Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923837
M. Valkama, M. Renfors, V. Koivunen
To achieve satisfactory performance in analog I/Q (inphase/quadrature) processing-based wireless receivers, the matching of amplitudes and phases of the I and Q branches becomes vital. In practice, there is always some imbalance and the image attenuation produced by the analog processing remains finite. Especially in wideband receivers, where the existence of strong image band signals makes the attenuation requirements extremely stringent, analog processing is incapable of providing adequate image rejection. We derive a general frequency-dependent signal model for an imbalanced analog front-end and present two alternative methods utilizing digital processing to enhance the analog front-end image rejection. Based on the obtained results, the proposed methods provide adequate image signal rejection with very few assumptions, even in the difficult cases of frequency-selective and/or time-varying imbalances.
{"title":"Compensation of frequency-selective I/Q imbalances in wideband receivers: models and algorithms","authors":"M. Valkama, M. Renfors, V. Koivunen","doi":"10.1109/SPAWC.2001.923837","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923837","url":null,"abstract":"To achieve satisfactory performance in analog I/Q (inphase/quadrature) processing-based wireless receivers, the matching of amplitudes and phases of the I and Q branches becomes vital. In practice, there is always some imbalance and the image attenuation produced by the analog processing remains finite. Especially in wideband receivers, where the existence of strong image band signals makes the attenuation requirements extremely stringent, analog processing is incapable of providing adequate image rejection. We derive a general frequency-dependent signal model for an imbalanced analog front-end and present two alternative methods utilizing digital processing to enhance the analog front-end image rejection. Based on the obtained results, the proposed methods provide adequate image signal rejection with very few assumptions, even in the difficult cases of frequency-selective and/or time-varying imbalances.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130796212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923868
Bor‐Sen Chen, Chang-Lan Tsai
The orthogonal frequency division multiplexing (OFDM) system has recently attracted increasing interest for its robustness of frequency selective fading, and is believed to be an important technique for future high-speed wireline and wireless communications, including cellular mobile communication systems. However, a well-known problem of such a multi-carrier modulation is its vulnerability to synchronization errors. The frequency offset, which results from a Doppler shift, due to mobile movement, as well as the inherent instability of the transmit and the receive reference, causes a loss of orthogonality between the subcarriers, and hence, produces intercarrier interference (ICI). To solve this problem, we trade on the correlation of the samples at the output of the discrete Fourier transform (DFT) to estimate the frequency offset by using the extended Kalman filter (EKF), which blindly tracks the frequency offset via a recursive procedure. Simulation results are given to illustrate the tracking performance of this algorithm.
{"title":"Frequency offset estimation in an OFDM system","authors":"Bor‐Sen Chen, Chang-Lan Tsai","doi":"10.1109/SPAWC.2001.923868","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923868","url":null,"abstract":"The orthogonal frequency division multiplexing (OFDM) system has recently attracted increasing interest for its robustness of frequency selective fading, and is believed to be an important technique for future high-speed wireline and wireless communications, including cellular mobile communication systems. However, a well-known problem of such a multi-carrier modulation is its vulnerability to synchronization errors. The frequency offset, which results from a Doppler shift, due to mobile movement, as well as the inherent instability of the transmit and the receive reference, causes a loss of orthogonality between the subcarriers, and hence, produces intercarrier interference (ICI). To solve this problem, we trade on the correlation of the samples at the output of the discrete Fourier transform (DFT) to estimate the frequency offset by using the extended Kalman filter (EKF), which blindly tracks the frequency offset via a recursive procedure. Simulation results are given to illustrate the tracking performance of this algorithm.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"88 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115891359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923829
L. Harju, M. Kuulusa, J. Nurmi
This paper presents a novel RAKE receiver architecture for WCDMA FDD downlink reception in mobile terminals. In contrast to the conventional RAKE finger approach, the proposed FlexRake architecture performs signal reception with a single correlator engine and a buffer which stores the entire delay spread of the baseband I/Q samples. This allows each of the tracked multipaths to be despread sequentially with codes that are exactly in the same phase. The main benefits of the proposed receiver architecture are flexible multipath allocation, symbol-synchronous operation, and straightforward receiver control.
{"title":"A flexible RAKE receiver architecture for WCDMA mobile terminals","authors":"L. Harju, M. Kuulusa, J. Nurmi","doi":"10.1109/SPAWC.2001.923829","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923829","url":null,"abstract":"This paper presents a novel RAKE receiver architecture for WCDMA FDD downlink reception in mobile terminals. In contrast to the conventional RAKE finger approach, the proposed FlexRake architecture performs signal reception with a single correlator engine and a buffer which stores the entire delay spread of the baseband I/Q samples. This allows each of the tracked multipaths to be despread sequentially with codes that are exactly in the same phase. The main benefits of the proposed receiver architecture are flexible multipath allocation, symbol-synchronous operation, and straightforward receiver control.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114690898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923886
S. Attallah, K. Abed-Meraim
We present two normalized versions of the Oja (1992) algorithm (NOja and NOOja) which can be used for the estimation of minor (noise) and principal (signal) subspaces of a vector sequence. The new algorithms offer, as compared to Oja, a faster convergence, a better orthogonality and numerical stability with a slight increase in computational complexity. These algorithms can find many applications, in particular, in wireless communications.
