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Fixed-Point Widely Linear MCCC for Bias-Compensated Adaptive Filtering

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Abstract

Recently, the widely linear complex-valued estimated-input adaptive filter (WLC-EIAF) used in processing noisy inputs and outputs has received increasing attention in machine learning and signal processing. In this paper, a fixed-point widely linear complex-valued estimated-input maximum complex correntropy criterion (FPWLC-EIMCCC) algorithm is proposed to deal with noncircular complex signals with noise in input and output. Compared with the existing algorithms, benefiting from the fixed-point method, the proposed FPWLC-EIMCCC can simultaneously have better steady-state performance and faster convergence speed. Furthermore, the theoretical analysis of the FPWLC-EIMCCC is performed by transforming FPWLC-EIMCCC into a gradient-like version based on the matrix inverse lemma and some approximations. Simulation results on system identification, channel estimation, and wind prediction show that FPWLC-EIMCCC significantly improves the filtering performance.

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Data Availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

This work was supported by Fundamental Research Funds for the Central Universities (19CX05003A-14).

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Correspondence to Guobing Qian.

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Appendices

Appendix

Appendix A: Evaluation of \(T_{1}\)

Taking \({\overline{\mathbf{R}}} = E\left[ {{\hat{\mathbf{x}}}_{c} {\hat{\mathbf{x}}}_{c}^{H} } \right]\) into consideration, we further obtain

$$ {\overline{\mathbf{R}}} = E\left[ {{\hat{\mathbf{x}}}_{c} {\hat{\mathbf{x}}}_{c}^{H} } \right] = \sigma_{x}^{2} \left[ {\begin{array}{*{20}c} {{\mathbf{I}}_{L} } & {(1 - 2\xi^{2} ){\mathbf{I}}_{L} } \\ {(1 - 2\xi^{2} ){\mathbf{I}}_{L} } & {{\mathbf{I}}_{L} } \\ \end{array} } \right]. $$
(46)

Based on (46) and the block matrix inverse lemma [47], \({\overline{\mathbf{R}}}^{ - 1}\) is derived as follows:

$$ \begin{aligned} {\overline{\mathbf{R}}}^{ - 1} & = \frac{1}{{\sigma_{x}^{2} }}\left[ {\begin{array}{*{20}c} {\frac{1}{{1 - (1 - 2\xi^{2} )^{2} }}{\mathbf{I}}_{L} } & {\frac{{1 - 2\xi^{2} }}{{(1 - 2\xi^{2} )^{2} - 1}}{\mathbf{I}}_{L} } \\ {\frac{{1 - 2\xi^{2} }}{{(1 - 2\xi^{2} )^{2} - 1}}{\mathbf{I}}_{L} } & {\frac{1}{{1 - (1 - 2\xi^{2} )^{2} }}{\mathbf{I}}_{L} } \\ \end{array} } \right] \\ & = \frac{1}{{\sigma_{x}^{2} }}\frac{1}{{1 - (1 - 2\xi^{2} )^{2} }}\left[ {\begin{array}{*{20}c} {{\mathbf{I}}_{L} } & {\mathbf{0}} \\ {\mathbf{0}} & {{\mathbf{I}}_{L} } \\ \end{array} } \right] + \frac{1}{{\sigma_{x}^{2} }}\frac{{1 - 2\xi^{2} }}{{(1 - 2\xi^{2} )^{2} - 1}}\left[ {\begin{array}{*{20}c} {\mathbf{0}} & {{\mathbf{I}}_{L} } \\ {{\mathbf{I}}_{L} } & {\mathbf{0}} \\ \end{array} } \right], \\ & = {\overline{\mathbf{R}}}_{1}^{ - 1} + {\overline{\mathbf{R}}}_{2}^{ - 1} \\ \end{aligned} $$
(47)

where \({\overline{\mathbf{R}}}_{1}^{ - 1} = \frac{1}{{\sigma_{x}^{2} }}\frac{1}{{1 - (1 - 2\xi^{2} )^{2} }}\left[ {\begin{array}{*{20}c} {{\mathbf{I}}_{L} } & {\mathbf{0}} \\ {\mathbf{0}} & {{\mathbf{I}}_{L} } \\ \end{array} } \right]\), \({\overline{\mathbf{R}}}_{2}^{ - 1} = - \frac{1}{{\sigma_{x}^{2} }}\frac{{1 - 2\xi^{2} }}{{1 - (1 - 2\xi^{2} )^{2} }}\)\(\left[ {\begin{array}{*{20}c} {\mathbf{0}} & {{\mathbf{I}}_{L} } \\ {{\mathbf{I}}_{L} } & {\mathbf{0}} \\ \end{array} } \right]\), and L represents the length of the filter.

