using-hilbert-pairs/padmam-kaimal
On Channel Estimation of OFDM-BPSK and -QPSK over Nakagami-m Fading ChannelsCSCJournals
This paper evaluates the performance of OFDM - BPSK & -QPSK based system with and without channel estimation over Nakagami-m fading channels. Nakagami-m variants are generated by decomposition of Nakagami random variable into orthogonal random variables with Gaussian distribution envelopes. Performance of OFDM system in Nakagami channel has been reported here. The results yield the optimum value of m based on BER and SNR. Using this optimum value of m, Channel estimation over flat fading has been reported here. It has been depicted clearly from simulated graphs that channel estimation has further reduced the BER. However, threshold value of m has played a vital role during channel estimation.
Improved Timing Estimation Using Iterative Normalization Technique for OFDM S...IJECEIAES
Conventional timing estimation schemes based on autocorrelation experience perfor- mance degradation in the multipath channel environment with high delay spread. To overcome this problem, we proposed an improvement of the timing estimation for the OFDM system based on statistical change of symmetrical correlator. The new method uses iterative normalization technique to the correlator output before the detection based on statistical change of symmetric correlator is applied. Thus, it increases the detection probability and achieves better performance than previously published methods in the multipath environment. Computer simulation shows that our method is very robust in the fading multipath channel.
Joint Timing and Frequency Synchronization in OFDMidescitation
With the advent of OFDM for WLAN
communications, as exemplified by IEEE 802.11a, it has become
imperative to have efficient and reliable synchronization
algorithms for OFDM WLAN receivers. The main challenges
with synchronization deal with the frequency offset and delay
spread introduced by the wireless channel. In this paper,
research is done into OFDM timing synchronization and
frequency synchronization techniques.
A novel delay dictionary design for compressive sensing-based time varying ch...TELKOMNIKA JOURNAL
Compressive sensing (CS) is a new attractive technique adopted for Linear Time Varying channel estimation. orthogonal frequency division multiplexing (OFDM) was proposed to be used in 4G and 5G which supports high data rate requirements. Different pilot aided channel estimation techniques were proposed to better track the channel conditions, which consumes bandwidth, thus, considerable data rate reduced. In order to estimate the channel with minimum number of pilots, compressive sensing CS was proposed to efficiently estimate the channel variations. In this paper, a novel delay dictionary-based CS was designed and simulated to estimate the linear time varying (LTV) channel. The proposed dictionary shows the suitability of estimating the channel impulse response (CIR) with low to moderate Doppler frequency shifts with acceptable bit error rate (BER) performance.
CS Based Channel Estimation for OFDM Systems under Long Delay Channels Using ...IJERA Editor
Orthogonal frequency division multiplexing (OFDM) is a technique which are used in the next-generation wireless communication. Channel estimation in the OFDM technique is one of the big challenges, ever since high-resolution channel estimation can significantly improve the equalization at the receiver and consequently enhance the communication performances. Channel computation using superimposed pilot sequences is also a fully new area, idea for using superimposed pilot sequences has been proposed by various authors for different applications. In this paper, we are introduced a high accurate, low complexity compressive sensing (CS) based channel estimation namely Auxiliary information based Subspace Pursuit (ASP) in TFT-OFDM systems. ASP based channel estimation in TFT-OFDM system is based on two steps. First is, by exploiting the signal structure of recently proposed TDM-OFDM scheme, the supporting channel information is obtained. Second is, we propose the supporting information based subspace pursuit (SP) algorithm to use a very small amount of frequency domain pilots embedded in the OFDM block used for the exact channel estimation. Moreover, the obtained auxiliary channel information is adopted to reduce the complexity of the conventional SP algorithm. Simulation results demonstrate a important reduction of the number of pilots relative to least-squares channel estimation and supporting high-order modulations like 256 QAM.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Review on Doubling the Rate of SEFDM Systems using Hilbert Pairsijtsrd
A novel multi carrier technique for spectrally efficient frequency division multiplexing SEFDM system for improving the spectral efficiency is discussed. A Hilbert pair is utilized as pulse shaping filters. At the the Hilbert pulse pair is generated using the square root raised cosine pulse and an equivalent matched filter configuration is utilized to generate the Hilbert pair at receiver. Simulations with different values of compression factor of the SEFDM signals were carried out to verify the data rate gain of the proposed system. The proposed system has no degradation in bit error rate performance with the data rate doubled relative to conventional SEFDM system. For system using turbo coding, there is significant BER improvement compared to uncoded transmission. Padmam Kaimal "Review on Doubling the Rate of SEFDM Systems using Hilbert Pairs" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-4 , June 2021, URL: https://www.ijtsrd.compapers/ijtsrd42348.pdf Paper URL: https://www.ijtsrd.comengineering/electronics-and-communication-engineering/42348/review-on-doubling-the-rate-of-sefdm-systems-using-hilbert-pairs/padmam-kaimal
A Subspace Method for Blind Channel Estimation in CP-free OFDM SystemsCSCJournals
In this paper, a subspace method is proposed for blind channel estimation in orthogonal frequency-division multiplexing (OFDM) systems over time-dispersive channel. The proposed method does not require a cyclic prefix (CP) and thus leading to higher spectral efficiency. By exploiting the block Toeplitz structure of the channel matrix, the proposed blind estimation method performs satisfactorily with very few received OFDM blocks. Numerical simulations demonstrate the superior performance of the proposed algorithm over methods reported earlier in the literature.
