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| 2. |
- Janssen, Gerard J. M., et al.
(författare)
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Antenna Diversity for a Narrow-band successive-Cancellation Multiuser Detector
- 2004
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Ingår i: IEEE Transactions on Vehicular Technology. - New York : IEEE. - 0018-9545 .- 1939-9359. ; 53:5, s. 1303-1315
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a successive-cancellation multiuser detector (SC-MUD) for narrow-band signals operating in the Rayleigh-fading channel is shown to deteriorate severely unless very large power margins at the receiver are maintained. To mitigate this deterioration, antenna diversity is applied and adapted to the SC-MUD. In each detection stage, the best signal for detection and the corresponding combining weights are determined jointly. Two criteria for selecting the best signal based on maximizing the signal-to-noise-plus-interference ratio and maximizing the minimum distance-to-noise ratio, respectively, are proposed and evaluated. For signal combining, zero forcing and minimum mean square error (mmse) combining are considered. The obtained results show that the SC-MUD with mmse combining performs close to maximum likelihood joint detection while keeping a much lower computational complexity when the number of users is less than the number of receive antennas. The effect of channel-estimation errors is investigated for orthogonal training sequences and shown to result in a minor degradation compared to perfect estimation.
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| 3. |
- Larsson, Erik G., et al.
(författare)
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On a Decoupled Approach to Adaptive Signal Separation Using an Antenna Array
- 2002
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 51:6, s. 1681-1685
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Tidskriftsartikel (refereegranskat)abstract
- A recent paper by Ranheim considered the problem of separating signal sources using an array of sensors. A main algebraic result in that paper states that a certain noise covariance matrix can be replaced in a weighted least squares criterion by the sample version of the data covariancematrix without changing the asymptotic properties of the signal estimates. As we demonstrate in this paper, this result appears to be flawed in the general case. However, despite this fact, we also demonstrate that the method in Ranheim’s paper is statistically sound under fairly weak conditions. Since it is also computationally attractive, we believe that it can be useful in practical applications.
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| 4. |
- Nordberg, Jörgen, et al.
(författare)
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Performance Improvements for Sector Antennas using Feature Extraction and Spatial Interference Cancellation
- 2002
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Ingår i: IEEE Transactions on Vehicular Technology. - : IEEE. - 0018-9545 .- 1939-9359. ; 51:6, s. 1685-89
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Tidskriftsartikel (refereegranskat)abstract
- Effective utilization of the spatial domain enhances the capacity of a mobile radio network. A common technique is to use sector antennas, where the sectors are formed by weighting the outputs from the antenna elements. This results in spatial domain selectivity, which significantly improves the signal-to-noise and interference ratio in the received signals. However, the operation of the sector antenna will be limited by the sidelobes of the corresponding beam patterns. By introducing a blind spatial interference canceler that combines the fix beamformers in the sector antenna with blind signal separation, a significant improvement in the multi-user interference suppression can be achieved. Thus, it will be able to efficiently handle the near-far problem, where the users are received with different power. The blind signal separation is performed by an independent component analysis algorithm. The convergence rate of the algorithm is significantly improved compared to the standard formulation by taking into account the modulation format. The algorithm is further improved by introducing a forgetting factor on the weight update. The blind spatial interference canceler is evaluated by simulations using the mean square error and the bit error rate as quality measures. The results show that the mean square error obtained from the blind blind spatial interference canceler is within 0.5 dB from the optimum Wiener solution for signal-to noise ratios greather than 0 dB.
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| 5. |
- Nordebo, Sven, et al.
(författare)
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On the Use of Remes exchange algorithm for General Specifications
- 2000
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Ingår i: IEEE Transactions on Education. - New York : IEEE. - 0018-9359. ; 43:4, s. 460-3
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Tidskriftsartikel (refereegranskat)abstract
- The celebrated Remes multiple exchange algorithm for linear-phase digital FIR filter design is most commonly described for ordinary filter types (low-pass, high-pass, etc.) where it is sufficient to consider only the magnitude of the error function. Convergence for general specifications will be guaranteed only when the sign of the error function is incorporated. However, a discussion of this feature of the Remes algorithm is lacking in the literature on digital signal processing. The aim of this presentation is to fill in this gap by recasting the Remes exchange algorithm for the design of linear-phase finite-impulse response (FIR) filters with a general amplitude response specification
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| 6. |
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| 7. |
- Yu, Kai, et al.
(författare)
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Modeling of wide-band MIMO radio channels based on NLoS indoor measurements
- 2004
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 53:3, s. 655-665
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we first verify a previously proposed Kronecker-structure-based narrow-band model for nonline-of-sight (NLoS) indoor multiple-input-multiple-output (MIMO) radio channels based on 5.2-GHz indoor MIMO channel measurements. It is observed that, for the narrow-band case, the measured channel coefficients are complex Gaussian distributed and, consequently, we focus on a statistical description using the first- and second-order moments of MIMO radio channels. It is shown that the MIMO channel covariance matrix can be well approximated by the Kronecker product of the covariance matrices, seen from the transmitter and receiver, respectively. A narrow-band model for NLoS indoor MIMO channels is thus verified by these results. As for the wide-band case, it is observed that the average power-delay profile of each element of the channel impulse response matrix fits the exponential decay curve and that the Kronecker structure of the second-order moments can be extended to each channel tap. A wide-band MIMO channel model is then proposed, combining a simple COST 259 single-input-single-output channel model and the Kronecker structure. Monte Carlo simulations are used to generate indoor MIMO channel realizations according to the models discussed. The results are compared with the measured data using the channel capacity and good agreement is found.
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