## 4 Crosstalk Analysis
### Crosstalk between Forward and Backward Information Transfer  
As shown in Figure 9, the process of bi-directional information transfer is not only influenced by crosstalk between information and power, but also interfered by the high-frequency signal source on the same side. According to the Section 3, \(G_{\mu\ell}(\omega)\) and \(G_{\mathrm{std}}(\omega)\) are the gain of forward and backward information transfer channel, respectively. Define \(G_{\mu\ell}(\omega)\) as the gain of the channel from \"Backward TX\" to \"Forward RX\" and define \(G_{\mathrm{s}\ell}(\omega)\) as the gain of the channel from \"Forward TX\" to \"Backward RX\".  
During the forward information transfer, the signal pick-up cell in the secondary side can not only receive the signal from the signal transmitter in the primary side, but also receive the signal from the signal transmitter in the secondary side.  
Therefore, the crosstalk comes from the signal transmitter in the secondary side. The gain of the crosstalk \(G_{\mu\ell}(\omega)\) is:  
\[G_{fdc}(\omega)=\frac{V_{rp}}{V_{ds}}=\frac{Z_{T2}(\omega)}{Z_{\mathrm{ss}}( \omega)}\cdot G_{T2}(\omega)\cdot G_{T4}(\omega) \tag{34}\]  
Figure 9: Equivalent circuit of crosstalk interference between forward information transfer and backward information transfer.  
The bode plot of crosstalk \(G_{\text{sdc}}(\omega)\) is shown in Figure 10a. There are only two extreme points. Point A is the power carrier, point B and point C are the information transfer gain in \(\omega_{ds}\) and \(\omega_{dp}\), respectively. However, point B is the gain of the channel from \"Backward TX\" to \"Forward RX\", called \(G_{\text{sdc}}(\omega_{ds})\). Comparing the gain of \(G_{\text{sdc}}(\omega_{dp})\) and \(G_{\text{sdc}}(\omega_{ds})\), it is clear that \(G_{\text{sdc}}(\omega_{dp})\) is greater than \(G_{\text{sdc}}(\omega_{ds})\). Therefore, during the process of forward information transfer, the crosstalk from \"Backward TX\" port would not interfere normal forward information transfer.  
Similarly, during the backward information transfer, the crosstalk comes from the signal transmitter in the primary side. The gain of the crosstalk \(G_{\text{sdc}}(\omega)\) is:  
\[G_{\text{sdc}}(\omega)=\frac{V_{rs}}{V_{dp}}=\frac{Z_{\text{T1}}(\omega)}{Z_{p} (\omega)}\cdot G_{\text{T1}}(\omega)\cdot G_{\text{T3}}(\omega) \tag{35}\]  
The bode of crosstalk \(G_{\text{sdc}}(\omega)\) is shown in Figure 10b. There are also only two extreme points. Point A is the power carrier, point B and point C are the information transfer gain in \(\omega_{ds}\) and \(\omega_{dp}\), respectively. Comparing the gain of \(G_{\text{sdc}}(\omega_{ds})\) and \(G_{\text{sdc}}(\omega_{dp})\), it is clear that \(G_{\text{sdc}}(\omega_{ds})\) is greater than \(G_{\text{sdc}}(\omega_{dp})\). So, during the process of forward information transfer, the crosstalk from \"Forward TX\" port to \"Backward RX\" port can be ignored.  
In conclusion, normal bidirectional information transmission channels are established in primary and secondary side, but the signal receiving cells in both sides are interfered by the high-frequency source at the same side and the power carrier. According to the models of interference channels and analysis, the coupled coils inductances and self-inductance of tightly coupled transformer affect system efficiency and the gain of information transfer to a certain degree. However, the effect of these crosstalk is limited and does not affect normal information transmission, and then can be ignored.