{"title":"Subspace estimation and tracking using enhanced versions of Oja's algorithm","authors":"S. Attallah, K. Abed-Meraim","doi":"10.1109/SPAWC.2001.923886","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923886","url":null,"abstract":"We present two normalized versions of the Oja (1992) algorithm (NOja and NOOja) which can be used for the estimation of minor (noise) and principal (signal) subspaces of a vector sequence. The new algorithms offer, as compared to Oja, a faster convergence, a better orthogonality and numerical stability with a slight increase in computational complexity. These algorithms can find many applications, in particular, in wireless communications.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"80 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123757280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923862
R. Pacheco, D. Hatzinakos
We propose a novel strategy for semi-blind spatio-temporal equalization and multiuser detection for short-burst asynchronous DS-CDMA systems. The technique is based on first performing semi-blind subspace-based channel identification and then semi-blind equalization via the constant modulus algorithm (CMA). In this way we are able to improve upon the traditional training-based least squares (LS) estimator by adding the constant modulus and cyclostationary properties of communication signals. Simulation results indicate a significant reduction in the required number of training symbols (for a short burst of data) compared with regularized LS estimators (both training-based and semi-blind). Application is in the reverse link of third-generation DS-CDMA systems.
{"title":"Semi-blind spatio-temporal equalization and multiuser detection for DS-CDMA systems","authors":"R. Pacheco, D. Hatzinakos","doi":"10.1109/SPAWC.2001.923862","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923862","url":null,"abstract":"We propose a novel strategy for semi-blind spatio-temporal equalization and multiuser detection for short-burst asynchronous DS-CDMA systems. The technique is based on first performing semi-blind subspace-based channel identification and then semi-blind equalization via the constant modulus algorithm (CMA). In this way we are able to improve upon the traditional training-based least squares (LS) estimator by adding the constant modulus and cyclostationary properties of communication signals. Simulation results indicate a significant reduction in the required number of training symbols (for a short burst of data) compared with regularized LS estimators (both training-based and semi-blind). Application is in the reverse link of third-generation DS-CDMA systems.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124274179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923827
Tongtong Li, Jitendra Tugnait
A code-constrained constant-modulus approach (CMA) was presented recently in Li et al., (2000) for blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. The equalizer was determined by minimizing the Godard/CMA cost function of the equalizer output with respect to the equalizer coefficients subject to the fact that the equalizer lies in a subspace associated with the desired user's code sequence. We analyze the identifiability properties of this approach. Global minima and some of the local minima of the cost function are investigated. These aspects were not discussed in Li. More extensive simulation comparisons with existing approaches are also provided.
{"title":"New results on blind asynchronous CDMA receivers using code-constrained CMA","authors":"Tongtong Li, Jitendra Tugnait","doi":"10.1109/SPAWC.2001.923827","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923827","url":null,"abstract":"A code-constrained constant-modulus approach (CMA) was presented recently in Li et al., (2000) for blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. The equalizer was determined by minimizing the Godard/CMA cost function of the equalizer output with respect to the equalizer coefficients subject to the fact that the equalizer lies in a subspace associated with the desired user's code sequence. We analyze the identifiability properties of this approach. Global minima and some of the local minima of the cost function are investigated. These aspects were not discussed in Li. More extensive simulation comparisons with existing approaches are also provided.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114534609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923863
K. Yang, T. Ohira
Electronically steerable passive array radiator (ESPAR) antennas are capable of spatially forming a beam toward the desired signal with the lowest cost, and are suitable to be employed in ad hoc wireless network systems. We propose a cascaded scheme for ESPAR antenna-based signal processing, where the beam toward the desired user terminal is formed in advance, and the equalizer for direct-sequence code division multiple access (DS-CDMA) signal waveforms is followed. According to the scheme, cochannel user-terminal signals and intersymbol interference signals are respectively suppressed by spatial filtering of the desired beam and the waveform-based adaptive equalization. The steady state and convergence performance of the proposed scheme is illustrated numerically by simulations.
