college of engineering capacity and throughput optimization in multi- cell 3g wcdma networks son...

College of Engineering

Capacity and Throughput

Optimization in Multi-cell 3G WCDMA

Networks

Capacity and Throughput

Optimization in Multi-cell 3G WCDMA

Networks

Son Nguyen, B.S.

Advisor: Dr. Akl

Dr. Brazile

Dr. Tate

Department of Computer Science and Engineering

Son Nguyen, B.S.

Advisor: Dr. Akl

Dr. Brazile

Dr. Tate

Department of Computer Science and Engineering

04/19/23 2/53

OutlineOutline

• Mobile Phone Systems History

• CDMA and WCDMA Overview

• User and Interference Modeling Using 2-D Gaussian Function

• Maximization of WCDMA Capacity

• Optimization of WCDMA Call Admission Control and Throughput

• Mobile Phone Systems History

• CDMA and WCDMA Overview

• User and Interference Modeling Using 2-D Gaussian Function

• Maximization of WCDMA Capacity

• Optimization of WCDMA Call Admission Control and Throughput

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Mobile Phone Systems HistoryMobile Phone Systems History

• 1st Generation

• First commercial cellular telephone system began operation in Tokyo in 1979

• AMPS (Advance Mobile Phone System)

• Available in Chicago by Ameritech in 1983

• 1st Generation

• First commercial cellular telephone system began operation in Tokyo in 1979

• AMPS (Advance Mobile Phone System)

• Available in Chicago by Ameritech in 1983

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Mobile Phone Systems History(cont)


• 2nd Generation

• TDMA Interim Standard 54 (TDMA IS-54) in 1991

• TDMA IS-136 (updated version)

• GSM (Global System for Mobile Communications)

• In 1987, standard created with hybrid of FDMA and TDMA technologies

• Accepted in the United States in 1995

• Operated in 1996

• Major carriers of GSM 1900: Omnipoint, Pacific Bell, BellSouth, Sprint Spectrum, Microcell, Western Wireless, Powertel and Aerial

• 2nd Generation

• TDMA Interim Standard 54 (TDMA IS-54) in 1991

• TDMA IS-136 (updated version)

• GSM (Global System for Mobile Communications)

• In 1987, standard created with hybrid of FDMA and TDMA technologies

• Accepted in the United States in 1995


• Major carriers of GSM 1900: Omnipoint, Pacific Bell, BellSouth, Sprint Spectrum, Microcell, Western Wireless, Powertel and Aerial

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• CDMA IS-95 (Code Division Multiple Access)

• Developing by Qualcomm corporation in late 1980s


• Major US carriers using CDMA: Air Touch, Bell Atlantic/Nynex, GTE, Primeco, and Sprint PCS

• CDMA IS-95 (Code Division Multiple Access)

• Developing by Qualcomm corporation in late 1980s


• Major US carriers using CDMA: Air Touch, Bell Atlantic/Nynex, GTE, Primeco, and Sprint PCS

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Latest Global Cellular Statistics(End of 2004)

Latest Global Cellular Statistics(End of 2004)

• Global Mobile Users: 1.57 billion

• GSM: 1.25 billion

• CDMA: 202m

• TDMA: 120m

• Facts

• #1 Mobile Country: China (300m)

• Total European users: 342.43m

• US Mobile users: 140m

• Total African users: 53m

• 1.87 billion mobile users by 2007 (27.4% of the world’s population)

• Global Mobile Users: 1.57 billion

• GSM: 1.25 billion

• CDMA: 202m

• TDMA: 120m

• Facts

• #1 Mobile Country: China (300m)

• Total European users: 342.43m

• US Mobile users: 140m

• Total African users: 53m

• 1.87 billion mobile users by 2007 (27.4% of the world’s population)

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CDMA and WCDMA OverviewCDMA and WCDMA Overview

• Introduction to CDMA

• Power Control

• Frequency Reuse

• Voice Activity Detection

• Soft Handoff

• WCDMA Overview

• Spectrum Allocation in Different Countries

• Main differences between WCDMA and IS-95 air interfaces

• Development to all-IP

• Introduction to CDMA

• Power Control

• Frequency Reuse

• Voice Activity Detection

• Soft Handoff

• WCDMA Overview

• Spectrum Allocation in Different Countries

• Main differences between WCDMA and IS-95 air interfaces

• Development to all-IP

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Code Division Multiple Access(CDMA)

Code Division Multiple Access(CDMA)

• Introduced by Qualcomm in 1989

• 2nd Generation (2G) of mobile phone networks

• Distinguishes different calls by unique codes.

