Scott Baxter 120_C5

Multi-Carrier Operation1x Data PerformancePractical OptimizationAdditional Resources

Multi-Carrier Operation1x Data PerformancePractical OptimizationAdditional Resources

Chapter 5

December, 2003 5 - 1Course 120 (c) 2003 Scott Baxter

It’s A Multi-Carrier/Multi-System/Multi-Manufacturer

World!


Systems are forced to use multiple carriers to achieve needed traffic capacity

• It’s important that the traffic load be divided between carriersPhysically adjacent friendly systems often desire to allow seamless mobile operation across their borders, although they use different carrier frequenciesEven within one large network, seamless mobile operation is desired across serving switch boundariesThese situations are not completely solved in the original IS-95 CDMA vision, so additional standards documents and additional proprietary processes provide the needed functionality

• IS-95: hashing or GSRMs can distribute idle mobiles among carriers• IS-41 - provides intersystem handoffs and call delivery• Proprietary algorithms can distribute in-call traffic among carriers• RF tricks and network proprietary algorithms can support inter-carrier

handoffMulti-Carrier Operation is a complex sport - a quadrathlon or pentathlon!

Multi-Carrier Operation:Mobiles Change Frequencies. When/Why/How?

f5

f4

f3

f2

f1

SystemAcquisition

Idle ModeReselection

Call Start:Ch. Assignment

In Call:Hard Handoff

MRUSDAPRL-AI

Hashing

GSRMMulti-FreqNbrs

ProprietaryNetwork

AlgorithmsNortel: MCTA

Lucent:Motorola: MFCLMF

AuxiliaryHandoff Triggers

•Beacons•Ec/Io, RTDProprietaryProcesses

Remember: Different Mechanisms Apply at Different Stages


Many Network/Carrier Configurations are Possible!

f1

f2

f3

f4

Basic Multi-CarrierOperation

IS-95

IS-95

IS-95

IS-95 f1

f2

f3

f4

Non-originating carrierscan carry more traffic!

IS-95

IS-95

IS-95

IS-95 f1

f2

f3

f4

Some Carriers maysupport 1xRTT

1xRTT

IS-95

IS-95

IS-95

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The Big Picture:CDMA Multicarrier System Overlaying Analog System

CDMA F2CDMA F3

CDMA F1

Analog System


Important Questions:How do idle dual-mode mobiles choose a system?

• When do they select analog operation?How do idle CDMA mobiles change carrier frequencies?How do CDMA mobiles in a call handoff to other carrier frequencies?Can CDMA mobiles in a call hand down to analog operation?When can a dual mode mobile return from analog to CDMA?

Adjoining CDMA Networks of Different Manufacturers

F2F3

F1F2

Brand X System Brand Y System

PSTNOrdinary Interswitch Trunks

(can’t transmit packets, so soft handoff impossible)

At present, only Hard Handoffs work between different manufacturersImportant Questions:

What happens if bordering cells are on the same frequency?• Advantages and drawbacks

What happens if bordering cells are on different frequencies?• Advantages and drawbacks


Adjoining CDMA Networks of the Same Manufacturer

F2F3

F1 F1

F4

Brand X System Brand X System

PSTNATM links

between CDMA packet networks(soft handoffs are desired)

At present, most manufacturers support intersystem soft handoffImportant Questions:

What happens if bordering cells are on the same frequency?• Advantages and drawbacks

What happens if bordering cells are on different frequencies?• Advantages and drawbacks


Basic Principles:System Determination in Idle Mode


CDMA Idle ModeMobile has control, follows the System Determination AlgorithmLook at most recently used frequency.Find Strongest Pilot > Read Sync >If system denied or not preferred, check other frequencies in PRL.Read Paging/Config MessagesIf Multiple Frequencies appear in CDMA Channel List Message, Hash and go to proper frequencyIf GSRM transmitted, go wherever directedMonitor Paging Channel

Analog Idle ModeMobile has control, follows procedures of the StandardFind Strongest CCHMonitor Paging ChannelEvery 3 minutes, rescan for CDMA signal

Avoiding Unwanted Acquisition of Supplemental CDMA Carriers

CDMA Carrier Frequency 2

CDMA Carrier Frequency 1

GSRM GSRM


System acquisition is primarily controlled by the mobile• dual-mode mobiles look for last-used frequency first

Distant mobiles may notice weak Carrier 2 signals beyond the edge of Carrier 2 coverage, and originate calls likely to drop

• system can transmit Global Service Redirection Messages on all out-looking Carrier 2 sectors to immediately force any distant mobiles to reacquire Carrier 1

– there will be no F2 originations on outermost F2 sectors!– However, still possible to soft-handoff into F2 outer sectors

System Determination During Call Setup and Call Continuation


CDMA Conversation StateSystem has control, follows Standard or proprietary procedures•Initial channel assignment: system can select which frequency(most common trigger would be congestion on present frequency)•Normal handoffs are soft, on same frequency, to mobile-selected pilots•Artificial trigger mechanisms can force mobile handoff to different:

1) CDMA frequency, 2) CDMA system, or 3) analog system

Analog Conversation StateSystem has control, follows procedures of the Standard•Mobile can be handed off to different analog cell or even different analog system based on locate receiver measurements•No handoff possible to CDMA from ongoing analog call

Interfrequency Hard Handoff

Mobiles in a call are receiving only their current operating frequency

• They’re unaware of the presence or absence of signals on different carrier frequencies, so they don’t realize when they need to do intercarrier handoffs

Networks use a variety of methods to trick mobiles into appropriate handoffs

• Pilot beacons - “decoy” signals on the current frequency that lure the mobile into disclosing needed information

• Tier-based triggers– Round trip delay thresholds– Ec/Io and other parameter

thresholds

f5

f4

f3

f2

f1

In Call:Hard Handoff

AuxiliaryHandoff Triggers

•Beacons•Ec/Io, RTDProprietaryProcesses

Mobiles in conversation can’t see pilots on different carrier frequencies.We must “trick” these mobiles into handoff by artificial means.


Intersystem Hard HandoffSame Frequency causes Interference Problems!

