Differences in commissioning a non-coherent system and a coherent system

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The main difference in commissioning a non-coherent system and a coherent system is the position of the transmit-end EVOA.
In a coherent system, the transmit-end EVOA is always located after the OA board. In a non-coherent system, the transmit-end EVOA is located after the OA board only in the non-standard fiber access mode.

Other related questions:
Difference in the CD and PMD processing mechanism between a coherent system and a non-coherent system
100G/40G ePDM-BPSK systems are coherent systems. They use DSP chips for coherent detection, delivering superior performance in mitigating dispersion. Therefore, no DCM is required in these systems for dispersion compensation. For 40G DQPSK systems and other non-coherent systems, DCMs are required for dispersion compensation. The DCU board can also be used on the line.

Reason why a coherent system uses fewer OA boards than a non-coherent system
OA boards are used to compensate for insertion loss. Only one OA board is required in case that Gmax (maximum gain) �?Fiber loss + DCM loss; otherwise, two OA boards are required. The coherent system does not require DCMs, and a single OA board can compensate for larger link loss. When the link loss is within the permitted range, the coherent and non-coherent systems require the same number of OA boards. When the fiber loss is out of the permitted range, the coherent system, however, requires fewer OA boards. For example, in a system with a 60 km span, 18 dB fiber loss, and 5 dB DCM loss: The gain required by a coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 18 dB + 0 dB (no DCM) = 18 dB < Gmax. Therefore, one OA board (OAU101) is required. The gain required by a non-coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 18 dB + 5 dB = 23 dB < Gmax. Therefore, one OA board (OAU101) is required. In a system with a 100 km span, 28 dB fiber loss, and 9 dB DCM loss: The gain required by a coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 28 dB + 0 dB (no DCM) = 28 dB < Gmax. Therefore, one OA board (OAU101) is required. The gain required by a non-coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 28 dB + 9 dB = 37 dB > Gmax (36 dB for an EDFA board). Therefore, two OA boards (OAU101 and OBU101) are required.

Coherent systems
As mobile networks evolve towards LTE, smart terminals are widely used, and new services such as FBB users' IPTV, VoD, and cloud computing continue to emerge, the transmission capacity of conventional networks cannot meet requirement. To address the requirements, Huawei introduces transmission systems using the coherent technology. Huawei coherent transmission systems use advanced technologies such as ePDM-QPSK, ePDM-BPSK, and coherent detection to meet the high-speed transmission requirements on OSNR, CD tolerance, PMD tolerance, and nonlinear effects. Huawei provides large-capacity coherent solutions, offering ultra-large bandwidths (100G and 40G). A system using a coherent board (such as LSC, LTX, TN15LSXL, TN55NS3, and TN54NS4) is a coherent transmission system.

Principles for commissioning the optical power of a network carrying both coherent and non-coherent wavelengths
Principally, a coherent network can be commissioned in the same way as a non-coherent network, without considering fiber access scenarios. In a scenario in which 100G coherent wavelengths need to be added on a non-coherent network for capacity expansion, the incident optical power can be reduced to increase the OSNR tolerance of the 100G wavelengths and the transmission distance without electrical regeneration. In this situation, the optical power of single non-coherent wavelengths will be definitely reduced. When this occurs, commission the network according to the network design.

Method used to distinguish coherent boards from non-coherent boards
40G boards have both coherent and non-coherent boards. All 100G boards are coherent boards. The following lists the coherent and non-coherent 40G boards, and 100G boards that are applicable to the OSN 8800: 40G coherent boards: TN15LSXL, TN55NS3, TN56NS3, TN54HUNS3 40G non-coherent boards: TN11LSXL, TN12LSXL, TN11LSXLR, TN12LSXLR, TN11LSQ, TN11LSQR 100G coherent boards: TN12LSC, TN14LSC, TN11LTX, TN12LTX, TN54NS4, TN56NS4

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