Method used to measure the OSNR on a coherent system

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In the coherent system, the OD solution can be used to measure the OSNR. The OD solution can measure the OSNR by modeling OAs and fibers and accurately measuring the signal power and noise power. E2E OSNR measurement is supported for 10G, 40G, and 100G systems in various scenarios.

Other related questions:
Detection of the OSNR of a 40G or 100G system using the traditional OSNR detection method
The optical spectrum of 40G or 100G signals is wider than that of 10G signals. Therefore, the signal spectra of adjacent channels overlap each other. The channel noise includes not only the ASE noise but also the power crosstalk of some signals. Therefore, the OSNR tested using the traditional OSA method is less than the actual OSNR. The traditional OSA method is implemented based on the interpolation of inter-channel noise that is equivalent to in-band noise. The traditional OSNR detection methods, including the scanning method and the integral method, have the following disadvantages: Scanning method: applicable only to a system with a 100G channel spacing and without traversing an OEQ node. The detection results have a low precision. Integral method: When there are a few wavelengths, turning on or off the lasers will cause noise power fluctuation and therefore affect the detection accuracy. In addition, the noise power cannot be measured by turning on or off the laser when there is only one wavelength.

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.

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

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

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.

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