Chapter 16 455
W-CDMA Uplink Digital Modulation for Receiver Test
Understanding the PRACH
To calculate the control part power, use the following formula:
Cntl
dBm
= Pre
dBm
+ Pp-m
Cntl
dBm
is the control part power that is the sum of the preamble power (Pre
dBm
) and the Pp-m value. The
preamble power is represented by the Max Pwr field on the ESG.
Since the control part power is directly related to the Pp-m value, this means that when the Pp-m value is
positive, the control part power is greater than the preamble power and the message part power will also be
greater than the preamble power by at least the Pp-m value. Conversely when the Pp-m value is negative, the
control part power is less than the preamble power and the message part can also be less than the preamble
power depending on the data part power level. Figure 16-8 shows an example of the influence of the control
part power when the Pp-m value is positive and the data part power is low enough that it has minimal impact
on the overall message part power.
Figure 16-8 Control Part Power Determining Message Part Power
Data Part Power
The data part power is not directly entered. It is adjusted and calculated using the difference between relative
power values. These relative powers are shown as Ctrl Pwr and Data Pwr on the ESG. The power values
can be entered using random values, or in compliance with the 3GPP standards, they can be controlled using
gain factors called betas. The 3GPP standard refers to them as B
c
(control beta) and B
d
(data beta). On the
ESG, they are shown as Ctrl Beta and Data Beta. Each beta (control and data) has 16 different values
numbered 0 to 15, and the values 1 through 15 are used to create an amplitude/voltage ratio for calculating
Pp-m
Message Part
Preamble
Control Part
Data Part
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