WCDMA Basics Overview

RAN OVERVIEW

Umts fdd air interface overview

SCRAMBLING CODES

• Scrambling Codes (SCs) are used to identify and distinguish sectors from one another in 3GPP compliant WCDMA networks.

• Mobile handsets utilize Scrambling Codes to report the accessible sectors to the network.

• There are a total of 512(0-511) unique Scrambling Codes available, which must be reused throughout the network to accommodate the thousands of sectors that have to be identified.

Pilot Coverage

• Pilot coverage is the area where the CPICH coming from best serving cell is detectable , i.e. Received by an UE with sufficient quality & signal strength to be able to camp to cell ,pilot coverage hole are the point where this condition is not met .

• Based on expereince from WCDMA network ,the pilot coverage creiteria for any UE is given below:

Coverage level RSCP [dBm] Ec/No [dB]

Sufficient RSCP > -100 Ec/No > -14

Poor -115 < RSCP < -100 -16 < Ec/No < -14

No coverage RSCP < -115 Ec/No < -16

• All other signals received that exceed the Active Set Size act as interference which degrades the performance of the system.

Pilot pollution

• Pilot pollution is the detection of many high power pilots as compared to best serving pilot that do not contribute to the received signal .

• The UE has the ability to constructively use signals in soft/softer handover,

• All the other signals received that exceeds the max Active Set act as interferers.this interference degrades the performance.

• As the power of CPICH (Common Pilot Channel) is reduced, the pilot signal of the cell becomes weaker both in its intended coverage area as well as in the areas where it causes interference and pilot pollution.

• While the reduction of pilot pollution is good, the reduction of pilot power in the intended coverage area might have negative consequences.

Accessibility ,Retainibility ,Throughput ,PDP Context Activation Failure

• Accessibility performance can be measured by call setup success rate. Call setup success rate is counted as the number of successful call set-ups divided by the total number of call setup attempts.

• Retainability performance can be measured by dropped call rate.

• Retainability = 100% - (dropped call rate)• Dropped call rate should be measured as the number of dropped

calls over the total number of calls.• Throughput is defined as packet data sent per second.• Average Throughput= Sent packet data / Total packet duration.• When RRC has been established the UE will send the “Activate

PDP Context Request” message to the system. . It happens that the UE will receive an “Activate PDP Context Reject” message.

Accessibility Flowchart(PS & CS Access Failure & Causes)

Definition and Key Performance Indicators

• Accessibility Definition– Ability to successfully establish a radio connection or

radio access bearer for a requested quality of service (i.e. QoS).

• Key Performance Indicators– Successful RRC connection setup– Successful RAB establishment

Definition and Key Performance indicators

• RRC Connection Success Rate - CS– 100 * (pmTotNoRrcConnectReqCsSucc/

pmTotNoRrcConnectReqCs)• RAB Establishment Success Rate - Speech

– 100* (pmNoRabEstablishSuccessSpeech/ pmNoRabEstablishAttemptSpeech)

• Accessibility - Speech– 100 * (pmTotNoRrcConnectReqCsSucc/

pmTotNoRrcConnectReqCs) * (pmNoRabEstablishSuccessSpeech/ pmNoRabEstablishAttemptSpeech)

• Note: Redirection of RRC connection attempts due to Load sharing and emergency calls are not considered in the above formulas

Definition and Key Performance indicators

• RRC Connection Success Rate – Packet– 100 * (pmTotNoRrcConnectReqPsSucc /

pmTotNoRrcConnectReqPs) • RAB Establishment Success Rate – Packet Interactive

– 100* (pmNoRabEstablishSuccessPacketInteractive / pmNoRabEstablishAttemptPacketInteractive)

• RAB Establishment Success Rate – Packet Interactive HS– 100 *(pmNoRabEstablishSuccessPacketInteractiveHs ) /

(pmNoRabEstablishAttemptPacketInteractiveHs• Packet Interactive Accessibility

– 100 * (pmTotNoRrcConnectReqPsSucc / pmTotNoRrcConnectReqPs) * (pmNoRabEstablishSuccessPacketInteractive / pmNoRabEstablishAttemptPacketInteractive)

Note: Redirection of RRC connection attempts due to Load sharing is not considered in the above formulas

