Thursday, June 30, 2011

What are the processing gains for CS and PS services?

CS12.2:      25dB
PS-64:        18dB
PS-128:      15dB
PS-384:      10dB
      HSDPA:       2dB

Click Here to Get
WCDMA Link Budget
GSM Link Budget

Tuesday, June 28, 2011

Why TMA are installed at the top near the antenna and not the bottom near the NodeB?

Based on Friis Equation, having a TMA near the BTS will have the top jumper and main feeder losses (noise figures) cascaded in and a TMA will not be able to help suppress the losses.

Download Useful Tools:

Monday, June 27, 2011

What is typical TMA gain?

TMA typically has a 12 dB gain; however, the effective gain comes from noise figure reduction and the gain is close or equivalent to the feeder loss.

Download Planning Tools:

WCDMA Planning Tool-MapInfo

Sunday, June 26, 2011

What are the pros and cons (advantages and disadvantages) of TMA?

On the upside, a TMA reduces system noise, improves uplink sensitivity and leads to longer UE battery life.  On the downside, TMA imposes an additional insertion loss (typically 0.5dB) on the downlink and increases site installation and maintenance complexity.

Download Good Documents:

Saturday, June 25, 2011

How does TMA work?

A TMA reduces system noise, improves uplink sensitivity and leads to longer UE battery life.
Sensitivity is the minimum input power needed to get a suitable signal-to-noise ratio (SNR) at the output of the receiver.  It is determined by receiver noise figure, thermo noise power and required SNR.  Thermo noise power is determined by bandwidth and temperature, SNR is determined by modulation technique, therefore the only variable is noise figure.
The cascading noise figure can be calculated by Friis equation (Herald Friis):
NFt = NF1 + (NF2-1)/G1 + (NF3-1)/(G1*G2) + ... + (NFi-1)/(G1*G2*...*Gi)
As the equation shows, the first block imposes the minimum and the most prominent noise figure on the system, and the following blocks imposes less and less impact to the system provided the gains are positive.  Linear passive devices have noise figure equal to their loss.  A TMA typically has a gain of 12dB.
There are typically top jumper, main feeder and a bottom jumper between antenna and BTS.  A TMA placed near antenna with a short jumper from antenna provides the best noise figure improvement – the noise figure will be restricted to the top jumper loss (NF1) and TMA ((NF2-1)/G1), and the remaining blocks (main feeder and bottom jumper) have little effect.
To summarize, a TMA has a gain that’s close to feeder loss.

More For You Only...



Friday, June 24, 2011

What is the difference between dB and dBm?


dBm is a unit of power level, measured in milli-watts in logarithm scale, that is,
dBm = 10 * log(W*1000)  where W is the power in Watts
dB is not a unit, it is the difference in dBm

Download Document on WCDMA Capacity Planning
Download WCDMA Radio Network Capacity Planning  
Download Document on RRC KPIs 

Wednesday, June 22, 2011

What is a typical maximum path loss?

The maximum path loss is dependent on the service and vendor recommendations; typically it is in between 135 to 140dB for urban areas and between 150 to 160dB for rural areas.

More From RF Optimization

Tuesday, June 21, 2011

What is a typical UE sensitivity level?

The service and load determines the UE sensitivity; in general, in no-load condition, the sensitivity is between -105dBm and -120dBm.  For Ericsson, the UE sensitivity level is calculated at around:
CS12.2:     -119 dBm
PS-64:        -112 dBm
PS-128:      -110 dBm
PS-384:      -105 dBm
HSDPA:      -95 dBm
Download Good Documents:

E Book on WCDMA for UMTS Networks
Download WCDMA IRAT Handover Document.
Good Discussion Topic on Congestion Control 

Monday, June 20, 2011

What is a typical NodeB sensitivity level?

The service and load determines the NodeB sensitivity; in general, in a no-load condition, the sensitivity is between -115dBm to -125dBm.  For Ericsson, the NodeB sensitivity level is calculated at around:
CS12.2:      -124 dBm
PS-64:        -119 dBm
PS-128:      -115 dBm
PS-384:      -115 dBm

Sunday, June 19, 2011

What do you understand by CQI Measurements?

Channel Quality Estimation (CQI) for HSDPA sessions only.
In order to aid scheduling and TFRC selection in the RBS, the UE sends a channel quality indicator (CQI) report on the uplink.
The CQI report estimates the number of bits that can be transmitted to the UE using a certain assumed HS-PDSCH power with a block error rate of 10%.

Saturday, June 18, 2011

How Power Control is implemented in HSDPA?

Initial Power is set in the same way as open Loop Power control of DCH & there is no further power control on HSDPA Shared Channel HS-DSCH. The Channel Rate is controlled by adaptive modulation & coding formats.
The principles and functionality of the power control for the HSDPA associated dedicated channels are the same as for the DPCH power control.
HS-DPCCH power is an offset relative to DPCCH depending upon whether the UE is in soft handoff or not.
The Power for HS-SCCH is fixed.