Thus, we have

$$ \begin{aligned} T_{1} & = E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}^{ - 1} {\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \quad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 1} {\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \\ & = E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}_{1}^{ - 1} {\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \quad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}_{1}^{ - 1} {\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \\ & \quad + E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \quad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \\ & = 2\frac{1}{{\sigma_{x}^{2} }}\frac{1}{{1 - (1 - 2\xi^{2} )^{2} }}E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right] \\ & \quad + E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \quad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right]. \\ \end{aligned} $$
(48)

Furthermore, we get

$$ \begin{aligned} & E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \qquad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \\ & \quad = \frac{1}{{\sigma_{x}^{2} }}\frac{{1 - 2\xi^{2} }}{{(1 - 2\xi^{2} )^{2} - 1}} \\ & \qquad \times E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right)\left[ {\begin{array}{*{20}c} {\left( {{\mathbf{x}}_{i} \left( n \right){\mathbf{x}}_{i}^{T} \left( n \right)} \right)^{*} } \\ {{\mathbf{x}}_{i} \left( n \right){\mathbf{x}}_{i}^{H} \left( n \right)} \\ \end{array} \;\;\begin{array}{*{20}c} {{\mathbf{x}}_{i}^{*} \left( n \right){\mathbf{x}}_{i}^{T} } \\ {{\mathbf{x}}_{i} \left( n \right){\mathbf{x}}_{i}^{T} \left( n \right)} \\ \end{array} } \right]{\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \qquad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right)\left[ {\begin{array}{*{20}c} {{\mathbf{x}}_{i} \left( n \right){\mathbf{x}}_{i}^{T} \left( n \right)} \\ {{\mathbf{x}}_{i} \left( n \right){\mathbf{x}}_{i}^{H} \left( n \right)} \\ \end{array} \;\;\;\begin{array}{*{20}c} {{\mathbf{x}}_{i}^{*} \left( n \right){\mathbf{x}}_{i}^{T} } \\ {\left( {{\mathbf{x}}_{i} \left( n \right){\mathbf{x}}_{i}^{T} \left( n \right)} \right)^{*} } \\ \end{array} } \right]{\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \\ & \quad \ge 2\frac{1}{{\sigma_{x}^{2} }}\frac{{1 - 2\xi^{2} }}{{(1 - 2\xi^{2} )^{2} - 1}}E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right], \\ \end{aligned} $$
(49)

and

$$ \begin{aligned} & E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \quad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \le 0, \\ \end{aligned} $$
(50)

where \({\mathbf{x}}_{c,i} \left( n \right) = \left[ {{\mathbf{x}}_{i}^{T} \left( n \right) {\mathbf{x}}_{i}^{H} \left( n \right)} \right]^{T}\), and \(\frac{{1 - 2\xi^{2} }}{{(1 - 2\xi^{2} )^{2} - 1}} \le {0}\).

Based on (49), we have

$$ \begin{aligned} T_{1} & = 2\frac{1}{{\sigma_{x}^{2} }}\frac{1}{{1 - (1 - 2\xi^{2} )^{2} }}E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right] \\ & \quad + E\left[ {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right. \\ & \quad + \left. {{\tilde{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\mathbf{x}}_{c,i} \left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}_{2}^{ - 1} {\tilde{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \\ & = T_{{0}} E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right] \\ & \ge 2\frac{1}{{\sigma_{x}^{2} }}\frac{{2\xi^{2} }}{{1 - (1 - 2\xi^{2} )^{2} }}E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right]. \\ \end{aligned} $$
(51)

Therefore, the range for \(T_{{0}}\) is

$$ 2\frac{1}{{\sigma_{x}^{2} }}\frac{{2\xi^{2} }}{{1 - (1 - 2\xi^{2} )^{2} }} \le T_{{0}} \le 2\frac{1}{{\sigma_{x}^{2} }}\frac{1}{{1 - (1 - 2\xi^{2} )^{2} }}. $$
(52)

Appendix B: Evaluation of \(T_{2}\) and \(T_{{4}}\)