BSC1 SW1

SW2 BSC2

Frequency 1

City 2

City 1Interference


Consider two adjacent CDMA systems:• Same frequency• If not equipped for intersystem soft handoff, only hard handoff is

possible between them; “dragged” handoffs become a big problemHandoff Performance Results:

• Mobiles CAN see pilots from adjoining system, so mobile-directed handoff is possible

• However, due to hard handoff mobiles can use only one system or the other, not both, and simultaneous shared power control is not possible

• “dragging” mobiles cause severe interference in border cells• border area has poor capacity, high access failures and dropped calls

Intersystem Soft Handoff:Avoids Border Area Interference Problems

BSC1 SW1

SW2 BSC2

Frequency 1

City 2

City 1Intersystem Soft Handoff

ATM link

no problems!

Consider two adjacent CDMA systems:• Same frequency• ATM connection between BSCs allows soft handoff

Handoff Performance Results:• Mobiles CAN see pilots from adjoining system, so mobile-directed

handoff is possible• Intersystem soft handoff is possible, so simultaneous power control is

possible for mobiles in border area• Border RF environment is the same as internal RF environment, no

special problemsDecember, 2003 5 - 13Course 120 (c) 2003 Scott Baxter

Avoid Interference, Use Different Frequencies?Hard Handoff Logistical Problems

Frequency 1

Frequency 2

BSC1 SW1

SW2 BSC2

City 2

City 1

F2 Mobiles can’t see F1 pilots!

F1 Mobiles can’t see F2 pilots!


Consider two adjacent CDMA systems:• Suppose intersystem soft handoff is not available• Systems are deliberately on different frequencies. This definitely

avoids interference in the border area, but causes other complicationsConversation-State Handoff Logistical Problems:

• Mobiles on one system can’t see the pilots of adjoining cells on the other system! So, the mobiles will never request trans-border handoff

• Some method must be employed to force unsuspecting mobiles into transborder handoffs

• Common solutions: 1) implement intersystem soft handoff, 2) Pilot beacon cells, 3) auxiliary trigger mechanisms (Ec/Io, RTD, etc.)

One Solution to the Multi-Frequency Problem2-Frequency Trigger Method: Beacon Cells

Frequency 1

Frequency 2

BSC1 SW1

SW2 BSC2

City 2

City 1

F2 Mobiles can see F2 beacon

F1 Mobiles can see F1 beacon


The Beacon Solution• A pilot beacon cell is a “mannequin” -- a signal which can be seen by

arriving mobiles from the other system on their own frequency, inducing them to request handoff as soon as it is appropriate

• When mobiles request soft handoff with the beacon, the old system steps in and instructs the mobiles to do intersystem hard handoff to the real cell which the mobiles are approaching on the other system

Special Logistical Concerns with Beacons• Of course, it’s possible for mobiles of one system to “wake up” looking

at the pilot of a beacon cell in the border area, rather than a real cell.• Therefore, a beacon cell must transmit not only its pilot, but also a

sync channel and a paging channel with global service redirection

Another Solution for Multi-Frequency HandoffsBridge Cells, RTD Trigger in Boundary Sectors

Frequency 1

Frequency 2

BSC1 SW1

SW2 BSC2

City 2

City 1

Boundary Sector

Boundary Sector


All along the intersystem border, a one-cell-thick “transition zone” is created. The “bridge” cells in this zone are equipped with dual equipment, one set operating on each system.

• The outlooking sector of each bridge cell is tagged in the site database as a “boundary sector”. Whenever a mobile is served exclusively by a boundary sector, the system continuously monitors that mobile’s round trip delay (RTD).

• When the mobile’s RTD passes upward through a datafilled threshold, the system steps in and orders a hard handoff to the matching sector of the bridge cell on the other system

– this ensures the handoffs happen in clean environments with highprobability of success

– disadvantage: more BTS hardware needed than otherwise

Another Solution for Multi-Frequency HandoffsArbitrary Ec/Io Trigger Mechanisms

Frequency 1

Frequency 2

BSC1 SW1

SW2 BSC2

City 2

City 1

Boundary Sector

Boundary Sector


Outlooking sectors of border cells are tagged as “boundary sectors” in the system database

• Whenever a mobile is served exclusively by a boundary sector, the system frequently interrogates the mobile with pilot measurementrequest messages

• When the mobile’s reports the boundary sector’s Ec/Io is below a preset threshold, the system immediately commands a hard handoffto a previously defined sector on the other system. Everyone hopes (prays?) that sector is able to hear the mobile for a successful handoff.

– The Ec/Io trigger threshold is sometimes a fixed value (usually 11 db above the T_Drop in the serving sector, although some networks’ later software allows an arbitrary trigger level to be set

CDMA2000 1xRTT SystemsData Performance Optimization

CDMA2000 1xRTT SystemsData Performance Optimization


The Big Picture:

IP D

ata

Envir

onm

entCDMA RF Environment

CDMA IOS PPPTraditional Telephony

IP Data Environment

t1t1 v CESEL

t1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent

BackboneNetworkInternet

VPNs

PSTN

T TSECURE TUNNELS

AuthenticationAuthorization

Accounting AAA

BTS

(C)BSC/Access ManagerSwitch WirelessMobile Device

•Coverage Holes•Pilot Pollution•Missing Neighbors•Fwd Pwr Ovld•Rev Pwr Ovld•Search Windows•Island Cells•Slow Handoff

1xRTT services may include both traditional circuit-switched voice and new fast IP data connections

• A User's link is in multiple jeopardy, both radio and packet worldsRadio environment portion

• Problems: FER, drops, access failures, capacity woes• Causes: mainly in the RF world, because of mainly RF problems

Packet environment• Problems: Setup failures, dropped connections, low throughput• Causes: could be IP-related, or could be RF related


Optimization Issues


Network Design and Configuration• Coverage holes, excessive coverage overlap

Call Processing Problems due to Misconfiguration• Neighbor Lists• Search Windows• Power control parameters

Physical Problems/Hardware Problems• Mismatched multicarrier sector coverage

Capacity Issues• Forward and Reverse Power Control Overload• Physical resource congestion

