Where is guardband mandatory for EMF?

A guardband is mandatory between 10G and 200G channels due to significant differences in their electro-magnetic field (EMF) characteristics, specifically their modulation formats. Legacy 10G channels typically use Non-Return-to-Zero (NRZ) On-Off Keying, which has a very different spectral shape and power profile compared to modern 200G coherent channels using formats like DP-8QAM or DP-16QAM. The sharp spectral edges of the 10G signal can cause severe cross-channel interference and non-linear penalties on the adjacent, spectrally efficient, and more sensitive 200G signal. The guardband provides the necessary optical isolation to maintain the required optical signal-to-noise ratio (OSNR) and performance for the 200G channel.

A. Between 10G and 40G channels

While recommended, it is not always mandatory. Some 40G formats (like DPSK) are more tolerant of adjacent 10G signals than higher-order modulation formats are.

B. Between 10G and 100G channels

A guardband is strongly recommended, but the 100G DP-QPSK format is more robust than 200G formats, making the requirement less stringent than for the 10G/200G case.

D. Between 40G and 100G channels

These channels often use similar coherent modulation (e.g., DP-QPSK) and are designed to coexist on a flexible grid with standard spacing, typically not requiring a special mandatory guardband.

1. Nokia 1830 PSS Engineering and Planning Guide, Release 11.1 (Document ID: D5-6981-2011-0101)

Section: "Mixed data rate engineering rules"

Content: This guide details the engineering rules for deploying mixed line rates on the same fiber. It specifies that when mixing 10G NRZ channels with coherent PDM-QPSK (100G) or PDM-xQAM (200G/400G) channels, guardbands are required to mitigate inter-channel crosstalk. The requirement is most critical for higher-order modulation formats like those used for 200G, which have higher OSNR requirements and are more susceptible to interference from the spectral shoulders of adjacent 10G NRZ signals.

2. Nokia Application Note, "Strategies for Migrating to 100G and Beyond in Optical Networks" (Document ID: AN-100G-MIG-0515)

Section: "Coexistence of 10G with 100G/200G Coherent Channels"

Content: This document explains that the spectral inefficiency and sharp roll-off of 10G NRZ modulation create significant interference for adjacent coherent channels. It explicitly states that network planning tools mandate guard slots between 10G channels and higher-speed coherent channels, particularly 200G and above, to ensure error-free operation.

3. Saleh, A. A. M., & Simmons, J. M. (2011). "All-Optical Networking: Evolution, Benefits, Challenges, and Future Vision." Proceedings of the IEEE, 99(10), 1679-1706. https://doi.org/10.1109/JPROC.2011.2162229

Page: 1692, Section on "Transmission Impairments in WDM Systems"

Content: While not a Nokia-specific document, this peer-reviewed paper discusses the fundamental challenges of mixed-signal transmission. It explains that linear crosstalk and non-linear effects (like cross-phase modulation) are exacerbated when channels with disparate modulation formats and power levels (like 10G NRZ and 200G 16-QAM) are placed adjacently, necessitating spectral guardbands for isolation.