11.
Edfors, Ove, et al.
(författare)
OFDM channel estimation by singular value decomposition
1998
Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 46:7, s. 931-939
Tidskriftsartikel (refereegranskat) abstract
We present and analyze low-rank channel estimators for orthogonal frequency-division multiplexing (OFDM) systems using the frequency correlation of the channel. Low-rank approximations based on the discrete Fourier transform (DFT) have been proposed, but these suffer from poor performance when the channel is not sample spaced. We apply the theory of optimal rank-reduction to linear minimum mean-squared error (LMMSE) estimators and show that these estimators, when using a fixed design, are robust to changes in channel correlation and signal-to-noise ratio (SNR). The performance is presented in terms of uncoded symbol-error rate (SER) for a system using 16-quadrature amplitude modulation (QAM).
12.
Eriksson, Håkan B., et al.
(författare)
A genie-aided detector with a probabilistic description of the side information
1995
Ingår i: Proceedings. - Piscataway, NJ : IEEE Communications Society. - 0780324536 ; , s. 332-
Konferensbidrag (refereegranskat) abstract
Building on Forney's concept of the genie (1972), and introducing the idea of an explicit statistical description of the side information provided to the genie-aided detector, we develop a generic tool for derivation of lower bounds on the bit-error rate of any actual receiver. With this approach, the side information statistics become design parameters, which may be chosen to give the resulting bound a desired structure. To illustrate this, we choose statistics in order to obtain a special case: the lower bound derived by Mazo (1975). The statistical description of the side information makes the lower bounding a transparent application of Bayesian theory
13.
Eriksson, Håkan B., et al.
(författare)
Multiple-antenna reception and reduced-state Viterbi detection for block transmission systems
1995
Ingår i: Gateway to the 21st century : record. - Piscataway, NJ : IEEE Communications Society. - 0780329554 ; , s. 37-41
Konferensbidrag (refereegranskat) abstract
This paper presents a receiver structure employing multiple receiving antennas and reduced-state Viterbi detection. The presentation is couched in terms of matrices representing a discrete-time, symbol-sampled system with frequency-selective, slow fading and additive Gaussian noise. The receiver design involves determining two matrices: one matrix defining the metric of the reduced-state Viterbi detector and one representing a pre-processor operating on the output from a maximal-ratio combiner. The presented receiver is a generalization of those used earlier in single-antenna, combined linear-Viterbi equalizers for continuous transmission systems. Performance comparisons are made with the minimum mean-square error (MMSE) linear equalizer and the MMSE decision-feedback equalizer for block transmission systems, indicating that the presented class of receivers offers superior performance
14.
Jakobsson, Andreas
(författare)
Model-based and matched-filterbank signal analysis
1999
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The dissertation deals with model-based and matched-filterbank signal analysis. The matched-filterbank (MAFI) spectral estimation approach is introduced, and it is shown that both the amplitude spectrum Capon (ASC) and the amplitude and phase estimation (APES) spectral estimators can be expressed as MAFI spectral estimators. A combined estimation procedure for data with mixed spectrum is introduced, as well as ASC and APES implementations for real-valued data. Computationally efficient implementations of the 2-D power spectrum Capon (PSC) and the 1-D and 2-D ASC are proposed. An asymptotic Cramér-Rao bound for line-spectra estimation is derived. It is shown that the non-linear least squares method (NLSM) will asymptotically achieve the same statistical performance as the maximum likelihood method (MLM) even in the colored noise case. Sufficient conditions for identifiability are derived for known and unknown waveforms received through a multipath channel. Statistically efficient subspace-based estimators for the estimation of the time-delay and Doppler parameters are presented.
15.
Landström, Daniel, et al.
(författare)
Symbol time offset estimation in coherent OFDM systems
1999
Ingår i: IEEE International Conference on Communications. - Piscataway, NJ : IEEE Communications Society. - 078035284X ; , s. 500-505
Konferensbidrag (refereegranskat) abstract
This paper presents a symbol time offset estimator for coherent OFDM systems. This estimator exploits both the redundancy in the cyclic prefix and the pilot symbols used for channel estimation. The estimator is robust against frequency offsets and is suitable for use in dispersive channels. We base the estimator on the ML estimator for the AWGN channel. Simulations of an example system indicate a system performance as close as 0.3 dB to a perfectly synchronized system. Compared to an estimator not using pilots, our estimator's performance could allow a shorter cyclic prefix and thus a more spectrally efficient system.
16.
Landström, Daniel, et al.
