82
3 Physical Theory of RFID System Physical Anti-Collision
Fig. 3.14 Scatter plot and fitted line for humidity and related reading range
the experimental data. The squares represent formula fitting. The experimental data
is consistent with the theoretical trend.
The system measures different reading distances of RFID tags at each humidity
value. By evaluating and verifying the model, the obtained humidity simulates the
reading range of the tag under different humidity. From Eq. (3.31), it can be seen
that the experimental humidity has a reciprocal relationship with the tag’s reading
distance. By using the relevant reading distance, the accuracy of the predictive model
can be verified and formula calculation can be simplified. The scatter plot of the
experiment is shown in Fig. 3.14. The abscissa represents the test humidity, and the
ordinate represents the tag’s relevant reading range. Asterisks represent experimental
data and squares represent the theoretical curve.
R is called the correlation coefficient, which is an indicator that measures the linear
relationship between two random variables. R-square is called the coefficient of determination. Determining coefficients indicate how good the relationship between two
random variables is. The larger the coefficient of determination is, the better the correlation between two random variables is. The evaluation index of the experimental
model is shown in Table 6.5. R-squared is 0.9406, which means there is a good linear
relationship between the experimental humidity and theoretical humidity.
It is found that in Fig. 3.13 there are some errors between the experimental data
and the theoretical curve. The average error of experimental data is 4.13%. In practical applications, in addition to generating additional noise, wireless communication channels will also suffer from channel impairments such as fading. Humidity
increases the power required to activate the tag which means it will change the tag
chip sensitivity threshold P th . At the same time, the reading range of the tag will also
3 Physical Theory of RFID System Physical Anti-Collision
Fig. 3.14 Scatter plot and fitted line for humidity and related reading range
the experimental data. The squares represent formula fitting. The experimental data
is consistent with the theoretical trend.
The system measures different reading distances of RFID tags at each humidity
value. By evaluating and verifying the model, the obtained humidity simulates the
reading range of the tag under different humidity. From Eq. (3.31), it can be seen
that the experimental humidity has a reciprocal relationship with the tag’s reading
distance. By using the relevant reading distance, the accuracy of the predictive model
can be verified and formula calculation can be simplified. The scatter plot of the
experiment is shown in Fig. 3.14. The abscissa represents the test humidity, and the
ordinate represents the tag’s relevant reading range. Asterisks represent experimental
data and squares represent the theoretical curve.
R is called the correlation coefficient, which is an indicator that measures the linear
relationship between two random variables. R-square is called the coefficient of determination. Determining coefficients indicate how good the relationship between two
random variables is. The larger the coefficient of determination is, the better the correlation between two random variables is. The evaluation index of the experimental
model is shown in Table 6.5. R-squared is 0.9406, which means there is a good linear
relationship between the experimental humidity and theoretical humidity.
It is found that in Fig. 3.13 there are some errors between the experimental data
and the theoretical curve. The average error of experimental data is 4.13%. In practical applications, in addition to generating additional noise, wireless communication channels will also suffer from channel impairments such as fading. Humidity
increases the power required to activate the tag which means it will change the tag
chip sensitivity threshold P th . At the same time, the reading range of the tag will also