A Novel CAZAC Sequence Based Timing Synchronization Scheme for OFDM SystemIJAAS Team
Several classical timing synchronization schemes have been proposed for the timing synchronization in OFDM systems based on the correlation between identical parts of OFDM symbol. These schemes show poor performance due to the presence of plateau and significant side lobe. In this paper we present a timing synchronization schemes with timing metric based on a Constant Amplitude Zero Auto Correlation (CAZAC) sequence. The performance of the proposed timing synchronization scheme is better than the classical techniques.
Classical Discrete-Time Fourier TransformBased Channel Estimation for MIMO-OF...IJCSEA Journal
In this document, we look at various time domain channel estimation methods with this constraint of null carriers at spectrumborders.We showin detail howto gauge the importance of the “border effect” depending on the number of null carriers, which may vary from one system to another. Thereby we assess the limit of the technique discussed when the number of null carriers is large. Finally the DFT with the truncated singular value decomposition (SVD) technique is proposed to completely eliminate the impact of the null subcarriers whatever their number. A technique for the determination of the truncation threshold for any MIMO-OFDM system is also proposed.
Performance Analysis of Ultra Wideband Receivers for High Data Rate Wireless ...graphhoc
For high data rate ultra wideband communication system, performance comparison of Rake, MMSE and Rake-MMSE receivers is attempted in this paper. Further a detail study on Rake-MMSE time domain equalizers is carried out taking into account all the important parameters such as the effect of the number of Rake fingers and equalizer taps on the error rate performance. This receiver combats inter-symbol interference by taking advantages of both the Rake and equalizer structure. The bit error rate performances are investigated using MATLAB simulation on IEEE 802.15.3a defined UWB channel models. Simulation results show that the bit error rate probability of Rake-MMSE receiver is much better than Rake receiver and MMSE equalizer. Study on non-line of sight indoor channel models illustrates that bit error rate performance of Rake-MMSE (both LE and DFE) improves for CM3 model with smaller spread compared to CM4 channel model. It is indicated that for a MMSE equalizer operating at low to medium SNR values, the number of Rake fingers is the dominant factor to improve system performance, while at high SNR values the number of equalizer taps plays a more significant role in reducing the error rate.
A COMPARATIVE PERFORMANCE STUDY OF OFDM SYSTEM WITH THE IMPLEMENTATION OF COM...ijcsa
This paper presents a comparative performance analysis of wireless orthogonal frequency division multiplexing (OFDM) system with the implementation of comb type pilot-based channel estimation algorithm over frequency selective multi-path fading channels. The Minimum Mean Square Error (MMSE) method is used for the estimation of channel at pilot frequencies. For the estimation of channel at data frequencies different interpolation techniques such as low-pass, linear, and second order interpolation are employed. The OFDM system simulation has been carried out with Matlab and the performance is analyzed in terms of bit error rate (BER) for various signal mapping (BPSK, QPSK, 4QAM, 16QAM, and 64QAM) and channel (Rayleigh and Rician) conditions. The impact of selecting number of channel taps on the BER performance is also investigated.
A New Approach for Speech Enhancement Based On Eigenvalue Spectral SubtractionCSCJournals
In this paper, a phase space reconstruction-based method is proposed for speech enhancement. The method embeds the noisy signal into a high dimensional reconstructed phase space and uses Spectral Subtraction idea. The advantages of the proposed method are fast performance, high SNR and good MOS. In order to evaluate the proposed method, ten signals of TIMIT database mixed with the white additive Gaussian noise and then the method was implemented. The efficiency of the proposed method was evaluated by using qualitative and quantitative criteria.
Multi carrier equalization by restoration of redundanc y (merry) for adaptive...IJNSA Journal
This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The
performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed
DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated
and less complexity also involved by the simulation of the DST-DMT system.
Projected Barzilai-Borwein Methods Applied to Distributed Compressive Spectru...Polytechnique Montreal
Cognitive radio allows unlicensed (cognitive) users to use licensed frequency bands by exploiting spectrum sensing techniques to detect whether or not the licensed (primary) users are present. In this paper, we present a compressed sensing applied to spectrum-occupancy detection in wide-band applications. The collected analog signals from each cognitive radio (CR) receiver at a fusion center are transformed to discrete-time signals by using analog-to-information converter (AIC) and then employed to calculate the autocorrelation. For signal reconstruction, we exploit a novel approach to solve the optimization problem consisting of minimizing both a quadratic (l2) error term and an l1-regularization term. In specific, we propose the Basic gradient projection (GP) and projected Barzilai-Borwein (PBB) algorithm to offer a better performance in terms of the mean squared error of the power spectrum density estimate and the detection probability of licensed signal occupancy.
Study of timing synchronization in mimoofdm systems using dvb tijitjournal
OFDM (Orthogonal Frequency Division Multiplexing)provides the promising physical layer for 4G and
3GPP LTE Systems in terms of efficient use of bandwidth and data rates. This paper highlights the
implementation of OFDM in Digital Video Broadcasting-Terrestrial (DVB-T). It mainly focuses on the
timing offset problem present in OFDM systems and its proposed solution using Cyclic Prefix (CP) as a
modified SC (Schmidl and COX) algorithm. It also highlights the timing synchronization as well as
performance comparison through bit error rate. Synchronization issues in OFDM are important and can
lead to information loss if not properly addressed. Simulations were performed to implement DVB-T system
and to compare different synchronization methods under certain distribution model.