– Channel elements, packet pipes– IP network congestion

Managing A New Dimension: circuit-switched and IP traffic blend• QoS-related competitive issues

Optimizing in Two Worlds


Circuit-Switched Voice Traffic• Some operators are implementing 1xRTT mainly to gain capacity for

additional voice traffic• Their optimization techniques remain about the same as for 2G voice

networks today– Keep network adequately dimensioned– Control RF environment– Monitor and manage capacity utilization

IP Data Traffic• Operators adding IP traffic to upgraded voice networks• Conventional optimization techniques are still appropriate for general

RF environment and circuit-switched network performance• New IP and QoS issues require a new optimization focus for the

blended total network– IP performance depends on both IP and RF factors– IP and Voice performance involve competitive tradeoffs

Managing Forward Link Sector Loading vs. TimeSe

ctor

Tot

al T

X Po

wer

or T

hrou

ghpu

t

Time, Seconds

Sector Maximum TX Power, Maximum Throughput

Voice Traffic

Packet Data Traffic

Both voice and data traffic loads a sector, driving up transmit power• Voice calls are typically given higher priority than data• MAC-layer throttling holds lower-priority data sessions off until there is

enough free power available


Basic Forward Link Physical Capacity


IS-95One Carrier, One Sector

CECECECECECECECECECECE

CECECECECECECECE

CECECECECECECECE

CECECECECECECECE

CECECECECECECECE

PILOTPAGING

SYNC9.6K1.2K

40 x 6K≈ 240K

QPSKModulatorQ

I

Σ Σ

~250Kb/s

CDMA2000 1xRTTOne Carrier, One Sector

CECECECECECECECECECECECECE

CECECECECECECECE

CECECECECECECECE

CECECECECECECECE

CECECECECECECECE

PILOTPAGING

SYNC

FCH 9.6K+SCH 38K

9.6K1.2K

40 x 6K≈ 240K

QPSKModulatorQ

I

Σ Σ

~500Kb/s

CECE

FCH 9.6K+SCH 153K

CECECECE

Active/bursting

Active/bursting

Active

Active

Active

Active

Dormant

Dormant

Dormant

Dormant

Dormant

Dormant

FCH 9.6K

FCH 9.6K

FCH9.6K

FCH9.6K

Dormant

Dormant

DormantDormant

1xRTT throughput is approximately twice IS-95 throughputExtra capacity of 1xRTT sectors can be used for fast data or more voice users

#6 Indicator: Data Latency

IP D

ata

Envir

onm



IP Data Environment

t1t1 v CESEL

t1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent


VPNs

PSTN

T TSECURE TUNNELS


Accounting AAA

BTS



Latency can occur because of RF channel congestion or from IP network causes

• RF overload can delay availability of supplemental channels• IP network congestion can delay availability of packets

Ping and loopback tests with local PDSN and servers can identify whether problem is in backbone networkDoes latency correlate with independent evidence of RF congestion?


#7 Indicator: Data Throughput

IP D

ata

Envir

onm



IP Data Environment

t1t1 v CESEL

t1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent


VPNs

PSTN

T TSECURE TUNNELS


Accounting AAA

BTS



Throughput can be limited by RF and IP causes• Traditional RF problems limit capacity of the channel• Congestion in the IP network can limit speed of data available

Does low throughput correlate with independent RF indicators?Does low throughput correlate with independent IP pings and tests?


System-Side 1xRTT ToolsSystem-Side 1xRTT Tools


Basic Philosophy of System Data


Each network manufacturer has its own data sets and counters• Access failures, TCCFs, blocks, drops, failed handoffs• These counters are normally available in 2G-only, 3G-only, and total

categories• Additional new statistics are available for IP traffic

The basic philosophy of system data analysis is to analyze and discriminate within the available data

• Identify and rank existing sectors based on– Traffic levels– raw failures/blocks/drops– percentage failures/blocks/drops

• Benchmark and track incremental changes• Investigate all significant problems uncovered

– Drive-testing or data testing may be requiredIn-Class activity: view manufacturer documentation and examples

Information on System-Side Statistics


Lucent• Technical Reference: Watchmark Prospect for Lucent, v17.0

Nortel• 411-2131-814 DMS-MTX Operational Measurements Reference

Manual version v. 12.02 June, 2001• 411-2131-900 DMS-MTX Operational Measurements Quick

Reference GuideMotorola

• “Performance Analysis 2.16.0” v O , Motorola Inc., January 2002.• “1x network Performance Matrix” v. 0.1, Motorola Inc., April 2001. • “CDMA 2000 – 1x Voice and Data – Cellular Application Note” , v. 1.1

– Draft; Motorola Inc.• “Impact on CDL and CFC in Version 2.16.0” v.1.4, Part No.

8700SCRP20GCDLCFC-D, Motorola Inc., August 2001• “CFC Resolution Document” v. 1.3, Motorola Inc Performance

Analysis 2.16.0” v O , Motorola Inc., January 2002

Data Flow Management:MAC/LAC Layer OperationData Flow Management:

MAC/LAC Layer Operation


System MAC/LAC Parameters

The answers to all these questions are determined by MAC & LAC layer processes and parametersEach network manufacturer implements some subset of the MAC/LAC states and parameters specified in the IS-2000 standardEach manufacturer has its own unique parameter set to control state transitionsMost networks begin operation using manufacturer-recommended defaults

• as networks and applications mature, parameters will be fully optimized

A basic knowledge of the manufacturers proprietary parameters gives very useful insights into configuration and performance issues

T_active orRelease

Initialization

Null

Reconnect

Dormant

Control Hold

Suspended

Packet ServiceRequest

Packet ServiceDeactivated

PPP TerminatedRelease Sent!

PPP TerminatedRelease Sent!

Service OptionConnected

Control Channel Exists

Service OptionConnected

Control ChannelExists

Traffic channelExists

Active

T_hold

Control Channelexists

T_suspend

Have New Datato send!

•How is data flow managed?•Can I keep my FCH all the time?•Will my connection drop in a fade?•When is an SCH turned on for me?•How long will my SCH burst last?•What is the data rate of my SCH?•If I can’t get a full-rate SCH, can I at least get a lower-rate SCH?•Which kinds of traffic have priority?•Do some users have higher priority?


