Hello all,
Today I would like to share and answer the question of
why Rx level value is always negative vale
Why RX is it negative value ??
dbm = decibel-milliwatt
It is measured power referenced to one milliwatt (mW).
Its value is 10 * log[ P(W) / 1mW ]
Rx level is the strength of the signal that the mobile receives from
a BTS (mobile tower). Here Rx level stands for Receiver Level
The mathematical formula to calculate the Rx level is
RxLev (dBm) = EIRP (dBm) - Path Loss (dB)
EIRP - Equivalent/Effective Isotropically Radiated Power is
the amount of power that an antenna that evenly distributes
power in all directions would emit to produce the peak
power density observed in the direction of maximum antenna gain.
EIRP (dBm) = Pt (dBm) + Ga (dBi)
i - antenna gain in reference to an isotropic antenna
t - output power transmitted
Path Loss - For a given antenna, the received power is inversely
proportional to the distance between the transmit and receive antennas &
also to the square of the frequency.
Ls ~ d^2 f^2
Path loss - Ls(dB) = 32.4(dB) + 20*log [ f (MHz) ] + 20*log [ d (km)]
where 32.4 is a constant of proportionality
The value of Path loss is always greater than EIRP, hence Rx level is negative
RX level Range
Rx level in a range of 0 to 63 (positive value).
Just subtract it from 110 dBm to get the value of Rx level. 0 to 63 equals -110 dBm to -47 dBm.
Up to - 65 dBm: Excellent RSL
-65 to -75: Good RSL (MW working normally )
-75 to -95: Normal RSL (maybe a problem in the alignment of dishes )
> -95: Weak RSL (MW link down may be due to power problem )
Rx Lev Sub and Rx Lev Full ??
Rx_Level_Full is measured when DTX is off.
RX Lev Full It is the Mobile transmit the measurement
report (SACCH multi-frame) for every 480ms. This
multi-frame contains 104 TDMA frames, in 104 TDMA frames 4 TDMA frames
for Decode the BSIC and remaining 100 TDMA
frames for Average measurement of the serving cell and neighboring cell.
This average measurement of 100 TDMA frames
are RX Lev Full
RX Lev Sub is when DTX is on.
DTX is a discontinuous transmission, When the mobile conversation
40% of the time either transmitter or Receiver is idle. When DTX is ON,
DTX will switch off the transmitter or Receiver when they are no speech Pulses. only
a few TDMA frames will transmit, the average of these
TDMA frames are called RX Lev Sub, give you a proper measurement of RX level
