Abstract
A novel hybrid channel estimator that gives robust performance with respect to the error in antenna-to-subcarrier assignment (ATSA) for spatially correlated MIMO-OFDM system with per-subcarrier transmit antenna, is proposed. In practice, the antenna selection information is transmitted through a binary symmetric control channel with a crossover probability. Though minimum mean-square error (MMSE) estimator performs well at low signal to noise ratio (SNR), in the presence of antenna selection error it introduces irreducible error at high SNR. In this paper, we have proved that relaxed MMSE estimator overcomes the performance degradation at high SNR, with less computational complexity. The proposed hybrid estimator combines the benefit of MMSE at low SNR and relaxed MMSE estimator at high SNR. Further, an analytical expression for SNR threshold at which the hybrid estimator is to be switched from MMSE to relaxed MMSE is also derived. The simulation results show that the proposed hybrid estimator gives robust performance, irrespective of the ATSA error and power delay profile of the channel.
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Abbreviations
- \(n_t\) :
-
Number of transmit antennas
- \(n_r\) :
-
Number of receive antennas
- \(L\) :
-
Length of channel
- \(N\) :
-
Number of subcarriers
- \(\mathbf G _l\) :
-
\(n_r\)x\(n_t\) Channel impulse response matrix of the \(l\)th path
- \(\mathbf F _k\) :
-
\(n_r\)x\(n_t\) Channel Frequency Response (CFR) matrix for the \(k\)th subcarrier
- h :
-
CFR after transmit antenna selection
- \(\mathbf h _k\) :
-
CFR after transmit antenna selection with error in \(k\)th subcarrier
- \(\sigma _w^2\) :
-
Noise variance
- S :
-
Block diagonal transmit antenna selection matrix
- Q :
-
MMSE linear transformation matrix
- \(\mathbf R _\mathbf h \) :
-
Autocorrelation of matrix of h
- \(\mathbf D _k\) :
-
Diagonal matrix with eigenvalues of \(\mathbf{R _\mathbf h }_k\) (auto-correlation matrix of \(\mathbf h _k\) )
- \(\mathbf U _k\) :
-
Matrix having eigenvectors of \(\mathbf{R _\mathbf h }_k\) as column vectors
- \(\mathbf Q _R\) :
-
RMMSE(Relaxed MMSE) linear transformation matrix
- \(\text {MSE}_c\) :
-
Average MSE of MMSE estimator with perfect ATSA
- \(\text {MSE}_{k,ATSA}\) :
-
Average MSE of MMSE estimator with ATSA error in \(k\)th subcarrier
- \(\text {MSE}_q\) :
-
Average MSE of MMSE estimator with crossover probability q
- \(\beta \) :
-
Signal to noise ratio per subcarrier
- \(SNR_{TH}\) :
-
SNR threshold
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Appendix
Appendix
Using the following property of trace \(Tr\left( A+B+C\right) =Tr\left( A\right) +Tr\left( B\right) +Tr\left( C\right) \), (10) can be rewritten as
With \(Tr\left( AB\right) =Tr\left( BA\right) \) and \(Tr\left( ABC\right) =Tr\left( CAB\right) =Tr\left( BCA\right) \), (37) becomes
Simplifying (38) results in,
(39) can be rewritten as
as in (12). \(\left( \mathbf I -\mathbf Q \right) =\sigma _w^2 \left( \mathbf{R _\mathbf h }_k+\sigma _w^2\mathbf{I _{Nn}}_r\right) ^{-1}\) in Sect. 3 can be verified by adding Q with it as below.
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Rajeswari, K., Sashiganth, M. & Thiruvengadam, S.J. A hybrid channel estimator for MIMO-OFDM system with per-subcarrier transmit antenna selection. Telecommun Syst 58, 81–89 (2015). https://doi.org/10.1007/s11235-014-9894-3
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DOI: https://doi.org/10.1007/s11235-014-9894-3