MAC StatesState

R-CCCH

R-EACH

F-TRAFFICF-FCH

F-SCH

R-TRAFFICR-FCH

R-SCHSCH driven

by trafficSCH driven

by traffic

F-TRAFFIC R-TRAFFIC

intermittent

F-DCCH R-DCCH

CESELt1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent


VPNs T TSECURE TUNNELSAuthentication

AuthorizationAccounting AAA

BTS

(C)BSC/Access Manager

CESELt1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent




BTS


CESELt1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent




BTS


SELt1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent




BTS


PAGING

R-CCCH

R-EACH

PAGING

intermittent

intermittent

ChannelElement

Selector/Svc Cfg (RLP) PPPIP

Session

ACTIVEexit timer:

a few seconds

CONTROLHOLD

(Optional State)exit timer: a few seconds

very fast return to active state

SUSPENDED(Optional State)

exit timer: a few secondsbetween data bursts

DORMANTexit timer: minutes, hours

between data bursts


Forward Link SCH Scheduling

CESELt1

R-PInterface

PDSN/Foreign Agent

BTS

(C)BSC/Access ManagerWireless

Mobile Device

data

FCH orFCH + SCH?

Buffer

BTSC

My F-SCHData Rate

PCF


The main bottleneck is the forward link itself: restricted by available transmitter power and walsh codesEach connected data User has a buffer in the PDSN/PCF complex

• When waiting data in the buffer exceeds a threshold, the PDSN/PCF asks the BTS for an F-SCH. Its data rate is limited by:

– Available BTS forward TX power; available walsh codes; competition from other users who also need F-SCHs; and mobile capability

• When the buffer is nearly empty, the SCH ends; FCH alone• Occupancy timers and other dynamic or hard-coded triggers may apply• QOS (Quality of Service) rules also may be implemented, giving

preference to some users and some types of traffic

Forward Link Events in a Typical User SessionData volume in PDSNbuffer triggers SCH assignment. SCH rate isdriven by amount of data in buffer and available TX power sector can allocate.

Data volume in buffer low, SCH released.Data flow continues on FCH until complete.


1.2

9.6

19.2

38.4

76.8

153.6

0

Dat

a R

ate,

kbp

s

Channel Legend:

DataIdle Data

FundamentalSupplemental

Session begins.No data, FCH idle, 1200 bps

Data in PDSNbuffer. Data flow beginson FCH


No data, FCH idle,1200 bps

FCHidle1200bps

Data volume in PDSNbuffer triggers SCH assignment. SCH rate isdriven by amount of data in buffer and available TX power sector can allocate.

Data volume in buffer low, SCH released. Flow continues on FCH.

Activetimerruns out!FCH drops.Session isdormant.

TA

Data volume in PDSNbuffer triggers SCH assignment. SCH rate isdriven by amount of data in buffer and available TX power sector can allocate.

Data volume in buffer low, SCH released.Data flow continues on FCH until complete.


Mobileendssession.

Init

NullRcon

Dorm

CHldSusp

Act

STATE



QOS algorithmgives SCH to another userbriefly. Datameanwhileflows on FCH.

1x Data Tests and Optimization1x Data Tests and Optimization


So S L O W ! ! Where’s My Data?!!

IP D

ata

Envir

onm



IP Data Environment

t1t1 v CESEL

t1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent


VPNs

PSTN

T TSECURE TUNNELS


AccountingAAA

BTS




Some sessions are tormented by long latency and slow throughputWhere is the problem? Anywhere between user and distant host:

• Is the mobile user’s data device mis-configured and/or congested?• Is the BTS congested, with no power available to produce an SCH?• Poor RF environment, causing low rates and packet retransmission?• Congestion in the local IP network (PCU, R-P, PDSN FA)?• Congestion in the wireless operator’s backbone (‘OSSN’) network?• Congestion in the PDSN HA?• Congestion in the outside-world internet or Private IP network?• Is the distant host congested, with long response times?

Finding Causes of Latency and Low Throughput

IP D

ata

Envir

onm



IP Data Environment

t1t1 v CESEL

t1

R-P Interface

PDSN/Foreign Agent

PDSNHome Agent


VPNs

PSTN

T TSECURE TUNNELS


AccountingAAA

BTS



TestServer

TestServer

TestServer


IP network performance can be measured using test serversProblems between mobile a local test server? The problem is local

• check RF conditions, stats: poor environment, SCH blocking?• if the RF is clean, investigate BSC/PCU/R-P/PDSN-FA

Local results OK, problems accessing test server at PDSN-HA?• problem is narrowed to backbone network, or PDSN-HA

Results OK even through test server at PDSN-HA• then the problem is in the public layers beyond.

PracticalCDMA Performance Optimization

PracticalCDMA Performance Optimization


Good Performance is really Simple!!

One, Two, or Three good signals in handoff• Composite Ec/Io > -10 db

Enough capacity for the offered traffic• No resource problems

BTS BTS

BTS

Pilot

Paging

TrafficChannels

In use

availablepower

Sync

BTS

A

BTS

B

BTS

C

Ec/Io -10

FORWARDLINK

In principle,A COW next door

Can solve almost anyCDMA problem!

Reality Check:1. But who has enough regular cells OR cows or money to

fix every problem location?!!2. Problems occur in the areas between cells’ dominant

coverage. Adding a cow only pushes the problems out to its own boundary with other cells.

Conclusion: We need to design better, and to use our existing cells more effectively. We need to provide one, two, or three dominant signals everywhere.


Bad Performance Has Many CausesWeak Signal / Coverage HolePilot Pollution

• Excessive Soft HandoffHandoff Failures, “Rogue” mobiles

• Missing Neighbors• Search Windows Too Small• BTS Resource Overload / No Resources

– No Forward Power, Channel Elements

– No available Walsh Codes– No space in Packet Pipes

Pilot “Surprise” ambush; Slow HandoffsPN Plan errorsSlow Data Problems: RF or IP congestionImproper cell or reradiator configurationHardware and software failuresBut on analysis, all of these problems’ bad effects happen because the simple few-signal ideal CDMA environment isn’t possible.

