Call-fail-safe and Distribution-effective Methods for Multi-band Multi-carrier Traffic Allocation in 3GB Wireless Networks - Parthasarathy Guturu EE Department,

Call-fail-safe and Distribution-Call-fail-safe and Distribution-effective Methods for Multi-band effective Methods for Multi-band Multi-carrier Traffic Allocation in Multi-carrier Traffic Allocation in

3GB Wireless Networks3GB Wireless Networks

- Parthasarathy Guturu Parthasarathy Guturu EE Department,EE Department,

University of North Texas, Denton University of North Texas, Denton

AgendaAgendaOverview of 3G CDMA/WCDMA Overview of 3G CDMA/WCDMA wireless communicationswireless communicationsSingle Band Multi-carrier Traffic Single Band Multi-carrier Traffic Allocation ProblemAllocation ProblemMulti-band Multi-carrier Traffic Multi-band Multi-carrier Traffic Allocation- How to contain increased Allocation- How to contain increased call failure probability? call failure probability? A class of Multiband AlgorithmsA class of Multiband AlgorithmsSimulation ResultsSimulation ResultsSummary and ConclusionSummary and Conclusion

Multiple Access TechnologiesMultiple Access TechnologiesHow multiple users How multiple users can share the same can share the same medium (air interface) medium (air interface) simultaneously?simultaneously?– FDMA (Frequency FDMA (Frequency

Division Multiple Division Multiple Access). Each user has Access). Each user has a private frequencya private frequency

– TDMA (Time Division TDMA (Time Division Multiple Access). Each Multiple Access). Each user has a private time user has a private time on a private frequencyon a private frequency

– CDMA (Code Division CDMA (Code Division Multiple Access). Users Multiple Access). Users co-mingle in time and co-mingle in time and frequency, but each frequency, but each user has a private code.user has a private code.

FrequencyTime

Pow

er

FrequencyTime

Pow

er

FrequencyTime

Pow

er

FDMA

TDMA

CDMA

CDMA- Spreading PrincipleCDMA- Spreading Principle

User 1 Data

User 2 Data

1.288 MHZ Spreading Code 1

1.288 MHZ Spreading Code 2

1.288 MHZ Spreading Code 1

1.288 MHZ Spreading Code 2

User 1 Data

User 2 Data

Receiver 1

Receiver 2

Medium (Air)

Transmitter 1

Transmitter 2

Orthogonal CodesOrthogonal CodesTwo Codes are orthogonal if Exclusive OR Two Codes are orthogonal if Exclusive OR operation on them yields equal number of 0’s and operation on them yields equal number of 0’s and 1’s.1’s.Orthogonal (Walsh) Code generation recursively:Orthogonal (Walsh) Code generation recursively:

Almost orthogonalAlmost orthogonal– Short PN (Pseudo-Noise)Short PN (Pseudo-Noise)– Long PN Long PN

Walsh codes used in forward (down, base-station Walsh codes used in forward (down, base-station to mobile) link. PN sequences used in reverse (up) to mobile) link. PN sequences used in reverse (up) link for transmission and scrambling at down link for transmission and scrambling at down link. link.

00 0 0 1

0 0 0 0 0 1 0 1 0 0 1 1 0 1 1 0

H2 = H1 H1H1 H1

Frequency Reuse: Cell Planning in Frequency Reuse: Cell Planning in AMPS/TDMA/GSMAMPS/TDMA/GSM

1

36

47

2

5

74

27

6

23

56

3

4

6

1

1

1

1

11

Since separation of users in CDMA is via orthogonal codes, frequency can be reused virtually every cell.

Generations of Wireless TechnologiesGenerations of Wireless Technologies

First Generation (1G)First Generation (1G)– AMPS (Analog Mobile Phone Service) AMPS (Analog Mobile Phone Service)

using FDMAusing FDMA– NAMPS (Narrow-band AMPS) using FDMANAMPS (Narrow-band AMPS) using FDMA– DAMPS (Digital AMPS) using TDMADAMPS (Digital AMPS) using TDMA

2G. Ex: GSM (European 2G TDMA)2G. Ex: GSM (European 2G TDMA)

3G3G– Some distinctive features compared to 2G Some distinctive features compared to 2G

(Next slide)(Next slide)– CDMA & WCDMA (Wideband CDMA) used CDMA & WCDMA (Wideband CDMA) used

