Link adaptation in LTE-A uplink with Turbo SIC receivers and imperfect channel estimation.
ABSTRACT In this paper, we propose an efficient link adaptation scheme for the 3GPP Long Term Evolution Advanced (LTEA) uplink with turbo successive interference cancelation (Turbo-SIC) receiver and imperfect channel estimation. Link adaptation for non-linear MIMO receivers such as Turbo SIC is not straightforward because the soft-outputs of such receiver cannot be simply modeled using a scalar Gaussian channel and the post-processing signal-to-interference-plus-noise ratio (SINR) does not have an explicit closed-form expression. In addition, the lack of perfect channel state information due to estimation errors imposes further uncertainty and challenges in the link adaptation design. To circumvent these difficulties, we propose a prediction method that can effectively characterize the Turbo SIC performance and derive an approximate post-detection SINR for each layer by considering the channel estimation error statistic. We particularly consider the link adaptation for precoded multi-rank MIMO transmission with both inter-codeword(CW) and intra-codeword(CW) interference cancelation. Realistic and extensive simulations reveal that the proposed link adaptation scheme accurately predicts the turbo SIC performance and results in highest spectrum efficiency and robustness compared to other competing schemes.
Conference Paper: Low-complexity methods for soft estimation of QAM Symbols[Show abstract] [Hide abstract]
ABSTRACT: In this paper, we develop low-complexity methods to compute the soft estimation of quadrature amplitude modulation (QAM) symbols with applications to iterative receivers. To reduce the complexity of the soft QAM estimation, we first consider squared QAM constellations and present a bit flipping based soft estimation scheme. With the gray mapping we derive an efficient approach which has a very low complexity of O(log N) for an NQAM constellation. To further simplify the approach, we propose a method which completely removes the multiplication operations at a cost of a slight performance degradation. Finally, we extend the proposed method to the non-squared QAM.Information Sciences and Systems (CISS), 2013 47th Annual Conference on; 01/2013
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ABSTRACT: In this paper, we develop low-complexity methods to compute the soft symbol and variance estimations for QAM constellations with applications to iterative MMSE-SIC receivers. In particular, we propose a bit flipping based estimation scheme. For an N-QAM constellation with Gray mapping, we derive efficient approaches for both soft symbol and variance estimations with the complexities of O(log N) and O(log2 N), respectively. We also present an improved approximation approach which completely removes the multiplications at a cost of a slight performance degradation. We later extend the proposed methods to the non-squared QAM.2013 Asilomar Conference on Signals, Systems and Computers; 11/2013