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| 2. |
- Li, Xi, et al.
(författare)
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Phase-shift-based time-delay estimators for proximity acoustic sensors
- 2002
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Ingår i: IEEE Journal of Oceanic Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 0364-9059 .- 1558-1691 .- 2373-7786. ; 27:1, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- Time-delay estimation is important in a wide range of applications in oceanic engineering. In this paper, we present a novel time-delay estimation algorithm based on maximum likelihood theory for the case that the measurements are corrupted by colored or nonuniform zero-mean Gaussian noise. It turns out that the likelihood function associated with the problem is highly oscillatory, and we propose a computationally efficient technique to maximize this function. Our algorithm first obtains an initial estimate based on a smooth approximate cost function, and then refines this estimate based on the true cost function. Simulation results show that our estimator outperforms a traditional phaseshift based estimator, and that the estimation error approaches the Cramer-Rao bound when the SNR increases without bound.
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| 3. |
- Liu, Jianhua, et al.
(författare)
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Differential space-code modulation for interference suppression
- 2001
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 49:8, s. 1786-1795
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Tidskriftsartikel (refereegranskat)abstract
- Space-time coding has been receiving much attention due to its potentials offered by fully exploiting the spatial and temporal diversities of multiple transmit and receive antennas. A differential space-time modulation (DSTM) scheme was previously proposed for demodulation without channel state information, which is attractive in fast fading channels where accurate channel estimates are difficult to obtain. However, this technique is sensitive to interference and is likely to deteriorate or even break down in a wireless environment, where interference (including intentional and unintentional jamming) signals exist. We propose a new coding and modulation scheme, referred to as the differential space-code modulation (DSCM), which is interference resistant. Our focus is on single-user communications. We show that DSCM outperforms DSTM significantly when interference is present. This advantage is achieved at the cost of a lower data rate or a wider bandwidth or a combination of both. To alleviate this problem, a high-rate DSCM (HR-DSCM) scheme is also presented, which increases the data rate considerably at the cost of a slightly higher bit-error rate (BER), while still maintaining the interference suppression capability.
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| 4. |
- Liu, Jianhua, et al.
(författare)
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High-rate differential space-code modulation for interference suppression
- 2001
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Ingår i: 2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings. - 0780367200 ; , s. 283-286
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Konferensbidrag (refereegranskat)abstract
- Space-time coding has been receiving much research attention recently due to the potential offered by fully exploiting spatial and temporal diversity. A differential space-time modulation (DSTM) scheme was recently proposed to perform demodulation without channel state information, which is attractive in fast fading channels where accurate channel estimates are difficult to obtain. More recently, a differential space-code modulation (DSCM) scheme, which is an improvement of DSTM for combating interference (including intentional and unintentional jamming) signals, was proposed. DSCM significantly outperforms DSTM when interference is present. This advantage, however, is achieved at the cost of a lower transmission rate, a wider bandwidth, or a combination of both. To alleviate this problem, we extend DSCM to a so-called high-rate DSCM (HR-DSCM) scheme, which increases the data rate considerably at the cost of a slightly higher bit error rate, while still maintaining the interference suppression capability.
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| 5. |
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| 6. |
- Larsson, Erik G., et al.
(författare)
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Amplitude spectrum estimation for two-dimensional gapped data
- 2002
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 50:6, s. 1343-1354
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Tidskriftsartikel (refereegranskat)abstract
- The amplitude and phase estimation (APES) approach to nonparametric spectrum estimation of uniformly sampled data has received considerable interest. We consider the extension of APES to gapped data, i.e., uniformly sampled data with missing samples. It has been shown that the APES estimate of the spectrum is the minimizer of a certain least-squares (LS) criterion, and our extension of APES is based on minimizing this LS criterion with respect to the missing data as well. A computationally efficient method for doing this based on cyclic minimization and the conjugate gradient algorithm is proposed. The new algorithm is called gapped-data APES (GAPES) and is developed for the two-dimensional (2-D) case, with the one-dimensional (1-D) case as a special instance. Numerical examples are provided to demonstrate the performance of the algorithm and to show the advantages of 2-D data processing over 1-D (row or column-wise) data processing, as well as to show the applicability of the algorithm to synthetic aperture radar (SAR) imaging.
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| 7. |
- Larsson, Erik G., et al.
(författare)
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An algorithm for joint symbol timing and channel estimation for OFDM systems
- 2001
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Ingår i: Proc. of IEEE Workshop on Statistical Signal Processing. 2001. - 0780370112 ; , s. 393-396
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of joint synchronization and channel estimation for orthogonal frequency division multiplexing (OFDM) systems. A new algorithm is proposed that estimates the channel and symbol timing simultaneously by using a technique based on maximum-likelihood (ML) theory and the generalized Akaike information criterion (GAIC). Finally, we demonstrate the performance of our algorithm by simulation results.
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| 8. |
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| 9. |
- Larsson, Erik G., et al.
(författare)
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High-resolution SAR imaging with angular diversity
- 2001
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Ingår i: IEEE Transactions on Aerospace and Electronic Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9251 .- 1557-9603 .- 2371-9877. ; 37:4, s. 1359-1372
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Tidskriftsartikel (refereegranskat)abstract
- We propose to use the APES (amplitude and phase estimation) approach for the spectral estimation of gapped data and synthetic aperture radar (SAR) imaging with angular diversity. A relaxation-based algorithm, referred to as GAPES (Gapped-data APES), is proposed, which includes estimating the spectrum via APES and filling in the gaps via a least squares (LS) fitting. For SAR imaging with angular diversity data fusion, we perform one-dimensional (1-D) windowed fast Fourier transforms (FFTs) in range, use the GAPES algorithm to interpolate the gaps in the aperture for each range, apply 1-D inverse FFTs (IFFTs) and dewindow in range, and finally apply the two-dimensional (2-D) APES algorithm to the interpolated matrix to obtain the 2-D SAR image. Numerical results are presented to demonstrate the effectiveness of the proposed algorithm.
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| 10. |
- Larsson, Erik G., et al.
(författare)
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Joint symbol timing and channel estimation for OFDM based WLANs
- 2001
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558 .- 2373-7891. ; 5:8, s. 325-327
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Tidskriftsartikel (refereegranskat)abstract
- The orthogonal frequency-division multiplexing access technique has been attracting considerable interest especially for wireless local area networks (WLANs). We consider the joint estimation of the symbol timing, the channel length and the channel-impulse response. A novel estimation algorithm based on maximum-likelihood principles and the generalized Akaike information criterion are proposed. We provide simulation results to illustrate the performance of our proposed algorithm.
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