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| 2. |
- Almers, Peter, et al.
(författare)
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Measured capacity gain using waterfilling in frequency selective MIMO channels
- 2002
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Ingår i: The 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2002 , vol 1-5, Proceedings. - 0780375890 ; , s. 1347-1351
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Konferensbidrag (refereegranskat)abstract
- We analyze the channel capacity of multiple-input multiple-output (MIMO) systems in frequcncy selective channels, with channel knowledge at the transmitter side. An optimum transmission scheme uses Shannon's principle of waterfilling jointly in the frequency and the spatial domain. However, we show in this paper that the largest gain by using waterfilling resides in the spatial domain, and that the capacity gain from the frequency domain is very small for MIMO systems. We quantify the gain for a theoretical Rayleigh fading channel model and for microcellular channels as measured in an enclosed court-yard.
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| 3. |
- Edfors, Ove, et al.
(författare)
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Analysis of DFT-Based Channel Estimators for OFDM
- 2000
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Ingår i: Wireless personal communications. - 0929-6212 .- 1572-834X. ; 12:1, s. 55-70
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we analyze the performance of three low-complexity channel estimators, based on the discrete Fourier transform (DFT), for orthogonal frequency-division multiplexing (OFDM) systems. Estimators of this type have been analyzed for discrete-time channels, and we extend this analysis to continuous-time channels. We present analytical expressions for their mean-squared error (MSE) and evaluate their complexity vs. symbol-error rate (SER) for 16-QAM. The analysis shows that this type of estimators may experience an irreducible error floor at high SNRs. However, in one of the three estimators the error floor can be eliminated while the complexity stays low and the performance is maximized.
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| 4. |
- Fernández-Getino Garcia, Maria Julia, et al.
(författare)
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Frequency Offset Correction for Coherent OFDM In Wireless Systems
- 2001
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Ingår i: IEEE Transactions on Consumer Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0098-3063. ; 47:1, s. 187-193
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a new frequency offset correction approach for OFDM is proposed to track a wider range of offsets than conventional proposals, without devoting specific pilot symbols for synchronization. This can be attained since, in coherent OFDM, channel estimation is usually performed employing pilot-symbol assisted-modulation (PSAM), based on inserting known symbols in the time-frequency grid. We show how this two-dimensional embedded signalling can also be used for frequency synchronization, with no need of additional synchronization symbols which reduce the data-rate. The ML estimator has been derived, but also, a frequency-domain low-complex estimator has been proposed, based on only the samples at pilot positions. Additionally, a novel decision-guided strategy is presented, working jointly with the channel-estimation signalling and reducing the variance of the estimation considerably. Also, the stability of the scheme is shown to get significantly better by averaging over a few OFDM symbols. This estimator is efficient against AWGN and multipath fading channels. Simulation results demonstrate that the presented frequency offset correction scheme provides the accuracy required in practical applications for OFDM wireless systems
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| 5. |
- Fernández-Getino Garcia, Maria Julia, et al.
(författare)
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Joint 2D-pilot-symbol-assisted-modulation and decision-directed frequency synchronization schemes for coherent OFDM
- 2000
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Ingår i: Proc. IEEE Acoustics, Speech, and Signal Processing Conference. - 0780362934 ; 5, s. 2961-2964
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Konferensbidrag (refereegranskat)abstract
- A new frequency offset tracking approach for OFDM has been addressed. Two-dimensional pilot-symbol assisted modulation (2D-PSAM) is employed in coherent OFDM for channel estimation and it is based on inserting known symbols spread out through the 2D time-frequency grid. We show that these scattered symbols can also be employed to perform frequency synchronization. Maximum likelihood estimation has been derived for both time and frequency domains. Also, if a decision-guided strategy is used jointly with the 2D-PSAM signalling, an improvement in performance can be attained
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| 6. |
- Fernández-Getino Garcia, Maria Julia, et al.
(författare)
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Joint channel estimation and peak-to-average power reduction in coherent OFDM: a novel approach
- 2001
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Ingår i: Proc. IEEE Vehicular Technology Conference. - 0780367286 ; 2, s. 815-819
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Konferensbidrag (refereegranskat)abstract
- A new peak-to-average power reduction approach for OFDM has been addressed. Two-dimensional pilot-symbol assisted modulation (2D-PSAM) is employed in coherent OFDM for channel estimation and it is based on inserting known symbols spreaded out throughout the 2D time-frequency grid. We show that these scattered symbols can also be employed to perform distortionless peak power reduction, with a negligible loss in data-rate. To reduce additional system complexity and side information, several suboptimal strategies are proposed. A comparison between the two schemes with different approaches to the joint design of pilot symbols for both channel estimation and peak power reduction, has also been carried out
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| 7. |
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| 8. |
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| 9. |
- Florén, Fredrik, et al.
(författare)
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The Effect of Feedback Quantization on the Throughput of a Multiuser Diversity Scheme
- 2003
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Ingår i: Conference Record / IEEE Global Telecommunications Conference. ; 1, s. 497-501
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Konferensbidrag (refereegranskat)abstract
- The impact of the quantization of SNR measurements on the throughput of a multiuser diversity scheme for constant-rate transmission is investigated under a block-Rayleigh fading assumption. In the downlink, each user measures its SNR, quantizes it, and feeds it back to the transmitter, which transmits a packet to the user with the highest quantized SNR. In the case of several users having the same quantized SNR, one of them is selected at random. It is concluded that using only a few quantization levels can yield a throughput that is only slightly less than the throughput obtained by using unquantized feedback.
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| 10. |
- Florén, Fredrik, et al.
(författare)
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Throughput analysis of strongly interfering slow frequency-hopping wireless networks
- 2001
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Ingår i: Proc. IEEE Vehicular Technology Conference. - 0780367286 ; 1, s. 496-500
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Konferensbidrag (refereegranskat)abstract
- We derive an approximation for the throughput of strongly interfering frequency-hopping wireless networks, where packet collisions always result in lost data. A system is defined to consist of a certain number of radio networks, each with an arbitrary number of communicating units, coordinated to communicate without interference. Using the approximation, we estimate upper and lower bounds on system throughput, as well as the number of networks which gives maximum system throughput
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