CDMA Power Control

CDMA Power Control

CDMA Power ControlCDMA Power Control

Power Control ?

Transmit power adjustment on Forward Channel and Reverse Channel performed by the base station or the mobile station depending on the radio link condition.

Channel Type System Power Control

Forward Channel

Pilot Channel IS-95/1x X

Sync Channel IS-95/1x X

Paging Channel IS-95/1x X

Fundamental Channel IS-95/1x O

Supplemental Channel 1x O

Reverse Channel

Pilot Channel 1x O

Access Channel IS-95/1x O

Fundamental Channel IS-95/1x O

Supplemental Channel 1x O


Why Power Control ?

The features of the CDMA system interference environment?

Autointerference system

the main interference is the other channel’s signal

Usually, all the base stations of an operator shall use the same frequency (i.e. same CDMA channel), and all the mobile stations shall use the same frequecy too. Consequently, for a Forward Channel the all other Forward Channel’s signal shall act as interference, and for a Reverse Channel the all other mobile stations’s signal shall act as interference.


The features of the CDMA system capacity?

The CDMA system capacity is restricted by the radio environment. To demodulate a specific signal successfully, the CDMA receiver requires that the received signal’s Eb/No value is greater than a threshold.

At the Reverse Link, the capacity of 1FA/3sector cell may be derived from following formula:

M = （ W/R ） / （ Eb/No ） F 1/v

W : CDMA channel bandwidth (1.2288MHz) F : Frequency reuse factor (0.6)

R : Data Rate (9.6kbps) : Sectorring factor (2.4~2.7)

Eb/No : Required Eb/No (6~7dB) v : Voice activity factor (0.35~0.5)

Soft Capacity

Dynamically changed depending on the radio environment


Near–Far Problem on the Reverse Link

If the mobile station A and B transmit at the same power (Pt(A)=Pt(B)), due to the different propagation loss, at the base station receiving antenna the signal of mobile station A shall be more stronger the signal of mobile station B ( Pr(A) >> Pr(B)). In this case, the base station receiver will not be able to demodulate the MS B signal successfully since the two mobile station use the same frequency.

On the Forward Link, the grave issue is how to distribute the total power among Forward Channels appropriately.

BTSDistance

MS A

MS B

r R

Pt(A)

Pt(B)

Pr(A)

Pr(B)


Fading

On the radio wave propagation, the reflection, diffraction and the scattering shall cause the multipath fading problem. The serious problem of the fading is the signal strength changes in a large range (60~70dB) and it changes irregularly. Morevoer, in case of the fast fading(short term fading) the signal strength changes rapidly (the period may be less than several milliseconds).

There are various technology to solve the fading problem, such as handoff technology, diversity technology and power control technology.

StrengthSlow Fading

Fast Fading

Propagation Loss

Distance


Conclusion

On the Reverse Link1. All of the mobile station transmit power should be controlled exactly in

order to demodulate the any one’s signal.

2. To maximize the cell capacity, as long as the target FER is maintained, all of the mobile station shuld transmit at the power level as low as p

ossible.

3. Incidentally, the power control can save the battery power.

On the Forward Link1. To maximize the cell capacity, as long as the target FER is maintained, the

base station shuld transmit at the power level as low as possible.

2. Because there are some limitations on the base station total transmit power, the cell capacity shall be limited by the base station total p

ower as well as the radio environment.


Classification of power controlClassification by target channel

Classification by power control manner

Classification by period

Forward Channel Power ControlForward Fundamental Channel (F-FCH) Power Control

Forward Supplemental Channel (F-SCH) Power Control

Reverse Channel Power Control

Reverse Pilot Channel (R-PICH) Power Contrl

Access Channel (ACH) Power Control

Reverse Fundamental Channel (R-FCH) Power Control

Reverse Supplemental Channel (R-SCH) Power Control

Open Loop Power Control Applied to the Reverse Channels of the IS-95 & 1x system

Closed Loop Power Control Applied to the Traffic Channels of the IS-95 & 1x system

Outer Loop Power Control Applied to the Traffic Channels of the IS-95 & 1x system except the Forward Traffic Channels of the IS-95 system

Slow Power Control Applied to Forward Traffic Channel of the IS-95 system

Fast Power Control Applied to the Traffic Channels of the IS-95 & 1x system except the Forward Traffic Channels of the IS-95 system


Open Loop Power Control

Applied to the Reverse Channels of the IS-95 & 1x system. The mobile station estimates the transmit power without the

control of the base station. The mobile station estimates the mean output power according

to the mean input power. The Open Loop power control has a long period(several tens

milliseconds) and a large range(may be greater than ±32dB) The Open Loop power control is used to solve the shadowing,

slow fading problem and it used to compensate the propagation loss.

The mean output power of each access probe shall be defined by the following formula:


mean output power (dBm) = - mean input power (dBm) + offset power

+ interference correction + NOM_PWRs - 16×NOM_PWR_EXT

s + INIT_PWRs

+ PWR_LVL × PWR_STEPs

offset powerA correction factor relative to the base station total transmit power, sensitivity and the unblanced path loss between the Forward Link and the Reverse Link.