• Capacity of a CDMA network is limited by interference

• Introduced by Qualcomm in 1989

• 2nd Generation (2G) of mobile phone networks

• Distinguishes different calls by unique codes.

• Capacity of a CDMA network is limited by interference

Frequen

cy

Time

Call 1

Call 2

Call 3

FDMA

Frequen

cy

Time

Call 5

TDMA

Call 6

Call 3 Call 4

Call 1 Call 2

Frequen

cy

CDMA

Time

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Spread SpectrumSpread Spectrum

• Spreading the information signal over a wider bandwidth to make jamming and interception more difficult

• Three types of SS: Frequency Hopping, Time Hopping, and Direct Sequence (DS)

• Spreading the information signal over a wider bandwidth to make jamming and interception more difficult

• Three types of SS: Frequency Hopping, Time Hopping, and Direct Sequence (DS)

Time HoppingFrequency Hopping

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Direct SequenceDirect Sequence

30 kbps

15 kbps

3.84 McpsSpreading

3.84 Mcps

Spreading

3.84 Mcps

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Power ControlPower Control

• Aims to reduce interference

• Near-far problem

• Reduces power consumption in the MS

• Methodologies

• Open-loop

• Sum of transmit power and the received power is kept constant

• Closed-loop

• Signifies the other party to increase or decrease transmit power by a pre-defined power step

• Aims to reduce interference

• Near-far problem

• Reduces power consumption in the MS

• Methodologies

• Open-loop

• Sum of transmit power and the received power is kept constant

• Closed-loop

• Signifies the other party to increase or decrease transmit power by a pre-defined power step

d1

d2

Base Station

c1

c2

Distance

Pr2

Pr1

Pt1: Power transmitted from c1Pt2: Power transmitted from c2Pr1: Power received at base station from c1Pr2: Power received at base station from c2

Pr1 = Pr2

Pt1

Pt2

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Frequency ReuseFrequency Reuse

• Reuse frequency

• Smaller = higher network capacity

• frequency reuse factor of 4, 7, or 12 in TDMA and FDMA

• 6 5 2 3 7 1 4

• CDMA cellular systems: universal frequency reuse or frequency reuse factor of 1

• Reuse frequency

• Smaller = higher network capacity

• frequency reuse factor of 4, 7, or 12 in TDMA and FDMA

• 6 5 2 3 7 1 4

• CDMA cellular systems: universal frequency reuse or frequency reuse factor of 1

7

2

3

5

6

2

6

5

4

1

4

7

1

3

2

7

2

3

5

6

5

4

6

1

7

4

7

1

3

2

3

5

2

6

4

5

4

6

1

7

4

1

7

35

6

4

13

2

5

61

7

3

2

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Voice Activity DetectionVoice Activity Detection

• Reducing multiple access interference

• Human speech: 42%

results in a capacity gain

• FDMA and TDMA cellular systems

• Frequencies are permanently assigned

Capacity in FDMA and TDMA systems is fixed and primarily bandwidth limited.

• Reducing multiple access interference

• Human speech: 42%

results in a capacity gain

• FDMA and TDMA cellular systems

• Frequencies are permanently assigned

Capacity in FDMA and TDMA systems is fixed and primarily bandwidth limited.

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New Requirements of 3G systems

New Requirements of 3G systems

• Data communication speeds up to 2 Mbps.

• Variable bit data rates on demand.

• Mix of services on a single connection

• Meet delay requirement constraints

• Quality of service (QoS),

• Frame error rate

• Bit error rate

• Data communication speeds up to 2 Mbps.

• Variable bit data rates on demand.

• Mix of services on a single connection

• Meet delay requirement constraints

• Quality of service (QoS),

• Frame error rate

• Bit error rate

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New Requirements of 3G systems (cont)New Requirements

of 3G systems (cont)

• Coexistence with second generation systems

• Support asymmetric uplink and downlink traffic

• Higher spectrum efficiency

• Coexistence of FDD and TDD modes.

• Coexistence with second generation systems

• Support asymmetric uplink and downlink traffic

• Higher spectrum efficiency

• Coexistence of FDD and TDD modes.

