Vodafone Idea engineers began overnight millimeter-wave backhaul trials this month on selected Delhi Metro tunnel stretches where fiber backhaul cuts have repeatedly interrupted passenger Wi-Fi and station-to-station trunk links, according to people briefed on the tests. The operator is pairing E-band and 26 GHz gear with existing duct paths rather than waiting for a full civil reopening of conduits that flood during monsoon seepage.
Why the tunnels became the bottleneck
Delhi Metro’s own operations network rides separate fiber, but licensed mobile operators lease dark fiber and colocation at interchange stations to feed in-tunnel small cells. When contractors snag ducts during civil works—or when water ingress corrodes splices—passenger-facing data rates collapse even though coverage maps still show bars at platform level. Vodafone Idea’s network planning team told regulators in a closed-door briefing that two Yellow Line segments accounted for a disproportionate share of Mumbai-style complaint spikes during the last quarter, even though the capital’s macro grid looks healthy on drive tests.
Millimeter-wave backhaul is not a passenger access technology here; it is a short-hop replacement for broken fiber spans between manholes that DMRC will not let operators open during revenue service hours. Field teams mount directional links on approved service walkways, with DMRC signaling staff logging interference budgets so train control frequencies stay protected.
What shipped in the trial kits
The trial bundles combine compact all-outdoor radios, twist-on waveguide, and battery-backed monitoring so links can fail over to a microwave hop if monsoon humidity pushes error rates up. Vodafone Idea is sourcing some units from its existing 5G vendor pool but re-flashing them for point-to-point profiles with tighter beam widths than street-level small cells use.
Throughput targets are modest by data-center standards—hundreds of megabits sustained—but that is enough to restore VoWiFi registration and streaming on crowded evening trains. Engineers are also testing whether a single mmWave hop can backhaul multiple unlicensed Wi-Fi access points without violating TRAI power-density rules for licensed bands in confined concrete.
Regulatory and safety constraints
TRAI’s recent consultations on backhaul liberalization matter because operators want clarity on whether E-band links inside transit tunnels need separate authorizations from macro 5G licenses. Department of Telecommunications officials have encouraged transit pilots in principle, but each city authority still signs its own safety memo. DMRC’s template requires flame-retardant cabling, hot-work permits, and escorted night shifts; Vodafone Idea’s contractors have been on that roster since earlier Wi-Fi refresh contracts.
Fire-safety officers asked for thermal imaging logs showing radios do not heat walkway panels beyond specified limits. The operator submitted those logs last week alongside a map of link azimuths that stay clear of tunnel evacuation signage.
Competitive context on the Vi balance sheet
Reliance Jio and Bharti Airtel already market aggressive Delhi Metro Wi-Fi partnerships; Vodafone Idea’s share is thinner but politically visible because the carrier still serves millions of prepaid subscribers who commute on the network daily. A successful tunnel backhaul pilot would not fix the company’s broader capex constraints, but it would reduce churn among urban postpaid families who judge networks by whether Instagram Reels buffer between Rajiv Chowk and Kashmere Gate.
Investors watching the government’s adjusted gross revenue relief package note that any capex must be targeted. Internal slides seen by InfoHandle describe the mmWave trial as “surgical,” with a full rollout contingent on DMRC granting standardized mounting brackets across lines.
What success would look like
Engineers set a 60-day evaluation window: mean time to repair after fiber cuts should drop from multi-day splicing jobs to hours-long radio alignment, and passenger throughput should recover without waiting for civil contractors. If metrics hold, Vodafone Idea will propose a framework agreement DMRC could offer other carriers, similar to how shared duct policies work on some European metros.
Until then, night crews will keep aligning horns on service walkways while trains rumble past on the adjacent track. The story is not 5G marketing—it is whether a distressed operator can keep a transit data pipe alive when the ground under the fiber keeps moving.
Integration with existing small cells
Backhaul restoration also has to match the VLAN plans station integrators already deployed. Vodafone Idea’s transport team mapped which small-cell clusters can accept radio backhaul without re-homing SIM authentication paths. Misconfiguration would strand roaming subscribers who expect seamless handoffs at interchange concourses.
DMRC asked for a rollback playbook: if a link flaps during peak hour, operators must revert to throttled offline caching rather than bouncing associations across platforms. That requirement pushed the vendor to ship firmware with slower beam steering so trains do not trigger constant re-locks.
Monsoon and maintenance windows
Humidity sensors on trial radios feed a dashboard DMRC shares with maintenance control. When condensation risk crosses a threshold, links power down automatically and traffic shifts to a protected microwave hop that sacrifices capacity but keeps safety systems reporting. Operators said the behavior mirrors what they already do on rooftop links during dust storms—only here the “weather” is underground seepage.
If the pilot clears technical review, Vodafone Idea will seek board approval for a limited capex tranche tied to DMRC lease renewals rather than a nationwide mmWave spend. For commuters, the measurable outcome is simpler: fewer dead zones between stations where fiber breaks once closed the only path out.
