Singapore’s Spectrum Rules Explained: What the Simba-M1 Investigation Means

An assignment can regulate more than the headline band name. The relevant conditions may include the permitted use, technical parameters and other operating requirements. IMDA’s 2022 5G auction materials, for example, state that winning bidders must comply with prescribed technical specifications and terms and conditions of use.

IMDA can also make separate arrangements for temporary or occasional use. Its spectrum-management materials describe temporary use for activities such as exhibitions, demonstrations and equipment testing, while earlier planning documents discuss reserving spectrum for temporary demands such as major national events. A temporary arrangement is therefore not the same as a permanent mobile-spectrum right.

What counts as unauthorised use?

For a telco, the issue is not merely whether a transmitter is technically capable of operating on a frequency. The question is whether the operator has the regulatory right and approval to use that frequency for the particular service and configuration.

IMDA and Singapore’s Ministry of Digital Development and Information have stated that mobile network operators must use only spectrum assigned to them. Use beyond the assigned bands without prior IMDA approval can cause interference and give an operator an unfair advantage over competitors.

Unauthorised operation could occur in several ways. These are general technical possibilities, not findings about Simba’s network:

• Configuration or engineering error: A base-station profile, software template or automatic frequency-selection setting could contain the wrong band or channel plan after an upgrade, equipment swap or site rollout.
• Unapproved carrier aggregation: 4G and 5G networks can combine component carriers to increase capacity. That feature remains lawful only when each component carrier is assigned to the operator and approved for the relevant use. Enabling an unassigned carrier could improperly expand the bandwidth available to customers.
• Incorrect network parameters: A mistaken duplex setting, channel bandwidth or other radio parameter could cause a site to transmit outside its approved plan.
• Equipment or filtering problems: Damaged or poorly tuned radio equipment, filters, duplexers, power amplifiers or antennas can create unwanted emissions in adjacent frequencies. Even without deliberate intent, those emissions may breach technical limits or interfere with another network.
• Excessive power: Increasing transmit power does not change the nominal assigned frequency, but it can intensify leakage into adjacent channels, enlarge the effective coverage area or interfere with nearby receivers. It may therefore violate technical conditions even when the carrier itself is authorised.
• Contractor-installed systems: A distributed antenna system, repeater, small cell or signal booster installed inside a building could contain the wrong frequency module or configuration. A network operator needs controls over third-party installations as well as its own equipment.
• Deliberate activation: An operator could intentionally enable an unassigned carrier to obtain additional capacity or coverage without acquiring the relevant spectrum right or securing temporary approval. Establishing that scenario would require evidence of what was configured, when it operated and who authorised it.

The important distinction is between a possible mechanism and a proven breach. A regulator would need technical investigation to determine whether transmissions occurred, which frequencies were involved, whether they were authorised, how long the activity lasted and whether it resulted from error or deliberate action.

Why operators must stay within their bands

Spectrum access affects competition

Spectrum is scarce, and mobile operators compete for rights to use it. IMDA’s allocation framework is designed to match different bands with appropriate uses and, where demand exceeds supply, to allocate scarce spectrum through mechanisms such as auctions.

An operator that used unassigned spectrum to provide extra capacity or coverage could gain a benefit without acquiring the corresponding right or meeting its conditions. That is why Singapore’s authorities describe unauthorised use as a potential unfair advantage, not merely an equipment fault.

Unwanted emissions can affect other networks

Mobile systems must coexist with other operators and radio services. Unauthorised carriers, excessive power or poor filtering can increase interference, reduce signal quality and consume capacity that neighbouring networks were engineered to use. For customers, the consequences can include poorer voice quality, dropped calls or slower data access, depending on the location and severity of the interference.

Spectrum planning also accounts for other services, future requirements and temporary assignments. Uncoordinated transmissions make that planning harder and can complicate the process of identifying the source of interference.

Breaches can trigger regulatory action

Spectrum rights are issued with conditions, and Singapore’s telecommunications framework provides for enforcement when those conditions or relevant directions are breached. The framework includes the possibility of financial penalties and suspension or cancellation of spectrum rights.

That regulatory risk is separate from the commercial consequences of a network investigation. A suspected breach can affect licensing, competition review, transaction approvals and the confidence of customers, partners and investors.

What happened in the Simba-M1 case?

On 18 May 2026, IMDA said that during its assessment of Simba Telecom’s proposed acquisition of M1’s telecommunications business, it learned that Simba could have been using radio-frequency bands that had not been assigned to it for mobile services. IMDA suspended its review of the proposed S$1.43 billion transaction while it investigated.

The wording matters. The reported issue was a possibility under investigation, not a final finding that Simba intentionally used unauthorised frequencies. The available announcement also does not establish whether any suspected use resulted from a software setting, a hardware problem, a contractor installation, an intentional configuration or another cause.

The deal later faced a contractual deadline: reporting said the proposed transaction was allowed to lapse, with M1 to be offered to other buyers. That commercial outcome should not be confused with the technical and regulatory question that IMDA was investigating.

The practical takeaway

A mobile operator’s spectrum entitlement is a controlled operating boundary, not a suggestion about which frequencies its equipment may technically support. IMDA assigns particular rights, conditions and uses; operators must keep their radio plans, software, power levels, filters, antennas and contractors aligned with those permissions.

For the Simba case, the central facts still depend on the investigation. What is clear is why the allegation was serious: using unassigned spectrum could affect network users, distort competition and undermine the allocation system through which operators obtain scarce frequencies.