Retainability Definition and Indicator

• Retainability Definition: The ability of a network to keep already established calls up until they are terminated by end-users

• Retainability is one the most imprtant KPI for network performance

• Performance Indicator: Abnormal release (drop)• Low Retainability performance could be due to:

– Poor coverage– High inteferance– Missing neighbour relation– Wrong parameters setting

Retainability Flowchart

Missing Neighbour

• Missing Neighbor Drop• – WNCS Analysis;• – Check Neighbor cell availability (RNC – MO Utrancell):• administrativestate and operationalstate;• pmCellDowntimeMan and pmCellDowntimeAuto;• – Check Propagation Delay in order to detect overshooter

cells:• RBS: pmx . pmpropagationdelay -m 72 -a• * Note: 72 is the time window that you want to analyze,• expressed in hours. You can set the time that best suits• your analysis

RL Add Failure Drop

• RL Add Failure Drop• – Check RBS Hardware faults / alarms• Check alarms through al, ala, alt, alk, etc.• Check hardware faults through lhsh commands• – Check T1/IMA Errors• RBS: pmx . pmes|pmses|pmuas –m 72 –a• pmxh . pmes|pmses|pmuas –m 72 –a• * Note: 72 is the time window that you want to analyze,• expressed in hours. You can set the time that best suits• your analysis.• – Check cell availability (RNC – MO Utrancell):• administrativestate and operationalstate;• pmCellDowntimeMan and pmCellDowntimeAuto

UL Synch Drop

• UL Synch Drop• – Check UE Tx Pwr:• WMRR• Parameter maxTxPowerUl (RNC – MO Utrancell)• – Check Propagation Delay (see command in slide 14 –

Missing• Neighbor Drop)• – GPEH analysis

IRAT Drop

• IRAT Drop• – Neighbor list optimization• – Check Cell Designation/Layer Management settings (RNC

–• MO Utrancell):• - hoType, qQualMin, qRxLevMin,• usedFreqThresh2dEcno,• usedFreqThresh2dRscp

Congestion Drop

• Congestion Drop• – Check Propagation Delay (see command in slide 14 –

Missing• Neighbor Drop)• – Check available CE the RBS (UL/DL): lget .

channelelements• – Check CE usage in the RNC (UL/DL): cedhr (it lists the CE• usage per Iub link)

IUR & other Drop

• IUR Drop• – Check IUR link (RNC: pmr)• Other Drop• – Check Transport issue:• T1 / IMA (see command in slide 15 – RL Add Failure• Drop)• AAL2 failures• - RNC: pmxh -m 24 .• pmUnSuccInConnsLocal|pmUnSuccInConnsRe• mote|pmUnsuccessfulConnsInternal -a• * Note: 24 is the time window that you want to analyze,• expressed in hours. You can set the time that best suits• your analysis.

Throughput

Uplink throughput :is defined as the number ofbits transmitted to the RLC layer from the MAC layer.

Downlink throughput :is defined as the number of bits transmitted from the RLC layer to the MAC layer. The RLC instances to be considered for the buffer load and throughput measure depends on the UE state and the algorithm using the measure

PDP Context Activation

Process PDP Context Activation

• The MS sends an Activate PDP Context Request (NSAPI, TI, PDP Type, PDP Address, Access Point Name, QoS Requested, PDP Configuration Options) message to the SGSN. The MS shall use PDP Address to indicate whether it requires the use of a static PDP address or whether it requires the use of a dynamic PDP address. The MS shall leave PDP Address empty to request a dynamic PDP address. The MS may use Access Point Name to select a reference point to a certain external network and/or to select a service. Access Point Name is a logical name referring to the external packet data network and/or to a service that the subscriber wishes to connect to. QoS Requested indicates the desired QoS profile

WCDMA HANDOVER

• 3 TYPES OF HANDOVER:• SOFT /SOFTER HANDOVER(UE communicating with 2 or more sectors on

different RBS.if the sectors belong to same RBS its known as softer handover.)

• Inter frequency handover(allows for an ongoing call to be transferred from one frequency to another in a case where a UE is moving out of coverage of the source frequency.)

• Inter Radio Access Technology (IRAT) handover(Handover to /from GSM for coverage reason.

• IRAT Principle: