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

WCDMA - Idle Mode Parameter

Idle Mode Parameter:

qQualMin:

Minimum required quality level in the cell measured in the UE.

qRxLevMin:

Parameter that indicates the min. required signal strength in the cell

qualMeasQuantity:

Used for decision as to whether the 3G ranking for cell selection and reselection is based on Ec/No or RSCP. Default is Ec/No.

qHyst1:

Hysteresis values used for serving cell, when ranking is based on CPICH RSCP

qHyst2:

Hysteresis values used for serving cell, when ranking is based on CPICHEc/No

qOffset1sn:

Signal strength offset b/w source and target cell for cell ranking based on CPICH RSCP.

qOffset2sn:

Signal offset between serving cell and neighbor cell, based on CPICHEc/No.

sIntraSearch:

Decision on when intra-freq. measurements should be performed. Following criteria is used:

sIntraSearch ≥ qQualmeas - qQualMin (where qQualmeas is the value measured by UE )

sInterSearch:

Parameter is used to make decision to start inter-freq. measurements.

sInterSearch ≥ qQualmeas - qQualMin (where qQualmeas is the value measured by UE )

sRatSearch:

Decision on when GSM measurement should be performed in relation to qQualMin.

sRatSearch ≥ qQualMeas – qQualMin (where qQualmeas is the value measured by UE )

sHcsRatSearch:

Decision on when GSM measurement should be performed in relation to qRxLevMin.

sHcsRatSearch ≥ qRxLevMeas – qRxLevMin (where qRxLevMeas is the value measured by UE)