360

+41

+8

360+33cA

BBTS

BTS

BTS BPN 99

BTS APN 100

1 mile 11 miles

ACTIVE SEARCH WINDOW

xPilot

PagingSync

TrafficChannels

In Use

NoAvailablePower!B

TS Sector Transmitter

CEsVocodersSelectors

BTS Rx PwrOverload


What is Performance Optimization?


“Performance Optimization” involves design and modification of the network, gathering and analysis of data, adjustments to network parameters, and constant evaluation of current network conditions

• The work includes complex design and simulations, nuts-and-bolts call processing troubleshooting and hardware testing, to growth management and planning

System Performance Optimization includes many different smaller processes at many points during a system’s life

• Evaluating the system design with simulation tools to evaluate the performance and capacity of the system

• Finding “workarounds” for design issues (can’t build a crucial site, too much overlap/soft handoff, coverage holes, etc.)

• “cluster testing” and “cell integration” to ensure new BTS hardware works, datafill is proper, and call processing is normal

• “fine-tuning” system parameters for the best possible call performance• Fixing root causes of specific problems and customer complaints• carefully watching system traffic growth and managing the problems it

causes - implementing short-term fixes to ease “hot spots”, and recognizing problems before they become critical

It takes many different skills and perspectives to optimize wireless networks

Early Assessment and RF Optimization StepsRF Coverage Control

• try to contain each sector’s coverage, avoiding gross spillover into other sectors

• tools: PN Plots, Handoff State Plots, Mobile TX plotsNeighbor List Tuning

• try to groom each sector’s neighbors to only those necessary but be alert to special needs due to topography and traffic

• tools: PSMM data from mobiles; propagation predictionSearch Window Settings

• find best settings for SRCH_WIN_A, _N, _R• especially optimize SRCH_WIN_A per sector using collected finger

separation data; has major impact on pilot search speedRepeat as necessary until no large problems remain

Access Failures, Dropped Call Analysis• finally, iterative corrections until within numerical goals

IP Data Performance Assessment• Identify, manage, resolve latency and throughput issues

Getting these items into shape provides a solid baseline and foundation for comparison, tracking, and planning in the future.


Performance Monitoring/Growth Management


Benchmark Existing Performance from system-side data• Dropped Call %, Access Failure %, traffic levels

Identify Problem Cells and Clusters• weigh cells and clusters against one another• Investigate and resolve any problems, using field drive data if needed

Look for signs of Overload• TCE or Walsh minutes -- excessive ? Soft handoff excessive?• Required number of channel elements -- excessive?• Forward Power Overloads: Originations, Handoffs blocked

Traffic Trending and Projection• track busy-hour traffic on each sector; predict exhaustion• develop plan for expansion and capacity relief

– split cells, multi-sector expansions, multiple carriers Use high-level simulation tools to gain insight into user statistics

• Compare different cell configurations against statistically generated traffic simulations to identify what works best, and try it out!

This process never ends. The community, the system, and the customers are always growing and presenting new problems and capacity needs.

CDMA Problems, Causes, and Cures


PROBLEMSExcessive Access FailuresExcessive Dropped CallsForward Link InterferenceSlow HandoffHandoff Pilot Search Window IssuesPN Planning ConsiderationsExcessive Soft HandoffGrooming Neighbor ListsSoftware Bugs, Protocol Violations

EXAMPLESNormal CallDropped Call - CoverageDropped Call - Neighbor ListDropped Call - Search Window

Troubleshooting Access FailuresTroubleshooting Access Failures


Investigating Access Failures


An access attempt failure can occur at any point in the process:Access probes exhausted (not received by system)Access probes exhausted (seen by system but ACK not reaching mobile station)Ack received by mobile station but Channel Assignment Message not seenChannel Assignment Message seen at mobile but mobile station does not acquire Forward Traffic ChannelMobile station acquires Forward Traffic Channel but system does not acquire Reverse Traffic ChannelSystem acquires Reverse Traffic Channel but Service Connect Message is not seen at mobile station.

BTS

Channel Assnmt. Msg.

Origination Msg

Base Sta. Acknlgmt. Order

TFC frames of 000s

TFC preamble of 000s


Mobile Sta. Ackngmt. Order

Service Connect Msg.

Svc. Connect Complete Msg


Call is Established!

MSProbing

ACCESS

PAGING

FW TFC

PAGING

RV TFC

FW FC

RV TFC

FW TFC

RV TFC

FW TFC

Successful Access Attempt

Troubleshooting Access Failures & TCCFs


Troubleshooting access failures (Traffic Channel Confirmation Failures) can be difficult There are many steps in the access process

• Finding which step failed is not easyRarely, circumstantial evidence points clearly to the problemUsually, it is necessary to debug the process leading up to the access failure

• Consider each step in the access process• Get evidence to determine whether this step occurred successfully• Move on to the next step and keep checking steps until the

unsuccessful step is found• Determine why this step failed

The following slides describe the steps in the access process, where they take place, and some of the factors which may cause them to failThis narrative might be useful as a “template” for organizing your own thinking as you investigate access failures you are tracking!

• Go out and capture actual drive tests of failed origination attempts• If possible, also collect system logs (RF call trace, etc.) for the same

event

Troubleshooting Access Failures (1)

Paging Channel Access ChannelSteps in the Access ProcessBTS

Origination Msg.Probe #1



Mobile waits to see if the BTS hears and acknowledges its probe within the time ACC_TMO. If not, the mobile must transmit the message again in another probe, this time PI db. louder.