Using Subspace Pursuit Algorithm to Improve Performance of the Distributed Co...Polytechnique Montreal
This paper applies a compressed algorithm to improve the spectrum sensing performance of cognitive radio technology.
At the fusion center, the recovery error in the analog to information converter (AIC) when reconstructing the
transmit signal from the received time-discrete signal causes degradation of the detection performance. Therefore, we
propose a subspace pursuit (SP) algorithm to reduce the recovery error and thereby enhance the detection performance.
In this study, we employ a wide-band, low SNR, distributed compressed sensing regime to analyze and evaluate the
proposed approach. Simulations are provided to demonstrate the performance of the proposed algorithm.
An identification of the tolerable time-interleaved analog-todigital convert...IJECEIAES
High-speed Terahertz communication systems has recently employed orthogonal frequency division multiplexing approach as it provides high spectral efficiency and avoids inter-symbol interference caused by dispersive channels. Such high-speed systems require extremely high-sampling time-interleaved analog-to-digital converters at the receiver. However, timing mismatch of time-interleaved analog-to-digital converters significantly causes system performance degradation. In this paper, to avoid such performance degradation induced by timing mismatch, we theoretically determine maximum tolerable mismatch levels for orthogonal frequency division multiplexing communication systems. To obtain these levels, we first propose an analytical method to derive the bit error rate formula for quadrature and pulse amplitude modulations in Rayleigh fading channels, assuming binary reflected gray code (BRGC) mapping. Further, from the derived bit error rate (BER) expressions, we reveal a threshold of timing mismatch level for which error floors produced by the mismatch will be smaller than a given BER. Simulation results demonstrate that if we preserve mismatch level smaller than 25% of this obtained threshold, the BER performance degradation is smaller than 0.5 dB as compared to the case without timing mismatch.
A Subspace Method for Blind Channel Estimation in CP-free OFDM SystemsCSCJournals
In this paper, a subspace method is proposed for blind channel estimation in orthogonal frequency-division multiplexing (OFDM) systems over time-dispersive channel. The proposed method does not require a cyclic prefix (CP) and thus leading to higher spectral efficiency. By exploiting the block Toeplitz structure of the channel matrix, the proposed blind estimation method performs satisfactorily with very few received OFDM blocks. Numerical simulations demonstrate the superior performance of the proposed algorithm over methods reported earlier in the literature.
A Novel CAZAC Sequence Based Timing Synchronization Scheme for OFDM SystemIJAAS Team
Several classical timing synchronization schemes have been proposed for the timing synchronization in OFDM systems based on the correlation between identical parts of OFDM symbol. These schemes show poor performance due to the presence of plateau and significant side lobe. In this paper we present a timing synchronization schemes with timing metric based on a Constant Amplitude Zero Auto Correlation (CAZAC) sequence. The performance of the proposed timing synchronization scheme is better than the classical techniques.
Classical Discrete-Time Fourier TransformBased Channel Estimation for MIMO-OF...IJCSEA Journal
In this document, we look at various time domain channel estimation methods with this constraint of null carriers at spectrumborders.We showin detail howto gauge the importance of the “border effect” depending on the number of null carriers, which may vary from one system to another. Thereby we assess the limit of the technique discussed when the number of null carriers is large. Finally the DFT with the truncated singular value decomposition (SVD) technique is proposed to completely eliminate the impact of the null subcarriers whatever their number. A technique for the determination of the truncation threshold for any MIMO-OFDM system is also proposed.
Performance Analysis of Ultra Wideband Receivers for High Data Rate Wireless ...graphhoc
For high data rate ultra wideband communication system, performance comparison of Rake, MMSE and Rake-MMSE receivers is attempted in this paper. Further a detail study on Rake-MMSE time domain equalizers is carried out taking into account all the important parameters such as the effect of the number of Rake fingers and equalizer taps on the error rate performance. This receiver combats inter-symbol interference by taking advantages of both the Rake and equalizer structure. The bit error rate performances are investigated using MATLAB simulation on IEEE 802.15.3a defined UWB channel models. Simulation results show that the bit error rate probability of Rake-MMSE receiver is much better than Rake receiver and MMSE equalizer. Study on non-line of sight indoor channel models illustrates that bit error rate performance of Rake-MMSE (both LE and DFE) improves for CM3 model with smaller spread compared to CM4 channel model. It is indicated that for a MMSE equalizer operating at low to medium SNR values, the number of Rake fingers is the dominant factor to improve system performance, while at high SNR values the number of equalizer taps plays a more significant role in reducing the error rate.
A COMPARATIVE PERFORMANCE STUDY OF OFDM SYSTEM WITH THE IMPLEMENTATION OF COM...ijcsa
This paper presents a comparative performance analysis of wireless orthogonal frequency division multiplexing (OFDM) system with the implementation of comb type pilot-based channel estimation algorithm over frequency selective multi-path fading channels. The Minimum Mean Square Error (MMSE) method is used for the estimation of channel at pilot frequencies. For the estimation of channel at data frequencies different interpolation techniques such as low-pass, linear, and second order interpolation are employed. The OFDM system simulation has been carried out with Matlab and the performance is analyzed in terms of bit error rate (BER) for various signal mapping (BPSK, QPSK, 4QAM, 16QAM, and 64QAM) and channel (Rayleigh and Rician) conditions. The impact of selecting number of channel taps on the BER performance is also investigated.
