high UL RSSI (3G) due to Signal Jammer

[baltoudi]

Hi Masters

I have experienced a small cluster of area got inteferred by RF signal jammer from a prison. All 3G/2G network providers to suffer from it.
Especially on 3G where I am working on, the indication of having too high UL RSSI level and poort retainabilities (mainly) rates have been observed, beside RRC.
the followings are my workaround which give me nothing to recover the performances:
- change the UARFCN to another value (the operator has more than 1 carrier) --> no impact
- reduce the idle and dedicated coverage by means of p-cpich, qrxlev, qqualmin, minpwrmax, interpwrmax, maxpwrmax --> no impact
- increasing minpwrrl --> no impact
- downtilting the antenna --> no impact

Does anybody know how to at least minimize the impact of the signal jammer to network performances?
Really appreciate that

[nomanpatrick]

Are they using the same freq band?

[baltoudi]

Are they using the same freq band?

do you mean the jammer? I believe this is a high power device with the wide-band channel interfering critically to GSM, DCS and WCDMA through its harmonics.
The UL RSSI reading on Node B is ranging -70 to -80 dBm while normally should be -100 to -108

[nomanpatrick]

Well then there is nothing that you can do to reduce the interference. Maybe you can tell them to reduce the power lol.

[wolverine]

Quite an interesting problem. Jammers are fairly simple devices but as you are finding out they can cause big problems. They usually cover the whole band e.g 2100 MHz, 900Mhz, 1800Mhz which explains why changing the UARFCN didn't accomplish much.

Have you done an RF survey of the area? Is the jamming signal fairly well contained within the prison? If it is, then the UL RSSI is degraded due to the handsets in the prison trying to access the network using ever increasing power.

As the RACH uses open loop power control they will keep ramping their power according to the step sizes and number of attempts you have dictated as the network operator.

If I was you I would have a look at the RACH related parameters and lower them so the handsets don't power up as much during access attempts. You can also limit the max power UEs can transmit as well (usually this is set to 21dBm).

Depending on your vendor you might be able to apply these changes on a per cell basis which will be ideal as you don't want to change your whole RNC parameter design just because of this jammer.

In some countries, the use of jammers is illegal (as the operator has paid to be able to use that part of the spectrum exclusively) so you might want to explore that aspect as well.

[baltoudi]

Quite an interesting problem. Jammers are fairly simple devices but as you are finding out they can cause big problems. They usually cover the whole band e.g 2100 MHz, 900Mhz, 1800Mhz which explains why changing the UARFCN didn't accomplish much.

Have you done an RF survey of the area? Is the jamming signal fairly well contained within the prison? If it is, then the UL RSSI is degraded due to the handsets in the prison trying to access the network using ever increasing power.

As the RACH uses open loop power control they will keep ramping their power according to the step sizes and number of attempts you have dictated as the network operator.

If I was you I would have a look at the RACH related parameters and lower them so the handsets don't power up as much during access attempts. You can also limit the max power UEs can transmit as well (usually this is set to 21dBm).

Depending on your vendor you might be able to apply these changes on a per cell basis which will be ideal as you don't want to change your whole RNC parameter design just because of this jammer.

In some countries, the use of jammers is illegal (as the operator has paid to be able to use that part of the spectrum exclusively) so you might want to explore that aspect as well.

Appreciate in your thought.
Regarding the RACH related parameters, i have far earlier configured the utrancell settings to follow the recommended ones:
maxPreambleCycle 32
powerOffsetP0 1
powerOffsetPpm -4
preambleRetransMax 32
preambleSignatures 65535

that would I believe makes the Ue slowly power up during access attempts. However I also agree w/ you to limit the Ue Txpower upto certain level eventhough the highness of UL RSSI (on node B) majority contributed by the Jammer rather than excessive UL Tx Power from simultaneous Ues.
Anyway thanks for sharing your thought, I'll update you later w/ the results...

[tsiz]

Appreciate in your thought.
Regarding the RACH related parameters, i have far earlier configured the utrancell settings to follow the recommended ones:
maxPreambleCycle 32
powerOffsetP0 1
powerOffsetPpm -4
preambleRetransMax 32
preambleSignatures 65535

that would I believe makes the Ue slowly power up during access attempts. However I also agree w/ you to limit the Ue Txpower upto certain level eventhough the highness of UL RSSI (on node B) majority contributed by the Jammer rather than excessive UL Tx Power from simultaneous Ues.
Anyway thanks for sharing your thought, I'll update you later w/ the results...

Try to change the max preamble cycle to 4, preamble retransmax to 8. I am sure this will not help in anyway the signals from the jammers..but you should see a decent improvement in accessibility.

As the previous poster had mentioned, make sure that Jammers are legal in your state..over here it is totally illegal to use jammers and you can bring in the legal department to take care of it.

There won't be any change if you change frequencies as jammers support many bands at the same time.