CDMA Network ArchitectureCDMA Network Architecture

MSC MSC

BSC BSC

BSCBSC

PSTN

VLR

HLR AC

MCVMS

MSC- Mobile Switching Center BSC- Base Station Controller BTS- Base-station Transceiver System VLR- Visiting Location Register HLR- Home Location Register MC- Messaging Center VMS- Voice Mail System AC- Authentication Center

BTS

PSTN- Public Switching Telephone Network PPDN- Public Packet Data Network IWF- Inter Working Function

123456789*0#

O K

CLR

BTS

WirelessPPDN

IWF

MS

RNC

Distinctive Features of 3GDistinctive Features of 3GAddressing of 2G limitations:Addressing of 2G limitations:– Bandwidth limitations (14.4 – 64 Kbps)Bandwidth limitations (14.4 – 64 Kbps)– Designed originally for voice; low capacity Designed originally for voice; low capacity – Low data rates (up to 14.4 Kbps)Low data rates (up to 14.4 Kbps)– Limited Roaming CapabilitiesLimited Roaming Capabilities– Limited support for packet dataLimited support for packet data– single-service networkssingle-service networks– No MultimediaNo Multimedia

Asymmetric Data RatesAsymmetric Data RatesBandwidth on DemandBandwidth on DemandAlways Connected (concept of Dormant Always Connected (concept of Dormant states)states)

3G Wireless Systems & Standards 3G Wireless Systems & Standards

3G Wireless Standards & Systems

CDMA 2000(Successor of IS-95)

1xRTT 3xRTT

1x EVDO 1x EVDV

UMTS

CDMA- Code Division Multiple Access

UMTS- Universal Mobile Telecommunications System

RTT- Radio Transmission Technology

FDD W-CDMA TDD W-CDMA

FDD- Frequency Division Duplex

TDD- Time Division Duplex

EV- Evolution DO- Data Only DV- Data and Voice.

Spectrum AllocationSpectrum Allocation800 MHZ (cellular) Band800 MHZ (cellular) Band– 824-894 MHz, divided into sub-bands, carriers 824-894 MHz, divided into sub-bands, carriers

from paired sub-bands used for up/down link from paired sub-bands used for up/down link communications.communications.

– Each RF Carrier is 1.25 MHZ wideEach RF Carrier is 1.25 MHZ wide– Cellular spectrum of 1 operator is 12.5 MHZ Cellular spectrum of 1 operator is 12.5 MHZ

wide, but only 9 carriers can be accommodated wide, but only 9 carriers can be accommodated because of the need to support AMPSbecause of the need to support AMPS

1900 (PCS) MHZ1900 (PCS) MHZ– 1850-1990 MHZ, divided into A, B, C sub-bands 1850-1990 MHZ, divided into A, B, C sub-bands

with 30 MHz each (for 11 carriers) and D, E, F with 30 MHz each (for 11 carriers) and D, E, F sub-bands 10 MHz each (supporting 3 carriers)sub-bands 10 MHz each (supporting 3 carriers)

– 260 KHz Guard band260 KHz Guard band

MCTA AlgorithmMCTA AlgorithmAvailable carrier capacity may be Available carrier capacity may be assessed using eitherassessed using either– Forward link power still available for call Forward link power still available for call

setup without service degradationsetup without service degradation– Unused Walsh codesUnused Walsh codes

Limiting the calls on a carrier based on Limiting the calls on a carrier based on either of the above criteria guarantees either of the above criteria guarantees QOS. QOS.

MCTA is a class of load distribution MCTA is a class of load distribution algorithms based on carrier capacities.algorithms based on carrier capacities.

Multi-Band Situation- Cell Multi-Band Situation- Cell Coverage ProblemCoverage Problem

AB C

D

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O KCLR

E

F

G

H

I

Naive Extension of MCTA to Multi-Band SituationNaive Extension of MCTA to Multi-Band SituationCellSiteNo

Cell Site Data

Current Cell Site Data Other Band Cell Sites covering theoriginal site range

Band BandPref.

BTS Data 450 800 1900

BTS-1 … BTS-M

1 450 0 - 3,5 2,4,6

2 1900 2 1 3 -

3 800 1 1 - 2,4

4 1900 2 1 5 -

5 800 1 1 - 2,6

6 1900 2 1 3 -

… … .. … … … … … …

Table-1: A typical Cell Site Data Table.

