Interview Questions

[tthach830]

1. What's the function of TMA in UMTS?
2. What would happenen when you change the Ec/Io to -23 in the unused frequency? Sorry i am not sure if the rephrase it right. Someone please hlep.


I got the TMA question partially right. I basically said it's a amplifier to imprve the signal strength with a typical gain of 10-15dBm. The interviewer then ask what's the signifcant in UMTS? I don't know.

[Irna]

easy man, TMA to improving DL Power Level but this is aleady included on vendor equipment (feature Huawei : Power Amplifier )

[Resistor]

1. What's the function of TMA in UMTS?


In my experience:
-----------------
(a) Improves the the noise figure of the RX in total (the noise figure of a passive element, such as a coax feeder is equal to its loss, thus if the RX feeder has a loss of 1.5 dB the noise figure of the receiver is worsened with 1.5dB, however, if a LNA is inserted _before_ the feeder then the resultant noise figure of the LNA+feeder is better than that of the feeder (see in Wikipedia "Noise Figure" for the formula how to calculate the noise figure of two devices connected in series). As a result of the improved noise figure the capacity of the uplink is increased (because it is the noise rise that limits the capacity in the UL, so if we reduce the noise figure this contributes to being able to handle stronger multi-user interference, which is the same as having greater capacity in the UL).

(b) Increases the range in the UL and reduces the drain of the UE battery, because the UEs will need lower TX to provide the needed signal level at the BTS antenna. This looks like much more interesting and important than point (a), however in reality point (a) is much more important.


2. What would happenen when you change the Ec/Io to -23 in the unused frequency? Sorry i am not sure if the rephrase it right. Someone please hlep.


Sorry, I am afraid I do not quite understand this question, perhaps someone else will help.

Regards,
Resistor

[Irna]

In my experience:
-----------------
(a) Improves the the noise figure of the RX in total (the noise figure of a passive element, such as a coax feeder is equal to its loss, thus if the RX feeder has a loss of 1.5 dB the noise figure of the receiver is worsened with 1.5dB, however, if a LNA is inserted _before_ the feeder then the resultant noise figure of the LNA+feeder is better than that of the feeder (see in Wikipedia "Noise Figure" for the formula how to calculate the noise figure of two devices connected in series). As a result of the improved noise figure the capacity of the uplink is increased (because it is the noise rise that limits the capacity in the UL, so if we reduce the noise figure this contributes to being able to handle stronger multi-user interference, which is the same as having greater capacity in the UL).

(b) Increases the range in the UL and reduces the drain of the UE battery, because the UEs will need lower TX to provide the needed signal level at the BTS antenna. This looks like much more interesting and important than point (a), however in reality point (a) is much more important.



Sorry, I am afraid I do not quite understand this question, perhaps someone else will help.

Regards,
Resistor

so sorry bro, this is TMA or TMB functionality? i think is for TMB

[Resistor]

so sorry bro, this is TMA or TMB functionality? i think is for TMB

My reply was about TMA -- Tower Mounted [RX] Amplifier.

Regards,
Resistor

[haryban]

TMA consist of TMB + LNA
TMB Consist only TMB and if implemented will generate high drop call in UL