(författare)
Time and frequency offset estimation in OFDM systems employing pulse shaping
1997
Ingår i: Bridging the way to the 21st century. - Piscataway, NJ : IEEE Communications Society. - 0780337778 ; , s. 279-283, s. 279-283
Konferensbidrag (refereegranskat) abstract
Time and frequency offset estimation is addressed in an OFDM system that uses a cyclic prefix and pulse shaping. Earlier work has presented a method that avoids the use of pilots by exploiting the inherent correlation in the cyclically extended OFDM symbol. In this paper this technique is extended to include systems with pulse shaping. The joint Maximum Likelihood estimator of time and frequency offsets for such systems is presented and evaluated. An implementable structure of the extended estimator is given. Simulations show that it is possible to maintain the performance when introducing pulse shaping into an OFDM system.
17.
Nilsson, Rickard, et al.
(författare)
A low complexity threshold detector making MLSD decisions in a multiuser environment
1998
Ingår i: Pathway to a global wireless revolution. - Piscataway, NJ : IEEE Communications Society. - 0780343204 ; , s. 333-337
Konferensbidrag (refereegranskat) abstract
In this paper we present a pipelined implementation of an iterative threshold detector, which makes the same decisions as a maximum likelihood sequence detector (MLSD) on some, but not necessarily all, bits. We apply this as a first stage detector in a direct sequence code division multiple access (DS-CDMA) interference-limited multiuser system. In combination with the single-user matched filter (MF) detector we obtain improved performance and lower complexity than with the decorrelating receiver for a limited number of simultaneous users, e.g. up to 25 users with a spreading factor of 127.
18.
Nilsson, Rickard, et al.
(författare)
An analysis of two-dimensional pilot-symbol assisted modulation for OFDM
1997
Ingår i: 1997 IEEE International Conference on Personal Wireless Communications, Mumbai, India, December 17 - 19, 1997. - Piscataway, NJ : IEEE Communications Society. - 0780342984 ; , s. 71-74
Konferensbidrag (refereegranskat) abstract
In this paper we analyze two-dimensional (2D) pilot-symbol assisted modulation (PSAM) for wireless orthogonal frequency-division multiplexing (OFDM). 2D-PSAM has been suggested for wireless OFDM by several authors and is included in a preliminary draft of the standard for European digital video broadcast. We generalize the analysis of single-carrier PSAM to the 2D time-frequency lattice of OFDM. We analyze 2D-PSAM for two different channel estimators: one with good performance and high complexity and one suboptimal with low complexity. We verify that a good rule of thumb is to place the pilots at least as twice as close, in time and frequency, as required by the 2D sampling theorem.
19.
Sandell, Magnus, et al.
(författare)
Performance analysis of coded OFDM on fading channels with non-ideal interleaving and channel knowledge
1997
Ingår i: Technology in motion. - Piscataway, NJ : IEEE Communications Society. - 0780336593 ; 3, s. 1380-1384
Konferensbidrag (refereegranskat) abstract
In this paper we investigate the coded bit-error rate (BER) in an orthogonal frequency-division multiplexing (OFDM) system in a Rayleigh-fading channel. The system uses a pilot-based channel estimator and the effects of non-ideal channel knowledge and non-ideal interleaving are analysed. The coded BER is estimated with an analytical method proposed by Cavers and Ho, which involves truncation of the union bound. For channels with several propagation paths the estimated BER agrees well with simulations. The transfer function bound may however in some cases diverge, thus reducing the accuracy of the estimated BER. We show that this can be the case for channels with few propagation paths.
20.
Sjöberg, Frank, et al.
(författare)
Asynchronous Zipper : [subscriber line duplex method]
1999
Ingår i: IEEE International Conference on Communications. - Piscataway, Nj : IEEE Communications Society. - 078035284X ; , s. 231-235
Konferensbidrag (refereegranskat) abstract
Previously the authors presented a novel duplex method for very high bit-rate digital subscriber lines (VDSL) called Zipper. With this method all VDSL-modems on different wires in the same bindergroup have to be time-synchronized to avoid near-end cross-talk (NEXT). We describe a method which enables Zipper to run in a time-asynchronous mode. By introducing pulse-shaping in the transmitter and windowing in the receiver the NEXT is almost completely suppressed even though the synchronization between modems on neighboring lines is skipped. The remaining NEXT and efficiency loss due to pulse-shaping and windowing results in only a small bit-rate performance loss, typically less than 10% compared to the time-synchronized Zipper. However, with the new freedom of optimizing the lengths of the cyclic suffices with asynchronous Zipper, there may even be a small improvement in bit-rate performance for short wires
