calculated from the MWA image and the CMB image. The images are cut into square of 20$\times$20 $\rm deg^2$ and the masked field could be a unique response on the signal. The mask effect is reduced using the Polspice [@Chon2004]. Same as the APS, we correct the weight caused from incomplete uv-coverage.

The CPS should be computed from the visibility to account for uv-coverage and avoid the systematics caused from imaging. For the calculation, one has to Fourier Tranform the CMB image into the visibility uv-plane. In this work, the CPS is calculated from images because we remove foreground using the line of sight fitting method. Computation via visibilities is left for future work.

The error of CPS is estimated using [@1995PhRvD..52.4307K], $$\begin{aligned}
\label{eq:error1}
\Delta C^2_{l} &=& A\left[\left(C_{l}^{\rm 21,CMB}\right)^2+\left(C_{l}^{\rm 21,obs}\right)\left(C_{l}^{\rm CMB,obs}\right)\right],\\
&=&A\left[\left(C_{l}^{\rm 21,CMB}\right)^2+\left(C_{l}^{\rm 21}+N_{l}^{\rm 21}+C_{l}^{\rm FG}\right)\left(C_{l}^{\rm CMB}+N_{l}^{\rm CMB}\right)\right],\nonumber\end{aligned}$$ where $A^{-1} = (2l+1)f_{\rm sky}\Delta l$, $f_{\rm sky}$ is the sky fraction of the image, $\Delta l$ is the bin width, $C_{l}^{\rm MWA,obs}$ is the APS of the images observed by the MWA and $C_{l}^{\rm CMB,obs}$ is the APS of the CMB image. The error consists of a sample variance term and a contribution of 21cm APS, noise of the 21cm observation, 