| 1. |
- Björnson, Emil, 1983-, et al.
(author)
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Beamforming utilizing channel norm feedback in multiuser MIMO systems
- 2007
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In: IEEE Workshop on Signal Processing Advances in Wireless Communications. - : IEEE. - 9781424409556 ; , s. 1-5
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Conference paper (peer-reviewed)abstract
- The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the largest norm to the transmitter and derive the conditional second and fourth order channel moments in order to design the downlink beamforming weights. Similar approaches have previously been presented for multi-user multiple-input single-output (MISO) systems. Herein, these techniques are generalized to MIMO systems, by either antenna selection or receive beamforming at the receiver. Two eigenbeamforming strategies are proposed and shown to outperform opportunistic beamforming, based on similar feedback information.
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| 2. |
- Jorswieck, Eduard A., et al.
(author)
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Multiuser gaussianity and constellation randomization for the MIMO multiple access channel : A unified view
- 2007
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In: 2007 IEEE 8th Workshop On Signal Processing Advances In Wireless Communications, Vols 1 And 2. - : IEEE. - 9781424409549 - 9781424409556 ; , s. 126-130
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Conference paper (peer-reviewed)abstract
- In recent analyses of multiuser MIMO systems and their capacity achieving transmit strategies, Gaussian codebooks; are usually used. For the case in which the input signals are constrained to belong to a finite constellation, we study and explain two effects, namely Multiuser Gaussianity (MuG) and constellation randomization (CoRa). MuG means that the more users transmit simultaneously, the higher is the similarity of the received density to the optimal Gaussian one. Hence, the instantaneous mutual information is increased by MuG. This leads to a tradeoff between multiuser diversity and MuG. On the other hand, CoRa is done by linear precoding by random unitary matrices. Based on the observations from MuG, we explain why the outage capacity is increased by CoRa. The effects are illustrated by various numerical simulations.
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| 3. |
- Nasiri Khormuji, Majid, et al.
(author)
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Analytical results on block length optimization for decode-and-forward relaying with CSI feedback
- 2007
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In: 2007 IEEE 8th Workshop on Signal Processing Advances in Wireless Communications. - : IEEE. - 9781424409549 - 9781424409556 ; , s. 96-100
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Conference paper (peer-reviewed)abstract
- We consider block length optimization for collaborative transmit diversity using a decode-and-forward protocol assuming that the source and the relay have access to the magnitudes of all path gains. Moreover, we propose a simple scheme which requires only one bit of channel state information (CSI) feedback. We analyze the outage probabilities of all schemes for both selection combining and maximum ratio combining (MRC) at the destination. Analytical results show that even one bit of CSI feedback can provide a significant gain over conventional (non-adaptive) collaborative schemes.
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| 4. |
- Pääjärvi, Patrik, et al.
(author)
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Blind equalization of PPM signals using third-order moments
- 2007
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In: 2007 IEEE 8th Workshop on Signal Processing Advances in Wireless Communications. - Piscataway, NJ : IEEE Communications Society. - 9781424409556
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Conference paper (peer-reviewed)abstract
- In pulse-position modulation (PPM) signaling, the time location of short-duration pulses are used to convey information over a communication channel. For successful noncoherent reception, the channel duration must be short compared to the symbol interval. This paper analyzes the use of third moments in a blind adaptive equalizer setting to limit the effective delay spread of the channel. Results detail the global convergence properties of the proposed method, showing that the parameters approach ISI-free settings under general conditions.
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| 5. |
- Thobaben, Ragnar
(author)
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A new transmitter concept for iteratively-decoded source-channel coding schemes
- 2007
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In: 2007 IEEE 8TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS. - NEW YORK : IEEE. - 9781424409556 ; , s. 480-484
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Conference paper (peer-reviewed)abstract
- We address the optimization of joint source-channel coding schemes for iterative source-channel decoding (ISCD) of first-order Markov sources. The optimization requires source encoders, providing code words with a minimum Hamming distance d(min) >= 2. Usually, specifically designed variable-length codes (VLCs) are applied for this purpose, leading, however, to an increased complexity of the decoder. In this paper, we propose a novel concept: a single parity-check code is employed for mapping the quantized source symbols to a binary representation. The additional redundancy introduced by this mapping is afterwards compensated by an inner channel code with rate R > 1. Simulation results for the AWGN channel show that the proposed scheme is superior to VLC-based approaches, while leading to a significantly reduced complexity at the same time.
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