enhancement and optimal utilization of cdma2000 network

7/28/2019 Enhancement and optimal utilization of CDMA2000 network

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Enhancement and

Optimal Utilization ofCDMA2000 Networks

Dr. Joseph ShapiraAlexander Chair Professor

IIT Madras

President, Comm&[email protected]


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When the Tire meets the Road..

Only then you feel the ride.

Nothing is more true for cellular systems.

Performance shows up only in large-scale

field deployment.

15 years of CDMA, and there are yet

lessons to learn.

Packet CDMA will teach yet more lessons


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Channel Impulse

response ina developed suburban


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CDMA Cellular

Reverse Link Forward link

Capacity limit Interference Power

Coverage limit Users power BTS power

Power control Controlled by aggregate

interference to the BTS

Controlled by

interference to the MS

Cell boundary Shrinks when loaded Expands when loaded

Responds to aggregate interference

No frequency planning and structured (hexagon) grids

Local environment and traffic density affects optimization

Forward and reverse links are not symmetrical


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CDMA outperforms

when optimized over all parameters

Reduce SHO overhead

Increase the transmission-loss slope

Balance up and down links Access Control

Balance the loads

Intersector

Intercell

Optimize the service

Dynamic optimization isthe next frontier

Improve the channel

reduce Eb/Nt required

margin

Receive diversity

Transmit diversity

Reduce link loss variations

Distributed antennas Repeaters


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Diversity Gain

Signal fading below threshold increases theBit Error Rate (BER)

Correlated fading: gain 3 dB

Threshold

Rx Diversity

MS

SDiversity gain is the rise of the average signal

level for the same BER (for the same fraction of

time below the threshold)

Uncorrelated fading: gain 7 dB

(at 1% FER)


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Cumulative Distribution Function (CDF)

for Diversity Combining

Single Branch

Diversity Gain (dB)

Signal [dB]

CDF

10%

100%

Prob. Signal 10 dB

Open, Line of SightSingle ray high Rician

Eb/Io -> 3 dB

Developed Suburban.

Long delay multipathEb/Io = 5 dB

Loss of orthogonality

Half of the power is lost if no EIRP

shaping is applied

Activity Eb/Nt EIRP

(dB)a1 (=1/3) 10 10/3

a2 (=1/3) 3 2/3

a3 (=1/3) 5 3/3

Total EIRP 15/3

(required )

Total EIRP 30/3

(available)


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Distributed Load Balancing

Intersector Hot Spot Repeater

Intercell Hot Spot

Repeater

Remote sector

BTS hotellingremote cells

Links:

F1/F2Microwave

Fiber Optics

Free Space Optics


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Network Optimization/ Capacity

Maximization Process

Reduce SHO overhead

Increase the transmission-loss slope

Balance up and down links Access Control

Balance the loads

Intersector

Intercell

Optimize service

Dynamic optimization isthe next frontier

Improve the channel

reduce Eb/Io required

margin

Receive diversity

Transmit diversity

Reduce link loss variations

Distributed antennas

Repeaters


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The Smart ClusterAdd-On Dynamic Optimization

Cluster size - 10 to 15 cells

Sensors

Optimization

Effectors

Communication Communication

Objectives

Mobile units

BTS RF state

Repeaters

Antenna state

Switchperformance parameters

RET and RBC Antennas

Repeater gainBTS pilot level

Neighbor list

Search window

Additional parameters


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3GThe cost of High Data Rate

Frequency

(band-width)

Time

(duration)

Power(signal-to-noise

and interference)

BIT

3G cellularBandwidth is fixed

CostHigher Eb/Nt needed

Higher modulation constellation,

Reduction of code protection

Protection by ARQ and Scheduling

The cost - latency


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DIGITAL MODULATION

Signal constellationA trade-off between spectral efficiency

(bits/Hz), and interference immunity

Cellular systems use2 and 4 state modulation.

Higher state8 PSK, 16 QAM

require high Eb/Nt.

