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Automatic Transmit Power Control (ATPC)

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What is ATPC

• What is ATPC: Automatic transmit power Control or Adaptive transmit power control •DTPC: Dynamic Transmit Power Control

• MTPC: Manual Transmit Power control

• ATPC:Is a feature of digital MW radio ,which increases near end station Transmit power when far end station RSL goes below pre defined/set Threshold either due to rain or due to other fades • It is a closed loop feature. Holds RSL with in 5dB (hysteresis), of reference/set level • Exponentially closes the gap for fast response

• Up to 30dB dynamic range. Tx Power adjustment in steps of 1dB

-55 dBm 5 dB,

Hysteresis RSL

-60 dBm Rx Threshold level

• Example: If Rx threshold is set to -60 dBm no output control is made unless RSL goes below -60 dBm or goes above -55 dBm, so that RSL is maintained between -60 to -55 dBm

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ATPC: How it works

ATPC TX Max

Station A

ATPC TX Min

Shallow Deep

-55dBm

Rx Threshold (-60dBm) Station B

Shallow Deep

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ATPC Settings

Tx Rx

IDU IDU ODU ODU Rx Tx

Site A Site B

Tx Max Tx Max

Tx Min Tx Min

Ref Ref

• Tx Max.=Nominal –(0-30 dB)

• Tx Min.= Nominal- (0-30dB)

• ATPC Rx Threshold (reference)= -30 to -70 dBm

• ATPC will start with Tx Min Power

• When RSL at the opposite site goes below the reference level,

• ATPC will start increasing the Tx Power up to Tx Max in 1 dB steps until

• RSL at the opposite site to be over the reference level

• ATPC will maintain the RSL with in 5 dB over reference level

• ATPC control transmits the information on the RSL to the opposite station and controls the

• Tx level of its own station in accordance with the RSL o0f the opposite station

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ATPC Settings

Tx Rx

IDU IDU ODU ODU Rx Tx

Site A Site B

• ATPC settings for PDH link 1. Fade margin =40dB( for regions point rain fall rate=120mm/Hr) 2. RSL Min=(-82+40) -42dBm

3. ATPC range= 30dB

4. ATPC RSL reference setting= -72 dBm

5. Minimum reference level setting to be 5dB more than the threshold ie -77dBm

• ATPC settings for SDH link

1. Fade margin =36 dB( for regions point rain fall rate=120mm/Hr) 2. RSL Min=(-68+36) -32dBm

3. ATPC range= 20dB

4. ATPC RSL reference setting= -52 dBm

5. Minimum reference level setting to be 5dB more than the threshold ie -63 dBm

Please note that for Nokia PDH hops the terminology is ALCQ (Adaptive Level Control with Quality Measure)

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•Advantages of ATPC

•Reduced average Power consumption • Eliminates of Up fade

• Extended MTBF

• Limits transmit power to that required to maintain a constant bit error rate (BER)regardless of the propagation conditions.

• Improved outage performance due to the reduced influence of adjacent channel • Reduced transmit power during clear sky conditions, meaning that the interference resulting from the ATPC link is correspondingly lower., compared to non ATPC links

•Facilitates operation of co channel links with acute branching angles

•Improves the frequency reuse factor associated with a given band and geographic area, providing a spectrum efficiency

•Facilitates mitigation of rain fades( above 10 Ghz)

•Prevents receiver front end over load in high frequency links( Metro links, Greater than 10 Ghz), designed for high rain fades

• Facilitates usage of larger Antenna sizes for short haul links ( Metro links) with out overloading the receiver front ends

• Facilitates reduction of interference levels at Hub locations and in to adjacent links in a frequency congested area.

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Important aspects to be understood on ATPC

1.During rain Spatio-temporal distribution of rain fields are not uniform and not correlated, Interfering signals are not attenuated in similar proportion to wanted signals, consequently ATPC enabled links may result in increased levels of interference.

2. As the distance increases rain field spatial autocorrelation function falls off approximately exponentially.

3. Introduction of ATPC may give rise to a number of additional outages in the presence of intense rain

(~10% increase for a frontal rain event).

10.Judicious adjustment of W/U ratio may be an appropriate technique for reduction of outages due to ATPC

11.ATPC may be more appropriate for combating temporary fading of wanted link rather than interference from the unwanted link (s). Otherwise, a situation may arise where two ATPC systems repeatedly increase their Tx power in response to each other’s interference until both are transmitting at their maximum Tx power. This situation negates the purpose of ATPC

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Impact of ATPC during rain(co channel operation) Co Channel Operation • In the below NW ATPC is enabled for all the 4 Links

• Link1: Is subjected to rain fade.RSL ofODU1reduces.Tx power of ODU2(siteB) increses.High Tx level of ODU2(site B) interfere with ODU1(siteA) of Link 2

• Link2:Consequent to this RSL of Link2 of ODU1(SiteA) reduces.Tx Power at ODU2 (SiteC) increases.High TX level of ODU2(SiteC) of Link 2 interfere with ODU1(SiteA) of Link3.Similary with ODU1 of Link1

• This process continue until both sites are transmitting to their maximum Tx power.

• It is noticed that in few geographies ATPC has resulted in 10% additional outages during rain SiteE

SiteA ATPC Site A Rain SiteB LInk1 ODU1 ODU2 ATPC

ATPC TX level High ATPC SiteA

Adjacent Channel Operation SiteA ATPC •Impact is same as co channel links.

ATPC •However adjacent frequency spot links may not be subjected to similar additional Outages during rain like co channel links in ATPC enabled links

SiteC ATPC

TX level Low ATPC SiteD

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Mitigation of ATPC induced outages during rain(co channel operation)

• Acute angle Links • In the below NW Link1,Link2 are acute angle co channel links due to low branching angle(<40 degrees)

• ODU1 ‘s mounted at Site A Link1 and Link2 are victim ODU’s and ODU2 of Site B,ODU2 of Site C are interfering sites

•Change ATPC to MTPC for both the ODU1’s of Link1& Link2,ODU2’s to be retained in ATPC mode

SiteE

SiteA ATPC Site A Rain SiteB LInk1 ODU1 ODU2 ATPC

MTPC TX level High ATPC SiteA

• Adjacent Channel Operation SiteA ATPC • ATPC to be enabled at both sites

MTPC

SiteC ATPC

TX level Low ATPC SiteD

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Conclusions & recommendations

1. ATPC to be used to combat temporary fading of the wanted link rather than interference from the unwanted link(s)

2. Judicious decision to be made during planning for enabling ATPC for co channel acute branching angle links

3. MTPC to be enabled for the acute branching angle links emanating from a common/hub site and ATPC to be enabled at the distant end

4. Since the spacial temporal distribution of rain field are not uniform and difficult correlate additional outages due to ATPC enabled links during rain it is recommended that ATPC be enabled for all the links

5. ATPC to be enabled for all hops irrespective of their hop length

6. ATPC to be enable for all the links falling in the service providing geographical area.

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ATPC Configuration Example – Ceragon Hops

CONFIGURATION>>RFU>>RIGHT>> RFU CONFIGURATION

TRANSMITTER CONFIGURATION>> SET TX LEVEL=MAXIMUM TX POWER & CHECK THE ATPC BOX

RECEIVER CONFIGURATION>> SET REFERENCE RX LEVEL=-45

APPLY

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ATPC Configuration Example – Flexi Hopper Hops

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Thank You