A New Approach for Speech Enhancement Based On Eigenvalue Spectral SubtractionCSCJournals
In this paper, a phase space reconstruction-based method is proposed for speech enhancement. The method embeds the noisy signal into a high dimensional reconstructed phase space and uses Spectral Subtraction idea. The advantages of the proposed method are fast performance, high SNR and good MOS. In order to evaluate the proposed method, ten signals of TIMIT database mixed with the white additive Gaussian noise and then the method was implemented. The efficiency of the proposed method was evaluated by using qualitative and quantitative criteria.
Multi carrier equalization by restoration of redundanc y (merry) for adaptive...IJNSA Journal
This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The
performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed
DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated
and less complexity also involved by the simulation of the DST-DMT system.
Projected Barzilai-Borwein Methods Applied to Distributed Compressive Spectru...Polytechnique Montreal
Cognitive radio allows unlicensed (cognitive) users to use licensed frequency bands by exploiting spectrum sensing techniques to detect whether or not the licensed (primary) users are present. In this paper, we present a compressed sensing applied to spectrum-occupancy detection in wide-band applications. The collected analog signals from each cognitive radio (CR) receiver at a fusion center are transformed to discrete-time signals by using analog-to-information converter (AIC) and then employed to calculate the autocorrelation. For signal reconstruction, we exploit a novel approach to solve the optimization problem consisting of minimizing both a quadratic (l2) error term and an l1-regularization term. In specific, we propose the Basic gradient projection (GP) and projected Barzilai-Borwein (PBB) algorithm to offer a better performance in terms of the mean squared error of the power spectrum density estimate and the detection probability of licensed signal occupancy.
Study of timing synchronization in mimoofdm systems using dvb tijitjournal
OFDM (Orthogonal Frequency Division Multiplexing)provides the promising physical layer for 4G and
3GPP LTE Systems in terms of efficient use of bandwidth and data rates. This paper highlights the
implementation of OFDM in Digital Video Broadcasting-Terrestrial (DVB-T). It mainly focuses on the
timing offset problem present in OFDM systems and its proposed solution using Cyclic Prefix (CP) as a
modified SC (Schmidl and COX) algorithm. It also highlights the timing synchronization as well as
performance comparison through bit error rate. Synchronization issues in OFDM are important and can
lead to information loss if not properly addressed. Simulations were performed to implement DVB-T system
and to compare different synchronization methods under certain distribution model.
Using Subspace Pursuit Algorithm to Improve Performance of the Distributed Co...Polytechnique Montreal
This paper applies a compressed algorithm to improve the spectrum sensing performance of cognitive radio technology.
At the fusion center, the recovery error in the analog to information converter (AIC) when reconstructing the
transmit signal from the received time-discrete signal causes degradation of the detection performance. Therefore, we
propose a subspace pursuit (SP) algorithm to reduce the recovery error and thereby enhance the detection performance.
In this study, we employ a wide-band, low SNR, distributed compressed sensing regime to analyze and evaluate the
proposed approach. Simulations are provided to demonstrate the performance of the proposed algorithm.
An identification of the tolerable time-interleaved analog-todigital convert...IJECEIAES
High-speed Terahertz communication systems has recently employed orthogonal frequency division multiplexing approach as it provides high spectral efficiency and avoids inter-symbol interference caused by dispersive channels. Such high-speed systems require extremely high-sampling time-interleaved analog-to-digital converters at the receiver. However, timing mismatch of time-interleaved analog-to-digital converters significantly causes system performance degradation. In this paper, to avoid such performance degradation induced by timing mismatch, we theoretically determine maximum tolerable mismatch levels for orthogonal frequency division multiplexing communication systems. To obtain these levels, we first propose an analytical method to derive the bit error rate formula for quadrature and pulse amplitude modulations in Rayleigh fading channels, assuming binary reflected gray code (BRGC) mapping. Further, from the derived bit error rate (BER) expressions, we reveal a threshold of timing mismatch level for which error floors produced by the mismatch will be smaller than a given BER. Simulation results demonstrate that if we preserve mismatch level smaller than 25% of this obtained threshold, the BER performance degradation is smaller than 0.5 dB as compared to the case without timing mismatch.
A Review: Compensation of Mismatches in Time Interleaved Analog to Digital Co...IJERA Editor
The execution of today's correspondence frameworks is exceedingly subject to the utilized Analog-to-Digital converters (ADCs), and with a specific end goal to give more flexibility and exactness to the developing correspondence innovations, superior-ADCs are needed. In this respect, the time-interleaved operation of an exhibit of ADCs (TI-ADC) might be a sensible result. A TI-ADC can build its throughput by utilizing M channel ADCs or sub converters in parallel and examining the data motion in a period-interleaved way. In any case, the execution of a TI-ADC gravely suffers from the bungles around the channel ADCs. In this paper we survey the advancement in the configuration of low-intricacy advanced remedy structures and calculations for time-interleaved ADCs in the course of the most recent five years. We devise a discrete-time model, state the outline issue, and finally infer the calculations and structures. Specifically, we examine proficient calculations to outline time-differing remedy filters and additionally iterative structures using polynomial based filters. Thusly, the remuneration structure may be utilized to repay time-differing recurrence reaction befuddles in time-interleaved ADCs, and in addition to remake uniform examples from nonuniformly tested indicators. We examine the recompense structure, research its execution, and exhibit requisition zones of the structure through various illustrations. At long last, we give a standpoint to future examination questions.
