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| 2. |
- Gustafsson, Ronnie, et al.
(författare)
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A Block Based Eigenvector Equalization for Time : Varying Channels
- 2002
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Konferensbidrag (refereegranskat)abstract
- In this paper we investigate the EigenVector Algorithm for Blind Equalization (EVA), and extend its application to the equalization of time-varying fading channels. The modified iterative algorithm, termed Block-Based EVA (BBEVA), is evaluated in terms of ISI suppression, MSE and by examining the signal constellation at the output of the equalizer. Simulation results show that the BBEVA performs better than the non-blind Least Mean Squares (LMS) algorithm.
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| 3. |
- Gustafsson, Ronnie, et al.
(författare)
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A Combined Channel Estimation Algorithm for Coherent Detection in Mobile Communication Systems
- 2002
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a coherent detection method that can reduce the estimation errors of the carrier phase resulting from Gaussian noise in communication systems where pilot symbol-assisted equalization is employed to compensate for fading distortion. The proposed approach is to use a combined algorithm consisting of the conventional feed-forward channel estimation and decision feedback channel estimation. Simulation results show that the proposed algorithm provides better performance than the conventional fading channel estimation approach.
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| 4. |
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| 5. |
- Gustafsson, Ronnie, et al.
(författare)
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Simulation of Wireless Fading Channels
- 2003
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Rapport (refereegranskat)abstract
- Future services in wireless communications will increase the need for high bit rates in the system because of the use of ``wideband'' contents such as streaming video and audio. For example, there might be services where the users can download movies to the car theatre system, or where a user can react to the doorbell ringing even though he or she is miles away from home. It will be possible to run business software remotely using mobile devices, removing the need for ``dumb down'' software in the terminal devices. Also, users might want to be able to seamlessly roam between different air interfaces or standards using the same device. Some basic services are already implemented in the existing 2G systems such as GSM or IS-136, more services are planned for the new 3G systems and other advanced features have to wait until 2011 when 4G is scheduled for release. The demands for higher bit rates combined with the ever-increasing number of users, however, introduces the need for clever and efficient usage of the limited resource of the wireless channel. Two major impediments to high-performance wireless communication systems are intersymbol interference (ISI) and cochannel interference (CCI). ISI is caused by the frequency selectivity (time dispersion) of the channel due to multipath propagation and CCI is due to cellular frequency reuse. Equalizers can be used to compensate for ISI and CCI can be reduced by the use of adaptive antenna arrays (also known as "smart antennas"). The smart antenna utilizes an array of antenna elements that provide directional (spatial) information about the received signals. Since the desired signal and unwanted cochannel interferers generally arrive from different directions, an adaptive beamforming algorithm can adjust the spatial gain to enhance the desired signal and mitigate the cochannel interferers. In this Report we discuss the basic propagation mechanisms affecting the performance of wireless communication systems. We also present the implementation of a simulator which takes these mechanisms into account and verifies its performance for different channels. We also introduce basic equalization and beamforming concepts. Finally, we evaluate the recursive least squares (RLS) equalizer and receiver structures and assess their performance in combating the destructive effects of the channel.
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| 6. |
- Gustafsson, Ronnie, et al.
(författare)
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Simulation of Wireless Fading Channels using Matlab
- 2003
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Konferensbidrag (refereegranskat)abstract
- Future services in wireless communications will increase the need for high bit rates in the system because of the use of "wideband" contents such as streaming video and audio. There might for example be services where the users can download movies to the car theatre system. The demands for higher bit rates combined with the ever-increasing number of users, however, introduces the need for clever and efficient usage of the limited resource of the wireless channel, by the use of properly designed transceivers. Simulations may be employed to investigate the performance of such transceivers in a cost effective way. In this paper, we discuss the basic propagation mechanisms affecting the performance of a wireless communication system and give hints and tips of how to implement these mechanisms in a simulator using Matlab.
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| 7. |
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| 8. |
- Hult, Tommy, et al.
(författare)
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Active Suppression of Electromagnetic Fields Using a MIMO Antenna System
- 2003
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Konferensbidrag (refereegranskat)abstract
- Active suppression of noise and vibrations is a well established field of research with many applications in acoustic and mechanical industries. In this paper we test some of these active control methods in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated is a model of a mobile telephone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to cancel out the electromagnetic field at a specific point in space (e.g. at your head).
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| 9. |
- Hult, Tommy, et al.
(författare)
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Estimation of the TOA performance of Loran-C
- 2004
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Konferensbidrag (refereegranskat)abstract
- Loran-C is a navigational aid that relies on the ability to make correct estimates of the Times of Arrival (TOAs) of signals received over a noisy radio channel. How good is the performance of Loran-C in this respect? Is it close to optimal? Are there perhaps better estimation techniques available than we currently employ? In this paper we use Estimation Theory to find the optimal limit of the accuracy of TOA estimates, for a given signal-to-noise ratio (SNR). Specifically, we compute the Cramer-Rao Lower Bound (CRLB) which specifies the absolute minimum error variance that can be achieved by an unbiased estimator. From the CRLB we can estimate the best repeatable accuracy that can be attained using a set of TOAs. We compute here the CRLBs for the TOA of a Loran-C signal with both Additive White Gaussian Noise (AWGN) and Additive Coloured Gaussian Noise (ACGN). We then employ the Maximum Likelihood Estimator (MLE) and compare its results with that of CRLB. Simulation results show that the MLE approaches the minimum variance obtained by CRLB for SNR values of practical and reliable Loran-C operation.
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| 10. |
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