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WCDMA OverviewWCDMA Overview

• 3rd Generation (3G) of mobile phone networks

• Designed for multimedia communication

• Cover both FDD and TDD operations

• 3rd Generation (3G) of mobile phone networks

• Designed for multimedia communication

• Cover both FDD and TDD operations

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Main differences between WCDMA and IS-95 air interfaces


WCDMA IS-95

Carrier spacing 5 MHz 1.25 MHz

Chip rate 3.84 Mcps 1.2288 Mcps

Power control frequency 1500 Hz, both uplink and downlink

Uplink: 800 Hz, downlink: slow power control

Base station synchronization

Not needed Yes, typically obtained via GPS

Inter-frequency handovers

Yes, measurements with slotted mode

Possible, but measurement method not specified

Efficient radio resource management algorithm

Yes, provides required quality of service

Not needed for speech only networks

Packet data Load-based packet scheduling

Packet data transmitted as short circuit switched calls

Downlink transmit diversity

Supported for improving downlink capacity

Not supported by the standard

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Development to all-IPDevelopment to all-IP

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CDMA with One Class of UsersCDMA with One Class of Users

Cell j

Cell i

jr

ir

10

2

, 10 ,

, /E

jm

jjji mCj ji i

r x y ndA x y

Ar x yI

2 ( , ) ( , )

( , )

ms j

ji miC j

nj r x ye dA x y

Aj r x yI

jiI Relative average interference at cell

i caused by nj users in cell j

dAln(10)

10

s

where

is the standard deviation of the attenuation for the shadow fading

m is the path loss exponent

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WCDMA with Multiple Classes of Users

WCDMA with Multiple Classes of Users

2( )

, ,

( , )( , ) ( , )

( , )

s

j

mj

ji g g g j g mj iC

r x yeI S v n w x y dA x y

A r x y

is the user distribution density at (x,y)

w(x,y)

• Inter-cell Interference at cell i caused by nj users in cell j of class g

• Inter-cell Interference at cell i caused by nj users in cell j of class g

2( )

,

( , )( , ) ( , ).

( , )

s

j

mj

ji g mj iC

r x yew x y dA x y

A r x y

is per-user (with service g) relative inter-cell interference factor from cell j to BS i

,ji g

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Total Inter-cell Interference Density in WCDMA

Total Inter-cell Interference Density in WCDMA

inter, ,

1, 1

1 M G

g g g j g ji gj j i g

I S nW

M is the total number of cells in the network

G total number of servicesW is the bandwidth of the

system

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Model User Density with 2D Gaussian Distribution

Model User Density with 2D Gaussian Distribution

2 21 2

1 2

1 1

2 2

1 2

( , )2

x y

w x y e e

own,

1

1 G

g g g i gg

I S nW

is the total intra-cell interference density caused by all users in cell i

• “means” is a user density normalizing parameter• “variances” of the distribution for every cell

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Signal-to-Noise Density in WCDMASignal-to-Noise Density in WCDMA

is the thermal noise density,

is the bit rate for service g

0N

Rg

own inter0 ,0

g

gb

g gi gi i

S

RESI

N I IW

is the minimum signal-to-noise ratio required

0 , , ,1 1, 1

g

gg G M G

gi g g j g g ji g g

g j j i g

S

R

SN n n

W

g

wherewhere

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Simultaneous Users in WCDMA Must Satisfy the Following Inequality Constraints

Simultaneous Users in WCDMA Must Satisfy the Following Inequality Constraints

( )

0

1 ggeff

g g g

RWc

R S N

is the minimum signal-to-noise ratio

g

is the maximum signal powergS

the number of users in BS i for given service g

,ni g

( ), , ,

1 1, 1

G M Gg

i g g j g g ji g g effg j j i g

n n c

1, 2, ,( , , , )g g M Gn n n1, ,g G

The capacity in a WCDMA network is defined as the maximumThe capacity in a WCDMA network is defined as the maximumnumber of simultaneous users for all servicesnumber of simultaneous users for all services

. This is for perfect power control (PPC).. This is for perfect power control (PPC).

wherewhere

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SimulationsSimulations

• Network configuration

• COST-231 propagation model

• Carrier frequency = 1800 MHz

• Average base station height = 30 meters

• Average mobile height = 1.5 meters

• Path loss coefficient, m = 4

• Shadow fading standard deviation, σs = 6 dB

• Processing gain, W/R = 21.1 dB

• Bit energy to interference ratio threshold, τ = 9.2 dB

• Interference to background noise ratio, I0/N0 = 10 dB

• Activity factor, v = 0.375

• Network configuration

• COST-231 propagation model

• Carrier frequency = 1800 MHz

• Average base station height = 30 meters

• Average mobile height = 1.5 meters

• Path loss coefficient, m = 4

• Shadow fading standard deviation, σs = 6 dB

• Processing gain, W/R = 21.1 dB




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Multi-Cell WCDMA SimulationUniform User Distribution

Multi-Cell WCDMA SimulationUniform User Distribution

• 2-D Gaussian approximation of users uniformly distributed in cells.

1 = 2 = 12000, μ1 = μ2 = 0. The maximum number of users is 548.