Problem with Naive Extension of Problem with Naive Extension of MCTA to Multi-Band SituationMCTA to Multi-Band Situation

Latest version of 3GGPP standard provides for up to Latest version of 3GGPP standard provides for up to 13 bands. Currently 800 and 1900 MHz bands are 13 bands. Currently 800 and 1900 MHz bands are operational. In Russia, they are trying to introduce operational. In Russia, they are trying to introduce 450 MHz band. Using all bands- not cost-effective.450 MHz band. Using all bands- not cost-effective.1-1 overlay systems (cell sites) in different bands may 1-1 overlay systems (cell sites) in different bands may not always be co-located.not always be co-located.

Even if they are, position of a mobile accessing a BTS Even if they are, position of a mobile accessing a BTS of one band may not covered by the co-located of one band may not covered by the co-located system of the other band. (Radio coverage of the system of the other band. (Radio coverage of the carriers of 800 band is roughly 3 times that of the carriers of 800 band is roughly 3 times that of the 1900 band carriers).1900 band carriers).

If call is redirected to the other band because of its If call is redirected to the other band because of its best capacity carrier, call may fail if the best capacity best capacity carrier, call may fail if the best capacity carrier accessible to mobile has no capacity.carrier accessible to mobile has no capacity.

Our Min-Max Solution to the Dual Our Min-Max Solution to the Dual Band Traffic Allocation ProblemBand Traffic Allocation Problem

The rationale behind the algorithm:The rationale behind the algorithm:

If a mobile can access a cell site, it can be If a mobile can access a cell site, it can be allocated the best capacity carrier of the cell site.allocated the best capacity carrier of the cell site.

It is not sure which of the other band cell sites It is not sure which of the other band cell sites (covering the range of the original cell site of (covering the range of the original cell site of access band) is accessible to the mobile because access band) is accessible to the mobile because of its position.of its position.

Hence find the best carrier of each one of the Hence find the best carrier of each one of the other band cell sites and choose the worst among other band cell sites and choose the worst among them (min-max carrier) to compare with the them (min-max carrier) to compare with the inband best carrier of non-zero capacity.inband best carrier of non-zero capacity.

Call is redirected to the other band if the min-max Call is redirected to the other band if the min-max carrier is better. Redirection is done even if carrier is better. Redirection is done even if inband best carrier has no capacity and at least inband best carrier has no capacity and at least one carrier in the other band has capacity.one carrier in the other band has capacity.

Implementation of the AlgorithmImplementation of the AlgorithmCell site information (addresses of co-Cell site information (addresses of co-located BTSes and the Cell site IDs of the located BTSes and the Cell site IDs of the other band cell sites covering this one) is other band cell sites covering this one) is provisioned and stored in an in-memory provisioned and stored in an in-memory database at the BSC.database at the BSC.

When MSC sends Call setup request with When MSC sends Call setup request with the original cell site information, BSC the original cell site information, BSC requests Capacity information from all the requests Capacity information from all the BTSes.BTSes.

Considering all the responses arrived Considering all the responses arrived within a pre-configured time, BSC finds the within a pre-configured time, BSC finds the best carrier of each cell site and applies best carrier of each cell site and applies the min-max algorithm the min-max algorithm

Implementation of the AlgorithmImplementation of the AlgorithmanMS::MS aBTS::BTS anMSC::MSC aBSC::BSC cellSiteInfoTable:: Table

Originate-Call()

Originate-Call()

Page-Mobile()

Page()

Process-Page-Response()

<< Mobile-Terminated Call >>

<< Mobile-Originated Call >>

Get-Access-Carrier-Info (…)

Setup-Call (…)

Setup-Call (…)

Get-Carrier-And-BTS-Info-Lists (…)

Execute-MBTA-Algorithm (…)

Process-Page-Response()

Extensions to the MCTA AlgorithmExtensions to the MCTA Algorithm

Development of an Enhanced Development of an Enhanced Capacity Measure (ECM) by Capacity Measure (ECM) by augmenting mobile-user specific augmenting mobile-user specific preferences.preferences.

Extension of the dual-band algorithm Extension of the dual-band algorithm to the case of more than two bands. to the case of more than two bands.

ND-Bit SC-Bit RC-Bit RB-bit BPR-Bits CPR-Bits Capacity Magnitude Bits CAC-Bit IBC-Bit

ND- Non-downgraded SC-: Spare Capacity RC: Retain Carrier BPR- Band Priority CPR- Carrier Priority CAC- Call Access Carrier

IBC- Inband Carrier

Multi-band algorithmsMulti-band algorithmsOptimistic algorithmOptimistic algorithm

Best-fit algorihmBest-fit algorihm

B

BjBiB

i

TBjBi,i

0

ECM

ECMECMBandNewcall AssignTo

TBiSj

ji

i SB

B ECMn

ECM1 k

Sj

jS CECMECM

C

kmax

0^

i

ii

B

TBB

MinMaxECM

CMMaxMinMaxEMinMaxECMBandNewcall AssignTo

jBiSj

i SB ECMMinMaxECM

min iTB

BTiMinMaxECMCMMaxMinMaxE

max

Multi-band algorithms (continued)Multi-band algorithms (continued)Best-band algorithmBest-band algorithm

Firs-fit algorithmFirs-fit algorithm– Simply assign call the first band non-zero Simply assign call the first band non-zero

MinMaxECM.MinMaxECM.

