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

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)

RRC operation modes?

What are the RRC operation modes?

There are two types of Mode 

1. Idle mode 

2. Connected mode.

There are 4 RRC States: Cell_DCH, Cell_FACH, URA_PCH and Cell_PCH.

Idle Mode: In idle mode, after the UE is switch ON and UE is able to receive system information message from cell.

CELL_DCH: In this state dedicated physical channel is allocated to the UE in UL and DL active set level

CELL_FACH: No dedicated channel is allocated to UE, But RACH and FACH cannel can be used, both transferring signaling message and small amount of data. And in this state UE perform cell re-selection and after a reselection always send a cell update message to RNC

CELL_PCH: In this state UE perform to monitoring of paging information

URA_PCH: It is similar to CELL_PCH expected that the UE does not execute cell update after each re-selection, but instead read URA (UTRA registration area) identities from the broadcast channel.

Cell Search procedure in WCDMA

Cell Search procedure:

During the cell search, the mobile station searches for a cell and determines the downlink scrambling code and common channel frame synchronization of that cell. The cell search is typically carried out in three steps: slot synchronization; frame synchronization and code-group identification; and scrambling-code identification.

Step 1: Slot synchronization.

During the first step of the cell search procedure, the mobile station uses the SCH’s primary synchronization code to acquire slot synchronization to a cell. This can be done with a single matched filter matched to the primary synchronization code that is common to all cells.

Step 2: Frame synchronization and code-group identification.

During the second step of the cell search procedure, the mobile station uses the SCH’s secondary synchronization code to find frame synchronization and identify the code group of the cell found in the first step. This is done by correlating the received signal with all possible secondary synchronization code sequences and identifying the maximum correlation value. Because the cyclic shifts of the sequences are unique, the code group and the frame synchronization are determined.

Step 3: Scrambling-code identification.

During the third and last step of the cell search procedure, the mobile station determines the exact primary scrambling code used by the found cell. The primary scrambling code is typically identified through symbol-by-symbol correlation over the CPICH with all codes within thecode group identified in the second step. Afterthe primary scrambling code has been identified; the primary CCPCH can be detected. And the system- and cell specific BCH information can be read.

WCDMA Air interface channel

Briefly describe UMTS air interface channel types and their functions.

There are 3 types of channels across air interface – physical channel, transport channel and logical channel:

·         Physical Channel: carries data between physical layers of UE and NodeB.

·         Transport Channel: carries data between physical layer and MAC layer.

·         Logical Channel: carries data between MAC layer and RRC layer.

1.      Logical Channel:

·         Control channel:   BCCH, PCCH, CCCH, DCCH.

·         Traffic channel:    DTCH, CTCH.

2. Transport Channel:

·         Common control channel:  BCH, FACH, PCH, RACH, CPCH.

·         Dedicated channel: DCH, DSCH.

3.      Physical Channel:

·         Common control channel: P-CCPCH, S-CCPCH, P-SCH, S-SCH, CPICH,        AICH, PICH, PDSCH, PRACH, PCPCH, CD/CA-ICH.

·         Dedicated channel:         DPDCH, DPCCH.

Broadcast Control Channel (BCCH):

 It broadcast system control information for all mobiles in a cell like Code values in the cell, neighbor information, allowed power levels in downlink direction.

Paging Control Channel (PCCH):

   It transfers paging information in downlink direction.  Network page the mobile to discover the UE location or UE in a cell connected state.

Common Control Channel (CCCH):

Network may have certain tasks which are or may be common to UE in the cell. It’s being used in both direction DL & UL. The CCCH is also used when UE is accessing a new cell after cell reselection.

Dedicated Control Channel (DCCH):

When there is dedicated/active connection means RRC connection between the network and the mobile, the control information transferred using DCCH. It’s a bi-directional channel.

Dedicated Traffic Channel (DTCH):

It is used transfer the user data between the network and the UE in both uplink and downlink directions.

Common Traffic Channel (CTCH):

It is used to transfer the data from one point to all mobiles or a specified group of mobiles.

Dedicated Channel (DCH):

 It is the channel used to send dedicated control and user data between UE and the network in both uplink & downlink directions

Random Access Channel (RACH):

It is used to send control information from UE in the uplink direction. Also may carry short user packets.

Forward Access Channel (FACH):

It is a downlink common channel used to send small amounts of control and user data.

Broadcast Channel (BCH):

It broadcast system information in the downlink direction for all mobile stations in a cell.

Paging Channel (PCH):

It’s a downlink common channel used to send paging notification messages.

Dedicated Channel (DCH):

It is a channel that is used to send dedicated control and user data between the UE and the network in both directions

(Paging Indicator Channel) PICH:

 It is used to carry paging and notification message to all UEs and it is always associated with SCCPCH

 (Acquisition Indicator channel) AICH:

It is used in random access procedure by network to indicate that the RACH preamble was detected

(Synchronization channel) SCH:

It is downlink channel. It is used to cell search procedure and synchronization with network. There is two type of SCH primary & secondary

 (Physical Random access channel) PRACH:

It is uplink channel and Initial message when UE want gain access to network and transfer small amount of data

(common Pilot channel) CPICH:

It is downlink channel and used to continuously sending scrambling code to cell. It is also aids channel estimation for cell re-selection and Handover for UEs. There are two types of CPICH- Primary and secondary.

 (Primary-common control physical channel) P-CCPCH:

It is downlink channel and used to carry Synchronization channel (SCH) and BCH. It has fixed rate of 30 Kbps.

 (Secondary- common control physical channel) S-CCPCH:

It is downlink channel and used to carry PCH and FACH. It has variable bit rate from 30kbps to 1,920 kbps.

Dedicated Channels:

Dedicated Physical Data Channel (DPDCH)

Dedicated Physical Control Channel (DPCCH)

Dedicated Physical Control Channel (DPCCH)

For each radio link, there is one DPCCH, it carries control information like

• Pilot bits (used to support channel estimation at rake receiver)
• Transmit Power Control (TPC) commands (Used power control)
• Feedback information (FBI) needed with transmit diversity
• Transport Format Combination Indicator (TFCI)

Spreading factor is always 256.

Dedicated Physical Data Channel (DPDCH)

 Each radio link may have no DPDCHs or several DPDCHs.

• Spreading factor for the DPDCH can be between 256 and 4.

DPCCH & DPDCH are time – multiplexed in downlink but uplink these are I/Q modulation.