• Simulated network capacity where users are uniformly distributed in the cells. The maximum number of users is 554.

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Extreme Cases Using Actual Interference Non-Uniform Distribution


• Simulated network capacity where users are densely clustered around the BSs causing the least amount of inter-cell interference. The maximum number of users is 1026 in the network.

• 2-D Gaussian approximation of users densely clustered around the

BSs. 1 = 2 = 100, μ1 = μ2 = 0. The maximum number of users is 1026.

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•Simulated network capacity where users are densely clustered at the boundaries of the cells causing the most amount of inter-cell interference. The maximum number of users is only 108 in the network.

•2-D Gaussian approximation of users densely clustered at the boundaries of the cells. The values of

1 = 2 = 300, μ1, and μ2 are differentin the different cells. The maximum number of users is 133.

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Results of User And Interference Modeling with 2-D Gaussian Function Results of User And Interference

Modeling with 2-D Gaussian Function

• Model inter-cell and intra-cell interference for different classes of users in multi-cell WCDMA.

• We approximate the user distribution by using 2-dimensional Gaussian distributions by determining the means and the standard deviations of the distributions for every cell.

• Compared our model with simulation results using actual interference and showed that it is fast and accurate to be used efficiently in the planning process of WCDMA networks.

• Model inter-cell and intra-cell interference for different classes of users in multi-cell WCDMA.

• We approximate the user distribution by using 2-dimensional Gaussian distributions by determining the means and the standard deviations of the distributions for every cell.

• Compared our model with simulation results using actual interference and showed that it is fast and accurate to be used efficiently in the planning process of WCDMA networks.

04/19/23 30/53

Optimized Capacity Calculation(Outline)

Optimized Capacity Calculation(Outline)

• Relationship between Spreading and Scrambling

• Spreading Factor

• Orthogonal Variable Spreading Factor (OVSF) codes

• Imperfect Power Control (IPC)

• Numerical Results

• Relationship between Spreading and Scrambling

• Spreading Factor

• Orthogonal Variable Spreading Factor (OVSF) codes

• Imperfect Power Control (IPC)

• Numerical Results

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Relationship between Spreading and Scrambling

Relationship between Spreading and Scrambling

• Channelization codes: separate communication from a single source

• Scrambling codes: separate MSs and BSs from each other

• Channelization codes: separate communication from a single source

• Scrambling codes: separate MSs and BSs from each other

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Channelization code Scrambling code

Usage Uplink: Separation of physical data (DPDCH) and control channels (DPCCH) from same MS

Downlink: Separation of downlink connections to different MSs within one cell.

Uplink: Separation of MSs

Downlink: Separation of sectors (cells)

Length Uplink: 4-256 chips same as SF

Downlink 4-512 chips same as SF

Uplink: 10 ms = 38400 chips

Downlink: 10 ms = 38400 chips

Number of codes

Number of codes under one scrambling code = spreading factor

Uplink: Several millions

Downlink: 512

Code family Orthogonal Variable Spreading Factor

Long 10 ms code: Gold Code

Short code: Extended S(2) code family

Spreading Yes, increases transmission bandwidth

No, does not affect transmission bandwidth

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Spreading FactorSpreading Factor

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Orthogonal Variable Spreading Factor (OVSF) codes

Orthogonal Variable Spreading Factor (OVSF) codes

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Imperfect Power ControlImperfect Power Control

• Transmitted signals between BSs and MSs are subject to multi-path propagation conditions

• The received signals vary according to a log-normal distribution with a standard deviation on the order of 1.5 to 2.5 dB. Thus in each cell for every user with service needs to be replaced

• Transmitted signals between BSs and MSs are subject to multi-path propagation conditions

• The received signals vary according to a log-normal distribution with a standard deviation on the order of 1.5 to 2.5 dB. Thus in each cell for every user with service needs to be replaced

0 ,

bEI i g

2, , ( )

0 0

( ) ( )cb o b b i b

i,g

E EE e

I I

, ,( ) ( )b i b i,g b o bE E

,( )b i bE ig

2( )2

( )( )

_ c

geffg

eff IPC

cc

e

04/19/23 36/53

Numerical ResultsNumerical Results

04/19/23 37/53


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Results of Optimized Capacity Calculation

Results of Optimized Capacity Calculation

• The SIR threshold for the received signals is decreased by 0.5 to 1.5 dB due to the imperfect power control.

• As expected, we can have many low rate voice users or fewer data users as the data rate increases.

• The determined parameters of the 2-dimensional Gaussian model matches well with the traditional method for modeling uniform user distribution.