In the steady state, assuming that \(\left| {e_{a,i} \left( n \right)} \right|^{2}\) is statistically independent of \({\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c,i} \left( n \right)\) [41] for long adaptive filter, we get

$$ \begin{aligned} T_{2} & = E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} {\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c,i} \left( n \right)} \right] = E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right]E\left[ {{\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c,i} \left( n \right)} \right] \\ & = E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right]E\left[ {{\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c,i} \left( n \right)} \right] \\ & = E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right]E\left[ {{\mathbf{x}}_{c}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c} \left( n \right) + i^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} i\left( n \right)} \right] \\ & = E\left[ {\left| {e_{a,i} \left( n \right)} \right|^{2} } \right]\left[ {Tr\left( {{\overline{\mathbf{R}}}^{ - 1} } \right) + \sigma_{i}^{2} Tr\left( {{\overline{\mathbf{R}}}^{ - 2} } \right)} \right]. \\ \end{aligned} $$
(53)

Similarly, \(T_{{4}}\) can be rewritten as

$$ T_{{4}} = E\left[ {{\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c,i} \left( n \right)} \right] = Tr\left( {{\overline{\mathbf{R}}}^{ - 1} } \right) + \sigma_{i}^{2} Tr\left( {{\overline{\mathbf{R}}}^{ - 2} } \right). $$
(54)

Appendix C: Evaluation of \(T_{{3}}\)

$$ \begin{aligned} T_{{3}} & = E\left[ {{{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} i\left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c,i} \left( n \right)i^{H} \left( n \right){{\varvec{\upomega}}}_{{{\text{opt}}}} } \right] \\ & = E\left[ {{{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} i\left( n \right){\mathbf{x}}_{c}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c} \left( n \right)i^{H} \left( n \right){{\varvec{\upomega}}}_{{{\text{opt}}}} } \right. \\ & \quad + \left. {{{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} i\left( n \right)i^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} i\left( n \right)i^{H} \left( n \right){{\varvec{\upomega}}}_{{{\text{opt}}}} } \right] \\ & = \sigma_{i}^{2} Tr\left( {{\overline{\mathbf{R}}}^{ - 1} } \right)\left\| {{\mathbf{w}}_{{{\text{opt}}}} } \right\|^{{2}} {\text{ + E}}\left[ {{{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} i\left( n \right)i^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} i\left( n \right)i^{H} \left( n \right){{\varvec{\upomega}}}_{{{\text{opt}}}} } \right]. \\ \end{aligned} $$
(55)

Based on the Gaussian fourth-order moment theorem [32], we get

$$ \begin{aligned} & {\text{E}}\left[ {{{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} i\left( n \right)i^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} i\left( n \right)i^{H} \left( n \right){{\varvec{\upomega}}}_{{{\text{opt}}}} } \right] \\ & \quad = {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} E\left[ {i\left( n \right)i^{H} \left( n \right){\overline{\mathbf{R}}}^{{ - {1}}} } \right]E\left[ {{\overline{\mathbf{R}}}^{{ - {1}}} i\left( n \right)i^{H} \left( n \right)} \right]{{\varvec{\upomega}}}_{{{\text{opt}}}} \\ & \qquad + {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} E\left[ {i\left( n \right)i^{H} \left( n \right){\overline{\mathbf{R}}}^{{ - {1}}} } \right]E\left[ {{\overline{\mathbf{R}}}^{{ - {1}}} i\left( n \right)i^{H} \left( n \right)} \right]{{\varvec{\upomega}}}_{{{\text{opt}}}} \\ & \qquad + {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} E\left[ {i\left( n \right)i^{H} \left( n \right)} \right]E\left[ {i^{H} \left( n \right){\overline{\mathbf{R}}}^{{ - {2}}} i\left( n \right)} \right]{{\varvec{\upomega}}}_{{{\text{opt}}}} \\ & \quad { = 2}\sigma_{i}^{4} {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} {\overline{\mathbf{R}}}^{{ - {2}}} {{\varvec{\upomega}}}_{{{\text{opt}}}} { + }\sigma_{i}^{4} {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} Tr\left( {{\overline{\mathbf{R}}}^{{ - {2}}} } \right){{\varvec{\upomega}}}_{{{\text{opt}}}} . \\ \end{aligned} $$
(56)

Substituting (56) into (55), we have

$$ T_{{3}} = \sigma_{i}^{2} Tr\left( {{\overline{\mathbf{R}}}^{ - 1} } \right)\left\| {{\mathbf{w}}_{{{\text{opt}}}} } \right\|^{{2}} { + 2}\sigma_{i}^{4} {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} {\overline{\mathbf{R}}}^{{ - {2}}} {{\varvec{\upomega}}}_{{{\text{opt}}}} { + }\sigma_{i}^{4} {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} Tr\left( {{\overline{\mathbf{R}}}^{{ - {2}}} } \right){{\varvec{\upomega}}}_{{{\text{opt}}}} . $$
(57)

