CDMA Cellular Radio Network

PRESENTED BYMd Khanjahan Ali

Outline

• System Design Philosophy• Key Element in Designing a CDMA System -Relationship Between C/I and FER• Uniform Cell Scenario -For the Forward Link -For the Reverse Link• Nonuniform Cell Scenario

-Transmit Power on the Forward Link Channel -Transmit Power on the Reverse Link Channel - Designing a CDMA System

System Design Philosophy

• In TDMA system, capacity increase as elimination of Interference from desire signal.

• In CDMA system, the capacity increase depend on how much interference the desire signal can tolerate.

• In CDMA , All user share the same radio channel.If one user take more power than it need, then other will be suffer and capacity will be decreased.

• This presentation adresses how to tune The CDMA cellular radio network in order to tolarate interference.

Key Element in Designing a CDMA System

• In analog and TDMA system ,the most importent key element is C/I.

-Measured C/I : indicate the voice quality of system. -Specified C/I : specified value for the system.• Therefore field strength meters use to design TDMA.• In CDMA all voice channels served by a single radio

channel. -m-voice channel cell, -1 is trafic channel and m-1 interference channel. - C/I is hard to obtain by using a signal strength meter.• The key element in designing a CDMA system are

different from Designin TDMA system.

Relationship Between C/I and FER

• In CDMA ,The key element Eb/Io which is related to FER (Frame Error Rate).• We can design CDMA On the basis of following equation.

where, Eb= Energy/Bit, Io=Power/Herz. Rb = Bit/sec, B = Bandwidth.

• Eb/Io always varies in order to meet a specified FER• From Equation We can find a required (C/I) from Specified Eb/Io

• Have two different Requirement for C/I: -(C/I)F for the forward link channel -(C/I)R for the Reverse link channel

BR

IE

IC b

o

b

Uniform Cell ScenarioFor the Forward link Channel

• The C/I received at a mobile station A to the transmitted powers of all cell sites:

home cell 2 adjacent cells 3 interim cells 6 distant cells (I1) (I2,I3) (I4,I5,I6) (I7,I8,I9,I10,I11,I12)

• The relationship between of the three maximum transmitted powers of the three cells is

1

4

1

4

1

33221

)633.2()2()1(

1/

mmm

IC

3

3

2

2

1

1

mp

mp

mp

For the Reverse link

• The received C/I at the desired voice channel can be expressed as:

• The worst-case scenario is when:

CmrCmrCmCIC

321 .)1(/

1312

321 131211

mrmrm

1/1

321 1312 IC

mrmrm

Nonuniform Cell ScenarioTransmitted Power on the Forward link Channels

• All the cell size are not the same in a nonuniform CDMA system

• Consider only the three cells most affected by location of three vehicles

• The (C/I)F Received at vehicle 1,2,3 Respectively:

14

3334

2224

111

411

11)1(

)/(

IRmRmRm

RIC F

24

3334

1114

222

422

22)1(

)/(

IRmRmRm

RIC F

34

2224

1114

333

433

33)1(

)/(

IRmRmRm

RIC F

Transmitted Power on the Forward link Channels

• Interference at cell site 1,2,3 respectively

• Under the physical condition ,the following relation have to be held.

''

'

14

133134

12124

111

411

112')1(

)/(

IRmrRmrRm

RIC R

423323

421121

4222

422

22''

'

')1()/(

RmrRmrRmRIC R

432232

431131

4333

433

33''

'

')1()/(

RmrRmrRmRIC R

1)/(

1,, 321 RIC

mmm

Designing a CDMA system

• First have to check whether all requirement express above equation are met with our condition

• Then find the transmit Power .

Thank You