CiteULike: dcastro's blind

Blind estimation of symbol timing and carrier frequency offset in wireless OFDM systems

H Bolcskei — 2008-02-25T15:35:54-00:00

Communications, IEEE Transactions on, Vol. 49, No. 6. (2001), pp. 988-999.

Orthogonal frequency-division multiplexing (OFDM) systems are highly sensitive to synchronization errors. We introduce an algorithm for the blind estimation of symbol timing and carrier frequency offset in wireless OFDM systems. The proposed estimator is an extension of the Gini-Giannakis (see IEEE Trans. Commun., vol.46, p.400-411, 1998) estimator for single-carrier systems. It exploits the cyclostationarity of OFDM signals and relies on second-order statistics only. Our method can be applied to pulse shaping OFDM systems with arbitrary time-frequency guard regions, OFDM based on offset quadrature amplitude modulation, and biorthogonal frequency-division multiplexing systems. We furthermore propose the use of different subcarrier transmit powers (subcarrier weighting) and periodic transmitter precoding to achieve a carrier frequency acquisition range of the entire bandwidth of the OFDM signal, and a symbol timing acquisition range of arbitrary length. Finally, we provide simulation results demonstrating the performance of the new estimator

Blind fractionally-spaced equalization, perfect-reconstruction filter banks and multichannel linear prediction

DTM Slock — 2007-11-28T10:35:41-00:00

Acoustics, Speech, and Signal Processing, 1994. ICASSP-94., 1994 IEEE International Conference on, Vol. iv (1994), pp. IV/585-IV/588 vol.4.

Equalization for digital communications constitutes a very particular blind deconvolution problem in that the received signal is cyclostationary. Oversampling (OS) (w.r.t. the symbol rate) of the cyclostationary received signal leads to a stationary vector-valued signal (polyphase representation (PR)). OS also leads to a fractionally-spaced channel model and equalizer. In the PR, channel and equalizer can be considered as an analysis and synthesis filter bank. Zero-forcing (ZF) equalization corresponds to a perfect-reconstruction filter bank. We show that in the OS case FIR ZF equalizers exist for a FIR channel. In the PR, the multichannel linear prediction of the noiseless received signal becomes singular eventually, reminiscent of the single-channel prediction of a sum of sinusoids. As a result, the channel can be identified from the received signal second-order statistics by linear prediction in the noise-free case, and by using the Pisarenko method when there is additive noise. In the given data case, MUSIC (subspace) or ML techniques can be applied

OFDM blind carrier offset estimation: ESPRIT

U Tureli — 2007-11-28T10:35:10-00:00

Communications, IEEE Transactions on, Vol. 48, No. 9. (2000), pp. 1459-1461.

In orthogonal frequency-division multiplex (OFDM) communications, the loss of orthogonality due to the carrier-frequency offset must be compensated before discrete Fourier transform-based demodulation can be performed. This paper proposes a new carrier offset estimation technique for OFDM communications over a frequency-selective fading channel. We exploit the intrinsic structure information of OFDM signals to derive a carrier offset estimator that offers the accuracy of a super resolution subspace method, ESPRIT

Blind equalization and multiuser detection in dispersive CDMA channels

Xiaodong Wang — 2007-11-28T10:33:56-00:00

Communications, IEEE Transactions on, Vol. 46, No. 1. (1998), pp. 91-103.

The problem of blind demodulation of multiuser information symbols in a high-rate code-division multiple-access (CDMA) network in the presence of both multiple-access interference (MAI) and intersymbol interference (ISI) is considered. The dispersive CDMA channel is first cast into a multiple-input multiple-output (MIMO) signal model framework. By applying the theory of blind MIMO channel identification and equalization, it is then shown that under certain conditions the multiuser information symbols can be recovered without any prior knowledge of the channel or the users' signature waveforms (including the desired user's signature waveform), although the algorithmic complexity of such an approach is prohibitively high. However, in practice, the signature waveform of the user of interest is always available at the receiver. It is shown that by incorporating this knowledge, the impulse response of each user's dispersive channel can be identified using a subspace method. It is further shown that based on the identified signal subspace parameters and the channel response, two linear detectors that are capable of suppressing both MAI and ISI, i.e., a zero-forcing detector and a minimum-mean-square-error (MMSE) detector, can be constructed in closed form, at almost no extra computational cost. Data detection can then be furnished by applying these linear detectors (obtained blindly) to the received signal. The major contribution of this paper is the development of these subspace-based blind techniques for joint suppression of MAI and ISI in the dispersive CDMA channels