{"title":"ESPAR antennas-based signal processing for DS-CDMA signal waveforms in ad hoc network systems","authors":"K. Yang, T. Ohira","doi":"10.1109/SPAWC.2001.923863","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923863","url":null,"abstract":"Electronically steerable passive array radiator (ESPAR) antennas are capable of spatially forming a beam toward the desired signal with the lowest cost, and are suitable to be employed in ad hoc wireless network systems. We propose a cascaded scheme for ESPAR antenna-based signal processing, where the beam toward the desired user terminal is formed in advance, and the equalizer for direct-sequence code division multiple access (DS-CDMA) signal waveforms is followed. According to the scheme, cochannel user-terminal signals and intersymbol interference signals are respectively suppressed by spatial filtering of the desired beam and the waveform-based adaptive equalization. The steady state and convergence performance of the proposed scheme is illustrated numerically by simulations.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"284 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114452307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923890
R. Punchalard, C. Benjangkaprasert, N. Anantrasirichai, K. Janchitrapongvej
The best adaptive algorithm requires fast convergence speed, low variance, unbias and low steady-state mean square error (MSE) in both low and high signal-to-noise ratio (SNR) situations. We have proposed a robust variable step-size LMS-like algorithm (VS-LMS-L) for a second-order adaptive IIR notch filter for frequency detection in radar, sonar and communication systems. This algorithm is compared with the conventional LMS-like algorithm called the plain gradient algorithm (PG). The time-varying step-size /spl mu/(n) is adjusted by using the square of the time-averaged estimate of autocorrelation of the present output signal y(n) and the past one y(n-1). This technique can reject the effect of the uncorrelated noise sequence on the step-size update, resulting in a small MSE due to the small final /spl mu/(n). Moreover, this algorithm can also improve the convergence speed by comparison with the PG at the same MSE value.
{"title":"A robust variable step-size LMS-like algorithm for a second-order adaptive IIR notch filter for frequency detection","authors":"R. Punchalard, C. Benjangkaprasert, N. Anantrasirichai, K. Janchitrapongvej","doi":"10.1109/SPAWC.2001.923890","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923890","url":null,"abstract":"The best adaptive algorithm requires fast convergence speed, low variance, unbias and low steady-state mean square error (MSE) in both low and high signal-to-noise ratio (SNR) situations. We have proposed a robust variable step-size LMS-like algorithm (VS-LMS-L) for a second-order adaptive IIR notch filter for frequency detection in radar, sonar and communication systems. This algorithm is compared with the conventional LMS-like algorithm called the plain gradient algorithm (PG). The time-varying step-size /spl mu/(n) is adjusted by using the square of the time-averaged estimate of autocorrelation of the present output signal y(n) and the past one y(n-1). This technique can reject the effect of the uncorrelated noise sequence on the step-size update, resulting in a small MSE due to the small final /spl mu/(n). Moreover, this algorithm can also improve the convergence speed by comparison with the PG at the same MSE value.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"310 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122783842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923931
Chii-Jen Chung, Wenyu Chen
A low-complexity voice recognition method in a car environment is proposed. Models of noise in the car environment are adaptable in an easy way. Power computation and memory storage for the proposed method are very low. Some real world tests are conducted and show that the proposed voice recognition method has potential for application to car cellular telephones.
{"title":"Low complexity voice recognition in car environment","authors":"Chii-Jen Chung, Wenyu Chen","doi":"10.1109/SPAWC.2001.923931","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923931","url":null,"abstract":"A low-complexity voice recognition method in a car environment is proposed. Models of noise in the car environment are adaptable in an easy way. Power computation and memory storage for the proposed method are very low. Some real world tests are conducted and show that the proposed voice recognition method has potential for application to car cellular telephones.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121400876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-20DOI: 10.1109/SPAWC.2001.923854
H. Artes, F. Hlawatsch
We propose two methods for deterministic blind equalization of linear time-varying (LTV) channels with multiple users. Our approach is based on an LTI (linear time invariant) multichannel representation of LTV channels. With the first method, the multiuser channel is equalized up to an instantaneous mixture that is subsequently resolved by means of a POCS (projections onto convex sets) algorithm. The second method performs the entire equalization (including resolution of the instantaneous mixture) by means of a POCS algorithm. Simulation results demonstrate the good performance of our methods.
{"title":"Blind multiuser equalization for time-varying channels","authors":"H. Artes, F. Hlawatsch","doi":"10.1109/SPAWC.2001.923854","DOIUrl":"https://doi.org/10.1109/SPAWC.2001.923854","url":null,"abstract":"We propose two methods for deterministic blind equalization of linear time-varying (LTV) channels with multiple users. Our approach is based on an LTI (linear time invariant) multichannel representation of LTV channels. With the first method, the multiuser channel is equalized up to an instantaneous mixture that is subsequently resolved by means of a POCS (projections onto convex sets) algorithm. The second method performs the entire equalization (including resolution of the instantaneous mixture) by means of a POCS algorithm. Simulation results demonstrate the good performance of our methods.","PeriodicalId":435867,"journal":{"name":"2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings (Cat. No.01EX471)","volume":"395 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126753004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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