• The SIR threshold for the received signals is decreased by 0.5 to 1.5 dB due to the imperfect power control.

• As expected, we can have many low rate voice users or fewer data users as the data rate increases.

• The determined parameters of the 2-dimensional Gaussian model matches well with the traditional method for modeling uniform user distribution.

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WCDMA Call Admission ControlWCDMA Call Admission Control

• Quality of Service (QoS) of current connections in a network

• Grade of Service (GoS), i.e., call blocking rate

• Global if the decision to admit a call is based on total calls in the network

• Local if the algorithm considers only a single cell for making that decision

• Quality of Service (QoS) of current connections in a network

• Grade of Service (GoS), i.e., call blocking rate

• Global if the decision to admit a call is based on total calls in the network

• Local if the algorithm considers only a single cell for making that decision

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Feasible StatesFeasible States

( )

0

1 ggeff

g g g

RWc

R S N

( ), , ,

1 1, 1

G M Gg

i g g j g g ji g g effg j j i g

n n c

1,1 1,

,1 ,

...

... ... ...

...

G

M M G

n n

n n

A set of calls n =A set of calls n = satisfying the above equations issatisfying the above equations isdefined to be in a “feasible state”defined to be in a “feasible state”

wherewhere

Adding a new call with service g to cell i, the call is blocked if Adding a new call with service g to cell i, the call is blocked ifthe new state of the network does not belong to any of thethe new state of the network does not belong to any of thefeasible state.feasible state.

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Handoff Rate & Total Offered TrafficHandoff Rate & Total Offered Traffic

, , , , , , ,(1 ) (1 )j

ji g j g j g ji g j g ji g xj gx A

v B q B q v

, , , , , ,( , , ) (1 )ji g j g j g j j g ji g j gv v B A B q

: the handoff rate out of cell j offered to cell i for service g,ji gv

: Call with arrival rate service g in cell j,j g,ij gq : Probability that a call with service g progress in cell i after completing its dwell

time does to cell j

: Blocking probability for service g in cell j,j gB

jA : Set of cells adjacent to cell j

, , , ,( , , )j

j g j g j j g xj gx A

A v

v,j g : Total offered traffic to cell j for service g

04/19/23 44/53

Blocking probability for service gBlocking probability for service g

,

,

, ,, , ,

,0

/ !( , )

/ !

i g

i g

N

i g i gi g i g i g N

ki g

k

A NB B A N

A k

, ,

, ,(1 )i g i g

ii g ii g

Aq

: Erlang traffic in cell i with service g

, ,i g i gn N for i = 1, …, M and g = 1, …, G

,i gn : the “new” total number of connection with service g in cell i

,i gN : the maximum number of calls with service g in cell i

Admissible States:Admissible States:

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Maximization of ThroughputMaximization of Throughput

max, N

subject to , ,( , ) ,i g i g gB A N

( ), , ,

1 1, 1

,G M G

gi g g j g g ji g g eff

g j j i g

N v N v v c

for i = 1, …, M

, , , , ,1 1

( , ) (1 ) ( )M G

i g i g i g i g i gi g

T , B B

B

B : vector of blocking probabilities

: matrix of call arrival rates

04/19/23 46/53

Numerical AnalysisNumerical Analysis

• Processing gain, W/R

• 24.08 dB for spreading factor = 256







• Processing gain, W/R








04/19/23 47/53

Three Mobility ModelsThree Mobility Models

,ii gq

probability that a call with service g in progress in cell i departs from the network.

,ij gq

,i gq

probability that a call with service g in progress in cell i remains in cell i after completing its dwell time.

probability that a call with service g in progress in cell i after completing its dwell time goes to cell j. It’s equaled zero (=0) if cell i and j are not adjacent.

No MobilityNo Mobility

Low MobilityLow Mobility

High MobilityHigh Mobility

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WCDMA Network Throughput Optimization with SF = 256


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Results of Optimized Network Throughput Calculation

Results of Optimized Network Throughput Calculation

• Results for the cases with no mobility and high mobility for each blocking probability are identical.

• Low mobility case has an equalizing effect on traffic resulting in slightly higher throughput.

• As the spreading factor increases, the optimized throughput is better for all the three mobility models due to trunking efficiency.

• Results for the cases with no mobility and high mobility for each blocking probability are identical.

• Low mobility case has an equalizing effect on traffic resulting in slightly higher throughput.

• As the spreading factor increases, the optimized throughput is better for all the three mobility models due to trunking efficiency.

04/19/23 53/53

Thank You!!Thank You!!

Questions?Questions?

college of engineering capacity and throughput optimization in multi- cell 3g wcdma networks son...

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