Blind estimation of multiple co-channel digital signals using an antenna array

S Talwar — 2007-11-28T10:29:31-00:00

Signal Processing Letters, IEEE, Vol. 1, No. 2. (1994), pp. 29-31.

Proposes a novel approach for separating and estimating multiple co-channel digital signals using an antenna array. The spatial response of the array is unknown. The authors exploit the temporal structure of the digital signals to simultaneously determine the array response and the bit sequence for each signal. Uniqueness of the estimates is established for signals with BPSK modulation format. This new approach is applicable to an unknown array geometry and propagation environment, which is particularly useful in digital mobile communications. Simulation results demonstrate its promising performance

Blind channel estimation for long code multiuser CDMA systems

Zhengyuan Xu — 2007-11-28T10:24:25-00:00

Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on], Vol. 48, No. 4. (2000), pp. 988-1001.

In CDMA systems with long codes, the users' signatures change in each bit period, impeding the estimation of the time-invariant multipath parameters. In this paper, correlation-matching methods are employed to blindly estimate those multipath parameters. For given code sequences, the output correlation matrix (parameterized by the unknown channel coefficients) is compared with its instantaneous approximation. By minimizing the Frobenius norm of the resulting error matrix, the channel parameters can be estimated up to a complex scalar ambiguity. Both batch and adaptive algorithms are derived. Under the assumption of i.i.d. code sequences, identifiability up to a complex scalar ambiguity for each channel is guaranteed, and the asymptotic convergence of the proposed algorithm is established. Furthermore, step-size selection for the adaptive version is investigated. When only the code sequence of the user of interest is available, a single user receiver is also derived. Simulation results verify those claims and provide comparisons with other methods

Blind modulation classification: a concept whose time has come

OA Dobre — 2007-11-14T10:20:14-00:00

Advances in Wired and Wireless Communication, 2005 IEEE/Sarnoff Symposium on (2005), pp. 223-228.

We address the problem of identifying the modulation format of an incoming signal. We review many existing techniques for digital modulation recognition in a systematic way, which helps the reader to see the main features of each technique. The goal is to provide useful guidelines for choosing appropriate classification algorithms for different modulations, from the large pool of available techniques. Furthermore, the performance of a benchmark classifier is presented, as well as its sensitivity to several model mismatches. Open problems and possible directions for further research are briefly discussed

A blind OFDM synchronization algorithm based on cyclic correlation

Byungjoon Park — 2007-11-11T15:43:34-00:00

Global Telecommunications Conference, 2001. GLOBECOM '01. IEEE, Vol. 5 (2001), pp. 3116-3119 vol.5.

Blind synchronization algorithm is developed for estimating jointly timing and frequency offset of OFDM signals transmitted through a frequency-selective fading channel. The proposed estimator exploits the second-order cyclostationarity of received signals. As a blind estimator, the information of impulse response of channel is not required. The performance of the estimator is evaluated through computer simulations

Blind estimation of time and frequency offset for PCC-OFDM

J Shentu — 2007-11-11T15:25:06-00:00

Vehicular Technology Conference, 2001. VTC 2001 Spring. IEEE VTS 53rd, Vol. 1 (2001), pp. 702-706 vol.1.

This paper presents blind estimation methods for timing and frequency offset in polynomial cancellation coded orthogonal frequency division multiplexing (PCC-OFDM) systems. The estimations are carried out in the frequency domain. The correct timing point is calculated by maximizing a timing metric and the frequency offset estimate is obtained by using pairs of demodulated subcarriers at the fast Fourier transform (FFT) output. No training symbols, pilot tones or cyclic prefix extensions are required. The methods can also be used in OFDM, however a training symbol is required