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Frequently Asked Questions of Signal Repeater


Abbreviations of Terminologies
BTS : Base Transmitting Station
MS : Mobile Service
RSSI : Receive Signal Strength
OSC : Signal Oscillation
DB : Decibel (Unit of measure)
LED : Light Emitting Diode
AGC : Automatic Gain Control
ALC : Automatic Limit Control
SNR : Signal to Noise Ratio
VSWR : Voltage Standing Wave Ratio

Q1. Repeater system consitution and application
A: The repeater system consists of donor antenna, repeater, server antennas and feeder cables, splitters, couplers and combiners are also need if when the solution is more complicated
The repeaters are widely applied to indoor signal distribution in small areas such as office buildings, meeting rooms, small hotels, tea shops, and cafes where signals are shielded, and are also used to cover signal blind areas outdoor. The repeaters not only assist BTS to extend its coverage, but also fill the gaps left by BTS, and optimize the BTS capacity allocation.

Q2. Important notes in site survey of outdoor repeater solutions
Installation position: Easy for installation, power abtainable, and capable to get best donor BTS signals.
Ensure donor BTS to have sufficient capacity margin
Ensure the donor signals to have strong enough signal level, and conduct multle tests by mobile phone and data card to ensure high and stable calling and data transmission quality, also try to avoid frequency handover
Select suitable equipment type, antenna types and the location and height of the antennas
Calculate accurately the necessary repeater gain, the targeted output power level, and etimate if there is enough isolation
Estimate the coverage size and coverage effect

Q3. What is the reason that the phone calls canot be made initially though there are full signals in the mobile phone after repeater installation, then the phone calls become successful after reducing the repeater''s UL and DL gain?
Answer: There are two possible reasons:
The repeater''s downlink gain is too high, and the power amplifier works at non lenear status, the signals can''t be demoduated, therefore the phone calls can''t be made, we recommend to use repeaters with ALC design.
There is self-oscillation due to not enough isolation. If this happens, please take below measures: try to enlarge the distance between the donor and server antennas; replace with antennas with higher front to back ratio; put antennas non line of sight, install antennas where there will be barriers in between; the last step is to reduce the repeater''s gain as shown in the quesion.

Q4. What is the lightening request of the repeater installation? What is the standard value of ground resistance?
Answer: Please refer to relevant document for repeater lightening protection design; the ground resistance is 0.3~3Ω, and it shall be designed according to the soil conditions, environment and whether the place is a thunder field or not.

Q5. What is the problem that the phone calls cannot be made in other coverage areas of donor BTS after repeater commissioning? Is it the problem of donor BTS or the repeater?
Answer: It is quite possible that the repeater’s gain is not proper, the repeater’s uplink gain might be so big that it increases donor BTS’s noise floor and reduce its sensitivity, we call this “deaf” BTS, it decreases BTS coverage size and may collapse BTS when it is serious.

Q6. Will CDMA breathing effect influence the repeater’s output power? To what degree will it influence if it is the case? How do we get to know if it is “breathing out” or “breathing in?
Answer: By “breathing effect”, it means the coverage size increases or descreases as per the different capacity. The breathing effect exists all the time due to CDMA network’s nature, and gaps are created when the BTS coverage decreases, therefore it shall be fully considered during network planning. The output power is not influenced since the repeater’s output power is fixed, however its coverage size will be influenced. So power margin shall be left during repeater commissioning, normally the repeater’s output power shall be set at its maximum power –7dB, and can not be more than its maximum power – 4dB, and for WCDMA, standard shall be its maximum – 10dB, and can’t be more than its maximum power level – 7dB.

Q7. What is 1dB compression point in repeater’s specifications?
Answer: There is a linear range for the power amplifier within which its output power increases linearly as per the increase of input power, and the ratio between them is called repeater gain. Then the power amplifier works non linearly out of this range, that is to say, the output power won’t increase by the same degree as per the input power. The 1dB compression point refers to the point where the output power is just 1dB less than the changing point between linearity and non-linearity.

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