Uplink System Noise; Introduction; Optimising Snr And Noise Level - ZinWave UNITIVITY 5000 User Manual

UNItivity 5000
User Manual

7.5 Uplink System Noise

7.5.1 Introduction

Anything with active electronics will generate some level of noise in addition to the desired function.
Usually this becomes a consideration in an amplifier system such as an Active DAS. Cellular systems
assess "noise" as part of their operation and its presence is monitored and can cause an alarm
condition.
Older 2G (GSM) technology usually has an alarm for "interference" which an excessive noise level will
trigger.
3G (UMTS W-CDMA) is a spread spectrum system and the signals also look like "noise" in the receiver.
The incoming noise level rise (wanted signal and /or unwanted noise) is used for "access control" in a
3G BTS which limits the number of users that can be connected. Due to this noise into the receiver is
a very critical issue for 3G and will affect the efficient operation of the BTS.
4G and 5G (OFDMA) is a multiple access system using multiple sub-carriers at low data rates to
achieve an overall high data rate. OFDMA is affected by intermodulation and excess system noise –
both may affect the performance of the system.

7.5.2 Optimising SNR and Noise Level

With most active systems a Point of Interconnection (POI) is used to match the BTS power and signals
to the input of the DAS. The POI must apply downlink (DL) power attenuation to manage the level into
the Primary Hub of the DAS.
The POI must also apply a suitable amount of UL attenuation. With 3G, 4G and 5G a lot more attention
must be paid to the uplink (UL) signals and noise such that the noise level fed to the base station (BTS)
is at or below the level which affects the BTS operation.
The Noise contribution of the Zinwave Active DAS is related to the amount of equipment in the system.
It is proportional to the additive noise power from each Remote Unit. It can be calculated from:
NF= 14 + 10 x LOG (SQRT(qty of RUs)) + 10 x LOG (SQRT(qty of SHs))
This an empirical formula that gives a "best fit" to the measured results of the system and was used to
generate the data below.
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BTS POI
Loss and
attenuation
UL Noise floor
connected to
BTS
DL
Zinwave Active DAS
UL
UL Noise floor
of DAS
(measured or
calculated)
7-4