If the mobile does not hear acknowledgment from the BTS within ACC_TMO, this could mean either:•The BTS did not hear the mobile

•Maybe the mobile collided with another mobile transmitting at the same time•Maybe mobile was too weak to overcome the existing reverse noise level at the BTS•In either case another probe should solve the problem, provided PI is set reasonably and additional probes are allowed (check the Access Parameters Message to see if Num_Step and the power parameters make sense; be sure also the cell size or Access Channel acquisition search width is set large enough and the number of access preamble frames is large enough for the cell size)

•The BTS is acknowledging but the mobile cannot hear the acknowledgment

•If the mobile can’t hear the BTS acknowledging, Ec/Io is likely quite poor. If so, check whether this is due to weak signal (poor coverage) or pilot pollution (lots of pilots all weak but no dominant server)

Collect system logs if necessary to determine definitely whether the system heard the mobile’s origination or not

Troubleshooting Comments

Mobile waits again to see if the BTS hears and acknowledges its probe within the time ACC_TMO. If not, the mobile must transmit the message again in another probe, this time PI db. louder.

The mobile keeps probing until NUM_STEP probes have been sent, then repeats the probe sequence again until Max_Probe_Sequences have been sent.



Paging Channel Access ChannelThe Access ProcessBTS

Reorder

If this problem happens frequently, the BTS traffic overload must be relieved. Here are some steps to try:•Investigate BTS TX hardware to ensure everything is working correctly and properly calibrated, particularly gain settings in the TX chain•To free up more forward power for traffic channels, try:

•Reduce PTXstart (initial traffic channel DGU) watching for less forward power control overloads. If you go too far, you will notice access failures increase.•Reduce PTXmax (maximum traffic channel DGU) watching for less forward power control overloads. If you go too far, dropped calls will increase.

•Reduce sector traffic by reorienting the sectors to more closely balance the load carried by each•Or, add another carrier •Or split cells


Mobile beeps and displays “Call Failed - System Busy”

One Dreaded Possibility:



Paging Channel Access ChannelThe Access ProcessBTS

After hearing the BTS acknowledgment, the mobile will stop probing and wait for further instructions on the paging channel.

If the mobile does not hear the Channel Assignment Message within 12 seconds, the mobile will beep and display “Call Failed”. Possible causes:•The BTS did not transmit the Channel Assignment Message

•Check system logs to see if this was not transmitted. If not transmitted, get troubleshooting help from the system manufacturer -- this should never occur

•The BTS did transmit the Channel Assignment Message, but the mobile did not hear it

•Was this because the paging channel faded? (Did the Ec/Io drop momentarily)? If so, see If this is a recurring problem such as a coverage hole or severe pilot pollution

Finally! The mobile hears the Channel Assignment Message!Now it will immediately leave the paging channel and start trying to hear the new Forward Traffic Channel.


Channel AssignmentMessage

Base StationAcknowledgment

STOP! Leave the Paging Channel, and don’t transmit again on the access channel.The mobile now goes to try to hear the Forward Traffic Channel.



FWD Traffic Channel REV Traffic ChannelThe Access ProcessBTS

The mobile listens to the Walsh Code # given in the Channel Assignment Message. It should hear N5M good frames full of all zeroes within T2M seconds (usually 2 frames in 10 frames).


Mobile beeps and displays “Call Failed”

000000000000000000000000000000000000000000000000000000000000

000000000000000000000000000000000000000000000000000000000000

If the mobile hears the required number of good empty frames, it starts transmitting its own “Reverse Traffic Channel Preamble” of empty all-zero frames.

If the mobile does not hear the required number of good empty frames, it will beep and give an error message, then reacquire the system.


Mobile StationAcknowledgment

If the BTS does NOT hear the mobile’s access preamble within a prescribed delay, it will abort the process and release all the resources, and the mobile will reacquire the system. . This is what Lucent terms a “Traffic Channel Confirmation Failure (TCCF).”

If the BTS DOES hear the mobile’s access preamble, it will send an acknowledgment.The mobile responds with an acknowledgment, or maybe even a pilot strength measurement message if it already needs a handoff.



FWD Traffic Channel REV Traffic ChannelThe Access ProcessBTS

Now that the BTS and mobile see each other on the traffic channels, the next step is service negotiation.The BTS sends a Service Connect message listing the type and rate set of the vocoder or other primary traffic source.

The mobile either accepts the proposal with a Service Connect Complete message, or counterproposes a different mode.

The BTS acknowledges the Service Connect Complete message.

The call is now officially in progress. If anything happens to interrupt it after this point, that is considered a dropped call.

If any of these steps is unsuccessful, the call attempt will probably fail. Suspect RF conditions on the link which was supposed to carry the unsuccessful command. Look at system logs and message logs from mobile drive testing to pin down just what happened.


Service ConnectMessage

Service ConnectComplete Message

This is still just an ongoing access attempt


Now this is officially a call in progress


Access Failure/TCCF TroubleshootingAccess Attempt Failed

Were any probes acknowledged?

Yes,Reorder

Weak Signal/Coverage Hole?

Strong Fwd interf / pollution?

yes

yes

no

Is T-1unstable/blocking?

no

Add coverage

Identify, eliminate

Report/repair

BlockingForward Power

Channel ElementsRev. Link Noise

Optmz Fpwr DGUsAdd chan cards

Identify, fix source

No,Nothing

Yes,BS Ack

Paging Channel faded, lost

Check System Logs. Was mobile heard?

Was Channel Assignment Message heard?

no Rev Link Overload? Identify, fix source

Num_Step, Pwr_Step appropriate?

Ensure reasonable values

Sector Size, Acq Width appropriate?

Ensure reasonable values for cell size

Check System Logs. Was CH ASN sent?

yes

System Problem.Investigate why

Software problem

Resource blockingDid mobile see N5M good

frames on F-TCH?

yes

no

Check System Logs.CH EL initialized OK?

noyes

Check System Logs. DidBTS see mobile preamble? no

yes

Did mobile see BS Ack?

Rev. Link Noise Identify, fix source

no Weak Signal/Coverage Hole?Strong Fwd interf / pollution?


Improve coverageIdentify, eliminate

Report/repair

F-TFC Channel faded, lostyes

Check System Logs.Did BTS see mobile Ack?

OK

no Weak Signal/Coverage Hole?Strong Rev Noise?


