What are the possible causes for a Drop Call on a UMTS network?


What are the possible causes for a Drop Call on a UMTS network?
             Poor Coverage (DL / UL)
 Pilot Pollution / Pilot Spillover
 Missing Neighbor
 SC Collisions
 Delayed Handovers
 No resource availability (Congestion) for Hand in
 Loss of Synchronization
 Fast Fading
 Delayed IRAT Triggers
 Hardware Issues
 External Interference

What are the possible causes for an Access Failure in UMTS?


What are the possible causes for an Access Failure in UMTS?      
·         Missing Neighbors
·         Poor Coverage
·         Pilot Pollution / Spillover
·         Poor Cell Reselection
·         Core Network Issues
·         Non – availability of resources. Admission Control denies
·         Hardware Issues
  • Improper RACH Parameters
  • External Interference

What are the processing gains for CS and PS services


What are the processing gains for CS and PS services?
CS12.2:    25dB
PS-64:      18dB
PS-128:    15dB
PS-384:    10dB
HSDPA:     2dB

3G Basic Parameter

Basic Parameters of WCDMA
Frequency Band                                     :           2100 MHz
1920-1980MHz (UL) &2110-2170 MHz (DL)
Duplex Space                                         :           190 MHz
Channel bandwidth                                 :           5 MHz
Coding Spacing                                      :           200 KHz (RASTER)
UARFCN Range                                       :           10562-10838 (Total ARFCN – 276)
Duplex mode                                          :           FDD and TDD
Downlink RF channel structure                 :           Direct spread
Chip rate& Chips                                    :           3.84 Mcps& It is pulse of spreading spectrum n 
                                                                        It’s in rectangular shape of +1 & -1
Frame length                                         :           10 ms (38400 chips) = 15Slots, & 1slot = 2650chips
Superframe                                           :           A Superframe has a duration of 720ms and consists
                                                                        Of 72 radio frames. The super frame boundaries are
Defined by the System Frame Number (SFN)
Spreading modulation                             :           Balanced QPSK (downlink)
Dual-channel QPSK (uplink)
Complex spreading circuit
Data modulation                                   :           QPSK (downlink) & BPSK (uplink)
Channel coding                                     :           Convolution (Voice) and turbo (data) codes
Coherent detection                               :           User dedicated time multiplexed pilot (DL and UL), 
Common pilot in the downlink
Channel multiplexing in downlink            :           Data and control channels time multiplexed
Channel multiplexing in uplink                :           Control and pilot channel time multiplexed
I&Q multiplexing for data and control channel
Spreading factors                                  :           4–256 (uplink), 4–512 (uplink)
Power control                                        :           Open and fast closed loop (1.6 kHz)
Power control period                              :           1500Hz
Power control step size                          :           0.5, 1, 1.5 and 2db
Power control range
Handover                                              :           Soft HO, softer HO, Inter frequency and IRAT HO

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About Us  Telecomstudy18
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This blog mainly focus on below categories:
GSM
WCDMA
CDMA

LTE 

SIR, Ec/Io, RTWP, RSCP, and Eb/No in WCDMA



What is SIR?
SIR is the Signal-to-Interference Ratio – the ratio of the energy in dedicated physical control channel bits to the power density of interference and noise after dispreading.
What is RSCP?
RSCP stands for Received Signal Code Power – the energy per chip in CPICH averaged over 512 chips.
What is Eb/No?
By definition Eb/No is energy bit over noise density, i.e. is the ratio of the energy per information bit to the power spectral density (of interference and noise) after dispreading.
Eb/No = Processing Gain + SIR
For example, if Eb/No is 5dB and processing gain is 25dB then the SIR should be -20dB or better.
What are the Eb/No targets in your design?
The Eb/No targets are dependent on the service:
 on the uplink, typically CS is 5 to 6dB and PS is 3 to 4dB – PS is about 2dB lower.
 on the downlink, typically CS has 6 to 7dB and PS is 5 to 6dB – PS is about 1dB lower.


Why is Eb/No requirement lower for PS than for CS?
PS has a better error correction capability and can utilize retransmission, therefore it can afford to a lower Eb/No.  CS is real-time and cannot tolerate delay so it needs a higher Eb/No to maintain a stronger RF link.
What is Ec/Io?
Ec/Io is the ratio of the energy per chip in CPICH to the total received power density (including CPICH itself).
Sometimes we say Ec/Io and sometimes we say Ec/No, are they different?
Io = own cell interference + surrounding cell interference + noise density
No = surrounding cell interference + noise density
That is, Io is the total received power density including CPICH of its own cell, No is the total received power density excluding CPICH of its own cell.  Technically Ec/Io should be the correct measurement but, due to equipment capability, Ec/No is actually measured.  In UMTS, Ec/No and Ec/Io are often used interchangeably.

What is RTWP? What is the significance of it?    
 Received Total Wide-band Power
         It gives the Total Uplink Power (Interference) level received at NodeB

WCDMA Handover Parameter



Handover Parameter

maxActiveSet: Maximum number of cells allowed in the Active Set.
IndividualOffset:
Offset value which can be assigned to each cell. It is added to the measurement quantity before the UE evaluates whether or not an event has occurred. It can either be positive or negative value.
measQuantity1:
Defines the measurement quantity for intra-frequency reporting evaluation. Default is Ec/No.
hsQualityEstimate:
Indicates whether Ec/No or RSCP should be used for indicating "best cell" for HS-DSCH Cell Change. Default is RSCP.
reportingRange1a:
Relative threshold referred to the CPICH of the best cell in the Active Set used as evaluation criteria for event 1a (a primary CPICH enters the reporting range).
reportingRange1b:
Relative threshold referred to CPICH of the best cell in the Active Set used as evaluation criteria for event 1b (a primary CPICH leaves the reporting range).
reportingInterval1a:
Time between periodic reports at event-triggered periodic reporting for event 1a
timeToTrigger1a:
If event 1a condition is fulfilled during at least a time greater than or equal to timeToTrigger1a milliseconds, then event 1a occurs.
timeToTrigger2dEcno:
If event 2d condition is fulfilled during at least a time greater than or equal to timeToTrigger2dEcno milliseconds, then event 2d occurs

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


 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.

Brief describe the advantages and disadvantages of soft handover?


Advantages:
  Overcome fading through macro diversity.
  Reduced Node B power which in turn decreases interference and increases capacity.
  Reduced UE power (up 4dB), decreasing interference and increasing battery life.
Disadvantages:
  UE using several radio links requires more channelization codes, and more resources on the Iub and Iur interfaces

What are the major differences between GSM and UMTS handover decision?


GSM:
 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.

WCDMA Handover



Handover: call transfer one cell to another cell without disconnecting
There are three types of handover used in WCDMA.
1.    Intra frequency Handover (Soft & Softer )
2.    Inter frequency handover
3.    IRAT Handover
Soft Handover:
            WhenHandover between two NodeB within same carrier frequency and add in active set.
Soft handover means that the radio links are added and removed in a way that the UE always keeps at least one radio link to the UTRAN. Soft handover is performed by means of macro diversity, which refers to the condition that several radio links are active at the same time.
Softer Handover:
                        When Handover between two cells within same NodeB and ADD in active set.
IRAT Handover:
                        When handover between WCDMA to GSM and GSM to WCDMA.

What are the three sets in handover?
The 3 sets in handover are:
§ Active set – the list of cells which are in soft handover with UE.
§ Monitored set – the list of cells not in active set but RNC has told UE to monitor.
§ Detected set – list of cells detected by the UE but not configured in the neighbor list.

 
4 events associated with soft (or softer) handover: UE view
•           1A  Add
•           1B  Remove
•           1C  Replace
•           1D  Change of best cell
•          1E   A Primary CPICH becomes better than an absolute threshold
•          1F   A Primary CPICH becomes worse than an absolute threshold Intrafrequency reporting events for TDD

WCDMA - Power Control


Power Control:
We know all users are in same frequency at same time soPower control is used to controlled the level of the transmitting power in order to minimize interference,improve quality of connection, reducing of NEAR-FAR effects and increase capacity of system.
There are three type of power control
Open loop power control
Inner loop Closed loop power control
Outer loop closed loop power control

Open loop power control:
                                      The UE determine an estimation of the downlink path-loss between thee base station and the UE by the measuring of UTRA carrier received signal strength at the mobile through the medium of the SI message on the P-CCPCH. 
Outer loop closed loop power control:
                                             It is used to compare the received BLER (Block error rate) and target the BLER.
Inner loop Closed loop power control:
                                   It is used to compare the received SIR (Signal to interference ratio) and target the SIR
Power control Parameter:
Primary CPICH Power:                                      Power to be used for transmitting the PCPICH.
BCH Power:    BCH power is the power to be used for transmitting on the BCH, relative to the primary CPICH Power value.
Primary SCH Power:
Secondary SCH Power:
AICH Power:     AICH power to be used for transmitting on AICH, relative to the primary CPICH Power value.
The value range is set in a short term to cover both the RRC and NBAP spec.

WCDMA Congestion Control and Its Parameter



What is Congestion Control?
Congestion Control monitors the dynamic utilization of specific cell resources and insures that overload conditions do not occur.  If overload conditions do occur, Congestion Control will immediately restrict Admission Control from granting additional resources.  In addition, Congestion Control will attempt to resolve the congestion by either down switching, or terminating existing users.  Once the congestion is corrected, the congestion resolution actions will cease, and Admission Control will be enabled.
Parameter of congestion control:
PwrAdm:
 Admission limit for admission on DL cell carrier power.

PwrAdmOffset:
Relative admission limit on DL cell carrier power.

PwrOffset:
 Used by Congestion Control.

PwrHyst:
 Hysteresis time setting for detection of congestion in the DL transmitted carrier power.

iFCong:
Threshold at which UL congestion is detected in the cell.

iFOffset:
Offset that, together with parameter iFCong, determinesthe RTWP measurement level at which UL congestionis to be resolved.

iFHyst:
Hysteresis time setting for detection of congestion in theUL RTWP in a cell.

WCDMA - Admission control Parameter


What is Admission Control?
Admission control is used to reduce soft congestion. Admission Control make decision on whether call should be admitted or NOT. It could be new call or handover call. In case, if a cell is heavily a loaded and enough resources in terms of power, codes or CEs are not available.
One of the following reasons to reject adm attempt:
-       OVSF code resource is low
-       Iub bandwidth resource is low
-       CPU resource is low
-       Call request is rejected by CAC module for DCH.
Parameter of Admission control:
Admission Control will be disabled in the RNC when ulHwAdm and dlHwAdm are set to 100.


UlHwAdm:
Admission limit on RBS UL HW resource utilization applicable to non-handover guaranteed admission requests. This parameter is also used together with beMarginUlHw for non-handover non-guaranteed admission requests.
The UL HW admission policy   :    UlHwAdm >= beMarginUlHw

DlHwAdm:
Admission limit on RBS DL HW resource utilization applicable to non-handover guaranteed admission requests. This parameter is also used together with beMarginDlHw for non-handover non-guaranteed admission requests.
DlHwAdm>= beMarginDlHw

DlCodeAdm:
Admission limit used for admission based on DL channelization code tree usage (percentage of the tree in use).
The following expression MUST be true: dlCodeAdm >= beMarginDlCode * 5
beMarginDlCode:
Admission margin for DL code utilization in DL (non-handover, non-compressed mode RLs only).
The following expression MUST be true: beMarginDlCode * 5 <= dlCodeAdm

CompModeAdm: Absolute admission limit for the number of radio links in compressed mode in a cell.
sf8Adm:
          Admission policy for admission on the number of Spreading Factor = 8 (traffic class=non-guaranteed, setup type=<all>) simultaneous connections in a cell in DL (SF histogram).
Default setting is to disable the admission policy.

sf16gAdm
                 Maximum number of radio links with Spreading Factor (SF) =16 in DL for which new guaranteed admission requests will continue to be allowed. Reaching or exceeding this number of radio links (any service class) using DL SF = 16 will block setup/adding any more guaranteed service class radio links requiring additional DL SF=16 for this cell.
16 means that no blocking of DL SF=16 requests will occur

PwrAdm:
Admission limit for admission on DL cell carrier power.The following expressions MUST be true:pwrAdm + pwrAdmOffset + pwrOffset <= 100%
PwrAdm>= beMarginDlPwr

PwrAdmOffset:
Relative admission limit on DL cell carrier power.The following expression MUST be true:
 PwrAdm +pwrAdmOffset+pwrOffset <= 100%

MinimumRate:
Minimum rate for maximum power mapping.

InterRate:
Intermediate rate for maximum power mapping.

MaxRate:
Maximum rate for maximum power mapping.                   MinimumRate <= interRate <= maxRate

AseUlAdm:
 Admission limit for admission on ASE in UL.
The following expression MUST be true: aseUlAdm >= beMarginAseUl

AseDlAdm:
Admission limit for admission on max capacity (ASE level) in DL.
The following expression MUST be true:aseDlAdm >= beMarginAseDl

BeMarginAseDl:
                           Relative admission limit for admission on ASE for nonguaranteed bitrate calls (traffic class 'background' or 'interactive') in DL.
The following expression MUST be true: beMarginAseDl <= aseDlAdm