A TMA reduces system noise, improves
uplink sensitivity and leads to longer UE battery life.
Sensitivity is the minimum input power
needed to get a suitable signal-to-noise ratio (SNR) at the output of the
receiver. It is determined by receiver noise figure, thermo noise power and
required SNR. Thermo noise power is determined by bandwidth and temperature,
SNR is determined by modulation technique, therefore the only variable is noise
figure.
The cascading noise figure can be
calculated by Friis equation (Herald Friis):
NFt = NF1 + (NF2-1)/G1 + (NF3-1)/(G1*G2)
+ ... + (NFi-1)/(G1*G2*...*Gi)
As the equation shows, the first block
imposes the minimum and the most prominent noise figure on the system, and the
following blocks imposes less and less impact to the system provided the gains
are positive. Linear passive devices have noise figure equal to their loss. A
TMA typically has a gain of 12dB. There are typically top jumper, main feeder
and a bottom jumper between antenna and BTS. A TMA placed near antenna with a short
jumper from antenna provides the best noise figure improvement – the noise
figure will be restricted to the top jumper loss (NF1) and TMA ((NF2-1)/G1),
and the remaining blocks (main feeder and bottom jumper) have little effect. To
summarize, a TMA has a gain that’s close to feeder loss.
TMA GAIN : TMA typically has a 12 dB gain; however, the effective gain comes from noise figure reduction and the gain is close or equivalent to the feeder loss.
TMA GAIN : TMA typically has a 12 dB gain; however, the effective gain comes from noise figure reduction and the gain is close or equivalent to the feeder loss.
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