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.
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