Improve coverageIdentify, eliminate

Report/repair

R-TFC Channel faded, lost

Init TCH DGU large enough? Raise DGU


Reducing Access Failures

1. If the failures occur in areas where one BTSis dominant, suspect BTS hardware problems.2. Plot the access failures to see if they correlatewith areas of BTS overlap. If so, suspectforward link problems. This is probablebecause the mobile does not have the normaladvantage it would get from soft handoff on atraffic channel. During access, it must successfully demodulate all five BTS messageswithout the benefit of soft handoff. If thehandset is in an area of multiple BTS overlapsor weak signal, this can be risky. In such cases,try to make the serving BTS more dominant. Also check the access/probing parameters.

If the base station never sees the mobile’s probes,the cause is probably coverage-related. If it happensin strong signal areas, suspect BTS hardware. Alsocheck datafill for proper NOM_PWR and PWR_INC.Be sure the BTS datafill access channel acquisition and demodulation search windows are adequate.

BTS

Channel Assnmt. Msg.

Origination Msg


TFC frames of 000s

TFC preamble of 000s


Mobile Sta. Ackngmt. Order

Service Connect Msg.

Svc. Connect Complete Msg


Call is Established!

MSProbing

ACCESS

PAGING

FW TFC

PAGING

RV TFC

FW FC

RV TFC

FW TFC

RV TFC

FW TFC

Access Attempt


Troubleshooting Dropped CallsTroubleshooting Dropped Calls


Dropped Call Troubleshooting - Mobile SideJust arrived on sync channel!

Is this a drop?

Were there release messages?

OK, normal end of call

This is a drop!

yes

no

Was the Sync Channel PNActive before the drop? Check

for:

yes Weak Signal/Coverage Hole?

Strong Fwd/Rev interference?no

Did mobile request Sync CH PN in PSMM before drop? Why didn’t handoff happen?

no

yes

Weak Signal/Coverage Hole?

FER already too bad?

Border configuration problems

Fast-rising pilot, slow reaction

PN not in neighbor list

Is PN in neighbor list?yes

Is SRCH_WIN_N adequate?

noAdd PN to Neighbor List!

BlockingForward Power

Channel ElementsRev. Link Noise

yes

Is cell in “island Mode”?yes

Repair/Re-initialize Cell!

no

Is T-1unstable/blocking?Is T-1unstable/blocking?


noWiden SRCH_WIN_N!

More information needed.Collect system logs and merge with mobile data,

analyze

Improve coverage

Identify, eliminate

Report/repair

Add PN to Nbr List!

Add coverage

Push earlier

Debug, reconfigure

Incr Sector OverlapSpeed up searcher

Optmz Fpwr DGUsAdd chan cards

Identify, fix source

Report/repair



CDMA Information ResourcesBibliography - Web Links

CDMA Information ResourcesBibliography - Web Links

Bibliography, 3G Air Interface Technologies


"Wireless Network Evolution 2G to 3G" by Vijay K. Garg. 764pp. 2002 Prentice-Hall, Inc. ISBN 0-13-028077-1. $130. Excellent technical tutorial and reference. The most complete and comprehensive technical detail seen in a single text on all these technologies: IS-95 2G CDMA, CDMA2000 3G CDMA, UMTS/WCDMA, Bluetooth, WLAN standards (802.11a, b, WILAN). Includes good foundation information on CDMA air interface traffic capacity, CDMA system design and optimization, and wireless IP operations. Excellent level of operational detail for IS-95 systems operating today as well as thorough explanations of 2.5G and 3G enhancements.

“3G Wireless Demystified” by Lawrence Harte, Richard Levine, and Roman Kitka488pp. Paperback, 2001 McGraw Hill, ISSBN 0-07-136301-7 $50. For both non-technical

and technical readers. An excellent starting point for understanding all the major technologies and the whole 3G movement. Comfortable plain-language explanations of all the 2G and 3G air interfaces, yet including very succinct, complete, and rigorously correct technical details. You will still want to read books at a deeper technical level in your chosen technology, and may sometimes turn to the applicable standards for finer details. This book will give you how your technology relates in the big picture, and probably all you care to know about technologies other than your own.

"3G Wireless Networks" by Clint Smith and Daniel Collins. 622pp. Paperback. 2002 McGraw-Hill, ISBN 0-07-136381-5. $60. An excellent overview of all 3G technologies coupled with good detail of network architectures, channel structures, and general operational details. Good treatment of both CDMA2000 and UMTS/WCDMA systems.

“WCDMA: Towards IP Mobility and Mobile Internet” by Tero Ojanpera and RamjeePrasad. 476pp. 2001 Artech House, ISSBN 1-58053-180-6. $100. A complete and definitive work on UMTS (good CDMA2000, too!). CDMA principles, Mobile Internet, RF Design, Air Interface, WCDMA FDD standard, WCDMA TDD, CDMA2000, Performance, Hierarchical Cell Structures, Implementation, Network Planning, Basic IP Principles, Network Architectures, Standardization, Future Directions.

More Bibliography, 3G Air Interface Technologies


“The UMTS Network and Radio Access Technology” by Dr. Jonathan P. Castro, 354 pp. 2001 John Wiley, ISBN 0 471 81375 3, $120. An excellent, well-organized, and understandable exploration of UMTS. Includes radio interface, channel explanations, link budgets, network architecture, service types, ipnetwork considerations, a masterful tour de force through the entire subject area. Very readable, too!

“WCDMA for UMTS” by Harri Holma and Antti Toskala, 322 pp. 2000 Wiley, ISBN 0 471 72051 8, $60. Very good overall treatment of UMTS. Excellent introduction to 3G and summary of standardization activities, every level of UMTS/UTRA. Good overview of CDMA-2000, too!

“The GSM Network - GPRS Evolution: One Step Towards UMTS” 2nd Edition by Joachim Tisal, 227pp. paperback, 2001 Wiley, ISBN 0 471 49816 5, $60. Readable but not overwhelming introduction to GSM in all its aspects (140pp), DECT (11pp), GPRS (6pp), UMTS (7pp), WAP (25pp), EDGE (10pp).

Bibliography, The IP Aspect of 3G


“Mobile IP: Design, Principles and Practices” by Charles E. Perkins, 275 pp., 200, 1998 Addison-Wesley, ISBN 0-201-63469-4. $60. Comprehensive view of Mobile IP including home and foreign agents, advertisement, discovery, registration,datagrams, tunneling, encapsulation, route optimization, handoffs, firewalls, IPv6, DHCP. Tour-de-force of mobile IP techniques.

