| 1. |
- Dumard, Charlotte, et al.
(author)
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Multi-User MIMO Receiver Processing for Time-Varying Channels
- 2011
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In: Wireless Communications Over Rapidly Time-Varying Channels. - : Elsevier Academic Press. - 9780123744838 ; , s. 337-374
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Book chapter (other academic/artistic)abstract
- Wireless broadband communications for mobile users at vehicular speed is the cornerstone of future fourth-generation systems. This chapter deals with joint iterative channel estimation and multiuser detection for the uplink of a multicarrier (MC) code division multiple access (CDMA) system. MCCDMA is based on orthogonal frequency division multiplexing (OFDM) and employs spreading sequences in the frequency domain. Several complexity reduction methods are discussed enabling a real-world low-complexity implementation, such as an iterative approximation of the maximum a posteriori (MAP) detector in combination with a reduced-rank model for the time-varying channel. This reduced-rank channel model projects the time-varying channel onto a subspace spanned by band-limited and time-concentrated prolate spheroidal sequences. Two different multiuser detection methods are investigated: First, the Krylov subspace method is used to reduce the complexity of multiuser detection using LMMSE filtering. Second, sphere decoding is investigated and a sphere decoder is developed that exploits the reduced-rank channel model for complexity reduction.
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| 2. |
- Durisi, Giuseppe, 1977, et al.
(author)
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Information Theory of underspread WSSUS channels
- 2011
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In: Wireless Communications over Rapidly Time-Varying Channels. - 9780123744838 ; , s. 65--115-
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Book chapter (other academic/artistic)abstract
- The chapter focuses on the ultimate limit on the rate of reliable communication through Rayleigh-fading channels that satisfy the wide-sense stationary (WSS) and uncorrelated scattering (US) assumptions and are underspread. Therefore, the natural setting is an information-theoretic one, and the performance metric is channel capacity. The family of Rayleigh-fading underspread WSSUS channels constitutes a good model for real-world wireless channels: their stochastic properties, like amplitude and phase distributions match channel measurement results. The Rayleigh-fading and the WSSUS assumptions imply that the stochastic properties of the channel are fully described by a two-dimensional power spectral density (PSD) function, often referred to as scattering function. The underspread assumption implies that the scattering function is highly concentrated in the delay-Doppler plane. Two important aspects need to be accounted for by a model that aims at being realistic: neither the transmitter nor the receiver knows the realization of the channel; and the peak power of the transmit signal is limited. Based on these two aspects the chapter provides an information-theoretic analysis of Rayleigh-fading underspread WSSUS channels in the noncoherent setting, under the additional assumption that the transmit signal is peak-constrained.
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