0

max

i

jE-TBjBi,

ii

B

BBB

ECM

ECMECMBandNewcall AssignTo

0

0

TB EBi

i CMMaxMinMaxEiffMinMaxECM

otherwise,

Call Distribution Effectiveness MeasureCall Distribution Effectiveness Measure

Between-and DispersionBetween-and Dispersion

Within-Band DispersionWithin-Band Dispersion

Overall dispersion measureOverall dispersion measure

2

.

1

TB

i

i

TBTT

D ECMECMECM

B

TB

i

i

BT

T ECMECM1

TB BiSj i

ij

i BBS

TD

21

ECM

ECMECM

nW

W2W1W2.DW1.D D WB

Simulation ExperimentSimulation ExperimentAlgorithms for comparisonAlgorithms for comparison– Optimistic, First-fit, Best-fit and Best-bandOptimistic, First-fit, Best-fit and Best-band– Best Distribution (Post-call assignment dispersion)Best Distribution (Post-call assignment dispersion)

Criteria for comparative analysisCriteria for comparative analysis– Distribution efficiency & Robustness against call Distribution efficiency & Robustness against call

failuresfailures

SetupSetup– 100000 8-site (Fig. 1) configurations with best 100000 8-site (Fig. 1) configurations with best

capacity of each site a random number between 0 capacity of each site a random number between 0 and Max-Resources-Available-At-Any-Site.and Max-Resources-Available-At-Any-Site.

– Experiment is repeated for values of the Max-Experiment is repeated for values of the Max-Resources-Available-At-Any-Site from 1 thru 35Resources-Available-At-Any-Site from 1 thru 35

ji-EBjBi,

i BDBDB

BandNewcall AssignTo

ik

ki

i

BSSD

BBD

n

1

Experimental ResultsExperimental Results

Figure 4: Variation of Call Failures with Availability of Resources.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 10 20 30

Average Available Capacity of Sites

Cal

l Fai

lure

Pro

bab

ility

- Min-MaxAlgorithms

Optimistic MBTAAlgorithm

Figure 5: Variation in Distribution Efficiencies of Algorithms with Call Resources

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 5 10 15 20 25 30 35

Average Avaialable Capacity of Sites

A

lgo

rith

m

Best-Fit Min-Max

First-Fit Min-Max

Optimistic MBTA

Best-Band Min-Max

Best-DistributionMin-Max

Conclusions and ReferencesConclusions and ReferencesConclusionsConclusions

Rule out:Rule out:– Best-band- Computationally IntensiveBest-band- Computationally Intensive– Optimistic- Failure-prone in overloaded networkOptimistic- Failure-prone in overloaded network– First-fit- Good for early call setup, but inefficient from First-fit- Good for early call setup, but inefficient from

call distribution perspectivecall distribution perspective

Best-fit and Best-band are competitive. Best-fit Best-fit and Best-band are competitive. Best-fit may be preferable because of simplicity.may be preferable because of simplicity.

ReferencesReferenceswww.uspto.govwww.uspto.gov search Published patents on string search Published patents on string “guturu.’“guturu.’Parthasarathy, Guturu and Abdennaceur, Lachtar, “An Parthasarathy, Guturu and Abdennaceur, Lachtar, “An Efficacious Method for Dual Band Multi-carrier Traffic Efficacious Method for Dual Band Multi-carrier Traffic Allocation in CDMA Wireless Systems,” Proc. IEEE Allocation in CDMA Wireless Systems,” Proc. IEEE GLOBECOM 2003, Vol. 1, pp.10-14. Also available in GLOBECOM 2003, Vol. 1, pp.10-14. Also available in IEEE Trans. On Wireless Comm., March 2006.IEEE Trans. On Wireless Comm., March 2006.Sarvesh Sharma and Ahmad Jalali, US Pat.#6,069,871Sarvesh Sharma and Ahmad Jalali, US Pat.#6,069,871