Cellular-WiFi Convergence and Internetworking

Introduction

The convergence of cellular and WiFi networks has been a pivotal focus in the wireless industry for decades. While WiFi offers localized, high-throughput connectivity, cellular networks provide extensive coverage and reliable mobility. Combining these complementary strengths is not new; in fact, WiFi Offload was first introduced in 3GPP Release 7 back in 2003. Fast forward to today, and the 2025 WBA Industry Report still identifies "WiFi and 5G/6G Convergence" as one of the top WiFi predictions for the year ahead!

Back in 2012, when Broadcom was already dominant in the WiFi SoC market but was still struggling to enter the cellular SoC market, I was tasked by our Wireless Connectivity BU management with leading a technical exploration into cellular-WiFi internetworking and help develop Broadcom's early strategies in this space. Over the course of a few months, I delved into many 3GPP specifications, IEEE articles, and whitepapers from organizations like the WiFi Alliance and WBA. These efforts revolved around understanding and addressing challenges such as network discovery and selection, connection management, IP mobility, and seamless vertical handovers. I even developed early network simulations to evaluate some early proposals. In 2013, I presented Broadcom’s perspective on cellular-WiFi convergence during a panel session at the RFIC Conference.

Despite significant advancements in both WiFi and cellular technologies, a truly seamless integration still remains elusive. For example, even today, you may still experience that transitioning from your home WiFi to a cellular network during a conference call often results in brief service interruptions. This raises the question: Why hasn’t seamless internetworking been fully realized? The answer lies in a mix of technical hurdles and, perhaps more importantly, complex business dynamics.

Let’s briefly explore the history, challenges, and ongoing efforts in this space.

Historical Evolution of Cellular-WiFi Convergence

1. Early Efforts in 3GPP (Release 6 & 7): The initial steps toward cellular-WiFi integration began in the mid-2000s with the advent of the IP Multimedia Subsystem (IMS) in 3GPP Release 6. IMS provided a framework for delivering IP-based services, including voice, video, and messaging, over both cellular and WiFi networks.

• WiFi Offload (Release 7): Cellular operators began to offload data traffic to WiFi networks to alleviate congestion, especially during the 3G era.

2. LTE and WiFi Integration (Release 10 & 11): With the rise of LTE, cellular-WiFi integration gained momentum:

• ANDSF (Access Network Discovery and Selection Function): Introduced in 3GPP Release 10, ANDSF enabled devices to discover and connect to WiFi networks based on operator-defined policies.
• WiFi Calling: Release 11 introduced support for seamless voice services over WiFi using IMS.

3. Advanced Convergence in 5G (Release 15 & Beyond): 5G takes cellular-WiFi convergence to new levels by treating WiFi as an integral part of the 5G ecosystem.

• Non-3GPP Access Integration: 3GPP Release 15 introduced support for integrating non-3GPP networks, including WiFi, into the 5G core via the Access Traffic Steering, Switching, and Splitting (ATSSS) framework.

Technical Challenges in Cellular-WiFi Convergence

1. Network Discovery and Selection: Efficiently discovering and selecting the optimal network is a significant challenge. Issues include:

• Policy Conflicts: Operators’ policies (via ANDSF) may conflict with users’ preferences or device algorithms.
• Dynamic Environments: Networks vary in link quality due to factors like interference, congestion, and user mobility.

2. Seamless Roaming: Seamless handover between cellular and WiFi networks requires:

• Authentication: Ensuring quick and secure authentication, often via EAP-SIM/AKA or Passpoint/Hotspot 2.0.
• Handover Latency: Reducing delays during internetwork transitions to maintain service continuity.

3. QoS and Traffic Management: Guaranteeing consistent Quality of Service (QoS) across both networks involves:

• Bandwidth Aggregation: Combining WiFi and cellular links for higher throughput (e.g., ATSSS in 5G).
• Load Balancing: Distributing traffic dynamically between networks to optimize performance.

4. Security and Privacy: WiFi networks are inherently less secure than cellular. Challenges include:

• Encryption and Authentication: Ensuring secure communication even on public WiFi networks.
• Data Privacy: Protecting user data during network transitions.

Business Challenges in Convergence

1. Inter-Operator Collaboration: Roaming agreements between cellular operators and WiFi providers can be complex due to differences in business models and revenue sharing.

2. Monetization Models: WiFi is often perceived as “free,” making it challenging for operators to monetize services effectively.

3. Spectrum Regulation: The unlicensed nature of WiFi spectrum can lead to interference and limited control, impacting service quality.

4. Device Ecosystem: Not all devices support advanced features like Hotspot 2.0 or 5G’s ATSSS, limiting the scope of convergence.

Technological Solutions and Developments

1. Hotspot 2.0/Passpoint: Developed by the WiFi Alliance, Hotspot 2.0 enables seamless and secure WiFi connectivity with cellular-like roaming capabilities.

2. Dual Connectivity and ATSSS: 5G’s ATSSS allows devices to simultaneously use cellular and WiFi networks, steering traffic dynamically based on conditions and policies.

3. Multi-Access Edge Computing (MEC): MEC brings processing closer to the user, enabling low-latency applications and enhancing inter-network collaboration.

4. AI-Driven Network Management: AI is increasingly used to predict network conditions, optimize traffic distribution, and improve QoS. This should further help balance the network load and the link quality in the cellular and WiFi networks.

Conclusion

Cellular-WiFi convergence has evolved significantly, driven by advancements in 3GPP specifications and IEEE standards. While technical and business challenges remain, innovative solutions like ATSSS, Hotspot 2.0, and AI-driven management are paving the way for seamless and efficient internetworking. As 5G and WiFi continue to mature, I sure hope to see their integration unlocking new possibilities for ubiquitous and high-quality connectivity.