“Mobile IP Technology for M-Business” by Mark Norris, 291 pp., 2001 Artech House, ISSBN 1-58053-301-9. $67. GPRS overview and background, Mobile IP, Addressing, Routing, M-business, future prospects, IPv4, IPv6, Bluetooth & IrDA summaries.

“TCP/IP Explained” by Phillip Miller, 1997 Digital Press, ISBN 1-55558-166-8, 518pp. $50. In-depth understanding of the Internet protocol suite, network access and link layers, addressing, subnetting, name/address resolution, routing, error reporting/recovery, network management. IF you’re not already strong in TCP/IP, you’ll need this to fully master Mobile IP.

“Cisco Networking Academy Program: First-Year Companion Guide” edited by Vito Amato, 1999 Cisco Press, ISBN 1-57870-126-0, 438pp. Textbook supporting a year-long course on networking technologies for aspiring LAN/WAN (and 3G) technicians and engineers. It covers every popular networking technology (including all its elements and devices) in deep and practical detail. Excellent real-world understanding of TCP/IP, as well as the nuts-and-bolts of everything from physical components to protocols to actual devices such as routers, switches, etc. You might even want to take the evening courses at a local community college near you.

“Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I” edited by Vito Amato, 1999 Cisco Press, ISBN 1-57870-126-x, 291pp. The workbook for the First Year Companion Guide above. If you want some external structure in your self-study, this workbook will hold your hand as you climb every step of the ladder, and will lead you step by step through the sister textbook, ensuring you absorb everything you need to know.

Bibliography - General CDMA


“IS-95 CDMA and CDMA2000: Cellular/PCS Systems Implementation” by Vijay K. Garg. 422 pp. 2000 Prentice Hall, ISBN 0-13-087112-5, $90. IS-95 and CDMA2000 Access technologies, DSSS, IS-95 air interface, channels, call processing, power control, signaling, soft handoff, netw. planning, capacity, data. CDMA2000 layers, channels, coding, comparison w/ WCDMA.

“CDMA Systems Engineering Handbook” by Jhong Sam Lee and Leonard E. Miller, 1998 Artech House, ISBN 0-89006-990-5. Excellent treatment of CDMA basics and deeper theory, cell and system design principles, system performance optimization, capacity issues. Recommended.

“CDMA RF System Engineering” by Samuel C. Yang, 1998 ArtechHouse, ISBN 0-89006-991-3. Good general treatment of CDMA capacity considerations from mathematical viewpoint.

“CDMA Internetworking: Deploying the Open A-Interface” by Low and Schneider. 616 pp. 2000 Prentice Hall, ISBN 0-13-088922-9, $75. A tour-de-force exposition of the networking between the CDMA BSC, BTS, and mobile, including messaging and protocols of IS-634. Chapters on SS7, Call Processing, Mobility Management, Supplementary Services, Authentication, Resource Management (both radio and terrestrial), 3G A-Interface details. One-of-a-kind work!

"CDMA: Principles of Spread Spectrum Communication" by Andrew J.Viterbi. 245 p. Addison-Wesley 1995. ISBN 0-201-63374-4, $65. Very deep CDMA Theory. Prestige collector’s item.

Bibliography - General Wireless


“Mobile and Personal Communication Services and Systems” by Raj Pandya, 334 pp. 2000 IEEE Press, $60. IEEE order #PC5395, ISBN 0-7803-4708-0. Good technical overview of AMPS, TACS< NMT, NTT, GSM, IS-136, PDC, IS-95, CT2, DECT, PACS, PHS, mobile data, wireless LANs, mobile IP, WATM, IMT2000 initiatives by region, global mobile satellite systems, UPT, numbers and identities, performance benchmarks.

“Wireless Telecom FAQs” by Clint Smith, 2001 McGraw Hill, ISBN 0-07-134102-1. Succint, lucid explanations of telecom terms in both wireless and landline technologies. Includes cellular architecture, AMPS, GSM, TDMA,iDEN, CDMA. Very thorough coverage; an excellent reference for new technical people or anyone wishing for clear explanations of wireless terms.

"Mobile Communications Engineering" 2nd. Edition by William C. Y. Lee. 689 pp. McGraw Hill 1998 $65. ISBN 0-07-037103-2 Lee’s latest/greatest reference work on all of wireless; well done.

Web Links and Downloadable ResourcesScott Baxter: http://www.howcdmaworks.com

Latest versions of all courses are downloadable. Category - Username - PasswordIntro - (none required) - (none required)RF/CDMA/Performance - shannon - hertz3G - generation - thirdGrayson - telecom - allenAgilent - nitro - viper

Dr. Ernest Simo’s Space2000: http://www.cdmaonline.com/ andhttp://www.3Gonline.com/

CDG: http://www.cdg.org (check out the digivents multimedia viewable sessions)The IS-95 and IS-2000 CDMA trade marketing webside, CDMA cheerleaders.

GSM: http://www.gsmworld.comThe GSM Association website. Worldwide GSM marketing cheerleaders but also includes some excellent GSM and GPRS technical overview whitepapers and documents; latest user figures.

RCR News: http://www.rcrnews.comWireless Industry trade publication - regulatory, technical, business, marketing news.Subscribers can access text archives of past articles; very handy in researching events.


More Web Links3GPP: http://www.3gpp.org/

The operators’ harmonization group concerned mainly with ETSI-related standards

3GPP2: http://www.3gpp2.org/The operators’ harmonization group concerned mainly with IS-95-derived CDMA standards

ITU: http://www.itu.int/imt/

ETSI: http://www.etsi.fr/

UMTS forum: http://www.umts-forum.org/

GSM MoU: http://www.gsmworld.com/

TIA: http://www.tiaonline.org/

T1: http://www.t1.org/

ARIB: http://www.arib.or.jp/arib/english/index.html

TTC: http://www.ttc.or.jp/

TTA: http://www.tta.or.kr/

ETRI: http://www.etri.re.kr/

RAST: http://www.rast.etsi.fi/


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