UMTS

UL Interference E. Eter

2

Possible Causes for UL interference

Too high UL RSSI (>-100 dbm) can be caused by:

External sources of uplink interference

Inter-mod product

Incorrect plumbing

Parameter TMA ulGain setting does not match the real TMA gain

Faulty devices along the Rx path Loose Connectors

Tight Cable Bends

High UL RSSI caused by external interference has significant impact on UL capacity and

coverage of a cell.

3

UL RTWP (Ericsson)

UL RSSI pmAverageRSSI is measured in the RU power sensor.

The result is translated to dBm at the Rx reference point by the factor K_dBM.

K_dBm = (RUG – FUG) + FAtt – TMAG

Where, FAtt is the Attenuation antenna feeder cable and TMAG is the TMA Total Gain

RUG and FUG are internal to the NodeB

Feeder attenuation and TMA Gain are provided by site

configuration. So it’s important the loss FAtt and gain TMAG

are accurate.

TMA

FU

RU

Power Sensor

RU

FAtt

TMAG

K_dBm

Rx Reference Point

NodeB

pmAverageRSSI

RUG

FUG

Antenna

Next 3 slides show how to input the TMA gain and feeder attenuation

In the OSS element manager

4

TMA Gain

5

Feeder Attenuation and delays

6

Feeder Attenuation and delays

7

pmAverageRssi

8

Ericsson Uplink RSSI Measurement

pmAverageRssi

UL RSSI counter can be checked through either RBS Performance Statistics

counter pmAverageRssi. It can be read by Business Object or Prospect.

9

UL Interference Monitoring

A macro was developed to graph ( see figure below) and flag any cell that has a

RTWP at least 2dB greater or less than the mean RTWP for all cells in a given

RNC.

A daily summary for the worst performing sectors will be available on NetTrack

(Ericsson and Lucent ).

Ericsson Measured Interference

0

5000

10000

15000

20000

25000

30000

35000

40000

< -110

dBm

-108

.5..-

108

dBm

-106

.5..-

106

dBm

-104

.5..-

104

dBm

-102

.5..-

102

dBm

-100

.5..-

100

dBm

-98.5..-

98 dBm

-96.5..-

96 dBm

-94.5..-

94 dBm

-92.5..-

92 dBm

-90.5..-

90 dBm

-88.5..-

88 dBm

-86.5..-

86 dBm

-84.5..-

84 dBm

-82.5..-

82 dBm

-80.5..-

80 dBm

Signal Level

Nu

mb

er

of

Sam

ple

s

CNU3007A

10

How to identify the cause of high UL RSSI

:

Swap antenna feeders between good and bad sectors on RBS cabinet top.

Wait for the next ROP and check the UL RSSI.

If the high interference stays with the antenna:

- then it may be external interference or TMA (A)

- otherwise check the FU/RU. (B)

Use spectrum analyzer to detect external interference sources

TMA

FU

RU

Power Sensor

RU

Rx Reference Point

NodeB

pmAverageRSSI

Antenna In case one or two sectors of a site has high UL RSSI

A

B

Too low UL RSSI (<-110 dbm) will cause PRACH preamble detection problem because UE uses

too low power to access the site. It may also cause UL synch loss drop call if the initial power of the

Radio Link is too low during handover.

11

LUCENT Uplink RSSI Measurement

RTWP VS.RF.Rtwp.LE110 to VS.RF.Rtwp.GT90

Description

• The measurement provides a distribution of the Received Total

Wideband Power(RTWP) within the granularity period.

• The RTWP provides separate counters on a 1dB step size in the

typical range used for detailed evaluation. This range is -110 dBm to -

90 dBm.

• Trigger condition

For every 100 ms sampling period the mean RTWP value for the

sampling period will be calculated and the appropriate counter

incremented. The ranges are defined as listed:

12

LUCENT

1. TMA equipped and controlled by the Node B

2. No TMA equipped

13

TMA equipped Node B

The reference point for RTWP is at the TMA input port (antenna side of the

TMA). For this configuration RTWP is computed by adding the Rx Path Gain

(consisting of the Node B's internal path gain plus the external path gain) to the RSSI

measured at the radio's receiver. The external path gain (between the reference

point and the Node B's External Antenna Connector (EAC)) is the combination of the Rx

Gain data contained in the associated TTLNA Descriptor plus that contained in the

Antenna Path Descriptor. RTWP reference point

824 MHz

Gain (dB)

TTLNA

12.00

Feeder Cable

-3.00 -0.15

Filter panel

30.50

Filter panel

attenuator

Cable

to

Radio

-0.70

Total

30.65-8.00

14

No TMA equipped NodeB

The reference point for RTWP is the Node B's External Antenna Connector

(EAC). In this case RTWP is computed by adding the RSSI measured at the radio

to the Node B's internal path gain. The Antenna Path Descriptor's Rx Gain

parameters are set to zero.

Gain (dB)

LNA _ _

38.00

_ Variable Attenuator

_ _

-3.00

1:3 Splitter _ _

-7.00

Cable to radio _ _

-1.60

Total

26.40

NodeB Filter

RTWP reference point

15

Other Cases

• There are variants of the "TMA equipped but NOT controlled by the

Node B" scenario described in Configuration 2, above. For example,

there are certain RxAIT configurations in Cingular's network where

RxAIT is equipped without the presence of TMA. In some cases the

RxAIT components appear to the Node B as the equivalent of a TMA in

the external path. Similarly, there are configurations where the Nokia

GSM base station hosts the Rx path. For this case the path through

the host GSM base station and antenna system appears as a TMA

equivalent.