Calculating DWDM Link Parameters for a 1000 km Backbone
For a 1000 km link in a remote area, G.652 optical fiber (OPGW) and an M800-2-8Q aggregator with a capacity of 2 channels at 200 Gbit/s each were selected. Mode: 2 × 200G, OSNR requirement 12.98 dB, baud rate 71.675 GBaud, Fractional QAM, SD-FEC 27%. Transmitter power 0 dBm per channel — a balance between OSNR and nonlinear effects (SPM, XPM, FWM, SBS).
Fiber attenuation 0.22 dB/km. Dispersion, PMD, and nonlinearities do not limit parameters at the chosen span lengths.
Calculation with Erbium-Doped Fiber Amplifiers (EDFA)
Noise figure NF = 9 dB. For a 140 km span:
- Attenuation: 0.22 × 140 = 30.8 dB
- Splices (35 splices × 0.05 dB): 1.75 dB
- Connectors: 0.5 dB
Total loss L = 33.05 dB
OSNR after span: OSNR = 0 − 33.05 − 9 + 58 = 15.95 dB (margin 2.97 dB).
For N spans: OSNR_total = 15.95 − 10×log10(N). With N=2 (280 km): 12.94 dB — at the requirement threshold.
Section (between regenerators): 280 km (2 spans, 1 OLA). For 1000 km:
| Element | Quantity |
|----------------------|----------|
| Terminal stations | 2 |
| Regenerators (3R) | 3 |
| OLA (EDFA) | 4 |
| Powered Points | 9 |
Regenerator (3R) — OEO conversion, resets noise and dispersion, but requires power and maintenance.
A 150 km span yields OSNR 10.59 dB after 2 spans — below standard, margin exhausted.
Calculation with Hybrid Amplifiers (HA)
NF = 2 dB. 170 km span:
- Attenuation: 37.4 dB
- Splices (2.15 dB)
- Connectors: 0.5 dB
L = 40.05 dB, OSNR = 15.95 dB (margin 3 dB).
With N=2 (340 km): 12.94 dB.
Section: 340 km (2 spans, 1 HA). For 1000 km:
| Element | Quantity |
|----------------------|----------|
| Terminal stations | 2 |
| Regenerators (3R) | 2 |
| HA | 3 |
| Powered Points | 7 |
Additional Limitations
- Dispersion: 17 ps/(nm·km), over 140 km ~1.9 ns (correction up to 256 ns).
- PMD: 1.18 ps over 140 km.
- SBS: margin at 0 dBm.
- SRS, FWM, SPM/XPM: within limits.
Receiver overload (+5 dBm): use an attenuator to reduce to –10…–20 dBm.
Practical Operational Aspects
Splice Accumulation: Each repair adds 2 splices (0.1 dB loss). 20 extra = 1 dB. A 3 dB margin over 140/170 km is critical for longevity.
Vandalism and Breaks: OPGW (Optical Ground Wire) with armor and suspension atop poles minimizes risks from gunfire and theft.
Logistics:
- OPGW (4 km): 1.6–2.1 tons, KamAZ with a manipulator.
Power Line Spans: 400–450 m (220–500 kV), 1 reel (4 km) — 9–10 spans.
Installation Equipment:
- Hydraulic braking and tensioning machines.
- Pulling winch (diameter >1500 mm for OPGW).
- Rollers, pulling rope, clamps.
Key Takeaways
- EDFA (NF=9 dB): 140 km spans, 9 powered points, simpler and cheaper.
- HA (NF=2 dB): 170 km spans, 7 points, less maintenance in remote areas.
- OSNR margin of 3 dB is mandatory for repairs and degradation.
- Regenerators (3R) are needed every 280/340 km to reset noise.
- OPGW is optimal for power lines: protection from vandalism, logistics account for weight.
— Editorial Team
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