Low Best Serving PPilot/PTot

The third possible reason is that the pilot power setting is not large enough to fulfill existing downlink load, because low received Ec/No of the best serving pilot channel (near or less than –16dB) can be observed even if there is no other cell

Recommendation

To add a new site with “good coverage control” in the problematic area is a common practice.

Pilot Pollution

Phenomena

In cell_DCH mode, pilot pollution refers to the phenomenon that a UE at one location alters its active set cells frequently (e.g. active set update rate is very high) because many received pilot channels have similar quality (or signal strength) such as Ec/No (or RSCP).

Reason – No Dominant Cell

Due to poor cell planning, a large number of overlapping cells exist at a particular area

Recommendation 1

To change the antenna configurations or reduce the pilot power of the undesired cells is a common practice to remove the cells overlapping.

An alternative solution to remove the cell overlapping is to increase the pilot channel power – Primary CPICH power of the desired cells.

Out of Pilot Coverage Phenomena

During the drive test, following phenomena might be observed.

• Received Ec/No of the pilot channel is less than –16dB and

• Received RSCP of the pilot channel is very low, e.g. <- 100dBm and

• DL RSSI is very low and

• The connection drops eventually Reason – low pilot channel power

To set the low pilot channel power can lead coverage holes. Recommendation 1

The most common solution to overcome this problem is to add a new site in the problematic area.

Recommendation 2

To increase the pilot channel power is an alternative solution.

Insufficient received UL DPCH power Phenomena

During the drive test, following phenomena might be observed through drive test tools and UE tracing function:

• Received Ec/No of the pilot channel is larger than –16dB and

• UE Tx power does not reach the maximum allowed value and

• UL SIR target of the radio connection reaches to the maximum allowed SIR target and

• UL BLER of the radio connection increases and

• The connection drops eventually

Reason

The possible reason that the base station cannot receive high enough power from the uplink dedicated physical channel is because the parameter - maximum allowed UL SIR Target is set too low.

Recommendation

The maximum allowed UL SIR Target should be justified to allow UEs to transmit with higher power.

High UE TX Transmit Power Phenomena

During the drive test, following phenomena might be observed though drive test tools and UE tracing function.

• Received Ec/No of the pilot channel is larger than –14dB and

• Received RSCP of the pilot channel is good, e.g. <-85dBm and

• UE Tx power reaches the maximum UE allowed value (23dB) and

• UL BLER of the radio connection increases

Reason – Uplink Interference

The possible reason that UE transmit with very high power even if with good the downlink quality (Ec/No) and high downlink signal strength (RSCP) is because of UL interference.

The UL interference could be internal interference (generate by other UEs) or external interference (repeater or industry interference).

Recommendation

Check cell UL loading in nearby cells to determine whether the interference is coming from internal. Check external interference with spectrum analyzer if there is external interference exsiting.

Swapped feeders

Phenomena

Due to swapped feeders, many problems will occur such as no downlink coverage, no uplink coverage or high UL/DL interference. The following are some (but not limited to) examples of swapped feeders:

 Case 1: Cell B Tx feeder is swapped with the cell A Tx feeder The following symptoms might be observed:

 Scrambling codes cover wrong directions.

 Handover fails from other cells to Cell A/Cell B because of improper handover relationship or uplink DPCH synchronization problem.

 Connection setup will fail during random access or uplink DPCH synchronization procedures. Connection setup fails during random access or uplink DPCH synchronization procedures.

 Case 2: Cell B Tx feeder is swapped with one of the cell A Rx feeder. The following symptoms might be observed.  There is no downlink coverage. (Cell B desired coverage

area)

 Downlink interference is high. (Cell A desired coverage area)

 Scrambling code covers wrong direction.

 When the UE tries to connect to cell B in cell A area, connection setup fails during random access or uplink DPCH synchronization procedures.

A

C

B

 If the UE tries to handover to cell B in cell A area, the UE may always send addition handover events to UTRAN but handover function always fails due to uplink DPCH synchronization problem.

 The UE connected to cell A transmits with higher UE Tx power than that in normal feeder case because of higher UL interference (e.g. UL RSSI).

 Connection drops when the UE moves to the planned cell B area

 Case 3: One of the cell B Rx feeder is swapped with another cell A Rx feeder. The following symptoms might be observed:

 The UE connected to cell A or/and cell B transmits with higher UE Tx power than that in normal feeder case because of higher UL interference (e.g. UL RSSI).

Recommendation

The direct solution to remove this problem is to ensure no crossed feeders and correct scrambling codes for the all cells in the site.

Low data throughput Phenomena

During the drive test, following phenomena might be observed when downloading files to/from the operator’s server (or the known public server) by FTP and pinging that server simultaneously.

• Average UL or DL throughput of the radio access bearer is much lower than the data rate of the known source or

• Long round trip time or

• Many missing packets.