This report discusses the planning Associate in
nursing the implementation of an OFDM system
in several information module schemes like MQPSK,
M-QAM. First, a short introduction is
provided by explaining the background and the
specification of the project. Then the report deals
with the system model, every block of the OFDM
system is represented (IFFT, FFT, Cyclic prefix,
modulation / reception, Channel estimation, bit
error rate). System design is analyzed. The
transmission techniques, further because the
system parameters for transmission and reception
are explained well. Finally, the results are
provided.
Multi-carrier Equalization by Restoration of RedundancY (MERRY) for Adaptive ...IJNSA Journal
This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated and less complexity also involved by the simulation of the DST-DMT system.
Using the Channel State Information (CSI) at the transmitter is fundamental for the precoder
design in Multi-user Multiple Input Single Output (MU-MISO-OFDM) systems. In Frequency
Division Duplex (FDD) systems, CSI can be just available at the transmitter through a limited
feedback channel [1], where we assume that each user quantizes its channel direction with a
finite number of quantization bits. In this paper, we consider a scalar quantization (SQ) scheme
of the Channel Direction Information (CDI). Although vector quantization (VQ) schemes [2],
[3] still outperform this scalar scheme in terms of quantization error and Sum rate, the former
scheme suffers from an exponential search complexity and high storage requirements at the
receiver for high number of feedback bits.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
Intersymbol interference caused by multipath in band limited frequency selective time dispersive channels distorts the transmitted signal, causing bit error at receiver. ISI is the major obstacle to high speed data transmission over wireless channels. Channel estimation is a technique used to combat the intersymbol interference. The objective of this paper is to improve channel estimation accuracy in MIMO-OFDM system by using modified variable step size leaky Least Mean Square (MVSSLLMS) algorithm proposed for MIMO OFDM System. So we are going to analyze Bit Error Rate for different signal to noise ratio, also compare the proposed scheme with standard LMS channel estimation method.
CHANNEL ESTIMATION AND MULTIUSER DETECTION IN ASYNCHRONOUS SATELLITE COMMUNIC...ijwmn
In this paper, we propose a new method of channel estimation for asynchronous additive white Gaussian noise channels in satellite communications. This method is based on signals correlation and multiuser interference cancellation which adopts a successive structure. Propagation delays and signals amplitudes are jointly estimated in order to be used for data detection at the receiver. As, a multiuser detector, a single stage successive interference cancellation (SIC) architecture is analyzed and integrated to the channel estimation technique and the whole system is evaluated. The satellite access method adopted is the direct sequence code division multiple access (DS CDMA) one. To evaluate the channel estimation and the detection technique, we have simulated a satellite uplink with an asynchronous multiuser access.
Implementation of Joint Network Channel Decoding Algorithm for Multiple Acces...csandit
In this paper, we consider a Joint Network Channel Decoding (JNCD) algorithm applied to a
wireless network consisting to M users. For this purpose M sources desire to send information
to one receiver by the help of an intermediate node which is the relay. The Physical Layer
Network Coding (PLNC) allows the relay to decode the combined information being sent from
different transmitters. Then, it forwards additional information to the destination node which
receives also signals from source nodes. An iterative JNCD algorithm is developed at the
receiver to estimate the information being sent from each transmitter. Simulation results show
that the Bit Error Rate (BER) can be decreased by using this concept comparing to the
reference one which doesn’t consider the network coding.
IMPLEMENTATION OF JOINT NETWORK CHANNEL DECODING ALGORITHM FOR MULTIPLE ACCES...cscpconf
In this paper, we consider a Joint Network Channel Decoding (JNCD) algorithm applied to a wireless network consisting to M users. For this purpose M sources desire to send information
to one receiver by the help of an intermediate node which is the relay. The Physical Layer Network Coding (PLNC) allows the relay to decode the combined information being sent from different transmitters. Then, it forwards additional information to the destination node which receives also signals from source nodes. An iterative JNCD algorithm is developed at the receiver to estimate the information being sent from each transmitter. Simulation results show that the Bit Error Rate (BER) can be decreased by using this concept comparing to the reference one which doesn’t consider the network coding.
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Method for Converter Synchronization with RF Injection
1. Joshua P. Bruckmeyer & Ivica Kostanic
Signal Processing: An International Journal (SPIJ), Volume (9) : Issue (4) : 2015 46
Method for Converter Synchronization with RF Injection
Joshua P. Bruckmeyer jbruckme@harris.com
Space and Intelligence Systems
Harris Corporation
Melbourne, FL- 32902, USA
Ivica Kostanic kostanic@fit.edu
Department of ECE
Florida Institute of Technology
Melbourne, FL- 32901, USA
Abstract
This paper presents an injection method for synchronizing analog to digital converters (ADC).
