Coherent Modules for 5G Backhaul — What an Operator in Poland and CEE Should Know

Why 5G Makes the Old Backhaul Stop Working

With 4G, a base station generated a few hundred megabits of traffic. You could handle that with a classic transceiver, a leased line, or in the worst case a microwave link. The optical budget was forgiving, and transport network engineers slept soundly. 5G changes that maths in three places at once.

The first place is throughput. A single 5G NR station can generate a dozen-plus gigabits per second per sector. With several sectors and traffic aggregated from a dozen stations in one node, you need 100G, 200G, or more. This is not future planning — it is a requirement for today.

The second place is latency. The applications 5G is built for — autonomous vehicles, real-time machine control, remote surgery — require latencies below a millisecond. Every additional signal-conversion layer in the transport network adds latency. The fewer devices between the station and the network core, the lower the delay.

The third place is scale. An operator building 5G coverage across a province has hundreds of nodes to connect. With a classic transponder architecture, this means hundreds of additional devices to purchase, power, cool, and service. Operational costs rise linearly with the number of nodes.

Three Segments of the 5G Transport Network

The 5G transport network is not one layer, but three — and each has different requirements.

Fronthaul connects the antennas (RU) with the distributed units (DU). It requires precise synchronisation and very low latency, and the distances are short, usually a few kilometres. Here, classic SFP28 25G modules or dedicated eCPRI solutions do the job, and coherence is not required. Midhaul connects the distributed units (DU) with the centralised units (CU). The distances are moderate and the throughputs rising, and here the first space for coherent modules appears — especially when an operator wants to aggregate traffic from multiple DUs over a single fibre instead of laying separate cables to each location. Backhaul connects the centralised units (CU) with the IP/MPLS network core. Here are the longest distances, the largest traffic aggregation, and the greatest pressure on cost per gigabit — and this is precisely where coherent modules have the strongest economic case.

What Specifically a Coherent Module Delivers in 5G Backhaul

Take a concrete example. An operator has an aggregation node serving ten 5G stations. The traffic from such a node totals 60 to 80 Gbit/s to be sent to the network core, dozens of kilometres away. In the classic approach this is several 10G links on separate fibres, or one 100G link with a dedicated transponder — a separate device, with separate power, separate management, and another item on the list of things to service.

With a GBC Photonics coherent module, you plug a 100G or 400G module directly into the port of the aggregation router. The module emits a signal on a specific DWDM wavelength, at 0 dBm, ready to enter the existing multiplexer without additional amplifiers. The transponder disappears from the architecture. When an operator has a hundred such aggregation nodes, that is a hundred fewer transponders. With the purchase, power, and service costs of each one, the difference in TCO over five years is a non-trivial budget item.

Why 0 dBm Matters Precisely in 5G Backhaul

This is a technical detail that, in the context of 5G backhaul, translates directly into project costs. Most coherent modules on the market transmit a signal at a power close to minus 10 dBm, while existing DWDM systems are calibrated for a signal power between minus 3 and 0 dBm. The effect is that at minus 10 dBm you have to add an EDFA amplifier between the module and the multiplexer — an additional device, additional cost, additional power draw, and a worse OSNR parameter.

GBC Photonics modules transmit a signal at 0 dBm natively, without a miniature EDFA bolted onto the module as a crutch. They plug directly into the existing DWDM system without any modifications, and the transmit power can be precisely tuned within a 10 dB range to match the specific optical path. When building a 5G backhaul network with dozens or hundreds of nodes, eliminating the amplifier per node is a real CAPEX saving and a simplification of the project that engineers appreciate at technical acceptance.

Modulation versus Range — a Practical Choice for Backhaul

GBC Photonics 400G OpenZR+ coherent modules support several modulation modes. This is not a specification detail, but a tool that a network engineer matches to a specific backhaul segment. The same physical module allows different configurations per node, so the operator standardises purchasing and warehousing on a single hardware type and adjusts the parameters to the reality of the specific route. In tests on the Poznań–Frankfurt route — nearly 1,000 km — 400G modules in 8QAM mode achieved stable 300G transmission without external transponders.

SRD — a Detail That Matters at 5G Scale

An operator building 5G backhaul across several provinces deals with a heterogeneous hardware environment — routers and switches from different manufacturers, bought in different tenders, with different module compatibility requirements. The GBC Photonics SRD (Smart Recode Device) environment lets you program a module to work with a specific hardware vendor from a smartphone app, without sending the module to a service centre and without waiting for a technician to arrive. An engineer in the field, at the aggregation node, configures the module in a few seconds. One type of module in stock instead of separate versions per vendor — and at 5G backhaul scale, with hundreds of nodes and several active-equipment suppliers, this is a logistics simplification that counts in both time and money.

What This Means for an Operator in Poland and CEE, Concretely

The 5G market in Poland and the CEE region is at a point where infrastructure decisions made today will determine operational costs for the entire decade. A backhaul built on classic transponders will cost more to maintain, will be harder to scale, and will need replacing sooner than a backhaul based on pluggable coherent modules.

Operators who have already deployed IPoDWDM architectures in their backbone networks report capital-expenditure savings of around 65 percent compared with traditional DWDM structures, a reduction in power draw from 70 percent at the network edge to 90 percent in the core, and a reduction in space occupied in nodes of up to 80 percent. 5G backhaul is not a backbone network on a nationwide scale, but the economic principles are the same — fewer devices, less power, simpler management, and scalability without replacing infrastructure.

A good 5G backhaul project with coherent modules starts with four questions: what are the distances between the aggregation nodes and the network core, what fibres are available on those routes, what active equipment is or will be running in the nodes, and what is the planned throughput per node over a three-year horizon. Answer these four questions, and we will prepare a recommendation with an optical budget and a TCO calculation!

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