CDMA2000 1x Key Technology-Power Control

ZTE University

CDMA BSS T&D Team

Objective

Know the principles of power control. Know the meanings of related parameters. Know how to modify the power control parameters

in various radio environments.

Content

Power Control Introduction Power Control Classification

Power Control Technology

Terrestrial mobile communication is involved in a complicated communication environment.

Multiple MSs and channels result in problems, such as co-frequency, self-interference and far-and-near effect.

Complex terrains and propagation environments result in multi-path fading and shadow effect.

Limited frequency resources conflict with the increasing number of users.

The power control technology is the core of the CDMA key technology.

The self-interference system based on the user number affects communication quality and system capacity.

It provides other characteristics such as soft capacity and cell breath.

CDMA Power Control Introduction

Function

Overcome the far-

and-near effect and

shadow effect. According to various

user requirements,

provide the proper

transmission power. Enhance the system

capacity.

Under the precondition of guaranteeing the call quality, reduce transmission power and inter-interference.

Guarantee the call quality.

Enhance the system capacity.

Decrease the transmission power of the MS.

Purpose Meaning

Content

Power Control Introduction Power Control Classification

CDMA Power Control Classification

The CDMA power control includes the reverse power control and forward power control.

Reverse power control: The transmission power of the MS is the controlled object and the BS plays an auxiliary role.

Open-loop power control Closed-loop power control Outer-loop power control

Forward power control: The transmission power of the BS is the controlled object and the MS plays an auxiliary role.

95 power control 1x power control

Reverse Open-loop Power Control Purpose: Eliminates propagation loss and shadow fading in free space (the

forward purpose is the same as the reverse purpose). Feature: It is a simple, direct, low-rate and rough control. It does not need

control information exchange between the MS and BS. Existing problems:

The forward and reverse are assumed as the completely same path loss, which does not reflect the asymmetrical path loss.

Initial judgment is based on the received total signal power. Therefore, that the MS receives the power from other BSs results in an inaccurate judgment.

Handset Initial transmission power (dbm) = - Handset receiving power (dbm) - Offset power+ Nominal transmission power offset (NOM_PWR)+ Initial power offset of access (INIT_PWR)+ Interference collection factor

Reverse open-loop power control

Reverse Closed-loop Power Control

Purpose: Makes up the loss that is not eliminated and is independent from the forward link, and realize accurate power control.

Control mechanism: The BS detects the SNR Eb/Nt from the MS and compares it with the threshold Eb/N0 to generate the power control bit for the MS. 0 indicates to increase power while 1 indicates to decrease power.

Transmit 800 times per second (that is, update once per 1.25ms). Each command needs the MS to add or reduce a step of

transmission power.

Reverse closed-loop power control

Eb/NtMeasurement

Eb/No threshold value

or

Reverse Outer-loop Power Control

Combining the FER that directly affects the voice quality with the SNR of the reverse closed-loop power, adjust the threshold Eb/E0 at real time according to change of the frame quality.

This function is performed on the SDU board. The adjustment speed of reverse outer loop: 20ms, that is, sampling per 50 frame/s.

The vendors do not recommend to modify the algorithm parameters of the outer-loop power control. Users learn the

contents of this part by themselves.

Frame quality

BSC

Reverse outer-loop power controlReverse closed-loop

power controlEb/Nt

Measurement

Eb/No threshold value

or

Forward Power Control Based on the feedback information from the MS, the forward power

control helps the MS to control the power of the assigned forward traffic channel. In this way, reduce the total forward transmission power of the sector, and avoid handoff failure to the sector or failure of new users’ access due to a shortage of the forward power.

The forward power control includes 95 power control and 1x power control.

The forward overhead channels (including pilot, synchronization and paging) do not need power control.

Forward traffic channel

or

95 System Forward Power Control

The BSC slowly decreases the power of each MS.

With increase of FER (measured by the MS), the MS sends the Power

Measurement Report Message (PMRM) to require to add the power of the

forward traffic channel.

According to the FFER reported by the PMRM message, the BSC adjusts the

sector to properly assigning the power of forward traffic channel to the MS.

BSC

FER

Adjust Fwd.Power

Forward link power control

95 System Forward Power Control

The control speed is slow and the period is 20ms to 2s.

Two control modes are available, respectively concentration (BSC)

and distribution (BTS).

RC1: By the PMRM, the MS reports the PMRs of traffic channels.

The threshold report mode and periodical report mode are available.

RC2:The MS uses EIB to indicate the state (good or bad) of the

forward link frame and sends this value to the BS through the

reverse link.Because now the IS95 system has exit the market, the detailed

contents of this part are omitted.

Overview of 1x System Forward Power Control It is compatible with the power control of the IS95 system. It adds the speedy forward power control (including the inner-loop power

control and outer-loop power control). It adds the power control for other code-division channels. It introduces the problem of the SCH power control. In the soft handoff process of RC3 ~ RC5 forward link, it complies with the

synchronization mechanism of the forward transmission power between BSs.

The BSC is not required to participate in the whole process. It is similar to the power control of the reverse closed loop.

Eb/No

Forward link power control

or

1x System Forward Inner-loop Power Control The MS performs the following operations:

Each PCG measures the received Eb/Nt on the F-FCH and F-SCH channels that are supervised per 1.25ms (speedy power control).

Compares the Eb/Nt measured by the PCG with the nominal value (Eb/N0) obtained by the forward outer-loop power control algorithm, and makes a power control decision.

Transmits the power control bit through the reverse power subchannel of the reverse pilot channel.

The BS performs the following operations: Obtains the power control bit. According to the corresponding power control step and the upper

and lower limits of the channel power, the CSM6700 chip automatically realizes adjustment of the forward transmission power for various PCGs.

Course Review

All types of power control collectively work. In this way, the power consumption of the MS decreases to the minimum and the whole capacity of the system increases.

BSC

FERFER

Signal StrengthMeasurement

Threshold Eb/Nt

or

Adjust Fwd.Power

Reverse outer-loop power control

Reverse closed-loop power control

Forward link power control

Reverse open-loop power control