Automatic Transmit Power Control (ATPC)
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
5 dB, Hysteresis
-55 dBm 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
ATPC: How it works ATPC TX Max Station A
t u O x T
ATPC TX Min Shallow
Deep
s d i s e x e r i F t B s y d H 5
-55dBm L S R
Rx Threshold (-60dBm)
Station B
Deep
Shallow
ATPC Settings
Tx IDU
ODU
Rx
Rx IDU
Tx
Site A Tx Max Tx Min Ref • • • • • • • • • •
ODU Site B
Tx Max Tx Min 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
ATPC Settings
Tx IDU
ODU
Rx
Rx Tx
IDU
ODU
Site A
• 1. . 3. 4. 5. • 1. 2. 3. 4. 5.
ATPC settings for PDH link Fade margin =40dB( for regions point rain fall rate=120mm/Hr) ATPC range= 30dB ATPC RSL reference setting= -72 dBm Minimum reference level setting to be 5dB more than the threshold ie -77dBm ATPC settings for SDH link Fade margin =36 dB( for regions point rain fall rate=120mm/Hr) RSL Min=(-68+36) -32dBm ATPC range= 20dB ATPC RSL reference setting= -52 dBm Minimum reference level setting to be 5dB more than the threshold ie -63 dBm
Site B
•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 • mproves e requency reuse ac or assoc a e w a g ven an an geograp c area, prov ng 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.
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. During rain events, what would be effect of ATPC ? Does it increase or decrease Interference to neighboring stations? 4. Over what geographical area can rain fading be considered to be correlated? Which will have an impact on the worst-case scenarios for the use of all-ATPC and mixed deployments.? 5. What is the most efficient way of maximizing the increase in usage of co channel frequency spots through the usage of ATPC ? 6. By employing ATPC does the co-ordination distance for neighboring links subjected to excessive be reduced with out compromising the quality of service .? 7. ATPC to be used to combat temporary fading of the wanted link rather than interference from the unwanted link(s).?. 8. When to use ATPC and when to Use MTPC? 9. 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
ATPC: How it works Case1 -42 dBm
Case2 RSL(Nom)
Station A
B e d d 0 f a 2
+27dBm (Tx Power Max) +17dBm
-62 dBm
-3 dBm,ATPC set -72 dBm
-TX Power
ATPC setting Rx Threshold (-82dBm)
-82 dBm
Resultant RSL = ATPC set RSL
Deep
+27dBm Tx Power Max
RSL(Nom)
-
e d a f B d 0 4
-82dBm
-3 dBm,ATPC set -TX Power
ATPC setting Rx Threshold (-82dBm)
Resultant RSL = ATPC set RSL
Station B Station A Station B Case 1: Deep fade=20 dB, which is well with in the Dynamic/Compensating range (30dB) of PDH radio Hence resultant/overall RSL is maintained at ATPC set level= -72 dBm Case 2: Deep fade=40 dB, which is beyond Dynamic/Compensating range (30dB) of PDH radio Hence resultant/overall RSL is 10 dB below the ATPC set level= -82 dBm L S R
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 ATPC
Adjacent Channel Operation • Impact is same as co channel links. • However adjacent frequency spot links may not be subjected to similar additional Outages during rain like co channel links in ATPC enabled links
SiteA ATPC
LInk1
ODU1
SiteB ODU2
ATPC
ATPCTX level High
SiteA ATPC
ATPC ATPC
Rain
SiteC TX level Low
SiteD
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 ATPC
• •
SiteA ATPC
Adjacent Channel Operation ATPC to be enabled at both sites
LInk1
Rain
ODU1
SiteB ODU2
MTPC
ATPCTX level High
SiteA MTPC
ATPC ATPC
SiteC TX level Low
SiteD
Waluj -Chitegaon Link: RSL log Before ATPC enabling Before Enabling ATPC,RSL of Both main & diversity Paths were Subjected to Interference/ Multipath And RSL was varying from
• Walj-Chitegaon:2 4 Kms 6 GHz SD Link •1) Blue Chart;RSL Log-Main path, 2) Red Chart;RSL Log-Diversity path Soc Classification level 11 © Nokia Siemens Networks
Presentation / Author / Date
-30dBm to -65 dBm.After Enabling ATPC RSL of both main and Diversity paths Maintained at -33 to -38( Main) & at -35 To -40 dBM (SD) paths
Waluj-Chitegaon Link: RSL log After ATPC enabling
• Walj-Chitegaon: 1)Blue Chart;-SL Log-Main path 2) Red Chart ,RSL Log-Diversity path • After enabling ATPC RSL is maintained with in 5dB Soc Classification level 12 © Nokia Siemens Networks
Presentation / Author / Date
Paithan - Pingli Link RSL & TX Logs after ATPC Chart 1: • Paithan site Tx & RX Logs after enabling AT PC • Before enabling ATPC RSL of Paithan & Pingli link was varying from -40 dBm to -60 dBm. •After enabling ATPC RSL held constant between -40 t0 -50 dBm •Blue chart indicates the RSL variation •Pink Chart indicates TX variation to compensate RSL variation
Chart 2: • Pingli site Tx & RX Logs after enabling AT PC •RSL variation •Pink Chart indicates TX variation to compensate RSL variation
Soc Classification level 13 © Nokia Siemens Networks
Presentation / Author / Date
Conclusions & recommendations 1. 2. 3. 4. 5. 6.
ATPC to be used to combat temporary fading of the wanted link rather than interference from the unwanted link(s) Judicious decision to be made during planning for enabling ATPC for co channel acute branching angle links 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 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 ATPC to be enabled for all hops irrespective of their hop length ATPC to be enable for all the links falling in the service providing geographical area.
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