Abstract
Modern wireless communication systems require high transmission rates, giving rise to frequency selectivity due to multipath propagation. In addition, high-mobility terminals and scatterers induce Doppler shifts that introduce time selectivity. Therefore, advanced techniques are needed to accurately model the time- and frequency-selective (i.e., doubly selective) channels and to counteract the related performance degradation. In this paper, we develop new receivers for orthogonal frequency-division multiplexing (OFDM) systems and single-carrier (SC) systems in doubly selective channels by embedding the channel estimation task within low-complexity block turbo equalizers. Linear minimum mean-squared error (MMSE) pilot-assisted channel estimators are presented, and the soft data estimates from the turbo equalizers are used to improve the quality of the channel estimates.
Highlights
Broadband wireless communication systems require high transmission rates, giving rise to frequency selectivity caused by multipath propagation, and to intersymbol interference (ISI)
The Long-Term Evolution (LTE) physical layer relies on a multipleaccess scheme based on orthogonal frequency-division multiplexing (OFDM) in the downlink, and on single-carrier frequency-division multiple access (SC-FDMA) in the uplink [3]
OFDM and single-carrier (SC) block transmissions share some similarities: since an SC system can be viewed as a discrete Fourier transform (DFT) precoded OFDM system [4], performance and complexity are comparable, but part of the complexity is moved from the transmitter to the receiver [4]
Summary
Broadband wireless communication systems require high transmission rates, giving rise to frequency selectivity caused by multipath propagation, and to intersymbol interference (ISI). To the best of our knowledge, all the turbo equalizers proposed so far for SC systems over doubly selective channels employ a serialwise data processing, that is, use a sliding window either in the time domain [14] or in the frequency domain [15, 17]. From the turbo-based channel estimators already proposed for SC transmissions over doubly selective channels [25, 26], the proposed turbo-like channel estimators are nonadaptive and more suitable for block transmissions For both OFDM and SC cases, the proposed iterative channel estimators firstly estimate the time-domain channel exploiting the BEM, and transform the time-domain channel into the frequency domain for equalization purposes. 0M×N and IN denote the M × N all-zero matrix and the N × N identity matrix, respectively
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