LOSS BUDGET CALCULATION OF FIBER
CABLE LINK
SECTION 1: DEFINITION OF TERMS
SECTION 2: LOSS BUDGET CALCULATION STEPS (SAMPLE)
SECTION 3: CALCULATION CASE STUDY
SECTION 1 Definition of terms
• FIBER ATTENUATION LOSS :this is an intrinsic loss of signal over distance
• CONNECTOR LOSS : loss recorded as a result of connectorisation
• SPLICE LOSS : loss recorded as a result of cable splicing
• LINK LOSS : the difference of the signal recorded on a link
• TRANSMITTER : the electronics that inject light into the fiber cable
• RECEIVER SENSITIVITY : This is the lowest optical signal that can be detected by the receiver
Cable operating system wavelength
@850nm
@1300nm
@1310nm
@1550nm
EIA/TIA STANDARDS
OPTICAL FIBER CABLE
WAVELENGHT (nm)
MAXIMUM ATTENUATION (dB/km)
50/125um multimode
850 3.5
1300 1.5
62.5/125um multimode
850 3.5
1300 1.5
Single mode inside plant cable
1310 1.0
1550 1.0
Single mode outside plant cable
1310 0.5
1550 0.5
T586 A&B STANDARDS
OPTICAL FIBER CABLE
WAVELENGHT (nm)
MAXIMUM ATTENUATION (dB/km)
50/125um multimode
850
3.0
1300
1.0
62.5/125um multimode
850
3.0
1300
1.0
Single mode inside plant cable
1310
1.0
1550
1.0
Single mode outside plant cable
1310
0.4
1550
0.4
Connector & Splice loss
Connectors loss 0.75db
Splice loss 0.2db
SPLITTER LOSS
SPLITTER RATIO 1:2 1:4 1:8 1:16 1:32
Ideal Loss / Port (dB) 3 6 9 12 15
Excess Loss (dB) 1 1 2 3 4
Actual Loss (dB) 4 7 11 15 19
SECTION 2: LOSS BUDGET CALCULATION STEPS
(SAMPLE)
STEP 1
CALCULATE THE FIBER ATTENUATION
LOSS
STEP 2 CALCULATE THE
CONNECTOR LOSS
connector loss =number of connectors X the maximum loss value
STEP 3 CALCULATE THE
TOTAL SPLICE LOSS
The number of splice x times the maximum loss value
STEP 4 CALCULATE OTHER COMPONENT LOSS
if ANY
OTHER COMPONENT SUCH AS SPLITER,ATTENUATOR,
STEP 5 CALCULATE THE PASIVE SYSTEM ATTENUATION
This is the addition of fiber loss + connector loss + splice loss + other components loss + safety buffer
STEP 6 CALCULATE THE LINK
LOSS BUDGET
Receiver sensitivity - transmitter’s average output power, (in dBm.)
STEP 7 VERIFY THE SYSTEM
PERFORMANCE MARGIN
Link loss budget - passive system attenuation
STEP 8 DETERMINE THE
RECEIVER’S DYNAMIC RANGE
Receiver maximum allowable input level - receiver
sensitivity
STEP 9 COMPARE
Determine the sum of the system’s performance margin and the safety buffer. The total must be less than the dynamic range.
SECTION 3: CASE STUDY
,
USE THE FOLLOWING INFORMATION TO CALCULATE THE LOSS BUGDET OF THE SPECIFIED LINK
• The system wavelength is 1300 nm. • The fiber type is 50/125 µm. • The average transmitter output power is -15.0
dBm. • The receiver sensitivity is -31.0 dBm. • The receiver’s maximum allowable input level is -
20.0 dBm. • The subject cable has 2 ST connector pairs. • The subject cable has 3 splices. • The subject cable’s length = 9.81 km.
(use TIA/EIA maximum loss per connector pair as 0.75 and 0.3 per splice loss for the calculation).
CABLE ATTENUATION LOSS
9.81 X 1.5 = 14.715dB
CONNECTOR LOSS
2 X 0.75 = 1.5dB
SPLICE LOSS
3 X 0.3 = 0.9dB
CALCULATE THE PASIVE SYSTEM ATTENUATION
14.715 dB + 1.5 dB + 0.9 dB + 2.0 dB = 19.12 dB
Passive System Attenuation = 19.12 dB
Calculate the link loss budget
Rx(max) – Rx (min) -10.0 dBm - (-33 dBm) = 23
dB
Link Loss Budget = 23 dB
Verify the system performance margin
Subtract the passive system attenuation from the link loss budget. 23.0 dB - 19.12 dB = 3.88 dB System Performance Margin = 3.88 dB
Determine the receiver’s dynamic range
Receiver maximum allowable input level - receiver sensitivity -20.0 dBm - (-33.0) dBm = 13 dB Receiver’s Dynamic Range = 13 dB
Determine the sum of the system’s performance margin and the safety buffer.
The total must be less than the dynamic range.
3.88 dB + 2.0 dB = 5.88 dB < 13 dB
INTERPRETAION
• Since the received signal (19.12dB) is less than the receiver dynamic range (23dB) , the fiber electronics (Tx, Rx equipment) in this case study is suitable to handle this cable link
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