4.7.1 Estimating the signal power in the first path
An estimate of the power in the first path signal may be calculated (in dBm) using the formula:
Where:
F1 = the First Path Amplitude (point 1) magnitude value reported in the FP_AMPL1 field of Register
file: 0x15 – Receive Time Stamp,
F2 = the First Path Amplitude (point 2) magnitude value reported in the FP_AMPL2 field of Register
file: 0x12 – Rx Frame Quality Information,
F3 = the First Path Amplitude (point 3) magnitude value reported in the FP_AMPL3 field of Register
file: 0x12 – Rx Frame Quality Information,
A= is the constant 113.77 for a PRF of 16 MHz, or, the constant 121.74 for a PRF of 64 MHz, and
N = the Preamble Accumulation Count value reported in the RXPACC field of Register file: 0x10 –
RX Frame Information Register. Note that RXPACC may need to be adjusted to remove SFD
symbol count before use, see the register field description in Register file: 0x10 – RX Frame
Information Register.
The resultant First Path Power Level (in dBm) may be compared with the estimated receive power figure
calculated as per section 4.7.2 – Estimating the receive signal power.
4.7.2 Estimating the receive signal power
It is possible to calculate an estimate of the receive power level (in dBm) using the formula:
Where:
C = the Channel Impulse Response Power value reported in the CIR_PWR field of Register file:
0x12 – Rx Frame Quality Information,
A= is the constant 113.77 for a PRF of 16 MHz, or, the constant 121.74 for a PRF of 64 MHz, and
N = the Preamble Accumulation Count value reported in the RXPACC field of Register file: 0x10 –
RX Frame Information Register. Note that RXPACC may need to be adjusted to remove SFD
symbol count before use, see the register field description in Register file: 0x10 – RX Frame
Information Register.
This resultant receive power estimate is very close to the actual receive power at lower receive levels, but is
lower than the actual receive power level at higher levels. Figure 22 below shows the relationship between
the actual receive power and the power estimated by this technique.
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