The service has a shorter range

Im

Re

BPSK

Im

Re

QPSKIm

Re

16 QAM

Im

Re

8 PSK


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Signal constellation -sensitivity to noise

BPSK,QPSK

Higher spectral efficiency goes with higher

sensitivity to co-channel interference (requires

higher Eb/Nt)


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3GServices and Constraints

Service Rate Session Latency ErrorTolerance

Voice Low Long Low High

PTT Low Long High Very High

SMS Low Short High Med

Large files High Long High Very Low

Video/games Med Long Low Med

Means

Circuit switched Packet switched - Scheduling:

Code Division Time Division


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IS 95 and 1xEV DO Fwd Link

Structure


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Forward vs Reverse

Forward link (FL) efficiency depends on Tx power per bit

Large variation of FL efficiency between MS and over time

DO, DV, and HSDPA all take advantage of short-term goodchannel condition by fast MS feedback

RL efficiency depends on the Rx power per bit

Schedule-to-Tx-when-channel-is-above-average reduces theinterference to other BSs statistically.


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C/I vs non-orthogonal multipath

-15

-10

-5

0

5

10

15

0.

05

0.

15

0.

25

0.

35

0.

45

0.

55

0.

65

0.

75

0.

85

0.

95

1.

05

1.

15

r/R

C/I[dB]

al=.99 al=.95 al=.7 al=.5

a=.99

a=.95

a=.7

a=.5


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FORWARD LINK Eb/Nt vs. Distance(The Geometry factor G)

Distance from BS (in cell radius units)

Relative Eb / I0 [dB]

Load full .75 .5 .25

Non Orthogonal InterferenceOther cells loaded 50%

-10

0

10

20

30

40

50

60

70

80

0.05

0.15

0.25

0.35

0.45

0.55

0.65

0.75

0.85

0.95

1.05

1.15

1.25

1.35

Distance from BS

Eb

Orthogonal Interference

(noise limited)

Orthogonality and Diversity govern Eb/Nt

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Time Division Duplexing/

Scheduling For moving MSthe channel fluctuates

The peaks exceed the average by typical 3dB.

The signal does not peak simultaneously for different MSs.

The scheduler allocates time slots to the user with the best

channel, thus getting max data rate

Many users activity offers more opportunities for signal

peaks to the scheduler and increase the throughput.. This is

user diversity.


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Radio Resource Management

3G sacrifices capacity for service versatility

Mixture of different Eb/Nt requirements and packet

schedulingVariance in Power Control

Soft HandOff common to allVariance in boundary and

link balance.

Dynamic control is desired for optimizing capacity,coverage and quality


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Congestion Control

Limits the traffic in the cell within desired quality

Means:

PowerAdmission Control

Load control

Packet Scheduler

Antenna Tilt / Orientation/ Pattern Change

- impacts all other means


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Coverage Transformation

Antennas above the scenery(suburban environment)

The dominant parameter is angle

The angular spread grows as theantenna is lower

Antennas below the roof level

The dominant parameter is the

locationThe array manifold is squeezedinto a narrow coverage area.Multiple reflections areattenuated.


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Summary

The cellular CDMA systems achieves superior performance

and capacitywhen optimized against traffic and

environmentlocally and globally.

Initial planning and deployment need optimization to reflect

the actual traffic and environment, and their changes.

The advent of wide range of services on one platform adds

dynamics and variance to the network balance. Dynamic

optimization will be most advantageous.


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Summary (2)

Most of the Radio Resources are controlled at the RF

access level and allow for low BTS-intervention.

The meaningful locality in a CDMA network is a cluster of

10 to 15 cells. This is the optimization subject.

Smart antenna is a local solution. Smart cluster is a

network solution.

Dynamic optimization of Smart clusters is the eventual

goal.


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Reference

CDMA Radio with Repeaters

Joseph Shapira

Shmuel Miller

SPRINGER, 2007ISBN 978-0-387-26329-8

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Thank You

enhancement and optimal utilization of cdma2000 network

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