This approach can eliminate the need for precision routed discrete synchronization signals of
current technologies, such as JESD204. By eliminating the setup and hold time requirements at
the conversion (or near conversion) clock rate, higher sample rate systems can be synchronized.
Measured data from an existing multiple ADC conversion system was used to evaluate the
method. Coherent beams were simulated to measure the effectiveness of the method. The
results show near theoretical coherent processing gain.
Keywords: Time Dissemination, Sampled Data Circuits, Calibration, Array Signal Processing,
and Phased Arrays.
1. INTRODUCTION
Radio Frequency (RF) sampling ADCs are replacing entire Intermediate Frequency (IF) sampling
and Zero Intermediate Frequency (ZIF) sampling subsystems, lowering the overall system power
[1]. As this technology matures, it is pushing converters to antenna enabling phased array
antennas with elemental digital beam formers. The key is to ensure every converter adds
coherently; this requires array level synchronization [2].
Modern converters support synchronization with a chip reset and/or auto sync function. For
example the emerging JESD204B standard provides two mechanisms to support synchronization
across several converters. Both methods require a synchronization signal to arrive at each
converter in the system at the same time [3]. The key is to ensure that the setup and hold time of
the synchronization signal relative to the clock is met across the entire span of data converters
[3][4]. This is impractical at best at high sample rates (above a Gigahertz) and in distributed
arrays.
The authors of [2] proposed a closed-loop deterministic phase synchronization algorithm as a
solution to distributed synchronization. Their method estimates the phase offset from each
transmitter and uses a feedback channel to command the transmitter to adjust its output phase in
a multiple input single output (MISO) system [2]. By expanding this method to a multiple input
multiple output (MIMO) or single input multiple output (SIMO) system, the receiver can perform
the phase adjustment, eliminating the receiver to transmitter feedback network. Furthermore, if an
internal injection calibration is used, the multiple output system can be synchronized without an
external corporative transmitter.
In [5] the authors proposed adaptively equalizing the channel mismatches in time-interleaved
ADCs (TIADCs) by injecting a known training signal into the ADC input. Since the analog input
and clock signal split after ADC input, they become part of the calibration loop itself. The authors
2. Joshua P. Bruckmeyer & Ivica Kostanic
Signal Processing: An International Journal (SPIJ), Volume (9) : Issue (4) : 2015 47
showed that this method could mitigate interleaving spurs while avoiding complicated error
estimation or measurement. To expand this method to synchronizing several ADCs inputs, a
distribution network is needed for the training signal. Since this distribution network will not be
used for normal operation, its characteristics need to be de-embedded.
Research on injection calibration for narrow band bean formers is also well established. The
authors of [6] studied an injection method, where a transmitted output is switched into all of the
receive channels. The goal stipulated is to correct amplitude and phase errors between the
channels. By expanding this method to estimate and correct for temporal delays, the injection
calibration method could correct for amplitude, phase, and temporal errors.
This paper expands upon the existing body of research by providing a converter synchronization
method that is not subject to the setup and hold time limitations of discrete signaling. An RF
injection method is proposed to correct time and phase delays between the converters. This
proposed method addresses the physical implications of clock and data routing and is easily
scaled to support several converters. A method to de-embed the contributions from the calibration
network itself will also be presented.
2. METHODOLOGY
To establish a representative context basis, a system model is first described. The system serves
as the basis for the mathematical assumptions and boundary conditions. The synchronization
method and sub functions are then described.
2.1 System Model
The injection calibration system spans RF to digital signal processing (DSP) fabric as shown in
figure 1. The DSP fabric contains a baseband calibration signal generator to generate a
pseudorandom signal, d . This calibration signal is modulated onto an RF carrier and is
represented by 'd . The signal 'd is injected into the RF analog input x , forming 'x . Where 'x is
a P x 1 vector, where P is the number of phase centers (converter channels). The DSP fabric
then uses training information, d , to synchronize the P phase centers in time.
FIGURE 1: System Block Diagram.
2.2 Assumptions and Boundary Conditions
We start with the assumption that the input signal is observed by each of the phase centers. We
also assume the presence of an additive white Gaussian noise channel. Furthermore we assume
that the transmitted signal is a data sequence that is linearly modulated onto a carrier. Therefore,
we can represent the input in its equivalent complex baseband form as [7]:
( ) ( ) ( )t t t= +x s q (1)
Where ( )ts is a modulated signal, ( )tq represents zero mean additive noise which is independent
of the data [7], and all vectors are P x 1 in dimension. Assuming the training injection operation is
an unbiased linear operation, x' can be represented in its baseband equivalent form as [8]:
[ ]'( ) ( ) ( )t t t= +x cf s q (2)
3. Joshua P. Bruckmeyer & Ivica Kostanic
Signal Processing: An International Journal (SPIJ), Volume (9) : Issue (4) : 2015 48
The vector ( )fcf is the calibration factor that compensates the circuits outside the calibration
loop and the inherent skew of the calibration network. The symbol is the Hadamard product
matrix operator commonly referred to as the element multiplication. All vectors are P x 1 in
dimension. The vector ( )fcf can be directly measured with standard network analyzer equipment
[9], or measured as a residual calibration vector on the system output after the calibration process
has been completed [10][11].
