325 research outputs found
Compressive sensing based Bayesian sparse channel estimation for OFDM communication systems: high performance and low complexity
In orthogonal frequency division modulation (OFDM) communication systems,
channel state information (CSI) is required at receiver due to the fact that
frequency-selective fading channel leads to disgusting inter-symbol
interference (ISI) over data transmission. Broadband channel model is often
described by very few dominant channel taps and they can be probed by
compressive sensing based sparse channel estimation (SCE) methods, e.g.,
orthogonal matching pursuit algorithm, which can take the advantage of sparse
structure effectively in the channel as for prior information. However, these
developed methods are vulnerable to both noise interference and column
coherence of training signal matrix. In other words, the primary objective of
these conventional methods is to catch the dominant channel taps without a
report of posterior channel uncertainty. To improve the estimation performance,
we proposed a compressive sensing based Bayesian sparse channel estimation
(BSCE) method which can not only exploit the channel sparsity but also mitigate
the unexpected channel uncertainty without scarifying any computational
complexity. The propose method can reveal potential ambiguity among multiple
channel estimators that are ambiguous due to observation noise or correlation
interference among columns in the training matrix. Computer simulations show
that propose method can improve the estimation performance when comparing with
conventional SCE methods.Comment: 24 pages,16 figures, submitted for a journa
Matrix Completion-Based Channel Estimation for MmWave Communication Systems With Array-Inherent Impairments
Hybrid massive MIMO structures with reduced hardware complexity and power
consumption have been widely studied as a potential candidate for millimeter
wave (mmWave) communications. Channel estimators that require knowledge of the
array response, such as those using compressive sensing (CS) methods, may
suffer from performance degradation when array-inherent impairments bring
unknown phase errors and gain errors to the antenna elements. In this paper, we
design matrix completion (MC)-based channel estimation schemes which are robust
against the array-inherent impairments. We first design an open-loop training
scheme that can sample entries from the effective channel matrix randomly and
is compatible with the phase shifter-based hybrid system. Leveraging the
low-rank property of the effective channel matrix, we then design a channel
estimator based on the generalized conditional gradient (GCG) framework and the
alternating minimization (AltMin) approach. The resulting estimator is immune
to array-inherent impairments and can be implemented to systems with any array
shapes for its independence of the array response. In addition, we extend our
design to sample a transformed channel matrix following the concept of
inductive matrix completion (IMC), which can be solved efficiently using our
proposed estimator and achieve similar performance with a lower requirement of
the dynamic range of the transmission power per antenna. Numerical results
demonstrate the advantages of our proposed MC-based channel estimators in terms
of estimation performance, computational complexity and robustness against
array-inherent impairments over the orthogonal matching pursuit (OMP)-based CS
channel estimator.Comment: This work has been submitted to the IEEE for possible publication.
Copyright may be transferred without notice, after which this version may no
longer be accessibl
Forward-Backward Greedy Algorithms for General Convex Smooth Functions over A Cardinality Constraint
We consider forward-backward greedy algorithms for solving sparse feature
selection problems with general convex smooth functions. A state-of-the-art
greedy method, the Forward-Backward greedy algorithm (FoBa-obj) requires to
solve a large number of optimization problems, thus it is not scalable for
large-size problems. The FoBa-gdt algorithm, which uses the gradient
information for feature selection at each forward iteration, significantly
improves the efficiency of FoBa-obj. In this paper, we systematically analyze
the theoretical properties of both forward-backward greedy algorithms. Our main
contributions are: 1) We derive better theoretical bounds than existing
analyses regarding FoBa-obj for general smooth convex functions; 2) We show
that FoBa-gdt achieves the same theoretical performance as FoBa-obj under the
same condition: restricted strong convexity condition. Our new bounds are
consistent with the bounds of a special case (least squares) and fills a
previously existing theoretical gap for general convex smooth functions; 3) We
show that the restricted strong convexity condition is satisfied if the number
of independent samples is more than where is the
sparsity number and is the dimension of the variable; 4) We apply FoBa-gdt
(with the conditional random field objective) to the sensor selection problem
for human indoor activity recognition and our results show that FoBa-gdt
outperforms other methods (including the ones based on forward greedy selection
and L1-regularization)
- …