
356 Chapter 15
W-CDMA Uplink Digital Modulation for Receiver Test
Understanding the PRACH
part and the preamble powers (Pp-m = Cntl
dBm
− Pre
dBm
). (See Figure 15-8.) So by adjusting
your Pp-m value, you change the control part power with respect to the preamble.
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 15-8 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 15-8 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 the
relative power levels. A beta of zero means the power has been turned
Pp-m
Message Part
Preamble
Control Part
Data Part
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