The channel u output contains the coherently down-converted and digitized signal for all P
phase centers. Assuming a well sampled signal and that ADC quantization noise has a negligible
contribution, the channel output may be described as:
[ ]( ) '( ) '( )t t d t= +u x h (3)
Assuming the following two factors: (1) a well-designed calibration signal, '( )d t , that does not
correlate to input signal, ( )tx , and (2) that the ADC quantization noise has a negligible
contribution , the input to the DSP can be expressed as:
( ) ( )n d n≅ ⋅u h | [ ]'( ) '( ) 0E t d t⋅ ≅x (4)
This equation bounds the problem and variables for the synchronization process: where ( )nu is
estimated by direct measurement, ( )d n is a priori known to the system and h is the variable
being solved for.
2.3 Synchronization Method
A representative synchronization circuit is shown in figure 2. The method is based on the well-
known cross correlation technique to establish the course sample alignment between the
channels [12].
FIGURE 2: Synchronization Method.
For this synchronization method, the key technique is how to estimate the sample and sub-
sample (phase) differences between the channels. To get the desired output, the following steps
are proposed:
Step 1: The calibration signal generator authors a known baseband modulated signal. The
calibration signal, d , is modulated outside the DSP fabric on an RF carrier and injected into the
circuit. This injection can be as simple as an RF switch or, as shown, an RF coupler.
4. Joshua P. Bruckmeyer & Ivica Kostanic
Signal Processing: An International Journal (SPIJ), Volume (9) : Issue (4) : 2015 49
Step 2: The DSP fabric performs a cross correlation between the received signal, u , and the
known calibration signal, d , for all phase centers. The ADC samples are also buffered to account
for the processing delay of the cross-correlation and phase estimator steps.
Step 3: The sample and sub-sample (phase) difference between the phase centers is estimated.
The integer sample delay is the sample index that contains the peak cross-correlation energy
[13]:
( ) [ ( ) ( )]E d t tτ τ= ⋅ −R u (5)
arg max[ ( )]τ τ∆ =t R (6)
The residual phase can be estimated by the complex angle of the peak cross-correlation energy
[14]:
arg [ ( )]τ τθ = ∠ R (7)
Step 4: Samples are read out of the buffer starting at the estimated ∆t for each phase center.
The depth of the buffer defines the amount of temporal channel-to-channel skew this method can
compensate for.
Step 5: The conjugant of the phase estimated in Step 3 is applied to each phase center. This
completes the temporal alignment of all of the phase centers to the calibration signal, d .
2.4 De-embedding Residual Offsets
To remove the temporal effects of the portion of the circuit not spanned by the calibration loop, an
external calibration signal is required. The following steps can be used to de-embed these offsets:
Step 1: In any practical system there will be amplitude and phase differences between the
external illumination signal and the phase centers. A calibrated external test apparatus, such as a
network analyzer, should be used to measure this. Let TS be the P x 1 complex vector that has
the channel-to-channel illumination differences.
Step 2: Use the synchronization method described in the synchronization method section to
temporally align the internal calibration network.
Step 3: Estimate the residual channel-to-channel steering vector of the illumination waveform.
There are many methods and waveforms available to do this. One common method is singular
value decomposition using a continuous-wave (CW) signal. A convenience matrix, Rxx , is
formed by:
(:, ) (:, )'
n
n n= ⋅∑Rxx u u (8)
Where the symbol, : , represents all P channels, and the symbol, '
, is the complex transpose.
Eigenvalue decomposition is used to solve for the eigenvectors. The eigenvalue with the highest
energy is assumed to correspond to the illumination waveform [15].
[ , ] ( )eig=V D Rxx (9)
arg max ( )nindex diag= D (10)
5. Joshua P. Bruckmeyer & Ivica Kostanic
Signal Processing: An International Journal (SPIJ), Volume (9) : Issue (4) : 2015 50
Finally, the steering vector representing the channel-to-channel estimate, SV , is formed by
normalizing the Eigenvector.
(:, )
(:, )
index
index
=
V
SV
V
(11)
Step 4: Remove the test setup, TS , bias:
*
=
SV
CalVector
TS
(12)
The Calibration Vector, CalVector , is a P x 1 complex vector containing the residual calibration
vector, and the symbol, *
, is the complex conjugant. Applying this vector can align all phase
centers at an approximate zero phase channel-to-channel offset.
2.5 Figure of Merit
To illustrate the performance of the proposed method, coherent beams are formed. If all of the
ADC channels are ideally time aligned, they should coherently add and result in a 10*log10(P)
power signal-to-noise gain [16].
To establish a performance improvement for both the pre- and post- synchronization cases, the
non-coherent video power is defined as:
*
VideoPower = ∑∑u u⊙ (13)
The steering vector used for the pre- synchronization beam is:
( ,1)ones P
P
=PreSV (14)
The pre-synchronization video power is estimated by:
.'= ⋅PreBeam PreSV u (15)
PrePower = ⋅∑ *
PreBeam PreBeam (16)
Where PreBeam is a 1 x n vector, n is the number of samples, and the symbol, .' , is a non-
conjugant transpose. Similarly the post-synchronization video power is estimated by:
.'= ⋅PostBeam CalVector u (17)
PostPower = ⋅∑ *
PostBeam PostBeam (18)
3. RESULTS AND DISCUSSION
To illustrate the system performance benefit from this method, simulations were performed using
measured hardware characteristics. The measured data are from an existing multiple ADC
elemental digital beam former array with elemental sample storage, also known as pre-detection
(PRE-D) capability. Specifically, two dual channel Texas Instruments ADC10D1000 devices
operating at 480 MSPS were used. The signal was injected at 225 MHz into all four channels and
the chip-to-chip synchronization methods were disabled.
