RNC Functions Explained: Handover, Power Control, and Admission Management

In the world of mobile infrastructure, function defines value. For the Radio Network Controller (RNC), this value lies not in transmitting radio waves, but in managing the intelligence behind them.

Often misunderstood as a mere legacy element in outdated 3G networks, the RNC is in fact a highly specialised control unit. It continuously balances spectrum availability, user mobility, service quality, and resource limitations—on a per-second, per-user basis.

This blog unpacks three of its most essential functions: handover management, power control, and admission control—each critical to the network’s quality, coverage, and capacity.

1. Handover Management: Seamless User Mobility

The most visible RNC function from a user perspective is handover. This ensures that mobile users don’t experience dropped calls or data interruptions when moving between cells.

Soft Handover in UMTS

Unlike 2G GSM systems (which perform hard handovers—breaking one connection before establishing another), UMTS supports soft handovers, where a mobile device can be connected to multiple Node Bs simultaneously during the transition. The RNC:

• Detects signal strength changes

• Initiates soft handover to additional cells

• Combines signals (macro diversity)

• Terminates old radio links once new ones stabilise

This process improves call reliability and signal quality but requires sophisticated coordination, especially in overlapping cell regions. The RNC must balance:

• Resource use (since multiple radio paths consume more spectrum)

• Interference management (avoiding oversaturation of air interface)

• User experience metrics (minimising latency and call drops)

Intra-RNC vs. Inter-RNC Handover

• Intra-RNC handover involves two Node Bs controlled by the same RNC and is handled internally

• Inter-RNC handover requires communication between RNCs over the Iur interface, and the core network is only minimally involved

This localised control improves handover speed and reduces the load on the mobile core.

2. Power Control: Optimising Signal Strength and Interference

The RNC performs both uplink and downlink power control, aiming to maintain the minimum transmit powerrequired for reliable communication. Too little power causes weak signals; too much increases interference.

Why Power Control Matters

• Minimises interference between users sharing the same frequency

• Preserves handset battery life

• Improves capacity by enabling frequency reuse

• Adapts to environmental changes (e.g. movement, obstructions)

Types of Power Control in UMTS

1. Open Loop Power Control:

   • Initial power settings based on received signal quality

   • Used during call setup

2. Closed Loop Power Control:

   • Real-time adjustments (1500+ times per second)

   • Based on feedback from the receiver

3. Inner and Outer Loop Control:

   • The inner loop handles rapid adjustments

   • The outer loop determines target signal quality based on service type (e.g. voice vs. data)

The RNC directs these functions, with the Node B implementing the physical signal changes. It ensures QoS parametersare met, particularly in high-density urban areas and edge-of-cell scenarios.

3. Admission Control: Managing Capacity and Access

Another crucial RNC function is admission control—deciding whether a new connection request can be accommodated without degrading service for existing users.

How It Works

When a mobile device initiates a new voice or data session, the RNC evaluates:

• Available radio resources (code space, power budget, backhaul)

• QoS requirements of the requested service

• Interference thresholds

• Current load in neighbouring cells (especially for handovers)

If accepting the new request would impact the stability of current sessions, the RNC will reject or defer the connection. This protects:

• Critical services (like emergency calls)

• Premium QoS subscribers

• System-wide network performance

Admission control also incorporates priority classes, enabling operators to implement differentiated service tiers or enforce regulatory access conditions (e.g. lawful interception, emergency services).

Other Critical RNC Functions

While this blog focuses on handover, power, and admission management, the RNC also plays roles in:

• Congestion control – redistributing or shedding load in saturated cells

• Traffic scheduling – managing data packet flows and queue priorities

• Encryption key handling – controlling the start of ciphering and integrity protection

• Measurement reporting – feeding performance KPIs to OMC (Operations and Maintenance Centre)

• Cell reconfiguration – adjusting broadcast channels and scrambling codes as needed

These capabilities are essential to operational continuity, especially in multi-technology networks where the RNC may coexist with newer systems like LTE or 5G.

Why Operators Still Rely on These Functions

Despite the global shift toward IP-based, virtualised networks, the RNC's functions are still mission-critical in:

• Rural and suburban areas with 3G-only coverage

• Developing markets where 3G remains primary

• Fallback environments where LTE/5G coverage is incomplete

• Industrial IoT systems still using embedded 3G modules

For such environments, downgrading or disabling RNC functionality introduces real business and reputational risk.

Strategic Implications for Boards and Investors

Operators considering the sunsetting of 3G or transitioning from physical to virtual RNCs should weigh:

• The cost of performance deterioration from premature decommissioning

• Customer churn risks if mobility or QoS falters in mixed environments

• Engineering talent shortages in legacy protocols

• Vendor lock-in issues around proprietary RNC software and upgrade paths

Understanding these hidden dependencies helps leadership teams avoid strategic blind spots in network transformation planning.

Conclusion: Control Is the Foundation of Service Quality

The Radio Network Controller may no longer dominate product roadmaps, but it continues to quietly govern some of the most essential functions in telecom networks: who gets access, at what quality, and with what continuity.

Handover, power control, and admission management form a critical trio that collectively determines user experience, network efficiency, and spectrum usage. They are not optional extras—they are core enablers of telecom economics and service delivery.