Appendix D: Evaluation of \(T_{{5}}\)

$$ \begin{aligned} T_{5} & = E\left[ {\varphi^{2} (n){\hat{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}^{ - 2} {\hat{\varvec{\upomega}}}\left( {n - 1} \right)} \right] \\ & \approx E\left[ {\left( {\frac{{\tau g\left( {e_{i} \left( n \right)} \right)\left| {e_{i} \left( n \right)} \right|^{2} }}{{1 + \tau g\left( {e_{i} \left( n \right)} \right)\left\| {{\hat{\varvec{\upomega}}}\left( {n - 1} \right)} \right\|^{2} }}} \right)^{{2}} {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} {\overline{\mathbf{R}}}^{ - 2} {{\varvec{\upomega}}}_{{{\text{opt}}}} } \right] \\ & \approx \sigma_{i}^{4} {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} {\overline{\mathbf{R}}}^{ - 2} {{\varvec{\upomega}}}_{{{\text{opt}}}} . \\ \end{aligned} $$
(58)

Appendix E: Evaluation of \(T_{{6}}\), \(T_{{7}}\), \(T_{{8}}\) and \(T_{{9}}\)

Based on the independence assumption and \({\hat{\varvec{\upomega}}}^{H} \left( {n - 1} \right) \approx {{\varvec{\upomega}}}_{{{\text{opt}}}}\), we can get the evaluation of \(T_{{6}}\), \(T_{{7}}\), \(T_{{8}}\) and \(T_{{9}}\) as follows:

$$ T_{{6}} \approx {0,}T_{{7}} \approx {0,}T_{{8}} \approx {0,}T_{{9}} \approx {0}{\text{.}} $$
(59)

Appendix F: Evaluation of \(T_{{{10}}}\)

$$ \begin{aligned} T_{{{10}}} & = E\left[ {\varphi (n)\Re \left[ {{{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} i\left( n \right){\mathbf{x}}_{c,i}^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {\hat{\varvec{\upomega}}}\left( {n - 1} \right)} \right]} \right] \\ & \approx E\left[ {\frac{{\tau g\left( {e_{i} \left( n \right)} \right)\left| {e_{i} \left( n \right)} \right|^{2} }}{{1 + \tau g\left( {e_{i} \left( n \right)} \right)\left\| {{\hat{\varvec{\upomega}}}\left( {n - 1} \right)} \right\|^{2} }}} \right]E\left[ {{{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} i\left( n \right)i^{H} \left( n \right){\overline{\mathbf{R}}}^{ - 2} {{\varvec{\upomega}}}_{{{\text{opt}}}} } \right] \\ & \approx \sigma_{i}^{4} {{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} {\overline{\mathbf{R}}}^{ - 2} {{\varvec{\upomega}}}_{{{\text{opt}}}} . \\ \end{aligned} $$
(60)

Appendix G: Evaluation of \(T_{{{11}}}\)

$$ \begin{aligned} T_{{{11}}} & = E\left[ {\varphi (n)\Re \left[ {o^{*} \left( n \right){\hat{\varvec{\upomega}}}^{H} \left( {n - 1} \right){\overline{\mathbf{R}}}^{ - 2} {\mathbf{x}}_{c,i}^{H} \left( n \right)} \right]} \right] \\ & \approx E\left[ {\frac{{\tau g\left( {e_{i} \left( n \right)} \right)\left| {e_{i} \left( n \right)} \right|^{2} }}{{1 + \tau g\left( {e_{i} \left( n \right)} \right)\left\| {{\hat{\varvec{\upomega}}}\left( {n - 1} \right)} \right\|^{2} }}} \right]E\left[ {\Re \left[ {o^{*} \left( n \right){{\varvec{\upomega}}}_{{{\text{opt}}}}^{H} {\overline{\mathbf{R}}}^{ - 2} i^{H} \left( n \right)} \right]} \right] \\ & = 0. \\ \end{aligned} $$
(61)

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Qiu, C., Ruan, Z. & Qian, G. Fixed-Point Widely Linear MCCC for Bias-Compensated Adaptive Filtering. Circuits Syst Signal Process 42, 2959–2985 (2023). https://doi.org/10.1007/s00034-022-02247-5

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