The power of the pre-synchronized channel response with a Pulse Position Modulation (PPM)
6. Joshua P. Bruckmeyer & Ivica Kostanic
Signal Processing: An International Journal (SPIJ), Volume (9) : Issue (4) : 2015 51
illumination waveform is shown figure 3. Notably, there is a clear temporal delay between the
ADC channels. The coherent beam also shows clear destructive interference.
2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.16 2.18 2.2
x 10
4
-10
0
10
20
30
40
50
60
70
80
Raw Uncorrected ADC Output
Sample
Power
ADC Channel 1
ADC Channel 2
ADC Channel 3
ADC Channel 4
Beam
FIGURE 3: Pre-synchronization Signal.
In contrast the power of the post-synchronized channel response with the same PPM illumination
waveform is shown in figure 4. All of the ADC channels are temporally aligned, and there is clear
coherent beam gain.
1.96 1.98 2 2.02 2.04 2.06 2.08 2.1 2.12
x 10
4
-10
0
10
20
30
40
50
60
70
80
Time Alligned ADC Output
Sample
Power
ADC Channel 1
ADC Channel 2
ADC Channel 3
ADC Channel 4
Beam
FIGURE 4: Post-synchronization Signal.
The numeric power estimates are shown in Table 1. As would be expected, the pre-
synchronization beam shows a numeric loss in gain compared to the non-coherent video beam.
In contrast, the post-synchronization method shows excellent performance, experiencing only
0.06 dB of loss compared to the optimal power combining of 6 dB.
Parameter Raw Video Pre-Sync. Beam Post-Sync. Beam
Power (MW) 1.03 1.27 4.06
Gain from Raw (dB) - 0.91 5.94
TABLE 1: Simulated Synchronization Gain.
The simulated performance is similar to the results from the Automatic Calibration method using
Transmitting signals (ACT). The ACT method used an injected source to calibrate channel-to-
7. Joshua P. Bruckmeyer & Ivica Kostanic
Signal Processing: An International Journal (SPIJ), Volume (9) : Issue (4) : 2015 52
channel amplitude and phase errors with a single tap correction term. ACT resulted in 0.05 dB
residual calibration error when calibrating a three phase center adaptive array [6]. The high
degree of correlation in the results indicates the injection based synchronization method was
successful in compensating for temporal delays without impacting system performance.
4. CONCLUSION AND FUTURE WORK
The simulation results show that injection based synchronization can be used to synchronize
several data converts. The signal processing required is straight forward, and can readily be
implemented in modern software defined radio fabric. Implementing this method can eliminate the
need for discrete synchronization signals and lower the complexity of implementing distributed
ADC systems.
Future work could focus on distribution of the injection signal over large distances to support
distributed aperture systems. This could include the use of a distributed precision timing base,
such as GPS, to synchronize the injection signal.
5. REFERENCES
[1] Texas Instruments Incorporated. “RF-Sampling and GSPS ADCs, Breakthrough ADCs
Revolutionize Radio Architectures.” 2012, [On-line]. Available: www.ti.com/litv/pdf/snwt001
[Feb. 23, 2015].
[2] R. Hu et al. "A closed-loop deterministic phase synchronization algorithm for distributed
beamforming." Wireless Communications and Networking Conference (WCNC), 2014 IEEE,
pp.452,456, 6-9 April 2014.
[3] H. Saheb, S. Haider. "Scalable high speed serial interface for data converters: Using the
JESD204B industry standard." Design & Test Symposium (IDT), 2014 9th International, vol.,
no., pp.6,11, 16-18 Dec. 2014.
[4] Texas Instruments Incorporated. “AN-2132 Synchronizing Multiple GSPS ADCs in a System:
The AutoSync Feature.” 2013, [On-line]. Available: www.ti.com/lit/an/snaa073f/snaa073f.pdf
[Feb. 27, 2015].
[5] S. Liu et al. "Adaptive Calibration of Channel Mismatches in Time-Interleaved ADCs Based
on Equivalent Signal Recombination." Instrumentation and Measurement, IEEE Transactions
on, vol.63, no.2, pp.277,286, Feb. 2014.
[6] K. Nishimori et al. "Automatic calibration method using transmitting signals of an adaptive
array for TDD systems." in Vehicular Technology, IEEE Transactions on, vol.50, no.6,
pp.1636-1640, Nov 2001
[7] M. Stojanovic, J.A. Catipovic, J.G. Proakis. "Reduced-complexity simultaneous beamforming
and equalization for underwater acoustic communications." OCEANS '93. Engineering in
Harmony with Ocean. Proceedings, pp.III426, III431 vol.3, 18-21 Oct 1993.
[8] S. Haykin. Adaptive Filter Theory, Upper Saddle River, New Jersey, Prentice Hall, 2002.
[9] K. R. Dandekar et al., "Smart antenna array calibration procedure including amplitude and
phase mismatch and mutual coupling effects." Personal Wireless Communications, 2000
IEEE International Conference on, pp. 293-297, 2000.
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