You might also like:

Wednesday, June 15, 2011

What can we try to improve when access failure is high?

When access failure is high we can try the following to improve RACH performance:
  • Increase maximum UE transmit power allowed: Max_allowed_UL_TX_Power. 
  • Increase power quickly: power_Offset_P0.
  • Increase number of preambles sent in a given preamble cycle:preamble_Retrans_Max.
  • Increase the number of preamble cycles: max_Preamble_Cycle.
  • Increase number of RRC Connection Request retries: N300.

Tuesday, June 14, 2011

What do you understand by Directed Retry?

When there is a co-existing GSM RAN, excess traffic in a WCDMA cell may be offloaded to GSM If a call is chosen for Directed Retry to GSM, the request for the speech RAB will be rejected with cause "Directed retry" and then a request is made to the core network to relocate the UE to a specific GSM cell, using the Inter-RAT handover procedure. This handover is a blind one since the target cell is chosen not based on UE measurements. Therefore, the target cell must be co-located with the WCDMA cell. Co-located GSM cells are assumed to have similar coverage and accessibility as their respective WCDMA cells.

Click Here to discuss Ericsson WCDMA and HSDPA issues 
Click Here to Discuss NSN GSM-GPRS-EDGE Problems        

Monday, June 13, 2011

How is inter-frequency Handover triggered?

The network decides that inter frequency measurements need to be performed and sends the MEASUREMENT CONTROL MESSAGE with Measurement type set to Inter-Frequency measurements. Generally it will set an Event as well along with the measurements. The following are list of Events that can trigger Measurement Report.
  •  Event 2a: Change of Best Frequency
  •  Event 2b: The estimated quality of the currently used frequency is below a certain threshold and the    estimated quality of a non-used frequency is above a certain threshold
  •  Event 2c: The estimated quality of a non-used frequency is above a certain threshold
  •  Event 2d: The estimated quality of the currently used frequency is below a certain threshold
  •  Event 2e: The estimated quality of a non-used frequency is below a certain threshold
  •  Event 2f: The estimated quality of the currently used frequency is above a certain threshold
The Inter-Frequency Handover Evaluation bases its decision on P-CPICH quality measures on the currently used frequency and on one or more non-used frequencies. If the evaluation result is positive, one cell on a non-used frequency is proposed to Inter-Frequency handover Execution.
Inter-Frequency Handover is a hard handover where the UE is ordered by the network to tune to another frequency. This means that there will be small interruptions in the data flow to and from the UE.


Sunday, June 12, 2011

What may happen when there’s a missing neighbor or an incorrect neighbor?

  • Access failure and handover failure: may attempt to access to a wrong scrambling code.
  • Dropped call: UE not aware of a strong scrambling code, strong interference.
  • Poor data throughput.
  • Poor voice quality.

Thursday, June 9, 2011

What are event 2a-2d and 3a-3d?

Events 2a-2d are for inter-frequency handover measurements and events 3a-3d are for IRAT handover measurements.
e3a: the UMTS cell quality has moved below a threshold and a GSM cell quality had moved above a threshold.
e3b: the GSM cell quality has moved below a threshold.
e3c: the GSM cell quality has moved above a threshold.
e3d: there was a change in the order of best GSM cell list.

Wednesday, June 8, 2011

What are the major differences between GSM and UMTS handover?


  • Time-based mobile measures of RxLev and RxQual – mobile sends measurement report every SACH period (480ms).
  • BSC instructs mobile to handover based on these reports.
UMTS:
  • Event-triggered reporting – UE sends a measurement report only on certain event “triggers”.
  • UE plays more part in the handover decision.

GSM:

Tuesday, June 7, 2011

What are the events 1a, 1b, 1c?

e1a – a Primary CPICH enters the reporting range, i.e. add a cell to active set.
e1b – a primary CPICH leaves the reporting range, i.e. removed a cell from active set.
e1c – a non-active primary CPICH becomes better than an active primary CPICH, i.e. replace a cell.
e1d: change of best cell.
e1e: a Primary CPICH becomes better than an absolute threshold.
e1f: a Primary CPICH becomes worse than an absolute threshold.

Sunday, June 5, 2011

What could be the cause of soft handover failure?

  • Undefined neighbors
  • One way Neighbor definition
  • UE issue
  • Resource unavailable at target NodeB
  • Inadequate SHO threshold defined
Discuss on Difference between Handover Failure and Reversion

Wednesday, June 1, 2011

How does UE camp (synchronize) to a NodeB?

1. UE uses the primary synchronization channel (P-SCH) for slot alignment (TS
synchronization).
2. After aligning to NodeB time slot, UE then uses secondary synchronization channel (SSCH) to obtain frame synchronization and scrambling code group identification.
3. UE then uses scrambling code ID to obtain CPICH, thus camping to a NodeB.