DCS -73, PSC - 76.

interference correctionInterference correction = min(max(-7-ECIO, 0), 7), ECIO is the Ec/Io (dB) per carrier of the strongest active set pilot, measured within the previous 500 ms.


NOM_PWRsNominal transmit power offset. If INIT_PWRs were 0, then NOM_PWRs - 16 × NOM_PWR_EXTs would be the correction that should provide the correct received power at the base station.

The total range of the NOM_PWRs - 16 × NOM_PWR_EXTs correction is –24 to +7 dB. While operating in Band Class 0, NOM_PWR_EXTs is set to 0, making the total range of the correction from –8 to +7 dB.

INIT_PWRsInitial power offset for access probes. INIT_PWRs is the adjustment that is made to the first Access Channel probe so that it should be received at somewhat less than the required signal power.

The range of the INIT_PWRs parameter is –16 to +15 dB, with a nominal value of 0 dB.


PWR_STEPsPower increment for successive Access probes on the Access Channel, inunits of 1.0 dB.

The range of the PWR_STEPs parameter is 0 to 7 dB.

PWR_LVLPower level adjustment of the Access probe, in units of PWR_STEPs. The PWR_LVL is a non-negative integer which is the power level adjustment step.

Note: During an Access probe transmission, the mobile station shall update the mean output power in response to changes in the mean input power. For subsequent Access probes in an Access probe sequence, the mobile station shall update the mean output power in response to changes in the mean input power, the interference correction, and PWR_LVL.


Access Probe Transmission

System Time

IP (Initial Power)

Access Probe 1 + NUM_STEP

(16 max)

Access Probe Sequence

TA RT

PI

Select Access Channel (RA), initialize transmit power

RT

Access Probe 3

Access Probe 2

Access Probe 1

TA TA

PI

PI: Power Increment, PI = PWR_STEP (0 ~ 7 dB)


Closed Loop Power Control

Applied to the Traffic Channels of the IS-95 & 1x system, except the Forward Traffic channels of the IS-95 system.

The mobile station and the base station shall adjust the mean output power according the Power Control Bit received from the opposite.

The mobile station and the base station shall compare the Eb/Nt measured on the Forward Traffic Channel and the Reverse Traffic Channel with a Setpoint provieded by the outer loop in order to decide the Power Control Bit.

The Closed Loop power control has a short period(1.25ms) and a large range(may be greater than ±24dB).

The Closed Loop power control is used to solve the shadowing, fast fading problem.


The mean output power on the Reverse Traffic Channel shall be defined bymean output power (dBm) = - mean input power (dBm)+ offset power+ interference correction+ ACC_CORRECTIONS+ RLGAIN_ADJs+ the sum of all closed loop power control corrections(dB)

ACC_CORRECTIONSTotal Access Channel corrections. The mobile station shall set this factor to NOM_PWRs – 16 × NOM_PWR_EXTs + INIT_PWRs + PWR_LVL × PWR_STEPs.

RLGAIN_ADJsGain adjustment applied to the Traffic Channel output power relative to the transmission power on the Access Channel.

NUM_RSCCHNumber of Reverse Supplemental Code Channels on which the mobile station is transmitting. The range of NUM_RSSCH is from 0 to 7.


Forward Traffic Channel power control

In the IS-95 DCS system:

The base station shall set the initial transmit power on the Forward Traffic Channel according to the parameter fdch_init_gain_rc1 value. After that, the base station shall adjust the transmit power on the Forward Traffic Channel according to the FER value reported by the mobile station in Power Measurement Report Message.

In the IS-95 PCS system:

The base station shall set the initial transmit power on the Forward Traffic Channel according to the parameter fdch_init_gain_rc2 value. After that, the base station shall adjust the transmit power on the Forward Traffic Channel according to the EIB bits received from mobile station via Reverse Traffic Channel.


In the 1x system:

The base station shall set the initial transmit power on the Forward Traffic Channel according to the parameter fdch_init_gain_rc3 or sch_init_gain_(rate)_rc3 value. After that, the base station shall adjust the transmit power on the Forward Traffic Channel according to the PCB bits received from mobile station via Reverse Power Control Subchannel.


Closed Loop Power Control (example of Reverse link power control)

sum of PWR_STEP

FDCH

mean input power measurem

ent（ -1 ）

INIT_PWRNOM_PWRK=-73

-Pr

Decision:

if PCB=1, then - 1dB;

if PCB=0, then +1dB.

Pr

Traffic Channel

Bit

Pt

PCB

Decision:

If Eb/Nt setpoint, set PCB =1;

If Eb/Nt setpoint, set PCB =0.

FDCH

Demodulator

FER Measurement

Setpoint Decision

Receiver

Transmitter

Eb/Nt Measurement

PCB

Outer Loop

Base station Mobile station

Transmitter

DemodulatorReceiver


Outer Loop Power Control

The outer loop power control shall be applied to the Traffic Channels of the IS-95 & 1x system, except the Forward Traffic Channels of the IS-95 system.

The outer loop estimaiton shall compare the current FER on the traffic channel to the target FER to decide a setpoint.

The setpoint shall be provided to the inner loop with period of 20ms.

Documents

CDMA Power Control